Quantum-well states at the surface of the heavy-fermion superconductor URu$_2$Si$_2$

TL;DR

This study demonstrates the formation of quantum-well states from strongly correlated electrons in a heavy-fermion superconductor, revealing new possibilities for quantum confinement in correlated materials.

Contribution

It provides the first evidence of quantum-well states formed by heavy fermions on a superconductor surface, expanding understanding of quantum confinement in correlated electron systems.

Findings

Observation of 2D heavy fermions with 17x effective mass

Quantized states separated by a fraction of a meV

Superconductivity induced at the surface from the bulk

Abstract

Electrons can form a two-dimensional electron gas at metal surfaces, where lateral confinement leads to quantum-well states. Such states have been observed for highly itinerant electrons, but it remains an open question whether quantum-well states can be formed from strongly correlated electrons. Here we study atomically flat terraces on surfaces of the heavy-fermion superconductor URu$_2$Si$_2$ using millikelvin scanning tunneling spectroscopy. We observe two-dimensional heavy fermions (2DHF) with an effective mass 17 times the free electron mass that form quantized states separated by a fraction of a meV. Superconductivity at the surface is induced by the bulk into the 2DHF. Our results provide a new route to realize quantum well states in correlated quantum materials.