@article{MTMT:32837271, title = {Semiclassical and thermal phase space entropies measuring complexity}, url = {https://m2.mtmt.hu/api/publication/32837271}, author = {Varga, Imre}, doi = {10.1007/s10910-022-01355-6}, journal-iso = {J MATH CHEM}, journal = {JOURNAL OF MATHEMATICAL CHEMISTRY}, volume = {61}, unique-id = {32837271}, issn = {0259-9791}, abstract = {Measures of delocalization in phase space are analyzed using Rényi entropies, especially two of which play an important role in characterizing extension and shape of distributions: the linear entropy related to the participation number and the Shannon-entropy. The difference of these two, termed as structural entropy, has been successfully applied in a large variety of physical situations and for various mathematical problems. A very similar quantity has coincidentally been used as a measure of complexity by some other authors. Hereby we show that various semiclassical phase space representations of quantum states can be well described by the structural entropy providing a transparent picture in relation to the thermodynamic description. Thermodynamic and quantum fluctuations are analytically treated for the special case of harmonic oscillators invoking the Einstein model of heat capacity. It is demonstrated that the thermal uncertainty relations are linked to the delocalization over the phase space. For respective limits of zero temperature implying quantum behavior or infinite temperature implying classical behavior we also show which quantities remain useful. As a byproduct the thermal extension of the phase space distribution can be calculated that is directly related to a decoherence parameter introduced by Zurek in a different context.}, year = {2023}, eissn = {1572-8897}, pages = {277-287}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:3415547, title = {A Wigner-Dyson-osztályozás és az Anderson-féle fém-szigetelő átmenet}, url = {https://m2.mtmt.hu/api/publication/3415547}, author = {Varga, Imre}, journal-iso = {TERMÉSZET VILÁGA}, journal = {TERMÉSZET VILÁGA}, volume = {148}, unique-id = {3415547}, issn = {0040-3717}, year = {2017}, pages = {509-512}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:3128426, title = {Lloyd-model generalization: Conductance fluctuations in one-dimensional disordered systems}, url = {https://m2.mtmt.hu/api/publication/3128426}, author = {Méndez-Bermúdez, JA and Martínez-Mendoza, AJ and Gopar, VA and Varga, Imre}, doi = {10.1103/PhysRevE.93.012135}, journal-iso = {PHYSICAL REVIEW E}, journal = {PHYSICAL REVIEW E: COVERING STATISTICAL NONLINEAR BIOLOGICAL AND SOFT MATTER PHYSICS (2016-)}, volume = {93}, unique-id = {3128426}, issn = {2470-0045}, year = {2016}, eissn = {2470-0053}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2990984, title = {Anderson transition and multifractals in the spectrum of the Dirac operator of quantum chromodynamics at high temperature}, url = {https://m2.mtmt.hu/api/publication/2990984}, author = {Ujfalusi, László and Giordano, Matteo and Pittler, Ferenc and Kovács, Tamás György and Varga, Imre}, doi = {10.1103/PhysRevD.92.094513}, journal-iso = {PHYS REV D}, journal = {PHYSICAL REVIEW D}, volume = {92}, unique-id = {2990984}, issn = {2470-0010}, year = {2015}, eissn = {2470-0029}, orcid-numbers = {Giordano, Matteo/0000-0003-0011-8669; Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2938470, title = {Finite-size scaling and multifractality at the Anderson transition for the three Wigner-Dyson symmetry classes in three dimensions}, url = {https://m2.mtmt.hu/api/publication/2938470}, author = {Ujfalusi, László and Varga, Imre}, doi = {10.1103/PhysRevB.91.184206}, journal-iso = {PHYS REV B}, journal = {PHYSICAL REVIEW B}, volume = {91}, unique-id = {2938470}, issn = {2469-9950}, abstract = {The disorder-induced metal-insulator transition is investigated in a three-dimensional simple cubic lattice and compared for the presence and absence of time-reversal and spin- rotational symmetry, i.e., in the three conventional symmetry classes. Large-scale numerical simulations have been performed on systems with linear sizes up to L = 100 in order to obtain eigenstates at the band center, E = 0. The multifractal dimensions, exponents Dq and αq , have been determined in the range of −1 q 2. The finite-size scaling of the generalized multifractal exponents provide the critical exponents for the different symmetry classes in accordance with values known from the literature based on high-precision transfer matrix techniques. The multifractal exponents of the different symmetry classes provide further characterization of the Anderson transition, which was missing from the literature so far.