Magnetotransport studies of the Sb square-net compound LaAgSb2 under high pressure and rotating magnetic fields

Abstract

Square-net-layered materials have attracted attention as an extended research platform of Dirac fermions and of exotic magnetotransport phenomena. In this study, we investigated the magnetotransport properties of LaAgSb 2 , which has Sb-square-net layers and shows charge density wave (CDW) transitions at ambient pressure. The application of pressure suppresses the CDWs, and above a pressure of 3.2 GPa a normal metallic phase with no CDWs is realized. By utilizing a mechanical rotator combined with a high-pressure cell, we observed the angular dependence of the Shubnikov-de Haas (SdH) oscillation up to 3.5 GPa, and we confirmed the notable two-dimensional nature of the Fermi surface. In the normal metallic phase, we also observed a remarkable field-angular-dependent magnetoresistance (MR), which exhibited a "butterflylike" polar pattern. To understand these results, we theoretically calculated the Fermi surface and conductivity tensor at the normal metallic phase. We showed that the SdH frequency and Hall coefficient calculated based on the present Fermi surface model agree well with the experiment. The transport properties in the normal metallic phase are mostly dominated by the anisotropic Dirac band, which has the highest conductivity due to linear energy dispersions. We also proposed that momentum-dependent relaxation time plays an important role in the large transverse MR and negative longitudinal MR in the normal metallic phase, which is experimentally supported by the considerable violation of Kohler's scaling rule. Although quantitatively complete reproduction was not achieved, the calculation showed that the elemental features of the butterfly MR could be reasonably explained as the geometrical effect of the Fermi surface.

Superconductivity and Charge-Density-Wave-Like Transition in Th2Cu4As5

“…It is important to consider that the As–As distance within the As(2) sheet measures 2.874 Å, indicating the presence of a covalent bond. We note that similar As or Sb planes also exist in 112-type LnCuPn 2 compounds (Ln represents lanthanide elements, Pn = As, Sb) and play a decisive role in their electrical transport properties. , …”

“…42 On the other hand, for LaCuSb 2 and LaAgSb 2 , which exhibit superconductivity with lower T c than that of Th 2 Cu 4 As 5 , the contribution of d-orbital to the conduction band is also less pronounced. 20,42,43 In short, the above-mentioned research collectively converges on an empirical rule: the transition temperatures of CDW and superconductivity are positively correlated with the contribution of the p-orbital and d-orbital to N(E F ), respectively. Therefore, it is reasonable to conjecture that in Th 2 Cu 4 As 5 , the superconductivity may be associated with the Cu 4 As 3 slabs, while the CDW-like phase transition could be ascribed to the As(2) square sheets.…”

“…Intriguingly, analogous As/Sb planes are prevalent in 112-type LnTPn 2 compounds, where Ln represents lanthanides, T denotes Cu, Ag, and Au, and Pn stands for As or Sb. ,− Some of these compounds, such as LaAgSb 2 and LaAuSb 2 , exhibit CDW states with even higher transition temperatures than those of Th 2 Cu 4 As 5 . ,, Notably, the primary contribution to N ( E F ) in the 112-type pnictides stems from the p orbital . On the other hand, for LaCuSb 2 and LaAgSb 2 , which exhibit superconductivity with lower T c than that of Th 2 Cu 4 As 5 , the contribution of d-orbital to the conduction band is also less pronounced. ,, In short, the above-mentioned research collectively converges on an empirical rule: the transition temperatures of CDW and superconductivity are positively correlated with the contribution of the p-orbital and d-orbital to N ( E F ), respectively. Therefore, it is reasonable to conjecture that in Th 2 Cu 4 As 5 , the superconductivity may be associated with the Cu 4 As 3 slabs, while the CDW-like phase transition could be ascribed to the As(2) square sheets.…”

“…We note that similar As or Sb planes also exist in 112-type LnCuPn 2 compounds (Ln represents lanthanide elements, Pn = As, Sb) and play a decisive role in their electrical transport properties. 19,20 Based on the atomic distances listed in 21 For Th 2 Cu 4 As 5 , the peaks exhibit a slight shift to lower binding energies of 952.4 and 932.5 eV, respectively. Additionally, the satellite feature is not visible.…”

Observation of superconductivity and its enhancement at the charge density wave critical point in LaAgSb2

“…At ambient pressure, LaAgSb 2 exhibits sequential CDW transitions at T CDW1 = 210 K and T CDW2 = 190 K [10,11], whose critical pressures are determined as P CDW1 ∼ 3.2 GPa and P CDW2 ∼ 1.7 GPa, respectively [12]. Although the origin of CDW2 is not conclusive at present, CDW1 is * akb@okayama-u.ac.jp assumed to be derived from the nesting within the characteristic hollow-shaped Fermi surface (FS) [11,13,14]. Previous studies have reported that the hollow-shaped FS exhibits a Dirac-like linear dispersion at the Fermi level [15,16].…”