Anomalous quantum critical spin dynamics in YFe2Al10

Abstract

We report results of a muon spin relaxation (µSR) study of YFe 2 Al 10 , a quasi-2D nearlyferromagnetic metal in which unconventional quantum critical behavior is observed. No static Fe 2+ magnetism, with or without long-range order, is found down to 19 mK. The dynamic muon spin relaxation rate λ exhibits power-law divergences in temperature and magnetic field, the latter for fields that are too weak to affect the electronic spin dynamics directly. We attribute this to the proportionality of λ(ω µ , T ) to the dynamic structure factor S(ω µ , T ), where ω µ ≈ 10 5 -10 7 s −1 is the muon Zeeman frequency. These results suggest critical divergences of S(ω µ , T ) in both temperature and frequency. Power-law scaling and a 2D dissipative quantum XY (2D-DQXY) model both yield forms for S(ω, T ) that agree with neutron scattering data (ω ≈ 10 12 s −1 ). Extrapolation to µSR frequencies agrees semi-quantitatively with the observed temperature dependence of λ(ω µ , T ), but predicts frequency independence for ω µ ≪ T in extreme disagreement with experiment. We conclude that the quantum critical spin dynamics of YFe 2 Al 10 are not well understood at low frequencies.

Muon spin rotation and relaxation study on Nb1−yFe2+y

“…Instead, it is more instructive to compare our results to those reported for YFe 2 Al 10 , a material believed to reside close to a ferromagnetic quantum critical point [40]. Broadly speaking, our experimental observations at quantum criticality for Nb 1.0117 Fe 1.9883 exhibit similarities to the findings for YFe 2 Al 10 .…”

“…Regarding our observations in the alloying range of Nb 1−y Fe 2+y with quantum critical fluctuations, we will compare our data to those from μSR studies on other materials at quantum criticality. Prominent examples are CeFePO [9], UCu 4 Pd [37,38], CePd 1−x Rh x [39], and YFe 2 Al 10 [40]. For the first three materials, in contrast to our case, the low temperature data have been fitted using stretched exponentials.…”

Energy-length scaling of critical phase fluctuations in the cuprate pseudogap phase

“…These fluctuations are intimately related to and affect the pseudogap phase. For instance, the emergence of magnetic fluctuations [66,67] and nematicity order coincide with the pseudogap opening temperature T* [53][54][55][56], while the superconducting phase fluctuations defines T c , the onset temperature of thermal vortices in the pseudogap phase [13,[68][69][70]. Therefore, we propose that the pseudogap phase can be treated as a "critical" phase (ansatz No.…”