arXiv subjects

V. Dobrosavljevic

Publications and source records attributed to V. Dobrosavljevic.

At least 37 records · Page 2Linked to original sources

arXiv2009

Valence-bond theory of highly disordered quantum antiferromagnets

We present a large-N variational approach to describe the magnetism of insulating doped semiconductors based on a disorder-generalization of the resonating-valence-bond theory for quantum antiferromagnets. This method captures all the qualitative and even quantitative predictions of the strong-disorder renormalization group approach over the entire experimentally relevant temperature range. Finally, by mapping the problem on a hard-sphere fluid, we could provide an essentially exact analytic solution without any adjustable parameters.

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arXiv2009

Electronic Griffiths phase of the d=2 Mott transition

We investigate the effects of disorder within the T=0 Brinkman-Rice (BR) scenario for the Mott metal-insulator transition (MIT) in two dimensions (2d). For sufficiently weak disorder the transition retains the Mott character, as signaled by the vanishing of the local quasiparticles (QP) weights Z_{i} and strong disorder screening at criticality. In contrast to the behavior in high dimensions, here the local spatial fluctuations of QP parameters are strongly enhanced in the critical regime, with a distribution function P(Z) ~ Z^{α-1} and αtends to zero at the transition. This behavior indicates a robust emergence of an electronic Griffiths phase preceding the MIT, in a fashion surprisingly reminiscent of the "Infinite Randomness Fixed Point" scenario for disordered quantum magnets.

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arXiv2009

Critical behavior at Mott-Anderson transition: a TMT-DMFT perspective

We present a detailed analysis of the critical behavior close to the Mott-Anderson transition. Our findings are based on a combination of numerical and analytical results obtained within the framework of Typical-Medium Theory (TMT-DMFT) - the simplest extension of dynamical mean field theory (DMFT) capable of incorporating Anderson localization effects. By making use of previous scaling studies of Anderson impurity models close to the metal-insulator transition, we solve this problem analytically and reveal the dependence of the critical behavior on the particle-hole symmetry. Our main result is that, for sufficiently strong disorder, the Mott-Anderson transition is characterized by a precisely defined two-fluid behavior, in which only a fraction of the electrons undergo a "site selective" Mott localization; the rest become Anderson-localized quasiparticles.

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arXiv2008

Energy-resolved spatial inhomogeneity of disordered Mott systems

We investigate the effects of weak to moderate disorder on the T=0 Mott metal-insulator transition in two dimensions. Our model calculations demonstrate that the electronic states close to the Fermi energy become more spatially homogeneous in the critical region. Remarkably, the higher energy states show the opposite behavior: they display enhanced spatial inhomogeneity precisely in the close vicinity to the Mott transition. We suggest that such energy-resolved disorder screening is a generic property of disordered Mott systems.

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arXiv2008

Coulomb Correlations and the Wigner-Mott Transition

Strong correlation effects, such as a dramatic increase in the effective mass of the carriers of electricity, recently observed in the low density electron gas have provided spectacular support for the existence of a sharp metal-insulator transitions in dilute two dimensional electron gases. Here we show that strong correlations, normally expected only for narrow integer filled bands, can be effectively enhanced even far away from integer filling, due to incipient charge ordering driven by non-local Coulomb interactions. This general mechanism is illustrated by solving an extended Hubbard model using dynamical mean-field theory. Our findings account for the key aspects of the experimental phase diagram, and reconcile the early view points of Wigner and Mott. The interplay of short range charge order and local correlations should result in a three peak structure in the spectral function of the electrons which should be observable in tunneling and optical spectroscopy.

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arXiv2008

Self-doping instability of the Wigner-Mott insulator

We present a theory describing the mechanism for the two-dimensional (2D) metal-insulator transition (MIT) in absence of disorder. A two-band Hubbard model is introduced, describing vacancy-interstitial pair excitations within the Wigner crystal. Kinetic energy gained by delocalizing such excitations is found to lead to an instability of the insulator to self-doping above a critical carrier concentration $n=n_c$, mapping the problem to a density-driven Mott MIT. This mechanism provides a natural microscopic picture of several puzzling experimental features, including the large effective mass enhancement, the large resistivity drop, and the large positive magneto-resistance on the metallic side of the transition. We also present a global phase diagram for the clean 2D electron gas as a function of $n$ and parallel magnetic field $B_{\shortparallel}$, which agrees well with experimental findings in ultra clean samples.

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arXiv2007

RKKY interactions in the regime of strong localization

We study the influence of strong nonmagnetic disorder on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions between diluted magnetic moments in metals. We find that the probability distribution for the RKKY interactions assumes strongly non-Gaussian form featuring long tails. Since such distributions cannot be characterized by its moments, we define a \textit{typical} value of the interaction amplitude, which we find to be exponentially suppressed in presence of Anderson localization. Our results present a plausible and physically transparent picture describing how Anderson localization effectively eliminates the long range nature of the RKKY interactions.

