arXiv subjects

M. J. Rozenberg

Publications and source records attributed to M. J. Rozenberg.

At least 37 records · Page 2Linked to original sources

arXiv2009

Asymmetry between the electron- and hole-doped Mott transition in the periodic Anderson model

We study the doping driven Mott metal-insulator transition (MIT) in the periodic Anderson model set in the Mott-Hubbard regime. A striking asymmetry for electron or hole driven transitions is found. The electron doped MIT at larger U is similar to the one found in the single band Hubbard model, with a first order character due to coexistence of solutions. The hole doped MIT, in contrast, is second order and can be described as the delocalization of Zhang-Rice singlets.

cond-mat.str-el↗

arXiv2008

Mottness scenario for non-Fermi liquid behavior in the periodic Anderson model within Dynamical Mean Field Theory

We study the Mott metal-insulator transition in the Periodic Anderson Model within Dynamical Mean Field Theory (DMFT). Near the quantum transition, we find a non-Fermi liquid metallic state down to a vanishing temperature scale. We identify the origin of the non-Fermi liquid behavior as due to magnetic scattering of the doped carriers by the localized moments. The non-Fermi liquid state can be tuned by either doping or external magnetic field. Our results show that the coupling to spatial magnetic fluctuations (absent in DMFT) is not a prerequisite to realize a non-Fermi liquid scenario for heavy fermion systems.

cond-mat.str-el↗

arXiv2008

Metal-Insulator transitions in the periodic Anderson model

We solve the Periodic Anderson model in the Mott-Hubbard regime, using Dynamical Mean Field Theory. Upon electron doping of the Mott insulator, a metal-insulator transition occurs which is qualitatively similar to that of the single band Hubbard model, namely with a divergent effective mass and a first order character at finite temperatures. Surprisingly, upon hole doping, the metal-insulator transition is not first order and does not show a divergent mass. Thus, the transition scenario of the single band Hubbard model is not generic for the Periodic Anderson model, even in the Mott-Hubbard regime.

cond-mat.str-el↗

arXiv2008

Impurity effects in the quantum kagome system ZnCu3(OH)6Cl2

Motivated by the recent experiments on the new spin half Kagome compound ZnCu3(OH)6Cl2, we study a phenomenological model of a frustrated quantum magnet. The model has a spin liquid groundstate and is constructed so as to mimic the macroscopically large quasi-degeneracies expected in the low-lying energy structure of a Kagome system. We use numerical studies of finite size systems to investigate the static as well as the dynamical response at finite temperatures. The results obtained using our simple model are compatible with a large number of recent experiments including neutron scattering data. Our study suggests that many of the anomalous features observed in experiments have a natural interpretation in terms of a spin-1/2 defects (impurities) coupled to an underlying Kagome-type spin liquid.

cond-mat.str-el↗

arXiv2008

Disorder effects in the quantum kagome antiferromagnet ZnCu3(OH)6Cl2

The recent NMR experiments on ZnCu3(OH)6Cl2 motivate our study of the effect of non- magnetic defects on the antiferromagnetic spin-1/2 kagome lattice. We use exact diagonalization methods to study the effect of two such defects on finite size systems. Our results, obtained without adjustable parameters, are in good quantitative agreement with recent Oxygen 17 NMR data. They provide support for the experimental interpretation of the presence of defects within the kagome layers due to Zn/Cu substitutions. Our results also show that disorder effects become relevant at lower temperatures, raising questions about the experimental evidence for the absence of an intrinsic spin gap in the kagome 2D layers.

cond-mat.str-el↗

arXiv2008

Non-volatile resistive switching in dielectric superconductor YBCO

We report on the reversible, nonvolatile and polarity dependent resistive switching between superconductor and insulator states at the interfaces of a Au/YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO)/Au system. We show that the superconducting state of YBCO in regions near the electrodes can be reversibly removed and restored. The possible origin of the switching effect may be the migration of oxygen or metallic ions along the grain boundaries that control the intergrain superconducting coupling. Four-wire bulk resistance measurements reveal that the migration is not restricted to interfaces and produce significant bulk effects.

