Seebeck Coefficient in a Cuprate Superconductor: Particle-Hole Asymmetry in the Strange Metal Phase and Fermi Surface Transformation in the Pseudogap Phase

Abstract

We report measurements of the Seebeck effect in both the ab plane (Sa) and along the c axis (Sc) 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 electronlike 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