Evidence of Topological Phase Transition with Excellent Catalytic Activity in the AgCaAs Heusler Alloy: A First-Principles Investigation

Abstract

Topological insulators are centered on the objective that a spin-locked surface state exhibits exceptional spin transport properties with an insulating bulk. In the present work, we predict biaxial strain-induced topological phase transition in the noncentrosymmetric compound AgCaAs, using first-principles calculations. Under ambient conditions, bulk AgCaAs exhibits a trivial nature with an insulating gap; however, on applying biaxial strain the system exhibits Dirac semimetallic behavior, indicating toward topological phase transition. At a 2% biaxial strain, a non-trivial topological phase emerges, which is verified by the orbital inversion across the Fermi level with a massless Dirac cone along the surfaces. Furthermore, by confining the bulk system in one dimension, we obtained a 2D AgCaAs (1T-MoS 2 type) system. The low-dimensional phase exhibits a trivial nature having a 0.48 eV energy gap. Under a moderate tensile strain, the system undergoes a topological phase transition with a 26.2 meV non-trivial energy gap. Such spin−orbit coupling-induced topological phase transition is further confirmed by computing and analyzing the 2 invariants, surface states, slab band structure, and evolution of Wannier charge centers. In terms of energy application, 2D AgCaAs exhibits excellent catalytic activity toward hydrogen evolution reactions. Investigating the catalytic properties of 2D AgCaAs in their non-trivial state has become a pathway for topological quantum catalysis. The Gibbs free energy for 2D AgCaAs was found to be −0.13 eV and suggests an opportunity for experimentalists to develop a catalyst for energy applications. Our findings deliver new insights into next-generation nano-electronics and better catalysts.

Coexistence of a spin–valley-coupled Dirac semimetal and robust quantum spin Hall state with significant Rashba spin-splitting in a halogenated BiAs film

“…6 Specifically, 2D-DMs with strong spin–orbit coupling (SOC) are an excellent choice to understand low-energy fermionic excitations, and provide an encouraging platform to intertwine spins and valleys. In this regard, SOC influences electronic band structure, from which DMs can be divided into three different classes: (i) SOC-induced non-trivial-energy-gap materials, classified into “quantum spin Hall insulators” and “quantum anomalous Hall phases”, which boast many exceptional properties, including dissipationless edge current with time-reversal-symmetry protected helical edge states; 7–9 (ii) Dirac points that are robust against SOC due to a nonsymmorphic space group; 10,11 (iii) a new type of DMs known as spin–valley-coupled Dirac semimetals (svc-DSMs), which have been recently proposed. 12 These compounds have two inequivalent but degenerate valley states that carry information.…”

Topological Phase Transition in Non-centrosymmetric LiCaBi Compound: A First-principles Study

“…If the strength of intrinsic SOC is not enough to realize the topological phases, external parameters such as pressure, electric field, chemical doping, etc., are used to achieve the topological phase transition (TPT). ,, Among others, pressure is an efficient way to induce the TPT as it circumvents the defects and inhomogeneity of doping . In fact, pressure-induced TPTs have been previously observed in BiTeI, Pb 1– x Sn x Se, NaBaBi, rocksalt chalcogenides, layered materials, Sb 2 Se 3 , AgCaAs, KZnAs, etc. At ambient conditions, surface states of TIs are investigated using experimental techniques like angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy .…”

“…Sb 2 Se 3 ,24 AgCaAs,25 KZnAs,26 etc. At ambient conditions, surface states of TIs are investigated using experimental techniques like angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy.…”

Non-trivial topological phases in transition metal rich half-Heusler oxides

“…Hence, ABO HH oxides can be realised in three different phases (α-, β-, and γ-) owing to the presence of three non-equivalent atomic arrangements within the unit cell [27]. These three distinct phases correspond to C1 b structure [28,29]. Such compounds are unique for example, the atomic arrangement of non-magnetic elements can lead to a magnetic ordering in the compound [30].…”