Charge Density Waves in chiral materials

Novel 2D materials that are currently been synthesized with an increasing experimental facility, offer a fantastic pool of compounds to discover new topological insulators with a large gap that can potentially be applied technologically. The main reason is that due to their reduced electronic screening the electron-ion interaction is enhanced, broadening the possibility of finding materials with a large gap. Moreover, for basically the same reason, reduced dimensionality might also enhance the emergence of Charge Density Wave (CDW) structural transitions [1] that can open the electronic gap. Finding topological phases that emerge after a CDW transition is of particular importance because it can yield the possibility of controlling with temperature or strain the topological properties of these materials, broadening the possibilities of developing new devices for electronic applications. In this way, by studying the contribution of anharmonic effects one can calculate at which temperature the phonon frequencies of the high-temperature high-symmetry phase collapse and determine whether a CDW can occur [1,2,3] . A CDW breaks spontaneously some spatial symmetries and this could induce a metal-TI transition, but this time the size of the gap will be given by correlations and not by the spin-orbit coupling interaction.

The interest in CDW-induced topological phase transition goes beyond the search for a new material. The axion insulator is another distinct topological phase that has a vanishing Chern number but a finite topological Chern-Simon term [4]. Thus CDW in topological semimetals might create novel topological phases. In particular we will focus on chiral semimetals. Chiral crystals are expected to display numerous exotic physical phenomena, including fermionic excitations with large topological charge and long Fermi arc surface states [5,6]. In this work we propose to study chiral semimetals in the presence of CDW and study the emerging topological phases.


[1] R. Bianco, I. Errea, L. Monacelli, M. Calandra, and F. Mauri
Quantum Enhancement of Charge Density Wave in NbS2 in the Two-Dimensional Limit
Nano Letters 19, 3098 (2019)
[2] I. Errea, M. Calandra, and F. Mauri
Anharmonic free energies and phonon dispersions from the stochastic self-consistent harmonic approximation: Application to platinum and palladium hydrides
Phys. Rev. B 89, 064302 (2014)
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High-pressure phase diagram of hydrogen and deuterium sulfides from first principles: Structural and vibrational properties including quantum and anharmonic effects
Phys Rev B 97, 214101 (2018)
[4] X.-L. Qi and S.-C. Zhang
Topological insulators and superconductors
Rev. Mod. Phys. 83, 1057 (2011)
[5] N.B.M. Schröter, D. Pei, M.G. Vergniory, Y. Sun, K. Manna, F. De Juan, J.A. Krieger, V. Süss, M. Schmidt, P. Dudin, B. Bradlyn, T.K. Kim, T. Schmitt, C. Cacho, C. Felser, V.N. Strocov, Y. Chen
Chiral topological semimetal with multifold band crossings and long Fermi arcs
Nature Physics 15 (8), 759-765 (2019)
[6] N.B.M. Schröter, S. Stolz, K. Manna, F. De Juan, M.G. Vergniory, J.A. Krieger, D. Pei, T. Schmitt,  P. Dudin, T.K. Kim, C. Cacho, B.Bradlyn, H. Borrmann, M. Schmidt, R. Widmer, V.N. Strocov, C. Felser
Observation and control of maximal Chern numbers in a chiral topological semimetal
Science 369 (6500), 179-183 (2020)

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