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Cheng G, Lin MH, Chen HY, Wang D, Wang Z, Qin W, Zhang Z, Zeng C. Reversible modulation of superconductivity in thin-film NbSe 2 via plasmon coupling. Nat Commun 2024; 15:6037. [PMID: 39019892 PMCID: PMC11255238 DOI: 10.1038/s41467-024-50452-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 07/10/2024] [Indexed: 07/19/2024] Open
Abstract
In recent years, lightwave has stood out as an ultrafast, non-contact control knob for developing compact superconducting circuitry. However, the modulation efficiency is limited by the low photoresponse of superconductors. Plasmons, with the advantages of strong light-matter interaction, present a promising route to overcome the limitations. Here we achieve effective modulation of superconductivity in thin-film NbSe2 via near-field coupling to plasmons in gold nanoparticles. Upon resonant plasmon excitation, the superconductivity of NbSe2 is substantially suppressed. The modulation factor exceeds 40% at a photon flux of 9.36 × 1013 s-1mm-2, and the effect is significantly diminished for thicker NbSe2 samples. Our observations can be theoretically interpreted by invoking the non-equilibrium electron distribution in NbSe2 driven by the plasmon-associated evanescent field. Finally, a reversible plasmon-driven superconducting switch is realized in this system. These findings highlight plasmonic tailoring of quantum states as an innovative strategy for superconducting electronics.
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Affiliation(s)
- Guanghui Cheng
- CAS Key Laboratory of Strongly Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, China.
- Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai, Japan.
| | | | | | - Dongli Wang
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
| | - Zheyan Wang
- CAS Key Laboratory of Strongly Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, China
| | - Wei Qin
- CAS Key Laboratory of Strongly Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, China.
| | - Zhenyu Zhang
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
- Hefei National Laboratory, Hefei, China
| | - Changgan Zeng
- CAS Key Laboratory of Strongly Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, China.
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.
- Hefei National Laboratory, Hefei, China.
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2
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Luo L, Cheng D, Song B, Wang LL, Vaswani C, Lozano PM, Gu G, Huang C, Kim RHJ, Liu Z, Park JM, Yao Y, Ho K, Perakis IE, Li Q, Wang J. A light-induced phononic symmetry switch and giant dissipationless topological photocurrent in ZrTe 5. NATURE MATERIALS 2021; 20:329-334. [PMID: 33462464 DOI: 10.1038/s41563-020-00882-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 11/17/2020] [Indexed: 06/12/2023]
Abstract
Dissipationless currents from topologically protected states are promising for disorder-tolerant electronics and quantum computation. Here, we photogenerate giant anisotropic terahertz nonlinear currents with vanishing scattering, driven by laser-induced coherent phonons of broken inversion symmetry in a centrosymmetric Dirac material ZrTe5. Our work suggests that this phononic terahertz symmetry switching leads to formation of Weyl points, whose chirality manifests in a transverse, helicity-dependent current, orthogonal to the dynamical inversion symmetry breaking axis, via circular photogalvanic effect. The temperature-dependent topological photocurrent exhibits several distinct features: Berry curvature dominance, particle-hole reversal near conical points and chirality protection that is responsible for an exceptional ballistic transport length of ~10 μm. These results, together with first-principles modelling, indicate two pairs of Weyl points dynamically created by B1u phonons of broken inversion symmetry. Such phononic terahertz control breaks ground for coherent manipulation of Weyl nodes and robust quantum transport without application of static electric or magnetic fields.
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Affiliation(s)
- Liang Luo
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Di Cheng
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Boqun Song
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Lin-Lin Wang
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Chirag Vaswani
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - P M Lozano
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA
| | - G Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA
| | - Chuankun Huang
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Richard H J Kim
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Zhaoyu Liu
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Joong-Mok Park
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Yongxin Yao
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Kaiming Ho
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA
| | - Ilias E Perakis
- Department of Physics, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Qiang Li
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA.
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA.
| | - Jigang Wang
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory, US Department of Energy, Ames, IA, USA.
