1
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Shilov AL, Kashchenko MA, Pantaleón Peralta PA, Wang Y, Kravtsov M, Kudriashov A, Zhan Z, Taniguchi T, Watanabe K, Slizovskiy S, Novoselov KS, Fal'ko VI, Guinea F, Bandurin DA. High-Mobility Compensated Semimetals, Orbital Magnetization, and Umklapp Scattering in Bilayer Graphene Moiré Superlattices. ACS NANO 2024; 18:11769-11777. [PMID: 38648369 DOI: 10.1021/acsnano.3c13212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
Twist-controlled moiré superlattices (MSs) have emerged as a versatile platform for realizing artificial systems with complex electronic spectra. The combination of Bernal-stacked bilayer graphene (BLG) and hexagonal boron nitride (hBN) can give rise to an interesting MS, which has recently featured a set of unexpected behaviors, such as unconventional ferroelectricity and the electronic ratchet effect. Yet, the understanding of the electronic properties of BLG/hBN MS has, at present, remained fairly limited. Here, we combine magneto-transport and low-energy sub-THz excitation to gain insights into the properties of this MS. We demonstrate that the alignment between BLG and hBN crystal lattices results in the emergence of compensated semimetals at some integer fillings of the moiré bands, separated by van Hove singularities where the Lifshitz transition occurs. A particularly pronounced semimetal develops when eight holes reside in the moiré unit cell, where coexisting high-mobility electron and hole systems feature strong magnetoresistance reaching 2350% already at B = 0.25 T. Next, by measuring the THz-driven Nernst effect in remote bands, we observe valley splitting, indicating an orbital magnetization characterized by a strongly enhanced effective gv-factor of 340. Finally, using THz photoresistance measurements, we show that the high-temperature conductivity of the BLG/hBN MS is limited by electron-electron umklapp processes. Our multifaceted analysis introduces THz-driven magnetotransport as a convenient tool to probe the band structure and interaction effects in van der Waals materials and provides a comprehensive understanding of the BLG/hBN MS.
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Affiliation(s)
- Artur L Shilov
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
| | - Mikhail A Kashchenko
- Programmable Functional Materials Lab, Center for Neurophysics and Neuromorphic Technologies, Moscow 127495, Russia
| | | | - Yibo Wang
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Mikhail Kravtsov
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Andrei Kudriashov
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Zhen Zhan
- IMDEA Nanoscience, Faraday 9, Madrid 28015, Spain
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - Sergey Slizovskiy
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, U.K
| | - Kostya S Novoselov
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Vladimir I Fal'ko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, U.K
| | - Francisco Guinea
- IMDEA Nanoscience, Faraday 9, Madrid 28015, Spain
- Donostia International Physics Center, Paseo Manuel de Lardizábal 4, San Sebastián 20018, Spain
| | - Denis A Bandurin
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
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2
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Zhang SH, Shao DF, Wang ZA, Yang J, Yang W, Tsymbal EY. Tunneling Valley Hall Effect Driven by Tilted Dirac Fermions. PHYSICAL REVIEW LETTERS 2023; 131:246301. [PMID: 38181146 DOI: 10.1103/physrevlett.131.246301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 11/21/2023] [Indexed: 01/07/2024]
Abstract
Valleytronics is a research field utilizing a valley degree of freedom of electrons for information processing and storage. A strong valley polarization is critical for realistic valleytronic applications. Here, we predict a tunneling valley Hall effect (TVHE) driven by tilted Dirac fermions in all-in-one tunnel junctions based on a two-dimensional (2D) valley material. Different doping of the electrode and spacer regions in these tunnel junctions results in momentum filtering of the tunneling Dirac fermions, generating a strong transverse valley Hall current dependent on the Dirac-cone tilting. Using the parameters of an existing 2D valley material, we demonstrate that such a strong TVHE can host a giant valley Hall angle even in the absence of the Berry curvature. Finally, we predict that resonant tunneling can occur in a tunnel junction with properly engineered device parameters such as the spacer width and transport direction, providing significant enhancement of the valley Hall angle. Our work opens a new approach to generate valley polarization in realistic valleytronic systems.
