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Hyowon Park - One of the best experts on this subject based on the ideXlab platform.
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oxygen vacancy induced site selective Mott Transition in lanio 3
Physical Review B, 2021Co-Authors: Xingyu Liao, Hyowon Park, Vijay SinghAbstract:While defects such as oxygen vacancies in correlated materials can modify their electronic properties dramatically, understanding the microscopic origin of electronic correlations in materials with defects has been elusive. Lanthanum nickelate with oxygen vacancies, ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$, exhibits the metal-to-insulator Transition as the oxygen vacancy level $x$ increases from the stoichiometric ${\mathrm{LaNiO}}_{3}$. In particular, ${\mathrm{LaNiO}}_{2.5}$ exhibits a paramagnetic insulating phase, also stabilizing an antiferromagnetic state below ${T}_{N}\ensuremath{\simeq}152\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Here, we study the electronic structure and energetics of ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$ using first principles. We find that ${\mathrm{LaNiO}}_{2.5}$ exhibits a ``site-selective'' paramagnetic Mott insulating state at $T\ensuremath{\simeq}290\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ as obtained using density functional theory plus dynamical mean field theory ($\mathrm{DFT}+\mathrm{DMFT}$). The Ni octahedron site develops a Mott insulating state with strong correlations as the Ni ${e}_{g}$ orbital is half-filled while the Ni square-planar site with apical oxygen vacancies becomes a band insulator. Our oxygen vacancy results cannot be explained by the pure change of the Ni oxidation state alone within the rigid band-shift approximation. Our $\mathrm{DFT}+\mathrm{DMFT}$ density of states explains that the peak splitting of unoccupied states in ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$ measured by the experimental x-ray absorption spectra originates from two nonequivalent Ni ions in the vacancy-ordered structure.
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site selective Mott Transition in rare earth element nickelates
Physical Review Letters, 2012Co-Authors: Hyowon Park, A J Millis, Chris A MarianettiAbstract:A combination of density functional and dynamical mean field theory calculations are used to show that the remarkable metal-insulator Transition in the rare-earth-element nickelate perovskites arises from a site-selective Mott phase, in which the d electrons on half of the Ni ions are localized to form a fluctuating moment while the d electrons on other Ni ions form a singlet with holes on the surrounding oxygen ions. The calculation reproduces key features observed in the nickelate materials, including an insulating gap in the paramagnetic state, a strong variation of static magnetic moments among Ni sites and an absence of charge order. A connection between structure and insulating behavior is documented. The site-selective Mott Transition may be a more broadly applicable concept in the description of correlated materials.
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cluster dynamical mean field theory of the Mott Transition
Physical Review Letters, 2008Co-Authors: Hyowon Park, Kristjan Haule, Gabriel KotliarAbstract:We address the nature of the Mott Transition in the Hubbard model at half-filling using cluster dynamical mean field theory (DMFT). We compare cluster-DMFT results with those of single-site DMFT. We show that inclusion of the short-range correlations on top of the on-site correlations does not change the order of the Transition between the paramagnetic metal and the paramagnetic Mott insulator, which remains first order. However, the short range correlations reduce substantially the critical U and modify the shape of the Transition lines. Moreover, they lead to very different physical properties of the metallic and insulating phases near the Transition point. Approaching the Transition from the metallic side, we find an anomalous metallic state with very low coherence scale. The insulating state is characterized by the narrow Mott gap with pronounced peaks at the gap edge.
Massimo Capone - One of the best experts on this subject based on the ideXlab platform.
