# Anomalous electron transport in epitaxial NdNiO$_3$ films

## TL;DR

This study investigates the electronic transport properties of epitaxial NdNiO$_3$ films, revealing partial Fermi surface gapping, strain-dependent Hall effects, and non-Fermi liquid behavior, which collectively resemble phenomena in high-temperature cuprate superconductors.

## Contribution

It provides new insights into the decoupled electronic and magnetic transitions in NdNiO$_3$ films and uncovers unconventional transport behaviors linked to strain and phase changes.

## Key findings

- Partial Fermi surface gapping at MIT
- Hall coefficient reduction and sign reversal under strain
- Non-Fermi liquid resistivity behavior with temperature exponent 1

## Abstract

The origin of simultaneous electronic, structural and magnetic transitions in bulk rare-earth nickelates ($RE$NiO$_3$) remains puzzling with multiple conflicting reports on the nature of these entangled phase transitions. Heterostructure engineering of these materials offers unique opportunity to decouple metal-insulator transition (MIT) from the magnetic transition. However, the evolution of underlying electronic properties across these decoupled transitions remains largely unexplored. In order to address this, we have measured Hall effect on a series of epitaxial NdNiO$_3$ films, spanning a variety of electronic and magnetic phases. We find that the MIT results in only partially gapped Fermi surface, whereas full insulating phase forms below the magnetic transition. In addition, we also find a systematic reduction of the Hall coefficient ($R_H$) in the metallic phase of these films with epitaxial strain and also a surprising transition to negative value at large compressive strain. Partially gapped weakly insulating, paramagnetic phase is reminiscence of pseudogap behavior of high $T_c$ cuprates. The precursor metallic phase, which undergoes transition to insulating phase is a non-Fermi liquid with the temperature exponent ($n$) of resistivity of 1, whereas the exponent increases to 4/3 in the non-insulating samples. Such nickelate phase diagram with sign-reversal of $R_H$, pseudo-gap phase and non Fermi liquid behavior are intriguingly similar to high $T_c$ cuprates, giving important guideline to engineer unconventional superconductivity in oxide heterostructure.