Casimir force screening by a quantum Boltzmann plasma

We develop a finite-temperature field-theoretical description of the Casimir interaction between two perfectly conducting boundaries with the intervening gap filled by a two-component quantum Boltzmann plasma embedded in a homogeneous dielectric background. The quantum motion of the charged particles is represented by imaginary-time worldlines, while the electromagnetic field is treated in the Gaussian approximation. The resulting partition function contains distinct longitudinal and transverse response contributions and an additional quantum-induced source term with no classical counterpart. In the classical limit, the theory reduces to the usual Casimir-screening picture: the static longitudinal mode is Debye screened, whereas the transverse electromagnetic sector is unaffected by classical mobile charges. Finite thermal de Broglie wavelengths modify the nonzero Matsubara response and produce the leading quantum correction to the force. In the static long-wavelength limit, the longitudinal dielectric function has, through the leading quantum correction, the same expansion structure as the Lindhard response of a degenerate electron gas under the correspondence kTF ↔ κD and kF↔λdB−1. In contrast, the static transverse response reproduces the leading high-temperature Landau orbital diamagnetic susceptibility. We investigate the crossover between classical and quantum plasma behavior in a regime where these corrections become appreciable while the plasma remains approximately nondegenerate and can still be treated, at leading order, within Maxwell–Boltzmann statistics. We illustrate this crossover for a weakly coupled electron–proton plasma and an effective Li+–solvated-electron plasma in liquid ammonia. The latter yields a sub-percent quantum correction to the force gradient for the parameters considered.