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two particle fermi liquid parameters at the Mott Transition vertex divergences landau parameters and incoherent response in dynamical mean field theory
arXiv: Strongly Correlated Electrons, 2018Co-Authors: Friedrich Krien, Erik G C P Van Loon, M I Katsnelson, A I Lichtenstein, Massimo CaponeAbstract:We consider the interaction-driven Mott Transition at zero temperature from the viewpoint of microscopic Fermi liquid theory. To this end, we derive an exact expression for the Landau parameters within the dynamical mean-field theory (DMFT) approximation to the single-band Hubbard model. At the Mott Transition the symmetric and the anti-symmetric Landau parameter diverge. The vanishing compressibility at the Mott Transition directly implies the divergence of the forward scattering amplitude in the charge sector, which connects the proximity of the Mott phase to a tendency towards phase separation. We verify the expected behavior of the Landau parameters in a DMFT application to the Hubbard model on the triangular lattice at finite temperature. Exact conservation laws and the Ward identity are crucial to capture vertex divergences related to the Mott Transition. We furthermore generalize Leggett's formula for the static susceptibility of the Fermi liquid to the static fermion-boson response function. In the charge sector the limits of small transferred momentum and frequency of this response function commute at the Mott Transition.
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correlation driven lifshitz Transition and orbital order in a two band hubbard model
Physical Review B, 2018Co-Authors: F Grandi, Massimo Capone, A Amaricci, Michele FabrizioAbstract:We study by dynamical mean field theory a quarter-filled Hubbard model of two bands with different bandwidths. At half-filling, this model is known to display an orbital selective Mott Transition, with the narrower band undergoing Mott localisation while the wider one being still itinerant. At quarter-filling, the physical behaviour is different and to some extent reversed. The interaction generates an effective crystal field splitting, absent in the Hamiltonian, that tends to empty the narrower band in favour of the wider one, which also become more correlated than the former at odds with the orbital selective paradigm. Upon increasing the interaction, the depletion of the narrower band can continue till it empties completely and the system undergoes a topological Lifshitz Transition into a half-filled single-band metal that eventually turns insulating. Alternatively, when the two bandwidths are not too different, a first order Mott Transition intervenes before the Lifshitz's one. The properties of the Mott insulator are significantly affected by the interplay between spin and orbital degrees of freedom.
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orbital selective Mott Transition out of band degeneracy lifting
Physical Review Letters, 2009Co-Authors: Luca De Medici, Massimo Capone, S R Hassan, Xi DaiAbstract:We outline a general mechanism for orbital-selective Mott Transition, the coexistence of both itinerant and localized conduction electrons, and show how it can take place in a wide range of realistic situations, even for bands of identical width and correlation, provided a crystal field splits the energy levels in manifolds with different degeneracies and the exchange coupling is large enough to reduce orbital fluctuations. The mechanism relies on the different kinetic energy in manifolds with different degeneracy. This phase has Curie-Weiss susceptibility and non-Fermi-liquid behavior, which disappear at a critical doping, all of which is reminiscent of the physics of the pnictides.
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dynamical behavior across the Mott Transition of two bands with different bandwidths
Physical Review B, 2005Co-Authors: Michel Ferrero, Michele Fabrizio, Federico Becca, Massimo CaponeAbstract:We investigate the role of the bandwidth difference in the Mott metal-insulator Transition of a two-band Hubbard model in the limit of infinite dimensions by means of a Gutzwiller variational wave function as well as by dynamical mean-field theory. The variational calculation predicts a two-stage quenching of the charge degrees of freedom, in which the narrower band undergoes a Mott Transition before the wider one, both in the presence and in the absence of a Hund's exchange coupling. However, this scenario is not fully confirmed by the dynamical mean-field theory calculation, which shows that, although the quasiparticle residue of the narrower band is zero within our numerical accuracy, low-energy spectral weight still exists inside the Mott-Hubbard gap, concentrated into two peaks symmetric around the chemical potential. This spectral weight vanishes only when the wider band ceases to conduct too. Although our results are compatible with several scenarios\char22{}e.g., a narrow-gap semiconductor or a semimetal\char22{}we argue that the most plausible one is that the two peaks coexist with a narrow resonance tied at the chemical potential, with a spectral weight below our numerical accuracy. This quasiparticle resonance is expected to vanish when the wider band undergoes the Mott Transition.
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phase separation close to the density driven Mott Transition in the hubbard holstein model
Physical Review Letters, 2004Co-Authors: Massimo Capone, G Sangiovanni, C Castellani, C Di Castro, M GrilliAbstract:: The density-driven Mott Transition is studied by means of dynamical mean-field theory in the Hubbard-Holstein model, where the Hubbard term leading to the Mott Transition is supplemented by an electron-phonon (e-ph) term. We show that an intermediate e-ph coupling leads to a first-order Transition at T=0, which is accompanied by a phase separation between a metal and an insulator. The compressibility in the metallic phase is substantially enhanced. At quite larger values of the coupling, a polaronic phase emerges coexisting with a nonpolaronic metal.