}, year = {2015}, eissn = {2469-9969}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2938490, title = {Dirac eigenmodes at the QCD Anderson transition}, url = {https://m2.mtmt.hu/api/publication/2938490}, author = {Giordano, Matteo and Kovacs, T and Pittler, F and Ujfalusi, László and Varga, Imre}, doi = {10.22323/1.214.0212}, journal-iso = {POS - PROCEEDINGS OF SCIENCE}, journal = {POS - PROCEEDINGS OF SCIENCE}, volume = {LATTICE2014}, unique-id = {2938490}, issn = {1824-8039}, year = {2014}, orcid-numbers = {Giordano, Matteo/0000-0003-0011-8669; Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2869747, title = {Quantum percolation transition in three dimensions: Density of states, finite-size scaling, and multifractality}, url = {https://m2.mtmt.hu/api/publication/2869747}, author = {Ujfalusi, László and Varga, Imre}, doi = {10.1103/PhysRevB.90.174203}, journal-iso = {PHYS REV B}, journal = {PHYSICAL REVIEW B}, volume = {90}, unique-id = {2869747}, issn = {2469-9950}, year = {2014}, eissn = {2469-9969}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2688029, title = {Kondo-Anderson transitions}, url = {https://m2.mtmt.hu/api/publication/2688029}, author = {Kettemann, S and Mucciolo, ER and Varga, Imre and Slevin, K}, doi = {10.1103/PhysRevB.85.115112}, journal-iso = {PHYS REV B}, journal = {PHYSICAL REVIEW B}, volume = {85}, unique-id = {2688029}, issn = {2469-9950}, abstract = {Dilute magnetic impurities in a disordered Fermi liquid are considered close to the Anderson metal-insulator transition (AMIT). Critical power-law correlations between electron wave functions at different energies in the vicinity of the AMIT result in the formation of pseudogaps of the local density of states. Magnetic impurities can remain unscreened at such sites. We determine the density of the resulting free magnetic moments in the zero-temperature limit. While it is finite on the insulating side of the AMIT, it vanishes at the AMIT, and decays with a power law as function of the distance to the AMIT. Since the fluctuating spins of these free magnetic moments break the time-reversal symmetry of the conduction electrons, we find a shift of the AMIT, and the appearance of a semimetal phase. The distribution function of the Kondo temperature T-K is derived at the AMIT, in the metallic phase, and in the insulator phase. This allows us to find the quantum phase diagram in an external magnetic field B and at finite temperature T. We calculate the resulting magnetic susceptibility, the specific heat, and the spin relaxation rate as a function of temperature. We find a phase diagram with finite-temperature transitions among insulator, critical semimetal, and metal phases. These new types of phase transitions are caused by the interplay between Kondo screening and Anderson localization, with the latter being shifted by the appearance of the temperature-dependent spin-flip scattering rate. Accordingly, we name them Kondo-Anderson transitions.