arXiv subjects

Gabriel Kotliar

Publications and source records attributed to Gabriel Kotliar.

At least 91 records · Page 5Linked to original sources

arXiv2016

Fermi surface topology and negative longitudinal magnetoresistance observed in centrosymmetric NbAs2 semimetal

We report transverse and longitudinal magneto-transport properties of NbAs2 single crystals. Attributing to the electron-hole compensation, non-saturating large transverse magnetoresistance reaches up to 8000 at 9 T at 1.8 K with mobility around 1 to 2 m^2V^-1S^-1. We present a thorough study of angular-dependent Shubnikov-de Haas (SdH) quantum oscillations of NbAs2. Three distinct oscillation frequencies are identified. First-principles calculations reveal four types of Fermi pockets: electron alpha pocket, hole beta pocket, hole gamma pocket and small electron delta pocket. Although the angular dependence of alpha, beta and delta agree well with the SdH data, it is unclear why the gamma pocket is missing in SdH. Negative longitudinal magnetoresistance is observed which may be linked to novel topological states in this material, although systematic study is necessary to ascertain its origin.

cond-mat.str-el↗

arXiv2015

Mott transition in a metallic liquid - Gutzwiller molecular dynamics simulations

We present a formulation of quantum molecular dynamics that includes electron correlation effects via the Gutzwiller method. Our new scheme enables the study of the dynamical behavior of atoms and molecules with strong electron interactions. The Gutzwiller approach goes beyond the conventional mean-field treatment of the intra-atomic electron repulsion and captures crucial correlation effects such as band narrowing and electron localization. We use Gutzwiller quantum molecular dynamics to investigate the Mott transition in the liquid phase of a single-band metal and uncover intriguing structural and transport properties of the atoms.

cond-mat.str-el↗

arXiv2015

Gutzwiller Renormalization Group

We develop a variational scheme called "Gutzwiller renormalization group" (GRG), which enables us to calculate the ground state of Anderson impurity models (AIM) with arbitrary numerical precision. Our method can exploit the low-entanglement property of the ground state in combination with the framework of the Gutzwiller wavefunction, and suggests that the ground state of the AIM has a very simple structure, which can be represented very accurately in terms of a surprisingly small number of variational parameters. We perform benchmark calculations of the single-band AIM that validate our theory and indicate that the GRG might enable us to study complex systems beyond the reach of the other methods presently available and pave the way to interesting generalizations, e.g., to nonequilibrium transport in nanostructures.

cond-mat.str-el↗

arXiv2015

Electric-field-driven resistive switching in dissipative Hubbard model

We study how strongly correlated electrons on a dissipative lattice evolve from equilibrium when driven by a constant electric field, focusing on the extent of the linear regime and hysteretic non-linear effects at higher fields. We access the non-equilibrium steady states, non-perturbatively in both the field and the electronic interactions, by means of a non-equilibrium dynamical mean-field theory in the Coulomb gauge. The linear response regime is limited by Joule heating effects and breaks down at fields orders of magnitude smaller than the quasi-particle energy scale. For large electronic interactions, strong but experimentally accessible electric fields can induce a resistive switching by driving the strongly correlated metal into a Mott insulator. Hysteretic $I$-$V$ curves suggest that the non-equilibrium current is carried through a spatially inhomogeneous metal-insulator mixed state.

cond-mat.str-el↗

arXiv2015

Electronic structure and energetics of praseodymium and $α$-plutonium under pressure

We develop a new implementation of the Gutzwiller approximation (GA) and interface it with the local density approximation (LDA). This formulation enables us to study complex $4f$ and $5f$ systems. We perform calculations of praseodymium and $α$-plutonium under pressure, which compare very well with the experiments. Our study of praseodymium indicates that both structure change and $f$-delocalization are important to obtain the correct phase diagram and, in particular, the pressure-induced volume-collapse transition. Our calculations of $α$-plutonium indicate that, even though the $f$ electrons are delocalized in this phase, the electron-correlations affect substantially its electronic structure and thermodynamical properties.

cond-mat.str-el↗

arXiv2015

Finite-Temperature Gutzwiller Approximation from Time-Dependent Variational Principle

We develop an extension of the Gutzwiller approximation to finite temperatures based on the Dirac-Frenkel variational principle. Our method does not rely on any entropy inequality, and is substantially more accurate than the approaches proposed in previous works. We apply our theory to the single-band Hubbard model at different fillings, and show that our results compare quantitatively well with dynamical mean field theory in the metallic phase. We discuss potential applications of our technique within the framework of first principle calculations.

