Transport signatures of the pseudogap critical point in the cuprate superconductor Bi2Sr2−xLaxCuO6

Abstract

Five transport coefficients of the cuprate superconductor Bi 2 Sr 2−x La x CuO 6+δ 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 n H 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.

High-order Van Hove singularities in cuprates and related high-Tc superconductors

“…Importantly, such a high-order VHS may have been observed recently near x pg in the cuprates [10], consistent with an earlier prediction [11]. For other cuprates, there can be a larger gap between x V HS and the superconducting or pseudogap doping [12]. Regardless, an analysis of the order of VHS evolution and the resulting anomalies in the cuprates may bring new insights for understanding and identifying new correlated states.…”

Compartmentalizing the cuprate strange metal

“…This is also the only regime where H{T scaling of the MR is observed. The precise location of p ˚in Bi2201 has been a longstanding controversy [25,74,[104][105][106]. A recent combined transport and ARPES study provided evidence that the pseudogap opens around p " 0.21 [74], below which a large anti-nodal gap persists up to temperatures far above T F , while the spectral function at the anti-node loses coherence, similar to what was observed in Bi2212 below p ˚ [67].…”

“…Certainly, the obtained quadratic behavior in Bi2201 contrasts with the predominantly T -linear resistivity observed in LSCO just below p (also extrapolated from high-field MR measurements) [11]. Nevertheless, a note of caution should be struck here, since (small) resistive upturns are often seen at low T in Bi2201 single crystals [74,103,104] that may mimic a crossover to T 2 resistivity. This seems unlikely however given the fact that in both LSCO and Bi2201 the MR exhibits pure H{T 2 scaling below p ˚indicating a significant T 2 component in ρpT q that is itself subject to impeded cyclotron motion in an applied magnetic field.…”

Stripes in oxygen-enriched cuprates

“…Instead, the carrier density is obtained from the size of the Fermi surface (Luttinger theorem). 42,52,53 XIV. IMPLICATIONS FOR SUPERCONDUCTIVITY Although details are not clear, it seems a fairly safe assumption that neutral oxygen atoms in the CuO 2 planes affect superconductivity.…”