High temperature surface state in Kondo insulator U$_3$Bi$_4$Ni$_3$

TL;DR

This study reports the discovery of a high-temperature surface state in the Kondo insulator U$_3$Bi$_4$Ni$_3$, which emerges above 250 K and dominates low-temperature transport, offering new insights into surface states in correlated materials.

Contribution

It introduces U$_3$Bi$_4$Ni$_3$ as a new Kondo insulator with a high-temperature surface state, expanding understanding beyond SmB$_6$ and YbB$_{12}$.

Findings

Surface state emerges below 250 K.

Surface conductivity exceeds bulk by tenfold at low temperatures.

Surface state is robust and inherently protected.

Abstract

The resurgence of interest in Kondo insulators has been driven by two major mysteries: the presence of metallic surface states and the observation of quantum oscillations. To further explore these mysteries, it is crucial to investigate another similar system beyond the two existing ones, SmB$_6$ and YbB$_{12}$. Here, we address this by reporting on a Kondo insulator, U$_3$Bi$_4$Ni$_3$. Our transport measurements reveal that a surface state emerges below 250 K and dominates transport properties below 150 K, which is well above the temperature scale of SmB$_6$ and YbB$_{12}$. At low temperatures, the surface conductivity is about one order of magnitude higher than the bulk. The robustness of the surface state indicates that it is inherently protected. The similarities and differences between U$_3$Bi$_4$Ni$_3$ and the other two Kondo insulators will provide valuable insights into the nature of metallic surface states in Kondo insulators and their interplay with strong electron correlations.