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

Abstract

In order to study the effects of strong magnetic field on Kondo insulators, we calculate magnetization curves and single-particle excitation spectra of the periodic Anderson model at half-filling under finite magnetic field by using the self-consistent second-order perturbation theory combined with the local approximation which becomes exact in the limit of infinite spatial dimensions. Without magnetic field, the system behaves as an insulator with an energy gap, describing the Kondo insulators. By applying magnetic field to f-electrons, we found that the energy gap closes and the first order transition from insulator to metal takes place at a critical field H c . The magnetization curve shows a jump at H c . These are consistent with our previous study in terms of the exact diagonalization. Relationship to the experiments on YbB 12 and some other Kondo insulators is discussed.

Interplay between strong correlations and magnetic field in the symmetric periodic Anderson model

“…23,24 The observed insulator-metal transition 10 has also been reproduced qualitatively in theoretical calculations. 23 However, a detailed understanding of the changes in singleparticle dynamics and the associated hybridization gap on the whole has been lacking, and a quantitative description of the experimentally observed field-induced behavior has not been achieved. We seek to bridge these gaps in this paper by studying the PAM with a Zeeman term using LMA + DMFT and with particular emphasis on the strongly correlated ͑or strong-coupling͒ regime.…”

“…11,15,[22][23][24][25][26][27][28][29] For the symmetric PAM the conduction band is located symmetrically about the Fermi level ͑i.e., ⑀ c =0͒, while ⑀ f =−U / 2. This corresponds to half filling of the f and c levels, i.e., n f = ͚ ͗f i † f i ͘ = 1 and n c = ͚ ͗c i † c i ͘ =1 for all U.…”

Thermal and dynamical properties of the two-band Hubbard model compared with FeSi

“…This result is in strong contrast with the periodic Anderson model, in which the gap is strongly reduced by the Coulomb repulsion between f-electrons. [22,25] We have also investigated a variation of the present model, where the band energies ε k and −ε k in the band 1 and 2 are replaced with ε k and −bε k , respectively, and the Coulomb repulsion U in band 1 is replaced with bU . If we set b = 0, the band 2 becomes dispersionless and the band b becomes free, so we obtain the periodic Anderson model, in which the gap is known to be reduced due to the correlation.…”

Calculation of Optical Conductivity of YbB12using Realistic Tight-binding Model

“…15 This is in contrast to the periodic Andersonlike model, in which the self-energy is finite at T = 0, so that the gap size is renormalized to a value of the order of the Kondo temperature. 16 At finite temperatures in the present model, the self-energy becomes finite and has the imaginary-part due to the scattering between the thermally excited carriers, so that the gap in the quasiparticle DOS is filled up gradually. Effects will be more enhanced in the optical conductivity (see eq.…”

“…The actual calculation is performed on the real energy axis. 16,17 The quasi-particle density of states is calculated by ρ α (ε) = −(1/π)ImG α (ε). It is noted that the second-order self-energy disappears at T → 0 in the present model, since all the carriers die out.…”