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Chung PF, Venkatesan B, Su CC, Chang JT, Cheng HK, Liu CA, Yu H, Chang CS, Guan SY, Chuang TM. Design and performance of an ultrahigh vacuum spectroscopic-imaging scanning tunneling microscope with a hybrid vibration isolation system. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:033701. [PMID: 38426899 DOI: 10.1063/5.0189100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Accepted: 02/06/2024] [Indexed: 03/02/2024]
Abstract
A spectroscopic imaging-scanning tunneling microscope (SI-STM) allows for the atomic scale visualization of the surface electronic and magnetic structure of novel quantum materials with a high energy resolution. To achieve the optimal performance, a low vibration facility is required. Here, we describe the design and performance of an ultrahigh vacuum STM system supported by a hybrid vibration isolation system that consists of a pneumatic passive and a piezoelectric active vibration isolation stage. We present the detailed vibrational noise analysis of the hybrid vibration isolation system, which shows that the vibration level can be suppressed below 10-8 m/sec/√Hz for most frequencies up to 100 Hz. Combined with a rigid STM design, vibrational noise can be successfully removed from the tunneling current. We demonstrate the performance of our STM system by taking high resolution spectroscopic maps and topographic images on several quantum materials. Our results establish a new strategy to achieve an effective vibration isolation system for high-resolution STM and other scanning probe microscopies to investigate the nanoscale quantum phenomena.
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Affiliation(s)
- Pei-Fang Chung
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Balaji Venkatesan
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
- Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica and National Taiwan University, Taipei 11529, Taiwan
| | - Chih-Chuan Su
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Jen-Te Chang
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Hsu-Kai Cheng
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Che-An Liu
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Henry Yu
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Chia-Seng Chang
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
- Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica and National Taiwan University, Taipei 11529, Taiwan
| | - Syu-You Guan
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
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2
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Marques CA, Cahlík A, Zengin B, Kurosawa T, Natterer FD. Vacuum cleaving of superconducting niobium tips to optimize noise filtering and with adjustable gap size for scanning tunneling microscopy. MethodsX 2023; 11:102483. [PMID: 38034321 PMCID: PMC10685302 DOI: 10.1016/j.mex.2023.102483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 11/09/2023] [Indexed: 12/02/2023] Open
Abstract
Superconducting (SC) tips for scanning tunneling microscopy (STM) can enhance a wide range of surface science studies because they offer exquisite energy resolution, allow the study of Josephson tunneling, or provide spatial contrast based on the local interaction of the SC tip with the sample. The appeal of a SC tip is also practical. An SC gap can be used to characterize and optimize the noise of a low-temperature apparatus. Unlike typical samples, SC tips can be made with less ordered materials, such as from SC polycrystalline wires or by coating a normal metal tip with a superconductor. Those recipes either require additional laboratory infrastructure or are carried out in ambient conditions, leaving an oxidized tip behind. Here, we revisit the vacuum cleaving of an Nb wire to prepare fully gapped tips in an accessible one-step procedure. To show their utility, we measure the SC gap of Nb on Au(111) to determine the base temperature of our microscope and to optimize its RF filtering. The deliberate coating of the Nb tip with Au fully suppresses the SC gap and we show how sputtering with Ar+ ions can be used to gradually recover the gap, promising tunability for tailored SC gaps sizes. • Oxide free superconducting STM tips • RF filter optimization.