Kazushi Kanoda - One of the best experts on this subject based on the ideXlab platform.
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electronic griffiths phase in disordered Mott Transition systems
Physical Review Letters, 2020Co-Authors: Riku Yamamoto, Tetsuya Furukawa, Kazuya Miyagawa, T Sasaki, Kazushi Kanoda, T ItouAbstract:Solid-state physics and soft-matter physics have been developed independently, with little mutual exchange of the underlying physical concepts. However, after many studies of correlated electron systems, it has been recognized that correlated electrons (especially in Mott-Transition systems) in solid matter sometimes show behavior similar to "structured fluids" in soft matter; that is, the electrons exhibit long-length self-organization (but without long-range order) and slow dynamics, which is inevitable for the long-length structures. The essential question is this: what condition causes such behavior in solid matter? We focused on an organic Mott-Transition system and demonstrated that the electrons of this system fluctuate very slowly only when the following two factors are met simultaneously: (i) the electronic system is on the metal and Mott-insulator boundary and (ii) the system is subject to quenched disorder. This electronic state with slow dynamics under this condition can be explained by the concept of the "(electronic) Griffiths phase." This concept will potentially be a key in connecting solid-state physics with soft-matter physics.
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pressure induced Mott Transition in an organic superconductor with a finite doping level
Physical Review Letters, 2015Co-Authors: Hiroshi Oike, Kazuya Miyagawa, Hiromi Taniguchi, Kazushi KanodaAbstract:We report the pressure study of a doped organic superconductor with a Hall coefficient and conductivity measurements. We find that maximally enhanced superconductivity and a marginal-Fermi liquid appear around a certain pressure where mobile carriers increase critically, suggesting a possible quantum phase Transition between strongly and weakly correlated regimes. This observation points to the presence of a criticality in Mottness for a doped Mott insulator with tunable correlation.
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Mott Transition from a spin liquid to a fermi liquid in the spin frustrated organic conductor kappa et 2cu2 cn 3
Physical Review Letters, 2005Co-Authors: Yosuke Kurosaki, Kazuya Miyagawa, Kazushi Kanoda, Yasuhiro Shimizu, G SaitoAbstract:The pressure-temperature phase diagram of the organic Mott insulator kappa-(ET)2Cu2(CN)3, a model system of the spin liquid on triangular lattice, has been investigated by 1H NMR and resistivity measurements. The spin-liquid phase is persistent before the Mott Transition to the metal or superconducting phase under pressure. At the Mott Transition, the spin fluctuations are rapidly suppressed and the Fermi-liquid features are observed in the temperature dependence of the spin-lattice relaxation rate and resistivity. The characteristic curvature of the Mott boundary in the phase diagram highlights a crucial effect of the spin frustration on the Mott Transition.
Michele Fabrizio - One of the best experts on this subject based on the ideXlab platform.
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correlation driven lifshitz Transition and orbital order in a two band hubbard model
Physical Review B, 2018Co-Authors: F Grandi, Massimo Capone, A Amaricci, Michele FabrizioAbstract:We study by dynamical mean field theory a quarter-filled Hubbard model of two bands with different bandwidths. At half-filling, this model is known to display an orbital selective Mott Transition, with the narrower band undergoing Mott localisation while the wider one being still itinerant. At quarter-filling, the physical behaviour is different and to some extent reversed. The interaction generates an effective crystal field splitting, absent in the Hamiltonian, that tends to empty the narrower band in favour of the wider one, which also become more correlated than the former at odds with the orbital selective paradigm. Upon increasing the interaction, the depletion of the narrower band can continue till it empties completely and the system undergoes a topological Lifshitz Transition into a half-filled single-band metal that eventually turns insulating. Alternatively, when the two bandwidths are not too different, a first order Mott Transition intervenes before the Lifshitz's one. The properties of the Mott insulator are significantly affected by the interplay between spin and orbital degrees of freedom.
