Photoinduced changes of the chemical potential in superconductingBi2Sr2CaCu2O8+δ

Abstract

The chemical potential of a superconductor is of critical importance since, at equilibrium, it is the energy where electrons pair and form the superconducting condensate. However, in non-equilibrium measurements, there may be a difference between the chemical potential of the quasiparticles and that of the pairs. Here we report a systematic time-and angle-resolved photoemission study of the pump-induced change in the chemical potential of an optimally doped Bi2Sr2CaCu2O 8+δ (Bi2212) sample in both its normal and superconducting states. The change in chemical potential can be understood by separately considering the change in the valence band energy relative to the vacuum, and the change in chemical potential relative to the valence band energy. We attribute the former effect to a changing potential barrier at the sample surface, and the latter effect to the conservation of charge in an asymmetrical density of states. The results indicate that the pair and quasiparticle chemical potentials follow each other even on picosecond timescales.

Nonequilibrium electron dynamics in a solid with a changing nodal excitation gap

“…[61] report a critical fluence near 40 µJ/cm 2 . We have found that an accurate measure of the onset for two-component dynamics can only be obtained after a careful treatment of pump-induced changes in the chemical potential [68], which may resolve this discrepancy.…”

Particle-Hole Asymmetry in the Cuprate Pseudogap Measured with Time-Resolved Spectroscopy

“…The experimental methods are identical to those in Ref. [29]. Figure 1 establishes the procedure for finding ∆µ ε with TARPES, starting with an overdoped (OD) Bi2212 sample (T c ∼ 70 K), where the pseudogap is small or absent [30].…”

“…However, as argued in Ref. [29], it is possible to change variables such that we consider the quasiparticle energy with the pairing interaction turned off. Under this change of variables, f (E − µ, T e ) is no longer a Fermi-Dirac distribution but now has an effective width w eff proportional to the size of the superconducting gap (∆ SC ) even at zero temperature.…”

“…Empty circles denote the data taken between a -0.3 and 0.3 ps delay, and gray bars indicate Tc. (a) uses data from Ref [29]…”

Influence of optically quenched superconductivity on quasiparticle relaxation rates inBi2Sr2CaCu2O8+δ

“…Energy, momentum, and time resolutions are 23 meV, 0.003Å −1 , and 300 fs. We have corrected for detector nonlinearity 27 , as well as for a pump-induced time-dependent but uniform energy shift in the electronic spectrum (≤ 4 meV) 36,38 . Figure 1 shows a fluence-dependent analysis of a nearly optimally doped sample (T c = 91 K), where two cuts through k-space are depicted, at φ = 45…”