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Affiliation(s)
- Shu-Hui Zhang
- College of Mathematics and Physics, Beijing University of Chemical Technology, Beijing 100029, China
| | - Ding-Fu Shao
- Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China
| | - Zi-An Wang
- Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China
- University of Science and Technology of China, Hefei 230026, China
| | - Jin Yang
- Beijing Computational Science Research Center, Beijing 100193, China
| | - Wen Yang
- Beijing Computational Science Research Center, Beijing 100193, China
| | - Evgeny Y Tsymbal
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588-0299, USA
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3
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Korkusinski M, Saleem Y, Dusko A, Miravet D, Hawrylak P. Spontaneous Spin and Valley Symmetry-Broken States of Interacting Massive Dirac Fermions in a Bilayer Graphene Quantum Dot. NANO LETTERS 2023; 23:7546-7551. [PMID: 37561956 DOI: 10.1021/acs.nanolett.3c02073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
We predict the existence of spontaneous spin and valley symmetry-broken states of interacting massive Dirac Fermions in a gated bilayer graphene quantum dot based on the exact diagonalization of the many-body Hamiltonian. The dot is defined by a vertical electric field and lateral gates, and its single-particle (SP) energies, wave functions, and Coulomb matrix elements are computed by using the atomistic tight-binding model. The effect of the Coulomb interaction is measured by the ratio of Coulomb elements to the SP level spacing. As we increase the interaction strength, we find the electrons in a series of spin and valley symmetry-broken phases with increasing valley and spin polarizations. The phase transitions result from the competition of the SP, exchange, and correlation energy scales. A phase diagram for N = 1-6 electrons is mapped out as a function of the Coulomb interaction strength.
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Affiliation(s)
- Marek Korkusinski
- Physics Department, University of Ottawa, Ottawa K1N6N5, Canada
- Security and Disruptive Technologies, National Research Council, Ottawa K1A0R6, Canada
| | - Yasser Saleem
- Physics Department, University of Ottawa, Ottawa K1N6N5, Canada
| | - Amintor Dusko
- Physics Department, University of Ottawa, Ottawa K1N6N5, Canada
| | - Daniel Miravet
- Physics Department, University of Ottawa, Ottawa K1N6N5, Canada
| | - Pawel Hawrylak
- Physics Department, University of Ottawa, Ottawa K1N6N5, Canada
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4
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Krishnan R, Biswas S, Hsueh YL, Ma H, Rahman R, Weber B. Spin-Valley Locking for In-Gap Quantum Dots in a MoS 2 Transistor. NANO LETTERS 2023. [PMID: 37363814 DOI: 10.1021/acs.nanolett.3c01779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
Spins confined to atomically thin semiconductors are being actively explored as quantum information carriers. In transition metal dichalcogenides (TMDCs), the hexagonal crystal lattice gives rise to an additional valley degree of freedom with spin-valley locking and potentially enhanced spin life and coherence times. However, realizing well-separated single-particle levels and achieving transparent electrical contact to address them has remained challenging. Here, we report well-defined spin states in a few-layer MoS2 transistor, characterized with a spectral resolution of ∼50 μeV at Tel = 150 mK. Ground state magnetospectroscopy confirms a finite Berry-curvature induced coupling of spin and valley, reflected in a pronounced Zeeman anisotropy, with a large out-of-plane g-factor of g⊥ ≃ 8. A finite in-plane g-factor (g∥ ≃ 0.55-0.8) allows us to quantify spin-valley locking and estimate the spin-orbit splitting 2ΔSO ∼ 100 μeV. The demonstration of spin-valley locking is an important milestone toward realizing spin-valley quantum bits.
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Affiliation(s)
- Radha Krishnan
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Sangram Biswas
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Yu-Ling Hsueh
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Hongyang Ma
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Rajib Rahman
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Bent Weber
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
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5
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Banszerus L, Möller S, Hecker K, Icking E, Watanabe K, Taniguchi T, Hassler F, Volk C, Stampfer C. Particle-hole symmetry protects spin-valley blockade in graphene quantum dots. Nature 2023:10.1038/s41586-023-05953-5. [PMID: 37138084 DOI: 10.1038/s41586-023-05953-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 03/14/2023] [Indexed: 05/05/2023]
Abstract
Particle-hole symmetry plays an important role in the characterization of topological phases in solid-state systems1. It is found, for example, in free-fermion systems at half filling and it is closely related to the notion of antiparticles in relativistic field theories2. In the low-energy limit, graphene is a prime example of a gapless particle-hole symmetric system described by an effective Dirac equation3,4 in which topological phases can be understood by studying ways to open a gap by preserving (or breaking) symmetries5,6. An important example is the intrinsic Kane-Mele spin-orbit gap of graphene, which leads to a lifting of the spin-valley degeneracy and renders graphene a topological insulator in a quantum spin Hall phase7 while preserving particle-hole symmetry. Here we show that bilayer graphene allows the realization of electron-hole double quantum dots that exhibit near-perfect particle-hole symmetry, in which transport occurs via the creation and annihilation of single electron-hole pairs with opposite quantum numbers. Moreover, we show that particle-hole symmetric spin and valley textures lead to a protected single-particle spin-valley blockade. The latter will allow robust spin-to-charge and valley-to-charge conversion, which are essential for the operation of spin and valley qubits.
