NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors

TL;DR

This study uses NMR to reveal inhomogeneous glassy behavior in iron arsenide superconductors, linked to nematic fluctuations and disorder effects, across various dopings and temperatures.

Contribution

It provides evidence that quenched disorder induces a nematic glass state affecting spin dynamics in iron arsenide superconductors.

Findings

Broad distribution of relaxation rates indicating glassy behavior

Dynamical heterogeneity correlates with nematic susceptibility

Nematic glass arises from quenched random fields affecting spin dynamics

Abstract

We present $^{75}$As nuclear magnetic resonance spin-lattice and spin-spin relaxation rate data in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$ as a function of temperature, doping and magnetic field. The relaxation curves exhibit a broad distribution of relaxation rates, consistent with inhomogeneous glassy behavior up to 100 K. The doping and temperature response of the width of the dynamical heterogeneity is similar to that of the nematic susceptibility measured by elastoresistance measurements. We argue that quenched random fields which couple to the nematic order give rise to a nematic glass that is reflected in the spin dynamics.