Superconducting Kondo phase in an orbitally-separated bilayer

TL;DR

This paper explores how adding a metallic layer to a Kondo lattice can induce a superconducting state with unconventional pairing, highlighting the role of proximity effects in heavy-fermion superconductivity.

Contribution

It demonstrates that proximity effects in a bilayer Kondo lattice induce a superconducting phase with unconventional pairing involving f-electrons, a novel mechanism in heavy-fermion systems.

Findings

Adding a metallic layer destroys the Kondo insulator, leading to a metallic state.

Superconductivity emerges due to proximity effects, with unconventional pairing involving f-electrons.

Critical temperature decreases with interlayer hybridization, following BCS-like behavior.

Abstract

The nature of superconductivity in heavy-fermion materials is a subject under intense debate, and controlling this many-body state is central for its eventual understanding. Here, we examine how proximity effects may change this phenomenon, by investigating the effects of an additional metallic layer on the top of a Kondo-lattice, and allowing for pairing in the former. We analyze a bilayer Kondo Lattice Model with an on-site Hubbard interaction, $-U$, on the additional layer, using a mean-field approach. For $U=0$, we notice a drastic change in the density-of-states due to multiple-orbital singlet resonating combinations. It destroys the well-known Kondo insulator at half filling, leading to a metallic ground state, which, in turn, enhances antiferromagnetism through the polarization of the conduction electrons. For $U\neq 0$, a superconducting Kondo state sets in at zero temperature, with the occurrence of unconventional pairing amplitudes involving $f$-electrons. We establish that this remarkable feature is only possible due to the proximity effects of the additional layer. At finite temperatures we find that the critical superconducting temperature, $T_c$, decreases with the interlayer hybridization. We have also established that a zero temperature superconducting amplitude tracks $T_c$, which reminisces the BCS proportionality between the superconducting gap and $T_c$.