Wiedemann-Franz law and non-vanishing temperature scale across the field-tuned quantum critical point of YbRh2Si2

Abstract

The in-plane thermal conductivity kappa(T) and electrical resistivity rho(T) of the heavy-fermion metal YbRh2Si2 were measured down to 50 mK for magnetic fields H parallel and perpendicular to the tetragonal c axis, through the field-tuned quantum critical point, Hc, at which antiferromagnetic order ends. The thermal and electrical resistivities, w(T) and rho(T), show a linear temperature dependence below 1 K, typical of the non-Fermi liquid behavior found near antiferromagnetic quantum critical points, but this dependence does not persist down to T = 0. Below a characteristic temperature T* ~ 0.35 K, which depends weakly on H, w(T) and rho(T) both deviate downward and converge in the T = 0 limit. We propose that T* marks the onset of short-range magnetic correlations, persisting beyond Hc. By comparing samples of different purity, we conclude that the Wiedemann-Franz law holds in YbRh2Si2, even at Hc, implying that no fundamental breakdown of quasiparticle behavior occurs in this material. The overall phenomenology of heat and charge transport in YbRh2Si2 is similar to that observed in the heavy-fermion metal CeCoIn5, near its own field-tuned quantum critical point.

8 figures, 8 pages

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• Low-Temperature Thermal Conductivity of CeRh${}_2$As${}_2$
• Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature
• Wiedemann-Franz law and abrupt change in conductivity across the pseudogap critical point of a cuprate superconductor
• Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCu${}_2$Si${}_2$ versus YbRh${}_2$Si${}_2$
• Quantum criticality and Lifshitz transition in the Ising system CeRu2Si2: Comparison with YbRh2Si2
• A Criterion for Strange Metallicity in the Lorenz Ratio
• Intact Quasiparticles at an Unconventional Quantum Critical Point
• Fate of the Wiedemann-Franz law near quantum critical points of electron systems in solids
• Wiedemann-Franz law demonstration in a student practicum