}, year = {2012}, eissn = {2469-9969}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2688028, title = {Multifractal dimensions for critical random matrix ensembles}, url = {https://m2.mtmt.hu/api/publication/2688028}, author = {Mendez-Bermudez, JA and Alcazar-Lopez, A and Varga, Imre}, doi = {10.1209/0295-5075/98/37006}, journal-iso = {EUROPHYS LETT}, journal = {EUROPHYSICS LETTERS}, volume = {98}, unique-id = {2688028}, issn = {0295-5075}, abstract = {Based on heuristic arguments we conjecture that an intimate relation exists between the eigenfunction multifractal dimensions D-q of the eigenstates of critical random matrix ensembles D-q' approximate to qDq[q' +(q - q')D-q](-1), 1 <= q <= 2. We verify this relation by extensive numerical calculations. We also demonstrate that the level compressibility chi describing level correlations can be related to D-q in a unified way as D-q = (1 - chi)[1 + (q - 1)chi](-1), thus generalizing existing relations with relevance to the disorder-driven Anderson transition. Copyright (C) EPLA, 2012}, year = {2012}, eissn = {1286-4854}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2688031, title = {Anderson localization at large disorder}, url = {https://m2.mtmt.hu/api/publication/2688031}, author = {Ujfalusi, László and Varga, Imre}, doi = {10.1103/PhysRevB.86.125143}, journal-iso = {PHYS REV B}, journal = {PHYSICAL REVIEW B}, volume = {86}, unique-id = {2688031}, issn = {2469-9950}, year = {2012}, eissn = {2469-9969}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2682610, title = {Quantum chaos in one dimension?}, url = {https://m2.mtmt.hu/api/publication/2682610}, author = {Ujfalusi, László and Varga, Imre and Schumayer, D}, doi = {10.1103/PhysRevE.84.016230}, journal-iso = {PHYS REV E STAT NONLIN}, journal = {PHYSICAL REVIEW E - STATISTICAL, NONLINEAR AND SOFT MATTER PHYSICS (2001-2015)}, volume = {84}, unique-id = {2682610}, issn = {1539-3755}, year = {2011}, eissn = {1550-2376}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2659780, title = {Modeling excitonic line shapes in weakly disordered semiconductor nanostructures}, url = {https://m2.mtmt.hu/api/publication/2659780}, author = {Kuznetsova, I and Gogh, N and Forstner, J and Meier, T and Cundiff, ST and Varga, Imre and Thomas, P}, doi = {10.1103/PhysRevB.81.075307}, journal-iso = {PHYS REV B}, journal = {PHYSICAL REVIEW B}, volume = {81}, unique-id = {2659780}, issn = {2469-9950}, abstract = {Excitonic spectra of weakly disordered semiconductor heterostructures are simulated on the basis of a one-dimensional tight-binding model. The influence of the length scale of weak disorder in quantum wells on the redshift of the excitonic peak and its linewidth is studied. By calculating two-dimensional Fourier-transform spectra we are able to determine the contribution of disorder to inhomogeneous and also to homogeneous broadenings separately. This disorder-induced dephasing is related to a Fano-type coupling and leads to contributions to the homogeneous linewidth that depends on energy within the inhomogeneously broadened line. The model includes heavy- and light-hole excitons and yields smaller inhomogeneous broadening for the light-hole exciton if compared to the heavy-hole exciton, which agrees qualitatively with the experiment.}, year = {2010}, eissn = {2469-9969}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @inproceedings{MTMT:2680536, title = {Conductance statistics for the power-law banded random matrix model}, url = {https://m2.mtmt.hu/api/publication/2680536}, author = {Martinez-Mendoza, AJ and Mendez-Bermudez, JA and Varga, Imre}, booktitle = {4th Mexican Meeting on Mathematical and Experimental Physics}, doi = {10.1063/1.3536612}, unique-id = {2680536}, abstract = {We study numerically the conductance statistics of the one-dimensional (ID) Anderson model with random long-range hoppings described by the Power-law Banded Random Matrix (PBRM) model. Within a scattering approach to electronic transport, we consider two scattering setups in absence and presence of direct processes: 2M single-mode leads attached to one side and to opposite sides of 1D circular samples. For both setups we show that (i) the probability distribution of the logarithm of the conductance T behaves as w(ln T) proportional to T(M2/2), for T << T(typ) = exp < ln T >, for both the critical and the non-critical samples; and (ii) at criticality there is a smooth crossover from localized-like to delocalized-like behavior in the transport properties of the PBRM model by decreasing the fractality of its eigenstates.