Possible Pairing Symmetry of BaPtAs$_{1-x}$Sb$_{x}$ with an Ordered Honeycomb Network

TL;DR

This study explores how the pairing symmetry in BaPtAs$_{1-x}$Sb$_{x}$ superconductors varies with Sb concentration, revealing a transition from TRSB chiral $d$-wave to non-TRSB states, influenced by Fermi surface changes.

Contribution

It demonstrates the potential change in pairing symmetry with Sb doping using first-principles calculations and muon-spin relaxation measurements.

Findings

TRSB chiral $d$-wave state stable at $x=1$

Nodal $f$-wave or $s$-wave states at $x=0$

Significant Fermi surface differences between $x=0$ and $x=1$

Abstract

We investigate the possible pairing symmetry of superconducting $\rm{BaPtAs}_{1-\it{x}}\rm{Sb}_{\it{x}}$ solid solution with an ordered-honeycomb network of Pt and pnictogens. A spontaneous internal magnetic field below the superconducting transition temperature is observed in BaPtSb ($x = 1$) via the muon-spin relaxation measurement. We then pursue a scenario where the pairing symmetry is changed from a time-reversal symmetry-breaking (TRSB) state to another one by changing the Sb-concentration utilizing the effective tight-binding model obtained from the first principles calculations for $x = 0$ and $x = 1$, at which we see a significant difference in the shape of the dominant Fermi surfaces. We find that the chiral $d$-wave state with TRSB is most stable at $x = 1$, whereas the nodal $f$-wave or the conventional $s$-wave states without TRSB are competitive at $x = 0$.