Local quantum phase transition in YFe ₂ Al ₁₀

Abstract

A phase transition occurs when correlated regions of a new phase grow to span the system and the fluctuations within the correlated regions become long lived. Here, we present neutron scattering measurements showing that this conventional picture must be replaced in YFeAl, a compound that forms naturally very close to a [Formula: see text] quantum phase transition. Fully quantum mechanical fluctuations of localized moments are found to diverge at low energies and temperatures; however, the fluctuating moments are entirely without spatial correlations. Zero temperature order in YFeAl is achieved by an entirely local type of quantum phase transition that may originate with the creation of the moments themselves.

Anomalous quantum critical spin dynamics in YFe2Al10

“…For this analysis to be valid, the applied field must be low enough that the fluctuating spin dynamics are not affected. This appears to be the case in YFe 2 Al 10 [4,11], and we attribute the field dependence of λ LF to the frequency dependence of the dynamic structure factor.…”

“…If the electronic spin fluctuations are not spatially correlated, as is the case in YFe 2 Al 10 [11], then χ ′′ (q, ω µ , T ) is independent of q, and from Eq. (3)…”

“…where ω µ = γ µ H L is the muon Zeeman frequency and A q is the spatial Fourier transform of the coupling magnetic field between electronic fluctuations and probe spins. Furthermore, the dynamic structure factor S(ω, T ) is given by [11] S(q, ω, T ) = 2(n + 1)…”

“…The dashed line in Fig. 2 is from a T −1.4 power-law scaling scenario [11], and the solid curve is from from the 2D-DQXY model [15]. The magnitudes of both predictions are normalized using neutron scattering data, as discussed in detail in Sec.…”

“…Recent neutron scattering experiments [11] revealed no long-range order in YFe 2 Al 10 (i.e., no divergence of the spatial correlation length), but indicated a divergence of the fluctuation time scale. This contrasts strongly with the usual paradigm for critical phenomena, in which both spatial and temporal correlation scales diverge at the transition.…”