Point-contact spectroscopy on URu$_2$Si$_2$

TL;DR

This study uses point-contact spectroscopy on URu$_2$Si$_2$ to observe a resonance at the Fermi level that splits across the hidden order transition, revealing insights into the electronic states and order parameter.

Contribution

First direct spectroscopic evidence of Fermi level resonance splitting associated with the hidden order transition in URu$_2$Si$_2$ using point-contact techniques.

Findings

Resonance at the Fermi level develops around 60 K.

Resonance splits and becomes asymmetric below 17.5 K.

Comparison with UAu$_2$Si$_2$ highlights material-specific behaviors.

Abstract

Tunnel and point contact experiments have been made in a URu$_2$Si$_2$ single crystal along the c-axis. The experiments were performed changing temperature and contact size in a low temperature scanning tunneling microscope. A resonance develops at the Fermi level at $T\sim 60$ K. This resonance splits and becomes asymmetric when the 17.5 K phase transition is crossed. These results are consistent with the existence of Kondo like bound states of the U$^{4+}$ ionic configurations and the conduction electrons. Below the transition, these configurations are split by the development of quadrupolar ordering. The peak separation can be interpreted as a direct measurement of the order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also reported, with a comparative study of the behavior of both materials.