}, year = {2010}, pages = {41-48}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2659779, title = {Scattering and transport statistics at the metal-insulator transition. A numerical study of the power-law banded random-matrix model}, url = {https://m2.mtmt.hu/api/publication/2659779}, author = {Mendez-Bermudez, JA and Gopar, VA and Varga, Imre}, doi = {10.1103/PhysRevB.82.125106}, journal-iso = {PHYS REV B}, journal = {PHYSICAL REVIEW B}, volume = {82}, unique-id = {2659779}, issn = {2469-9950}, abstract = {We study numerically scattering and transport statistical properties of the one-dimensional Anderson model at the metal-insulator transition described by the Power-law Banded Random Matrix (PBRM) model at criticality. Within a scattering approach to electronic transport, we concentrate on the case of a small number of single-channel attached leads. We observe a smooth transition from localized to delocalized behavior in the average scattering matrix elements, the conductance probability distribution, the variance of the conductance, and the shot noise power by varying $b$ (the effective bandwidth of the PBRM model) from small ($b\ll 1$) to large ($b>1$) values. We contrast our results with analytic random matrix theory predictions which are expected to be recovered in the limit $b\to \infty$. We also compare our results for the PBRM model with those for the three-dimensional (3D) Anderson model at criticality, finding that the PBRM model with $b \in [0.2,0.4]$ reproduces well the scattering and transport properties of the 3D Anderson model.}, year = {2010}, eissn = {2469-9969}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2659781, title = {Broken time-reversal symmetry scattering at the Anderson transition}, url = {https://m2.mtmt.hu/api/publication/2659781}, author = {Alcazar-Lopez, A and Mendez-Bermudez, JA and Varga, Imre}, doi = {10.1002/andp.200910375}, journal-iso = {ANN PHYS-BERLIN}, journal = {ANNALEN DER PHYSIK}, volume = {18}, unique-id = {2659781}, issn = {0003-3804}, abstract = {We study numerically the statistical properties of some scattering quantities for the Power-law Banded Random Matrix model at criticality in the absence of time-reversal symmetry, with a small number of single-channel leads attached to it. We focus on the average scattering matrix elements, the conductance probability distribution, and the shot noise power as a function of the effective bandwidth b of the model. We find a smooth transition from insulating- to metallic-like behavior in the scattering properties of the model by increasing b. We contrast our results with existing random matrix theory predictions.}, year = {2009}, eissn = {1521-3889}, pages = {896-900}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2650433, title = {Analytical analysis of single-photon correlations emitted by disordered semiconductor heterostructures}, url = {https://m2.mtmt.hu/api/publication/2650433}, author = {Bozsoki, P and Hoyer, W and Kira, M and Varga, Imre and Thomas, P and Koch, SW and Schomerus, H}, doi = {10.1007/s10854-007-9424-0}, journal-iso = {J MATER SCI: MATER EL}, journal = {JOURNAL OF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS}, volume = {20}, unique-id = {2650433}, issn = {0957-4522}, abstract = {In a recent publication [Phys. Rev. Lett. 97, 227402 (2006)], it has been demonstrated numerically that a long-range disorder potential in a semiconductor quantum well can be reconstructed reliably via single-photon interferometry of spontaneously emitted light. In the present paper, a simplified analytical model of independent two-level systems is presented in order to study the reconstruction procedure in more detail. With the help of this model, the measured photon correlations can be calculated analytically and the influence of parameters, such as the disorder length scale, the wavelength of the used light, or the spotsize can be investigated systematically. Furthermore, the relation between the proposed angle-resolved single-photon correlations and the disorder potential can be understood and the measured signal is expected to be closely related to the characteristic strength and length scale of the disorder.