2021/06/30 by A. Gourgout, G. Grissonnanche, F. Laliberté +8 · 1 citation
Physics and Astronomy · #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevx.12.011037
published as Physical Review X 12, 011037 (2022) · 12 pages, 12 figures
arxiv created 2021/12/07 · arxiv updated 2022/03/11
We report measurements of the Seebeck effect in both the ab plane (S\rm a) and along the c axis (S\rm c) of the cuprate superconductor La1.6-xNd0.4SrxCuO4 (Nd-LSCO), performed in magnetic fields large enough to suppress superconductivity down to low temperature. We use the Seebeck coefficient as a probe of the particle-hole asymmetry of the electronic structure across the pseudogap critical doping p⋆ = 0.23. Outside the pseudogap phase, at p = 0.24 > p⋆, we observe a positive and essentially isotropic Seebeck coefficient as T → 0. That S > 0 at p = 0.24 is at odds with expectations given the electronic band structure of Nd-LSCO above p⋆ and its known electron-like Fermi surface. We can reconcile this observation by invoking an energy-dependent scattering rate with a particle-hole asymmetry, possibly rooted in the non-Fermi liquid nature of cuprates just above p⋆. Inside the pseudogap phase, for p < p⋆, S\rm a is seen to rise at low temperature as previously reported, consistent with the drop in carrier density n from n ≃ 1 + p to n ≃ p across p⋆ as inferred from other transport properties. In stark contrast, S\rm c at low temperature becomes negative below p⋆, a novel signature of the pseudogap phase. The sudden drop in S\rm c reveals a change in the electronic structure of Nd-LSCO upon crossing p⋆. We can exclude a profound change of the scattering across p⋆ and conclude that the change in the out-of-plane Seebeck coefficient originates from a transformation of the Fermi surface.