| 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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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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| 3. |
- Benjaminsson, Daniel, et al.
(författare)
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Advanced study techniques for university students
- 2023
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Ingår i: Proceedings Chalmers Conference on Teaching and Learning 2023. - 9789188041548 ; , s. 61-67
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Konferensbidrag (refereegranskat)abstract
- The students starting at the Engineering Physics and Engineering Mathematics educations at Chalmers face challenges in terms of greatly increased workload and complexity of the subject matter compared to their previous education. Based on the experiences from teaching an introductory course in mechanics for nearly ten years (Ulf), the lack of efficient study techniques for a large number of students was identified. We have this year therefore offered the students a course in advanced study techniques (Daniel) tailored for university students, and also for their specific educations. We will here briefly describe the contents of the course and the preliminary impact on student learning.
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| 4. |
- 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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| 5. |
- Gran, Ulf, 1973, et al.
(författare)
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Shear viscosity in interacting two-dimensional Fermi liquids
- 2023
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Ingår i: arXiv:2312.09977.
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Tidskriftsartikel (refereegranskat)abstract
- In interaction-dominated two-dimensional electron gases at intermediate temperatures, electron transport is not diffusive as in the conventional Drude picture but instead hydrodynamic. The relevant transport coefficient in this regime is the shear viscosity. Here, we develop a numerically exact basis expansion to solve the Fermi liquid equation, and apply it to compute the shear viscosity of the electron gas with screened Coulomb interactions. Our calculations are valid at all temperatures and in particular describe the response beyond the asymptotic low-temperature limit, where perturbative approaches exist. We show that even in this low-temperature limit, there is a nonanalytic exchange contribution to the shear viscosity, highlighting the need for a full nonperturbative solution of the Fermi liquid equation. We hope that the techniques developed in this work will serve as a platform to determine the response of interacting Fermi liquids.
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| 6. |
- Hofmann, Johannes, 1988, et al.
(författare)
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Anomalously long lifetimes in two-dimensional Fermi liquids
- 2023
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 108:12
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Tidskriftsartikel (refereegranskat)abstract
- A precise characterization of the recently discovered crossover to hydrodynamic transport in electron liquids, and in particular of a conjectured exotic odd-parity transport regime, requires a full solution of the Fermi-liquid collision integral at all temperatures beyond state-of-the-art analytic leading-logarithmic approximations. We develop a general basis expansion of the linearized collision integral applicable at all temperatures, and employ this to determine the decay rates of Fermi surface perturbations in two-dimensional electron liquids. In particular, we provide exhaustive data on the decay rates for a new odd-parity regime, in which parity-even Fermi surface deformations decay rapidly but odd-parity modes are anomalously longlived. We find that this transport regime exists at fairly large temperatures T≲0.1TF, putting this regime within the reach of current experiments.
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| 7. |
- Wahlberg, Eric, 1992, et al.
(författare)
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Restored strange metal phase through suppression of charge density waves in underdoped YBa2Cu3O7–δ
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 373:6562, s. 1506-1510
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Tidskriftsartikel (refereegranskat)abstract
- The normal state of optimally doped cuprates is dominated by the “strange metal” phase that shows a linear temperature (T) dependence of the resistivity persisting down to the lowest T. For underdoped cuprates, this behavior is lost below the pseudogap temperature T*, where charge density waves (CDWs), together with other intertwined local orders, characterize the ground state. We found that the T-linear resistivity of highly strained, ultrathin, underdoped YBa2Cu3O7–δ films is restored when the CDW amplitude, detected by resonant inelastic x-ray scattering, is suppressed. This observation suggests an intimate connection between the onset of CDWs and the departure from T-linear resistivity in underdoped cuprates. Our results illustrate the potential of using strain control to manipulate the ground state of quantum materials.
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