We study the dynamics and the relaxation of bulk plasmons in strongly coupled and quantum critical systems using the holographic framework. We analyze the dispersion relation of the plasmonic modes in detail for an illustrative class of holographic bottom-up models. Comparing to a simple hydrodynamic formula, we entangle the complicated interplay between the three least damped modes and shed light on the underlying physical processes. Such as the dependence of the plasma frequency and the effective relaxation time in terms of the electromagnetic coupling, the charge and the temperature of the system. Introducing momentum dissipation, we then identify its additional contribution to the damping. Finally, we consider the spontaneous symmetry breaking (SSB) of translational invariance. Upon dialing the strength of the SSB, we observe an increase of the longitudinal sound speed controlled by the elastic moduli and a decrease in the plasma frequency of the gapped plasmon. We comment on the condensed matter interpretation of this mechanism.

Stockholm University, Nordic Institute for Theoretical Physics (Nordita).

Exotic holographic dispersion2019In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, article id 032Article in journal (Refereed)

Abstract [en]

For strongly interacting systems, where perturbation theory is not applicable, holographic duality is a powerful framework for computing e.g. dispersion relations. Using the standard Reissner-Nordstrom black hole as a holographic model for a (strange) metal, we obtain exotic dispersion relations for both plasmon modes and quasinormal modes for certain intermediate values of the charge of the black hole.The obtained dispersion relations show dissipative behavior which we compare to the generic expectations from the Caldeira-Leggett model for quantum dissipation. Based on these considerations, we investigate how holography can predict higher order corrections for strongly coupled physics.

Stockholm University, Nordic Institute for Theoretical Physics (Nordita).

Holographic plasmons2018In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 11, article id 176Article in journal (Refereed)

Abstract [en]

Since holography yields exact results, even in situations where perturbation theory is not applicable, it is an ideal framework for modeling strongly correlated systems. We extend previous holographic methods to take the dynamical charge response into account and use this to perform the first holographic computation of the dispersion relation for plasmons. As the dynamical charge response of strange metals can be measured using the new technique of momentum-resolved electron energy-loss spectroscopy (M-EELS), plasmon properties are the next milestone in verifying predictions from holographic models of new states of matter.

Stockholm University, Nordic Institute for Theoretical Physics (Nordita).

Holographic response of electron clouds2019In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, article id 019Article in journal (Refereed)

Abstract [en]

In order to make progress towards more realistic models of holographic fermion physics, we use gauge/gravity duality to compute the dispersion relations for quasinormal modes and collective modes for the electron cloud background, i.e. the non-zero temperature version of the electron star. The results are compared to the corresponding results for the Schwarzschild and Reissner-Nordstrom black hole backgrounds, and the qualitative differences are highlighted and discussed.

Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Frankfurt Institute for Advanced Studies, Germany.

Zingg, Tobias

Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Helsinki, Finland.

Analog models for holographic transport2019In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 100, no 5, article id 056015Article in journal (Refereed)

Abstract [en]

The gauge-gravity duality and analog gravity both relate a condensed matter system to a gravitational theory. This makes it possible to use gravity as an intermediary to establish a relation between two different condensed matter systems: the strongly coupled system from the gauge-gravity duality and the weakly coupled gravitational analog. We here offer some examples for relations between observables in the two different condensed matter systems. In particular, we show how the equations characterizing Green functions and fast order transport coefficients in holographic models can be mapped to those describing phenomena in an analog gravitational system, which allows, in principle, to obtain the former by measuring the latter.

Analogue gravity is based on a mathematical identity between quantum field theory in curved space-time and the propagation of perturbations in certain condensed matter systems. But not every curved space-time can be simulated in such a way. For analogue gravity to work, one needs not only a condensed matter system that generates the desired metric tensor, but this system then also has to obey its own equations of motion. However, the relation to the metric tensor usually overdetermines the equations of the underlying condensed matter system, such that they in general cannot be fulfilled. In this case the desired metric does not have an analogue. Here, we show that the class of metrics that have an analogue is larger than previously thought. The reason is that the analogue metric is only defined up to a choice of parametrization of the perturbation in the underlying condensed matter system. In this way, the class of analogue gravity models can be vastly expanded.

Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Iceland, Iceland.

We present a holographic perspective on magnetic oscillations in strongly correlated electron systems via a fluid of charged spin 1/2 particles outside a black brane in an asymptotically anti-de-Sitter spacetime. The resulting backreaction on the spacetime geometry and bulk gauge field gives rise to magnetic oscillations in the dual field theory, which can be directly studied without introducing probe fermions, and which differ from those predicted by Fermi liquid theory.