In the quest of controlling materials’ properties on demand, light presents a promising avenue due to its ability to provide ultrafast control and induce phases of matter that are otherwise inaccessible through traditional adiabatic means. This unlocks states exhibiting tailored emergent properties, named hidden phases. Here, we demonstrate how to reach in the same system two distinct...
Nonthermal fixed points are far from equilibrium weak-coupling phenomena in which the distribution function of particles exhibit self-similarity in time in the absence of spatial dependence. In 2504.18754 with Berges, Denicol and Preis we proposed that introducing spatial gradients leads to the emergence of a novel form of hydrodynamics, defined intrinsically far from equilibrium. I will...
I will overview the theory of viscous electron fluids, describe why this regime is uncommon in real quantum materials (but still observable under the right conditions), and discuss some experimental signatures of viscous electron flow. I will explain why the detection of viscous electron flow reveals new information about electron interactions and scattering, that can be very difficult to...
Ultra-clean materials now routinely access regimes where electron flow is neither purely Ohmic nor purely hydrodynamic, and where boundaries and device geometry are part of the physics rather than a complication. Toward quantitatively modelling the realities of electronic transport and correlated quantum systems more broadly, in this talk I develop geometry-aware transport models from two...
Clean two-dimensional Fermi liquids are now known to exhibit an intermediate tomographic regime, between ballistic and Navier-Stokes transport, caused by the anomalously slow relaxation of parity-odd multipolar deformations of the Fermi surface. Here we show that this anomaly extends to the dynamical realm. Starting from a microscopic numerical evaluation of the linearized electron-electron...
Herbertsmithite is a leading candidate to host a quantum spin liquid -- a long sought state of matter featuring long-range quantum entanglement and fractionalised 'spinon' excitations. However, despite two decades' work, definitive evidence remains lacking. One complicating factor is that the material features significant disorder in the form of magnetic impurities.
I will outline recent...
The local equilibration time $\tau_{\rm eq}$ of quantum many-body systems is conjectured to be bounded below by the Planckian time $\hbar /T$. We formalize this conjecture by defining $\tau_{\rm eq}$ as the time scale at which a hydrodynamic description emerges for conserved densities. Drawing on analytic properties of real time thermal correlators, we establish a rigorous lower bound...
Strongly correlated and low-dimensional materials host exotic ground states whose out-of-equilibrium dynamics remain poorly understood and are notoriously difficult to predict from first principles. Pump-probe photoemission spectroscopy using high-harmonic-generated extreme ultraviolet pulses offers direct, momentum-resolved access to these dynamics on their natural femtosecond timescales. In...
First order phase transitions are of interest in a wide range of systems, from condensed matter to cosmology, and typically proceed through bubble nucleation. While some properties are purely determined by thermodynamics, other quantities, like the bubble wall velocity, are more challenging to obtain. I will review recent results concerning the holographic description of first order phase...
We propose a class of lattice models, including Weyl semimetals, realizable in condensed matter systems whose low-energy dynamics exactly reduces to Dirac fields subjected to gravitational backgrounds. Wave-packets propagating on the lattice exhibit eternal slowdown, signalling the formation of black hole event horizons. We show that the semiclassical wave packets trajectories coincide with...
The dynamics of systems close the equilibrium is captured by the modes found in the analytic structure of the retarded correlation function. Due to the universality of this description, these mode structures allow a direct comparison between various out of equilibrium systems in otherwise very different regimes. In this talk I will explain how to interpret mode structures emerging from quantum...
We construct fully backreacted charged black brane solutions with a spatially disordered chemical potential in asymptotically AdS$_3$ and AdS$_4$, providing holographic duals of strongly coupled disordered systems. At intermediate temperatures these geometries display highly inhomogeneous horizons, though their geometric averages reproduce the clean BTZ and Reissner–Nordström solutions. The...
Nature hosts both massless particles with linear dispersions and massive particles whose energies scale quadratically with momentum and exhibit finite gaps. In condensed matter systems, analogous behaviour appears in the form of collective modes, i.e., measurable excitations with well-defined energy–momentum relations. A long-discussed third possibility is that of a superluminal tachyon,...