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3
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Vaswani C, Kang JH, Mootz M, Luo L, Yang X, Sundahl C, Cheng D, Huang C, Kim RHJ, Liu Z, Collantes YG, Hellstrom EE, Perakis IE, Eom CB, Wang J. Light quantum control of persisting Higgs modes in iron-based superconductors. Nat Commun 2021; 12:258. [PMID: 33431843 PMCID: PMC7801641 DOI: 10.1038/s41467-020-20350-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 11/30/2020] [Indexed: 11/28/2022] Open
Abstract
The Higgs mechanism, i.e., spontaneous symmetry breaking of the quantum vacuum, is a cross-disciplinary principle, universal for understanding dark energy, antimatter and quantum materials, from superconductivity to magnetism. Unlike one-band superconductors (SCs), a conceptually distinct Higgs amplitude mode can arise in multi-band, unconventional superconductors via strong interband Coulomb interaction, but is yet to be accessed. Here we discover such hybrid Higgs mode and demonstrate its quantum control by light in iron-based high-temperature SCs. Using terahertz (THz) two-pulse coherent spectroscopy, we observe a tunable amplitude mode coherent oscillation of the complex order parameter from coupled lower and upper bands. The nonlinear dependence of the hybrid Higgs mode on the THz driving fields is distinct from any known SC results: we observe a large reversible modulation of resonance strength, yet with a persisting mode frequency. Together with quantum kinetic modeling of a hybrid Higgs mechanism, distinct from charge-density fluctuations and without invoking phonons or disorder, our result provides compelling evidence for a light-controlled coupling between the electron and hole amplitude modes assisted by strong interband quantum entanglement. Such light-control of Higgs hybridization can be extended to probe many-body entanglement and hidden symmetries in other complex systems. A collective excitation called Higgs mode may arise in multi-band superconductors via strong interband interaction, but it is yet to be accessed. Here, the authors observe a tunable coherent amplitude oscillation of the order parameter in Ba(Fe1−xCox)2As2, suggesting appearance and control of the Higgs mode by light tuning interband interaction.
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Affiliation(s)
- C Vaswani
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - J H Kang
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - M Mootz
- Department of Physics, University of Alabama at Birmingham, Birmingham, AL, 35294-1170, USA
| | - L Luo
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - X Yang
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - C Sundahl
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - D Cheng
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - C Huang
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - R H J Kim
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - Z Liu
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA
| | - Y G Collantes
- Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA
| | - E E Hellstrom
- Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA
| | - I E Perakis
- Department of Physics, University of Alabama at Birmingham, Birmingham, AL, 35294-1170, USA
| | - C B Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - J Wang
- Department of Physics and Astronomy, Iowa State University, and Ames Laboratory, Ames, IA, 50011, USA.
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4
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Chen J, Zhang Z, Luo L, Lu Y, Song C, Cheng D, Chen X, Li W, Ren Z, Wang J, Tian H, Zhang Z, Han G. Reversible magnetism transition at ferroelectric oxide heterointerface. Sci Bull (Beijing) 2020; 65:2094-2099. [PMID: 36732962 DOI: 10.1016/j.scib.2020.09.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 08/11/2020] [Accepted: 09/01/2020] [Indexed: 02/04/2023]
Abstract
Oxide heterointerface is a platform to create unprecedented two-dimensional electron gas, superconductivity and ferromagnetism, arising from a polar discontinuity at the interface. In particular, the ability to tune these intriguing effects paves a way to elucidate their fundamental physics and to develop novel electronic/magnetic devices. In this work, we report for the first time that a ferroelectric polarization screening at SrTiO3/PbTiO3 interface is able to drive an electronic construction of Ti atom, giving rise to room-temperature ferromagnetism. Surprisingly, such ferromagnetism can be switched to antiferromagnetism by applying a magnetic field, which is reversible. A coupling of itinerant electrons with local moments at interfacial Ti 3d orbital was proposed to explain the magnetism. The localization of the itinerant electrons under a magnetic field is responsible for the suppression of magnetism. These findings provide new insights into interfacial magnetism and their control by magnetic field relevant interfacial electrons promising for device applications.
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Affiliation(s)
- Jialu Chen
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China
| | - Zijun Zhang
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Liang Luo
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory-USDOE, Ames, IA 50011, USA
| | - Yunhao Lu
- Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Cheng Song
- Key Laboratory of Advanced Materials (Ministry of Education), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Di Cheng
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory-USDOE, Ames, IA 50011, USA
| | - Xing Chen
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Wei Li
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China
| | - Zhaohui Ren
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China.
| | - Jigang Wang
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory-USDOE, Ames, IA 50011, USA.
| | - He Tian
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Ze Zhang
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Gaorong Han
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China.
