Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems

Abstract

Abstract. Muon spin rotation and relaxation (µSR) experiments have yielded evidence that structural disorder is an important factor in many f-electron-based non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour are suggested by the observed broad and strongly temperature-dependent µSR (and NMR) linewidths in several NFL compounds and alloys. Local disorderdriven theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not capable of describing the time-field scaling seen in muon spin relaxation experiments, which suggest cooperative and critical spin fluctuations rather than a distribution of local fluctuation rates. A strong empirical correlation is established between electronic disorder and slow spin fluctuations in NFL materials.

Effect of annealing on glassy dynamics and non-Fermi liquid behavior in Pd

“…Both the 1-week and 2-week annealed samples exhibit a reduction of Λ at low temperatures, indicating that annealing shifts fluctuation noise power to higher frequencies. This behavior is expected from the previouslyobserved correlation between low-temperature relaxation and residual resistivity [1].…”

“…The correlation with residual resistivity previously observed for a number of NFL heavy-electron materials is also found in the present work. As previously found from comparison of a number of different NFL systems [1,6], low-frequency divergences characterize NFL spin fluctuations independently of the degree of disorder with, however, a strong increase of low-frequency fluctuation noise power in disordered NFL materials.…”

“…Muon spin relaxation (µSR) experiments in a number of f -electron non-Fermi liquid compounds and alloys have revealed anomalous behavior in the low-frequency spectrum of thermally-excited spin fluctuations in these materials [1]. The noise spectrum exhibits divergent behavior at low frequencies, with an increase in low-frequency noise power that correlates with increasing disorder as measured by the residual resistivity.…”

Susceptibility inhomogeneity and non-Fermi liquid behavior in

“…In these alloys the transverse-field µSR (TF-µSR) relaxation rate (i.e., the width of the µSR line) is due to an inhomogeneous spread δK of muon Knight shifts K [5,6]. This spread is in turn a measure of the spread δχ in magnetic susceptibility χ from the basic relation K ∝ χ.…”

“…This spread is in turn a measure of the spread δχ in magnetic susceptibility χ from the basic relation K ∝ χ. The relaxation rate becomes very large at low temperatures in a number of NFL materials including UCu 5−x Pd x and UCu 4 Pt [6]. Early NMR observations of this effect in UCu 5−x Pd x [7] were taken as evidence for the "Kondo disorder" model [8,9] for disorderdriven NFL behavior.…”