PCP2-4

Unconventional superconductivity in BaPtAs1-xSbx with the ordered honeycomb network

13:15-14:45 Dec.4

*Tsuyoshi Imazu1, Jun Goryo1, Naoya Furutani2, Tadashi Adachi3, Kazutaka Kudo4,5, Yoshiki Imai2
Department of Mathematics and Physics, Hirosaki University, 3 Bunkyo-cho, Hirosaki 036-8561, Japan1
Department of Physics, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan2
Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan3
Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Japan4
Institute for Open and Transdisciplinary Research Initiatives, Osaka University, 1-1 Yamadaoka, Suita 565-0871, Japan5
Abstract Body

The topological superconductivity has attracted much interest over the last few decades [1]. The chiral superconductivity is one of the topological superconducting states with spontaneous time-reversal symmetry breaking (TRSB). SrPtAs (transition temperature Tc=2.4K, point group; D6h) is one of the candidates for TRSB superconductor and it is the first discovered compound as the series of the honeycomb network superconductors [2,3]. The crystal structure of SrPtAs contains Pt-As honeycomb layers with local inversion symmetry breaking piled up with pi/3 rotation(Fig.1a). It is suggested that the chiral d-wave superconducting state is the most plausible candidate of pairing symmetry [3-6].

Recently the honeycomb pnictide superconductorBaPtAs1-xSbx (Tc=1.6-3.2K, point group; D3h) with broken inversion symmetry was discovered (Fig.1b) [7-9]. Tc shows non-monotonic behavior with increasing x and the TRSB is observed at x=1 [9,10]. A possible way to explain these results is to consider the change of the pairing symmetry with varying x.

In order to investigate the electronic structures of BaPtSb (x=1) and BaPtAs (x=0), we carry out the first principles calculations using the Quantum Espresso package [11,12]. Fig. 1c(d) shows the electronic band structure with and without spin-orbit coupling and the density of states without spin-orbit coupling for BaPtSb (BaPtAs), and we clearly see that they have quite similar band structures. In  BaPtSb (BaPtAs), Pt 5d and Sb 5p (As 4p) orbitals are dominant around the Fermi level and they compose three Fermi surfaces. Therefore, we construct low-energy effective tight-binding models which reproduce their band structure around the Fermi level using Wannier90 package [13]. We solve the gap equation for each pairing state classified by the group theoretical analysis and examine a condensation energy. We found that the spin singlet chiral d-wave state could be a potential candidate for the stable pairing symmetry in BaPtSb [14].

References

[1] N. Read et al., Phys. Rev. B 61, 10267 (2000).
[2] Y. Nishikubo et al., J. Phys. Soc. Jpn. 80, 055002 (2011).
[3] P. K. Biswas et al., Phys. Rev. B 87, 180503 (2013).
[4] J Goryo et al., Phys. Rev. B 86, 100507(R) (2012).
[5] M. H. Fischer et al., Phys. Rev. B 89, 020509(R) (2014).
[6] H. Ueki et al., Phys. Rev. B 99, 144510 (2019).
[7] K. Kudo et al., J. Phys. Soc. Jpn. 87, 063702 (2018).
[8] K. Kudo et al., J. Phys. Soc. Jpn. 87, 073708 (2018).
[9] T. Ogawa et al., J. Phys. Soc. Jpn. 91, 123702 (2022).
[10] T. Adachi et al., submitted.
[11] P. Giannozzi et al., J. Phys.: Condens. Matter 21, 395502 (2009).
[12] P. Giannozzi et al., J. Phys.: Condens. Matter 29, 465901 (2017).
[13] G. Pizzi et al., J. Phys. Cond. Matt. 32, 165902 (2020).
[14] T. Imazu et al., in preparation.

pict

Figure 1. The crystal structure of (a) SrPtAs and (b) BaPtSb, BaPtAs. The electronic band structure and the density of state of (c) BaPtSb and (d) for BaPtAs.

Keywords: chiral superconductivity, time-reversal symmetry breaking