Evidence of a normal-state pseudogap in bulk superconducting tunneling junctions of YBa₂Cu₃O_7-δ

Authors

Leandro Guerra ⋅ PH National Institute of Physics, University of the Philippines Diliman
Mildred Reyes ⋅ PH National Institute of Physics, University of the Philippines Diliman
Ayn Manuel ⋅ PH National Institute of Physics, University of the Philippines Diliman
Roland Sarmago ⋅ PH National Institute of Physics, University of the Philippines Diliman
Arnel Salvador ⋅ PH National Institute of Physics, University of the Philippines Diliman

Abstract

It is now apparent that the electronic properties of high-temperature superconductors are very different from that of conventional superconductors. Various experiments have shown clear differences in the electronic and magnetic properties of both materials. Despite this, a mechanism of superconductivity for these high-temperature cuprates has yet to be arrived at.
Recent measurements on the superconducting energy gap of these materials may provide the missing clues on the mechanism. Note that the superconducting energy gap defines a range of energy levels that are forbidden to electrons (with all the states below the gap completely filled). In conventional low-temperature (BCS) superconductivity, the presence of this gap signifies the sudden transition at Tc, the superconducting transition temperature. However, underdoped high temperature superconductors show the onset of a gap far above this transition temperature.
It is therefore important to determine if this transition, which begins in the normal state, is connected to the superconducting transition. Understanding this normal-state pseudogap, will shed light on the mechanism of high-temperature superconductivity. One central question is the relationship of these properties with those of the superconducting state. The results of experiments studying these relationships may provide the needed hints on which theories of high-temperature superconductivity are correct.
In this paper, we present direct experimental evidence for the existence of this normal state pseudogap in optimally-doped bulk superconducting samples YBa₂Cu₃O_7-δ. Fully de oxygenated YBa₂Cu₃O_7-δ samples were prepared (with Tc=90K determined through resistivity measurements) from which planar contact tunneling experiments have been performed in the temperature range 12K-295K. The I-V plots of the prepared junctions have shown the expected nonlinearity observed previously at 77.0K. The dl/dV-V plots, on the other hand, show a clear depression at zero bias (attributed to the pseudogap) up to temperatures, Tc < T < 280K. This result agrees with the current understanding ofthe phenomenology of this pseudogap.

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Issue

1999: Proceedings of the 17th National Physics Congress of the Samahang Pisika ng Pilipinas

Article ID

SPP-1999-CM-04

Section

Condensed Matter Physics

Published

1999-10-22

How to Cite

[1]

L Guerra, M Reyes, A Manuel, R Sarmago, and A Salvador, Evidence of a normal-state pseudogap in bulk superconducting tunneling junctions of YBa2Cu3O7-δ, Proceedings of the Samahang Pisika ng Pilipinas 17, SPP-1999-CM-04 (1999). URL: https://proceedings.spp-online.org/article/view/SPP-1999-CM-04.