cond-mat.str-el↗

arXiv2007

A mechanism for unipolar resistance switching in oxide non-volatile memory devices

Building on a recently introduced model for non-volatile resistive switching, we propose a mechanism for unipolar resistance switching in metal-insulator-metal sandwich structures. The commutation from the high to low resistance state and back can be achieved with successive voltage sweeps of the same polarity. Electronic correlation effects at the metal-insulator interface are found to play a key role to produce a resistive commutation effect in qualitative agreement with recent experimental reports on binary transition metal oxide based sandwich structures.

cond-mat.other↗

arXiv2007

Mott transition in the Hubbard model away from particle-hole symmetry

We solve the Dynamical Mean Field Theory equations for the Hubbard model away from the particle-hole symmetric case using the Density Matrix Renormalization Group method. We focus our study on the region of strong interactions and finite doping where two solutions coexist. We obtain precise predictions for the boundaries of the coexistence region. In addition, we demonstrate the capabilities of this precise method by obtaining the frequency dependent optical conductivity spectra.

cond-mat.str-el↗

arXiv2006

Electronic state of a doped Mott-Hubbard insulator at finite temperatures studied using the dynamical mean-field theory

We study the electronic state of the doped Mott-Hubbard insulator within Dynamical Mean Field Theory. The evolution of the finite temperature spectral functions as a function of doping show large redistributions of spectral weight in both antiferromagnetic and paramagnetic phases. In particular, a metallic antiferromagnetic state is obtained with a low frequency Slater-splitted quasiparticle peak coexisting with Hubbard bands. In the high temperature paramagnetic metallic phase, upon reducing doping, the system has a crossover through a ``bad metal'' state characterized by an anomalous shift of the quasiparticle peak away from the Fermi energy. We find that the {\it charge} compressibility of the antiferromagnetic metal is dramatically enhanced upon approaching the second order Néel line.

cond-mat.str-el↗

arXiv2003

Melting transition of an Ising glass driven by magnetic field

The quantum critical behavior of the Ising glass in a magnetic field is investigated. We focus on the spin glass to paramagnet transition of the transverse degrees of freedom in the presence of finite longitudinal field. We use two complementary techniques, the Landau theory close to the T=0 transition and the exact diagonalization method for finite systems. This allows us to estimate the size of the critical region and characterize various crossover regimes. An unexpectedly small energy scale on the disordered side of the critical line is found, and its possible relevance to experiments on metallic glasses is briefly discussed.

cond-mat.str-el↗

arXiv2002

Quantum and thermal fluctuations in the SU(N) Heisenberg spin-glass model near the quantum critical point

We solve for the SU(N) Heisenberg spin-glass in the limit of large N focusing on small S and T. We study the effect of quantum and thermal fluctuations in the frequency dependent response function and observed interesting transfers of spectral weight. We compute the T-dependence of the order parameter and the specific heat and find an unusual T^2 behavior for the latter at low temperatures in the spin-glass phase. We find a remarkable qualitative agreement with various experiments on the quantum frustrated magnet SrCr_{9p}Ga_{12-9p}O_{19}.

cond-mat.str-el↗

arXiv2002

The infinite-range quantum random Heisenberg magnet

We study with exact diagonalization techniques the Heisenberg model for a system of SU(2) spins with S=1/2 and random infinite-range exchange interactions. We calculate the critical temperature T_g for the spin-glass to paramagnetic transition. We obtain T_g ~ 0.13, in good agreement with previous quantum Monte Carlo and analytical estimates. We provide a detailed picture for the different kind of excitations which intervene in the dynamical response chi''(w,T) at T=0 and analyze their evolution as T increases. We also calculate the specific heat Cv(T). We find that it displays a smooth maximum at TM ~ 0.25, in good qualitative agreement with experiments. We argue that the fact that TM>Tg is due to a quantum disorder effect.

