Showing papers on "Mott transition published in 2004"
TL;DR: Signs for increased fluctuations characteristic for 1D trapped Bose gases are observed and the collective oscillations cease near the transition to the Mott insulator phase.
Abstract: We study 1D trapped Bose gases in the strongly interacting regime. The systems are created in an optical lattice and are subject to a longitudinal periodic potential. Bragg spectroscopy enables us to investigate the excitation spectrum in different regimes. In the superfluid phase a broad continuum of excitations is observed which calls for an interpretation beyond the Bogoliubov spectrum taking into account the effect of strong interactions. In the Mott insulating phase a discrete spectrum is measured. Both phases are compared to the 3D situation and to the crossover regime from 1D to 3D. The coherence length and coherent fraction of the gas are measured in all configurations. We observe signatures for increased fluctuations characteristic for 1D systems. Moreover, the collective oscillations cease near the transition to the Mott insulator phase.
783 citations
TL;DR: When holes of about 0.018% are induced into a conduction band (breakdown of critical on-site Coulomb energy), an abrupt first-order Mott metal-insulator transition (MIT) was observed on an inhomogeneous VO2 film, a strongly correlated Mott insulator.
Abstract: When holes of about 0.018% are induced into a conduction band (breakdown of critical on-site Coulomb energy), an abrupt first-order Mott metal–insulator transition (MIT) rather than a continuous Hubbard MIT near a critical on-site Coulomb energy U/Uc=1, where U is on-site Coulomb energy between electrons, is observed on an inhomogeneous VO2 film, a strongly correlated Mott insulator. As a result, discontinuous jumps of the density of states on the Fermi surface are observed and inhomogeneity inevitably occurs. The off-current and temperature dependences of the abrupt MIT in a two-terminal device and the gate effect in a three-terminal device are clear evidence that the abrupt Mott MIT was induced by the excitation of holes. Raman spectra measured by a micro-Raman system show an MIT without the structural phase transition. Moreover, the magnitude of the observed jumps ΔJobserved at the abrupt MIT is an average over an inhomogeneous measurement region of the maximum true jump, ΔJtrue, deduced from the Brinkman–Rice picture. A brief discussion of whether VO2 is a Mott insulator or a Peierls insulator is presented.
437 citations
TL;DR: The interplay of correlation effects and cation covalency (GdFeO3-type distortions) is found to suppress orbital fluctuations in LaTiO3 and even more in Y TiO3, and to favor the transition to the insulating state.
Abstract: Using t(2g) Wannier functions, a low-energy Hamiltonian is derived for orthorhombic 3d(1) transition-metal oxides. Electronic correlations are treated with a new implementation of dynamical mean-field theory for noncubic systems. Good agreement with photoemission data is obtained. The interplay of correlation effects and cation covalency (GdFeO3-type distortions) is found to suppress orbital fluctuations in LaTiO3 and even more in YTiO3, and to favor the transition to the insulating state.
350 citations
TL;DR: In this article, the stability of itinerant quasiparticle states in two-band Hubbard models with different bandwidths was investigated and it was shown that separate Mott transitions occur at different Coulomb interaction strengths in general, which merge to a single transition under special conditions.
Abstract: We investigate the Mott transitions in two-band Hubbard models with different bandwidths. Applying dynamical mean field theory, we discuss the stability of itinerant quasiparticle states in each band. We demonstrate that separate Mott transitions occur at different Coulomb interaction strengths in general, which merge to a single transition only under special conditions. This kind of behavior may be relevant for the physics of the single-layer ruthenates, Ca2-xSrxRuO4.
213 citations
TL;DR: In this paper, the multiorbital Hubbard model is expressed in terms of quantum phase variables conjugate to the local charge, and of auxiliary fermions, providing an economical representation of the Hilbert space of strongly correlated systems.
Abstract: The multiorbital Hubbard model is expressed in terms of quantum phase variables (``slave rotors'') conjugate to the local charge, and of auxiliary fermions, providing an economical representation of the Hilbert space of strongly correlated systems. When the phase variables are treated in a local mean-field manner, similar results to the dynamical mean-field theory are obtained, namely a Brinkman-Rice transition at commensurate fillings together with a ``preformed'' Mott gap in the single-particle density of states. The slave-rotor formalism allows to go beyond the local description and take into account spatial correlations, following an analogy to the superfluid-insulator transition of bosonic systems. We find that the divergence of the effective mass at the metal-insulator transition is suppressed by short range magnetic correlations in finite-dimensional systems. Furthermore, the strict separation of energy scales between the Fermi-liquid coherence scale and the Mott gap, found in the local picture, holds only approximately in finite dimensions, due to the existence of low-energy collective modes related to zero-sound.