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Affiliation(s)
- L Banszerus
- JARA-FIT and 2nd Institute of Physics A, RWTH Aachen University, Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - S Möller
- JARA-FIT and 2nd Institute of Physics A, RWTH Aachen University, Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - K Hecker
- JARA-FIT and 2nd Institute of Physics A, RWTH Aachen University, Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - E Icking
- JARA-FIT and 2nd Institute of Physics A, RWTH Aachen University, Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - K Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - F Hassler
- JARA-Institute for Quantum Information, RWTH Aachen University, Aachen, Germany
| | - C Volk
- JARA-FIT and 2nd Institute of Physics A, RWTH Aachen University, Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - C Stampfer
- JARA-FIT and 2nd Institute of Physics A, RWTH Aachen University, Aachen, Germany.
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany.
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6
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Tomić P, Rickhaus P, Garcia-Ruiz A, Zheng G, Portolés E, Fal'ko V, Watanabe K, Taniguchi T, Ensslin K, Ihn T, de Vries FK. Scattering between Minivalleys in Twisted Double Bilayer Graphene. PHYSICAL REVIEW LETTERS 2022; 128:057702. [PMID: 35179933 DOI: 10.1103/physrevlett.128.057702] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 11/29/2021] [Accepted: 12/08/2021] [Indexed: 06/14/2023]
Abstract
A unique feature of the complex band structures of moiré materials is the presence of minivalleys, their hybridization, and scattering between them. Here, we investigate magnetotransport oscillations caused by scattering between minivalleys-a phenomenon analogous to magnetointersubband oscillations-in a twisted double bilayer graphene sample with a twist angle of 1.94°. We study and discuss the potential scattering mechanisms and find an electron-phonon mechanism and valley conserving scattering to be likely. Finally, we discuss the relevance of our findings for different materials and twist angles.
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Affiliation(s)
- Petar Tomić
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Peter Rickhaus
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Aitor Garcia-Ruiz
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Giulia Zheng
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Elías Portolés
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Vladimir Fal'ko
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Henry Royce Institute for Advanced Materials, M13 9PL Manchester, United Kingdom
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Klaus Ensslin
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
- Quantum Center, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Thomas Ihn
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
- Quantum Center, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Folkert K de Vries
- Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
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7
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Geisenhof FR, Winterer F, Seiler AM, Lenz J, Xu T, Zhang F, Weitz RT. Quantum anomalous Hall octet driven by orbital magnetism in bilayer graphene. Nature 2021; 598:53-58. [PMID: 34616059 DOI: 10.1038/s41586-021-03849-w] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 07/22/2021] [Indexed: 11/09/2022]
Abstract
The quantum anomalous Hall (QAH) effect-a macroscopic manifestation of chiral band topology at zero magnetic field-has been experimentally realized only by the magnetic doping of topological insulators1-3 and the delicate design of moiré heterostructures4-8. However, the seemingly simple bilayer graphene without magnetic doping or moiré engineering has long been predicted to host competing ordered states with QAH effects9-11. Here we explore states in bilayer graphene with a conductance of 2 e2 h-1 (where e is the electronic charge and h is Planck's constant) that not only survive down to anomalously small magnetic fields and up to temperatures of five kelvin but also exhibit magnetic hysteresis. Together, the experimental signatures provide compelling evidence for orbital-magnetism-driven QAH behaviour that is tunable via electric and magnetic fields as well as carrier sign. The observed octet of QAH phases is distinct from previous observations owing to its peculiar ferrimagnetic and ferrielectric order that is characterized by quantized anomalous charge, spin, valley and spin-valley Hall behaviour9.
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Affiliation(s)
- Fabian R Geisenhof
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Felix Winterer
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Anna M Seiler
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Jakob Lenz
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Tianyi Xu
- Department of Physics, University of Texas at Dallas, Richardson, TX, USA
| | - Fan Zhang
- Department of Physics, University of Texas at Dallas, Richardson, TX, USA.
| | - R Thomas Weitz
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Munich, Germany. .,Center for Nanoscience (CeNS), Munich, Germany. .,Munich Center for Quantum Science and Technology (MCQST), Munich, Germany. .,1st Physical Institute, Faculty of Physics, University of Göttingen, Göttingen, Germany.
