P. Metcalf

Prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3.

We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.

Zener double exchange from local valence fluctuations in magnetite.

Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below T(V)=123 K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B site sublattice (approximately 80 meV) are shifted upwards in energy above T_{V} due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of Delta(5) symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above T(V).

3D {ital XY} and Lowest Landau Level Fluctuations in Deoxygenated YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} Thin Films

Conductivity measurements reflect vortex solid melting in YBCO films. Field-independent glass exponents nu_g=1.9 and z_g=4.0 describe the transition T_g(H) for 0<H<26 T. At low fields, 3D XY exponents nu_{XY}=0.63 and z_{XY}=1.25 are also observed, with z_{XY} smaller than expected. These compete with glass scaling according to multicritical theory. A predicted power-law form of T_g(H) is observed for 0.5T_c<T_g<T_c. For T_g<0.5T_c, 3D XY scaling fails, but a lowest Landau level analysis becomes possible, obtaining T_{c2}(H) with positive curvature.

Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V2O3

Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V_2O_3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V_(2-y)O_3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V_2O_3, and the antiferromagnetic and paramagnetic phases of insulating V_(1.944)Cr_(0.056)O_3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a single lobe"" spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V_2O_3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ħω<k_BT in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V_2O_3.

Photoemission study of ( V 1 − x M x ) 2 O 3 ( M = Cr , Ti )

We present high-resolution bulk-sensitive photoemission spectra of (V

Filling of the mott-hubbard gap in the high temperature photoemission spectrum of (V0.972Cr0.028)2O3.

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Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

M

Optical properties of V2O3 in its whole phase diagram

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Fermi Surface of Metallic V 2 O 3 from Angle-Resolved Photoemission: Mid-level Filling of e g π Bands

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UNIVERSALITY OF GLASS SCALING IN A YBA2CU3O7-DELTA THIN FILM

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