Microwave Absorption Peaks : Signatures of Spin Dynamics in Cuprates

TL;DR

This paper identifies microwave absorption peaks in cuprates as signatures of spin dynamics, suggesting a magnetic mechanism underlying these features across insulating, pseudogap, and superconducting states.

Contribution

It demonstrates that microwave absorption peaks are due to magnetic relaxation processes, providing new insight into spin behavior in cuprate materials.

Findings

Absorption peaks occur when magnetic relaxation time crosses measurement frequency.

Features are observed across insulating, pseudogap, and superconducting states.

Magnetic (spin) mechanism likely causes the peaks, not quasiparticles.

Abstract

We show that a common feature of temperature-dependent microwave absorption is the presence of absorption peaks. $ac$ loss peaks can arise when the internal $T$-dependent magnetic relaxation time crosses the measurement frequency. These features are observed in the \QTR{em}{insulating} ($Sr_{x}Ca_{14-x}Cu_{24}O_{41}$, $La_{5/3}Sr_{1/3}NiO_{4}$ and $YBa_{2}Cu_{3}O_{6.0}$), \QTR{em}{pseudo-gap} ($T>T_{c}$ in underdoped $YBa_{2}Cu_{3}O_{7-\delta}$, $Hg:1223$ and $Hg:1201$) and \QTR{em}{superconducting} ($T<T_{c}$) states of the oxides. The commonality of these features suggests a magnetic (spin) mechanism, rather than a quasiparticle origin, for the so-called ``conductivity'' peaks observed in the cuprate superconductors.