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8
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Effective Landé factors for an electrostatically defined quantum point contact in silicene. Sci Rep 2021; 11:19892. [PMID: 34615912 PMCID: PMC8494940 DOI: 10.1038/s41598-021-99074-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 09/17/2021] [Indexed: 12/01/2022] Open
Abstract
The transconductance and effective Landé \documentclass[12pt]{minimal}
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\begin{document}$$g^*$$\end{document}g∗ factors for a quantum point contact defined in silicene by the electric field of a split gate is investigated. The strong spin–orbit coupling in buckled silicene reduces the \documentclass[12pt]{minimal}
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\begin{document}$$g^*$$\end{document}g∗ factor for in-plane magnetic field from the nominal value 2 to around 1.2 for the first- to 0.45 for the third conduction subband. However, for perpendicular magnetic field we observe an enhancement of \documentclass[12pt]{minimal}
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\begin{document}$$g^*$$\end{document}g∗ factors for the first subband to 5.8 in nanoribbon with zigzag and to 2.5 with armchair edge. The main contribution to the Zeeman splitting comes from the intrinsic spin–orbit coupling defined by the Kane–Mele form of interaction.
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9
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Ge Z, Slizovskiy S, Joucken F, Quezada EA, Taniguchi T, Watanabe K, Fal'ko VI, Velasco J. Control of Giant Topological Magnetic Moment and Valley Splitting in Trilayer Graphene. PHYSICAL REVIEW LETTERS 2021; 127:136402. [PMID: 34623864 DOI: 10.1103/physrevlett.127.136402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Accepted: 08/17/2021] [Indexed: 06/13/2023]
Abstract
Bloch states of electrons in honeycomb two-dimensional crystals with multivalley band structure and broken inversion symmetry have orbital magnetic moments of a topological nature. In crystals with two degenerate valleys, a perpendicular magnetic field lifts the valley degeneracy via a Zeeman effect due to these magnetic moments, leading to magnetoelectric effects which can be leveraged for creating valleytronic devices. In this work, we demonstrate that trilayer graphene with Bernal stacking (ABA TLG), hosts topological magnetic moments with a large and widely tunable valley g factor (g_{ν}), reaching a value g_{ν}∼1050 at the extreme of the studied parametric range. The reported experiment consists in sublattice-resolved scanning tunneling spectroscopy under perpendicular electric and magnetic fields that control the TLG bands. The tunneling spectra agree very well with the results of theoretical modeling that includes the full details of the TLG tight-binding model and accounts for a quantum-dot-like potential profile formed electrostatically under the scanning tunneling microscope tip.
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Affiliation(s)
- Zhehao Ge
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | - Sergey Slizovskiy
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- National Graphene Institute, University of Manchester, Booth Street East, Manchester M13 9PL, United Kingdom
| | - Frédéric Joucken
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | - Eberth A Quezada
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectronics National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Vladimir I Fal'ko
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- National Graphene Institute, University of Manchester, Booth Street East, Manchester M13 9PL, United Kingdom
- Henry Royce Institute for Advanced Materials, Manchester M13 9PL, United Kingdom
| | - Jairo Velasco
- Department of Physics, University of California, Santa Cruz, California 95064, USA
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10
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Rickhaus P, de Vries FK, Zhu J, Portoles E, Zheng G, Masseroni M, Kurzmann A, Taniguchi T, Watanabe K, MacDonald AH, Ihn T, Ensslin K. Correlated electron-hole state in twisted double-bilayer graphene. Science 2021; 373:1257-1260. [PMID: 34516786 DOI: 10.1126/science.abc3534] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Peter Rickhaus
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | | | - Jihang Zhu
- Department of Physics, University of Texas at Austin, Austin, TX 78712, USA
| | - Elías Portoles
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Giulia Zheng
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Michele Masseroni
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Annika Kurzmann
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Allan H MacDonald
- Department of Physics, University of Texas at Austin, Austin, TX 78712, USA
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland.,Quantum Center, ETH Zürich, 8093 Zürich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland.,Quantum Center, ETH Zürich, 8093 Zürich, Switzerland
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11
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Joucken F, Bena C, Ge Z, Quezada-Lopez EA, Ducastelle F, Tanagushi T, Watanabe K, Velasco J. Sublattice Dependence and Gate Tunability of Midgap and Resonant States Induced by Native Dopants in Bernal-Stacked Bilayer Graphene. PHYSICAL REVIEW LETTERS 2021; 127:106401. [PMID: 34533366 DOI: 10.1103/physrevlett.127.106401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 07/08/2021] [Indexed: 06/13/2023]
Abstract
The properties of semiconductors can be crucially impacted by midgap states induced by dopants, which can be native or intentionally incorporated in the crystal lattice. For Bernal-stacked bilayer graphene (BLG), which has a tunable band gap, the existence of midgap states induced by dopants or adatoms has been investigated theoretically and observed indirectly in electron transport experiments. Here, we characterize BLG midgap states in real space, with atomic-scale resolution with scanning tunneling microscopy and spectroscopy. We show that the midgap states in BLG-for which we demonstrate gate tunability-appear when the dopant is hosted on the nondimer sublattice sites. We further evidence the presence of narrow resonances at the onset of the high-energy bands (valence or conduction, depending on the dopant type) when the dopants lie on the dimer sublattice sites. Our results are supported by tight-binding calculations that agree remarkably well with the experimental findings.