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Affiliation(s)
- Carolina A. Marques
- Department of Physics, University of Zurich, Winterthurerstrasse 190, Zurich CH-8057, Switzerland
| | - Aleš Cahlík
- Department of Physics, University of Zurich, Winterthurerstrasse 190, Zurich CH-8057, Switzerland
| | - Berk Zengin
- Department of Physics, University of Zurich, Winterthurerstrasse 190, Zurich CH-8057, Switzerland
| | - Tohru Kurosawa
- Department of Applied Sciences, Muroran Institute of Technology, Muroran 050-8585, Japan
| | - Fabian D. Natterer
- Department of Physics, University of Zurich, Winterthurerstrasse 190, Zurich CH-8057, Switzerland
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3
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Wang J, Li W, Meng W, Hou Y, Lu Y, Lu Q. Atomic imaging with a 12 T magnetic field perpendicular or parallel to the sample surface by an ultra-stable scanning tunneling microscope. Ultramicroscopy 2023; 251:113774. [PMID: 37270856 DOI: 10.1016/j.ultramic.2023.113774] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Accepted: 05/30/2023] [Indexed: 06/06/2023]
Abstract
We present the first nonmetallic scanning tunneling microscope (STM) featuring an ultra-stable tip-sample mechanical loop and capable of atomic-resolution imaging within a 12 T magnetic field that could be either perpendicular or parallel to the sample surface. This is also the first STM with an ultra-stable tip-sample mechanical loop but without a standalone scanner. The STM head is constructed only with two parts: an improved spider-drive motor and a zirconia tip holder. The motor performs both the coarse approach and atomic imaging. A supporting spring is set at the fixed end of the motor tube to decrease the tip-sample mechanical loop. The zirconia tip holder performs as the frame of the whole STM head. With the novel design, the STM head in three dimensions can be as small as 7.9 mm × 7.9 mm × 26.5 mm. The device's excellent performance is demonstrated by atomic-resolution images of graphite and NbSe2 obtained at 300 K and 2 K, as well as the high-resolution dI/dV spectrums of NbSe2 at variable temperatures. Low drift rates in the X-Y plane and Z direction further prove the imaging stability of our new STM. High-quality imaging of the Charge Density Wave (CDW) structure on a TaS2 surface shows the STM's good application capability. Continuous atomic images obtained in magnetic fields rangs from 0 T to 12 T with the direction of the magnetic field perpendicular or parallel to the sample surface show the STM's good immunity to high magnetic fields. Our results illustrate the new STM's broad application ability in extreme conditions of low temperature and high magnetic field.
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Affiliation(s)
- Jihao Wang
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China; The High Magnetic Field Laboratory of Anhui Province, Hefei, Anhui 230031, China
| | - Weixuan Li
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China; The High Magnetic Field Laboratory of Anhui Province, Hefei, Anhui 230031, China
| | - Wenjie Meng
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China; The High Magnetic Field Laboratory of Anhui Province, Hefei, Anhui 230031, China
| | - Yubin Hou
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China; The High Magnetic Field Laboratory of Anhui Province, Hefei, Anhui 230031, China.
| | - Yalin Lu
- Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China; Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026 China
| | - Qingyou Lu
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China; The High Magnetic Field Laboratory of Anhui Province, Hefei, Anhui 230031, China; Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China; Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026 China; Hefei Science Center, Chinese Academy of Sciences, Hefei 230031, China.
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4
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Xue H, Wang L, Wang Z, Zhang G, Peng W, Wu S, Gao CL, An Z, Chen Y, Li W. Fourfold Symmetric Superconductivity in Spinel Oxide LiTi 2O 4(001) Thin Films. ACS NANO 2022; 16:19464-19471. [PMID: 36331279 DOI: 10.1021/acsnano.2c09338] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The charge frustration with the mixed-valence state inherent to LiTi2O4, which is found to be the only oxide superconductor with spinel structure, is the impetus for paying special attention to unveil the underlying intriguing superconducting properties. Here, we report a pronounced fourfold rotational symmetry of the superconductivity in high-quality single-crystalline LiTi2O4(001) thin films. Both the magnetoresistivity and upper critical field under an applied magnetic field manifest striking fourfold oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the unconventional d-wave superconducting Cooper pairs with the irreducible representation of Eg protected by the Oh point group in cubic LiTi2O4. Our findings show the nontrivial character of the pairing interaction in a three-dimensional spinel oxide superconductor.
