Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6

The impact of nonmagnetic and magnetic impurities on topological insulators is a central focus concerning their fundamental physics and possible spintronics and quantum computing applications. Combining scanning tunneling spectroscopy with transport measurements, we investigate, both locally and globally, the effect of nonmagnetic and magnetic substituents in SmB6, a predicted topological Kondo insulator. Around the so-introduced substitutents and in accord with theoretical predictions, the surface states are locally suppressed with different length scales depending on the substituent’s magnetic properties. For sufficiently high substituent concentrations, these states are globally destroyed. Similarly, using a magnetic tip in tunneling spectroscopy also resulted in largely suppressed surface states. Hence, a destruction of the surface states is always observed close to atoms with substantial magnetic moment. This points to the topological nature of the surface states in SmB6 and illustrates how magnetic impurities destroy the surface states from microscopic to macroscopic length scales.

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Spintronics Based on Topological Insulators

SPIN ◽

10.1142/s2010324716400014 ◽

2016 ◽

Vol 06 (02) ◽

pp. 1640001 ◽

Cited By ~ 38

Author(s):

Yabin Fan ◽

Kang L. Wang

Keyword(s):

Topological Insulators ◽

Spin Injection ◽

Surface States ◽

Research Field ◽

Spin Torque ◽

Spin Orbit ◽

Challenges And Opportunities ◽

Potential Applications ◽

Topological Surface ◽

A Charge

Spintronics using topological insulators (TIs) as strong spin–orbit coupling (SOC) materials have emerged and shown rapid progress in the past few years. Different from traditional heavy metals, TIs exhibit very strong SOC and nontrivial topological surface states that originate in the bulk band topology order, which can provide very efficient means to manipulate adjacent magnetic materials when passing a charge current through them. In this paper, we review the recent progress in the TI-based magnetic spintronics research field. In particular, we focus on the spin–orbit torque (SOT)-induced magnetization switching in the magnetic TI structures, spin–torque ferromagnetic resonance (ST-FMR) measurements in the TI/ferromagnet structures, spin pumping and spin injection effects in the TI/magnet structures, as well as the electrical detection of the surface spin-polarized current in TIs. Finally, we discuss the challenges and opportunities in the TI-based spintronics field and its potential applications in ultralow power dissipation spintronic memory and logic devices.

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Back Cover: An STM Perspective on Hexaborides: Surface States of the Kondo Insulator SmB 6 (Adv. Quantum Technol. 12/2021)

Advanced Quantum Technologies ◽

10.1002/qute.202170123 ◽

2021 ◽

Vol 4 (12) ◽

pp. 2170123

Author(s):

Steffen Wirth ◽

Pedro Schlottmann

Keyword(s):

Surface States ◽

Kondo Insulator ◽

Back Cover

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Deep tuning of photo-thermoelectricity in topological surface states

Scientific Reports ◽

10.1038/s41598-020-73950-z ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Shouyuan Huang ◽

Ireneusz Miotkowski ◽

Yong P. Chen ◽

Xianfan Xu

Keyword(s):

Surface State ◽

Spin Injection ◽

Three Dimensional ◽

Polarized Light ◽

Surface States ◽

Linear Dispersion ◽

Circularly Polarized Light ◽

Spin Polarized ◽

Topological Surface ◽

Topological Surface State

Abstract Three-dimensional topological insulators have been demonstrated in recent years, which possess intriguing gapless, spin-polarized Dirac states with linear dispersion only on the surface. The spin polarization of the topological surface states is also locked to its momentum, which allows controlling motion of electrons using optical helicity, i.e., circularly polarized light. The electrical and thermal transport can also be significantly tuned by the helicity-control of surface state electrons. Here, we report studies of photo-thermoelectric effect of the topological surface states in Bi2Te2Se thin films with large tunability using varied gate voltages and optical helicity. The Seebeck coefficient can be altered by more than five times compared to the case without spin injection. This deep tuning is originated from the optical helicity-induced photocurrent which is shown to be enhanced, reduced, turned off, and even inverted due to the change of the accessed band structures by electrical gating. The helicity-selected topological surface state thus has a large effect on thermoelectric transport, demonstrating great opportunities for realizing helicity control of optoelectronic and thermal devices.

