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Trzaskowska A, Mielcarek S, Wiesner M, Lombardi F, Mroz B. Dispersion of the surface phonons in semiconductor/topological insulator Si/Bi 2Te 3 heterostructure studied by high resolution Brillouin spectroscopy. ULTRASONICS 2021; 117:106526. [PMID: 34303926 DOI: 10.1016/j.ultras.2021.106526] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 06/11/2021] [Accepted: 07/16/2021] [Indexed: 06/13/2023]
Abstract
The dynamics and dispersion of surface phonons in heterostructure semiconductor/ topological insulator Si/Bi2Te3 was investigated using high resolution Brillouin light scattering method in the GHz frequency range. Both Rayleigh and Sezawa surface acoustic waves have been observed for wave vectors ranging from 0.006 to 0.023 nm-1. Anomaly in dispersion relations ω(q) for both surface waves were detected for the wave vector q = 0.016 nm-1. The finite element method (FEM) was used to simulate the observed shapes of ω(q) and to find the deformation profiles of surface acoustic waves. We attribute the observed changes to the coupling between low energy electrons and surface phonons. The coupling between helical Dirac states and surface phonons is discussed in the frame of accessible theoretical models.
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Affiliation(s)
- A Trzaskowska
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznan, Poland.
| | - S Mielcarek
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznan, Poland
| | - M Wiesner
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznan, Poland
| | - F Lombardi
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96, Göteborg, Sweden
| | - B Mroz
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznan, Poland
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2
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Kiphart D, Harkavyi Y, Balin K, Szade J, Mróz B, Kuświk P, Jurga S, Wiesner M. Investigations of proximity-induced superconductivity in the topological insulator Bi 2Te 3 by microRaman spectroscopy. Sci Rep 2021; 11:22980. [PMID: 34837028 PMCID: PMC8626455 DOI: 10.1038/s41598-021-02475-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 11/01/2021] [Indexed: 11/12/2022] Open
Abstract
We used the topological insulator (TI) Bi2Te3 and a high-temperature superconductor (HTSC) hybrid device for investigations of proximity-induced superconductivity (PS) in the TI. Application of the superconductor YBa2Cu3O7-δ (YBCO) enabled us to access higher temperature and energy scales for this phenomenon. The HTSC in the hybrid device exhibits emergence of a pseudogap state for T > Tc that converts into a superconducting state with a reduced gap for T < Tc. The conversion process has been reflected in Raman spectra collected from the TI. Complementary charge transport experiments revealed emergence of the proximity-induced superconducting gap in the TI and the reduced superconducting gap in the HTSC, but no signature of the pseudogap. This allowed us to conclude that Raman spectroscopy reveals formation of the pseudogap state but cannot distinguish the proximity-induced superconducting state in the TI from the superconducting state in the HTSC characterised by the reduced gap. Results of our experiments have shown that Raman spectroscopy is a complementary technique to classic charge transport experiments and is a powerful tool for investigation of the proximity-induced superconductivity in the Bi2Te3.
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Affiliation(s)
- D Kiphart
- Adam Mickiewicz University, Faculty of Physics, Uniwersytetu Poznanskiego 2, 61-614, Poznan, Poland
| | - Y Harkavyi
- Adam Mickiewicz University, Faculty of Physics, Uniwersytetu Poznanskiego 2, 61-614, Poznan, Poland
| | - K Balin
- A. Chełkowski Institute of Physics and Silesian Center for Education and Interdisciplinary Research, University of Silesia, 75 Pułku Piechoty 1A, 41-500, Chorzow, Poland
| | - J Szade
- A. Chełkowski Institute of Physics and Silesian Center for Education and Interdisciplinary Research, University of Silesia, 75 Pułku Piechoty 1A, 41-500, Chorzow, Poland
| | - B Mróz
- Adam Mickiewicz University, Faculty of Physics, Uniwersytetu Poznanskiego 2, 61-614, Poznan, Poland
| | - P Kuświk
- Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179, Poznan, Poland
| | - S Jurga
- The NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej 3, 61-614, Poznan, Poland
| | - M Wiesner
- Adam Mickiewicz University, Faculty of Physics, Uniwersytetu Poznanskiego 2, 61-614, Poznan, Poland.