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Affiliation(s)
| | | | | | | | - Wei Peng
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, and Center for Excellence in Superconducting Electronics, Chinese Academy of Sciences, Shanghai 200050, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
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5
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Kasahara S, Suzuki H, Machida T, Sato Y, Ukai Y, Murayama H, Suetsugu S, Kasahara Y, Shibauchi T, Hanaguri T, Matsuda Y. Quasiparticle Nodal Plane in the Fulde-Ferrell-Larkin-Ovchinnikov State of FeSe. PHYSICAL REVIEW LETTERS 2021; 127:257001. [PMID: 35029441 DOI: 10.1103/physrevlett.127.257001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Accepted: 11/16/2021] [Indexed: 06/14/2023]
Abstract
The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, characterized by Cooper pairs condensed at finite momentum, has been a long-sought state that remains unresolved in many classes of fermionic systems, including superconductors and ultracold atoms. A fascinating aspect of the FFLO state is the emergence of periodic nodal planes in real space, but its observation is still lacking. Here we investigate the superconducting order parameter at high magnetic fields H applied perpendicular to the ab plane in a high-purity single crystal of FeSe. The heat capacity and magnetic torque provide thermodynamic evidence for a distinct superconducting phase at the low-temperature/high-field corner of the phase diagram. Despite the bulk superconductivity, spectroscopic-imaging scanning tunneling microscopy performed on the same crystal demonstrates that the order parameter vanishes at the surface upon entering the high-field phase. These results provide the first demonstration of a pinned planar node perpendicular to H, which is consistent with a putative FFLO state.
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Affiliation(s)
- S Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
| | - H Suzuki
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - T Machida
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Y Sato
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Y Ukai
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - H Murayama
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - S Suetsugu
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Y Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - T Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Chiba 277-8561, Japan
| | - T Hanaguri
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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6
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Martín-Vega F, Barrena V, Sánchez-Barquilla R, Fernández-Lomana M, Benito Llorens J, Wu B, Fente A, Perconte Duplain D, Horcas I, López R, Blanco J, Higuera JA, Mañas-Valero S, Jo NH, Schmidt J, Canfield PC, Rubio-Bollinger G, Rodrigo JG, Herrera E, Guillamón I, Suderow H. Simplified feedback control system for scanning tunneling microscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:103705. [PMID: 34717388 DOI: 10.1063/5.0064511] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 09/18/2021] [Indexed: 06/13/2023]
Abstract
A Scanning Tunneling Microscope (STM) is one of the most important scanning probe tools available to study and manipulate matter at the nanoscale. In a STM, a tip is scanned on top of a surface with a separation of a few Å. Often, the tunneling current between the tip and the sample is maintained constant by modifying the distance between the tip apex and the surface through a feedback mechanism acting on a piezoelectric transducer. This produces very detailed images of the electronic properties of the surface. The feedback mechanism is nearly always made using a digital processing circuit separate from the user computer. Here, we discuss another approach using a computer and data acquisition through the universal serial bus port. We find that it allows successful ultralow noise studies of surfaces at cryogenic temperatures. We show results on different compounds including a type II Weyl semimetal (WTe2), a quasi-two-dimensional dichalcogenide superconductor (2H-NbSe2), a magnetic Weyl semimetal (Co3Sn2S2), and an iron pnictide superconductor (FeSe).
