Talks

Cavity-mediated electron interactions and Mott polaritons in quantum materials

Recent years have witnessed the development of a new generation of nanoplasmonic cavities, which can reach the ultrastrong coupling regime with cyclotron transitions in two-dimensional electron gases. First experiments demonstrate cavity-induced changes to quasiparticle lifetimes [1] or even an astonishing enhancement of critical temperatures in superconductors by 50% [2]. This has created considerable interest in the possibility of manipulating electronic ground states and shaping collective excitations in two-dimensional materials with cavities, e.g. [3-8]. In my talk, I will provide an overview of current ideas and challenges in this emerging field. I will then discuss our proposal of inducing electronic interactions through the coupling to a cavity [3]. Such interactions, mediated by the transverse electromagnetic field, are restricted to unobservably low temperatures in free space. I will argue that the strong confinement in nanoplasmonic cavities could enhance these exotic effects to experimentally accessible temperatures. Furthermore, at the hand of the 1D Fermi-Hubbard model, I will describe how the strong coupling to a cavity can affect the ground and excited states of correlated electron materials [4, 5]. [1] G. L. Paravicini-Bagliani et al., Nature Phys. 15, 186 (2019). [2] A. Thomas et al., arXiv: 1911.01459. [3] F. Schlawin, A. Cavalleri and D. Jaksch, Phys. Rev. Lett. 122, 133602 (2019). [4] M. Kiffner, J. R. Coulthard, F. Schlawin, A. Ardavan and D. Jaksch, Phys. Rev. B 99, 085116 (2019). [5] M. Kiffner, J. R. Coulthard, F. Schlawin, A. Ardavan and D. Jaksch, New J. Phys. (2019). [6] G. Mazza and A. Georges, Phys. Rev. Lett. 122, 017401 (2019). [7] J. B. Curtis, Z. M. Raines, A. A. Allocca, M. Hafezi and V. M. Galitski, Phys. Rev. Lett. 122, 167002 (2019). [8] M. A. Sentef, M. Ruggenthaler and A. Rubio, Science Adv. 4, eaau6969 (2018).

Paradoxical crossovers in fractional diffusing diffusivity

Quantum Dynamic

Intermittency in a high-dimensional model of evolutionary ecology

According to the Neutral Theories of biodiversity in Ecology, the dynamics of the origin of the species is essentially stochastic. But this hypothesis does not address the stability of the process. In this regard, the theory of Punctuated Equilibria postulates that once a species appears it is stable, and undergoes no important mutations in a long evolutionary time, until some sufficiently relevant evolutionary event such as a catastrophe, occurs. The model known as Tangled Nature model is a model of biodiversity that takes the underlying assumptions of the aforementioned theories into account. By means of stochastic evolution laws, this model originates time series with periods of stable behavior interrupted by random events similar to catastrophes, that are reminiscent of Punctuated Equilibria. In our work, we performed a mean field approximation of the model to reduce it from $2^{L}$ dimensions to only one dimension. With this mean field map, it is shown that the observed stable behavior interrupted by chaotic bursts is actually due to the underlying dynamical phenomenon known as type-I intermittency.

Absence of Diffusion on the Edge

The edge of a FQH droplet supports gapless excitations that are protected by a U(1) anomaly. At small but finite temperature, diffusive spreading is expected to occur around the chiral ballistic front. I will show that this chiral diffusive fixed point is never stable. Hydrodynamic long-time tails give large corrections to dissipative transport on the edge, leading to a breakdown of diffusion and driving the edge to a dissipative fixed point in the KPZ universality class. Translation invariance is not assumed. This rather simple setup presents several striking features: (i) a hydrodynamic theory describes a condensed matter system, but the long lived collective excitation is not momentum, and (ii) a quantum anomaly has dramatic consequences, leading to (iii) large hydrodynamic long-time tails.

Topological waves, from condensed matter to the atmosphere

Uni-directionnal boundary modes are the hallmark of Chern insulators. Such topological states have been engineered in various platforms, from condensed matter to artificial crystals e.g. in photonics, acoustics or cold atoms physics. Remarkably, such chiral modes also exist in continuous media encountered in nature. This is the case of oceanic and atmospheric equatorial waves that only propagate their energy eastward. This remarkable property, that triggers the El niño southern oscillations and impacts the climate over the globe, has a topological interpretation analogous to those of Chern insulators [1]. Similar topological arguments also allow the prediction of new kinds of waves in strongly stratified fluids that might be observed e.g. in stars [2]. In the presence of a solid boundary, Kelvin already pointed out the existence of one-way directional waves propagating along the coasts of lakes. In strong contrast with crystals, the existence of these chiral modes in continuous media depends on the boundary conditions: they are not topologically protected as one would naively expect from the analogy with the celebrated bulk-boundary correspondence in condensed matter. However, a generalization to this cornerstone concept of topological physics can be formulated, leading to the prediction of ”ghost modes” that coexist with the bulk states [3]. [1] Topological origin of equatorial waves. P. Delplace, B. Marston and A. Venaille, Science 358, 1075 (2017) [2] Topological transition in stratified fluids. M. Perrot,P. Delplace and A. Venaille, Nature Physics volume 15, 781-784(2019) [3] Anomalous bulk-edge correspondence in continuous media. C. Tauber, P. Delplace and A. Venaille, arXiv:1902.10050 (2019).

Hydrodynamics for integrable systems

Hydrodynamics is a powerful framework for large-wavelength phenomena in many-body systems. It was extended recently to include integrable models, giving "generalised hydrodynamics". In this talk, I will review fundamental aspects of the hydrodynamics of integrable systems, with the simple examples of the quantum Lieb-Liniger and the classical Toda models. I will discuss a recent cold-atom experiment that confirmed the theory, and, if time permits, show some of the exact results that can be obtained with this formalism, such as exact nonequilibrium steady states and exact asymptotics of correlation functions at large space-time separations in Gibbs and generalised Gibbs states.

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Quantum Dynamics

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