Breakdown of Fermi degeneracy in the simplest liquid metal

TL;DR

This study observes the breakdown of electron degeneracy in metallic deuterium, revealing a transition from quantum to classical behavior at high temperatures, with implications for astrophysics and plasma physics.

Contribution

It provides the first experimental evidence of Fermi degeneracy breakdown in a simple liquid metal, extending quantum statistical models to new regimes.

Findings

Optical reflectance saturation consistent with Mott limit

Reflectance increase indicating Fermi surface breakdown at T > 0.4 TF

Collisional time behavior matches classical plasma predictions

Abstract

We are reporting the observation of the breakdown of electrons degeneracy and emergence of classical statistics in the simplest element: metallic deuterium. We have studied the optical reflectance, shock velocity and temperature of dynamically compressed liquid deuterium up to its Fermi temperature, TF. Above the insulator-metal transition, the optical reflectance shows the distinctive temperature-independent resistivity saturation, which is prescribed by Mott minimum metallic limit, in agreement with previous experiments. At T > 0.4 TF, however, the reflectance of metallic deuterium starts to rise with a temperature-dependent slope, consistent with the breakdown of the Fermi surface. The experimentally inferred collisional time in this region exhibits the characteristic temperature dependence expected for classical Landau-Spitzer plasma. Our observation of electron degeneracy lifting extends studies of degeneracy to new fermionic species, electron Fermi systems and offers an invaluable benchmark for quantum statistical models of Coulomb systems over a wide range of temperatures relevant to dense astrophysical objects and ignition physics.