Low-temperature collective quantum effects in solid-state plasma

In this work, we develop a theoretical framework for dual length-scale quasiparticle excitations in solid-state electron–ion plasmas based on the quantum multistream model. Our analysis of elementary collective quantum excitations and the associated matter-wave energy dispersion reveals the emergence of an additional low-energy collective excitation band arising from the ion charge effect, in addition to the previously reported upper band of collective quantum excitations in interacting electron gases. The upper band is accessed at higher excitation energies and elevated electron temperatures. These lower and upper bands are separated by a characteristic energy gap that depends sensitively on the electron number density and the ion charge state. The appearance of the lower-energy band introduces fundamentally new features at low temperatures, providing a coherent-state collective quantum excitations well below the Fermi surface, where electrons are densely populated in the zero-temperature limit. Solutions of the state-function equations, subject to appropriate boundary conditions at sub-Fermi orbitals, reveal the existence of stable collective quasiparticle states that can be excited beneath the Fermi level of spin-coupled electron sea. The very-low-temperature quasiparticle excitations in current model are reminiscent of the collective quantum behavior encountered in superconducting and superfluid systems. Furthermore, analysis of the time evolution of the modified Wigner distribution function demonstrates the exceptional character of the sub-Fermi orbital, in which Landau damping is strongly suppressed. This study offers new insights into the low-temperature behavior of collective quantum electron excitations in solid-state plasmas and provides a novel theoretical avenue for exploring their thermodynamic and dynamical properties. In particular, it highlights the essential role of neutralizing ions in shaping the collective excitation spectrum and stabilizing low-energy quasiparticle states.