Destruction of surface states of ($d_{zx}+id_{yz}$)-wave superconductor by surface roughness: application to Sr$_2$RuO$_4$

TL;DR

This study demonstrates that surface roughness significantly suppresses the surface states of a ($d_{zx}+id_{yz}$)-wave superconductor, providing insights into the fragile nature of chiral surface currents relevant to Sr$_2$RuO$_4$.

Contribution

It reveals the fragility of ($d_{zx}+id_{yz}$)-wave surface states against roughness and compares it with ($p_x+ip_y$)-wave pairing, explaining experimental observations in Sr$_2$RuO$_4$.

Findings

Chiral surface current of ($d_{zx}+id_{yz}$)-wave superconductor is highly sensitive to surface roughness.

The ($d_{zx}+id_{yz}$)-wave surface states are more fragile than ($p_x+ip_y$)-wave states.

Results explain the absence of spontaneous magnetization in Sr$_2$RuO$_4$ experiments.

Abstract

The fragility of the chiral surface current of ($d_{zx}+id_{yz}$)-wave superconductor, a potential candidate for Sr$_2$RuO$_4$, against surface roughness is demonstrated utilizing the quasiclassical Eilenberger theory. Comparing the chiral surface currents of ($d_{zx}+id_{yz}$)-wave and ($p_{x}+ip_{y}$)-wave pairings, we conclude the chiral current for ($d_{zx}+id_{yz}$)-wave SC is much more fragile than that for the ($p_x+ip_y$)-wave one. The difference can be understood in terms of the orbital symmetry of the odd-frequency Cooper pairs arising at the surface. Our results show the ($d_{zx}+id_{yz}$)-wave scenario can explain the null spontaneous magnetization in Sr$_2$RuO$_4$ experiments.