Merging of single-particle levels in finite Fermi systems

TL;DR

This paper investigates how interactions in finite Fermi systems cause degenerate single-particle levels near the Fermi surface to merge, leading to the loss of well-defined excitations and impacting various physical systems.

Contribution

It uncovers a new phenomenon where level merging occurs, causing the disappearance of single-particle excitations in finite Fermi systems.

Findings

Interaction lifts degeneracy of levels near Fermi surface

Level merging results in disappearance of single-particle excitations

Implications for nuclear, solid-state, and atomic systems

Abstract

Properties of the distribution of single-particle levels adjacent to the Fermi surface in finite Fermi systems are studied, focusing on the case in which these levels are degenerate. The interaction of the quasiparticles occupying these levels lifts the degeneracy and affects the distance between the closest levels on opposite sides of the Fermi surface, as the number of particles in the system is varied. In addition to the familiar scenario of level crossing, a new phenomenon is uncovered, in which the merging of single-particle levels results in the disappearance of well-defined single-particle excitations. Implications of this finding are discussed for nuclear, solid-state, and atomic systems.