  Fermi liquid theory has been a foundation in understanding the electronic
properties of materials. For weakly interacting two-dimensional (2D) electron
or hole systems, electron-electron interactions are known to introduce quantum
corrections to the Drude conductivity in the FL theory, giving rise to
temperature dependent conductivity and magneto-resistance. Here we study the
magneto-transport in a strongly interacting 2D hole system over a broad range
of temperatures ($T$ = 0.09 to $>$1K) and densities $p=1.98-0.99\times10^{10}$
cm$^{-2}$ where the ratio between Coulomb energy and Fermi energy $r_s$ = 20 -
30. We show that while the system exhibits a negative parabolic
magneto-resistance at low temperatures ($\lesssim$ 0.4K) characteristic of an
interacting FL, the FL interaction corrections represent an insignificant
fraction of the total conductivity. Surprisingly, a positive magneto-resistance
emerges at high temperatures and grows with increasing temperature even in the
regime $T \sim E_F$, close to the Fermi temperature. This unusual positive
magneto-resistance at high temperatures is attributed to the collective viscous
transport of 2D hole fluid in the hydrodynamic regime where holes scatter
frequently with each other. These findings highlight the collective transport
in a strongly interacting 2D system in the $r_s\gg 1$ regime and the
hydrodynamic transport induced magneto-resistance opens up possibilities to new
routes of magneto-resistance at high temperatures.

Strongly Correlated Electrons;Mesoscale and Nanoscale Physics