On Strong f-Electron Localization Effect in a Topological Kondo Insulator

We study a strong f-electron localization effect on the surface state of a generic topological Kondo insulator (TKI) system by performing a mean-field theoretic (MFT) calculation within the framework of the periodic Anderson model (PAM) using the slave boson technique. The surface metallicity, together with bulk insulation, requires this type of localization. A key distinction between surface states in a conventional insulator and a topological insulator is that, along a course joining two time-reversal invariant momenta (TRIM) in the same BZ, there will be an intersection of these surface states, an even/odd number of times, with the Fermi energy inside the spectral gap. For an even (odd) number of surface state crossings, the surface states are topologically trivial (non-trivial). The symmetry consideration and the pictorial representation of the surface band structure obtained here show an odd number of crossings, leading to the conclusion that, at least within the PAM framework, the generic system is a strong topological insulator.

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Effect of Rashba Impurities on Surface State of a Topological Kondo Insulator

Surfaces ◽

10.3390/surfaces3030035 ◽

2020 ◽

Vol 3 (3) ◽

pp. 484-504

Author(s):

Partha Goswami

Keyword(s):

Critical Point ◽

Wave Vector ◽

Surface State ◽

Quantum Critical Point ◽

Mean Field ◽

Electron Localization ◽

Present Communication ◽

Kondo Insulator ◽

Dirac Spectrum ◽

Rashba Coupling

In this communication, we report surface state, with Rashba impurities, of a generic topological Kondo insulator (TKI) system by performing a mean-field theoretic (MFT) calculation within the framework of slave-boson protocol. The surface metallicity together with bulk insulation is found to require very strong f-electron localization. The possibility of intra-band as well as inter-band unconventional plasmons exists for the surface state spectrum. The paramountcy of the bulk metallicity, and, in the presence of the Rashba impurities, the TKI surface comprising of ‘helical liquids’ are the important outcomes of the present communication. The access to the gapless Dirac spectrum leads to spin-plasmons with the usual wave vector dependence q1/2. The Rashba coupling does not impair the Kondo screening and does not affect the quantum critical point (QCP) for the bulk.

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Termination switching of antiferromagnetic proximity effect in topological insulator

Science Advances ◽

10.1126/sciadv.aaz8463 ◽

2020 ◽

Vol 6 (33) ◽

pp. eaaz8463

Author(s):

Chao-Yao Yang ◽

Lei Pan ◽

Alexander J. Grutter ◽

Haiying Wang ◽

Xiaoyu Che ◽

...

Keyword(s):

Curie Temperature ◽

Topological Insulator ◽

Surface State ◽

Proximity Effect ◽

Surface States ◽

Double Exchange ◽

Exchange Interactions ◽

Stacking Order ◽

Bst Films ◽

Magnetic Proximity Effect

This work reports the ferromagnetism of topological insulator, (Bi,Sb)2Te3 (BST), with a Curie temperature of approximately 120 K induced by magnetic proximity effect (MPE) of an antiferromagnetic CrSe. The MPE was shown to be highly dependent on the stacking order of the heterostructure, as well as the interface symmetry: Growing CrSe on top of BST results in induced ferromagnetism, while growing BST on CrSe yielded no evidence of an MPE. Cr-termination in the former case leads to double-exchange interactions between Cr3+ surface states and Cr2+ bulk states. This Cr3+-Cr2+ exchange stabilizes the ferromagnetic order localized at the interface and magnetically polarizes the BST Sb band. In contrast, Se-termination at the CrSe/BST interface yields no detectable MPE. These results directly confirm the MPE in BST films and provide critical insights into the sensitivity of the surface state.

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Spin Ordering on the Surface of a Topological Insulator with Magnetic Ions

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.190.494 ◽

2012 ◽

Vol 190 ◽

pp. 494-497

Author(s):

V.N. Men'shov ◽

V.V. Tugushev ◽

E.V. Chulkov

Keyword(s):

Topological Insulator ◽

Chemical Potential ◽

Mean Field ◽

Three Dimensional ◽

Surface States ◽

Dirac Fermions ◽

Uniform Magnetization ◽

Out Of Plane ◽

Different Temperatures ◽

Magnetic Ions

We study the effect of magnetic doping on appearance of ferromagnetic (FM) order on the surface of a three-dimensional topological insulator. Assuming the exchange coupling of the Dirac fermions with the dilute magnetic ions, we find that the system under consideration is unstable with respect to a spontaneous uniform magnetization along the out-of-plane direction. The appearance of the magnetization is accompanied by opening of a gap in the spectrum of surface states. In the framework of a mean-field approach, we analyze the possibility of the FM order on the magnetically doped surface of topological insulator at different temperatures and positions of the chemical potential.

