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Hedayat H, Bugini D, Yi H, Chen C, Zhou X, Cerullo G, Dallera C, Carpene E. Ultrafast evolution of bulk, surface and surface resonance states in photoexcited [Formula: see text]. Sci Rep 2021; 11:4924. [PMID: 33649414 PMCID: PMC7921141 DOI: 10.1038/s41598-021-83848-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 02/05/2021] [Indexed: 11/09/2022] Open
Abstract
We use circular dichroism (CD) in time- and angle-resolved photoemission spectroscopy (trARPES) to measure the femtosecond charge dynamics in the topological insulator (TI) [Formula: see text]. We detect clear CD signatures from topological surface states (TSS) and surface resonance (SR) states. In time-resolved measurements, independently from the pump polarization or intensity, the CD shows a dynamics which provides access to the unexplored electronic evolution in unoccupied states of [Formula: see text]. In particular, we are able to disentangle the unpolarized electron dynamics in the bulk states from the spin-textured TSS and SR states on the femtosecond timescale. Our study demonstrates that photoexcitation mainly involves the bulk states and is followed by sub-picosecond transport to the surface. This provides essential details on intra- and interband scattering in the relaxation process of TSS and SR states. Our results reveal the significant role of SRs in the subtle ultrafast interaction between bulk and surface states of TIs.
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Affiliation(s)
- Hamoon Hedayat
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, 20133 Milan, Italy
- Dipartimento di Fisica, Politecnico di Milano, 20133 Milan, Italy
| | - Davide Bugini
- Dipartimento di Fisica, Politecnico di Milano, 20133 Milan, Italy
| | - Hemian Yi
- National Lab for Superconductivity, Institute of Physics, Chinese Academy of Science, Beijing, 100190 China
| | - Chaoyu Chen
- National Lab for Superconductivity, Institute of Physics, Chinese Academy of Science, Beijing, 100190 China
| | - Xingjiang Zhou
- National Lab for Superconductivity, Institute of Physics, Chinese Academy of Science, Beijing, 100190 China
| | - Giulio Cerullo
- Dipartimento di Fisica, Politecnico di Milano, 20133 Milan, Italy
| | - Claudia Dallera
- Dipartimento di Fisica, Politecnico di Milano, 20133 Milan, Italy
| | - Ettore Carpene
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, 20133 Milan, Italy
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Krasovskii EE. Spin-orbit coupling at surfaces and 2D materials. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:493001. [PMID: 26580290 DOI: 10.1088/0953-8984/27/49/493001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Spin-orbit interaction gives rise to a splitting of surface states via the Rashba effect, and in topological insulators it leads to the existence of topological surface states. The resulting k(//) momentum separation between states with the opposite spin underlies a wide range of new phenomena at surfaces and interfaces, such as spin transfer, spin accumulation, spin-to-charge current conversion, which are interesting for fundamental science and may become the basis for a breakthrough in the spintronic technology. The present review summarizes recent theoretical and experimental efforts to reveal the microscopic structure and mechanisms of spin-orbit driven phenomena with the focus on angle and spin-resolved photoemission and scanning tunneling microscopy.
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Affiliation(s)
- E E Krasovskii
- Departamento de Física de Materiales, Universidad del Pais Vasco UPV/EHU, 20080 San Sebastián/Donostia, Spain. Donostia International Physics Center (DIPC), 20018 San Sebastián/Donostia, Spain. IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
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Xu CZ, Liu Y, Yukawa R, Zhang LX, Matsuda I, Miller T, Chiang TC. Photoemission Circular Dichroism and Spin Polarization of the Topological Surface States in Ultrathin Bi2Te3 Films. PHYSICAL REVIEW LETTERS 2015; 115:016801. [PMID: 26182112 DOI: 10.1103/physrevlett.115.016801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Indexed: 06/04/2023]
Abstract
Circular dichroism (CD) observed by photoemission, being sensitive to the orbital and spin angular momenta of the electronic states, is a powerful probe of the nontrivial surface states of topological insulators, but the experimental results thus far have eluded a comprehensive description. We report a study of Bi2Te3 films with thicknesses ranging from one quintuple layer (two-dimensional limit) to 12 layers (bulk limit) over a wide range of incident photon energy. The data show complex variations in magnitude and sign reversals, which are nevertheless well described by a theoretical calculation including all three photoemission mechanisms: dipole transition, surface photoemission, and spin-orbit coupling. The results establish the nontrivial connection between the spin-orbit texture and CD.