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3
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Yin JX, Shumiya N, Mardanya S, Wang Q, Zhang SS, Tien HJ, Multer D, Jiang Y, Cheng G, Yao N, Wu S, Wu D, Deng L, Ye Z, He R, Chang G, Liu Z, Jiang K, Wang Z, Neupert T, Agarwal A, Chang TR, Chu CW, Lei H, Hasan MZ. Fermion-boson many-body interplay in a frustrated kagome paramagnet. Nat Commun 2020; 11:4003. [PMID: 32778651 PMCID: PMC7417595 DOI: 10.1038/s41467-020-17464-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Accepted: 07/01/2020] [Indexed: 11/09/2022] Open
Abstract
Kagome-nets, appearing in electronic, photonic and cold-atom systems, host frustrated fermionic and bosonic excitations. However, it is rare to find a system to study their fermion-boson many-body interplay. Here we use state-of-the-art scanning tunneling microscopy/spectroscopy to discover unusual electronic coupling to flat-band phonons in a layered kagome paramagnet, CoSn. We image the kagome structure with unprecedented atomic resolution and observe the striking bosonic mode interacting with dispersive kagome electrons near the Fermi surface. At this mode energy, the fermionic quasi-particle dispersion exhibits a pronounced renormalization, signaling a giant coupling to bosons. Through the self-energy analysis, first-principles calculation, and a lattice vibration model, we present evidence that this mode arises from the geometrically frustrated phonon flat-band, which is the lattice bosonic analog of the kagome electron flat-band. Our findings provide the first example of kagome bosonic mode (flat-band phonon) in electronic excitations and its strong interaction with fermionic degrees of freedom in kagome-net materials.
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Affiliation(s)
- J-X Yin
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA.
| | - Nana Shumiya
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - Sougata Mardanya
- Department of Physics, National Cheng Kung University, 701, Tainan, Taiwan
| | - Qi Wang
- Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials&Micro-nano Devices, Renmin University of China, 100872, Beijing, China
| | - Songtian S Zhang
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - Hung-Ju Tien
- Department of Physics, National Cheng Kung University, 701, Tainan, Taiwan
| | - Daniel Multer
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - Yuxiao Jiang
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - Guangming Cheng
- Princeton Institute for Science and Technology of Materials (PRISM), Princeton University, Princeton, NJ, 08544, USA
| | - Nan Yao
- Princeton Institute for Science and Technology of Materials (PRISM), Princeton University, Princeton, NJ, 08544, USA
| | - Shangfei Wu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Desheng Wu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Liangzi Deng
- Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX, 77204-5002, USA
| | - Zhipeng Ye
- Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX, 79409, USA
| | - Rui He
- Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX, 79409, USA
| | - Guoqing Chang
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - Zhonghao Liu
- State Key Laboratory of Functional Materials for Informatics and Center for Excellence in Superconducting Electronics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 200050, Shanghai, China
| | - Kun Jiang
- Department of Physics, Boston College, Chestnut Hill, MA, 02467, USA
| | - Ziqiang Wang
- Department of Physics, Boston College, Chestnut Hill, MA, 02467, USA
| | - Titus Neupert
- Department of Physics, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland
| | - Amit Agarwal
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Tay-Rong Chang
- Department of Physics, National Cheng Kung University, 701, Tainan, Taiwan
- Center for Quantum Frontiers of Research and Technology (QFort), 701, Tainan, Taiwan
- Physics Division, National Center for Theoretical Sciences, 30013, Hsinchu, Taiwan
| | - Ching-Wu Chu
- Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX, 77204-5002, USA
- Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Hechang Lei
- Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials&Micro-nano Devices, Renmin University of China, 100872, Beijing, China
| | - M Zahid Hasan
- Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA.
- Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
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4
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Li M, Fang Y, Pei C, Qi Y, Wang L. Phonon softening and higher-order anharmonic effect in the superconducting topological insulator Sr xBi 2Se 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:385701. [PMID: 32408275 DOI: 10.1088/1361-648x/ab9344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 05/14/2020] [Indexed: 06/11/2023]
Abstract
We report the anharmonic effect of the Raman-scattering spectrum in the low-carrier density superconductor SrxBi2Se3, which is dominated by the quartic term. Compared to the parent Bi2Se3, the superconducting SrxBi2Se3crystals show obvious phonon softening in the three optical phonon modesA1g1,Eg2, andA1g2. Based on the simulations by the Fano function, we present compelling evidence of the enhanced electron-phonon coupling in SrxBi2Se3for its smaller asymmetric parameterq. Moreover, an anomalous broadening and intensity antiresonance in the characteristic Raman peaks were observed as the temperature decreased to around 160 K. Thus, the superconducting topological material SrxBi2Se3represents a counterintuitive example where the electron-phonon interaction is strengthened by the accumulation of electron carriers.
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Affiliation(s)
- Mingtao Li
- Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China
| | - Yifei Fang
- Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, People's Republic of China
- Department of Physics, Fudan University, Shanghai 200433, People's Republic of China
| | - Cuiying Pei
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, People's Republic of China
| | - Yanpeng Qi
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, People's Republic of China
| | - Lin Wang
- Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China
- Center for High Pressure Science (CHIPS), State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei 066004, People's Republic of China
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5
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Tamtögl A, Campi D, Bremholm M, Hedegaard EMJ, Iversen BB, Bianchi M, Hofmann P, Marzari N, Benedek G, Ellis J, Allison W. Nanoscale surface dynamics of Bi 2Te 3(111): observation of a prominent surface acoustic wave and the role of van der Waals interactions. NANOSCALE 2018; 10:14627-14636. [PMID: 30028450 DOI: 10.1039/c8nr03102a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We present a combined experimental and theoretical study of the surface vibrational modes of the topological insulator Bi2Te3. Using high-resolution helium-3 spin-echo spectroscopy we are able to resolve the acoustic phonon modes of Bi2Te3(111). The low energy region of the lattice vibrations is mainly dominated by the Rayleigh mode which has been claimed to be absent in previous experimental studies. The appearance of the Rayleigh mode is consistent with previous bulk lattice dynamics studies as well as theoretical predictions of the surface phonon modes. Density functional perturbation theory calculations including van der Waals corrections are in excellent agreement with the experimental data. Comparison of the experimental results with theoretically obtained values for films with a thickness of several layers further demonstrate, that for an accurate theoretical description of three-dimensional topological insulators with their layered structure the inclusion of van der Waals corrections is essential. The presence of a prominent surface acoustic wave and the contribution of van der Waals bonding to the lattice dynamics may hold important implications for the thermoelectric properties of thin-film and nanoscale devices.
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Affiliation(s)
- Anton Tamtögl
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge CB3 0HE, UK.
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6
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Liu F, Hu L, Karakaya M, Puneet P, Rao R, Podila R, Bhattacharya S, Rao AM. A micro-Raman study of exfoliated few-layered n-type Bi 2 Te 2.7Se 0.3. Sci Rep 2017; 7:16535. [PMID: 29184191 PMCID: PMC5705651 DOI: 10.1038/s41598-017-16479-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 10/25/2017] [Indexed: 11/09/2022] Open
Abstract
Previously we showed that the thermoelectric (TE) performance of bulk n-type Bi2Te2.7Se0.3 can be enhanced by subjecting it to a combined process of chemical or mechanical exfoliation (C/ME) followed by a rapid densification and restacking of the exfoliated layers via the spark-plasma-sintering technique (SPS). Here, we present a systematic micro-Raman study of two-dimensional flakes of n-type Bi2Te2.7Se0.3 produced by the C/ME process, as a function of the flake thickness. We found Raman evidence for flakes with: (i) integer number of quintuples which exhibited a strong electron-phonon coupling, and (ii) non-integer number of quintuples, or sub-quintuples which exhibited the forbidden IR active mode due to symmetry lowering. Detailed atomic force microscopy was used to confirm the number of quintuples in all flakes examined in this study. The restacking and densification of these flakes by SPS promoted the formation of charged grain boundaries, which led to the enhanced TE properties via the energy filtering process.
