Low-velocity anisotropic Dirac fermions on the side surface of topological insulators

AbstractTopological insulators (TIs) are materials which exhibit topologically protected electronic surface states, acting as mass-less Dirac fermions. Beside their fascinating fundamental physics, TIs are also promising candidates for future spintronic devices. In this regard, generation of spin-polarized currents in TIs is the first and most important step towards their application in spin-based devices. Here we demonstrate that when electrons are scattered from the surface of bismuth selenide, a prototype TI, not only the elastic channel but also the inelastic channel is strongly spin dependent. In particular collective charge excitations (plasmons) excited at such surfaces show a large spin-dependent electron scattering. Electrons scattered by these excitations exhibit a high spin asymmetry, as high as 40%. The observed effect opens up new possibilities to generate spin-polarized currents at the surface of TIs or utilize the collective charge excitations to analyze the electrons’ spin. The results are also important to understand the spin polarization of the photo-excited electrons excited at TIs surfaces. Moreover, our finding will inspire new ideas for using these plasmonic excitations in the field of spin-plasmonics.

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THz Generation and Detection on Dirac Fermions in Topological Insulators

Advanced Optical Materials ◽

10.1002/adom.201300221 ◽

2013 ◽

Vol 1 (11) ◽

pp. 804-808 ◽

Cited By ~ 33

Author(s):

Chih Wei Luo ◽

Hsueh-Ju Chen ◽

Chien Ming Tu ◽

Chia Ching Lee ◽

Shin An Ku ◽

...

Keyword(s):

Topological Insulators ◽

Dirac Fermions ◽

Thz Generation

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New classes of topological crystalline insulators having surface rotation anomaly

Science Advances ◽

10.1126/sciadv.aat2374 ◽

2019 ◽

Vol 5 (12) ◽

pp. eaat2374 ◽

Cited By ~ 26

Author(s):

Chen Fang ◽

Liang Fu

Keyword(s):

Rotation Axis ◽

Side Surface ◽

Dirac Fermions ◽

Two Dimensional ◽

Rotation Symmetry ◽

Quantum Device ◽

Quantum Anomalies ◽

Topological Crystalline Insulators ◽

Topological Crystalline Insulator ◽

Helical Mode

We discover new types of quantum anomalies in two-dimensional systems with time-reversal symmetry (T) and discrete rotation symmetry with order of n = 2, 4, and 6 (Cn). The new anomalous states have n flavors of massless Dirac fermions protected by T and Cn, whereas any two-dimensional lattices having the two symmetries must have a multiple of 4, 8, and 12 Dirac cones for n = 2, 4, and 6, respectively. We show that these anomalous states are physically realized on the surface of new classes of topological crystalline insulators, normal to the rotation axis. Moreover, these topological crystalline insulators support n gapless one-dimensional helical mode on the otherwise fully gapped side surface, connecting the anomalous two-dimensional states on the top and bottom surfaces. The presence of these helical modes enables a new quantum device made from a topological crystalline insulator nanorod, a “helical nanorod,” which has a quantized longitudinal conductance of ne2/h.

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