204 citations
TL;DR: The possibility of creating and controlling an ideal and trimerized optical Kagomé lattice is demonstrated, and the low temperature physics of various atomic gases in such lattices are studied.
Abstract: We demonstrate the possibility of creating and controlling an ideal and trimerized optical Kagom\'e lattice, and study the low temperature physics of various atomic gases in such lattices. In the trimerized Kagom\'e lattice, a Bose gas exhibits a Mott transition with fractional filling factors, whereas a spinless interacting Fermi gas at $2/3$ filling behaves as a quantum magnet on a triangular lattice. Finally, a Fermi-Fermi mixture at half-filling for both components represents a frustrated quantum antiferromagnet with a resonating-valence-bond ground state and quantum spin liquid behavior dominated by a continuous spectrum of singlet and triplet excitations. We discuss the method of preparing and observing such a quantum spin liquid employing molecular Bose condensates.
172 citations
TL;DR: Density functional theory calculations on large supercells demonstrate that for dilute Li-vacancy concentrations, the vacancy binds a hole and forms impurity states yielding a Mott insulator.
Abstract: Despite many years of experimental searches for a first-order Mott transition in crystalline-doped semiconductors, none have been found Extensive experimental work has characterized a first-order metal-insulator transition in Li(x)CoO(2), the classic material for rechargeable Li batteries, with a metallic state for x 095 Using density functional theory calculations on large supercells, we identify the mechanism of this hereto anomalous metal-insulator transition as a Mott transition of impurities Density functional theory demonstrates that for dilute Li-vacancy concentrations, the vacancy binds a hole and forms impurity states yielding a Mott insulator The unique feature of Li(x)CoO(2) as compared with traditional doped semiconductors, such as Si:P, is the high mobility of the Li vacancies, which allows them to rearrange into two distinct phases at the temperature of the metal-insulator transition
161 citations
TL;DR: This analysis implies that the lowest-energy transitions around 2 eV are intersite d-d transitions, and that LaMnO3 is a Mott-Hubbard insulator.
Abstract: Spectral ellipsometry is used to determine the dielectric function of an untwinned crystal of LaMnO3 in the range 0.5-5.6 eV at temperatures 50
131 citations
123 citations
TL;DR: In this article, a review of the state of the art on the studies for understanding physics contained in the properties of the perovskite titanates is presented, which allows the single-band descriptions of the ground-state and the low-energy electronic structures as a good starting point.
Abstract: Titanate compounds have been recognized as key materials for understanding the coupling of magnetism and orbitals in strongly correlated electron systems. In the perovskite Ti oxide RTiO3 (where R represents the trivalent rare-earth ions), which is a typical Mott?Hubbard insulator, the Ti t2g orbitals and spins in the 3d1 state couple each other through the strong electron correlations, resulting in a rich variety of orbital?spin phases. One way of controlling the coupling is to change the tiltings of the TiO6 octahedra (namely the GdFeO3-type distortion) by varying the R ions, through which the relative ratio of the electron bandwidth to the Coulomb interaction is controlled. With this control, these Mott insulators exhibit an antiferromagnetic-to-ferromagnetic (AFM?FM) phase transition, which has turned out to be a consequence of rich orbital physics in these materials. The origin and nature of orbital?spin structures of these Mott insulators have been intensively studied both experimentally and theoretically. When the Mott insulators are doped with carriers, the titanates show touchstone properties of the filling controlled Mott transition. In this paper, we first review the state of the art on the studies for understanding physics contained in the properties of the perovskite titanates. On the properties of the insulators, we focus on the following three topics: (1) the origin and nature of the ferromagnetism as well as the orbital ordering in the compounds with relatively small R ions such as GdTiO3 and YTiO3, (2) the origin of the G-type antiferromagnetism and the orbital state in LaTiO3 and (3) the orbital?spin structures in other AFM(G) compounds with relatively large R ions (R = Ce, Pr, Nd and Sm). On the basis of these discussions, we discuss the whole phase diagram together with mechanisms of the magnetic phase transition. On the basis of the microscopic understanding of the orbital?spin states, we show that the Ti t2g degeneracy is inherently lifted in the titanates, which allows the single-band descriptions of the ground-state and the low-energy electronic structures as a good starting point. Our analyses indicate that these compounds offer good touchstone materials described by the single-band Hubbard model on the cubic lattice. From this insight, we also re-analyse the hole-doped titanates TiO3 (where A represents the divalent alkaline-earth ions). Experimentally revealed filling- and bandwidth-dependent properties and the critical behaviour of the metal?insulator transitions are discussed in the light of theories based on the single-band Hubbard models.
