The electronic structure of Bi₂Sr₂CaCu₂Oy in the presence of a super-current: Flux-flow, Doppler shift and quasiparticle pockets

There are several ways to turn a superconductor into a normal conductor: increase the temperature, apply a high magnetic field, or run a large current. High-Tc cup rate superconductors are unusual in the sense that experiments suggest that destroying superconductivity by heating the sample to temperatures above Tc or by applying a high magnetic field result in different 'normal' states. Spectroscopic probes show that above Tc, in the pseudo gap regime, the Fermi surface is partly gapped and there are no well-defined quasiparticles. Transport measurements, on the contrary, reveal quantum oscillations in high magnetic fields and at low temperatures, suggesting a more usual Fermi liquid state. Studying the electronic structure while suppressing superconductivity by using current, will hopefully shed new light on this problem. We perform edangle-resolved photoemission experiments in thin films ofBi₂Sr₂CaCu₂Oy while running high-density current through the samples. Clear evidence was found for non-uniform flux flow, leaving most of the sample volume free of mobile vortices and dissipation. The super-current changes the electronic spectrum, creating quasiparticle and quasihole pockets. The size of these pockets as a function of the current is found to be doping dependent; it depends both on the superfluid stiffness and on the strength of interactions.