E.S. Konovalova

Magnetic excitation spectrum of mixed-valence SmB6 studied by neutron scattering on a single crystal

The paramagnetic response of mixed-valence samarium hexaboride has been studied by inelastic neutron scattering using a low-absorption double-isotope single crystal of 154Sm11 B6. Measurements were performed for energy transfers 0<or=h(cross) omega <or=50 meV at temperatures ranging from 2 to 100 K. Two main contributions were observed in the spectra: a broad intermultiplet transition of single-ion type at h(cross) omega approximately=36 meV, and a narrow low-energy excitation centred at h(cross) omega approximately=14 meV, which is strongly anisotropic and temperature dependent and exhibits a weak but visible dispersion. The latter excitation appears to be an inherent feature of the mixed-valence state due to f-electron hybridization effects, which denotes the formation of a local bound state around the Sm sites.

Lattice Dynamics of Intermediate Valence Semiconductor SmB6.

All acoustic and the lowest optic branches in three main symmetry directions have been determined by inelastic neutron scattering at room temperature using a double isotope monocrystal 154Sm11B6. In comparison with the integer valence system LaB6 the phonons are softer, and the LA branches exhibit remarkable anomalies. These features are interpreted on the basis of a specific coupling of the lattice vibrations with the dipole (f-d) and monopole (f-f) excitations of the Sm shells, the latter being characteristic for the mixed valence semiconductor. A weak broad signal has been observed in the energy gap between acoustic and optic modes, which can be ascribed to an additional mode appearing due to the nonadiabatic interaction of phonons with valence fluctuations.

Neutron Scattering Study of the Intermediate-Valent Ground State in SmB6

Inelastic-neutron-scattering spectra were measured on the polycrystalline double isotopic sample 154Sm 11B6 in a wide range of the energy transfer. The intermultiplet transitions corresponding to f6 and f5 configurations of the intermediate-valent state of the Sm ion, as well as a low-energy excitation with unusual momentum transfer and temperature dependences have been observed in the magnetic part of the scattering function.

High pressure studies of cerium hexaboride

Magnetic susceptibility and magnetoresistance of CeB 6 have been measured in magnetic fields H 6 and SmB 6 lattice parameters at pressures p⩽100 kbar.

Low temperature resistivity of valence fluctuation compound SmB6

Abstract The electrical resistivity of SmB6 single crystal has been measured down to 50mK. At temperatures below 3 K a rather complicated behavior of electrical conductivity including the temperature activated and temperature non-activated term was observed. The activated conductivity term can be well described by σ = c exp [-( T 0 T ) x ] with x equal to or close to 1 and T0 = 2.68 K, while the non-activated conductivity is dominating below about 0.2 K and shows presence of the logarithmic Kondo-like contribution to resistivity. To explain observed results a model based on introducing a fine structure into the hybridization gap is proposed. This fine structure may consist of two narrow low-density bands with a gap between them of few tenths of meV wide.

Transport and magnetic properties of mixed valent SmB6

Abstract We present the results of transport and magnetic measurements performed on two intermediate valent SmB6 single crystals. The received results above 15 K are in agreement with the results obtained by other groups. At the lowest temperatures, however, the resistivity, magnetization, and susceptibility seem to be strongly influenced by the presence of impurities in the investigated samples.

Ground state formation in intermediate valent SmB6

Abstract Electrical resistivity measurements have been carried out on the intermediate valent small gap compound SmB 6 at temperatures between 90 and 0.08 K. From the local activation energy we were able to determine directly the width of the hybridization gap which controls the conductivity between 70 and 15 K, and the distance between the bottom of the conduction band and in-gap states which are formed in this energy gap and provide extrinsic conduction in the temperature range 15–3 K. Below about 3 K the activation energy of all the samples decreases rapidly to values which are much lower than the available thermal energy. This result implies that the residual conductivity of SmB 6 is of non-activated (metallic) nature. The metallic behaviour can be attributed to a many-particle ground state formed from the in-gap states of this compound.

Electrical resistivity of doped EuB6 down to 50 mK

Abstract Results of electrical resistivity measurements of C-doped EuB 6 between 50 mK and 300 K are discussed. The attention is concentrated on the high residual resistivity of this material below its magnetic transition temperature. Results have shown that the high resistivity at lowest temperatures originates from the scattering of conduction electrons on mixed magnetic structure of the sample.

Investigation of in-gap states in SmB6 ∗ )

We have investigated the low temperature properties of the narrow-gap semiconductor SmB6 by means of electrical resistivity and specific heat measurements. Results imply that the residual resistivity below about 3 K is non-activated and the corresponding state, which is formed within the in-gap states, has a metallic-like nature. Heat capacity measurements confirmed the metallic-like properties of the in-gap states and revealed, moreover, an enhancement of the specific heat below 2 K which is more expressive for the sample with a lower amount of impurities. The observed behaviour can be attributed to the formation of a coherent state within the in-gap states of this compound.

Low-temperature magnetic properties of SmB6

Abstract We have performed measurements of the magnetic susceptibility of three SmB 6 single crystals with various purities in the temperature range between 300 and 2 K. In the high-temperature region the observed data follow the Curie–Weiss-like dependence indicating a local-moment behavior. Below 10 K, where a temperature-independent behavior due to Van Vlecks theory is expected, all samples exhibit an increase of magnetization which can be accounted for by a small amount of bare Sm 3+ ions, magnetic 4f 5 5d 1 states or by magnetic rare-earth impurities.