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Affiliation(s)
- Fengjiao Liu
- Clemson Nanomaterials Institute, Department of Physics & Astronomy, Clemson University, Clemson, 29634, SC, USA
| | - Longyu Hu
- Department of Chemistry, Clemson University, Clemson, SC, 29634, USA
| | - Mehmet Karakaya
- Clemson Nanomaterials Institute, Department of Physics & Astronomy, Clemson University, Clemson, 29634, SC, USA
| | - Pooja Puneet
- Clemson Nanomaterials Institute, Department of Physics & Astronomy, Clemson University, Clemson, 29634, SC, USA
| | - Rahul Rao
- Materials and Manufacturing Directorate, Air Force Research Laboratory, WPAFB, Dayton, OH, 45433, USA.
- UES Inc., Dayton, OH, 45432, USA.
| | - Ramakrishna Podila
- Clemson Nanomaterials Institute, Department of Physics & Astronomy, Clemson University, Clemson, 29634, SC, USA
- Laboratory of Nano-biophysics, Clemson University, Clemson, SC, 29634, USA
| | - Sriparna Bhattacharya
- Clemson Nanomaterials Institute, Department of Physics & Astronomy, Clemson University, Clemson, 29634, SC, USA.
| | - Apparao M Rao
- Clemson Nanomaterials Institute, Department of Physics & Astronomy, Clemson University, Clemson, 29634, SC, USA
- Laboratory of Nano-biophysics, Clemson University, Clemson, SC, 29634, USA
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7
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Kung HH, Maiti S, Wang X, Cheong SW, Maslov DL, Blumberg G. Chiral Spin Mode on the Surface of a Topological Insulator. PHYSICAL REVIEW LETTERS 2017; 119:136802. [PMID: 29341673 DOI: 10.1103/physrevlett.119.136802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2017] [Indexed: 05/05/2023]
Abstract
Using polarization-resolved resonant Raman spectroscopy, we explore collective spin excitations of the chiral surface states in a three dimensional topological insulator, Bi_{2}Se_{3}. We observe a sharp peak at 150 meV in the pseudovector A_{2} symmetry channel of the Raman spectra. By comparing the data with calculations, we identify this peak as the transverse collective spin mode of surface Dirac fermions. This mode, unlike a Dirac plasmon or a surface plasmon in the charge sector of excitations, is analogous to a spin wave in a partially polarized Fermi liquid, with spin-orbit coupling playing the role of an effective magnetic field.
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Affiliation(s)
- H-H Kung
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
| | - S Maiti
- Department of Physics, University of Florida, Gainesville, Florida 32611, USA
| | - X Wang
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- Rutgers Center for Emergent Materials, Rutgers University, Piscataway, New Jersey 08854, USA
| | - S-W Cheong
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- Rutgers Center for Emergent Materials, Rutgers University, Piscataway, New Jersey 08854, USA
| | - D L Maslov
- Department of Physics, University of Florida, Gainesville, Florida 32611, USA
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
| | - G Blumberg
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- National Institute of Chemical Physics and Biophysics, 12618 Tallinn, Estonia
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8
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Jia X, Zhang S, Sankar R, Chou FC, Wang W, Kempa K, Plummer EW, Zhang J, Zhu X, Guo J. Anomalous Acoustic Plasmon Mode from Topologically Protected States. PHYSICAL REVIEW LETTERS 2017; 119:136805. [PMID: 29341707 DOI: 10.1103/physrevlett.119.136805] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Indexed: 06/07/2023]
Abstract
Plasmons, the collective excitations of electrons in the bulk or at the surface, play an important role in the properties of materials, and have generated the field of "plasmonics." We report the observation of a highly unusual acoustic plasmon mode on the surface of a three-dimensional topological insulator (TI) Bi_{2}Se_{3}, using momentum resolved inelastic electron scattering. In sharp contrast to ordinary plasmon modes, this mode exhibits almost linear dispersion into the second Brillouin zone and remains prominent with remarkably weak damping not seen in any other systems. This behavior must be associated with the inherent robustness of the electrons in the TI surface state, so that not only the surface Dirac states but also their collective excitations are topologically protected. On the other hand, this mode has much smaller energy dispersion than expected from a continuous media excitation picture, which can be attributed to the strong coupling with surface phonons.
