Observation of Andreev reflection in the c-axis transport of Bi2Sr2CaCu2O8+x single crystals near Tc and search for the preformed-pair state
Abstract
We observed an enhancement of the c-axis differential conductance around the zero-bias in Au/Bi2Sr2CaCu2O8+x (Bi2212) junctions near the superconducting transition temperature Tc. We attribute the conductance enhancement to the Andreev reflection between the surface Cu-O bilayer with suppressed superconductivity and the neighboring superconducting inner bilayer. The continuous evolution from depression to an enhancement of the zero-bias differential conductance, as the temperature approaches Tc from below, points to weakening of the barrier strength of the non-superconducting layer between adjacent Cu-O bilayers. We observed that the conductance enhancement persisted up to a few degrees above Tc in junctions prepared on slightly overdoped Bi2212 crystals. However, no conductance enhancement was observed above Tc in underdoped crystals, although recently proposed theoretical consideration suggests an even wider temperature range of enhanced zero-bias conductance. This seems to provide negative perspective to the existence of the phase-incoherent preformed pairs in the pseudogap state.
Turn this paper into a full lesson
ArcXiv compiles a staged curriculum from this paper: 8-12 lessons across beginner → advanced, synthesised section guides, visuals, flashcards, a quiz, exercises, and on-demand deep dives per section. Grounded in the abstract, never invented.