Biomedical subjects
Publications and source records attributed to V Dobrosavljević.
We examine the interplay of the Kondo effect and the RKKY interactions in electronic Griffiths phases using extended dynamical mean-field theory methods. We find that sub-Ohmic dissipation is generated for sufficiently strong disorder, leading to the suppression of Kondo screening on a finite fraction of spins, and giving rise to universal spin-liquid behavior.
Effects of disorder are examined in itinerant systems close to quantum critical points. We argue that spin fluctuations due to the long-range part of the RKKY interactions generically induce non-Ohmic dissipation due to rare disorder configurations. This dissipative mechanism is found to destabilize quantum Griffiths phase behavior in itinerant systems with arbitrary symmetry of the order parameter, leading to the formation of a "cluster glass" phase preceding uniform ordering.
By using a combination of detailed experimental studies and simple theoretical arguments, we identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca2-xSrxRuO4 near the metal-insulator transition. The hopping exponent alpha shows a systematic evolution from a value of alpha=1/2 deeper in the insulator to the conventional Mott value alpha=1/3 closer to the transition. This behavior, which we argue to be a universal feature of disordered Mott systems close to the metal-insulator transition, is shown to reflect the gradual emergence of disorder-induced localized electronic states populating the Mott-Hubbard gap.
Electron-electron interactions generally reduce the low temperature resistivity due to the screening of the impurity potential by the electron gas. In the weak-coupling limit, the magnitude of this screening effect is determined by the thermodynamic compressibility which is proportional to the inverse screening length. We show that when strong correlations are present, although the compressibility is reduced, the screening effect is nevertheless strongly enhanced. This phenomenon is traced to the same nonperturbative Kondo-like processes that lead to strong mass enhancements, but which are absent in weak-coupling approaches. We predict metallicity to be strongly stabilized in an intermediate regime where the interactions and the disorder are of comparable magnitude.
The emergence of glassy behavior of electrons is investigated for systems close to disorder-driven and interaction-driven metal-insulator transitions. Our results indicate that Anderson localization effects strongly stabilize such glassy behavior, while Mott localization tends to suppress it. We predict the emergence of an intermediate metallic glassy phase separating the insulator from the normal metal. This effect is expected to be most pronounced for sufficiently disordered systems, in agreement with recent experimental observations.
Experiments on a sufficiently disordered two-dimensional (2D) electron system in silicon reveal a new and unexpected kind of metallic behavior, where the conductivity decreases as sigma(n(s),T) = sigma(n(s),T = 0)+A(n(s))T(2) (where n(s) is carrier density) to a nonzero value as temperature T-->0. In 2D, the existence of a metal with dsigma/dT>0 is very surprising. In addition, a novel type of a metal-insulator transition obtains, which is unlike any known quantum phase transition in 2D.