arXiv subjects

Mucio A. Continentino

Publications and source records attributed to Mucio A. Continentino.

45 records · Page 3Linked to original sources

arXiv2004

Quantum first order phase transitions

The scaling theory of critical phenomena has been successfully extended for classical first order transitions even though the correlation length does not diverge in these transitions. In this paper we apply the scaling ideas to quantum first order transitions. The usefulness of this approach is illustrated treating the problems of a superconductor coupled to a gauge field and of a biquadratic Heisenberg chain, at zero temperature. In both cases there is a latent energy associated with their discontinuous quantum transitions. We discuss the effects of disorder and give a general criterion for it's relevance in these transitions.

cond-mat.str-el↗

arXiv2004

Pomeranchuk effect in unstable Ytterbium systems

$YbInCu_{4}$ and its alloys present discontinuous, first order iso-structural transitions at pressure dependent temperatures $T_V(P)$, where a local moment phase coexist with a renormalized Fermi liquid phase. We show that along the coexistence line $T_V(P)$ the entropy of the large volume renormalized Fermi liquid phase is smaller than that of the higher density, local moment phase. This implies the existence of a Pomeranchuk effect in these Kondo lattice materials in analogy with $^3He$. The theoretical possibility of using these systems as cooling machines is discussed.

cond-mat.str-el↗

arXiv2003

Local criticality close to a quantum Lifshitz point

Near quantum Lifshitz points the stiffness of the lifetime of the spin fluctuations is very small. This gives rise to a regime where the critical fluctuations are local in space but extended along the time directions. The Fermi liquid properties in this local quantum regime is governed by a single energy scale, the coherence temperature. These results are relevant for heavy fermions and frustrated systems whenever there is a competition between different instabilities in $q$-space.

cond-mat.str-el↗

arXiv2003

Remarks on quantum critical behavior in heavy fermions

Generalized scaling relations and renormalization group results are used to discuss the phase diagrams of heavy fermion systems. We consider the cases where these materials are driven to a magnetic quantum critical point either by applying external pressure or a magnetic field. The Ehrenfest equation relating the pressure derivative of the critical temperature to the ratio of thermal expansion and specific heat close to a magnetic quantum critical point (QCP) is analyzed from the scaling point of view. We consider different phase diagrams of antiferromagnetic heavy fermions in an external uniform magnetic field and the implication of renormalization group results for predicting their behavior.

cond-mat.str-el↗

arXiv2001

Griffiths phases in the strongly disordered Kondo necklace model

The effect of strong disorder on the one-dimensional Kondo necklace model is studied using a perturbative real-space renormalization group approach which becomes asymptotically exact in the low energy limit. The phase diagram of the model presents a random quantum critical point separating two phases; the {\em random singlet phase} of a quantum disordered XY chain and the random Kondo phase. We also consider an anisotropic version of the model and show that it maps on the strongly disordered transverse Ising model. The present results provide a rigorous microscopic basis for non-Fermi liquid behavior in disordered heavy fermions due to Griffiths phases.

cond-mat.str-el↗

arXiv1999

Wilson and Kadowaki-Woods Ratios in Heavy Fermions

Recently we have shown that a one-parameter scaling, $T_{coh}$, describes the physical behavior of several heavy fermions in a region of their phase diagram. In this paper we fully characterize this region, obtaining the uniform susceptibility, the resistivity and the specific heat in terms of the coherence temperature $T_{coh}$. This allows for an explicit evaluation of the Wilson and the Kadowaki-Woods ratios in this regime. These quantities turn out to be independent of the distance $|δ|$ to the quantum critical point (QCP). The theory of the one-parameter scaling corresponds to a local interacting model. Although spatial correlations are irrelevant in this case, time fluctuations are critically correlated as a consequence of the quantum character of the transition.

cond-mat.str-el↗

arXiv1998

Dimensional Crossover in Heavy Fermions

Recently we have shown that a one-parameter scaling, the Coherence Temperature, describes the physical behavior of several heavy fermions in a region of their phase diagram. In this paper we fully characterize this region, obtaining the uniform susceptibility, the resistivity and the specific heat. This allows for an explicit evaluation of the Wilson and the Kadowaki-Woods ratios in this regime. These quantities turn out to be independent of the distance to the critical point. The theory of the one-parameter scaling corresponds to a zero dimensional approach. Although spatial correlations are irrelevant in this case, time fluctuations are critically correlated and the quantum hyperscaling relation is satisfied for $d=0$. The crossover from $d=0$ to $d=3$ is smooth. It occurs at a lenght scale which is inversely related to the stiffness of the lifetime of the spin fluctuations.

cond-mat.str-el↗

arXiv1998

Universality in Heavy Fermions Revisited

A previous scaling analysis of pressure experiments in heavy fermion is reviewed and enlarged. We show that the critical exponents obtained from this analysis indicate that a one-parameter scaling describes these experiments. We obtain explicitly the enhancemente factors showing that these systems are indeed near criticality and that the scaling approach is appropriate. The physics responsible for the one-parameter scaling and breakdown of hyperscaling is clarified. We discuss a microsocopic theory that is in agreement with the experiments. The scaling theory is generalized for the case the shift and crossover exponents are different. The exponents governing the physical behavior along the non-Fermi liquid trajectory are obtained for this case.

cond-mat.str-el↗

arXiv1996

On The Zero Temperature Critical Point in Heavy Fermions

We generalize the scaling theory of heavy fermions for the case the shift exponent describing the critical Neel line is different from the crossover exponent characterizing the coherence line. We obtain the properties of the non-Fermi liquid system at the critical point and in particular the electrical resistivity. We study violation of hyperscaling in the Fermi liquid regime below the coherence line where the properties of heavy fermions are described by mean-field exponents.

cond-mat↗