Studies of non-trivial band topology and electron-hole compensation in YSb
Introduction
Topological insulators (TI) are of supreme interest to the scientific community in recent years because of their extraordinary properties for applications in quantum computing and spintronics [[1], [2], [3], [4], [5]]. With protection by time-reversal symmetry, topological insulators possess intriguing physical properties like gapless surface states and unconventional spin texture with forbidden electron's backscattering [1,6,7]. More interestingly, topological phases of matter made an important breakthrough in physics theory, as not being characterized by symmetry breaking process like the one in conventional phase transitions given by Landau [8]. Recently, the research on non-trivial band topology has been directed to semi-metals [[9], [10], [11], [12], [13]], which could establish many phenomena such as quantum magnetoresistance [14], chiral anomaly [15], and Weyl fermion quantum transport [16].
More recently, extremely large magnetoresistance (XMR) materials like WTe2 [17,18], Bi2Te3 [19], NbP [20], LaBi [21], etc. have attracted tremendous attention for studying their exotic topological properties [[22], [23], [24]]. In many reports, XMR effect is explained by compensation of electron and hole densities [17,25,26] and non-trivial topological protection [18,27]. From two-band model, XMR effect is well established by perfect electron-hole compensation [17,25,26]. Since, many XMR materials like LaSb, YSb, etc. are topologically trivial [[28], [29], [30]], therefore the significance of topology in leading to XMR effect is yet to be established. Therefore, it would be very interesting to find a XMR material having topologically trivial phase and a lack of perfect electron-hole compensation, so that non-trivial topological phase may be induced in it by enhancing the spin-orbit coupling (SOC) strength. In many recent reports, XMR effect is greatly pronounced in rare-earth monopnictide compounds [21,28,[31], [32], [33], [34], [35], [36]] in which YSb have a lack of topological protection and perfect electron-hole compensation [29]. It is also known that chemical doping or alloying composition or applying pressure or strain can increase the strength of SOC [[37], [38], [39], [40], [41]], which may cause topological quantum phase transition (TQPT) in the material. But unlike chemical doping, external pressure is a strong tool to tune the electronic properties exempted from unwanted impurities arising from chemical doping. It inspired us to investigate the topological phase in YSb under hydrostatic pressure. In addition, we also studied electron to hole density ratio as a function of pressure, which may pave a path to correlate non-trivial band topology and XMR effect.
Section snippets
Computational details
Vienna ab initio simulation package (VASP) is used for electronic structure calculations within the framework of Density Functional Theory (DFT) [42]. Exchange-correlation functions are included within the approximation of Perdew-Burke-Ernzehrof (PBE) under Generalized gradient approximation (GGA) and Heyd-Scuseria-Ernzerhof (HSE06) [43,44]. Electron-ion interactions are included within the formalism of projected augmented wave (PAW) [45]. Theoretical calculations are performed with a cut-off
Results and discussions
YSb is found to have rocksalt crystal structure at ambient pressure with a space group of Fmm (225) in which ‘Sb’ atom is present at the origin (0, 0, 0), and ‘Y’ atom is present at (0.5, 0.5, 0.5) [31]. The optimized lattice constant of YSb is found to be 6.201 Å consistent with the experimental value of 6.163 Å [32,35] (see Fig. 1).
In order to investigate the non-trivial topological phase under pressure, first we calculated the band structure of YSb at ambient pressure using PBE and HSE
Conclusion
It is concluded that XMR material YSb undergoes reentrant topological quantum phase transition under hydrostatic pressure. From the detailed Fermi surface calculations, it is found that the ratio of ne/nh increases with the pressure, but perfect electron-hole compensation is absent in non-trivial topological phase. It indicates that non-trivial topological phase may appear without a maximal effect on the magnetoresistance under hydrostatic pressure, and need further experimental investigations
Credit author statement
Rakesh Kumar conceived the idea and supervised the study. All authors developed the model for the study. Payal Wadhwa performed all the theoretical calculations. All authors discussed and analyzed the results, and reviewed the manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors would like to thank IIT Ropar for High performance computing facility.
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