Microscopic theory of electron quadrupling condensates

TL;DR

This paper develops a microscopic theory for electron quadrupling condensates, a novel four-electron state beyond traditional superconductivity, and analyzes their properties in specific models.

Contribution

It introduces a general microscopic framework for four-fermion composite states and applies it to a model exhibiting time-reversal symmetry-breaking quadrupling order.

Findings

Derived and solved a fermionic model in 2D and 3D

Estimated specific heat and density of states for the quadrupling state

Identified conditions for emergence of electron quadrupling order

Abstract

Electron pairing at low temperatures leads to superconductivity. A fundamental question is whether more complex states - characterized by order in four-electron composite objects, termed electron quadrupling or composite order - can exist in materials, and if so, under what conditions they emerge and what properties they exhibit. These states lie beyond the scope of Bardeen-Cooper-Schrieffer theory, and a microscopic description of them remained elusive. In the first part of the paper, we provide a general microscopic framework to describe these and the other four-fermion composite states. In the second part of the paper, we derive and solve a specific fermionic model in two and three dimensions that hosts time-reversal symmetry-breaking electron quadrupling order. The fermionic microscopic theory is used to estimate the specific heat and electron density of states.