Pressure effect on band inversion in AECd2As2 (AE=Ca, Sr, Ba<

Abstract

Recent studies have predicted that magnetic EuCd 2 As 2 can host several different topological states depending on its magnetic order, including a single pair of Weyl points. Here we report on the bulk properties and band inversion induced by pressure in the nonmagnetic analogs AECd 2 As 2 (AE = Ca, Sr, Ba) as studied with density functional theory calculations. Under ambient pressure we find that these compounds are narrow band gap semiconductors, in agreement with experiment. The size of the band gap is dictated by both the increasing ionicity across the AE series which tends to increase the band gap, as well as the larger nearest neighbor Cd-As distance from increasing atomic size which can decrease the band gap because the conduction band edge is an antibonding state derived mostly from Cd 5s orbitals. The combination of these two competing effects results in a nonmonotonic change of the band gap size across the AE series with SrCd 2 As 2 having the smallest band gap among the three compounds. The application of negative pressure reduces this band gap and causes the band inversion between the Cd 5s and As 4p orbitals along the -A direction to induce a pair of Dirac points. The topological nature of the Dirac points is then confirmed by finding the closed Fermi arcs on the (10 10) surface.

The Zintl phase compounds AEIn2As2 (AE = Ca, Sr, Ba): topological phase transition under pressure

“…However, it can be seen in Fig. 3(b), that in contrast to the reported findings for AECd 2 As 2 , 22 the three AEIn 2 As 2 systems show a monotonically increasing band gap in the AE series from Ca to Sr and Ba. As mentioned in the previous study, 22 the band gap should increase with the ionicity of the AE elements, and our calculation results just coincides with this feature.…”

“…The specific band gap values at atmospheric pressure containing SOC are also presented in Table 1, corresponding AE = Ca, Sr, and Ba are 0.06 eV, 0.10 eV, and 0.11 eV, respectively. As with AECd 2 As 2 , 22 the lattice constants of AEIn 2 As 2 all increase with the atomic radius of the AE atom. However, it can be seen in Fig.…”

“…With reference to the results of theoretical and experimental studies, SrX 2 As 2 (X = Cd, Sn) have a narrow band gap characteristic that is easily modulated by the external field. 22,24 In this study, we report the discovery of topological phase transition and metal–insulator phase transition in AEIn 2 As 2 induced via pressure. At atmospheric pressure, AEIn 2 As 2 systems are capable of band inversion phenomena, symbolizing non-trivial topological properties.…”

“…Notably, the topological quantum phase transitions obtained from the non-magnetic novel structures of alkaline earth (AE) metal substituted Eu positions are reflected in both Sr(Ba)Cd 2 As 2 21–23 and SrSn 2 As 2 . 24,25 It proposes that the Zintl CaAl 2 Si 2 type material CaM 2 Bi 2 (M = Zn or Cd) is a topological insulator.…”

LaN Structural and Topological Transitions Driven by Temperature and Pressure

“…In contrast, LaAs and LaSb are found to be topologically trivial in ARPES experiments [2,21,22]. Recently, topological phase transitions (TPTs) are especially intriguing, because of the possibility to control different topological phases [23][24][25][26][27][28][29]. In LaAs and LaSb, pressure-induced TPTs have been proposed [30,31].…”