Wiedemann-Franz Law and Abrupt Change in Conductivity across the Pseudogap Critical Point of a Cuprate Superconductor

Abstract

The thermal conductivity κ of the cuprate superconductor La1.6−xNd0.4SrxCuO4 was measured down to 50 mK in seven crystals with doping from p = 0.12 to p = 0.24, both in the superconducting state and in the magnetic field-induced normal state. We obtain the electronic residual linear term κ0/T as T → 0 across the pseudogap critical point p = 0.23. In the normal state, we observe an abrupt drop in κ0/T upon crossing below p , consistent with a drop in carrier density n from 1+p to p, the signature of the pseudogap phase inferred from the Hall coefficient. A similar drop in κ0/T is observed at H = 0, showing that the pseudogap critical point and its signatures are unaffected by the magnetic field. In the normal state, the Wiedemann-Franz law, κ0/T = L0/ρ(0), is obeyed at all dopings, including at the critical point where the electrical resistivity ρ(T ) is T -linear down to T → 0. We conclude that the non-superconducting ground state of the pseudogap phase at T = 0 is a metal whose fermionic excitations carry heat and charge as conventional electrons do.

Superconductivity in Perovskite Ba1−xKxBi0.30Pb0.70O3−δ

“…This is similar to the doping of K in Ba site for BaBiO 3 to form superconductor Ba 1‐x K x BiO 3 , where with an increase of K in the compound (below this temperature, the superconductor shows minus magnetic moment) first increases and then decreases. Similar behavior has been also observed in cuprate superconductors …”

Magnetotransport of dirty-limit van Hove singularity quasiparticles

“…Hence this information can be applied to, for example, the pseudogap problem [4][5][6] found in La-based cuprates. Assuming β ≈ 0.3 for La 1.36 Nd 0.4 Sr 0.24 CuO 4 , where W DOS~1 5 meV 32 , yields T FL~1 5 K. However, since ρ~T [C=T $ log ð1=TÞ] is observed down to 1 (0.5) K [33][34][35][36] , we conclude that quantum criticality must be taken into account. Our results thus have direct implications for the interpretation of the strange metal properties in cuprates.…”

“…High density of states (DOS) systems 4,5,11,16,17,31,64,65 plotted as a function of dimensionality and disorder gauged, respectively, by ρ ab /ρ c (in-plane resistivity over out-of-plane resistivity) and ρ 0 (from refs. 11,13,33,34,57,[66][67][68][69][70][71][72][73] ). The third axis labeled T refers to temperature.…”

Die hard holographic phenomenology of cuprates

“…This effect was attributed to the superconducting fluctuations and/or disordered vortex pairs whose (positive) contribution dominates over that of the quasiparticles (whose sign, in turn, depends on the dominant type of carriers) upon approaching T c . Besides, e N turned out to be strongly affected by a proximity to the pseudogap regime and can even become anisotropic [11][12][13][14].…”