112 citations
TL;DR: The Mott transition in a quasi-two-dimensional organic conductor was investigated by resistance measurements under continuously controllable He gas pressure in this article, which revealed the phase diagram and the critical characteristics of the mott transition.
Abstract: The Mott transition in a quasi-two-dimensional organic conductor, $\ensuremath{\kappa}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}\mathrm{Cu}[\mathrm{N}(\mathrm{CN}{)}_{2}]\mathrm{Cl}$ was investigated by resistance measurements under continuously controllable He gas pressure. We constructed the resistance diagram as functions of temperature and pressure, which has unveiled the phase diagram and the critical characteristics of the Mott transition. The observation of the huge resistance jump by nearly two orders of magnitude provides an unambiguous evidence for the first-order nature of the Mott transition. At elevated temperatures, the jump is diminished gradually and vanishes at a critical end point 38 K, above which the resistance variation against pressure is continuous. It is also found that the end point is featured by critical divergence in pressure derivative of resistance, $|(1/R)\ensuremath{\partial}R/\ensuremath{\partial}P|,$ which was consistent with the prediction of the dynamical mean-field theory and has phenomenological correspondence with the liquid-gas transition. The present results provide the experimental basis for physics of the Mott transition criticality.
TL;DR: In this article, the Mott transition was investigated using a cluster extension of dynamical mean field theory (DMFT), and no evidence for a finite temperature Mott critical point was found.
Abstract: We investigate the Mott transition using a cluster extension of dynamical mean field theory (DMFT). In the absence of frustration we find no evidence for a finite temperature Mott transition. Instead, in a frustrated model, we observe signatures of a finite temperature Mott critical point in agreement with experimental studies of $\ensuremath{\kappa}$ organics and with single-site DMFT. As the Mott transition is approached, a clear momentum dependence of the electron lifetime develops on the Fermi surface with the formation of cold regions along the diagonal direction of the Brillouin zone. Furthermore, the variation of the effective mass is no longer equal to the inverse of the quasiparticle residue, as in DMFT, and is reduced approaching the Mott transition.
13 Sep 2004
TL;DR: In this article, the main reasons for strong correlations in several classes of materials are discussed, and the basic principles of dynamical mean field theory (DMFT) are briefly reviewed, emphasizing the formal analogies with classical mean-field theory and density functional theory through the construction of free energy functionals of a local observable.
Abstract: These are introductory lectures to some aspects of the physics of strongly correlated electron systems. I first explain the main reasons for strong correlations in several classes of materials. The basic principles of dynamical mean‐field theory (DMFT) are then briefly reviewed. I emphasize the formal analogies with classical mean‐field theory and density functional theory, through the construction of free‐energy functionals of a local observable. I review the application of DMFT to the Mott transition, and compare to recent spectroscopy and transport experiments. The key role of the quasiparticle coherence scale, and of transfers of spectral weight between low‐ and intermediate or high energies is emphasized. Above this scale, correlated metals enter an incoherent regime with unusual transport properties. The recent combinations of DMFT with electronic structure methods are also discussed, and illustrated by some applications to transition metal oxides and f‐electron materials.
TL;DR: The occurrence of superconductivity is shown to be connected with a pressure-induced decrease of the MSe6 octahedral distortion and simultaneous softening of the phonon associated with M-Se bonds.
Abstract: Electronic conduction in GaM4Se8 (M=Nb,Ta) compounds with the fcc GaMo4S8-type structure originates from hopping of localized unpaired electrons (S=1 / 2) among widely separated tetrahedral M4 metal clusters. We show that under pressure these systems transform from Mott insulators to a metallic and superconducting state with T(C)=2.9 and 5.8 K at 13 and 11.5 GPa for GaNb4Se8 and GaTa4Se8, respectively. The occurrence of superconductivity is shown to be connected with a pressure-induced decrease of the MSe6 octahedral distortion and simultaneous softening of the phonon associated with M-Se bonds.