The higher-spin Kitaev models possess an extensive set of local conserved quantities, much like the spin-1/2 Kitaev honeycomb model, although they are not exactly solvable. In this talk, I will present the exact gauge structure of the spin-S Kitaev honeycomb model and show that these conserved quantities are precisely the Z2 gauge fluxes. A striking even-odd effect emerges: the Z2 gauge...
Wigner crystals–phases in which itinerant electrons spontaneously crystallize–feature prominently in the phase diagrams of modern two-dimensional materials. Unlike conventional two-dimensional electron gases, these crystals may form in bands with substantial Berry curvature, which can qualitatively change the nature of the crystalline state. I will present variational calculations showing...
The strange metal is thought to represent a universal limit on quantum entanglement in a many-body system, though this hypothesis remains unproven. In 1989, theorists proposed that universality might manifest in strange metals as scale-invariant behavior in the dynamic charge susceptibility, $\chi''(q, \omega)$, at finite momentum, $q$. In this talk I will describe the first measurements of...
We study DC and AC thermoelectric and magnetotransport in 2D quantum critical theories with strong translational symmetry breaking due to a varying chemical potential lattice with zero average \barμ=0. The combination of quantum criticality and the absence of the average natural scale implies that such systems have idiosyncratic signatures that may apply more generally when the variance in the...
I will present our work on the development of cavities and metamaterials operating in the Terahertz (THz) frequency range and using a surface plasmonic mechanism for light confinement. In the first part of the talk, I will discuss equilibrium properties of this system and how the plasmonic approach enables the confinement of THz photons to volumes up to 10⁻⁸ times smaller than the free-space...
Nonthermal fixed points are universal, attractive phenomena arising in far-from-equilibrium systems. They have been studied in different physical systems, such as theoretical models of heavy-ion conditions and cold-atom experiments. In analogy to strongly-coupled CFTs or black holes, one can study the attractive nature of nonthermal fixed points by calculating their quasinormal mode spectra....
The system of N fermions, interacting randomly, q at a time is called the SYK dot. These dots are put on a 1D chain and allow for q body interactions between nearest neighbor sites. At large N, this model is known to have two channels of energy transport at very low temperatures: a diffusive (Drude like) mode and a set of critical gapped modes. While these models are not analytically tractable...
We will show how hydrodynamics in the presence of a weak lattice and by extension in the presence of weak translational symmetry breaking cannot explain the observed T-squared scaling of the Hall angle in high Tc cuprates. Building on this we present numerical studies of SYK-AdS2 fixed points in the presence of strong translational symmetry breaking, showing promising signs of Drude-like...
Near-extremal black holes are known to contain strong quantum fluctuations in their near-horizon near-AdS2 throat region governed by an effective action that includes Schwarzian modes. These fluctuations lead to one-loop corrections in the gravitational path integral that are essential in understanding the thermodynamics of near-extremal black holes at low temperatures where they become more...
Constraints on infrared (IR) physics arising from ultraviolet (UV) consistency have provided deep insights into the structure of relativistic quantum field theories and their IR phases. I am interested in how analogous constraints can be formulated for systems with spontaneously or explicitly broken Lorentz symmetry. One such system of interest is relativistic Fermi liquid which describes a...
Van der Waals (vdW) materials have revolutionized our understanding of correlated quantum phenomena, where structural confinement and reduced screening give rise to strongly bound excitons and a wide variety of emergent electronic and magnetic phases. Among these, magnetic vdW semiconductors open an entirely new frontier where Coulomb correlations can be tuned in situ by the material’s...
The interplay between lattice and electron degrees of freedom can give rise to complex ordered states in quantum materials. Here, we use high-resolution optical spectroscopy to investigate TiSe2, a material whose charge-ordered phase has been debated for decades. We discover a previously unobserved pronounced splitting of a doubly degenerate Eu optical phonon at the charge-density-wave...
Describing the transition between normal and superfluid phases requires an effective theory that captures the coupled dynamics of the order parameter and the conserved charges of the system. In this talk, I present a relativistic effective field theory for nearly critical superfluids, constructed through three complementary approaches. I first outline the derivation within the framework of...
Mott insulators are phases in which strong electron–electron interactions suppress charge transport despite partially filled bands. In terms of single-particle observables, this physics is often associated with zeros of the Green’s function rather than poles. In this talk, I will present a semi-holographic model that exhibits a Mott–metal transition. The setup consists of an elementary fermion...
