| 1. |
- Baggioli, Matteo, et al.
(författare)
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Collective modes of polarizable holographic media in magnetic fields
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2021:6
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Tidskriftsartikel (refereegranskat)abstract
- We consider a neutral holographic plasma with dynamical electromagnetic interactions in a finite external magnetic field. The Coulomb interactions are introduced via mixed boundary conditions for the Maxwell gauge field. The collective modes at finite wave-vector are analyzed in detail and compared to the magneto-hydrodynamics results valid only at small magnetic fields. Surprisingly, at large magnetic field, we observe the appearance of two plasmon-like modes whose corresponding effective plasma frequency grows with the magnetic field and is not supported by any background charge density. Finally, we identify a mode collision which allows us to study the radius of convergence of the linearized hydrodynamics expansion as a function of the external magnetic field. We find that the radius of convergence in momentum space, related to the diffusive transverse electromagnetic mode, increases quadratically with the strength of the magnetic field.
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| 2. |
- Baggioli, Matteo, et al.
(författare)
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Holographic plasmon relaxation with and without broken translations
- 2019
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Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :9
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Baggioli, Matteo, et al.
(författare)
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Transverse collective modes in interacting holographic plasmas
- 2020
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Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2020:4
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Tidskriftsartikel (refereegranskat)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-to-diffusion 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 quasi-particles, 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.
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| 4. |
- Gran, Ulf, 1973, et al.
(författare)
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Exotic holographic dispersion
- 2019
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Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2019:2
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Tidskriftsartikel (refereegranskat)abstract
- 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-Nordström 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.
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| 5. |
- Gran, Ulf, 1973, et al.
(författare)
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Holographic fundamental matter in multilayered media
- 2019
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Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2019:12
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Tidskriftsartikel (refereegranskat)abstract
- We describe a strongly coupled layered system in 3+1 dimensions by means of a top-down D-brane construction. Adjoint matter is encoded in a large-Nc stack of D3-branes, while fundamental matter is confined to (2 + 1)-dimensional defects introduced by a large-Nf stack of smeared D5-branes. To the anisotropic Lifshitz-like background geometry, we add a single flavor D7-brane treated in the probe limit. Such bulk setup corresponds to a partially quenched approximation for the dual field theory. The holographic model sheds light on the anisotropic physics induced by the layered structure, allowing one to disentangle flavor physics along and orthogonal to the layers as well as identifying distinct scaling laws for various dynamical quantities. We study the thermodynamics and the fluctuation spectrum with varying valence quark mass or baryon chemical potential. We also focus on the density wave propagation in both the hydrodynamic and collisionless regimes where analytic methods complement the numerics, while the latter provides the only resource to address the intermediate transition regime.
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| 6. |
- Gran, Ulf, 1973, et al.
(författare)
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Holographic plasmons
- 2018
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Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2018:11
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Gran, Ulf, 1973, et al.
(författare)
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Holographic response of electron clouds
- 2019
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Ingår i: Journal of High Energy Physics. - : SPRINGER. - 1029-8479 .- 1126-6708. ; 2019:3
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Gran, Ulf, 1973, et al.
(författare)
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Plasmons in holographic graphene
- 2020
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Ingår i: SciPost Physics. - : SCIPOST FOUNDATION. - 2542-4653. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how self-sourced collective modes - of which the plasmon is a prominent example due to its relevance in modern technological applications - are identified in strongly correlated systems described by holographic Maxwell theories. The characteristic ω ∝ pk plasmon dispersion for 2D materials, such as graphene, naturally emerges from this formalism. We also demonstrate this by constructing the first holographic model containing this feature. This provides new insight into modeling such systems from a holographic point of view, bottom-up and top-down alike. Beyond that, this method provides a general framework to compute the dynamical charge response of strange metals, which has recently become experimentally accessible due to the novel technique of momentum-resolved electron energy-loss spectroscopy (M-EELS). This framework therefore opens up the exciting possibility of testing holographic models for strange metals against actual experimental data.
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| 9. |
- Tornsö, Marcus, 1993
(författare)
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Holographic descriptions of collective modes in strongly correlated media
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solving the puzzle of high temperature superconductivity may be one of the most desired scientific breakthroughs of our time, as access to room temperature superconductivity could revolutionize society as we know it. In this thesis, we strive to increase the theoretical understanding of such matter, by studying the phase above, in temperature, the superconducting phase - the "strange metal". The strange metal phase is a phase characterized by the absence of a quasi-particle description. The electrons in this phase are strongly coupled, which means that conventional methods, such as perturbation theory in quantum field theory and Monte Carlo methods fall short of being able to describe their dynamics. Perhaps surprisingly, string theory provides a different method, capable of describing precisely such systems - the holographic duality. Whereas there has been significant effort devoted to the applications of the duality since its inception in 1997, and even more so in the last decade after it was observed that it worked remarkably well for condensed matter theory, it wasn't until our project that the dynamical polarization of such strongly coupled systems where properly treated. In this thesis, we introduce the minimal constraints required for a sensible description of a polarizing medium, and convert those to boundary conditions to the equations of motion provided by the holographic dual. These boundary conditions deviate from previous holographic studies, and we contrast the quasinormal modes previously studied with the emergent collective modes we find for some different models. We find novel results, as well as confirm the predictions of less general models in their respective regions of validity and pave the way for more complex future models.
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| 10. |
- Tornsö, Marcus, 1993
(författare)
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Plasma Oscillations in Holographic Quantum Matter
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we explore strongly correlated matter in the framework of holographic duality. Specifically, we examine the quasinormal modes of such systems, and we extend the current framework to efficiently and naturally cover plasmons and other collective modes that may be found within strongly correlated matter. The interest in strongly correlated matter is motivated by the presence of a “strange metal” phase both in high temperature superconductors and in near charge neutral graphene, both being materials of immense scientific interest. The strange metal phase is a phase characterized by the absence of quasi-particles. This implies that conventional methods, such as perturbation theory in quantum field theory and Monte Carlo methods fall short of being able to describe the dynamics. Perhaps surprisingly, string theory provides a novel method, capable of precisely describing such systems - the holographic duality. With the holographic duality, strongly coupled matter is mapped onto a weakly coupled gravity theory in one additional dimension, allowing for a conventional treatment of the dual system. In this thesis, we extend the existing framework to also describe polarizing media. This is explicitly done in the form of new boundary conditions on the holographic dual, which deviate from previous holographic studies, and we contrast the quasinormal modes previously studied with the emergent collective modes we find for some studied models. We find new results, as well as confirm the predictions of less general models in their respective regions of validity and pave the way for more complex future models.
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