Two energy gaps observed in tunneling measurements on hole-doped cuprates: pairing gap and coherent gap

TL;DR

This paper explains the discrepancy in energy-gap measurements in 90 K hole-doped cuprates by identifying two distinct gaps—pairing and coherent—and analyzing how structural and measurement direction factors influence which gap is observed.

Contribution

It reveals that tunneling measurements detect either the pairing or the coherent gap depending on the cuprate's structure and measurement direction, clarifying previous inconsistencies.

Findings

Tunneling detects two different gaps: pairing and coherent.

Structural factors determine which gap is observed in measurements.

Measurement direction influences the observed energy gap.

Abstract

There is a clear discrepancy among the energy-gap values for different 90 K cuprates, inferred from tunneling measurements. By using the phase diagram for hole-doped cuprates we show that tunneling measurements performed on 90 K cuprates, simply, detect two different energy gaps: the pairing gap and the coherent gap, which are identical in conventional superconductors. We find that there are two reasons why tunneling measurements show in one cuprate exclusively the coherent gap while, in another cuprate, they show the pairing gap: (i) the number of CuO2 planes per unit cell in the cuprate, and (ii) the directionality of the tunneling current (along c-axis or ab-plane).