Showing papers on "Mott transition published in 1999"

Lecture notes on electron correlation and magnetism

Abstract: Atoms, ions, and molecules crystal field theory Mott transition and Hubbard model Mott insulators Heisenberg magnets itinerant electron magnetism ferromagnetism in Hubbard models the Gutzwiller variational method the correlated metallic state mixed valence and heavy fermions quantum hall effect hydrogen atom single-spin-flip ansatz Gutzwiller approximation Schrieffer-Wolff transformation.

Breakdown of the Mott-Hubbard State in Fe 2 O 3 : A First-Order Insulator-Metal Transition with Collapse of Magnetism at 50 GPa

Abstract: Electronic and structural properties of the high-pressure phase of Fe{sub 2}O {sub 3} were determined by combining the methods of M{umlt o}ssbauer spectroscopy, x-ray diffraction, and electrical resistance, R(P,thinspT) , to 80thinspthinspGPa. Because of a first-order phase transition taking place in the 50{endash}75thinspthinspGPa range and accompanied by a volume decrease of {approximately}10{percent} , a breakdown of the electronic d-d correlation occurred, leading to a Mott transition, a metallic and a nonmagnetic single Fe{sup 3+} electronic state. The high-pressure structure is of the distorted Rh{sub 2}O {sub 3}- II type. The accommodation of the denser phase within this six-coordinated structure is attributable to the metallic state. {copyright} {ital 1999} {ital The American Physical Society}

Current-induced insulator-metal transition and pattern formation in an organic charge-transfer complex

Abstract: Organic molecular Mott insulators, in which carriers are localized as a result of the electron correlation, showed nonlinear electric conduction upon application of a high electric field along the molecular stacking axis. The current-driven low-resistive state of potassium 7,7,8,8-tetracyanoquinodimethanane was stabilized down to 2 kelvin, where a metallic path was visible with a microscope. The current flow caused a stripe-like periodic phase-segregation into the carrier-rich and carrier-poor regions along the current path.

High-excitation photoluminescence in GaN: Hot-carrier effects and the Mott transition

Abstract: Photoluminescence under intense excitation is studied in GaN. As the excitation density increases, we show the Mott transition between an excitonic recombination to a plasma-type recombination. The carrier density at the Mott transition is given. At and above the Mott density, we show that the carrier temperature is higher than the lattice temperature. The energy relaxation of the hot plasma is shown to be dominated by LO-phonon emission. Coulomb screening and band-gap renormalization are observed from the photoluminescence peak position and the measured renormalization factor is in good agreement with elementary many-body theory. Finally the dependence of the Mott density on carrier temperature is shown to follow a Debye-H\"uckel model.

Dual order parameter for the nodal liquid

Abstract: The guiding conception of vortex-condensation-driven Mott insulating behavior is central to the theory of the nodal liquid. We amplify our earlier description of this idea and show how vortex condensation in two-dimensional (2D) electronic systems is a natural extension of 1D Mott insulating and 2D bosonic Mott insulating behavior. For vortices in an underlying superconducting pair field, there is an important distinction between the condensation of flux $hc/2e$ and flux $hc/e$ vortices. The former case leads to spin-charge confinement, exemplified by the band insulator and the charge-density wave. In the latter case, spin and charge are liberated, leading directly to a 2D Mott insulator exhibiting spin-charge separation. Possible upshots include not only the nodal liquid, but also an undoped antiferromagnetic insulating phase with gapped excitations exhibiting spin-charge separation.

Finite temperature mott transition in the hubbard model in infinite dimensions

Abstract: We study the second order finite temperature Mott transition point in the fully frustrated Hubbard model at half filling, within dynamical mean field theory. Using quantum Monte Carlo simulations and analytical arguments, we show the existence of a finite temperature second order critical point by explicitly demonstrating the existence of a divergent susceptibility as well as by finding coexistence in the low temperature phase. We determine the precise location of the finite temperature Mott critical point in the $(U,T)$ plane. Our study verifies and quantifies a scenario for the Mott transition proposed in earlier studies of this problem.

