arXiv subjects

C. J. Bolech

Publications and source records attributed to C. J. Bolech.

50 records · Page 3Linked to original sources

arXiv2006

Mapping of the Anisotropic Two-channel Anderson Model onto a Fermi-Majorana bi-Resonant Level Model

We establish the correspondence between an extended version of the two-channel Anderson model and a particular type of bi-resonant level model. For certain values of the parameters the new model becomes quadratic. We calculate in closed form the entropy and impurity occupation as functions of temperature and identify the different physical energy scales of the problem. We show how, as the temperature goes to zero, the model approaches a universal line of fixed points non-Fermi liquid in nature.

cond-mat.str-el↗

arXiv2005

Tunnelling in organic superconductors

We discuss the possibility of deciding on the symmetry of the superconducting phase in the organic superconductors (Bechgaard salts), using tunnelling experiments. We first briefly review the properties of organic superconductors, and the possibility to have unconventional (triplet) superconductivity in these systems. We then present a simple scheme for computing the full current-voltage characteristics for tunnelling experiments within the framework of the non-equilibrium Keldysh Green function formalism. This formalism is flexible enough to address different pairing symmetries combined with magnetic fields and finite temperatures at arbitrary bias voltages. We then discuss extensively how to apply these results to probe for the symmetry of the superconducting order parameter.

cond-mat.str-el↗

arXiv2005

Two-channel Anderson Impurity Model: Single-electron Green's function, self-energies, and resistivity

We compute exactly the low-energy single-electron Green's function, the impurity and electron self-energies, and the resistivity for the two-channel Anderson impurity model. These results are obtained by exploiting the boundary conformal field theory identified from the Bethe Ansatz solution of the model. Using that solution we can make contact with the parameters of the original Hamiltonian and provide the detailed crossover between the two integer valence limits. Our results generalize those obtained previously in the context of the two-channel Kondo model.

cond-mat.str-el↗

arXiv2005

Solution of the Multi-Channel Anderson Impurity Model: Ground state and thermodynamics

We present the solution of the SU(N) x SU(M) Anderson impurity model using the Bethe-Ansatz. We first explain what extensions to the formalism were required for the solution. Subsequently we determine the ground state and derive the thermodynamics over the full range of temperature and fields. We identify the different regimes of valence fluctuation at high temperatures, followed by moment formation or intrinsic mixed valence at intermediate temperatures and a low temperature non-Fermi liquid phase. Among other things we obtain the impurity entropy, charge valence and specific heat over the full range of temperature. We show that the low-energy physics is governed by a line of fixed points. This describes non-Fermi-liquid behavior in the integral valence regime, associated with moment formation, as well as in the mixed valence regime where no moment forms.

cond-mat.str-el↗

arXiv2005

Conformal Field Theory Approach to the Two-channel Anderson Model

The two-channel Anderson impurity model serves as a prototype for describing heavy-fermion materials with a possible mixed-valent regime with both quadrupolar and magnetic character. We report on the low-energy physics of the model, using a conformal field theory approach with exact Bethe Ansatz results as input.

cond-mat.str-el↗

arXiv2005

Keldysh study of point-contact tunneling between superconductors

We revisit the problem of point-contact tunnel junctions involving one-dimensional superconductors and present a simple scheme for computing the full current-voltage characteristics within the framework of the non-equilibrium Keldysh Green function formalism. We address the effects of different pairing symmetries combined with magnetic fields and finite temperatures at arbitrary bias voltages. We discuss extensively the importance of these results for present-day experiments. In particular, we propose ways of measuring the effects found when the two sides of the junction have dissimilar superconducting gaps and when the symmetry of the superconducting states is not the one of spin-singlet pairing. This last point is of relevance for the study of the superconducting state of certain organic materials like the Bechgaard salts and, to some extent, for ruthenium compounds.

cond-mat.supr-con↗

arXiv2004

Prediction of the capacitance lineshape in two-channel quantum dots

We propose a set-up to realize two-channel Kondo physics using quantum dots. We discuss how the charge fluctuations on a small dot can be accessed by using a system of two single electron transistors arranged in parallel. We derive a microscopic Hamiltonian description of the set-up that allows us to make connection with the two-channel Anderson model (of extended use in the context of heavy-Fermion systems) and in turn make detailed predictions for the differential capacitance of the dot. We find that its lineshape, which we determined precisely, shows a robust behavior that should be experimentally verifiable.