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Affiliation(s)
- Francisco Martín-Vega
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Víctor Barrena
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Raquel Sánchez-Barquilla
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Marta Fernández-Lomana
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José Benito Llorens
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Beilun Wu
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Antón Fente
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - David Perconte Duplain
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Ignacio Horcas
- Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Raquel López
- SEGAINVEX, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Javier Blanco
- SEGAINVEX, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | | | - Samuel Mañas-Valero
- Instituto de Ciencia Molecular (ICMol), Universidad de Valencia, Catedrático José Beltrán 2, 46980 Paterna, Spain
| | - Na Hyun Jo
- Ames Laboratory, U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Juan Schmidt
- Ames Laboratory, U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Paul C Canfield
- Ames Laboratory, U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Gabino Rubio-Bollinger
- Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José Gabriel Rodrigo
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Edwin Herrera
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Isabel Guillamón
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Hermann Suderow
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
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7
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Fernández-Lomana M, Wu B, Martín-Vega F, Sánchez-Barquilla R, Álvarez-Montoya R, Castilla JM, Navarrete J, Marijuan JR, Herrera E, Suderow H, Guillamón I. Millikelvin scanning tunneling microscope at 20/22 T with a graphite enabled stick-slip approach and an energy resolution below 8 μeV: Application to conductance quantization at 20 T in single atom point contacts of Al and Au and to the charge density wave of 2H-NbSe 2. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:093701. [PMID: 34598511 DOI: 10.1063/5.0059394] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 08/21/2021] [Indexed: 06/13/2023]
Abstract
We describe a scanning tunneling microscope (STM) that operates at magnetic fields up to 22 T and temperatures down to 80 mK. We discuss the design of the STM head, with an improved coarse approach, the vibration isolation system, and efforts to improve the energy resolution using compact filters for multiple lines. We measure the superconducting gap and Josephson effect in aluminum and show that we can resolve features in the density of states as small as 8 μeV. We measure the quantization of conductance in atomic size contacts and make atomic resolution and density of states images in the layered material 2H-NbSe2. The latter experiments are performed by continuously operating the STM at magnetic fields of 20 T in periods of several days without interruption.
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Affiliation(s)
- Marta Fernández-Lomana
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Beilun Wu
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Francisco Martín-Vega
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Raquel Sánchez-Barquilla
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Rafael Álvarez-Montoya
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José María Castilla
- Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José Navarrete
- SEGAINVEX, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | | | - Edwin Herrera
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Hermann Suderow
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Isabel Guillamón
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
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8
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Esat T, Borgens P, Yang X, Coenen P, Cherepanov V, Raccanelli A, Tautz FS, Temirov R. A millikelvin scanning tunneling microscope in ultra-high vacuum with adiabatic demagnetization refrigeration. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:063701. [PMID: 34243501 DOI: 10.1063/5.0050532] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 05/23/2021] [Indexed: 06/13/2023]
Abstract
We present the design and performance of an ultra-high vacuum scanning tunneling microscope (STM) that uses adiabatic demagnetization of electron magnetic moments for controlling its operating temperature ranging between 30 mK and 1 K with an accuracy of up to 7 μK rms. At the same time, high magnetic fields of up to 8 T can be applied perpendicular to the sample surface. The time available for STM experiments at 50 mK is longer than 20 h, at 100 mK about 40 h. The single-shot adiabatic demagnetization refrigerator can be regenerated automatically within 7 h while keeping the STM temperature below 5 K. The whole setup is located in a vibrationally isolated, electromagnetically shielded laboratory with no mechanical pumping lines penetrating its isolation walls. The 1 K pot of the adiabatic demagnetization refrigeration cryostat can be operated silently for more than 20 days in a single-shot mode using a custom-built high-capacity cryopump. A high degree of vibrational decoupling together with the use of a specially designed minimalistic STM head provides outstanding mechanical stability, demonstrated by the tunneling current noise, STM imaging, and scanning tunneling spectroscopy measurements, all performed on an atomically clean Al(100) surface.
