Second roton feature in the strongly coupled electron liquid.

Area of Science:

• Condensed matter physics
• Quantum many-body systems
• Computational physics

Background:

• The uniform electron gas (UEG) is a fundamental model in condensed matter physics.
• Understanding its dynamic properties is crucial for describing various materials.
• Previous studies identified a roton-type feature in the UEG's dynamic response.

Purpose of the Study:

• To present extensive ab initio path integral Monte Carlo (PIMC) results for the dynamic properties of the finite temperature UEG.
• To rigorously assess the density and temperature dependence of the roton-type feature.
• To investigate the emergence of new dynamic features and their implications.

Main Methods:

• Extensive ab initio path integral Monte Carlo (PIMC) simulations.
• Direct analysis of the imaginary-time density-density correlation function (ITCF).
• Analytic continuation of PIMC results to compute the dynamic structure factor.

Main Results:

• Detailed dynamic properties of the UEG across a wide density range (2 ≤ rs ≤ 300).
• Confirmation and detailed characterization of the roton-type feature's density and temperature dependence.
• Resolution of a second roton feature at the second harmonic for rs ≳ 100, identified as incipient phonon dispersion.
• Substantiation of the second roton in the strongly coupled electron liquid via dynamic structure factor calculations.

Conclusions:

• The study elucidates the complex interplay between quantum delocalization and Coulomb coupling in the UEG.
• The identified second roton provides new insights into the collective excitations of the electron gas.
• Freely available PIMC data serve as valuable benchmarks for theoretical methodologies.