Transport signatures of the pseudogap critical point in the cuprate superconductor Bi2Sr2-xLaxCuO6+δ

Five transport coefficients of the cuprate superconductor Bi2Sr2-xLaxCuO6+delta were measured in the normal state down to low temperature, reached by applying a magnetic field (up to 66 T) large enough to suppress superconductivity. The electrical resistivity, Hall coefficient, thermal conductivity, Seebeck coefficient, and thermal Hall conductivity were measured in two overdoped single crystals, with La concentration x = 0.2 (T-c = 18 K) and x = 0.0 (T-c = 10 K). The samples have dopings p very close to the critical doping p* where the pseudogap phase ends. The resistivity displays a linear dependence on temperature whose slope is consistent with Planckian dissipation. The Hall number n(H) decreases with reduced p, consistent with a drop in carrier density from n = 1 + p above p* to n = p below p*. This drop in nH is concomitant with a sharp drop in the density of states inferred from prior NMR Knight shift measurements. The thermal conductivity satisfies the Wiedemann-Franz law, showing that the pseudogap phase at T = 0 is a metal whose fermionic excitations carry heat and charge as do conventional electrons. The Seebeck coefficient diverges logarithmically at low temperature, a signature of quantum criticality. The thermal Hall conductivity becomes negative at low temperature, showing that phonons are chiral in the pseudogap phase. Given the observation of these same properties in other, very different cuprates, our study provides strong evidence for the universality of these five signatures of the pseudogap phase and its critical point.

Automated summary

This study measured five transport coefficients of Bi2Sr2-xLaxCuO6+delta cuprate superconductor in the normal state, revealing the universality of five signatures of the pseudogap phase and its critical point. The pseudogap phase at T = 0 behaves as a metal with fermionic excitations carrying heat and charge, and exhibits quantum criticality properties at low temperature.