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Affiliation(s)
- Taner Esat
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Peter Borgens
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Xiaosheng Yang
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Peter Coenen
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Vasily Cherepanov
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | | | - F Stefan Tautz
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Ruslan Temirov
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
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9
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Kohsaka Y. Removing background and estimating a unit height of atomic steps from a scanning probe microscopy image using a statistical model. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:033702. [PMID: 33820037 DOI: 10.1063/5.0038852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 02/20/2021] [Indexed: 06/12/2023]
Abstract
We present a statistical method to remove background and estimate a unit height of atomic steps of an image obtained using a scanning probe microscope. We adopt a mixture model consisting of multiple statistical distributions to describe an image. This statistical approach provides a comprehensive way to subtract a background surface even in the presence of atomic steps as well as to evaluate terrace heights in a single framework. Moreover, it also enables us to extract further quantitative information by introducing additional prior knowledge about the image. An example of this extension is estimating a unit height of atomic steps together with the terrace heights. We demonstrate the capability of our method for a topographic image of a Cu(111) surface taken using a scanning tunneling microscope. The background subtraction corrects all terraces to be parallel to a horizontal plane, and the precision of the estimated unit height reaches the order of a picometer. An open-source implementation of our method is available on the web.
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Affiliation(s)
- Yuhki Kohsaka
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
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10
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van Weerdenburg WMJ, Steinbrecher M, van Mullekom NPE, Gerritsen JW, von Allwörden H, Natterer FD, Khajetoorians AA. A scanning tunneling microscope capable of electron spin resonance and pump-probe spectroscopy at mK temperature and in vector magnetic field. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:033906. [PMID: 33820009 DOI: 10.1063/5.0040011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Accepted: 02/19/2021] [Indexed: 06/12/2023]
Abstract
In the last decade, detecting spin dynamics at the atomic scale has been enabled by combining techniques such as electron spin resonance (ESR) or pump-probe spectroscopy with scanning tunneling microscopy (STM). Here, we demonstrate an ultra-high vacuum STM operational at milliKelvin (mK) temperatures and in a vector magnetic field capable of both ESR and pump-probe spectroscopy. By implementing GHz compatible cabling, we achieve appreciable RF amplitudes at the junction while maintaining the mK base temperature and high energy resolution. We demonstrate the successful operation of our setup by utilizing two experimental ESR modes (frequency sweep and magnetic field sweep) on an individual TiH molecule on MgO/Ag(100) and extract the effective g-factor. We trace the ESR transitions down to MHz into an unprecedented low frequency band enabled by the mK base temperature. We also implement an all-electrical pump-probe scheme based on waveform sequencing suited for studying dynamics down to the nanoseconds range. We benchmark our system by detecting the spin relaxation time T1 of individual Fe atoms on MgO/Ag(100) and note a field strength and orientation dependent relaxation time.
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Affiliation(s)
| | - Manuel Steinbrecher
- Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands
| | - Niels P E van Mullekom
- Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands
| | - Jan W Gerritsen
- Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands
| | - Henning von Allwörden
- Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands
| | - Fabian D Natterer
- Department of Physics, University of Zurich, CH-8057 Zurich, Switzerland
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11
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Gong W, Liu Y, Liao WT, Gibbons J, Hoffman JE. Design and characterization of a low-vibration laboratory with cylindrical inertia block geometry. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:013703. [PMID: 33514250 DOI: 10.1063/5.0004964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Accepted: 12/27/2020] [Indexed: 06/12/2023]
Abstract
Many modern nanofabrication and imaging techniques require an ultra-quiet environment to reach optimal resolution. Isolation from ambient vibrations is often achieved by placing the sensitive instrument atop a massive block that floats on air springs and is surrounded by acoustic barriers. Because typical building noise drops off above 120 Hz, it is advantageous to raise the flexural resonance frequencies of the inertia block and instrument far above 120 Hz. However, it can be challenging to obtain a high fundamental frequency of the floating block using a simple rectangular design. Here, we design, construct, and characterize a vibration isolation system with a cylindrical inertia block, whose lowest resonance frequency of 249 Hz shows good agreement between finite element analysis simulation and directly measured modes. Our simulations show that a cylindrical design can achieve a higher fundamental resonance frequency than a rectangular design of the same mass.
