Transport properties of strongly correlated metals:a dynamical mean-field approach

The temperature dependence of the transport properties of the metallic phase of a frustrated Hubbard model on the hypercubic lattice at half-filling are calculated. Dynamical mean-field theory, which maps the Hubbard model onto a single impurity Anderson model that is solved self-consistently, and becomes exact in the limit of large dimensionality, is used. As the temperature increases there is a smooth crossover from coherent Fermi liquid excitations at low temperatures to incoherent excitations at high temperatures. This crossover leads to a non-monotonic temperature dependence for the resistance, thermopower, and Hall coefficient, unlike in conventional metals. The resistance smoothly increases from a quadratic temperature dependence at low temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar a/e^2 (where "a" is a lattice constant) associated with mean-free paths less than a lattice constant. Further signatures of the thermal destruction of quasiparticle excitations are a peak in the thermopower and the absence of a Drude peak in the optical conductivity. The results presented here are relevant to a wide range of strongly correlated metals, including transition metal oxides, strontium ruthenates, and organic metals.Comment: 19 pages, 9 eps figure

Investigation of the potential of the dissolution dynamic nuclear polarization method for general sensitivity enhancement in small-molecule NMR spectroscopy

We report results of applying a commercial implementation of the dissolution dynamic nuclear polarization (DNP) methodology developed by K. G. Golman et al. to a range of molecular species in the mass range of 100-400 Da. The molecules are typical of those that might be encountered in natural product chemistry or pharmaceutical analysis. Using an experimental protocol previously reported, in combination with the ERETIC method for generating a reference signal for estimation of concentrations, we determine the signal enhancement and high-field, liquid-state T-1 values for many of the carbon atoms in the six species studied. The results presented in this work suggest that the measured variation in nuclear magnetic resonance enhancements within a given molecule, arising from the dissolution DNP method, is accounted for principally by relaxation of C-13 atoms towards thermal polarization values in the liquid state. We conclude that dissolution DNP will be able to be employed for a wide range of chemical species, provided that the total time taken for dissolution and transfer of solutions is comparable to, or shorter than, the high-field, liquid-state T-1 values in the species being studied