Square-Net Topological Semimetals: How Spectroscopy Furthers Understanding and Control

Abstract

Square-net materials are well positioned to lead optical spectroscopic explorations into the electronic structure, photoinduced dynamics, and phase transitions in topological semimetals. Hundreds of square-net topological semimetals can be prepared that have remarkably different electronic and optical properties despite having similar structures. Here we present what has been gleaned recently from these materials with the whole gamut of optical spectroscopies, ranging from steady-state reflectance and Raman investigations into topological band structures, electronic correlations, and equilibrium phase transitions to time-resolved techniques used to decipher ultrafast relaxation dynamics and nonequilibrium photoinduced phase transitions. We end with a discussion of some major remaining questions and possible future research directions.

In-plane and out-of-plane optical response of the nodal-line semimetals ZrGeS and ZrGeSe

“…The ZrSiS-type family of square-net materials with the general formula WXY (with W = Zr, Hf; X = Si, Ge, Sn; Y = O, S, Se, Te) has been extensively investigated experimentally and theoretically in recent years, since they provide an ideal platform for exploring exotic states of quantum matter, namely the nodal-line semimetal phase [1][2][3][4][5][6] and novel two-dimensional Dirac states protected by non-symmorphic symmetry [7].…”

Lu–H–N Phase Diagram from First-Principles Calculations

“…The fact that the density of states is vanishing at the Fermi level makes LuH3 an ideal system to study fundamental physics of topological node-line semimetals. With eliminated contributions of the topologically trivial bands, it is a unique platform to investigate manifestations of electron-hole interactions such as the linear frequency dependent optical conductivity [33] and the hot carrier dynamics. [34] Moreover, pressure-dependent band structure indicates that the nodal line is robust under hydrostatic pressure, yet it can serve as a manipulation of the Fermi velocity of the linearly dispersed bands.…”

Unveiling the Catalytic Potential of Topological Nodal-Line Semimetal AuSn4 for Hydrogen Evolution and CO2 Reduction

“…Quantum materials have attracted considerable attention in the past decade for the exotic phenomena enabled by their topologically nontrivial states. − While most existing investigations are still focused on fundamental physics, it is well recognized that the goal of this vast scientific community is to (i) identify and (ii) implement technological applications, possibly scalable at the industrial level, exploiting the quantum phenomena associated with the topological protection of their electronic states. In recent years, topological materials have been proposed for applications in various fields, such as energy, optoelectronics, electronics, and recently topological catalysis. − Especially, catalysis with quantum materials represents a new promising route in electrochemistry, considering that topological surface states mediate the charge transfer between the substrate and the adsorbed chemical species.…”