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Affiliation(s)
- Wenjie Gong
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Yu Liu
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Wan-Ting Liao
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Joseph Gibbons
- Wilson HGA Architects, 374 Congress St., Boston, Massachusetts 02210, USA
| | - Jennifer E Hoffman
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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12
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Schwenk J, Kim S, Berwanger J, Ghahari F, Walkup D, Slot MR, Le ST, Cullen WG, Blankenship SR, Vranjkovic S, Hug HJ, Kuk Y, Giessibl FJ, Stroscio JA. Achieving μeV tunneling resolution in an in-operando scanning tunneling microscopy, atomic force microscopy, and magnetotransport system for quantum materials research. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:071101. [PMID: 32752869 PMCID: PMC7678032 DOI: 10.1063/5.0005320] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 06/04/2020] [Indexed: 06/11/2023]
Abstract
Research in new quantum materials requires multi-mode measurements spanning length scales, correlations of atomic-scale variables with a macroscopic function, and spectroscopic energy resolution obtainable only at millikelvin temperatures, typically in a dilution refrigerator. In this article, we describe a multi-mode instrument achieving a μeV tunneling resolution with in-operando measurement capabilities of scanning tunneling microscopy, atomic force microscopy, and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design and sample and tip transport systems, along with wiring, radio-frequency filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulator-superconductor tunnel junctions, with Josephson tunneling as a noise metering detector. After extensive testing and optimization, we have achieved less than 8 μeV instrument resolving capability for tunneling spectroscopy, which is 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.
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Affiliation(s)
- Johannes Schwenk
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Sungmin Kim
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Julian Berwanger
- Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany
| | - Fereshte Ghahari
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Daniel Walkup
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Marlou R. Slot
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Department of Physics, Georgetown University, Washington, DC 20007, USA
| | - Son T. Le
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Theiss Research, La Jolla, CA 92037, USA
| | - William G. Cullen
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Steven R. Blankenship
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Sasa Vranjkovic
- Institute of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Hans J. Hug
- Institute of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Young Kuk
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
| | - Franz J. Giessibl
- Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany
| | - Joseph A. Stroscio
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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13
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Chiu CK, Machida T, Huang Y, Hanaguri T, Zhang FC. Scalable Majorana vortex modes in iron-based superconductors. SCIENCE ADVANCES 2020; 6:eaay0443. [PMID: 32158938 PMCID: PMC7048414 DOI: 10.1126/sciadv.aay0443] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2019] [Accepted: 11/22/2019] [Indexed: 06/09/2023]
Abstract
The iron-based superconductor FeTe x Se1-x is one of the material candidates hosting Majorana vortex modes residing in the vortex cores. It has been observed by recent scanning tunneling spectroscopy measurement that the fraction of vortex cores having zero-bias peaks decreases with increasing magnetic field on the surface of FeTe x Se1-x . The hybridization of two Majorana vortex modes cannot simply explain this phenomenon. We construct a three-dimensional tight-binding model simulating the physics of over a hundred Majorana vortex modes in FeTe x Se1-x . Our simulation shows that the Majorana hybridization and disordered vortex distribution can explain the decreasing fraction of the zero-bias peaks observed in the experiment; the statistics of the energy peaks off zero energy in our Majorana simulation are in agreement with the experiment. These agreements lead to an important indication of scalable Majorana vortex modes in FeTe x Se1-x . Thus, FeTe x Se1-x can be one promising platform having scalable Majorana qubits for quantum computing.