Metallic surface of a Mott insulator-Mott insulating surface of a metal

Abstract: The dynamical mean-field theory (DMFT) is employed to study the correlation-driven metal-insulator transition in the semi-infinite Hubbard model at half-filling and zero temperature. We consider the low-index surfaces of the three-dimensional simple-cubic lattice, and systematically vary the model parameters at the very surface, the intralayer and interlayer surface hopping, and the surface Coulomb interaction. Within the DMFT the self-energy functional is assumed to be local. Therewith, the problem is self-consistently mapped onto a set of coupled effective impurity models corresponding to the inequivalent layers parallel to the surface. Assuming that the influence of the high-energy Hubbard bands on the low-energy quasiparticle resonance can be neglected at the critical point, a simplified ``linearized DMFT'' becomes possible. The linearized theory, however, is formally equivalent to the Weiss molecular-field theory for the semi-infinite Ising model. This implies that qualitatively the rich phenomenology of the Landau description of second-order phase transitions at surfaces has a direct analog for the surface Mott transition. Motivated by this formal analogy, we work out the predictions of the linearized DMFT in detail. It is found that under certain circumstances the surface of a Mott insulator can be metallic, while a Mott-insulating surface of a normal metal is not possible. We derive the corresponding phase diagrams, the (mean-field) critical exponents and the critical profiles of the quasiparticle weight. The results are confirmed by a fully numerical evaluation of the DMFT equations using the exact-diagonalization (ED) method. By means of the ED approach, we especially investigate the noncritical parts of the phase diagrams and discuss the U and layer dependence of the quasi-particle weight. For strong modifications of the surface model parameters, the surface low-energy electronic structure dynamically decouples from the bulk.

Dynamical mean field theory of the antiferromagnetic metal to antiferromagnetic insulator transition

Abstract: The correlation driven metal insulator transition (MIT) or Mott transition is one of the central problems of condensed matter physics. Recently, a great deal of progress has been made in understanding the MIT using the dynamical mean field approach (DMFT), a method which becomes exact in the well-defined limit of infinite lattice coordination [1,2]. However, all studies so far have been confined to the paramagnetic metal (PM) to paramagnetic insulator (PI) transition. In this Letter, we use DMFT to study the transition from the antiferromagnetic metal (AM) to an antiferromagnetic insulator (AI) at zero temperature. The motivation for this work is twofold. Experimentally, the interaction or pressure driven MIT in V2O3 [3,4] and NiS22xSex [4,5] takes place between magnetically ordered states. The Neel temperatures are much smaller than the respective characteristic electronic energy scales. We interpret this as a sign of reduced effective magnetic correlations as compared to estimates obtained from a simple one band Hubbard model. Close to the MIT, the behavior of physical quantities like the specific heat coefficient is, however, different in these two materials. Furthermore, measurements of the magnetic moment seem to indicate that the magnetism in V2O3 is much weaker than in NiS22xSex [6]. This suggests that the strength of the magnetic correlations influences the MIT. We would therefore like to understand how magnetic correlations, which control the scale at which the spin entropy is quenched, affect the MIT and hence, various physical quantities. While we are still far from a realistic modeling of these materials (in this work we consider only commensurate magnetic order and ignore orbital degeneracy and realistic band structure), we present a simple model which, we believe, captures the generic effects of the magnetic correlations on the MIT. We consider a simple one band Hamiltonian,

Metal-insulator transition in the one-dimensional su(n) hubbard model

Abstract: We investigate the metal-insulator transition of the one-dimensional $\mathrm{SU}(N)$ Hubbard model for repulsive interaction. Using the bosonization approach a Mott transition in the charge sector at half filling ${(k}_{F}=\ensuremath{\pi}{/Na}_{0})$ is conjectured for $Ng2.$ Expressions for the charge and spin velocities as well as for the Luttinger-liquid parameters and some correlation functions are given. The theoretical predictions are compared with numerical results obtained with an improved zero-temperature quantum Monte Carlo approach. The method used is a generalized Green's function Monte Carlo scheme in which the stochastic time evolution is partially integrated out. Very accurate results for the gaps, velocities, and Luttinger-liquid parameters as a function of the Coulomb interaction $U$ are given for the cases $N=3$ and $N=4.$ Our results strongly support the existence of a Mott-Hubbard transition at a nonzero value of the Coulomb interaction. We find ${U}_{c}\ensuremath{\sim}2.2$ for $N=3$ and ${U}_{c}\ensuremath{\sim}2.8$ for $N=4.$