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Affiliation(s)
- Xun Jia
- 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 100049, China
| | - Shuyuan Zhang
- 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 100049, China
| | - Raman Sankar
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
- Centre for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
| | - Fang-Cheng Chou
- Centre for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
| | - Weihua Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - K Kempa
- Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
| | - E W Plummer
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70808, USA
| | - Jiandi Zhang
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70808, USA
| | - Xuetao 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 100049, China
| | - Jiandong Guo
- 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 100049, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
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9
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Electron-phonon coupling in topological surface states: The role of polar optical modes. Sci Rep 2017; 7:1095. [PMID: 28439125 PMCID: PMC5430646 DOI: 10.1038/s41598-017-01128-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 03/27/2017] [Indexed: 11/10/2022] Open
Abstract
The use of topological edge states for spintronic applications could be severely hampered by limited lifetimes due to intrinsic many-body interactions, in particular electron-phonon coupling. Previous works to determine the intrinsic coupling strength did not provide a coherent answer. Here, the electron-phonon interaction in the metallic surface state of 3D topological insulators is revised within a first principles framework. For the archetypical cases of Bi2Se3 and Bi2Te3, we find an overall weak coupling constant of less than 0.15, but with a characteristic energy dependence. Derived electronic self-energies compare favorably with previous angle-resolved photoemission spectroscopy results. The prevailing coupling is carried by optical modes of polar character, which is weakly screened by the metallic surface state and can be reduced by doping into bulk bands. We do not find any indication of a strong coupling to the A1g mode or the presence of a Kohn anomaly in the surface phonon spectrum. The weak intrinsic electron-phonon coupling guarantees long-lived quasiparticles at elevated temperatures.
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10
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Hada M, Norimatsu K, Tanaka SI, Keskin S, Tsuruta T, Igarashi K, Ishikawa T, Kayanuma Y, Miller RJD, Onda K, Sasagawa T, Koshihara SY, Nakamura KG. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements. J Chem Phys 2016; 145:024504. [PMID: 27421417 DOI: 10.1063/1.4955188] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.
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Affiliation(s)
- Masaki Hada
- Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
| | - Katsura Norimatsu
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Sei Ichi Tanaka
- Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551, Japan
| | - Sercan Keskin
- The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761, Germany
| | - Tetsuya Tsuruta
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Kyushiro Igarashi
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Tadahiko Ishikawa
- Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551, Japan
| | - Yosuke Kayanuma
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - R J Dwayne Miller
- The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761, Germany
| | - Ken Onda
- PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
| | - Takao Sasagawa
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Shin-Ya Koshihara
- Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551, Japan
| | - Kazutaka G Nakamura
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
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11
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Kogar A, Vig S, Thaler A, Wong MH, Xiao Y, Reig-I-Plessis D, Cho GY, Valla T, Pan Z, Schneeloch J, Zhong R, Gu GD, Hughes TL, MacDougall GJ, Chiang TC, Abbamonte P. Surface Collective Modes in the Topological Insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. PHYSICAL REVIEW LETTERS 2015; 115:257402. [PMID: 26722943 DOI: 10.1103/physrevlett.115.257402] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Indexed: 06/05/2023]
Abstract
We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. Our goal was to identify the "spin plasmon" predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ^{"}(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.