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Affiliation(s)
- Ching-Kai Chiu
- Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - T. Machida
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Yingyi Huang
- Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
| | - T. Hanaguri
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Fu-Chun Zhang
- Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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14
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Wong D, Jeon S, Nuckolls KP, Oh M, Kingsley SCJ, Yazdani A. A modular ultra-high vacuum millikelvin scanning tunneling microscope. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:023703. [PMID: 32113373 DOI: 10.1063/1.5132872] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 01/18/2020] [Indexed: 06/10/2023]
Abstract
We describe the design, construction, and performance of an ultra-high vacuum (UHV) scanning tunneling microscope (STM) capable of imaging at dilution-refrigerator temperatures and equipped with a vector magnet. The primary objective of our design is to achieve a high level of modularity by partitioning the STM system into a set of easily separable, interchangeable components. This naturally segregates the UHV needs of STM instrumentation from the typically non-UHV construction of a dilution refrigerator, facilitating the usage of non-UHV materials while maintaining a fully bakeable UHV chamber that houses the STM. The modular design also permits speedy removal of the microscope head from the rest of the system, allowing for repairs, modifications, and even replacement of the entire microscope head to be made at any time without warming the cryostat or compromising the vacuum. Without using cryogenic filters, we measured an electron temperature of 184 mK on a superconducting Al(100) single crystal.
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Affiliation(s)
- Dillon Wong
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Sangjun Jeon
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Kevin P Nuckolls
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Myungchul Oh
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Simon C J Kingsley
- Oxford Instruments, Tubney Woods, Abingdon, Oxfordshire OX13 5QX, United Kingdom
| | - Ali Yazdani
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
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15
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Zhu S, Kong L, Cao L, Chen H, Papaj M, Du S, Xing Y, Liu W, Wang D, Shen C, Yang F, Schneeloch J, Zhong R, Gu G, Fu L, Zhang YY, Ding H, Gao HJ. Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor. Science 2019; 367:189-192. [PMID: 31831637 DOI: 10.1126/science.aax0274] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 07/29/2019] [Accepted: 11/07/2019] [Indexed: 01/31/2023]
Abstract
Majorana zero modes (MZMs) are spatially localized, zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold promise for topological quantum computing. Owing to the particle-antiparticle equivalence, MZMs exhibit quantized conductance at low temperature. By using variable-tunnel-coupled scanning tunneling spectroscopy, we studied tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e 2/h quantum conductance (where e is the electron charge and h is Planck's constant). By contrast, no plateaus were observed on either finite energy vortex bound states or in the continuum of electronic states outside the superconducting gap. This behavior of the zero-mode conductance supports the existence of MZMs in FeTe0.55Se0.45.
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Affiliation(s)
- Shiyu Zhu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Lingyuan Kong
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Lu Cao
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Hui Chen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Michał Papaj
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Shixuan Du
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China.,Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Yuqing Xing
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Wenyao Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Dongfei Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Chengmin Shen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Fazhi Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - John Schneeloch
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Ruidan Zhong
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Genda Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Yu-Yang Zhang
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China. .,Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Hong Ding
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. .,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China.,Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Hong-Jun Gao
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. .,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China.,Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
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16
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Machida T, Sun Y, Pyon S, Takeda S, Kohsaka Y, Hanaguri T, Sasagawa T, Tamegai T. Zero-energy vortex bound state in the superconducting topological surface state of Fe(Se,Te). NATURE MATERIALS 2019; 18:811-815. [PMID: 31209388 DOI: 10.1038/s41563-019-0397-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Accepted: 05/08/2019] [Indexed: 06/09/2023]
Abstract
Majorana quasiparticles in condensed matter are important for topological quantum computing1-3, but remain elusive. Vortex cores of topological superconductors may accommodate Majorana quasiparticles that appear as the Majorana bound state (MBS) at zero energy4,5. The iron-based superconductor Fe(Se,Te) possesses a superconducting topological surface state6-9 that was investigated by scanning tunnelling microscopy (STM) studies, which suggest such a zero-energy vortex bound state (ZVBS)10,11. Here we present ultrahigh energy-resolution spectroscopic imaging (SI)-STM to clarify the nature of the vortex bound states in Fe(Se,Te). We found the ZVBS at 0 ± 20 μeV, which constrained its MBS origin, and showed that some vortices host the ZVBS but others do not. We show that the fraction of vortices hosting the ZVBS decreases with increasing magnetic field and that local quenched disorders are not related to the ZVBS. Our observations elucidate the necessary conditions to realize the ZVBS, which paves the way towards controllable Majorana quasiparticles.
