**Time/Venue** Wednesday, February 8 at 2 pm in Physics South 402 and via Zoom:

https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704**Host **Joel Moore**Title **Hydrodynamics and Hall viscosity in GaAs versus graphene**Abstract **Motivated by Hall viscosity measurements in graphene sheets [1], we study hydrodynamic transport of electrons in a channel of finite width in external electric and magnetic fields. We consider electric charge densities in graphene varying from close to the Dirac point up to the Fermi liquid regime and compare the results with GaAs Fermi liquid regime [2]. We find in graphene two competing contributions to the hydrodynamic Hall and inverse Nernst (generation of transverse gradient of temperature in the channel) signals that originate from the Hall viscous and Lorentz force [3]. This competition leads to a non-linear dependence of the full signals on the magnetic field and even a cancellation at different critical field values for both signals. In particular, the hydrodynamic inverse Nernst signal in the Fermi liquid regime is dominated by the Hall viscous contribution [3]. We further show that a finite channel width leads to a suppression of the Lorenz ratio, while the magnetic field enhances this ratio [3]. All of these effects are predicted in parameter regimes accessible in experiments.

[1] A. I. Berdyugin, S. G. Xu, F. M. D. Pellegrino, R. Krishna Kumar, A. Principi, I. Torre, M. Ben Shalom, T. Taniguchi, K. Watanabe, I. V. Grigorieva, M. Polini, A. K. Geim and D. A. Bandurin, Science

**364**, 162 (2019).

[2]I. Matthaiakakis, D. Rodríguez Fernández, C. Tutschku, E. M. Hankiewicz, J. Erdmenger, and R. Meyer

*Phys. Rev. B*

**101**, 045423 (2020).

[3] Z.-Y. Xian, S. Danz, D. Rodríguez Fernández, I. Matthaiakakis, C. Tutschku, R. L. Klees, J. Erdmenger, R. Meyer, E. M. Hankiewicz arXiv:2207.10528, submitted to PRL.