Thermopower across the phase diagram of the cuprate La1.6−xNd0.4SrxCuO4 : Signatures of the pseudogap and charge density wave

Abstract

The Seebeck coefficient (thermopower) S of the cuprate superconductor La 1.6−x Nd 0.4 Sr x CuO 4 was measured across its doping phase diagram (from p = 0.12 to p = 0.25), at various temperatures down to T 2 K, in the normal state accessed by suppressing superconductivity with a magnetic field up to H = 37.5 T. The magnitude of S/T in the T = 0 limit is found to suddenly increase, by a factor 5, when the doping is reduced below p = 0.23, the critical doping for the onset of the pseudogap phase. This confirms that the pseudogap phase causes a large reduction of the carrier density n, consistent with a drop from n = 1 + p above p to n = p below p , as previously inferred from measurements of the Hall coefficient, resistivity, and thermal conductivity. When the doping is reduced below p = 0.19, a qualitative change is observed whereby S/T decreases as T → 0, eventually to reach negative values at T = 0. In prior work on other cuprates, negative values of S/T at T → 0 were shown to result from a reconstruction of the Fermi surface caused by charge density wave (CDW) order. We therefore identify p CDW 0.19 as the critical doping beyond which there is no CDW-induced Fermi surface reconstruction. The fact that p CDW is well separated from p reveals that there is a doping range below p where the transport signatures of the pseudogap phase are unaffected by CDW correlations, as previously found in YBa 2 Cu 3 O y and La 2−x Sr x CuO 4 .

Vanishing nematic order beyond the pseudogap phase in overdoped cuprate superconductors

“…S4). The onset temperature of CDW order is consistent with the recent Seebeck coefficient measurement (36) in Nd-LSCO. In contrast, SDW order has been observed at low temperature up to a doping as high as x = 0.26 by elastic neutron scattering.…”

Positive Seebeck coefficient in highly doped La$_{2-x}$Sr$_x$CuO$_4$ ($x$=0.33); its origin and implication

“…Our LSCO33 data, which extends down to sub-kelvin temperature, agrees well with these earlier studies in the overlapping temperature ranges. Our data also smoothly connects to what was recently reported by Collignon et al in Eu-substituted LSCO for x < 0.26 [13].…”

Transport signatures of the pseudogap critical point in the cuprate superconductor Bi2Sr2−xLaxCuO6Lizaire1, Legros2, Gourgout3 et al. 2021Phys. Rev. BSelf Cite253160View full textAdd to dashboardCite

“…Thermoelectricity was first measured in Sherbrooke using a cryostat with a VTI and a superconducting magnet up to H = 18 T, and then at the LNCMI in Grenoble under a static field up to H = 34 T, as in Ref. [39]. The thermal Hall conductivity was measured in Sherbrooke at H = 15 T (see Refs.…”