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Affiliation(s)
- A Kogar
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - S Vig
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - A Thaler
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - M H Wong
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - Y Xiao
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - D Reig-I-Plessis
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - G Y Cho
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Z Pan
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - J Schneeloch
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - R Zhong
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - T L Hughes
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - G J MacDougall
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - T-C Chiang
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - P Abbamonte
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
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12
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Wu L, Tse WK, Brahlek M, Morris CM, Aguilar RV, Koirala N, Oh S, Armitage NP. High-Resolution Faraday Rotation and Electron-Phonon Coupling in Surface States of the Bulk-Insulating Topological Insulator Cu_{0.02}Bi_{2}Se_{3}. PHYSICAL REVIEW LETTERS 2015; 115:217602. [PMID: 26636873 DOI: 10.1103/physrevlett.115.217602] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2015] [Indexed: 06/05/2023]
Abstract
We have utilized time-domain magnetoterahertz spectroscopy to investigate the low-frequency optical response of the topological insulator Cu_{0.02}Bi_{2}Se_{3} and Bi_{2}Se_{3} films. With both field and frequency dependence, such experiments give sufficient information to measure the mobility and carrier density of multiple conduction channels simultaneously. We observe sharp cyclotron resonances (CRs) in both materials. The small amount of Cu incorporated into the Cu_{0.02}Bi_{2}Se_{3} induces a true bulk insulator with only a single type of conduction with a total sheet carrier density of ~4.9×10^{12}/cm^{2} and mobility as high as 4000 cm^{2}/V·s. This is consistent with conduction from two virtually identical topological surface states (TSSs) on the top and bottom of the film with a chemical potential ~145 meV above the Dirac point and in the bulk gap. The CR broadens at high fields, an effect that we attribute to an electron-phonon interaction. This assignment is supported by an extended Drude model analysis of the zero-field Drude conductance. In contrast, in normal Bi_{2}Se_{3} films, two conduction channels were observed, and we developed a self-consistent analysis method to distinguish the dominant TSSs and coexisting trivial bulk or two-dimensional electron gas states. Our high-resolution Faraday rotation spectroscopy on Cu_{0.02}Bi_{2}Se_{3} paves the way for the observation of quantized Faraday rotation under experimentally achievable conditions to push the chemical potential in the lowest Landau level.
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Affiliation(s)
- Liang Wu
- The Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Wang-Kong Tse
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
- Department of Physics and Astronomy, MINT Center, University of Alabama, Tuscaloosa, Alabama 35487, USA
| | - M Brahlek
- Department of Physics and Astronomy, Rutgers the State University of New Jersey, New Jersey, Piscataway 08854, USA
| | - C M Morris
- The Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - R Valdés Aguilar
- The Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - N Koirala
- Department of Physics and Astronomy, Rutgers the State University of New Jersey, New Jersey, Piscataway 08854, USA
| | - S Oh
- Department of Physics and Astronomy, Rutgers the State University of New Jersey, New Jersey, Piscataway 08854, USA
| | - N P Armitage
- The Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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13
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Politano A, Silkin VM, Nechaev IA, Vitiello MS, Viti L, Aliev ZS, Babanly MB, Chiarello G, Echenique PM, Chulkov EV. Interplay of Surface and Dirac Plasmons in Topological Insulators: The Case of Bi_{2}Se_{3}. PHYSICAL REVIEW LETTERS 2015; 115:216802. [PMID: 26636863 DOI: 10.1103/physrevlett.115.216802] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2015] [Indexed: 06/05/2023]
Abstract
We have investigated plasmonic excitations at the surface of Bi_{2}Se_{3}(0001) via high-resolution electron energy loss spectroscopy. For low parallel momentum transfer q_{∥}, the loss spectrum shows a distinctive feature peaked at 104 meV. This mode varies weakly with q_{∥}. The behavior of its intensity as a function of primary energy and scattering angle indicates that it is a surface plasmon. At larger momenta (q_{∥}~0.04 Å^{-1}), an additional peak, attributed to the Dirac plasmon, becomes clearly defined in the loss spectrum. Momentum-resolved loss spectra provide evidence of the mutual interaction between the surface plasmon and the Dirac plasmon of Bi_{2}Se_{3}. The proposed theoretical model accounting for the coexistence of three-dimensional doping electrons and two-dimensional Dirac fermions accurately represents the experimental observations. The results reveal novel routes for engineering plasmonic devices based on topological insulators.
