In our group, we are exploring a novel electron transport regime, which appears in a high-quality graphene device under elevated temperatures. Typically, current propagation in solids is described as the journey of a single electron, which experiences collisions with crystal structure defects, sample boundaries, and phonons, and does not know anything about other electrons in the system. However, this is not the case in graphene. Under elevated temperatures (T > 150 Kelvin), electrons in graphene experience frequent interparticle collisions, with the electron-electron collision length becoming the smallest length scale in the problem. As a result, electrons start to behave as a very viscous fluid, with a viscosity comparable to that of honey. It's no surprise that such a fluid exhibits a number of unconventional properties, typically inaccessible in typical fluids. Our group focuses on exploring these unconventional electronic properties.
We have observed that under an applied magnetic field, in contrast to conventional fluids, electrons in graphene have two viscosities: the first is the conventional viscosity observed in all fluids, and the second is the so-called Hall viscosity, which should appear only in fluids with broken time reversal symmetry. As a result, the Hall effect in graphene is locally suppressed due to the presence of this new viscosity, as observed in our work.
More recently, we have explored the electron fluid in graphene in the regime of Dirac plasma, which appears in high-quality graphene devices exactly at the neutrality point, under elevated temperatures. Such plasma also exhibits a number of intriguing properties: the viscosity of an ideal fluid, the violation of the Widemann-France law, and finally, the giant magnetoresistance effect which we have recently discovered in graphene devices at room temperature. This magnetoresistance is a record high, being several orders of magnitude higher than the intrinsic magnetoresistance of all known materials at room temperature, opening the route for the development of novel magnetic field sensors.