Orbital magnetoresistance of two-dimensional electron systems in the hydrodynamic regime*

We develop a theory of magnetoresistance of two-dimensional electron systems in the hydrodynamic regime. It applies to two-dimensional semiconductor structures with strongly correlated carriers when the electron-electron scattering length is sufficiently short. We find that the magnetoresistance is positive quadratic at weak fields. Although the resistivity is governed by both viscosity and thermal conductivity of the electron fluid, the temperature dependence of magnetoresistance depends on the viscosity only. This enables extration of viscosity of the electron liquid from magnetotranspot measurements.