08:00  16:30

registration

08:45  09:00

opening  Frank Jülicher, director of the MPIPKS and the scientific coordinators

09:00  09:30

Andrew Mackenzie
(Max Planck Institute for Chemical Physics of Solids)
Nonlocal transport in ultrapure delafossite metals (onsite)
I will give an update on nonlocal transport measurements on delafossite layered metals, discussing the extent to which the observations are consistent with ballistic transport and whether viscouslike effects also play a role in determining the observed properties.

09:30  10:00

Alessandro Principi
(University of Manchester)
Hydrodynamic thermal transport in graphene (onsite)
I will review theoretical results and experimental observations of charge and heat conduction in the hydrodynamics regime of transport in monolayer graphene. Among the many effects, the WiedemannFranz law, which connects heat and charge transport in metals, is intrinsically violated in the hydrodynamics regime. In doped systems, this fact can be used to increase thermoelectric conversion efficiencies of graphenebased devices. More stringent conditions yield, in undoped graphene, to a quantumcritical Diracfluid regime, where electronic heat can flow more efficiently than charge. We show that disorder is essential to observe the Diracfluid regime under transport conditions. Conversely, the transition to this regime can also be revealed, at room temperature, using spatiotemporal thermoelectric microscopy with femtosecond temporal and nanometre spatial resolution. Finally, I will comment on the violation of the WiedemannFranz law in compensated semimetals, on the role of electronhole recombination in defining the direction of the violation, discussing how graphene can help shed light on this longstanding problem.

10:00  11:00

coffee break

11:00  11:30

Adolfo Grushin
(Néel Institute, CNRS)
TolmanEhrenfest temperature and gravitational anomalies for thermal transport (onsite)
In the sixties, Luttinger introduced a convenient and widespread trick to calculate thermal transport caused by
a thermal gradient, which is to restore equilibrium with an auxiliary, but small, gravitational field.
Using thermal transport, a handfull of recent experiments have been interpreted as a measurement of a gravitational anomaly, an elusive quantum mechanical phenomenon that is associated to strong gravitational fields, like those near blackholes.
However, a direct link between the Luttinger trick and gravitational anomalies is absent. More problematically, these two ideas have been argued to be both related and unrelated to each other in the literature, a paradoxical approach that uncovers a deeper multidisciplinary problem: How can gravitational anomalies, that require strong gravitational fields, be measured in tabletop experiments, that are performed in flat spacetime? This is the question I will revisit in my talk. First, I will show how to generalize the TolmanEhrenfest temperature, the parent concept of the Luttinger trick, to include gravitational anomalies. This will allow us to revisit black hole, quench and Floquet physics to highlight novel instances where gravitational anomalies are at play, even when spacetime itself is flat, as in condensed matter experiments.

11:30  12:00

Maxim Chernodub
(University of Tours, CNRS)
Pseudohydrodynamic flow of quasiparticles in semimetal \(WTe_2\) at room temperature (onsite)
Recently, much interest has emerged in fluidlike electric charge transport in various solidstate systems. The hydrodynamic behavior of the electronic fluid reveals itself as a decrease of the electrical resistance with increasing temperature (the Gurzhi effect) in narrow conducting channels, polynomial scaling of the resistance as a function of the channel width, substantial violation of the WiedemannFranz law supported by the emergence of the Poiseuille flow. Similarly to whirlpools in flowing water, the viscous electronic flow generates vortices, resulting in abnormal signchanging electrical response driven by the backflow of electrical current. Experimentally, the presence of the hydrodynamic vortices was observed in lowtemperature graphene as a negative voltage drop near the currentinjecting contacts. However, the question of whether the longranged signchanging electrical response can be produced by a mechanism other than hydrodynamics has not been addressed so far. Here we use polarizationsensitive laser microscopy to demonstrate the emergence of visually similar abnormal signalternating patterns in charge density in multilayer tungsten ditelluride at room temperature where this material does not exhibit true electronic hydrodynamics. We argue that this pseudohydrodynamic behavior appears due to a subtle interplay between the diffusive transport of electrons and holes. In particular, the signalternating charge accumulation in WTe2 is supported by the unexpected backflow of compressible neutral electronhole current, which creates chargeneutral whirlpools in the bulk of this nearly compensated semimetal. We demonstrate that the exceptionally large spatial size of the charge domains is sustained by the long recombination time of electronhole pairs.

12:00  12:30

Paweł Matus
(Max Planck Institute for the Physics of Complex Systems)
Skin effect as a probe of transport regimes in Weyl semimetals (onsite)
We study propagation of an oscillatory electromagnetic field inside a Weyl semimetal. In conventional conductors, the motion of the charge carriers in the skin layer near the surface can be diffusive, ballistic, or hydrodynamic. We show that the presence of chiral anomalies, intrinsic to the massless Weyl particles, leads to a hitherto neglected transport regime, in which the relation between the current and the electric field becomes nonlocal as a result of the diffusion of the valley charge imbalance into the bulk of the material. We propose to use this novel regime as a diagnostic of the presence of chiral anomalies in optical conductivity measurements. These results are obtained from a generalized kinetic theory which includes various relaxation mechanisms, allowing us to investigate different transport regimes of Weyl semimetals.

12:30  13:15

lunch break

13:15  14:00

posters & discussion via gather.town

14:00  14:30

Yuan Yan
(JuliusMaximiliansUniversität Würzburg)
Electron hydrodynamics in topological material HgTe (onsite)

14:30  15:00

Michael Stone
(University of Illinois at UrbanaChampaign)
Topological superconductors and Theta terms (virtual)
I will discuss several puzzles related to the electromagnetic response of topological superconductors in 3+1 dimensions, in partcular the role of the theta term in the effective action of the superconducting Weyl gas.
Work based on arXiv:2103.08960 by Marcus Stålhammar, MS, Masatoshi Sato and Thors Hans Hansson.

15:00  15:30

Pavel Wiegmann
(University of Chicago)
Quantum anomalies as a kinematic properties of the Euler equation (virtual)
I review recent works with A. Abanov. In these works, we show that anomalies of quantum field theories with Dirac fermions appear as kinematic properties of the classical Euler equation for a perfect fluid.

15:30  16:00

Anton Burkov
(University of Waterloo)
Anomalies and generalized Luttinger theorems in topological semimetals (virtual)

16:00  16:30

coffee break

16:30  17:30

HYDRO22 colloquium (chair: Matt Eiles, MPIPKS)
Igor Shovkovy (Arizona State University)
Relativisticlike electron hydrodynamics in Dirac semimetals (onsite)
Electron quasiparticles in Dirac semimetals may exhibit a hydrodynamic regime under certain conditions. Since the corresponding quasiparticle fluid is relativisticlike, anomalous, and electrically charged, it has a range of unusual properties. Anomalous physics affects properties of lowenergy collective modes, relativisticlike effects show up in novel instabilities, and the charged nature of the electron fluid is responsible for the strong suppression of convection. In this talk, I will review some of these unusual properties of the electron fluid in Dirac semimetals.

17:30  18:00

discussion

18:00  19:00

dinner
