E. Pomjakushina

Spin-State Transition in LaCoO3: Direct Neutron Spectroscopic Evidence of Excited Magnetic States

A gradual spin-state transition occurs in LaCoO3 around T approximately 80-120 K, whose detailed nature remains controversial. We studied this transition by means of inelastic neutron scattering and found that with increasing temperature an excitation at approximately 0.6 meV appears, whose intensity increases with temperature, following the bulk magnetization. Within a model including crystal-field interaction and spin-orbit coupling, we interpret this excitation as originating from a transition between thermally excited states located about 120 K above the ground state. We further discuss the nature of the magnetic excited state in terms of intermediate-spin (t(2g)(5)e(g)(1), S=1) versus high-spin (t(2g)(4)e(g)(2), S=2) states. Since the g factor obtained from the field dependence of the inelastic neutron scattering is g approximately 3, the second interpretation is definitely favored.

Coexistence of magnetism and superconductivity in the iron-based compound Cs0.8(FeSe0.98)2.

We report on muon-spin rotation and relaxation (μSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs(0.8)(FeSe(0.98))(2). Whereas our transport and magnetization data confirm the bulk character of the superconducting state below T(c)=29.6(2)u2009u2009K, the μSR data indicate that the system is magnetic below T(N)=478.5(3)u2009u2009K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs(0.8)(FeSe(0.98))(2) a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed T(N) is the highest reported to date for a magnetic superconductor.

Surface and bulk electronic structure of the strongly correlated system SmB6 and implications for a topological Kondo insulator

Recent theoretical calculations and experimental results suggest that the strongly correlated material SmB6 may be a realization of a topological Kondo insulator. We have performed an angle-resolved photoemission spectroscopy study on SmB6 in order to elucidate elements of the electronic structure relevant to the possible occurrence of a topological Kondo insulator state. The obtained electronic structure in the whole three-dimensional momentum space reveals one electron-like 5d bulk band centered at the X point of the bulk Brillouin zone that is hybridized with strongly correlated f electrons, as well as the opening of a Kondo band gap (Delta(B) similar to 20 meV) at low temperature. In addition, we observe electron-like bands forming three Fermi surfaces at the center Gamma point and boundary (X) over bar point of the surface Brillouin zone. These bands are not expected from calculations of the bulk electronic structure, and their observed dispersion characteristics are consistent with surface states. Our results suggest that the unusual low-temperature transport behavior of SmB6 is likely to be related to the pronounced surface states sitting inside the band hybridization gap and/or the presence of a topological Kondo insulating state.

Spin structure and magnetic phase transitions in TbBaCo 2 O 5.5

Spin ordering in

Superconductivity in a new layered bismuth oxyselenide: LaO0.5F0.5BiSe2

{mathrm{TbBaCo}}_{2}{mathrm{O}}_{5.5}

Effect of oxygen ordering on the structural and magnetic properties of the layered perovskites PrBaCo2O5+δ

and its temperature transformation reproducible for two differently synthesized samples are studied. One of the ceramic samples, in addition to the main phase

Iron isotope effect on the superconducting transition temperature and the crystal structure of FeSe1−x

{a}_{p}ifmmodetimeselsetexttimesfi{}2{a}_{p}ifmmodetimeselsetexttimesfi{}2{a}_{p},phantom{rule{0.3em}{0ex}}Pmmm

Oxygen isotope effect on metal–insulator transition in layered cobaltites RBaCo2O5.5 (R = Pr, Dy, Ho and Y)

(Z=2)

Evolution of two-gap behavior of the superconductor FeSe_{1-x}

, where