cond-mat.str-el↗

arXiv2001

Compressibility Divergence and Mott Endpoints

In the context of the dynamical mean field theory of the Hubbard model, we study the compressibility near the density driven Mott transition at finite temperatures. We demonstrate this divergence using dynamical mean field theory and Quantum Monte Carlo simulations in the one band and the two band Hubbard model. We supplement this result with considerations based on the Landau theory framework and discuss the relevance of our results to the alpha-gamma endpoint in Cerium.

cond-mat.str-el↗

arXiv2001

Electronic structure of Ca$_{1-x}$Sr$_x$VO$_3$: a tale of two energy-scales

We investigate the electronic structure of Ca$_{1-x}$Sr$_x$VO$_3$ using photoemission spectroscopy. Core level spectra establish an electronic phase separation at the surface, leading to distinctly different surface electronic structure compared to the bulk. Analysis of the photoemission spectra of this system allowed us to separate the surface and bulk contributions. These results help us to understand properties related to two vastly differing energy-scales, namely the low energy-scale of thermal excitations (~$k_{B}T$) and the high-energy scale related to Coulomb and other electronic interactions.

cond-mat.str-el↗

arXiv2000

Landau Theory of the Finite Temperature Mott Transition

In the context of the dynamical mean-field theory of the Hubbard model, we identify microscopically an order parameter for the finite temperature Mott endpoint. We derive a Landau functional of the order parameter. We then use the order parameter theory to elucidate the singular behavior of various physical quantities which are experimentally accessible.

cond-mat.str-el↗

arXiv1999

The anomalous metallic ferromagnetic state of Sr doped manganites

We deduce a model relevant for the anomalous metallic state of Sr doped manganites at low temperatures within the ferromagnetic phase. It provides a natural explanation to several anomalous features observed experimentally, such as the vanishing Drude contribution in optical conductivity, the pseudo-gap in the density of states, an the unusual dispersion observed in photoemission.

cond-mat.str-el↗

arXiv1999

Non-Fermi Liquid Behavior in a Disordered Kondo Alloy Model

We study a mean-field model of a Kondo alloy using numerical techniques and analytic approximations. In this model, randomly distributed magnetic impurities interact with a band of conduction electrons and have a residual RKKY coupling of strength $J$. This system has a quantum critical point at $J=J_{c} \sim T_{K}^0$, the Kondo scale of the problem. The $T$ dependence of the spin susceptibility near the quantum critical point is singular with $χ(0)-χ(T) \propto T^γ$ and non-integer $γ$. At $J_{c}$, $γ= 3/4$. For $J\lesssim J_{c}$ there are two crossovers with decreasing $T$, first to $γ=3/2$ and then to $γ=2$, the Fermi-liquid value. The dissipative part of the time-dependent susceptibility $χ''(ω)\propto ω$ as $ω\to 0$ except at the quantum critical point where we find $χ''(ω) \propto \sqrtω$. The characteristic spin-fluctuation energy vanishes at the quantum critical point with $ω_{\rm sf} \sim (1-J/J_{c})$ for $J\lesssim J_{c}$, and $ω_{\rm sf} \propto T^{3/2}$ at the critical coupling.

cond-mat.str-el↗

arXiv1998

Band-width control in a perovskite-type 3d^1 correlated metal Ca_1-xSr_xVO_3. II. Optical spectroscopy investigation

Optical conductivity spectra of single crystals of Ca_1-xSr_xVO_3 have been studied to elucidate how the electronic behavior depends on the strength of the electron correlation without changing the nominal number of electrons per vanadium atom. The effective mass deduced by the analysis of the Drude-like contribution do not show critical enhancement, even though the system is close to the Mott transition. Besides the Drude-like contribution, two anomalous features were observed in the optical conductivity spectra of the intraband transition within the 3d band. These features can be assigned to transitions involving the incoherent and coherent bands near the Fermi level. The large spectral weight redistribution in this system, however, does not involve a large mass enhancement.

cond-mat.str-el↗