Probing the Fermi surface of Nd-LSCO with angle-dependent magnetoresistance measurements

Characterizing the Fermi surface of high-temperature sperconductors in the pseudogap phase is one of the major challenges in understanding the origin of this mysterious partial gap in the electronic density of states. The Fermi surface between p=0.08 and p=0.15, the same doping range where charge order is observed, has been determined via quantum oscillations to be a small electron pocket. Above the critical doping p*, in the Fermi-liquid phase, a single large hole surface has been reported. However, in the pseudogap phase, the topology of the Fermi surface at low temperature in the absence of superconductivity or charge-density-wave order is still unknown. To study the topology of this Fermi surface, we performed an angle-dependent magetoresistance (ADMR) study of Nd-LSCO. We measured the ADMR of single crystal La_1.6-xNd_0.4Sr_xCuO₄ (Nd-LSCO) with x=p=0.2,0.21,0.22,0.23,0.25, up to 45 tesla and down to 6 kelvin. At p=0.25, above p*, we find a large Fermi surface whose geometry is consistent with that observed by ARPES, but with a strongly anisotropic quasiparticle lifetime. Below p*, in the pseudogap state, we observe a dramatic change in the ADMR, and preliminary analysis suggests that strong anti-nodal scattering is responsible.