Transverse collective modes in interacting holographic plasmas

Abstract

We study in detail the transverse collective modes of simple holographic models in presence of electromagnetic Coulomb interactions. We render the Maxwell gauge field dynamical via mixed boundary conditions, corresponding to a double trace deformation in the boundary field theory. We consider three different situations: (i) a holographic plasma with conserved momentum, (ii) a holographic (dirty) plasma with finite momentum relaxation and (iii) a holographic viscoelastic plasma with propagating transverse phonons. We observe two interesting new features induced by the Coulomb interactions: a mode repulsion between the shear mode and the photon mode at finite momentum relaxation, and a propagation-todiffusion crossover of the transverse collective modes induced by the finite electromagnetic interactions. Finally, at large charge density, our results are in agreement with the transverse collective mode spectrum of a charged Fermi liquid for strong interaction between quasiparticles, but with an important difference: the gapped photon mode is damped even at zero momentum. This property, usually referred to as anomalous attenuation, is produced by the interaction with a quantum critical continuum of states and might be experimentally observable in strongly correlated materials close to quantum criticality, e.g. in strange metals.

Magnetophonons & type-B Goldstones from hydrodynamics to holography

“…This decoupling at larger momenta is typical of interacting modes, and appears also in the context of plasmons, induced by Coulomb interactions (see [110,111] for the same effect in holography systems with Coulomb interactions). We confirm these predictions in figure 14, in which we see both the modes approaching the decoupled phonon dispersion relations as discussed in section 4.…”

“…The presence of a particlehole continuum in the holographic model -the so called incoherent sector -can be a possible mechanism behind the ∼ k 2 imaginary term observed. 9 The continuum is not taken into account in the EFT description and it is known to have already important consequences in other situations, such as Fermi liquid theory [107] and holographic models [108][109][110]. We examine the behavior of the coefficients A, B appearing in the dispersion relations in eq.…”

Field theory of dissipative systems with gapped momentum states

“…Despite the action being typically non-Hermitian (i.e., containing a finite but positive imaginary part, ImðS eff Þ > 0), a unitary evolution is ensured by the KMS constraint [7]. In the regime where dissipation is slow, τ=T ≫ 1, an interesting phenomenological formalism (not derived from an action formalism) known as quasihydrodynamics [79] has been proposed and verified explicitly in several holographic constructions [17][18][19][20].…”

“…Another approach relies on holographic techniques [14], where dissipation is encoded into the black hole horizon dynamics. These methods have been very fruitful in describing strongly coupled dissipative fluids [15][16][17][18][19][20]. However, the nature of the dual field theory is not easily accessible and is often obscure.…”

Propagation of shear stress in strongly interacting metallic Fermi liquids enhances transmission of terahertz radiation

“…A first product of this coupling is the usual “light-like” transversally polarized plasmon–polariton, which is universal: indeed, at both transverse and longitudinal “plasmons” precisely match. However, its partner is the phonon-like “shear-polariton”: this mode continues to be massless, but it acquires a quadratic dispersion at small momenta 5 , 6 (a similar mechanism occurs in a particular viscoelastic-like holographic strange metal, see reference 25 ). The shear mode of the heavy-mass Fermi liquid shares an analogous fate, see Fig.…”