Landau theory of the Mott transition in the fully frustrated Hubbard model in infinite dimensions

Abstract: We discuss the solution of the Mott transition problem in a fully frustrated lattice with a semicircular density of states in the limit of infinite dimensions from the point of view of a Landau free energy functional. This approach provides a simple relation between the free energy of the lattice model and that of its local description in terms of an impurity model. The character of the Mott transition in infinite dimensions, (as reviewed by Georges, Kotliar, Krauth and Rozenberg, Rev. Mod. Phys. 68, 13 (1996)) follows simply from the form of the free energy functional and the physics of quantum impurity models. At zero temperature, below a critical value of the interaction U, a Mott insulator with a finite gap in the one particle spectrum, becomes unstable to the formation of a narrow band near the Fermi energy. Using the insights provided by the Landau approach we answer questions raised about the dynamical mean field solution of the Mott transition problem, and comment on its applicability to three dimensional transition metal oxides.

Spectral Evolution in ( C a , S r ) RuO 3 near the Mott-Hubbard Transition

Abstract: We investigated optical properties of (Ca,Sr)RuO {sub 3} films on the borderline of a metal-insulator transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc limit, (ii) a U/2 excitation, and (iii) a U excitation. Also, self-consistency is exploited within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials. However, low frequency behaviors of electrodynamic quantities suggest extra scattering mechanisms in addition to the Mott-Hubbard correlation. {copyright} {ital 1999} {ital The American Physical Society }

Screening, Coulomb Pseudopotential, and Superconductivity in Alkali-Doped Fullerenes

Abstract: We study the static screening in a Hubbard-like model using quantum Monte Carlo methods. We find that the random phase approximation is surprisingly accurate almost up to the Mott transition. We argue that in alkali-doped fullerenes the Coulomb pseudopotential ${\ensuremath{\mu}}^{*}$ is not very much reduced by retardation effects. Therefore efficient screening is important in reducing ${\ensuremath{\mu}}^{*}$ sufficiently to allow for an electron-phonon driven superconductivity. In this way the fullerides differ from the conventional picture, where retardation effects play a major role in reducing the electron-electron repulsion.

RKKY interactions and the Mott transition

Abstract: A two-site cluster generalization of the Hubbard model in large dimensions is examined in order to study the role of short-range spin correlations near the metal-insulator transition (MIT). The model is mapped to a two-impurity Kondo-Anderson model in a self-consistently determined bath, making it possible to directly address the competition between the Kondo effect and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in a lattice context. Our results indicate that the RKKY interactions lead to qualitative modifications of the MIT scenario even in the absence of long-range antiferromagnetic ordering.

Strongly correlated electrons on a silicon surface : theory of a mott insulator

Abstract: Complex Systems Theory Branch, Naval Research Laboratory, Washington, D.C. 20375(February 1, 2008)We demonstrate theoretically that the electronic ground state of the potassium-covered Si(111)-B surface is a Mott insulator, explicitly contradicting band theory but in good agreement withrecent experiments. We determine the physical structure by standard density-functional methods,and obtain the electronic ground state by exact diagonalization of a many-body Hamiltonian. Themany-body conductivity reveals a Brinkman-Rice metal-insulator transition at a critical interactionstrength; the calculated interaction strength is well above this critical value.73.20.-r, 71.30.+h, 71.10.Fd, 71.27.+a

Polarization in Mott Scattering of Multi-MeV Electrons from Heavy Nuclei

Abstract: To aid fundamental studies on the polarization of electrons in beta decay, measurements were made of the spin dependence in the scattering of 14 MeV electrons from Pb as a function of scattering angle and foil thickness. The experiment made use of a beam of polarized electrons from a strained GaAsP cathode. A simple theoretical model based on plural scattering explains the observed dependence of the analyzing power on foil thickness. The results extrapolated to infinitely thin targets are in excellent agreement with theory if the finite nuclear size is taken into account.

Filling dependence of the Mott transition in the degenerate Hubbard model

Abstract: Describing the doped Fullerenes using a generalized Hubbard model, we study the Mott transition for different integer fillings of the t{sub 1u} band. We use the opening of the energy-gap E{sub g} as a criterion for the transition. E{sub g} is calculated as a function of the on-site Coulomb interaction U using fixed-node diffusion Monte Carlo. We find that for systems with doping away from half filling the Mott transitions occurs at smaller U than for the half-filled system. We give a simple model for the doping dependence of the Mott transition. (c) 1999 The American Physical Society.