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Affiliation(s)
- T Machida
- RIKEN Center for Emergent Matter Science, Wako, Japan.
| | - Y Sun
- Department of Physics and Mathematics, Aoyama Gakuin University, Chuou-ku, Sagamihara, Japan
| | - S Pyon
- Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Japan
| | - S Takeda
- Laboratory for Materials and Structures, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan
| | - Y Kohsaka
- RIKEN Center for Emergent Matter Science, Wako, Japan
| | - T Hanaguri
- RIKEN Center for Emergent Matter Science, Wako, Japan.
| | - T Sasagawa
- Laboratory for Materials and Structures, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan
| | - T Tamegai
- Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Japan
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17
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de Wit M, Welker G, Heeck K, Buters FM, Eerkens HJ, Koning G, van der Meer H, Bouwmeester D, Oosterkamp TH. Vibration isolation with high thermal conductance for a cryogen-free dilution refrigerator. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:015112. [PMID: 30709182 DOI: 10.1063/1.5066618] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Accepted: 12/24/2018] [Indexed: 06/09/2023]
Abstract
We present the design and implementation of a mechanical low-pass filter vibration isolation used to reduce the vibrational noise in a cryogen-free dilution refrigerator operated at 10 mK, intended for scanning probe techniques. We discuss the design guidelines necessary to meet the competing requirements of having a low mechanical stiffness in combination with a high thermal conductance. We demonstrate the effectiveness of our approach by measuring the vibrational noise levels of an ultrasoft mechanical resonator positioned above a superconducting quantum interference device. Starting from a cryostat base temperature of 8 mK, the vibration isolation can be cooled to 10.5 mK, with a cooling power of 113 µW at 100 mK. We use the low vibrations and low temperature to demonstrate an effective cantilever temperature of less than 20 mK. This results in a force sensitivity of less than 500 zN/Hz and an integrated frequency noise as low as 0.4 mHz in a 1 Hz measurement bandwidth.
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Affiliation(s)
- Martin de Wit
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Gesa Welker
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Kier Heeck
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Frank M Buters
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Hedwig J Eerkens
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Gert Koning
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Harmen van der Meer
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Dirk Bouwmeester
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
| | - Tjerk H Oosterkamp
- Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
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18
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Balashov T, Meyer M, Wulfhekel W. A compact ultrahigh vacuum scanning tunneling microscope with dilution refrigeration. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:113707. [PMID: 30501324 DOI: 10.1063/1.5043636] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 10/25/2018] [Indexed: 06/09/2023]
Abstract
We have designed and built a scanning tunneling microscope (STM) setup for operation at millikelvin temperatures in an ultrahigh vacuum. A compact cryostat with an integrated dilution refrigerator has been built that allows measurements at a base temperature of 25 mK in the magnetic field up to 7.5 T with low mechanical and electronic noise. The cryostat is not larger than conventional helium bath cryostats (23 and 13 l of nitrogen and helium, respectively) so that the setup does not require a large experimental hall and fits easily into a standard lab space. Mechanical vibrations with running dilution circulation were kept below 1 pm/ Hz by mechanically decoupling the STM from the cryostat and the pumping system. All electronic input lines were low-pass filtered, reducing the electronic temperature to below 100 mK, as deduced from the quasiparticle peaks of superconducting aluminum. The microscope is optically accessible in the parked position, making sample and tip exchange fast and user-friendly. For measurement, the STM is lowered 60 mm down so that the sample ends in the middle of a wet superconducting magnetic coil.
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Affiliation(s)
- T Balashov
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
| | - M Meyer
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
| | - W Wulfhekel
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
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