Phase transitions under quasi-equilibrium conditions, e.g., induced by a slow variation of temperature, are well described by Landau theory. In contrast, the situation far from equilibrium, e.g., after ultrafast laser excitation, differs fundamentally from a thermodynamic scenario, and it remains an open question how our understanding of static phase transitions in complex matter has to be adapted to capture a dynamical, photoinduced melting and recovery of order. In particular, even the thermal critical temperature might not provide a valid description in a system exhibiting strong non-equilibrium between different degrees of freedom, such as electrons [more...]

Electrical resistance of magnets with and without electron collisions
Electrical resistance R of metals arises from collisions of the conduction electrons with obstacles in the surrounding material and from the mass of the electrons. Interestingly, in a magnetic metal, R is larger when the current flows parallel to the magnetic moment M (see Figure (a), left), and it is smaller when the electrons flow perpendicular to it (Figure (b), left). This “anisotropic magnetoresistance” (AMR) is a mature effect, which is usually explained by the assumption that electrons moving parallel to M [more...]