Progress and Prospects of Novel Topological Phases of Materials

Abstract

The field of topological phases has captivated the condensed matter physics (CMP) community with its unique blend of theoretical elegance and practical relevance. The defining characteristic of the most celebrated topological insulator (TI) phase is their insulating bulk paired with a conductive surface; a property stemming from the non-trivial topology of their wavefunctions (Hasan et al 2023). In general, a d-dimensional system is classified as a TI if it has an insulating bulk and features boundary states that remain gapless, unaffected by local boundary perturbations unless the symmetry is broken. The TIs are characterized by the non-zero Z2 invariant which signifies odd number of gapless spinhelical topological surface states (TSS) protected by time-reversal symmetry (TRS). Thus, this provides a solid framework that the scientific community continues to build upon for the potential applications of TIs in spintronics, quantum computing and nano-electronics. The adoption of topological classification in the last decade has unveiled various quantum materials, from insulators and superconductors to Dirac, Weyl semimetals, and fragile topological phases (Chen et al 2023). This letter to the editor outlines the recent advancements in TIs which pave the way for investigation of TIs and multifunctional quantum materials.

The non-trivial band topology is intricately embedded within the band structure of an insulator through band inversion. Intrinsic spin-orbit coupling (SOC) present in the system is a key factor in realizing the bulk band inversion or parity exchanges in most of the known TI genome. Numerous SOC induced TIs were theoretically and experimentally investigated ranging from HgTe/CdTe quantum wells, quintuple layered V2VI3 binary compounds, half-Heusler compounds, ternary noncentrosymmetric compounds etc (Patel et al 2024, Hsieh et al 2008, Dhori et al 2022, Dhori et al 2024, Sattigeri et al 2021). Despite theoretical predictions, the practical applications of TIs remain elusive largely due to the interference from the conduction contribution from the bulk in small bandgap semiconductor, precise control over material purity and challenging control over spin-momentum locking at elevated temperatures. Thus, in recent years, there has been a renewed interest in discovering materials that could bridge the gaps