TL;DR: In this article, the authors give a theoretical analysis of published experimental studies of the effects of impurities and disorder on the superconducting transition temperature Tc of the organic molecular crystals kappa-(BEDT-TTF)2X (where X = I3 and IBr2).
Abstract: We give a theoretical analysis of published experimental studies of the effects of impurities and disorder on the superconducting transition temperature Tc of the organic molecular crystals kappa-(BEDT-TTF)2X (where X = Cu[N(CN)2]Br and Cu(NCS)2 and BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) and beta-(BEDT-TTF)2X (for X = I3 and IBr2). The Abrikosov-Gorkov (AG) formula describes the suppression of Tc both by magnetic impurities in singlet superconductors, including s-wave superconductors and by nonmagnetic impurities in a non-s-wave superconductor. We show that various sources of disorder (alloying anions, fast electron irradiation, disorder accidentally produced during fabrication, and cooling rate induced disorder) lead to the suppression of Tc as described by the AG formula. This is confirmed by the excellent fit to the data, the fact that these materials are in the clean limit and the excellent agreement between the value of the interlayer hopping integral t[perpendicular] calculated from this fit and the value of t[perpendicular] found from angular-dependent magnetoresistance and quantum oscillation experiments. There are only two scenarios consistent with the current state of experimental knowledge. If the disorder induced by all of the four methods considered in this paper is, as seems most likely, nonmagnetic then the pairing state cannot be s wave. We show that published measurements of the cooling rate dependence of the magnetization are inconsistent with paramagnetic impurities. Triplet pairing is ruled out by NMR and upper critical field experiments. Thus if the disorder is nonmagnetic then this implies that l>=2, in which case Occam's razor suggests that d-wave pairing is realized in both beta-(BEDT-TTF)2X and kappa-(BEDT-TTF)2X. However, particularly given the proximity of these materials to an antiferromagnetic Mott transition, it is possible that the disorder leads to the formation of local magnetic moments via some atypical mechanism. Thus we conclude that either beta-(BEDT-TTF)2X and kappa-(BEDT-TTF)2X are d-wave superconductors or else they display an atypical mechanism for the formation of localized moments, possibly related to the competition between the antiferromagnetic and superconducting grounds states. We suggest systematic experiments to differentiate between these two scenarios.
TL;DR: In this paper, the phase diagram of the half-filled Holstein-Hubbard model is analyzed as a function of the on-site electron-electron interaction U and the electron-phonon coupling g.
Abstract: We investigate metal-insulator transitions in the half-filled Holstein-Hubbard model as a function of the on-site electron-electron interaction U and the electron-phonon coupling g. We use several different numerical methods to calculate the phase diagram, the results of which are in excellent agreement. When the electron-electron interaction U is dominant, the transition is to a Mott insulator; when the electron-phonon interaction dominates, the transition is to a localized bipolaronic state. In the former case, the transition is always found to be second order. This is in contrast to the transition to the bipolaronic state, which is clearly first order for larger values of U. We also present results for the quasiparticle weight and the double occupancy as functions of U and g.
TL;DR: In this article, the Mott transition in a multiorbital Hubbard model involving subbands of different widths is studied within the dynamical mean-field theory, using the iterated perturbation theory for the quantum impurity problem.
Abstract: The Mott transition in a multiorbital Hubbard model involving subbands of different widths is studied within the dynamical mean-field theory. Using the iterated perturbation theory for the quantum impurity problem it is shown that at low temperatures interorbital Coulomb interactions give rise to a single first-order transition rather than a sequence of orbital selective transitions. Impurity calculations based on the Quantum Monte Carlo method confirm this qualitative behavior. Nevertheless, at finite temperatures, the degree of metallic or insulating behavior of the subbands differs greatly. Thus, on the metallic side of the transition, the narrow band can exhibit quasi-insulating features, whereas on the insulating side the wide band exhibits pronounced bad-metal behavior. This complexity might partly explain contradictory results between several previous works.
