# Unconventional full-gap superconductivity in Kondo lattice with semi-metallic conduction bands

## TL;DR

This paper proposes a novel mechanism for superconductivity in Kondo lattices with semi-metallic bands, involving entangled states of localized spins and conduction electrons, leading to unconventional full-gap superconductivity.

## Contribution

It introduces a new superconducting pairing mechanism based on composite three-body bound states in Kondo lattices with semi-metallic conduction bands.

## Key findings

- The order parameter involves a three-body bound state of spins, electrons, and holes.
- Superconductivity arises from induced pairing of conduction electrons, not directly from composite pairs.
- Potential relevance to heavy-electron materials is discussed.

## Abstract

A mechanism of superconductivity is proposed for the Kondo lattice which has semi-metallic conduction bands with electron and hole Fermi surfaces. At high temperatures, the $f$ electron's localized spins/pseudospins are fluctuating between electron and hole Fermi surfaces to seek for a partner to couple with. This system tries to resolve this frustration at low temperatures and chooses to construct a quantum mechanically entangled state composed of the Kondo singlet with electron surface and that with hole surface, to break the U(1) gauge symmetry. The corresponding order parameter is given by a composite pairing amplitude as a three-body bound states of localized spin/pseudospin, electron and hole. The electromagnetic response is considered, where composite pair itself does not contribute to the Meissner effect, but the induced pair between conduction electrons, which inevitably mixes due to e.g. a band cutoff effect at high energies, carries the superconducting current under the external field. Possible applications to real heavy-electron materials are also discussed.