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Affiliation(s)
- Frédéric Joucken
- Department of Physics, University of California, Santa Cruz, California 95064, USA
- Department of Physics, Box 871504, Arizona State University, Tempe, Arizona 85287, USA
| | - Cristina Bena
- Institut de Physique Théorique, Université Paris Saclay, CEA CNRS, Orme des Merisiers, 91190 Gif-sur-Yvette Cedex, France
| | - Zhehao Ge
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | | | - François Ducastelle
- Laboratoire d'Etude des Microstructures, ONERA-CNRS, UMR104, Université Paris-Saclay, B.P. 72, 92322 Châtillon Cedex, France
| | - Takashi Tanagushi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Jairo Velasco
- Department of Physics, University of California, Santa Cruz, California 95064, USA
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12
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Banszerus L, Möller S, Steiner C, Icking E, Trellenkamp S, Lentz F, Watanabe K, Taniguchi T, Volk C, Stampfer C. Spin-valley coupling in single-electron bilayer graphene quantum dots. Nat Commun 2021; 12:5250. [PMID: 34475394 PMCID: PMC8413270 DOI: 10.1038/s41467-021-25498-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 08/13/2021] [Indexed: 11/30/2022] Open
Abstract
Understanding how the electron spin is coupled to orbital degrees of freedom, such as a valley degree of freedom in solid-state systems, is central to applications in spin-based electronics and quantum computation. Recent developments in the preparation of electrostatically-confined quantum dots in gapped bilayer graphene (BLG) enable to study the low-energy single-electron spectra in BLG quantum dots, which is crucial for potential spin and spin-valley qubit operations. Here, we present the observation of the spin-valley coupling in bilayer graphene quantum dots in the single-electron regime. By making use of highly-tunable double quantum dot devices we achieve an energy resolution allowing us to resolve the lifting of the fourfold spin and valley degeneracy by a Kane-Mele type spin-orbit coupling of ≈ 60 μeV. Furthermore, we find an upper limit of a potentially disorder-induced mixing of the \documentclass[12pt]{minimal}
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\begin{document}$$K^{\prime}$$\end{document}K′ states below 20 μeV. Understanding the interaction between spin and valley degrees of freedom in graphene-based quantum dots underpins their applications in electronics and quantum information. Here, the authors study the low-energy spectrum and resolve the spin-valley coupling in single-electron quantum dots in bilayer graphene.
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Affiliation(s)
- L Banszerus
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany. .,Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany.
| | - S Möller
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany.,Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - C Steiner
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany.,Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - E Icking
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany.,Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - S Trellenkamp
- Helmholtz Nano Facility, Forschungszentrum Jülich, Jülich, Germany
| | - F Lentz
- Helmholtz Nano Facility, Forschungszentrum Jülich, Jülich, Germany
| | - K Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - C Volk
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany.,Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
| | - C Stampfer
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany.,Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, Jülich, Germany
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13
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Gold C, Knothe A, Kurzmann A, Garcia-Ruiz A, Watanabe K, Taniguchi T, Fal'ko V, Ensslin K, Ihn T. Coherent Jetting from a Gate-Defined Channel in Bilayer Graphene. PHYSICAL REVIEW LETTERS 2021; 127:046801. [PMID: 34355933 DOI: 10.1103/physrevlett.127.046801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 05/18/2021] [Indexed: 06/13/2023]
Abstract
Graphene has evolved as a platform for quantum transport that can compete with the best and cleanest semiconductor systems. Here, we report on the observation of distinct electronic jets emanating from a narrow split-gate-defined channel in bilayer graphene. We find that these jets, which are visible via their interference patterns, occur predominantly with an angle of 60° between each other. This observation is related to the trigonal warping in the band structure of bilayer graphene, which, in conjunction with electron injection through a constriction, leads to a valley-dependent selection of momenta. This experimental observation of electron jetting has consequences for carrier transport in two-dimensional materials with a trigonally warped band structure in general, as well as for devices relying on ballistic and valley-selective transport.