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Affiliation(s)
- C-Z Xu
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Y Liu
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- X-ray science division, Argonne National Lab, 9700 South Cass Avenue, Lemont, Illinois 60439, USA
| | - R Yukawa
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - L-X Zhang
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - I Matsuda
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - T Miller
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - T-C Chiang
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Scholz MR, Sánchez-Barriga J, Braun J, Marchenko D, Varykhalov A, Lindroos M, Wang YJ, Lin H, Bansil A, Minár J, Ebert H, Volykhov A, Yashina LV, Rader O. Reversal of the circular dichroism in angle-resolved photoemission from Bi2Te3. PHYSICAL REVIEW LETTERS 2013; 110:216801. [PMID: 23745908 DOI: 10.1103/physrevlett.110.216801] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 03/09/2013] [Indexed: 06/02/2023]
Abstract
The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpretations conflict with our data from Bi(2)Te(3) which depend on the photon energy and show several sign changes. Our one-step photoemission calculations coupled to ab initio theory confirm the sign change and assign the dichroism to a final-state effect. Instead, the spin polarization of the photoelectrons excited with linearly polarized light remains a reliable probe for the spin in the initial state.
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Affiliation(s)
- M R Scholz
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Strasse 15, 12489 Berlin, Germany
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Bahramy M, King P, de la Torre A, Chang J, Shi M, Patthey L, Balakrishnan G, Hofmann P, Arita R, Nagaosa N, Baumberger F. Emergent quantum confinement at topological insulator surfaces. Nat Commun 2012; 3:1159. [DOI: 10.1038/ncomms2162] [Citation(s) in RCA: 211] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Accepted: 09/25/2012] [Indexed: 11/09/2022] Open
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Park CH, Louie SG. Spin polarization of photoelectrons from topological insulators. PHYSICAL REVIEW LETTERS 2012; 109:097601. [PMID: 23002885 DOI: 10.1103/physrevlett.109.097601] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Indexed: 06/01/2023]
Abstract
We show that the degree of spin polarization of photoelectrons from the surface states of topological insulators is 100% if fully polarized light is used as in typical photoemission measurements, and, hence, can be significantly higher than that of the initial state. Further, the spin orientation of these photoelectrons in general can also be very different from that of the initial surface state and is controlled by the photon polarization. A rich set of predicted phenomena have recently been confirmed by spin- and angle-resolved photoemission experiments.
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Affiliation(s)
- Cheol-Hwan Park
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
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Bian G, Zhang L, Liu Y, Miller T, Chiang TC. Illuminating the surface spin texture of the giant-Rashba quantum-well system Bi/Ag(111) by circularly polarized photoemission. PHYSICAL REVIEW LETTERS 2012; 108:186403. [PMID: 22681094 DOI: 10.1103/physrevlett.108.186403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Indexed: 06/01/2023]
Abstract
We have mapped out the spin texture of a Bi/Ag surface alloy prepared on a thin Ag film by circularly polarized angle-resolved photoemission spectroscopy. A term proportional to ∇·A in the interaction Hamiltonian gives rise to strong surface photoexcitation, which interferes with a Rashba contribution to yield a pronounced circular dichroic effect in Bi/Ag. The dipole transition, often taken to be the only important photoexcitation mechanism, is actually negligible. A parameter-free calculation yields a dichroic pattern in excellent agreement with experiment.
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Affiliation(s)
- Guang Bian
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
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Wang YH, Hsieh D, Pilon D, Fu L, Gardner DR, Lee YS, Gedik N. Observation of a warped helical spin texture in Bi2Se3 from circular dichroism angle-resolved photoemission spectroscopy. PHYSICAL REVIEW LETTERS 2011; 107:207602. [PMID: 22181776 DOI: 10.1103/physrevlett.107.207602] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Indexed: 05/31/2023]
Abstract
A differential coupling of topological surface states to left- versus right-circularly polarized light is the basis of many optospintronics applications of topological insulators. Here we report direct evidence of circular dichroism from the surface states of Bi(2)Se(3) using laser-based time-of-flight angle-resolved photoemission spectroscopy. By employing a novel sample rotational analysis, we resolve unusual modulations in the circular dichroism photoemission pattern as a function of both energy and momentum, which perfectly mimic the predicted but hitherto unobserved three-dimensional warped spin texture of the surface states. By developing a microscopic theory of photoemission from topological surface states, we show that this correlation is a natural consequence of spin-orbit coupling. These results suggest that our technique may be a powerful probe of the spin texture of spin-orbit coupled materials in general.
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Affiliation(s)
- Y H Wang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, 02139, USA
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