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5
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Vaswani C, Mootz M, Sundahl C, Mudiyanselage DH, Kang JH, Yang X, Cheng D, Huang C, Kim RHJ, Liu Z, Luo L, Perakis IE, Eom CB, Wang J. Terahertz Second-Harmonic Generation from Lightwave Acceleration of Symmetry-Breaking Nonlinear Supercurrents. PHYSICAL REVIEW LETTERS 2020; 124:207003. [PMID: 32501057 DOI: 10.1103/physrevlett.124.207003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 03/29/2020] [Accepted: 04/23/2020] [Indexed: 06/11/2023]
Abstract
We report terahertz (THz) light-induced second harmonic generation, in superconductors with inversion symmetry that forbid even-order nonlinearities. The THz second harmonic emission vanishes above the superconductor critical temperature and arises from precession of twisted Anderson pseudospins at a multicycle, THz driving frequency that is not allowed by equilibrium symmetry. We explain the microscopic physics by a dynamical symmetry breaking principle at sub-THz-cycle by using quantum kinetic modeling of the interplay between strong THz-lightwave nonlinearity and pulse propagation. The resulting nonzero integrated pulse area inside the superconductor leads to light-induced nonlinear supercurrents due to subcycle Cooper pair acceleration, in contrast to dc-biased superconductors, which can be controlled by the band structure and THz driving field below the superconducting gap.
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Affiliation(s)
- C Vaswani
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - M Mootz
- Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294-1170, USA
| | - C Sundahl
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - D H Mudiyanselage
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - J H Kang
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - X Yang
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - D Cheng
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - C Huang
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - R H J Kim
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Z Liu
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - L Luo
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - I E Perakis
- Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294-1170, USA
| | - C B Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - J Wang
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
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6
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Liu Z, Vaswani C, Yang X, Zhao X, Yao Y, Song Z, Cheng D, Shi Y, Luo L, Mudiyanselage DH, Huang C, Park JM, Kim RHJ, Zhao J, Yan Y, Ho KM, Wang J. Ultrafast Control of Excitonic Rashba Fine Structure by Phonon Coherence in the Metal Halide Perovskite CH_{3}NH_{3}PbI_{3}. PHYSICAL REVIEW LETTERS 2020; 124:157401. [PMID: 32357060 DOI: 10.1103/physrevlett.124.157401] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2019] [Revised: 02/17/2020] [Accepted: 03/13/2020] [Indexed: 06/11/2023]
Abstract
We discover hidden Rashba fine structure in CH_{3}NH_{3}PbI_{3} and demonstrate its quantum control by vibrational coherence through symmetry-selective vibronic (electron-phonon) coupling. Above a critical threshold of a single-cycle terahertz pump field, a Raman phonon mode distinctly modulates the middle excitonic states with persistent coherence for more than ten times longer than the ones on two sides that predominately couple to infrared phonons. These vibronic quantum beats, together with first-principles modeling of phonon periodically modulated Rashba parameters, identify a threefold excitonic fine structure splitting, i.e., optically forbidden, degenerate dark states in between two bright ones with a narrow, ∼3 nm splitting. Harnessing of vibronic quantum coherence and symmetry inspires light-perovskite quantum control and sub-THz-cycle "Rashba engineering" of spin-split bands for ultimate multifunction device.
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Affiliation(s)
- Z Liu
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - C Vaswani
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - X Yang
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - X Zhao
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Y Yao
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Z Song
- Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, Ohio 43606, USA
| | - D Cheng
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - Y Shi
- ICQD/Hefei National Laboratory for Physical Sciences at the Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - L Luo
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - D-H Mudiyanselage
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - C Huang
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - J-M Park
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - R H J Kim
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - J Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at the Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Y Yan
- Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, Ohio 43606, USA
| | - K-M Ho
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
| | - J Wang
- Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
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Ultrafast manipulation of topologically enhanced surface transport driven by mid-infrared and terahertz pulses in Bi 2Se 3. Nat Commun 2019; 10:607. [PMID: 30723197 PMCID: PMC6363774 DOI: 10.1038/s41467-019-08559-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 01/18/2019] [Indexed: 11/17/2022] Open
Abstract
Topology-protected surface transport of ultimate thinness in three-dimensional topological insulators (TIs) is breaking new ground in quantum science and technology. Yet a challenge remains on how to disentangle and selectively control surface helical spin transport from the bulk contribution. Here we use the mid-infrared and terahertz (THz) photoexcitation of exclusive intraband transitions to enable ultrafast manipulation of surface THz conductivity in Bi2Se3. The unique, transient electronic state is characterized by frequency-dependent carrier relaxations that directly distinguish the faster surface channel than the bulk with no complication from interband excitations or need for reduced bulk doping. We determine the topological enhancement ratio between bulk and surface scattering rates, i.e., γBS/γSS ~3.80 in equilibrium. The ultra-broadband, wavelength-selective pumping may be applied to emerging topological semimetals for separation and control of the protected transport connected with the Weyl nodes from other bulk bands. It remains challenging on how to selectively control terahertz conductivity at surface from the bulk contribution in topological insulators. Here, Luo et al. discover and manipulate topologically enhanced surface transport due to helical spin structure using mid-infrared and terahertz ultrafast photoexcitations.
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