# Microwave Conductivity Distinguishes Between Different d-wave States: Umklapp Scattering in Unconventional Superconductors

## TL;DR

This paper demonstrates that microwave conductivity measurements, combined with Fermi surface knowledge, can distinguish between different d-wave superconducting states, and applies this method to identify a new d$_{xy}$ superconductor.

## Contribution

The paper introduces a novel method using microwave conductivity and Fermi surface data to differentiate closely related d-wave superconducting states.

## Key findings

- Confirmed YBa2Cu3O7-δ as d_{x^2-y^2} superconductor
- Identified κ-(BEDT-TTF)2Cu[N(CN)2]Br as d_{xy} superconductor
- Showed the method's effectiveness in distinguishing superconducting order parameters

## Abstract

Microwave conductivity experiments can directly measure the quasiparticle scattering rate in the superconducting state. We show that this, combined with knowledge of the Fermi surface geometry, allows one to distinguish between closely related superconducting order parameters, e.g., d$_{x^2-y^2}$ and d$_{xy}$ superconductivity. We benchmark this method on YBa$_2$Cu$_3$O$_{7-\delta}$ and, unsurprisingly, confirm that this is a d$_{x^2-y^2}$ superconductor. We then apply our method to $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, which we discover is a d$_{xy}$ superconductor.