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T M Rice

Publications and source records attributed to T M Rice.

15 recordsLinked to original sources
PubMed2006

Role of inelastic tunneling through the insulating barrier in scanning-tunneling-microscope experiments on cuprate superconductors.

The tunneling path between the CuO2 layers in cuprate superconductors and a scanning-tunneling-microscope tip passes through a barrier made from other oxide layers. This opens up the possibility that inelastic processes in the barrier contribute to the tunneling spectra. Such processes cause one or possibly more peaks in the second derivative current-voltage spectra displaced by phonon energies from the density of states singularity associated with superconductivity. Calculations of inelastic processes generated by apical O phonons show good qualitative agreement with recent experiments reported by Lee et al. Further tests to discriminate between these inelastic processes and coupling to planar phonons are proposed.

Journal Article↗
PubMed2006

Magnetic domain formation in itinerant metamagnets.

We examine the effects of long-range dipolar forces on metamagnetic transitions and generalize the theory of Condon domains to the case of an itinerant electron system undergoing a first-order metamagnetic transition. We demonstrate that, within a finite range of the applied field, dipolar interactions induce a spatial modulation of the magnetization in the form of stripes or bubbles. Our findings are consistent with recent observations in the bilayer ruthenate Sr(3)Ru(2)O(7).

Journal Article↗
PubMed2006

Doped spin liquid: Luttinger sum rule and low temperature order.

We analyze a model of two-leg Hubbard ladders weakly coupled by interladder tunneling. At half filling a semimetallic state with small Fermi pockets is induced beyond a threshold tunneling strength. The sign changes in the single electron Green's function relevant for the Luttinger sum rule now take place at surfaces with both zeros and infinities with important consequences for the interpretation of angle-resolved photoemission spectroscopy experiments. Residual interactions between electron and holelike quasiparticles cause a transition to long range order at low temperatures. The theory can be extended to small doping leading to superconducting order.

Journal Article↗
PubMed2004

Orbital-selective mott transitions in the degenerate Hubbard model.

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.

Journal Article↗
PubMed2004

d-Mott phases in one and two dimensions.

We use exact diagonalization to determine the spectrum of reduced Hamiltonians based on renormalization group flows to strong coupling. For the half-filled two-leg Hubbard ladder we reproduce the known insulating d-Mott ground state with spin and charge gaps. For the saddle point regions of the two-dimensional Hubbard model near half filling we find a crossover to a similar strong coupling state, which truncates the Fermi surface near the saddle points. At lower scales d-wave superconductivity appears on the remaining Fermi surface.

Journal Article↗
PubMed2003

Single-particle spectrum in the electron-doped cuprates.

We study the evolution of the single-particle spectrum with electron doping in a scheme which adds multiple exchange of transverse spin excitations to the mean-field antiferromagnetic insulator. Away from half-filling small Fermi surface pockets appear first around the X points, and simultaneously new spectral weight grows in the insulating gap. With further doping the in-gap states develop the character of a renormalized quasiparticle band near the chemical potential. The essential features in momentum-energy space agree well with recent studies using angle-resolved photoemission spectroscopy on electron-doped cuprates. We interpret the origins and the nature of the in-gap states using a simple variational wave function.

Journal Article↗
PubMed2003

Nighttime driving, passenger transport, and injury crash rates of young drivers.

OBJECTIVE: This study examines the association of nighttime driving and the carrying of passengers with the rate of motor vehicle crashes that resulted in severe or fatal injury to young drivers in California before the implementation of a graduated licensing system. METHOD: Passenger vehicle drivers aged 16 or 17 involved in injury crashes in California from 1 January 1993 to 30 June 1998 were identified through a police crash database. An induced exposure method was used to estimate driving exposure. Odds ratios for driver injury crashes were estimated with logistic regression. RESULTS: Driving at night, driving without adult supervision, driving with passengers, using alcohol, being 16, and being male were associated with high rates of driver injury crash. CONCLUSIONS: The injury crash rate for drivers aged 16 or 17 increases during nighttime hours and in the absence of adult supervision, with or without other passengers. Driving between 10 pm and midnight is particularly dangerous for young drivers. Nighttime driving restrictions that begin at 10 pm or earlier and restrictions on carrying passengers at any hour may increase the effectiveness of graduated licensing systems.

Accidents, Traffic↗
PubMed2002

First-order transition between a small gap semiconductor and a ferromagnetic metal in the isoelectronic alloy FeSi1-xGex.

The contrasting ground states of isoelectronic, isostructural FeSi and FeGe are explained within an extended local density approximation scheme (LDA+U) by an appropriate choice of the Coulomb repulsion U on the Fe sites. A minimal two-band model with interband interactions leads to a phase diagram for the alloys FeSi1-xGex. A mean field approximation gives a first-order transition between a small gap semiconductor and a ferromagnetic metal as a function of magnetic field, temperature, and concentration x. Unusually the transition from metal to insulator is driven by broadening, not narrowing, the bands and it is the metallic state that shows magnetic order.

