Evidence for Multimodal Superfluidity of Neutrons

TL;DR

This paper provides theoretical and experimental evidence for a novel multimodal superfluid phase in neutron-rich systems, characterized by coexisting s-wave, p-wave, and quartet condensates, with implications for nuclear physics and neutron star crusts.

Contribution

It introduces the concept of multimodal superfluidity in fermionic systems with attractive interactions, supported by ab initio calculations and experimental data analysis.

Findings

Identification of coexisting s-wave, p-wave, and quartet condensates in neutron systems

Evidence of superfluid gaps in atomic nuclei consistent with multimodal superfluidity

Implications for neutron star crust structure and dynamics

Abstract

We present theoretical and experimental evidence for a new phase of matter in neutron-rich systems that we call multimodal superfluidity. Using ab initio lattice calculations, we show that the condensate consists of coexisting s-wave pairs, p-wave pairs in entangled double pair combinations, and quartets composed of bound states of two s-wave pairs. We identify multimodal superfluidity as a general feature of single-flavor spin-1/2 fermionic systems with attractive s-wave and p-wave interactions, provided the system is stable against collapse into a dense droplet. Beyond neutrons at sub-saturation densities, we demonstrate that this phase appears in generalized attractive extended Hubbard models in one, two, and three dimensions. We elucidate the mechanism for this coexistence using self-consistent few-body Cooper models and compare with Bardeen-Cooper-Schrieffer theory. We also derive the form of the effective action and show that spin, rotational, and parity symmetries remain unbroken. Finally, we analyze experimental data to show that p-wave pair gaps and quartet gaps are present in atomic nuclei, and we discuss the consequences of this new phase for the structure and dynamics of neutron star crusts.