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arXiv2007

Quantum Critical Behavior of the Cluster Glass Phase

In disordered itinerant magnets with arbitrary symmetry of the order parameter, the conventional quantum critical point between the ordered phase and the paramagnetic Fermi-liquid (PMFL) is destroyed due to the formation of an intervening cluster glass (CG) phase. In this Letter we discuss the quantum critical behavior at the CG-PMFL transition for systems with continuous symmetry. We show that fluctuations due to quantum Griffiths anomalies induce a first-order transition from the PMFL at T=0, while at higher temperatures a conventional continuous transition is restored. This behavior is a generic consequence of enhanced non-Ohmic dissipation caused by a broad distribution of energy scales within any quantum Griffiths phase in itinerant systems.

cond-mat.dis-nn↗

arXiv2007

Disorder screening near the Mott-Anderson transition

Correlation-driven screening of disorder is studied within the typical-medium dynamical mean-field theory (TMT-DMFT) of the Mott-Anderson transition. In the strongly correlated regime, the site energies epsilon_R^i characterizing the effective disorder potential are strongly renormalized due to the phenomenon of Kondo pinning. This effect produces very strong screening when the interaction U is stronger then disorder W, but applies only to a fraction of the sites in the opposite limit (U<W).

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arXiv2007

2D-MIT as self-doping of a Wigner-Mott insulator

We consider an interaction-driven scenario for the two-dimensional metal-insulator transition in zero magnetic field (2D-MIT), based on melting the Wigner crystal through vacancy-interstitial pair formation. We show that the transition from the Wigner-Mott insulator to a heavy Fermi liquid emerges as an instability to self-doping, resembling conceptually the solid to normal liquid transition in He3. The resulting physical picture naturally explains many puzzling features of the 2D-MIT.

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arXiv2006

Scaling behavior of an Anderson impurity close to the Mott-Anderson transition

The scaling behavior of Anderson impurity models each of which with a different site energy epsilon_i is examined close to the Mott-Anderson transition. Depending on the impurity energy epsilon_i, in the critical regime the site turns into a local magnetic moment, as indicated by a vanishing quasiparticle weight Z -> 0, or remains nearly doubly occupied or nearly empty, corresponding to Z -> 1. In this paper, we present the scaling behavior of Z as a function of the on-site energy epsilon_i and the distance t to the transition, and interpret our result in terms of an appropriate beta function beta(Z).

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arXiv2005

Spin Liquid Behavior in Electronic Griffiths Phases

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 suppression of Kondo screening on a finite fraction of spins, and giving rise to universal spin-liquid behavior.

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arXiv2005

Disorder-Driven Non-Fermi Liquid Behavior of Correlated Electrons

Systematic deviations from standard Fermi-liquid behavior have been widely observed and documented in several classes of strongly correlated metals. For many of these systems, mounting evidence is emerging that the anomalous behavior is most likely triggered by the interplay of quenched disorder and strong electronic correlations. In this review, we present a broad overview of such disorder-driven non-Fermi-liquid behavior, and discuss various examples where the anomalies have been studied in detail. We describe both their phenomenological aspects as observed in experiment, and the current theoretical scenarios that attempt to unravel their microscopic origin.

cond-mat.dis-nn↗

arXiv2005

Green functions for nearest- and next-nearest-neighbor hopping on the Bethe lattice

We calculate the local Green function for a quantum-mechanical particle with hopping between nearest and next-nearest neighbors on the Bethe lattice, where the on-site energies may alternate on sublattices. For infinite connectivity the renormalized perturbation expansion is carried out by counting all non-self-intersecting paths, leading to an implicit equation for the local Green function. By integrating out branches of the Bethe lattice the same equation is obtained from a path integral approach for the partition function. This also provides the local Green function for finite connectivity. Finally, a recently developed topological approach is extended to derive an operator identity which maps the problem onto the case of only nearest-neighbor hopping. We find in particular that hopping between next-nearest neighbors leads to an asymmetric spectrum with additional van-Hove singularities.

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arXiv2005

Absence of conventional quantum phase transitions in itinerant systems with disorder

Effects of disorder are examined in itinerant systems close to quantum critical points. We argue that spin fluctuations associated with 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.

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arXiv2005

Effects of disorder on the non-zero temperature Mott Transition

The physics of the metal-insulator coexistence region near the non-zero temperature Mott transition is investigated in presence of weak disorder. We demonstrate that disorder reduces the temperature extent and the general size of the coexistence region, consistent with recent experiments on several Mott systems. We also discuss the qualitative scenario for the disorder-modified Mott transition, and present simple scaling arguments that reveal the similarities to, and the differences from, the clean limit.

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arXiv2005

Nonlinear screening theory of the Coulomb glass

A nonlinear screening theory is formulated to study the problem of gap formation and its relation to glassy freezing in classical Coulomb glasses. We find that a pseudo-gap ("plasma dip") in a single-particle density of states begins to open already at temperatures comparable to the Coulomb energy. This phenomenon is shown to reflect the emergence of short range correlations in a liquid (plasma) phase, a process which occurs even in the absence of disorder. Glassy ordering emerges when disorder is present, but this occurs only at temperatures more then an order of magnitude lower, which is shown to follow from nonlinear screening of the Coulomb interaction. Our result suggest that the formation of the "plasma dip" at high temperatures is a process distinct from the formation of the Efros-Shklovskii (ES) pseudo-gap, which in our model emerges only within the glassy phase.

cond-mat.dis-nn↗

arXiv2004

Effective model of the electronic Griffiths phase

We present simple analytical arguments explaining the universal emergence of electronic Griffiths phases as precursors of disorder-driven metal-insulator transitions in correlated electronic systems. A simple effective model is constructed and solved within Dynamical Mean Field Theory. It is shown to capture all the qualitative and even quantitative aspects of such Griffiths phases.

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