Dual gate field effect transistor utilizing Mott transition materials

Abstract: A Field effect transistor semiconductor switch in which the channel of same is made from materials having an electrical conductivity which can undergo an insulator-metal transistor (i.e., Mott transition) upon application of an electric field. The channel contains the Mott material in which the charge carriers, either holes or electrons, are strongly correlated. The Mott transition determines the metal-insulator switching and is demonstrated to be controlled by an external gate electrode.

Optical conductivity of the two-dimensional Hubbard model

Abstract: Charge dynamics of the two-dimensional Hubbard model is investigated. Lancz$\ddot{\rm o}$s-diagonalization results for the optical conductivity and the Drude weight of this model are presented. Near the Mott transition, large incoherence below the upper-Hubbard band is obtained together with a remarkably suppressed Drude weight in two dimensions while the clearly coherent character is shown in one dimension. The two-dimensional results are consistent with previous results from quantum Monte Carlo calculations indicating that the Mott transition in this two-dimensional model belongs to the universality class characterized by the dynamical exponent of $z=4$.

Magnetotransport in the doped Mott insulator

Abstract: We investigate the Hall effect and the magnetoresistance of strongly correlated electron systems using the dynamical mean-field theory. We treat the low- and high-temperature limits analytically, and explore some aspects of the intermediate-temperature regime numerically. We observe that a bipartite-lattice condition is responsible for the high-temperature result s xy;1/T 2 obtained by various authors, whereas the generic behavior is s xy;1/T, as for the longitudinal conductivity. We find that Kohler’s rule is obeyed neither at high nor at intermediate temperatures. @S0163-1829~99!06203-7# I. INTRODUCTION The Hubbard model 1‐3 of strongly correlated electron systems has been an enduring problem in condensed-matter theory. It is believed to capture some of the anomalous physics of heavy-fermion systems and high-Tc superconductors. 4 Its crucial feature is the interplay of itineracy and a local interaction U that is either comparable with or much greater than the bare bandwidth. In this paper, we investigate the impact of a magnetic field on the charge transport in strongly correlated electron systems within the Hubbard model. This issue involves different quantities that are closely related, and should therefore be considered within the same approximation scheme. We meet this condition by using the dynamical mean-field theory which becomes exact in the limit of infinite dimensions. A major though nontrivial simplification of this approach is that transport properties are described solely by the singleparticle spectrum. 5‐8 While the dynamical mean-field theory still captures many properties of real three-dimensional transition-metal oxides, it fails to describe cuprate superconductors equally well, mainly because it does not properly take into account magnetic correlations. Nevertheless, it is important to explore this approximation scheme fully in order to establish a sound starting point for future improvements. The Hall constant of the single-band Hubbard model has already been considered within the dynamical mean-field theory by Pruschke, Jarrell, and Freericks 8 and Majumdar and Krishnamurthy. 9 The former authors computed the Hall constant and Hall angle as functions of temperature for various doping levels at—in our units— U52A2D(D is the halfbandwidth! using the noncrossing approximation ~NCA! and a quantum Monte Carlo ~QMC! technique to solve the single-impurity problem. Majumdar and Krishnamurthy mainly focused on the relation between the infinitefrequency Hall constant investigated by Shastry, Shraiman and Singh, 10 and the dc Hall constant, using the iteratedperturbation theory ~IPT! of Ref. 11. In addition to the Hall effect and the ordinary resistivity, we investigate the magnetoresistance. We tie our numerical analysis at intermediate temperatures to analytical results valid in the low- and high-temperature limits. This allows to disentangle the coherent and incoherent contributions of the single-particle spectrum to the magnetotransport and to gain some understanding of either. We always mainly focus on the parameter regime close to the density-driven Mott transition. This paper is organized as follows: In Sec. II, we briefly summarize the dynamical mean-field theory within the single-band Hubbard model, and derive expressions for the quantities to be calculated. Then, by using a Fermi-liquid parametrization for the spectral function, we examine all quantities in the low-temperature regime ~Sec. III!, and study their dependences on temperature and on the doping level. Moreover, we discuss the impact of correlations close to half-filling. In Sec. IV, we employ a recently developed scheme to expand transport coefficients in powers of 1/T ~Ref. 12! within the U5‘ Hubbard model to study the opposite limit of high temperatures. We show that the hightemperature behaviors of the Hall constant and Hall angle can be affected by specific lattice symmetries, and that the Hall angle increases at most linearly with temperature. Then we explore the intermediate-temperature regime numerically ~Sec. V! by either using the NCA or the IPT, depending on whether our focus is more on higher or lower temperatures, respectively. Finally, in Sec. VI, we summarize and discuss our results.