Journal Article↗
PubMed2002

Magnon dispersion in the field-induced magnetically ordered phase of TlCuCl3.

The magnetic properties of the interacting dimer system TlCuCl3 are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.

Journal Article↗
PubMed2002

Li-induced spin and charge excitations in a spin ladder.

A lithium dopant in a cuprate spin ladder acts as a vacant (nonmagnetic) site accompanied by an extra hole bound by a Coulomb potential. We find that, although the undoped ladder spin gap is not essentially altered by Li doping, a dopant-magnon bound state appears just below the gap. Contrary to Zn-doped ladders, the spin liquid character of a Li-doped ladder should be robust against antiferromagnetism. We give a possible explanation for the similarity of Zn and Li dopants in underdoped cuprates and propose experimental tests.

Journal Article↗
PubMed2001

Differential ability of transition metals to induce pulmonary inflammation.

Transition metals are components of airborne particles and have been implicated in adverse health effects. The relative inflammatory potential of these metals is usually inferred from separate studies that focus on only one or a few individual metals. Comparisons of relative potency among several metals from these separate studies can be difficult. In one comprehensive study, we measured the pulmonary effects of equimolar doses of six metals in soluble form. Our purpose was to compare inflammatory potential and pulmonary toxicity among individual transition metals. Rats received saline, 0.1 or 1.0 micromol/kg of vanadium, nickel, iron(II), copper, manganese, or zinc as sulfates. Bronchoalveolar lavage (BAL) was performed at 0, 4, 16, or 48 h postinstillation. All treatments except V showed increased lactate dehydrogenase activity in BAL fluid; Cu- and Ni-exposed animals had the highest levels. Protein levels in BAL fluid were more than five times higher in Cu-exposed animals compared to other metal treatments at 16 and 48 h. At the 0.1 micromol/kg dose, only Cu induced significant neutrophilia at 16 and 48 h. For the 1.0 micromol/kg dose, all metals tested induced significant neutrophilia, with mean neutrophil numbers for Cu and Mn significantly higher compared to the other metals. At 48 h, neutrophil numbers were still elevated in all metal exposures. Only Mn caused substantial eosinophilia. At the 1.0 micromol/kg dose, only Cu induced macrophage inflammatory protein-2 (MIP-2) mRNA at 4 h. By 48 h, induction of MIP-2 mRNA was observed for all metal exposures except Cu, which subsequently returned to baseline levels. On an equimolar basis, Cu was the most proinflammatory metal, followed by Mn and Ni, while V, Fe(II), and Zn induced similar levels of inflammation. Overall, there were many similarities in the pulmonary responses of the metals we tested. However, we also observed divergent, metal-specific responses. These differential responses suggest that metals induce pulmonary inflammation by differing pathways or combinations of signals.

Actins↗
PubMed2001

Interband proximity effect and nodes of superconducting gap in Sr2RuO4.

The power-law temperature dependences of the specific heat, the nuclear relaxation rate, and the thermal conductivity suggest the presence of line nodes in the superconducting gap of Sr2RuO4. These recent experimental observations contradict the scenario of a nodeless (k(x)+ik(y))-type superconducting order parameter. We propose that interaction of superconducting order parameters on different sheets of the Fermi surface is a key to understanding the above discrepancy. A full gap exists in the active band, which drives the superconducting instability, while line nodes develop in passive bands by the interband proximity effect.

Journal Article↗
PubMed2001

Toxicokinetics, available source, and route of entry of lead in fed and food-deprived bullfrog (Rana catesbeiana) larvae.

Several toxic effects of lead (Pb) have been documented in amphibians, but few studies have measured tissue levels of exposed specimens or examined toxicokinetics, availability of dietary versus waterborne sources, or route of entry. We modeled the toxicokinetics and examined the availability of dietary and waterborne Pb in both fed and food-deprived bullfrog (Rana catesbeiana) larvae. Uptake rates of Pb (1,000 microg Pb/L nominal exposure) were similar between fed and unfed larvae, but unfed larvae eliminated Pb slowly. Consequently, food-deprived larvae accumulated significantly more Pb compared to fed larvae. The intestinal tract contained > 90% of total body Pb in both fed and unfed larvae. Total body concentrations of Pb in fed larvae did not increase over 7 days although levels in food did increase. We concluded that food consumption influenced Pb accumulation through changes in elimination rates rather than in uptake rates. Pb appeared to enter the body of larvae through ingestion of contaminated water rather than food.

Animals↗