Multiband Electronic Structure Research Articles

Theory of magnetic properties in the spin-triplet superconducting state of Sr 2RuO 4

We analyze the magnetic susceptibility in the triplet-pairing state of Sr 2RuO 4, assuming the chiral p-wave state d ( k ) ∼ ( k x + i k y ) z ^ . The article consists of two separate parts. In the first part we use the random phase approximation, starting from a three-band repulsive Hubbard model, and calculate the NMR relaxation rate ( 1 / T 1 ) as a function of temperature. In the second part we use another model containing effective triplet-pairing interaction, and discuss possible collective spin excitation in the long-wavelength region. In the both parts we take full account of the realistic multi-band electronic structure of Sr 2RuO 4, and use the superconducting gap determined microscopically from the electron correlation effect.

Transport properties and magnetic-field-induced localization in the misfit cobaltite[Bi2Ba1.3K0.6Co0.1O4]RS[CoO2]1.97 single crystal

Resistivity under magnetic field, thermopower and Hall coefficient are systematically studied for the[Bi2Ba1.3K0.6Co0.1O4]RS[CoO2]1.97 single crystal.In-plane resistivity (ρab(T)) shows metallic behavior down to 2 K with aT2 dependence below 30 K, while out-of-plane resistivity(ρc(T)) shows metallic behavior at high temperature and a thermal activation semiconductingbehavior below about 12 K. The striking feature is that magnetic field induces aln(1/T) divergingbehavior in both ρab and ρc(T) at low temperature. The positive magnetoresistance (MR) could bewell fitted by the formula based on multiband electronic structure. Theln(1/T) divergingbehavior in ρab and ρc(T) could arise from the magnetic-field-induced 2D weak localization or spin densitywave.

Localization of 4 f State in YbRh2Si2 under Magnetic Field and High Pressure: Comparison with CeRh2Si2

We present detailed measurements of the electrical resistivity and microcalorimetry under magnetic field and high pressure which confirm the proximity of YbRh 2 Si 2 to a quantum critical point at ambient pressure. Our data seems to rule out the divergence of the heavy quasiparticle mass at the magnetic field tuned quantum critical point. Further Mössbauer spectroscopy gives evidence that the observed ESR resonance cannot be assigned directly to the trivalent Yb local spin dynamics. We report for the first time on quantum oscillations in YbRh 2 Si 2 . The obtained angular dependence is compared with band-structure calculation. A significant change of the resistivity and specific heat under high pressure and magnetic field is observed. Above 5 GPa ferromagnetic coupling plays the dominant role. The unusual high pressure phase diagram of YbRh 2 Si 2 cannot be explained in term of the Doniach phase diagram. In Yb heavy fermion case, slow valence fluctuations may occur due to an occupation number of the trivalent state which differs notably from unity. The differences between the Ce and Yb heavy fermion systems are discussed. In particular a comparison is made between CeRh 2 Si 2 and YbRh 2 Si 2 . The observed field and pressure variations of the Hall voltage in CeRh 2 Si 2 are not straightforwardly linked to the change in the Fermi surface topology. A tiny change in the 4 f electron occupation number will have a huge effect on the effective mass of different orbits of the complex band structure and thus on the Hall effect in this multiband electronic structure. A similar scenario must be certainly considered for YbRh 2 Si 2 .

Point-contact investigations of challenging superconductors: two-band MgB 2, antiferromagnetic HoNi 2B 2C, heavy-fermion UPd 2Al 3, paramagnetic MgCNi 3

An overview on recent efforts in point-contact (PC) spectroscopy of title superconductors is given. Distinct phonon features and crystalline-electric field effects are observed in PC spectra of HoNi 2B 2C. Results of study of superconducting (SC) gap and excess current versus temperature and magnetic field reflecting specific multi-band electronic structure in MgB 2 are presented. The nature of the extremely nonlinear I ( V ) curves in the antiferromagnetic (AF) and SC state are elucidated for UPd 2Al 3 break junctions and MgCNi 3 point contacts.

A unique new multiband molecular conductor: [BDTA][Ni(dmit)2

A new molecular conducting material, [BDTA][Ni(dmit)2]2, with a novel multiband electronic structure has been prepared by simple mixing of precursor salts of the components.

Anisotropic resistivity and Hall effect inMgB2single crystals

We report resistivity and the Hall-effect measurements in the normal and superconducting states of ${\mathrm{MgB}}_{2}$ single crystals. The resistivity has been found to be anisotropic with slightly temperature-dependent resistivity ratio of about 3.5. The Hall constant, with a magnetic field parallel to the Mg and B sheets, is negative in contrast to the holelike Hall response with a field directed along the c axis, indicating presence of both types of charge carriers and, thus, the multiband electronic structure of ${\mathrm{MgB}}_{2}.$ The Hall effect in the mixed state shows no sign change anomaly, reproducing Hall-effect behavior in clean limit type-II superconductors.

Multiband coupling and electronic structure ofshort-period (GaAs)N/(AlAs)N(001)superlattices

It is shown that the effective mass approximationtogether with interface short-range corrections can be used tocalculate short-period abrupt (GaAs)N/(AlAs)N(001)superlattices. The results obtained are in excellent agreementwith the results of pseudopotential calculations in a widerange of superlattice periods (from N = 1 to 20).

THE DESTABILIZATION OF ZHANG-RICE SINGLET DUE TO THE p-p-TRANSFER IN COPPER OXIDES

An exact diagonalization of the CuO 4 cluster multielectron Hamiltonian is carried out in the atomic limit U d =U p =∞. The Zhang-Rice spin singlet state of two holes becomes unstable when t pp is growing due to crossover with a spin triplet state. It results in a multiband electronic structure of copper oxides.

S−phybridization effects on the metal-nonmetal phase transition in expanded liquid mercury

The metal-nonmetal phase transition in expanded mercury is studied within a tight-binding Hamiltonian that takes into account $s\ensuremath{-}p$ hybridization. The multiband electronic structure is solved by means of the cluster Bethe-lattice method. Analytic expressions are given for the appearance of energy gaps in terms of the average coordination number and the Hamiltonian parameters. It is shown that $s\ensuremath{-}p$ hybridization effects play an important role in the metal-nonmetal phase transition.

Multi-band electronic structure of non-simple liquid and amorphous metals and their alloys

A method is developed for evaluating the electronic properties of non-simple liquid and amorphous metals their alloys and liquid semiconductors. By non-simple metals we mean those for which the nearly free electron model does not hold, such as transition, noble and rare earth metals. Explicit expressions are evaluated within a tight binding self consistent single site framework. The formalism presented effects considerable simplification of the previously encountered technical difficulties involved in a matrix generalization of the one-band equations. Numerical applications to the density of states for dilute liquid mercury are shown.