Abstract
In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O8+δ and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc.
Highlights
In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair
Angle-resolved photoemission spectroscopy (ARPES) is a powerful method to investigate the electronic structures of matter, and it has been continuously deepening the insights into the cuprates[3,4]
Various peculiar electronic structures of the cuprates have been revealed by ARPES that can be summarized as follows: (1) The superconducting gap has a d-wave symmetry[3]; (2) Across Tc, the gap is diminished only near the d-wave node in momentum (k) space, resulting in a seemingly disconnected Fermi surface, or Fermi arcs, above Tc5; (3) Quasi-particle dispersions commonly exhibit kink structures below ~70 meV6, indicating that individual-electron excitations are coherently dressed by some kink boson modes[7,8,9]
Summary
Superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. It is a challenge to understand the connection between the peculiar electronic structures and unconventional phenomena such as the signatures of incoherent Cooper pairs remaining at temperatures above Tc, which is an indication that the gluing of a Cooper pair is still substantial in the normal state[12,13,14,15,16,17]. The step would be to understand the microscopic mechanism of the temperature-dependent spectral broadening that fills the d-wave gap around the node, forms the Fermi arcs, and quenches the macroscopic superconductivity at Tc. Recently, a pump-and-probe method based on femto-second pulsed laser sources has been implemented into ARPES, and it became possible to investigate the responses of the cuprate’s electronic structures to a light pulse[22,23,24,25,26,27,28,29,30].
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