Interaction driven subgap spin exciton in the Kondo insulator SmB6.

Using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB6 and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering. We find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.

Intermediate-valence state of the Sm and Eu in SmB6 and EuCu2Si2: neutron spectroscopy data and analysis.

Magnetic neutron scattering data for Sm (SmB6, Sm(Y)S) and Eu (EuCu2Si2-x Ge x ) intermediate-valence compounds have been analysed in terms of a generalized model of the intermediate-radius exciton. Special attention is paid to the correlation between the average ion's valence and parameters of the low-energy excitation in the neutron spectra, such as the resonance mode, including its magnetic form factor. Along with specific features of the formation of the intermediate-valence state for Sm and Eu ions, common physical mechanisms have been revealed for systems based on these elements from the middle of the rare-earth series. A consistent description of the existing experimental data has been obtained by using the concept of a loosely bound hole for the Eu f-electron shell in the intermediate-valence state, in analogy with the previously established loosely bound electron model for the Sm ion.

Screened moments and extrinsic in-gap states in samarium hexaboride.

Samarium hexaboride (SmB6) is a Kondo insulator, with a narrow gap due to hybridization between localized and conduction electrons. Despite being an insulator, many samples show metal-like properties. Rare-earth purification is exceedingly difficult, and nominally pure samples may contain 2% or more of impurities. Here to determine the effects of rare-earth doping on SmB6, we synthesized and probed a series of gadolinium-doped samples. We found a relationship between specific heat and impurity moment screening which scales systematically. Consistent with this finding, our neutron scattering experiments of a high purity sample of doubly isotopic 154Sm11B6 show no intrinsic excitations below the well-established 13 meV spin-exciton. The result of introducing impurities into a Kondo insulator is incompletely understood, but it is clear from our measurements that there is a systematic relationship between rare-earth impurities and metal-like properties in SmB6.

[Effect of hypotensive therapy on oxygen metabolism in middle-aged and elderly hypertensive patients]. / Vliianie gipotenzivnoi terapii na kislorodnyi obmen u bol'nykh gipertonicheskoi bolezn'iu pozhilogo i starcheskogo vozrasta.

The authors studied the effect of hypotensive therapy with Rauwolfia preparations, dopegit and hemiton on oxygen tension in tissues (PO2), oxygen consumption by the body (QO2) and the state of hemodynamics: arterial pressure (AP), cardiac index (CI) and total peripheral vascular resistance (TPVR). They examined 108 elderly and old patients with II stage hypertensive disease. It was established that the tissue PO2 increases in decrease of AP attended by a decrease in TPVR and increase in CI, but reduces in decrease in CI and increase in TPVR. In the last case, however, the work of the heart diminishes. Maintenance hypotensive therapy in the period of normalized AP in individuals with unstable hypertension aggravates hypoxia. The decrease in QO2 encountered in half the patients who were treated was attended by a reduction in systolic pressure; no decrease of AP was encountered in cases of increase in QO2 which testifies to a connection between the changes in hemodynamics and the state of tissue oxygen requirements.

Interplay of low-energy phonons and magnetic excitations in the Kondo insulator YbB12.

Peculiarities in the lattice dynamics of the Kondo insulator Y bB(12) have been studied by inelastic neutron scattering. Selected phonon modes were traced above and below the temperature region (T ~ 50 K) where the gap opens in the electron density of states. The intensities of some low-energy modes exhibit an anomalous temperature dependence for q vectors close to the Brillouin zone boundary, suggesting a renormalization of the phonon eigenvectors. This effect is thought to arise from a coupling with magnetic excitations of the same symmetry, which exist at nearby energies. It is argued that this magnetovibrational coupling may in turn play a role in the steep temperature crossover existing in Y bB(12) between the low-temperature (Kondo insulator) and high-temperature (incoherent spin-fluctuation) regimes, which is rapidly suppressed by lighter Zr substitution.

Magnetic excitations in EuCu2(Si(x)Ge(1-x))2: from mixed valence towards magnetism.

We report the inelastic neutron scattering study of spin dynamics in EuCu(2)(Si(x)Ge(1-x))(2) (x = 1, 0.9, 0.75, 0.6), performed in a wide temperature range. At x = 1 the magnetic excitation spectrum was found to be represented by the double-peak structure well below the energy range of the Eu(3+) spin-orbit (SO) excitation (7)F(0)→(7)F(1), so that at least the high-energy spectral component can be assigned to the renormalized SO transition. Change of the Eu valence towards 2 + with increased temperature and/or Ge concentration results in further renormalization (lowering the energy) and gradual suppression of both inelastic peaks in the spectrum, along with developing sizeable quasielastic signal. The origin of the spectral structure and its evolution is discussed in terms of excitonic model for the mixed valence state.

Polarized-neutron study of spin dynamics in the Kondo insulator YbB12.

Inelastic neutron scattering experiments have been performed on the archetype compound YbB(12), using neutron polarization analysis to separate the magnetic signal from the phonon background. With decreasing temperature, components characteristic for a single-site spin-fluctuation dynamics are suppressed, giving place to specific, strongly Q-dependent, low-energy excitations near the spin-gap edge. This crossover is discussed in terms of a simple crystal-field description of the incoherent high-temperature state and a predominantly local mechanism for the formation of the low-temperature singlet ground state.

[Use of exercise tests and echocardiography during long-term observation of patients with mitral stenosis and cardiac insufficiency]. / Primenenie nagruzochnykh testov i ékhokardiografii pri dlitel'nom nabliudenii bol'nykh s mitral'nym stenozom i serdechnoi nedostatochnost'iu.

Findings of echocardiography and bicycle exercise testing were considered objective hemodynamic criteria during long-term follow-up studies of patients with mitral stenosis and early stages of cardiac insufficiency. In patients with the first degree cardiac insufficiency the most sensitive parameters were: exercise tolerance, physical adaptation index and left atrial size. In patients with the second A degree cardiac insufficiency additional information has also been obtained upon studying the ejection fraction and the rate of left ventricular circular shortening.