Spontaneous Magnetic field and chiral superconductivity in BaPtAs_1-xSb_x with honeycomb network

In recent years, a time-reversal symmetry-breaking superconducting (SC) state in which spontaneous magnetic field appears has attracted much attention. In materials with a so-called honeycomb network, the possibility of chiral d-wave superconductivity has been discussed [1]. Muon spin relaxation (μSR) is one of powerful tools for detecting spontaneous magnetic field.

In the layered pnictide BaPtAs_1-xSb_x with a honeycomb network, superconductivity appears over the entire range of x = 0 – 1.0 [2]. However, it has been unknown whether chiral d-wave superconductivity appears in this compound. Therefore, we performed μSR measurements on BaPtAs_1-xSb_x changing x widely [3].

It was found that the relaxation rate of muon spins increased below T_c = 1.7 K at x = 1.0, suggesting that spontaneous magnetic field is generated and time-reversal symmetry is broken. Moreover, the spontaneous magnetic field almost disappeared at x = 0.9, where a small amount of As was substituted for Sb, indicating that this superconductivity was weak to disorder. These suggest that the time-reversal symmetry-breaking SC state at x = 1.0 may have nodes on the SC gap. In the talk, I will compare these results with the band structure and Fermi surfaces obtained from the first-principles calculation and discuss the possibility of chiral d-wave superconductivity.

[1] P. K. Biswas et al. Phys. Rev. B 87, 180503(R) (2013).

[2] T. Ogawa et al., J. Phys. Soc. Jpn. 91, 123702 (2022).

[3] T. Adachi et al., submitted.