Electronic structure calculations for PrFe4P12 filled skutterudite using Extended Huckel tight-binding method

To get insight into the electronic properties of PrFe4P12 skutterudite, band electronic structure calculations, Total and Projected Density of States, Crystal Orbital Overlap Population and Mulliken Population Analysis were performed. The energy bands yield a semi metallic behavior with a direct gap (at gamma) of 0.02 eV. Total and Projected Density of States provided information of the contribution from each orbital of each atom to the total Density of States. Moreover, the bonding strength between some atoms within the unit cell was obtained. Mulliken Population analysis suggests ionic behavior for this compound

Thermal transport of the XXZ chain in a magnetic field

We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic fields where magnetothermal effects arise. Due to the integrability of this model, all transport coefficients diverge, signaled by finite Drude weights. Using exact diagonalization and mean-field theory, we analyze the temperature and field dependence of the thermal Drude weight for various exchange anisotropies under the condition of zero magnetization-current flow. First, we find a strong magnetic field dependence of the Drude weight, including a suppression of its magnitude with increasing field strength and a non-monotonic field-dependence of the peak position. Second, for small exchange anisotropies and magnetic fields in the massless as well as in the fully polarized regime the mean-field approach is in excellent agreement with the exact diagonalization data. Third, at the field-induced quantum critical line between the para- and ferromagnetic region we propose a universal low-temperature behavior of the thermal Drude weight.Comment: 9 pages REVTeX4 including 5 figures, revised version, refs. added, typos correcte

Coherent spin-current oscillations in transverse magnetic fields

We address the coherence of the dynamics of spin-currents with components transverse to an external magnetic field for the spin-1/2 Heisenberg chain. We study current autocorrelations at finite temperatures and the real-time dynamics of currents at zero temperature. Besides a coherent Larmor oscillation, we find an additional collective oscillation at higher frequencies, emerging as a coherent many-magnon effect at low temperatures. Using numerical and analytical methods, we analyze the oscillation frequency and decay time of this coherent current-mode versus temperature and magnetic field.Comment: 4 pages, 5 figures (and supplemental material: 4 pages, 6 figures

Long-time behavior of the momentum distribution during the sudden expansion of a spin-imbalanced Fermi gas in one dimension

We study the sudden expansion of spin-imbalanced ultracold lattice fermions with attractive interactions in one dimension after turning off the longitudinal confining potential. We show that the momentum distribution functions of majority and minority fermions approach stationary values quickly due to a quantum distillation mechanism that results in a spatial separation of pairs and majority fermions. As a consequence, Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations are lost during the expansion. Furthermore, we argue that the shape of the stationary momentum distribution functions can be understood by relating them to the integrals of motion in this integrable quantum system. We discuss our results in the context of proposals to observe FFLO correlations, related to recent experiments by Liao et al., Nature 467, 567 (2010).Comment: 8 pages including supplementary material, 9 eps figures, revised version as published, some text moved to the supplemental materia

Exact results for nonlinear ac-transport through a resonant level model

We obtain exact results for the transport through a resonant level model (noninteracting Anderson impurity model) for rectangular voltage bias as a function of time. We study both the transient behavior after switching on the tunneling at time t = 0 and the ensuing steady state behavior. Explicit expressions are obtained for the ac-current in the linear response regime and beyond for large voltage bias. Among other effects, we observe current ringing and PAT (photon assisted tunneling) oscillations.Comment: 7 page

Electronic Structure and Thermoelectric Prospects of Phosphide Skutterudites

The prospects for high thermoelectric performance in phosphide skutterudites are investigated based on first principles calculations. We find that stoichiometric CoP_3 differs from the corresponding arsenide and antimonide in that it is metallic. As such the band structure must be modified if high thermopowers are to be achieved. In analogy to the antimonides it is expected that this may be done by filling with La. Calculations for LaFe_4P_12 show that a gap can in fact be opened by La filling, but that the valence band is too light to yield reasonable p-type thermopowers at appropriate carrier densities; n-type La filled material may be more favorable.Comment: 3 pages, 3 figures, 1 tabl

Effects of partial substitution of Ni by Pd on the thermoelectric properties of ZrNiSn-based half-Heusler compounds

We report on the effects of partial substitution of nickel by palladium on the thermoelectric properties of ZrNiSn-based half-Heusler compounds. It is shown that the substitution of palladium for nickel results in a significant, beneficial reduction of the thermal conductivity. The Seebeck coefficient also decreases, but only by a small amount. In the Hf0.5Zr0.5Ni0.8Pd0.2Sn0.99Sb0.01Hf0.5Zr0.5Ni0.8Pd0.2Sn0.99Sb0.01 compound, a power factor of 22.1 μW K−2 cm−1 and a thermal conductivity as low as 4.5 W/m K are measured at room temperature. The dimensionless figure of merit ZT increases with increasing temperature and reaches a maximum value of 0.7 at about 800 K. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70206/2/APPLAB-79-25-4165-1.pd

Charge-Density-Wave Ordering in the Metal-Insulator Transition Compound PrRu4P12

X-ray and electron diffraction measurements on the metal-insulator (M-I) transition compound PrRu$_4$P$_{12}$ have revealed the emergence of a periodic ordering of charge density around the Pr atoms. It is found that the ordering is associated with the onset of a low temperature insulator phase. These conclusions are supported by the facts that the space group of the crystal structure transforms from Im$\bar{3}$ to Pm$\bar{3}$ below the M-I transition temperature and also that the temperature dependence of the superlattice peaks in the insulator phase follows the squared BCS function. The M-I transition could be originated from the perfect nesting of the Fermi surface and/or the instability of the $f$ electrons.Comment: 4 pages, 5 figures, Phys. Rev. B (2004) (in press

Thermomagnetic Power and Figure of Merit for Spin-1/2 Heisenberg Chain

Transport properties in the presence of magnetic fields are numerically studied for the spin-1/2 Heisenberg XXZ chain. The breakdown of the spin-reversal symmetry due to the magnetic field induces the magnetothermal effect. In analogy with the thermoelectric effect in electron systems, the thermomagnetic power (magnetic Seebeck coefficient) is provided, and is numerically evaluated by the exact diagonalization for wide ranges of temperatures and various magnetic fields. For the antiferromagnetic regime, we find the magnetic Seebeck coefficient changes sign at certain temperatures, which is interpreted as an effect of strong correlations. We also compute the thermomagnetic figure of merit determining the efficiency of the thermomagnetic devices for cooling or power generation.Comment: 8 page