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Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb2

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2002361117 ◽

2020 ◽

Vol 117 (27) ◽

pp. 15409-15413 ◽

Cited By ~ 2

Author(s):

Ke-Jun Xu ◽

Su-Di Chen ◽

Yu He ◽

Junfeng He ◽

Shujie Tang ◽

...

Keyword(s):

Low Temperature ◽

Surface States ◽

Metallic Surface ◽

Large Temperature ◽

High Symmetry ◽

Strong Correlations ◽

Band Shift ◽

Kondo Insulator ◽

Angle Resolved Photoemission Spectroscopy ◽

Temperature Resistivity

The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB6has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB6and YbB12may also exist in systems with d instead of f electrons.

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Observation of possible topological in-gap surface states in the Kondo insulator SmB6 by photoemission

Nature Communications ◽

10.1038/ncomms4010 ◽

2013 ◽

Vol 4 (1) ◽

Cited By ~ 195

Author(s):

J. Jiang ◽

S. Li ◽

T. Zhang ◽

Z. Sun ◽

F. Chen ◽

...

Keyword(s):

Surface States ◽

Kondo Insulator

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Topological surface states interacting with bulk excitations in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1606042113 ◽

2016 ◽

Vol 113 (24) ◽

pp. 6599-6604 ◽

Cited By ~ 25

Author(s):

Wan Kyu Park ◽

Lunan Sun ◽

Alexander Noddings ◽

Dae-Jeong Kim ◽

Zachary Fisk ◽

...

Keyword(s):

Surface States ◽

Spectroscopic Properties ◽

Recent Theory ◽

Tunneling Conductance ◽

Strong Electron ◽

Kondo Insulator ◽

Single Crystal Surfaces ◽

Planar Tunneling ◽

Topological States ◽

Protected Surface

Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi2Se3. Here, we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB6. The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveals linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB6.

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Spectral properties of strongly correlated multi-impurity models in the Kondo insulator regime: Emergent coherence, metallic surface states, and quantum phase transitions

Physical Review B ◽

10.1103/physrevb.104.165105 ◽

2021 ◽

Vol 104 (16) ◽

Author(s):

Fabian Eickhoff ◽

Frithjof B. Anders

Keyword(s):

Phase Transitions ◽

Spectral Properties ◽

Quantum Phase Transitions ◽

Surface States ◽

Quantum Phase ◽

Metallic Surface ◽

Strongly Correlated ◽

Kondo Insulator ◽

Impurity Models

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Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6

Scientific Reports ◽

10.1038/srep03071 ◽

2013 ◽

Vol 3 (1) ◽

Cited By ~ 31

Author(s):

M. Ciomaga Hatnean ◽

M. R. Lees ◽

D. McK. Paul ◽

G. Balakrishnan

Keyword(s):

Single Crystals ◽

Heavy Fermion ◽

Surface States ◽

Strongly Correlated ◽

Floating Zone ◽

Topological Properties ◽

High Quality ◽

Kondo Insulator ◽

Bulk Properties ◽

Topological Surface

Abstract SmB6 has recently been predicted to be a Topological Kondo Insulator, the first strongly correlated heavy fermion material to exhibit topological surface states. High quality crystals are necessary to investigate the topological properties of this material. Single crystal growth of the rare earth hexaboride, SmB6, has been carried out by the floating zone technique using a high power xenon arc lamp image furnace. Large, high quality single-crystals are obtained by this technique. The crystals produced by the floating zone technique are free of contamination from flux materials and have been characterised by resistivity and magnetisation measurements. These crystals are ideally suited for the investigation of both the surface and bulk properties of SmB6.

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