Acoustic plasmons in a two-component Fermi system

Two-fluid hydrodynamic model for semiconductors

“…The appearance of an optical and an acoustic branch in systems with two different kinds of charge carriers has been observed before in random-phase-approximation models for infinite media [45,48,49]. Here we have found the formation of an optical and an acoustic mode in a two-fluid hydrodynamic model for an infinite medium, something that was briefly touched upon by Schaefer and von Baltz [47]. In Sec.…”

“…We will restrict ourselves to include only two different types of charge carriers, e.g., electrons and holes or heavy and light holes, and call the model the hydrodynamic two-fluid model (as opposed to the HDM which contains only one hydrodynamic fluid). Other models that include multiple charge carriers already exist in the form of transport equations [43,44], and quantum-mechanical and semiclassical theories [45][46][47][48][49][50]. And while Ref.…”

“…And while Ref. [47] briefly considers the hydrodynamic model for a two-fluid system, we will here present a more detailed analysis of the optical properties as well as consider finite systems. Our extension of a single fluid (appropriate for majority-carrier systems) to a two-fluid description shows interesting phenomena beyond the independent-fluids approximation that constitute an integral part of the local-response electrodynamics of doped semiconductors, i.e., the mere addition of electron and hole conductivities [44].…”

Power law singularities inn-vector models

“…If we assume the corrections to scaling proposed by the standard theory, then the asymptotic exponent λ can be quite well evaluated by fitting these smallest-h data as functions of k. Recall that these corrections are represented by an expansion in powers of k 4−d and k d−2 [18,19], corresponding to the expansion λ eff (k) = λ + j≥1 a j k j in three dimensions. Accordingly, we have plotted λ eff (k) vs k in Fig.…”

“…Moreover, a qualitative analysis is performed here [16] without cutting the perturbation series. More recently, this approach has been generalized [17] to study the ϕ 4 model below the critical temperature, where the so called Goldstone mode singularity (see, e. g., [18,19,20,21,22,23,24]) is observed. It refers to certain models, further called n-vector models, in which the order parameter is an n-component vector with n > 1.…”