cond-mat.mes-hall↗

arXiv2004

On the Multi-channel Anderson Model of Uranium Compounds

In this talk we will present the solution of the two-channel Anderson impurity model, proposed in the context of the heavy fermion compound UBe13, and discuss briefly the more general multi-channel case. We will show results for the thermodynamics in the full range of temperature and fields and make the connection with the current experimental situation.

cond-mat.str-el↗

arXiv2004

Universal Statistics of the Critical Depinning Force of Elastic Systems in Random Media

We study the rescaled probability distribution of the critical depinning force of an elastic system in a random medium. We put in evidence the underlying connection between the critical properties of the depinning transition and the extreme value statistics of correlated variables. The distribution is Gaussian for all periodic systems, while in the case of random manifolds there exists a family of universal functions ranging from the Gaussian to the Gumbel distribution. Both of these scenarios are a priori experimentally accessible in finite, macroscopic, disordered elastic systems.

cond-mat.dis-nn↗

arXiv2004

Point-contact tunneling involving low-dimensional spin-triplet superconductors

We modify and extend previous microscopic calculations of tunneling in superconducting junctions based on a non-equilibrium Green function formalism to include the case of spin-triplet pairing. We show that distinctive features are present in the I-V characteristics of different kinds of junctions, in particular when the effects of magnetic fields are taken into account, that permit to identify the type of pairing. We discuss the relevance of these results in the context of quasi one-dimensional organic superconductors like (TMTSF)_2(PF_6) and layered compounds like Sr_2RuO_4.

cond-mat.supr-con↗

arXiv2004

Critical Theory of the Two-Channel Anderson Impurity Model

We construct the boundary conformal field theory that describes the low-temperature behavior of the two-channel Anderson impurity model. The presence of an exactly marginal operator is shown to generate a line of stable fixed points parameterized by the charge valence of the impurity. We calculate the exact zero-temperature entropy and impurity thermodynamics along the fixed line. We also derive the critical exponents of the characteristic Fermi edge singularities caused by time-dependent hybridization between conduction electrons and impurity. Our results suggest that in the mixed-valent regime the electrons participate in two competing processes, leading to frustrated screening of spin and channel degrees of freedom. By combining the boundary conformal field theory with the Bethe Ansatz solution we obtain a complete description of the low-energy dynamics of the model.

cond-mat.str-el↗

arXiv2002

Cellular Dynamical Mean Field Theory for the 1D Extended Hubbard Model

We explore the use of exact diagonalization methods for solving the self consistent equations of the cellular dynamical mean field theory (CDMFT) for the one dimensional regular and extended Hubbard models. We investigate the nature of the Mott transition and convergence of the method as a function of cluster size as well as the optimal allocation of computational resources between bath and `cluster-impurity' sites, with a view to develop a renormalization group method in higher dimensions. We assess the performance of the method by comparing results for the Green's functions in both the spin density wave (SDW) and charge density wave (CDW) phases with accurate density matrix renormalization group (DMRG) calculations.

cond-mat.str-el↗

arXiv2002

Solution of the Two-Channel Anderson Impurity Model - Implications for the Heavy Fermion UBe$_{13}$ -

We solve the two-channel Anderson impurity model using the Bethe-Ansatz. We determine the ground state and derive the thermodynamics, obtaining the impurity entropy and specific heat over the full range of temperature. We show that the low temperature physics is given by a line of fixed points decribing a two-channel non Fermi liquid behavior in the integral valence regime associated with moment formation as well as in the mixed valence regime where no moment forms. We discuss relevance for the theory of UBe$_{13}$.

cond-mat.str-el↗

arXiv2000

Optical response in one dimensional Mott Insulators

We study the optical response of a Mott Hubbard system in the framework of the half--filled Extended Hubbard Model using the Density Matrix Renormalization Group (DMRG) method. We discuss the appearance of excitonic features inside the spectral gap as the system goes from the Spin Density Wave (SDW) to the Charge Density Wave (CDW) phase.

cond-mat.str-el↗