Abstract Body

The series of the honeycomb network superconductors have attracted much interest due to some intriguing experimental report. The first discovered compound is SrPtAs (the transition temperature T_c=2.4K, the point group;D_6h) with local inversion symmetry breaking (Fig.a), in which spontaneous magnetization is observed under T_c, it is known for a candidate of the chiral d-wave superconductors [1-4]. The recently discovered other pnictogen compound superconductors BaPtSb (T_c=1.6K, the point group; D_3h) and BaPtAs (T_c=2.8K, the point group; D_3h) with broken global inversion symmetry (Fig.b) have attracted much attention from experimental reports shown below [5,6]. The superconductivity has been found also in their solid solution, BaPt(As_1-xSb_x), and its T_c shows non-monotonic behavior with increasing x [7]. For the Sb end (x=1), the spontaneous magnetization implying the time-reversal symmetry breaking in the superconducting phase was found below T_c by the muon spin relaxation experiment [8]. A possible way to explain these results is to consider the symmetry change of the pairing symmetry by varying x.

In order to investigate the electronic structures of both compounds BaPtSb and BaPtAs, we carry out the first principles calculations for them using the Quantum Espresso package [9,10]. Fig. (c)-(d) shows the electronic band structure and the density of states without spin-orbit coupling for (a) BaPtSb and (b) BaPtAs, and we clearly see that they have quite similar band structures. In BaPtSb (BaPtAs), Pt 5d_x2-y2, 5d_xy and Sb 5p_z (As 4p_z) orbitals are dominant around the Fermi level and they compose 3 Fermi surfaces. Therefore, we construct 3 bands low-energy effective tight-binding models which reproduce their band structure around the Fermi level using Wannier90 package [11]. We solve the gap equation for each pairing state classified by the group theoretical analysis and examine a condensation energy and T_c. We found that the spin singlet chiral d-wave state could be a potential candidate for the stable pairing symmetry in BaPtSb.

References

[1] Y. Nishikubo et al., J. Phys. Soc. Jpn. 80, 055002 (2011).
[2] H. Ueki et al., Phys. Rev. B 99, 144510 (2019).
[3] P. K. Biswas et al., Phys. Rev. B 87, 180503 (2013).
[3] K. Matano et al., Phys. Rev. B 89, 140504 (2014).
[5] K. Kudo et al., J. Phys. Soc. Jpn. 87, 063702 (2018).
[6] K. Kudo et al., J. Phys. Soc. Jpn. 87, 073708 (2018).
[7] T. Ogawa et al., J. Phys. Soc. Jpn. 91, 123702 (2022).
[8] T. Adachi et al., KEK-MSL REPORT 2017, 54 (2018).
[9] P. Giannozzi et al., J. Phys.: Condens. Matter 21, 395502 (2009).
[10] P. Giannozzi et al., J. Phys.: Condens. Matter 29, 465901 (2017).
[11] G. Pizzi et al., J. Phys. Cond. Matt. 32, 165902 (2020).