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Affiliation(s)
- Carolin Gold
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Angelika Knothe
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Annika Kurzmann
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Aitor Garcia-Ruiz
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Vladimir Fal'ko
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Department of Physics, University of Manchester, Manchester M13 9PL, United Kingdom
- Henry Royce Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
- Quantum Center, ETH Zürich, 8093 Zürich, Switzerland
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
- Quantum Center, ETH Zürich, 8093 Zürich, Switzerland
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14
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Jo M, Brasseur P, Assouline A, Fleury G, Sim HS, Watanabe K, Taniguchi T, Dumnernpanich W, Roche P, Glattli DC, Kumada N, Parmentier FD, Roulleau P. Quantum Hall Valley Splitters and a Tunable Mach-Zehnder Interferometer in Graphene. PHYSICAL REVIEW LETTERS 2021; 126:146803. [PMID: 33891444 DOI: 10.1103/physrevlett.126.146803] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Accepted: 02/18/2021] [Indexed: 06/12/2023]
Abstract
Graphene is a very promising test bed for the field of electron quantum optics. However, a fully tunable and coherent electronic beam splitter is still missing. We report the demonstration of electronic beam splitters in graphene that couple quantum Hall edge channels having opposite valley polarizations. The electronic transmission of our beam splitters can be tuned from zero to near unity. By independently setting the beam splitters at the two corners of a graphene p-n junction to intermediate transmissions, we realize a fully tunable electronic Mach-Zehnder interferometer. This tunability allows us to unambiguously identify the quantum interferences due to the Mach-Zehnder interferometer, and to study their dependence with the beam-splitter transmission and the interferometer bias voltage. The comparison with conventional semiconductor interferometers points toward universal processes driving the quantum decoherence in those two different 2D systems, with graphene being much more robust to their effect.
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Affiliation(s)
- M Jo
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - P Brasseur
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - A Assouline
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - G Fleury
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - H-S Sim
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
| | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - W Dumnernpanich
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - P Roche
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - D C Glattli
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - N Kumada
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi 243-0198, Japan
| | - F D Parmentier
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
| | - P Roulleau
- SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex France
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15
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Omata T, Asano H, Sakai M, Terai Y, Kita M. Enhanced Valley Splitting of Exciton Emission in Colloidal PbSe Quantum Dots When the Interdot Distance Coincides with Onset of Förster Resonance Energy Transfer. J Phys Chem Lett 2021; 12:3120-3126. [PMID: 33755486 DOI: 10.1021/acs.jpclett.1c00165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Photoluminescence (PL) emission of colloidal PbSe/CdSe core/shell quantum dots (QDs, CdSe shell thickness: 0.2 nm) at the lowest exciton state was investigated at room temperature and varying inter-QD distance (L = 7-240 nm) by changing the QD concentration. A distinct enhancement of the valley splitting of PbSe QDs was observed upon reducing L. Simultaneously, there was a redshift in the emission due to Förster resonance energy transfer (FRET), when the L value was still sufficiently large (7 nm ≤ L ≤ 50 nm) so that the wave functions of different QDs do not overlap. The enhanced valley splitting under no apparent external field is quite interesting as a method to control the valley splitting. The electronic coupling leading to FRET may enhance the valley splitting, because it occurs in an identical range of L.
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Affiliation(s)
- Takahisa Omata
- Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, Japan
- Division of Material and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan
| | - Hiroshi Asano
- Division of Material and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan
| | - Masahiro Sakai
- Panasonic Research Alliance Laboratories, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan
| | - Yoshikazu Terai
- Department of Computer Science and Electronics, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka 820-8502, Japan
| | - Masao Kita
- Department of Mechanical Engineering, Toyama National College of Technology, 13 Hongo-machi, Toyama 939-8630, Japan
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16
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Tong C, Garreis R, Knothe A, Eich M, Sacchi A, Watanabe K, Taniguchi T, Fal'ko V, Ihn T, Ensslin K, Kurzmann A. Tunable Valley Splitting and Bipolar Operation in Graphene Quantum Dots. NANO LETTERS 2021; 21:1068-1073. [PMID: 33449702 DOI: 10.1021/acs.nanolett.0c04343] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Quantum states in graphene are 2-fold degenerate in spins, and 2-fold in valleys. Both degrees of freedom can be utilized for qubit preparations. In our bilayer graphene quantum dots, we demonstrate that the valley g-factor gv, defined analogously to the spin g-factor gs for valley splitting in a perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90, by gate voltage adjustments only. Larger gv results from larger electronic dot sizes, determined from the charging energy. On our versatile device, bipolar operation, charging our quantum dot with charge carriers of the same or the opposite polarity as the leads, can be performed. Dots of both polarities are tunable to the first charge carrier, such that the transition from an electron to a hole dot by the action of the plunger gate can be observed. Addition of gates easily extends the system to host tunable double dots.