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Affiliation(s)
- A Politano
- Department of Physics, University of Calabria, 87036 Rende (CS), Italy
| | - V M Silkin
- Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain
- Departamento de Física de Materiales, Universidad del País Vasco, Apartado 1072, 20080 San Sebastián/Donostia, Spain
- IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain
| | - I A Nechaev
- Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain
- Tomsk State University, 634050 Tomsk, Russian Federation
- Saint Petersburg State University, 198504 Saint Petersburg, Russian Federation
| | - M S Vitiello
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - L Viti
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - Z S Aliev
- Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain
- Institute of Catalysis and Inorganic Chemistry, ANAS, AZ1143 Baku, Azerbaijian
- Institute of Physics, ANAS, AZ1143 Baku, Azerbaijian
| | - M B Babanly
- Institute of Catalysis and Inorganic Chemistry, ANAS, AZ1143 Baku, Azerbaijian
| | - G Chiarello
- Department of Physics, University of Calabria, 87036 Rende (CS), Italy
- CNISM, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Via della Vasca Navale, 84, 00146 Roma, Italy
| | - P M Echenique
- Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain
- Departamento de Física de Materiales, Universidad del País Vasco, Apartado 1072, 20080 San Sebastián/Donostia, Spain
- Centro de Física de Materiales CFM-Materials Physics Center MPC, Centro Mixto CSIC-UPV/EHU, Paseo de Manuel Lardizabal 5, 20018 San Sebastián/Donostia, Spain
| | - E V Chulkov
- Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain
- Departamento de Física de Materiales, Universidad del País Vasco, Apartado 1072, 20080 San Sebastián/Donostia, Spain
- Tomsk State University, 634050 Tomsk, Russian Federation
- Saint Petersburg State University, 198504 Saint Petersburg, Russian Federation
- Centro de Física de Materiales CFM-Materials Physics Center MPC, Centro Mixto CSIC-UPV/EHU, Paseo de Manuel Lardizabal 5, 20018 San Sebastián/Donostia, Spain
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14
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Nanoscale determination of the mass enhancement factor in the lightly doped bulk insulator lead selenide. Nat Commun 2015; 6:6559. [PMID: 25814140 PMCID: PMC4389230 DOI: 10.1038/ncomms7559] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 02/09/2015] [Indexed: 11/16/2022] Open
Abstract
Bismuth chalcogenides and lead telluride/selenide alloys exhibit exceptional thermoelectric properties that could be harnessed for power generation and device applications. Since phonons play a significant role in achieving these desired properties, quantifying the interaction between phonons and electrons, which is encoded in the Eliashberg function of a material, is of immense importance. However, its precise extraction has in part been limited due to the lack of local experimental probes. Here we construct a method to directly extract the Eliashberg function using Landau level spectroscopy, and demonstrate its applicability to lightly doped thermoelectric bulk insulator PbSe. In addition to its high energy resolution only limited by thermal broadening, this novel experimental method could be used to detect variations in mass enhancement factor at the nanoscale level. This opens up a new pathway for investigating the local effects of doping and strain on the mass enhancement factor. Electron–phonon coupling influences the thermal and electronic properties of many solid materials. Zeljkovic et al. now combine Landau level spectroscopy and scanning tunnelling microscopy to extract quantitative information on electron–phonon coupling in the insulator lead selenide.