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dynamical behavior across the Mott Transition of two bands with different bandwidths
Physical Review B, 2005Co-Authors: Michel Ferrero, Michele Fabrizio, Federico Becca, Massimo CaponeAbstract:We investigate the role of the bandwidth difference in the Mott metal-insulator Transition of a two-band Hubbard model in the limit of infinite dimensions by means of a Gutzwiller variational wave function as well as by dynamical mean-field theory. The variational calculation predicts a two-stage quenching of the charge degrees of freedom, in which the narrower band undergoes a Mott Transition before the wider one, both in the presence and in the absence of a Hund's exchange coupling. However, this scenario is not fully confirmed by the dynamical mean-field theory calculation, which shows that, although the quasiparticle residue of the narrower band is zero within our numerical accuracy, low-energy spectral weight still exists inside the Mott-Hubbard gap, concentrated into two peaks symmetric around the chemical potential. This spectral weight vanishes only when the wider band ceases to conduct too. Although our results are compatible with several scenarios\char22{}e.g., a narrow-gap semiconductor or a semimetal\char22{}we argue that the most plausible one is that the two peaks coexist with a narrow resonance tied at the chemical potential, with a spectral weight below our numerical accuracy. This quasiparticle resonance is expected to vanish when the wider band undergoes the Mott Transition.
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nontrivial fixed point in a twofold orbitally degenerate anderson impurity model
Physical Review Letters, 2003Co-Authors: Michele Fabrizio, A F Ho, Giuseppe SantoroAbstract:We study a twofold orbitally degenerate Anderson impurity model which shows a nontrivial fixed point similar to that of the two-impurity Kondo model, but remarkably more robust, as it can only be destabilized by orbital- or gauge-symmetry breaking. The impurity model is interesting per se, but here our interest is rather in the possibility that it might be representative of a strongly correlated lattice model close to a Mott Transition. We argue that this lattice model should unavoidably encounter the nontrivial fixed point just before the Mott Transition and react to its instability by spontaneous generation of an orbital, spin-orbital or superconducting order parameter.
Igor N Karnaukhov - One of the best experts on this subject based on the ideXlab platform.
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Mott Transition in two band fermion model with on site coulomb repulsion
Annals of Physics, 2020Co-Authors: Igor N KarnaukhovAbstract:Abstract We provide analytical and numerical solutions of the two band fermion model with on-site Coulomb at half filling. In limiting cases for generate bands and one flat band, the model reduces to the Hubbard and Falicov–Kimball models, respectively. We have shown that the insulator state emerges at half filling due to hybridization of fermions of different bands with momenta k and k + π . Such hybridization breaks the conservation of the number of particles in each band, the Mott Transition is a consequence of spontaneous symmetry breaking. A gap in the spectrum is calculated depending on the magnitude of on-site Coulomb repulsion and the width of the band for the chain, as well as for square and cubic lattices. The proposed approach allows us to describe the formation of the gap in the fermion spectra in the Hubbard and Falicov–Kimball models within the framework of the same mechanism for an arbitrary dimension of the system.
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Mott Transition in two band fermion model with on site coulomb repulsion
arXiv: Strongly Correlated Electrons, 2020Co-Authors: Igor N KarnaukhovAbstract:We provide analytical and numerical solution of the two band fermion model with on-site Coulomb at half filling. In limiting cases for generate bands and one flat band, the model reduces to the Hubbard and Falikov-Kimball models, respectively. We have shown that the insulator state emerges at half filling due to hybridization of fermions of different bands with momenta $\text{k}$ and $\text{k}+\pi$. Such hybridization breaks the conservation of the number of particles in each band, the Mott Transition is a consequence of spontaneous symmetry breaking. A gap in the spectrum is calculated depending on the magnitude of on-site Coulomb repulsion and the width of the band for the chain, as well as for square and cubic lattices. The proposed approach allows us to describe the formation of the gap in the fermion spectra in the Hubbard and Falikov-Kimball models within the framework of the same mechanism for an arbitrary dimension of the system.