Thermopower of the Hubbard model: Effects of multiple orbitals and magnetic fields in the atomic limit

We consider strongly-correlated systems described by the multi-orbital Hubbard model in the atomic limit and obtain exact expressions for the chemical potential and thermopower. We show that these expressions reduce to the Heikes formula in the appropriate limits ($k_BT \gg U$) and ($k_BT \ll U$) and obtain the full temperature dependence in between these regimes. We also investigate the effect of a magnetic field introduced through a Zeeman term and observe that the thermopower of the multi-orbital Hubbard model displays spikes as a function of magnetic field at certain special values of the field. This effect might be observable in experiments for materials with a large magnetic coupling.Comment: 8 pages, 4 figures Typos in eqns. 3 and 4 and reference 17 correcte

Computation efficiency of master-slave processors in multitasking applications: a performance analysis

Examines the computational efficiency of the master slave Multiple processor architectures system by considering a system consisting of a master M and p slave processors. The system performance is found by modelling it as a Markov process and a new method presented for computing the steady-state performance by dividing the state space into an interior and boundary space. The throughput of the system is then compared with that of a cost equivalent single processor using different values for the well-known Grosch parameter. It is demonstrated that the system is computationally efficient only for a sufficiently large number of jobs

Understanding the nature of electronic effective mass in double-doped SrTiO3_{3}

We present an approach to tune the effective mass in an oxide semiconductor by a double doping mechanism. We demonstrate this in a model oxide system Sr$_{1-x}$La$_x$TiO$_{3-\delta}$, where we can tune the effective mass ranging from 6--20$\mathrm{m_e}$ as a function of filling or carrier concentration and the scattering mechanism, which are dependent on the chosen lanthanum and oxygen vacancy concentrations. The effective mass values were calculated from the Boltzmann transport equation using the measured transport properties of thin films of Sr$_{1-x}$La$_x$TiO$_{3-\delta}$. Our method, which shows that the effective mass decreases with carrier concentration, provides a means for understanding the nature of transport processes in oxides, which typically have large effective mass and low electron mobility, contrary to the tradional high mobility semiconductors.Comment: 5 pages with 4 figure

Dynamical thermal response functions for strongly correlated one-dimensional systems: Hubbard and spinless fermion t-V model

In this paper, we study the thermal response functions for two one-dimensional models, namely, the Hubbard and spinless fermion t-V model, respectively. By exactly diagonalizing finite sized systems, we calculate dynamical, electrical, thermoelectrical, and thermal conductivities via the Kubo formalism [J. Phys. Soc. Jpn. 12, 570 (1957)]. The thermopower (Seebeck coefficient), Lorenz number, and dimensionless figure of merit are then constructed, which are quantities of great interest to the physics community both theoretically and experimentally. We also geometrically frustrate these systems and destroy integrability by the inclusion of a second-neighbor hop in the kinetic energy operator. These frustrated systems are shown to have enhanced thermopower and Lorenz number at intermediate and low temperatures