Metal–insulator transitions in layered ruthenates

Abstract: We present the phenomenological systematics of a series of ruthenates, (Ca, Sr) n +1 Ru n O 3 n +1 , which exhibits a rich variety of ground states. We will also discuss in some detail the physical properties of the two-dimensional Mott-transition system, Ca 2− x Sr x RuO 4 , in which the Mott insulator Ca 2 RuO 4 evolves into the spin-triplet superconductor Sr 2 RuO 4 by means of a band-width control.

Dynamical mean-field study of the Mott transition in thin films

Abstract: The correlation-driven transition from a paramagnetic metal to a paramagnetic Mott-Hubbard insulator is studied within the half-filled Hubbard model for a thin-film geometry. We consider simple-cubic films with different low-index surfaces and film thickness d ranging from d=1 (two-dimensional) up to d=8. Using the dynamical mean-field theory, the lattice (film) problem is self-consistently mapped onto a set of d single-impurity Anderson models which are indirectly coupled via the respective baths of conduction electrons. The impurity models are solved at zero temperature using the exact-diagonalization algorithm. We investigate the layer and thickness dependence of the electronic structure in the low-energy regime. Effects due to the finite film thickness are found to be the more pronounced the lower is the film-surface coordination number. For the comparatively open sc(111) geometry we find a strong layer dependence of the quasi-particle weight while it is much less pronounced for the sc(110) and the sc(100) film geometries. For a given geometry and thickness d there is a unique critical interaction strength Uc2(d) at which all effective masses diverge and there is a unique strength Uc1(d) where the insulating solution disappears. Uc2(d) and Uc1(d) gradually increase with increasing thickness eventually approaching their bulk values. A simple analytical argument explains the complete geometry and thickness dependence of Uc2. Uc1 is found to scale linearly with Uc2.

Studies of Pressure-Induced Mott Metal-Insulator Transition of BaCoS2.

Abstract: Transport, thermal and elastic properties under the hydrostatic pressure p up to 21.2 kbar have been studied on the layered compound BaCoS 2 , which exhibits the Mott insulator→metal transition wit...

Effects of Electron Correlation, Orbital Degeneracy and Jahn-Teller Coupling in Perovskite Manganites

Abstract: Roles of Coulomb interaction, orbital degeneracy and Jahn-Teller coupling in double-exchange models are examined for perovskite Mn oxides. We study the undoped insulator as well as metal-insulator transitions by hole doping, and especially strong incoherence of ferromagnetic metal. We derive models where all the spins are fully polarized in two-dimensional planes as indicated by experimental results, and investigate their ground-state properties by the quantum Monte Carlo method. At half filling where the number of e g electrons is one per site on average, the Coulomb interaction opens a Mott gap and induces a staggered orbital ordering. The opening of the gap is, however, substantially slower than the mean-field results if the Jahn-Teller coupling is absent. The synergy between the strong correlation and the Jahn-Teller coupling largely enhances the charge gap amplitude and reproduces realistic amplitudes and stabilization energy of the Jahn-Teller distortion. Doping of carriers destroys the orbital orde...

Metal to insulator transition for Ca1-xNaxPd3O4

Abstract: The resistivity and the Seebeck coefficient were measured for sintered Ca 1- x Na x Pd 3 O 4 (0≦ x ≦1). There occurs a metal to insulator transition at x =0.3, and the material is nonmetallic for s...