TL;DR: This new mechanism of the core-level photoemission satellite can be utilized to reveal the Mott transition phenomenon in various strongly correlated electron systems, especially in nanoscale devices and phase-separated materials.
Abstract: Core-level x-ray photoemission spectra for the Mott-Hubbard systems are calculated by the dynamical mean-field theory based on the exact diagonalization method. The spectra show a two-peak structure, screened and unscreened peaks. The screened peak is absent in a Mott insulator, but develops into the main peak when the correlation strength becomes weak and the system turns metallic. The calculated spectral behavior is consistent with the experimental Ru $3d$ core-level spectra of various ruthenates. This new mechanism of the core-level photoemission satellite can be utilized to reveal the Mott transition phenomenon in various strongly correlated electron systems, especially in nanoscale devices and phase-separated materials.
TL;DR: It is shown 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.
Abstract: 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.
TL;DR: In this article, the authors identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca2-xSrxRuO4 near the metal-insulator transition.
Abstract: By using a combination of detailed experimental studies and simple theoretical arguments, we identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca2-xSrxRuO4 near the metal-insulator transition. The hopping exponent alpha shows a systematic evolution from a value of alpha=1/2 deeper in the insulator to the conventional Mott value alpha=1/3 closer to the transition. This behavior, which we argue to be a universal feature of disordered Mott systems close to the metal-insulator transition, is shown to reflect the gradual emergence of disorder-induced localized electronic states populating the Mott-Hubbard gap.
TL;DR: Near a Mott transition, strong electron correlations may enhance Cooper pairing and this is demonstrated in the dynamical mean field theory solution of a twofold-orbital degenerate Hubbard model with an inverted on-site Hund rule exchange, favoring local spin-singlet configurations.
Abstract: Near a Mott transition, strong electron correlations may enhance Cooper pairing. This is demonstrated in the dynamical mean field theory solution of a twofold-orbital degenerate Hubbard model with an inverted on-site Hund rule exchange, favoring local spin-singlet configurations. Close to the Mott insulator (which here is a local version of a valence bond insulator) a pseudogap non-Fermi-liquid metal, a superconductor, and a normal metal appear, in striking similarity with the physics of cuprates. The strongly correlated s-wave superconducting state has a larger Drude weight than the corresponding normal state. The role of the impurity Kondo problem is underscored.
Abstract: As a generic model describing quasi-one-dimensional Mott and Peierls insulators, we investigate the Holstein-Hubbard model for half-filled bands using numerical techniques Combining Lanczos diagonalization with Chebyshev moment expansion we calculate exactly the photoemission and inverse photoemission spectra, and use these to establish the phase diagram of the model While polaronic features emerge only at strong electron-phonon couplings, pronounced phonon signatures, such as multiquanta band states, can be found in the Mott insulating regime as well In order to corroborate the Mott to Peierls transition scenario, we determine the spin- and charge-excitation gaps by a finite-size scaling analysis based on density-matrix renormalization-group calculations
TL;DR: In this paper, an exploration of internanocrystal coupling in assemblies of CoPt3 nanocrystals probed by variable temperature charge transport measurements is reported, and it is shown that the observed insulator-to-metal transition is due to melting and reorganization of the nanocrystal ligand shells causing a reduction in mean internan-ocrystal distance.
Abstract: We report on exploration of internanocrystal coupling in assemblies of CoPt3 nanocrystals (i.e., artificial atom solids) probed by variable temperature charge transport measurements. Nanocrystal devices can be tuned in situ from Mott insulating to metallic behavior using mild thermal annealing. Thermal analysis suggests that the observed insulator-to-metal transition is due to melting and reorganization of the nanocrystal ligand shells causing a reduction in mean internanocrystal distance and is not due to nanocrystal ligand desorption or nanocrystal sintering.
TL;DR: In this article, the authors employed dynamical mean field theory to calculate the properties of multilayered inhomogeneous devices composed of semi-infinite metallic lead layers coupled via barrier planes that are made from a strongly correlated material.
Abstract: Dynamical mean field theory is employed to calculate the properties of multilayered inhomogeneous devices composed of semi-infinite metallic lead layers coupled via barrier planes that are made from a strongly correlated material (and can be tuned through the metal-insulator Mott transition). We find that the Friedel oscillations in the metallic leads are immediately frozen in and do not change as the thickness of the barrier increases from one to 80 planes. We also identify a generalization of the Thouless energy that describes the crossover from tunneling to incoherent ohmic transport in the insulating barrier. We qualitatively compare the results of these self-consistent many-body calculations with the assumptions of non-self-consistent Landauer-based approaches to shed light on when such approaches are likely to yield good results for the transport.
