Topological electronic states in HfRuP family superconductors

Abstract

Based on the first-principles calculations and experimental measurements, we report that the hexagonal phase of ternary transition metal pnictides TT'X (T=Zr, Hf; T'=Ru; X=P, As), which are well-known noncentrosymmetric superconductors with relatively high transition temperatures, host nontrivial bulk topology. Before the superconducting phase transition, we find that HfRuP belongs to a Weyl semimetal phase with 12 pairs of type-II Weyl points, while ZrRuAs, ZrRuP and HfRuAs belong to a topological crystalline insulating phase with trivial Fu-Kane Z 2 indices but nontrivial mirror Chern numbers. High-quality single crystal samples of the noncentrosymmetric superconductors with these two different topological states have been obtained and the superconductivity is verified experimentally. The wide-range band structures of ZrRuAs have been identified by ARPES and reproduced by theoretical calculations. Combined with intrinsic superconductivity, the nontrivial topology of the normal state may generate unconventional superconductivity in both bulk and surfaces. Our findings could largely inspire the experimental searching for possible topological superconductivity in these compounds.

Probing the superconducting gap structure in the noncentrosymmetric topological superconductor ZrRuAs

“…Figure 1(b) shows the temperature dependence of the ZFC and FCC dc magnetic susceptibility χ dc (T ) in an applied magnetic field of 2 mT. A clear diamagnetic signal is observed in both the ZFC and FCC curves with an onset superconducting critical temperature T onset c = 7.9(1) K. It is to be noted that the T onset c of our sample is very similar to that reported for the single crystal of ZrRuAs (T onset c = 7.9 K) by Qian et al [27], but lower than the T c = 12 K reported by Meisner et al [20,21], even though the crystal structure of the samples studied is the same. One possible reason for this discrepancy could be the different preparation methods used.…”

“…189). The measured lattice parameters are a = 6.587(1) Å and c = 3.886(1) Å, in agreement with the published work [20,27]. It is to be noted that ZrAs has been reported to exhibit diamagnetic behavior with metallic resistivity without any sign of superconductivity down to 2 K [33].…”

“…One possible reason for this discrepancy could be the different preparation methods used. It was argued by Qian et al [27] that the difference in annealing temperatures is responsible for the different T c 's. Following the same line of reasoning, it is also anticipated that the lower T c in the sample is mainly due to the different heat treatment procedure.…”

“…Two members of the Fe 2 P type are HfRuP (T c = 12.7 K) and ZrRuAs (T c = 7. 9-12 K) [18,20,27]. Recent angleresolved photoemission spectroscopy studies on these compounds reveal that HfRuP is a Weyl semimetal with 12 pairs of type-II Weyl points, while ZrRuAs does not have any Weyl point and is suggested to belong to a topological crystalline insulating phase with nontrivial mirror Chern numbers [27].…”

Discovery of $${\hat{\boldsymbol{C}}}_2$$ rotation anomaly in topological crystalline insulator SrPb

“…Given that the mapping from symmetry-based indicators to topological invariants is one-to-many mapping (it is a one-to-four mapping for SrPb), the mirror Chern numbers ( and ) are calculated in order to confirm the exact topological phase in SrPb. In the presence of time-reversal symmetry, the Chern number ( ) can be identified in half of the plane by the 1D Wilson loops of the two mirror eigenvalues ( and ) subspaces 36 . The Wannier charge centers of the k z -directed and k x -directed Wilson loops as a function of k y for the k x = 0 and k z = 0 planes are shown in Fig.…”