The antiferromagnetic transition of UPd2Al3 break-junctions: A new realization of N-shaped current-voltage characteristics

TL;DR

This study investigates UPd2Al3 break junctions at very low temperatures, revealing antiferromagnetic and superconducting transitions, hysteretic I(V) characteristics, and N-shaped current-voltage behavior akin to tunnel diodes.

Contribution

It demonstrates that UPd2Al3 break junctions exhibit N-shaped I(V) characteristics with negative differential resistance, modeled as thermal constrictions, providing new insights into heavy-fermion junction behavior.

Findings

Observed antiferromagnetic and superconducting transitions in junctions.

Hysteretic I(V) curves can be modeled thermally.

Junctions show N-shaped I(V) with negative differential resistance.

Abstract

We have investigated metallic break junctions of the heavy-fermion compound UPd2Al3 at low temperatures between 0.1K and 9K and in magnetic fields up to 8T. Both the current-voltage I(V) characteristics and the dV/dI (V) spectra clearly showed the superconducting ($T_{\rm c}\simeq$ 1.8K) as well as the antiferromagnetic ($T_{\rm N}\simeq$14K) transition at low temperatures when the bias voltage is raised. The junctions with lateral size of order 200nm had huge critical current densities around $5\times 10^{10} A/m^2 at the antiferromagnetic transition and hysteretic I(V) characteristics. Degrading the quality of the contacts by in situ increasing the local residual resistivity reduced the hysteresis. We show that those hysteretic I(V) curves can be reproduced theoretically by assuming the constriction to be in the thermal regime. It turns out that these point contacts represent non-linear devices with N-shaped I(V) characteristics that have a negative differential resistance like an Esaki tunnel diode.