Signatures of superconductivity and pseudogap formation in nonequilibrium nodal quasiparticles revealed by ultrafast angle-resolved photoemission

Abstract

We use time-and angle-resolved photoemission to measure the nodal non-equilibrium electronic states in various dopings of Bi2Sr2CaCu2O 8+δ . We find that the initial pump-induced transient signal of these ungapped states is strongly affected by the onset of the superconducting gap at Tc, superconducting pairing fluctuations at Tp, and the pseudogap at T * . Moreover, Tp marks a suggestive threshold in the fluence-dependent transient signal, with the appearance of a critical fluence below Tp that corresponds to the energy required to break apart all Cooper pairs. These results challenge the notion of a nodal-antinodal dichotomy in cuprate superconductors by establishing a new link between nodal quasiparticles and the cuprate phase diagram.

Time- and momentum-resolved gap dynamics inBi2Sr2CaCu2Smallwood1, Zhang2, Miller3 et al. 2014Phys. Rev. BSelf Cite539860View full textAdd to dashboardCite

“…The delayed gap closure noted above is especially visible here and occurs at all fluences: the gap magnitude does not drop to its minimum until 300-600 fs after the application of the pump pulse. A similar dynamic occurs in the nonequilibrium quasiparticle population, 22,23 and it is likely that the delays in the two phenomena are causally connected. Theoretical models of nonequilibrium superconductivity 45,46 predict that an increased quasiparticle population should result in a decreased gap size if it helps the system's overall free energy achieve a minimum.…”

“…The study expands upon previous timeresolved ARPES works on cuprates [19][20][21][22][23][24] by providing gap measurements at a larger range of fluences than has previously been presented, by exploring a range of momentum space extending definitively beyond the normal-state Fermi arc, and by employing more advanced methods to characterize the nonequilibrium gap. We report three primary findings.…”

Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor

“…The experimental setup is the same as that reported previously45811. Transient states in the solids are created by pumping with infrared laser pulses ( hν  = 1.48 eV), then they are probed by a following ultra-violet pulse ( hν  = 5.93 eV) using ARPES setup equipped with a SPECS PHOIBOS 150 electron spectrometer.…”

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

“…This can be ascribed to the quasi-2D nature of our SLG/2DEG heterostructure and shares similarities with other 2D systems where fluctuations play an important role, such as cuprate superconductors (see, for example, ref. 59) and ultracold Fermi gases 60 .…”