Tetsuro Saso

Insulator-to-metal transition in Kondo insulators under a strong magnetic field

Magnetization curve and changes of the single-particle excitation spectra by magnetic field are calculated for the periodic Anderson model at half-filling in infinite spatial dimension by using the exact diagonalization method. It is found that the field-induced insulator-to-metal transition occurs at a critical field

Formation Mechanism of Hybridization Gap in Kondo Insulators based on a Realistic Band Model and Application to YbB12

{\mathit{H}}_{\mathit{c}}

Thermoelectric power of Kondo insulators

, which is of the order of the single-ion Kondo temperature. The transition is of first order, but could be of second order in the infinite system size limit. These results are compared with the experiments on the Kondo insulator

Correlation Effects on Optical Conductivity of FeSi.

{\mathrm{YbB}}_{12}

A Unified Theory of Dynamical Mean Field and Spin Fluctuations

. \textcopyright{} 1996 The American Physical Society.

Quantum Monte Carlo simulation of one-dimensional periodic Anderson model

A new LDA+U band calculation is performed on the Kondo insulator material YbB 12 and an energy gap of about 0.001 Ryd is obtained. Based on this, a simple tight-binding model with 5d e and 4f Γ 8 orbitals on Yb atoms and the nearest neighbor σ-bonds between them is constructed with a good agreement to the above the LDA+U calculation near the gap. The density of states is also calculated and the shape is found to be very asymmetric with respect to the gap. A formation mechanism of the gap is clarified for the first time in a realistic situation with the orbital degeneracies in both conduction bands and the f states. This model can be a useful starting point for incorporating the strong correlation effect, and for understanding all the thermal, thermoelectric, transport and magnetic properties of YbB 12 .

Calculation of Optical Conductivity of YbB12 using Realistic Tight-binding Model

Abstract Thermoelectric power (TEP) of the Kondo insulators is investigated theoretically within the framework of the dynamical mean field theory. It is found that the temperature dependence of the Seebeck coefficient changes from the ordinary behavior S ( T )∝ T −1 in semiconductors to S ∝ T at low temperatures due to the finite imaginary part of the electron self-energy in the Kondo insulators with strong correlation. Realistic models for YbB 12 and FeSi based on the band calculations are also studied.

Magnetic Field Effects on Transport Properties of a Quantum Dot Studied by Modified Perturbation Theory

The effects of electron correlation in FeSi are studied in terms of the two-band Hubbard model with the density of states obtained from the band calculation. Using the self-consistent second-order ...

Self-Consistent Perturbational Study of Insulator-to-Metal Transition in Kondo Insulators due to Strong Magnetic Field

A new approach is proposed which encompasses the dynamical mean field theory (DMFT) for strongly correlated electron systems and the self-consistent renormalization (SCR) theory of spin fluctuations. The latter is incorporated into DMFT as a O (1/ d ) correction, where d is the spatial dimensionality, but in a phenomenological way. The DMFT is completely recovered when the effect of spin fluctuation is omitted, whereas the properties at the quantum critical point (QCP) is the same as the SCR theory. An example of calculation is presented for the single band Hubbard model and the non-Fermi liquid behavior is demonstrated at QCP.

Anomalous Metal–Insulator Transition in Filled Skutterudite CeOs4Sb12

Quantum Monte Carlo[MC] calculation of one-dimensional periodic Anderson model without orbital degeneracy is performed by use of the path-integral formulation. Local f moment coincides well with the recent MC calculation for single impurity by Hirsch and Fye above the temperature at which antiferromagnetic correlation starts to grow, and decreases faster than those for single impurity and coupled two impurities below that temperature. Overall features, including susceptibilities, resemble one-dimensional Hubbard model with half-filled band.