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15
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Sobota JA, Yang SL, Leuenberger D, Kemper AF, Analytis JG, Fisher IR, Kirchmann PS, Devereaux TP, Shen ZX. Distinguishing bulk and surface electron-phonon coupling in the topological insulator Bi(2)Se(3) using time-resolved photoemission spectroscopy. PHYSICAL REVIEW LETTERS 2014; 113:157401. [PMID: 25375740 DOI: 10.1103/physrevlett.113.157401] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Indexed: 06/04/2023]
Abstract
We report time- and angle-resolved photoemission spectroscopy measurements on the topological insulator Bi(2)Se(3). We observe oscillatory modulations of the electronic structure of both the bulk and surface states at a frequency of 2.23 THz due to coherent excitation of an A(1g) phonon mode. A distinct, additional frequency of 2.05 THz is observed in the surface state only. The lower phonon frequency at the surface is attributed to the termination of the crystal and thus reduction of interlayer van der Waals forces, which serve as restorative forces for out-of-plane lattice distortions. Density functional theory calculations quantitatively reproduce the magnitude of the surface phonon softening. These results represent the first band-resolved evidence of the A(1g) phonon mode coupling to the surface state in a topological insulator.
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Affiliation(s)
- J A Sobota
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - S-L Yang
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Department of Physics, Stanford University, Stanford, California 94305, USA
| | - D Leuenberger
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - A F Kemper
- Computational Research Division, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, California 94720, USA
| | - J G Analytis
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - I R Fisher
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - P S Kirchmann
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - T P Devereaux
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - Z-X Shen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Department of Physics, Stanford University, Stanford, California 94305, USA
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16
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Topological transport and atomic tunnelling-clustering dynamics for aged Cu-doped Bi2Te3 crystals. Nat Commun 2014; 5:5022. [PMID: 25247692 PMCID: PMC4199107 DOI: 10.1038/ncomms6022] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 08/20/2014] [Indexed: 12/02/2022] Open
Abstract
Enhancing the transport contribution of surface states in topological insulators is vital if they are to be incorporated into practical devices. Such efforts have been limited by the defect behaviour of Bi2Te3 (Se3) topological materials, where the subtle bulk carrier from intrinsic defects is dominant over the surface electrons. Compensating such defect carriers is unexpectedly achieved in (Cu0.1Bi0.9)2Te3.06 crystals. Here we report the suppression of the bulk conductance of the material by four orders of magnitude by intense ageing. The weak antilocalization analysis, Shubnikov–de Haas oscillations and scanning tunnelling spectroscopy corroborate the transport of the topological surface states. Scanning tunnelling microscopy reveals that Cu atoms are initially inside the quintuple layers and migrate to the layer gaps to form Cu clusters during the ageing. In combination with first-principles calculations, an atomic tunnelling–clustering picture across a diffusion barrier of 0.57 eV is proposed. Enhancing the transport properties of surface states in topological insulators is vital if they are to be incorporated into practical devices. Towards this end, Chen et al. study the transport in aged (Cu0.1Bi0.9)2Te3.06, where the ageing process suppresses bulk conductance by up to four orders of magnitude.
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17
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Yang SA, Pan H, Zhang F. Dirac and Weyl superconductors in three dimensions. PHYSICAL REVIEW LETTERS 2014; 113:046401. [PMID: 25105637 DOI: 10.1103/physrevlett.113.046401] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Indexed: 06/03/2023]
Abstract
We introduce the concept of three-dimensional Dirac (Weyl) superconductors (SC), which have protected bulk fourfold (twofold) nodal points and surface Majorana arcs at zero energy. We provide a sufficient criterion for realizing them in centrosymmetric SCs with odd-parity pairing and mirror symmetry. Pairs of Dirac nodes appear in a mirror-invariant plane when the mirror winding number is nontrivial. Breaking mirror symmetry may gap Dirac nodes producing a topological SC. Each Dirac node evolves to a nodal ring when inversion-gauge symmetry is broken, whereas it splits into a pair of Weyl nodes when, and only when, time-reversal symmetry is broken.
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Affiliation(s)
- Shengyuan A Yang
- Engineering Product Development, Singapore University of Technology and Design, Singapore 138682, Singapore
| | - Hui Pan
- Department of Physics, Beihang University, Beijing 100191, China
| | - Fan Zhang
- Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA and Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA
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