}, year = {2009}, eissn = {1573-482X}, pages = {23-29}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2659783, title = {Localization of excitons in weakly disordered semiconductor structures: A model study}, url = {https://m2.mtmt.hu/api/publication/2659783}, author = {Gogh, N and Thomas, P and Kuznetsova, I and Meier, T and Varga, Imre}, doi = {10.1002/andp.200910382}, journal-iso = {ANN PHYS-BERLIN}, journal = {ANNALEN DER PHYSIK}, volume = {18}, unique-id = {2659783}, issn = {0003-3804}, abstract = {Localization of the center-of-mass (com) motion of an exciton in a disordered semiconductor structure is studied theoretically by focusing on nonlinear optical spectroscopy. A one-dimensional tight-binding model with diagonal disorder is applied and the Coulomb interaction is treated consistently. In the ordered situation the center-of-mass momentum (K) selection rule leads to only the lowest transition for K = 0. The break down of the com-K-selection rule produces the well known asymmetric excitonic lines of disordered semiconductors. The coupling between the lowest dominant transition to this modified com-continuum yields Fano-like features in the nonlinear spectra.}, year = {2009}, eissn = {1521-3889}, pages = {905-909}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2650432, title = {Critical metal phase at the Anderson metal-insulator transition with Kondo impurities}, url = {https://m2.mtmt.hu/api/publication/2650432}, author = {Kettemann, S and Mucciolo, ER and Varga, Imre}, doi = {10.1103/PhysRevLett.103.126401}, journal-iso = {PHYS REV LETT}, journal = {PHYSICAL REVIEW LETTERS}, volume = {103}, unique-id = {2650432}, issn = {0031-9007}, abstract = {It is well known that magnetic impurities can change the symmetry class of disordered metallic systems by breaking spin and time-reversal symmetry. At low temperature, these symmetries can be restored by Kondo screening. It is also known that at the Anderson metal-insulator transition, wave functions develop multifractal fluctuations with power-law correlations. Here, we consider the interplay of these two effects. We show that multifractal correlations open local pseudogaps at the Fermi energy at some random positions in space. When dilute magnetic impurities are at these locations, Kondo screening is strongly suppressed. When the exchange coupling J is smaller than a certain value J(*), the metal-insulator transition point extends to a critical region in the disorder strength parameter and to a band of critical states.}, year = {2009}, eissn = {1079-7114}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2659782, title = {Conductance distribution at criticality: One-dimensional Anderson model with random long-range hopping}, url = {https://m2.mtmt.hu/api/publication/2659782}, author = {Mendez-Bermudez, JA and Gopar, VA and Varga, Imre}, doi = {10.1002/andp.200910390}, journal-iso = {ANN PHYS-BERLIN}, journal = {ANNALEN DER PHYSIK}, volume = {18}, unique-id = {2659782}, issn = {0003-3804}, abstract = {We study numerically the conductance distribution function w(T) for the one-dimensional Anderson model with random long-range hopping described by the Power-law Banded Random Matrix model at criticality. We concentrate on the case of two single-channel leads attached to the system. We observe a smooth transition from localized to delocalized behavior in the conductance distribution by increasing b, the effective bandwidth of the model. Also, for b < 1 we show that w(ln T/Ttyp) is scale invariant, where Ttyp = exp 〈 ln T 〉 is the typical value of T. Moreover, we find that for T < Ttyp, w(ln T/Ttyp) shows a universal behavior proportional to (T/Ttyp)-1/2.}, year = {2009}, eissn = {1521-3889}, pages = {891-895}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} } @article{MTMT:2680537, title = {Special Topic Issue Transport in Interacting Disordered Systems Preface}, url = {https://m2.mtmt.hu/api/publication/2680537}, author = {Varga, Imre}, journal-iso = {ANN PHYS-BERLIN}, journal = {ANNALEN DER PHYSIK}, volume = {18}, unique-id = {2680537}, issn = {0003-3804}, year = {2009}, eissn = {1521-3889}, pages = {821-821}, orcid-numbers = {Varga, Imre/0000-0001-5288-0722} }