Transport properties of metallic LiV2O4 single crystals—heavy mass Fermi liquid behavior

Abstract: Single crystals of the spinel oxide, LiV2O4, were grown hydrothermally and the transport, magnetic and thermal properties of these crystals were studied extensively. We observed an electronic specific heat coefficient γ as large as 0.35 J/mol K2, which confirms the previous work on polycrystalline samples, and a T2 behavior of the resistivity below 2 K. The coefficient of the T2 term, A, and γ were found to satisfy the Kadowaki–Woods relation for strongly correlated Fermi liquids. These results are consistent with the formation of a Fermi liquid with extraordinarily heavy quasiparticles. We speculate that electron correlation’s, which place the system close to a Mott transition, and the strong magnetic frustration inherent to the cubic spinel structure play a substantial role in realizing the extremely heavy-mass Fermi liquid in LiV2O4.

Magneto-optical Sum Rules Close to the Mott Transition

Abstract: We derive new sum rules for the real and imaginary parts of the frequency-dependent Hall constant and Hall conductivity. As an example, we discuss their relevance to the doped Mott insulator that we describe within the dynamical mean-field theory of strongly correlated electron systems.

Electron Energy-Loss Spectroscopy Study of the Metal-Insulator Transition in (V1-xCrx)2O3 (x=0.012)

Abstract: Electron energy-loss spectra of (V1-xCrx)2O3 (x=0.012) at the antiferromagnetic insulating (AFI), paramagnetic metallic (PM) and paramagnetic insulating (PI) phases have been measured using a high-resolution transmission electron energy-loss spectroscopy (EELS) microscope. The changes in the EELS spectra at the transition from the PM phase to the AFI phase are interpreted in a similar manner to the case of V2O3 [Jpn. J. Appl. Phys. 37 (1998) 584]. The change in the electronic structure at the transition from the PM phase to the PI phase (Mott transition) was revealed for the first time. A sharp peak observed at 1.0 eV in the PM phase did not appear in the PI phase. The t2g peak of the O 1s → V 3d(t2g) EELS spectra shows an energy increase of 0.5 eV at the transition from the PM phase to the PI phase. This increase is interpreted to occur by the splitting of the bonding egπ band, which is partially filled in the PM phase, into the fully occupied lower band and the unoccupied upper band, and by the lifting of the unoccupied band to an energy higher than the Fermi level in the PM phase. The t2g peak also shows a decrease in intensity but an increase in the full width at half-maximum (FWHM) at the transition. The decrease in intensity occurs due to the decrease of the hybridization of the V 3d with the O 2p orbitals resulting from an increase of the V–O distance. The increase in the FWHM results from the lifting of the a1g* band due to the decrease of the lattice constant cH and the splitting of the egπ and egπ* bands each into two bands due to electron correlation.

Lattice Distortions and Charge Carriers in Cuprates

Abstract: A phenomenological model with itinerant bands and local states trapped by thelattice on the Cu-sites, is discussed to describe global features ofcuprates. Relative energy positions of localized and itinerant states beingtuned (thermodynamically or by doping), the system must undergo first-orderMott metal-insulator transition. Decreasing the local level (from themetallic end of a stoichiometric compound), charge separation instabilityoccurs first before the Mott transition. Crossing and hybridization betweenlocal (flat) and itinerant bands introduce a structure in density of stateswhich may account for “pseudogap” features in cuprates. Modelresults in polaronic lattice effects and is rich enough to serve as aphenomenology of cuprates.

Spin-spin correlations in the insulating and metallic phases of the Mott system V2O3

Abstract: The magnetic response in V 2 O 3 has been investigated using polarised neutron scattering with polarisation analysis. Measurements were carried out at three temperatures corresponding to the antiferromagnetic insulating ground state, the metallic phase and the high temperature metallic phase. At the first order metal insulator transition there is a dramatic change in the magnetic response with the metallic and high temperature metallic phases being characterised by ferromagnetic spatial correlations of the paramagnetic response. The establishment of ferromagnetic correlations at the metal insulator transition accounts for the abrupt jump in the uniform susceptibility. It is proposed that the differentiation of the V-V distances across the edges of VO 6 octahedra is of critical importance for the change in electronic conductivity but also for the establishment of the spatial correlations. The gradual high temperature evolution of the conductivity then occurs by the reduction in the vanadium d overlap brought about by thermal expansion. The first order reduction in atomic volume which occurs on the establishment of the metallic phase results from an instability of the vanadium local moment arising from the change in electronic structure.