Identifying possible pairing states in Sr$_2$RuO$_4$ by tunneling spectroscopy

TL;DR

This study uses tunneling spectroscopy and theoretical modeling to differentiate between possible pairing symmetries in Sr$_2$RuO$_4$, finding that certain states are inconsistent with experiments and proposing ways to distinguish others.

Contribution

It applies Blonder-Tinkham-Klapwijk theory to analyze tunneling conductance for various pairing states in Sr$_2$RuO$_4$, providing a method to identify the correct pairing symmetry.

Findings

Chiral d-wave pairing is inconsistent with c-axis tunneling experiments.

In-plane tunneling spectroscopy can distinguish between helical p-wave and f-wave states.

The study offers a theoretical framework for identifying pairing symmetry in Sr$_2$RuO$_4$.

Abstract

We examine the tunneling spectroscopy of three-dimensional normal-metal/Sr$_2$RuO$_4$ junctions as an experimental means to identify pairing symmetry in Sr$_2$RuO$_4$. In particular, we consider three different possible pairing states in Sr$_2$RuO$_4$: spin-singlet chiral $d$-wave, spin-triplet helical $p$-wave, and spin-nematic $f$-wave ones, all of which are consistent with recent nuclear-magnetic-resonance experiments [A. Pustogow et al., Nature 574, 72 (2019)]. The Blonder-Tinkham-Klapwijk theory is employed to calculate the tunneling conductance, and the cylindrical two-dimensional Fermi surface of Sr$_2$RuO$_4$ is properly taken into account as an anisotropic effective mass and a cutoff in the momentum integration. It is pointed out that the chiral $d$-wave pairing state is inconsistent with previous tunneling conductance experiments along the $c$-axis. We also find that the remaining candidates, the spin-triplet helical $p$-wave pairing state and the spin-nematic $f$-wave ones, can be distinguished from each other by the in-plane tunneling spectroscopy along the $a$- and $b$-axes.