# Normal State Gap in Parent Cuprate Pr2CuO4+/-{\delta}

## TL;DR

This study investigates the normal state gap in parent cuprate Pr2CuO4+/-{eta} using tunneling spectroscopy, revealing its robustness against magnetic fields and its enhancement with disorder, explained by electron-electron interactions.

## Contribution

It provides the first detailed tunneling analysis of the normal state gap in parent cuprates and links it to disorder-induced electron-electron interactions based on AAL theory.

## Key findings

- Normal state gap observed in Ce-free Pr2CuO4+/-{eta} samples.
- Gap magnitude increases with junction resistance and disorder.
- Gap remains robust under magnetic fields up to 16 T.

## Abstract

We present a tunneling study on single crystalline parent cuprate thin films, i.e. a series of Pr2CuO4+/-{\delta}(PCO) with tunable superconducting transition temperature. The zero-bias anomaly of differential conductance, well reported in the normal state of R2-xCexCuO4 (R = Pr, Nd, La) and named as normal state gap (NSG), is observed in the Ce-free samples. This NSG behaves quite robust against the magnetic field up to 16 T, but fades away with increasing the temperature. Most importantly, we find that the magnitude of the NSG becomes larger with increasing point-contact junction resistance on the superconducting films, which is further enhanced in the non-superconducting samples of more oxygen disorders. The origination of NSG can be understood in the framework of Altshuler-Aronov-Lee (AAL) theory, where the disorder-induced electron-electron interactions suppress the density of states and thereby result in a soft Coulomb gap.