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THE SURFACE BAND STRUCTURE OF Li/Be$(10\bar{1}0)$

Surface Review and Letters ◽

10.1142/s0218625x02003913 ◽

2002 ◽

Vol 09 (03n04) ◽

pp. 1493-1496

Author(s):

L. I. JOHANSSON ◽

T. BALASUBRAMANIAN ◽

C. VIROJANADARA

Keyword(s):

Band Structure ◽

Fermi Level ◽

Surface State ◽

Room Temperature ◽

Surface States ◽

High Symmetry ◽

Clean Surface ◽

Surface Band ◽

State Band ◽

Li Adsorption

A photoemision study of the surface states on Be[Formula: see text] after Li adsorption at room temperature is reported. The surface band structure was mapped along four high symmetry directions of the SBZ. Fairly large shifts in the surface band locations were obtained but all surface states observed experimentally after Li adsorption were found to correspond to Be-derived states and no Li-derived surface states could be identified. The surface state bands located close to the Fermi level (E F ) were found to be affected the most and it is suggested that one surface state band which on the clean surface is located above E F is pulled down below E F after Li adsorption.

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Enhanced surface state protection and band gap in the topological insulator PbBi4Te4S3

Physical Review Materials ◽

10.1103/physrevmaterials.2.104201 ◽

2018 ◽

Vol 2 (10) ◽

Cited By ~ 2

Author(s):

K. Sumida ◽

T. Natsumeda ◽

K. Miyamoto ◽

I. V. Silkin ◽

K. Kuroda ◽

...

Keyword(s):

Band Gap ◽

Topological Insulator ◽

Surface State ◽

Enhanced Surface ◽

State Protection

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Dynamic Opening of a Gap in Dirac Surface States of the Thin-Film 3D Topological Insulator Bi2Se3 Driven by the Dynamic Rashba Effect

The Journal of Physical Chemistry Letters ◽

10.1021/acs.jpclett.1c01601 ◽

2021 ◽

pp. 5593-5600

Author(s):

Yuri D. Glinka ◽

Tingchao He ◽

Xiao Wei Sun

Keyword(s):

Thin Film ◽

Topological Insulator ◽

Surface States ◽

Rashba Effect

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Many-impurity scattering on the surface of a topological insulator

Scientific Reports ◽

10.1038/s41598-021-84801-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

José Luis Hernando ◽

Yuriko Baba ◽

Elena Díaz ◽

Francisco Domínguez-Adame

Keyword(s):

Green’S Function ◽

Green's Function ◽

Topological Insulator ◽

Disordered Systems ◽

Spectral Properties ◽

Random Distribution ◽

Surface States ◽

Impurity Scattering ◽

Self Consistent ◽

The Impact

AbstractWe theoretically address the impact of a random distribution of non-magnetic impurities on the electron states formed at the surface of a topological insulator. The interaction of electrons with the impurities is accounted for by a separable pseudo-potential method that allows us to obtain closed expressions for the density of states. Spectral properties of surface states are assessed by means of the Green’s function averaged over disorder realisations. For comparison purposes, the configurationally averaged Green’s function is calculated by means of two different self-consistent methods, namely the self-consistent Born approximation (SCBA) and the coherent potential approximation (CPA). The latter is often regarded as the best single-site theory for the study of the spectral properties of disordered systems. However, although a large number of works employ the SCBA for the analysis of many-impurity scattering on the surface of a topological insulator, CPA studies of the same problem are scarce in the literature. In this work, we find that the SCBA overestimates the impact of the random distribution of impurities on the spectral properties of surface states compared to the CPA predictions. The difference is more pronounced when increasing the magnitude of the disorder.

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Understanding Topological Insulators in Real Space

Molecules ◽

10.3390/molecules26102965 ◽

2021 ◽

Vol 26 (10) ◽

pp. 2965

Author(s):

Angel Martín Pendás ◽

Francisco Muñoz ◽

Carlos Cardenas ◽

Julia Contreras-García

Keyword(s):

Quantum Theory ◽

Chiral Symmetry ◽

Topological Insulator ◽

Real Space ◽

Electron Delocalization ◽

Electron Localization ◽

Visualization Tool ◽

Atom Pairs ◽

Chemical Concepts ◽

Bulk Behavior

A real space understanding of the Su–Schrieffer–Heeger model of polyacetylene is introduced thanks to delocalization indices defined within the quantum theory of atoms in molecules. This approach enables to go beyond the analysis of electron localization usually enabled by topological insulator indices—such as IPR—enabling to differentiate between trivial and topological insulator phases. The approach is based on analyzing the electron delocalization between second neighbors, thus highlighting the relevance of the sublattices induced by chiral symmetry. Moreover, the second neighbor delocalization index, δi,i+2, also enables to identify the presence of chirality and when it is broken by doping or by eliminating atom pairs (as in the case of odd number of atoms chains). Hints to identify bulk behavior thanks to δ1,3 are also provided. Overall, we present a very simple, orbital invariant visualization tool that should help the analysis of chirality (independently of the crystallinity of the system) as well as spreading the concepts of topological behavior thanks to its relationship with well-known chemical concepts.

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