Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

Sharp Raman anomalies and broken adiabaticity at a pressure induced
transition from band to topological insulator in Sb 2 Se 3
Achintya Bera 1 , Koushik Pal 2, 3 , D. V. S. Muthu 1 , Somaditya Sen 4 , Prasenjit Guptasarma 4 ,
U. V. Waghmare 3 , and A. K. Sood 1
1 Department of Physics, Indian Institute of Science, Bangalore-560012, India
2 Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific
Research, Bangalore-560064, India
3 Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore-560064, India and
4 Department of Physics, University of Wisconsin-Milwaukee, Wisconsin-53211, USA
Recently discovered three-dimensional Topological insulators (TI) have attracted a lot of
attention of researchers from diverse backgrounds due to robust and exotic phenomena, such
as quantum spin Hall states, arise from the geometric and topological properties of the
manifold of their electronic states. However, experimental evidence for nontrivial topology of
electronic states is so far mainly based on the time-reversal symmetry protected chiral surface
states. Signatures of the nontrivial topology of a TI in its bulk behaviour are subtle, and not
yet identified. Our work presented here establishes that (a) bulk signatures of the electronic
topology become significant and detectable as anomalies in the phonon frequency and
linewidth of E g Raman mode at an electronic topological transition (specifically in single
crystal Sb 2 Se 3 ), (b) their origin lies in physical mechanisms that involve going beyond
adiabatic approximation as a metallic (vanishing gap) state of the bulk appears at the
transition, and (c) they involve electron-phonon couplings some of which are not captured by
the standard methods to calculate electronic structure.
References:
[1] Zhang, H. et al. “Topological insulators in Bi 2 Se 3 , Bi 2 Te 3 and Sb 2 Te 3 with a single Dirac
cone on the surface”. Nature Phys. 5, 438-442 (2009).
[2] G.K. Pradhan et al. “Raman signatures of pressure induced electronic topological and
structural transitions in Bi 2 Te 3 ”. Solid State Commun. 152, 284–287 (2012)