Pressure induced suppression of the Pseudogap in the cuprate superconductor Nd-LSCO probed by thermoelectric measurements

In cuprate superconductors, one of the most mysterious phase is the Pseudogap (PG). It seems linked to the superconducting dome, but the nature of their connection remains unknown. It onsets at a doping p* and is characterized by a drop in carrier density n from n=1+p above p* to n=p below. In resistivity and Hall effect, an upturn is seen at low temperature in both quantities[1]. In Nd_0.4La_1.6-xSr_xCuO₄ (Nd-LSCO), at ambient pressure, p*=0.23. A recent study from our group showed that by applying hydrostatic pressure, one can suppress the PG in Nd-LSCO and move p* to a lower doping[2]. At p=0.22, the upturns in resitivity and Hall effect are fully suppressed with 2GPa. The underlying mechanism for this effect is rooted in the Fermi Surface (FS), which imposes that the PG cannot open on an electron-like FS. Here we present a confirmation of these results, by means of Seebeck and Nernst effect measurements under pressure up to 2GPa and in magnetic fields up to 31.2T. In both quantities, the increase due to the PG is strongly suppressed by pressure at p=0.22, but shows only a weak effect at p=0.24, which further supports our interpretation that pressure tunes the pseudogap critical point p* to lower dopings in Nd-LSCO.

[1]Badoux et al Nature 2016
[2]Doiron-Leyraud et al Nat Comm 2017