cond-mat.str-el↗

arXiv2015

Transport properties of Metallic Ruthenates: a DFT+DMFT investigation

We present a systematical theoretical study on the transport properties of an archetypal family of Hund's metals, Sr$_2$RuO$_4$,Sr$_3$Ru$_2$O$_7$, SrRuO$_3$ and CaRuO$_3$, within the combination of first principles density functional theory and dynamical mean field theory. The agreement between theory and experiments for optical conductivity and resistivity is good, which indicates that electron-electron scattering dominates the transport of ruthenates. We demonstrate that in the single-site dynamical mean field approach the transport properties of Hund's metals fall into the scenario of "resilient quasiparticles". We explains why the single layered compound Sr$_2$RuO$_4$ has a relative weak correlation with respect to its siblings, which corroborates its good metallicity.

cond-mat.str-el↗

arXiv2015

Guided design of copper oxysulfide superconductors

We describe a framework for designing novel materials, combining modern first-principles electronic structure tools, materials databases, and evolutionary algorithms capable of exploring large configurational spaces. Guided by the chemical principles introduced by Antipov, \emph{et. al.}, for the design and synthesis of the Hg-based high-temperature superconductors, we apply our framework to design a new layered copper oxysulfide, Hg(CaS)$_2$CuO$_2$. We evaluate the prospects of superconductivity in this oxysulfide using theories based on charge-transfer energies, orbital distillation and uniaxial strain.

cond-mat.mtrl-sci↗

arXiv2015

Analytic theory of Hund's metals: a renormalization group perspective

We study the emergence of quasiparticles in Hund's metals with an SU($M$)$\times$SU($N$)-symmetric Kondo impurity model carrying both spin and orbital degrees of freedom. We show that the coupling of the impurity spin to the conduction electrons can be \emph{ferromagnetic}, notably for hole-doped iron pnictides. We derive the weak-coupling renormalization group (RG) equations for arbitrary representations of SU($M$)$\times$SU($N$). A ferromagnetic spin coupling results in a protracted RG flow, accounting for the surprising particle-hole asymmetry that is observed in the iron-pnictide systems. We establish the low coherence scale $T_{\rm K}$ which depends on the filling through the impurity representation. We also discuss the temperature dependence of the spin and orbital susceptibilities. Finally, we argue that this mechanism explains the strong valence dependence of the coherence scale observed in dilute transition-metal magnetic alloys.

cond-mat.str-el↗

arXiv2014

Covalency in transition metal oxides within all-electron Dynamical Mean Field Theory

A combination of dynamical mean field theory and density functional theory, as implemented in Phys. Rev. B 81, 195107 (2010), is applied to both the early and late transition metal oxides. For fixed value of the local Coulomb repulsion, without fine tuning, we obtain the main features of these series, such as the metallic character of SrVO$_3$ and the the insulating gaps of LaVO$_3$, LaTiO$_3$ and La$_2$CO$_4$ which are in good agreement with experiment. The study highlights the importance of local physics and high energy hybridization in the screening of the Hubbard interaction and how different low energy behaviors can emerge from the a unified treatment of the transition metal series.

cond-mat.str-el↗

arXiv2014

Interplay of spin-orbit and entropic effects in Cerium

We perform first-principle calculations of elemental cerium and compute its pressure-temperature phase diagram, finding good quantitative agreement with the experiments. Our calculations indicate that, while a signature of the volume-collapse transition appears in the free energy already at low temperatures, at larger temperatures this signature is enhanced because of the entropic effects, and originates an actual thermodynamical instability. Furthermore, we find that the catalyst determining this feature is --- in all temperature regimes --- a pressure-induced effective reduction of the $f$-level degeneracy due to the spin-orbit coupling. Our analysis suggests also that the lattice vibrations might be crucial in order to capture the behavior of the pressure-temperature transition line at large temperatures.

cond-mat.str-el↗

arXiv2014

Energetics and Electronic Structure of Plutonium

Plutonium is the most exotic and mysterious element in the periodic table. It has 6 metallic phases and peculiar physical properties not yet understood. One of the most intriguing properties of Pu is that relatively small changes of temperature can induce transitions between different structures, that are accompanied by very large changes of equilibrium volumes. This fact has stimulated extensive theoretical and experimental studies. In spite of this, a convincing explanation of the metallurgic properties of Pu based on fundamental principles is still lacking, and none of the previous theories has been able to describe simultaneously the energetics and the $f$ electronic structure of all of the phases of Pu on the same footing. Here we provide a bird's eye view of Pu by studying the zero-temperature pressure-volume phase diagram and the $f$ electronic structure of all of its crystalline phases from first principles. In particular, we clarify the way in which the $f$-electron correlations determine its unusual energetics. Our theoretical energetics and ground-state $f$ electronic structure are both in good quantitative agreement with the experiments.