A local symmetry is required to formulate fluid dynamics from a modern effective-field-theory perspective. Black hole horizons possess the same redundancy. In this talk, I will show how asymptotic symmetries of horizons can be interpreted as symmetries of a dual hydrodynamic theory in the context of holography. I will also show how the horizon structure implies additional symmetries and how...
Hydrodynamics provides a universal low-energy effective description of interacting many-body systems. The Schwinger–Keldysh effective field theory (SK EFT) offers a Wilsonian, action-based formulation of hydrodynamics that systematically incorporates fluctuations. In this approach, the effective action is generically complex, encoding macroscopic dissipation. The framework features a discrete...
We consider the fluctuation equations in the background of an eternal traversable wormhole. We first construct the appropriate boundary conditions for the corresponding two-boundary problem, then we solve for the correlation functions and find hydro-like quasiparticle poles, contrary to naive expectations. Then we discuss how to detect the onset of teleportation.
A key frontier of modern condensed matter is to harness light–matter interaction to coherently engineer quantum states in materials. Under optical driving, quantum materials exhibit emergent many-body phenomena, from ultrafast switching to dynamical quantum states without equilibrium analogs. Progress hinges on using light to both uncover new nonequilibrium states and devise strategies to...
The mechanisms that quantum systems can use to avoid thermalization and retain information in their local degrees of freedom have been of great research interest for both new fundamental physics and novel applications. These mechanisms, for example, are of great importance for quantum technologies since they can be used to build quantum memory devices. In quantum materials, there has been a...
Nanometer-scale modulations can spontaneously emerge in complex materials when multiple degrees of freedom interact. In this talk, I will demonstrate that SrTiO₃ lies near an incipient structurally modulated phase. I will then explore how Ca doping and an applied electric field influence this phase, revealing that it cooperates with—rather than competes against—the other lattice instabilities...
Active particles are self-propelled units that continuously convert energy into directed motion, making them paradigmatic examples of far-from-equilibrium systems. Their intrinsic non-equilibrium nature gives rise to a wide range of collective phenomena, including flocking, pattern formation, and non-equilibrium phase transitions. Despite significant progress, a fundamental understanding of...
Hydrodynamics is expected to govern the universal long-time and large-scale dynamics of interacting systems. However, its applicability to intrinsically non-equilibrium states with topological defects remains poorly understood. Superfluids containing vortices provide a paradigmatic example: such configurations exhibit singular phase structures, strong spatial inhomogeneities, and additional...
The band-structure picture of metals is very successful in many materials where the electron correlations are weak. On the other extreme, when correlations are very strong, one expects interaction-induced insulators – due to Mott localization or symmetry breaking. However, the intermediate regime where correlations are strong but the material remains gapless, harbors many open questions in our...
Optical driving can trigger emergent symmetry breaking and offers a route to superconducting-like states far from equilibrium. In correlated quantum materials, superconductivity often emerges from strongly fluctuating regimes proximate to quantum spin-liquid phases. Yet it remains unclear whether light can drive a quantum spin liquid into a genuine condensate, rather than a transient...
Extremal black holes have the particularity to exhibit an emergent geometry close to their horizon that contains an AdS2 factor. For compact internal spaces, the theory can be dimensionally reduced to obtain a dilaton gravity in two dimensions. At the linearised level, this reduces to JT gravity. The low-energy effective theory is governed by the Schwarzian action, enabling corrections to the...
In this talk, I address the question of how hydrodynamics can be extended to incorporate non-hydrodynamic excitations. To this end, I consider the construction of an effective linear-response theory that reproduces the Mittag–Leffler expansion of a charge current correlator with an arbitrary number of simple poles. The resulting framework is compatible with hydrostatics and does not require...
Holography can describe non-Hermitian PT-symmetric systems. I will present novel results about the phase diagram of these systems, focusing on the interior geometry of the dual black holes and its imprint on field-theoretic observables.
When the electron mean-free-path exceeds the sample thickness in a metal, Sondheimer oscillations of electric conductivity, which are periodic in magnetic field, can emerge. Our study of longitudinal and transverse conductivity in cadmium single crystals with thicknesses ranging from 12.6 to 475 μm demonstrate that the amplitude of the first ten oscillations is determined by the quantum of...