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Affiliation(s)
- Chuyao Tong
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Rebekka Garreis
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Angelika Knothe
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Marius Eich
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Agnese Sacchi
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Vladimir Fal'ko
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Henry Royce Institute for Advanced Materials, M13 9PL, Manchester, U.K
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Annika Kurzmann
- Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich, Switzerland
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17
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Ge Z, Joucken F, Quezada E, da Costa DR, Davenport J, Giraldo B, Taniguchi T, Watanabe K, Kobayashi NP, Low T, Velasco J. Visualization and Manipulation of Bilayer Graphene Quantum Dots with Broken Rotational Symmetry and Nontrivial Topology. NANO LETTERS 2020; 20:8682-8688. [PMID: 33226819 DOI: 10.1021/acs.nanolett.0c03453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Electrostatically defined quantum dots (QDs) in Bernal stacked bilayer graphene (BLG) are a promising quantum information platform because of their long spin decoherence times, high sample quality, and tunability. Importantly, the shape of QD states determines the electron energy spectrum, the interactions between electrons, and the coupling of electrons to their environment, all of which are relevant for quantum information processing. Despite its importance, the shape of BLG QD states remains experimentally unexamined. Here we report direct visualization of BLG QD states by using a scanning tunneling microscope. Strikingly, we find these states exhibit a robust broken rotational symmetry. By using a numerical tight-binding model, we determine that the observed broken rotational symmetry can be attributed to low energy anisotropic bands. We then compare confined holes and electrons and demonstrate the influence of BLG's nontrivial band topology. Our study distinguishes BLG QDs from prior QD platforms with trivial band topology.
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Affiliation(s)
- Zhehao Ge
- Department of Physics, University of California, Santa Cruz, California 95064, United States
| | - Frederic Joucken
- Department of Physics, University of California, Santa Cruz, California 95064, United States
| | - Eberth Quezada
- Department of Physics, University of California, Santa Cruz, California 95064, United States
| | - Diego R da Costa
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
| | - John Davenport
- Department of Physics, University of California, Santa Cruz, California 95064, United States
| | - Brian Giraldo
- Jack Baskin School of Engineering, University of California, Santa Cruz, California 95064, United States
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectronics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Nobuhiko P Kobayashi
- Jack Baskin School of Engineering, University of California, Santa Cruz, California 95064, United States
| | - Tony Low
- Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Jairo Velasco
- Department of Physics, University of California, Santa Cruz, California 95064, United States
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18
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Moriya R, Kinoshita K, Crosse JA, Watanabe K, Taniguchi T, Masubuchi S, Moon P, Koshino M, Machida T. Emergence of orbital angular moment at van Hove singularity in graphene/h-BN moiré superlattice. Nat Commun 2020; 11:5380. [PMID: 33097720 PMCID: PMC7584618 DOI: 10.1038/s41467-020-19043-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 09/25/2020] [Indexed: 11/21/2022] Open
Abstract
Bloch electrons lacking inversion symmetry exhibit orbital magnetic moments owing to the rotation around their center of mass; this moment induces a valley splitting in a magnetic field. For the graphene/h-BN moiré superlattice, inversion symmetry is broken by the h-BN. The superlattice potential generates a series of Dirac points (DPs) and van Hove singularities (vHSs) within an experimentally accessible low energy state, providing a platform to study orbital moments with respect to band structure. In this work, theoretical calculations and magnetothermoelectric measurements are combined to reveal the emergence of an orbital magnetic moment at vHSs in graphene/h-BN moiré superlattices. The thermoelectric signal for the vHS at the low energy side of the hole-side secondary DP exhibited significant magnetic field-induced valley splitting with an effective g-factor of approximately 130; splitting for other vHSs was negligible. This was attributed to the emergence of an orbital magnetic moment at the second vHS at the hole-side.
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Affiliation(s)
- Rai Moriya
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan.
| | - Kei Kinoshita
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
| | - J A Crosse
- New York University Shanghai and NYU-ECNU Institute of Physics at NYU Shanghai, Shanghai, China
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Satoru Masubuchi
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
| | - Pilkyung Moon
- New York University Shanghai and NYU-ECNU Institute of Physics at NYU Shanghai, Shanghai, China
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Mikito Koshino
- Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Tomoki Machida
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan.