TL;DR: In this article, the authors present results on the dynamical correlation functions of the particle-hole symmetric Holstein-Hubbard model at zero temperature, calculated using dynamical mean field theory which is solved by the numerical renormalization group method.
Abstract: We present results on the dynamical correlation functions of the particle-hole symmetric Holstein-Hubbard model at zero temperature, calculated using the dynamical mean-field theory which is solved by the numerical renormalization group method. We clarify the competing influences of the electron-electron and electron-phonon interactions particularity at the different metal to insulator transitions. The Coulomb repulsion is found to dominate the behavior in large parts of the metallic regime. By suppressing charge fluctuations, it effectively decouples electrons from phonons. The phonon propagator shows a characteristic softening near the metal to bipolaronic transition but there is very little softening on the approach to the Mott transition.
TL;DR: In this paper, the authors investigated the one-dimensional Hubbard model by means of two different cluster schemes suited to introduce short-range spatial correlations beyond the single-site dynamical mean field theory.
Abstract: The one-dimensional Hubbard model is investigated by means of two different cluster schemes suited to introduce short-range spatial correlations beyond the single-site dynamical mean-field theory, namely, the cellular dynamical mean-field theory, which does not impose the lattice symmetries, and its periodized version in which translational symmetry is recovered. It is shown that both cluster schemes are able to describe with extreme accuracy the evolution of the density as a function of the chemical potential from the Mott insulator to the metallic state. Using exact diagonalization to solve the cluster-impurity model, we discuss the role of the truncation of the Hilbert space of the bath, and propose an algorithm that gives higher weights to the low-frequency hybridization matrix elements and improves the speed of the convergence of the algorithm.
TL;DR: In this article, the phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition, and real space imaging of phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation.
Abstract: Systematic investigation of the electronic phase separation on macroscopic scale is reported in the organic Mott system $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears near the Mott boundary and changes its metal-insulator fraction with the substitution ratio $x$ in $\kappa$-[($h$-BEDT-TTF)$_{1-x}$($d$-BEDT-TTF)$_{x}$]$_{2}$Cu[N(CN)$_{2}$]Br, of which band width is controlled by the substitution ratio $x$ between the hydrogenated BEDT-TTF molecule ($h$-BEDT-TTF) and the deuterated one ($d$-BEDT-TTF). The phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition.
TL;DR: In this article, the spin-singlet Mott phase and the nematic mott phase were investigated in high-dimensional bipartite lattices and it was shown that phase transitions are generally weakly first order.
Abstract: We present microscopic wave functions of spin-singlet Mott insulating states and nematic Mott insulating states. We also investigate quantum phase transitions between the spin-singlet Mott phase and the nematic Mott phase in both large-N limit and small-N limit ( N being the number of particles per site! in high-dimensional bipartite lattices. In the mean-field approximation employed in this article we find that phase transitions are generally weakly first order.
TL;DR: In this paper, the effect of Mn site substitution of Al on the structural, magnetic and transport properties of charge ordered Pr0.5Ca 0.5MnO3 was investigated.
Abstract: We report on the effect of Mn site substitution of Al on the structural, magnetic and transport properties of charge ordered Pr0.5Ca0.5MnO3. This substitution introduces non-magnetic impurities in the Mn–O–Mn network, causes the Mn3+/Mn4+ ratio to deviate away from unity and is seen to predominantly replace Mn4+ without introducing any appreciable change in the structure. The strength of charge ordering is suppressed with increasing Al doping, as is seen from AC susceptibility, the magnetocaloric effect and DC resistivity. The observation of traces of charge ordering over an extended range of impurity doping of 10%, besides being indicative of the robust nature of charge ordering in Pr0.5Ca0.5MnO3, also underscores the relatively insignificant effect that Al substitution has on the lattice distortions and the importance of non-magnetic substitutions. For all the samples, the conductivity in the temperature range above the charge ordering transition is observed to be due to the adiabatic hopping of small polarons, whereas below the charge ordering transition, Mott's variable range hopping mechanism is seen to be valid.