Crystal-field effects in the first-order valence transition in YbInCu4 induced by an external magnetic field

As it was shown earlier [Dzero, Gor'kov, and Zvezdin, J. Phys.:Condens. Matter 12, L711 (2000)] the properties of the first-order valence phase transition in YbInCu4 in the wide range of magnetic fields and temperatures are perfectly described in terms of a simple entropy transition for free Yb ions. Within this approach, the crystal field effects have been taken into account and we show that the phase diagram in the $B-T$ plane acquires some anisotropy with respect to the direction of an external magnetic field.Comment: 4 pages, 3 eps figures; minor changes; to be piblished in J. of Physics: Cond. Ma

Kondo insulator SmB6 under strain: surface dominated conduction near room temperature

SmB6 is a strongly correlated mixed-valence Kondo insulator with a newly discovered surface state, proposed to be of non-trivial topological origin. However, the surface state dominates electrical conduction only below T* ~ 4 K limiting its scientific investigation and device application. Here, we report the enhancement of T * in SmB6 under the application of tensile strain. With 0.7% tensile strain we report surface dominated conduction at up to a temperature of 240 K, persisting even after the strain has been removed. This can be explained in the framework of strain-tuned temporal and spatial fluctuations of f-electron configurations, which might be generally applied to other mixed-valence materials. We note that this amount of strain can be indued in epitaxial SmB6 films via substrate in potential device applications.Comment: to appear in Nature Material

Peculiarities in Low Temperature Properties of Doped Manganites A1-xBxMnO3

The phase diagram and low temperature properties of the doped manganites A1-xBxMnO3 are discussed for the concentrations x < 0.4. The transition from insulating antiferromagnetic to metallic ferromagnetic state at x_cr = 0.16 is treated by means of percolation theory. The unifying description of insulating and metallic states is presented. The undoped manganite is a band insulator consisting of ferromagnetic layers, which are coupled antiferromagnetically along the c direction with a low Neel temperature. The metallic phase can be described by the two-band Fermi liquid picture. The behavior of conductivity, spin wave excitations, etc. is analyzed and the comparison with experimental data is carried out.Comment: To appear in EPJ, 35 pages, 5 figure

Magnetic penetration depth in disordered iron-based superconductors

We study the effect of disorder on the London penetration depth in iron-based superconductors. The theory is based on a two-band model with quasi-two-dimensional Fermi surfaces, which allows for the coexistence region in the phase diagram between magnetic and superconducting states in the presence of intraband and interband scattering. Within the quasiclassical approximation we derive and solve Eilenberger's equations, which include a weak external magnetic field, and provide analytical expressions for the penetration depth in the various limiting cases. A complete numerical analysis of the doping and temperature dependence of the London penetration depth reveals the crucial effect of disorder scattering, which is especially pronounced in the coexistence phase. The experimental implications of our results are discussed.Comment: 10 pages, 6 figure

Electron Cotunneling into a Kondo Lattice

Motivated by recent experimental interest in tunneling into heavy electron materials, we present a theory for electron tunneling into a Kondo lattice. The passage of an electron into the Kondo lattice is accompanied by a simultaneous spin flip of the localized moments via cotunneling mechanism. We compute the tunneling current with the large-$N$ mean field theory. In the absence of disorder, differential tunneling conductance exhibits two peaks separated by the hybridization gap. Disorder effects lead to the smearing of the gap resulting in a Fano lineshape.Comment: 4 pages, 2 eps figure