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19
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Banszerus L, Rothstein A, Fabian T, Möller S, Icking E, Trellenkamp S, Lentz F, Neumaier D, Watanabe K, Taniguchi T, Libisch F, Volk C, Stampfer C. Electron-Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots. NANO LETTERS 2020; 20:7709-7715. [PMID: 32986437 PMCID: PMC7564435 DOI: 10.1021/acs.nanolett.0c03227] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 09/28/2020] [Indexed: 05/21/2023]
Abstract
Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron-hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g-factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B-fields. Our measurements agree well with tight-binding calculations for our device.
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Affiliation(s)
- L. Banszerus
- JARA-FIT
and 2nd Institute of Physics, RWTH Aachen
University, 52074 Aachen, Germany, E.U
- Peter
Grünberg Institute (PGI-9), Forschungszentrum
Jülich, 52425 Jülich, Germany, E.U
| | - A. Rothstein
- JARA-FIT
and 2nd Institute of Physics, RWTH Aachen
University, 52074 Aachen, Germany, E.U
| | - T. Fabian
- Institute
for Theoretical Physics, TU Wien, 1040 Vienna, Austria, E.U
| | - S. Möller
- JARA-FIT
and 2nd Institute of Physics, RWTH Aachen
University, 52074 Aachen, Germany, E.U
- Peter
Grünberg Institute (PGI-9), Forschungszentrum
Jülich, 52425 Jülich, Germany, E.U
| | - E. Icking
- JARA-FIT
and 2nd Institute of Physics, RWTH Aachen
University, 52074 Aachen, Germany, E.U
- Peter
Grünberg Institute (PGI-9), Forschungszentrum
Jülich, 52425 Jülich, Germany, E.U
| | - S. Trellenkamp
- Helmholtz
Nano Facility, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - F. Lentz
- Helmholtz
Nano Facility, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - D. Neumaier
- AMO
GmbH, Gesellschaft für
Angewandte Mikro- und Optoelektronik, 52074 Aachen, Germany, E.U
- University
of Wuppertal, 42285 Wuppertal, Germany, E.U
| | - K. Watanabe
- Research
Center for Functional Materials, National
Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T. Taniguchi
- International
Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - F. Libisch
- Institute
for Theoretical Physics, TU Wien, 1040 Vienna, Austria, E.U
| | - C. Volk
- JARA-FIT
and 2nd Institute of Physics, RWTH Aachen
University, 52074 Aachen, Germany, E.U
- Peter
Grünberg Institute (PGI-9), Forschungszentrum
Jülich, 52425 Jülich, Germany, E.U
| | - C. Stampfer
- JARA-FIT
and 2nd Institute of Physics, RWTH Aachen
University, 52074 Aachen, Germany, E.U
- Peter
Grünberg Institute (PGI-9), Forschungszentrum
Jülich, 52425 Jülich, Germany, E.U
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20
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Banszerus L, Frohn B, Fabian T, Somanchi S, Epping A, Müller M, Neumaier D, Watanabe K, Taniguchi T, Libisch F, Beschoten B, Hassler F, Stampfer C. Observation of the Spin-Orbit Gap in Bilayer Graphene by One-Dimensional Ballistic Transport. PHYSICAL REVIEW LETTERS 2020; 124:177701. [PMID: 32412294 DOI: 10.1103/physrevlett.124.177701] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 04/13/2020] [Indexed: 05/21/2023]
Abstract
We report on measurements of quantized conductance in gate-defined quantum point contacts in bilayer graphene that allow the observation of subband splittings due to spin-orbit coupling. The size of this splitting can be tuned from 40 to 80 μeV by the displacement field. We assign this gate-tunable subband splitting to a gap induced by spin-orbit coupling of Kane-Mele type, enhanced by proximity effects due to the substrate. We show that this spin-orbit coupling gives rise to a complex pattern in low perpendicular magnetic fields, increasing the Zeeman splitting in one valley and suppressing it in the other one. In addition, we observe a spin polarized channel of 6e^{2}/h at high in-plane magnetic field and signatures of interaction effects at the crossings of spin-split subbands of opposite spins at finite magnetic field.
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Affiliation(s)
- L Banszerus
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany, EU
| | - B Frohn
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
| | - T Fabian
- Institute for Theoretical Physics, TU Wien, 1040 Vienna, Austria, EU
| | - S Somanchi
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
| | - A Epping
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany, EU
| | - M Müller
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany, EU
| | | | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - F Libisch
- Institute for Theoretical Physics, TU Wien, 1040 Vienna, Austria, EU
| | - B Beschoten
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
| | - F Hassler
- JARA-Institute for Quantum Information, RWTH Aachen University, 52056 Aachen, Germany, EU
| | - C Stampfer
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany, EU
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