cond-mat.str-el↗

arXiv2014

Shining light on transition metal oxides: unveiling the hidden Fermi Liquid

We use low energy optical spectroscopy and first principles LDA+DMFT calculations to test the hypothesis that the anomalous transport properties of strongly correlated metals originate in the strong temperature dependence of their underlying resilient quasiparticles. We express the resistivity in terms of an effective plasma frequency $ω_p^*$ and an effective scattering rate $ 1/τ^*_{tr}$. We show that in the archetypal correlated material V2O3, $ω_p^*$ increases with increasing temperature, while the plasma frequency from partial sum rule exhibits the opposite trend . $ 1/τ^*_{tr}$ has a more pronounced temperature dependence than the scattering rate obtained from the extended Drude analysis. The theoretical calculations of these quantities are in quantitative agreement with experiment. We conjecture that these are robust properties of all strongly correlated metals, and test it by carrying out a similar analysis on thin film NdNiO3 on LaAlO3 substrate.

cond-mat.str-el↗

arXiv2013

Highly Dispersive Electron Relaxation and Colossal Thermoelectricity in the Correlated Semiconductor FeSb$_2$

We show that the colossal thermoelectric power, $S(T)$, observed in the correlated semiconductor FeSb$_2$ below 30\,K is accompanied by a huge Nernst coefficient $ν(T)$ and magnetoresistance MR$(T)$. Markedly, the latter two quantities are enhanced in a strikingly similar manner. While in the same temperature range, $S(T)$ of the reference compound FeAs$_2$, which has a seven-times larger energy gap, amounts to nearly half of that of FeSb$_2$, its $ν(T)$ and MR$(T)$ are intrinsically different to FeSb$_2$: they are smaller by two orders of magnitude and have no common features. With the charge transport of FeAs$_2$ successfully captured by the density functional theory, we emphasize a significantly dispersive electron-relaxation time $τ(ε_k)$ due to electron-electron correlations to be at the heart of the peculiar thermoelectricity and magnetoresistance of FeSb$_2$.

cond-mat.str-el↗

arXiv2013

Principle of Maximum Entanglement Entropy and Local Physics of Correlated many-body Electron-Systems

We argue that, because of the quantum-entanglement, the local physics of the strongly-correlated materials at zero temperature is described in very good approximation by a simple generalized Gibbs distribution, which depends on a relatively small number local quantum thermodynamical potentials. We demonstrate that our statement is exact in certain limits, and we perform numerical calculations of the iron compounds FeSe and FeTe and of the elemental cerium by employing the Gutzwiller Approximation (GA) that strongly support our theory in general.

cond-mat.str-el↗

arXiv2013

Plutonium hexaboride is a correlated topological insulator

We predict that plutonium hexaboride (PuB6) is a strongly correlated topological insulator, with Pu in an intermediate valence state of Pu^2.7+ . Within the combination of dynamical mean field theory and density functional theory, we show that PuB6 is an insulator in the bulk, with non-trivial Z2 topological invariants. Its metallic surface states have large Fermi pocket at X Dirac cones inside the bulk derived electronic states causing a large surface thermal conductivity. PuB6 has also a very high melting temperature therefore it has ideal solid state properties for a nuclear fuel material.

cond-mat.str-el↗

arXiv2013

Observation of antiferromagnetic order collapse in the pressurized insulator LaMnPO

The emergence of superconductivity in the iron pnictide and cuprate high temperature superconductors usually accompanies the suppression of an antiferromagnetically (AFM) ordered state in a corresponding parent compound through the use of chemical doping or external pressure1-5. A great deal of effort has been made to find superconductivity in Mn-based compounds6-14, which are thought to bridge the gap between the two families of high temperature superconductors7,15,16, but long-ranged AFM order was not successfully suppressed via chemical doping in these investigations. Here we report the first observation of the pressure-induced elimination of long-ranged AFM order in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor15,17. By combining in-situ high pressure resistance and ac susceptibility measurements, we found that LaMnPO undergoes a crossover from an AFM insulating to an AFM metallic state at a pressure ~20 GPa and that the long-ranged AFM order collapses at a higher pressure ~32 GPa. Our findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.

cond-mat.supr-con↗

arXiv2013

The $γ$-$α$ iso-structural Transition in Cerium, a Critical Element

Below the critical temperature $T_c\simeq 600 K$, an iso-structural transition, named $γ$-$α$ transition,can be induced in Cerium by applying pressure. This transition is first-order, and is accompanied by a sizable volume collapse. A conclusive theoretical explanation of this intriguing phenomenon has still not been achieved, and the physical pictures proposed so far are still under debate. In this work, we illustrate zero-temperature first-principle calculations which clearly demonstrate that the $γ$-$α$ transition is induced by the interplay between the electron-electron Coulomb interaction and the spin-orbit coupling. We address the still unresolved problem on the existence of a second low-$T$ critical point, i.e., whether the energetic effects alone are sufficient or not to induce the $γ$-$α$ transition at zero temperature.

cond-mat.str-el↗