Rajesh Narayanan

The Mott metal to insulator transition Mott!transition is a remarkable phenomenon observed in strongly correlated materials, where the localization of electronic waves is driven by on-site electron-electron repulsion (see [7] for a review). Although the appearance of a Mott gap Mott!gap is clearly a charge-related effect, magnetism is expected to play a key role in elucidating the true nature of this phase transition. Indeed, since the Mott insulating state is purely paramagnetic, local moments Local moments are well-defined objects between their formation at high temperature (about the local Coulomb interaction Coulomb interaction ) and their ultimate ordering at the Neel temperature. This offers a window for the Mott transition to occur, in which the behavior of these local spin excitations is yet to be clearly understood. The simplest situation lies in case where the low-temperature magnetic ordering is first order, as in Cr-doped . Accordingly magnetic fluctuations should be expected to be weak, so that many predictions can be made from a single-site approach such as the Dynamical Mean Field Theory (DMFT) Dynamical Mean Field Theory (DMFT) [4]. In particular, the fact that a low-temperature metallic state leads upon heating to an insulating phase can be understood as a Pomeranchuk effectPomeranchuk effect , where the entropy gain benefits the state with magnetic degeneracy. © 2010 Springer-Verlag Berlin Heidelberg.

Quantum phase transitions (QPT) Quantum phase transition have recently become a widespread topic in the realm of modern condensed matter physics. QPT are phase transformations that occur at the absolute zero of temperature and are triggered by varying a temperature-independent control parameter like pressure, doping concentration, or magnetic field. There are various examples of systems showing quantum critical behavior, which include the antiferromagnetic transition in heavy fermion material like , that is brought about by changing the doping [10]. Another prototypical example of a system exhibiting quantum critical behavior is the quantum Hall effect, wherein a two-dimensional electron gas is tuned, via an externally applied magnetic field, through a quantum critical point (QCP) that intervenes between two quantized Hall plateaux. Other examples of QPT include the ferromagnetic transition in metallic magnets as a function of applied pressure and the superconducting transition in thin films. © 2010 Springer-Verlag Berlin Heidelberg.