Abstract
The loss of single-particle coherence going from the superconducting state to the normal state in underdoped cuprates is a dramatic effect that has yet to be understood. Here, we address this issue by performing angle resolved photoemission spectroscopy (ARPES) measurements in the presence of a transport current. We find that the loss of coherence is associated with the development of an onset in the resistance, in that well before the midpoint of the transition is reached, the sharp peaks in the ARPES spectra are completely suppressed. Since the resistance onset is a signature of phase fluctuations, this implies that the loss of single-particle coherence is connected with the loss of long-range phase coherence.
Highlights
In the classic theory of superconductivity of Bardeen, Cooper, and Schrieffer [1], an underlying assumption is the presence of sharp quasiparticles in the normal state
When current is flowing in the sample, electric and magnetic fields exist in the vacuum, which deflect the outgoing photoelectrons
We focus the photon beam to a fine spot ∼20 μm in size along the current direction. (Detailed considerations of the effects of current, voltage, and magnetic field in angle resolved photoemission spectroscopy (ARPES) experiment are discussed in Appendix A.)
Summary
In the classic theory of superconductivity of Bardeen, Cooper, and Schrieffer [1], an underlying assumption is the presence of sharp quasiparticles in the normal state In underdoped cuprates, this condition is violated in that the pseudogap phase is associated with broad, incoherent electronic excitations [2,3,4]. The idea here is to use current flow to destroy the superconducting state, distinct from raising the temperature above Tc, and use spectroscopy to probe the question of singleparticle coherence of the electronic excitations. The new methodology we develop here can be used to probe the single-particle spectroscopy of nonequilibrium steady states in the presence of current flow. We conclude with some remarks on the broader implication of our results for cuprates
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