Dimensionality tuning of heavy-fermion states in ultrathin CeSi2 films

TL;DR

This study investigates how reducing the thickness of CeSi2 films affects their heavy-fermion electronic states, revealing a suppression of crystal electric field excitations and a decrease in the magnetic resistivity maximum temperature, highlighting quantum confinement effects.

Contribution

It provides the first direct experimental evidence of dimensionality effects on heavy-fermion states in ultrathin CeSi2 films using combined spectroscopic and transport measurements.

Findings

Suppression of crystal electric field satellites in ultrathin films

Reduction of the magnetic resistivity maximum temperature from 100 K to 35 K

Persistence of the Kondo peak at the Fermi level in ultrathin films

Abstract

Dimensionality tuning is an important method to modify the electronic states of quantum materials. However, the mechanism of such tuning in heavy fermion systems and its connection with transport properties remain largely unexplored. Here by combining molecular beam epitaxy (MBE), in-situ angle-resolved photoemission spectroscopy (ARPES) and transport measurements, we study the electronic states of the heavy-fermion compound CeSi2 as a function of film thickness. In three dimensional thick films, our measurements reveal a dispersive Kondo peak at the Fermi level (EF) and satellite peaks originating from crystal electric field (CEF) excitations, characteristic of heavy fermion systems. For two-dimensional ultrathin films, the CEF satellites are largely suppressed while the ground-state Kondo peak at EF remains strong, although it develops at lower temperatures. Simultaneously, the maximum temperature Tmax of the magnetic resistivity, \r{ho}m(T), changes from ~100 K in thick films to ~35 K in ultrathin films. This can be attributed to the dimensionality driven reduction of CEF excitations during the Kondo process, in good agreement with spectroscopic results. Our work provides direct insight to understand the quantum confinement effects on strongly correlated 4f-electron systems and opens up new opportunities to explore emergent phenomena in two-dimensional heavy-fermion materials.