A. V. Inyushkin

Isotope effect in the thermal conductivity of germanium single crystals

The thermal conductivity of chemically, structurally, and isotopically highly pure germanium single crystals is investigated experimentally in the temperature range from 2 to 300 K. It is found that the thermal conductivity of germanium enriched to 99.99% 70Ge is 8 times higher at the maximum than the thermal conductivity of germanium with the natural isotopic composition.

On the Phonon Hall Effect in a Paramagnetic Dielectric

The phonon Hall effect in the paramagnetic dielectric garnet Tb3Ga5O12 has been investigated. It has been found that the coefficient of the phonon Hall effect is positive and is equal to (3.5 ± 2) × 10−5T−1 in a magnetic field of 3 T at a temperature of 5.13 K. The results are experimental evidence of the phonon Hall effect in the paramagnetic dielectric found by C. Strohm, G. L. J. A. Rikken, and P. Wyder, Phys. Rev. Lett. 95, 155901 (2005).

Thermal conductivity of polycrystalline CVD diamond: Experiment and theory

The temperature dependences of thermal conductivity κ of polycrystalline CVD diamond are measured in the temperature range from 5 to 410 K. The diamond sample is annealed at temperatures sequentially increasing from 1550 to 1690°C to modify the properties of the intercrystallite contacts in it. As a result of annealing, the thermal conductivity decreases strongly at temperatures below 45 K, and its temperature dependence changes from approximately quadratic to cubic. At T > 45 K, the thermal conductivity remains almost unchanged upon annealing at temperatures up to 1650°C and decreases substantially at higher annealing temperatures. The experimental data are analyzed in terms of the Callaway theory of thermal conductivity [9], which takes into account the specific role of normal phonon-phonon scattering processes. The thermal conductivity is calculated with allowance for three-phonon scattering processes, the diffuse scattering by sample boundaries, the scattering by point and extended defects, the specular scattering by crystallite boundaries, and the scattering by intercrystallite contacts. A model that reproduces the main specific features of the thermal conductivity of CVD diamond is proposed. The phonon scattering by intercrystallite contacts plays a key role in this model.

Anomalous isotope effect in high-temperature superconductor LSCO with 3d-impurities

Abstract The influence of transition metal substitutions (Ni, Fe, Co) and Zn at the Cu sites on T c and the oxygen isotope effect α o has been studied in the system La 2− y Sr y Cu 1− x M x O 4 with the optimum ( y = 0.15) and overdoped ( y = 0.20) compositions. Essential distinctions in the behavior of parameter α o for systems with heterovalent Fe and Co substitutions and isovalent Ni and Zn substitutions have been revealed. For Fe doped compounds with y = 0.15 the isotope effect was found to be very large: α o ≈ 1.3 at x = 0.011. The dependence of the isotope effect on the substituted atom concentration changes substantially when the degree of strontium doping varies. The experimental data were theoretically analyzed on the basis of the phonon mechanism of superconductivity and the concept of the existence of a singularity in the electron density of state N ( E F ). It is shown that the influence of paramagnetic impurities on the T c isotope shift of superconductors is enhanced when there is a sharp peak in N ( E F ). The difference in these effects for a system with the optimum strontium composition and for an overdoped system is also explained.

Low-temperature thermal conductivity of terbium-gallium garnet

Thermal conductivity of paramagnetic Tb3Ga5O12 (TbGG) terbium-gallium garnet single crystals is investigated at temperatures from 0.4 to 300 K in magnetic fields up to 3.25 T. A minimum is observed in the temperature dependence κ(T) of thermal conductivity at Tmin = 0.52 K. This and other singularities on the κ(T) dependence are associated with scattering of phonons from terbium ions. The thermal conductivity at T = 5.1 K strongly depends on the magnetic field direction relative to the crystallographic axes of the crystal. Experimental data are considered using the Debye theory of thermal conductivity taking into account resonance scattering of phonons from Tb3+ ions. Analysis of the temperature and field dependences of the thermal conductivity indicates the existence of a strong spin-phonon interaction in TbGG. The low-temperature behavior of the thermal conductivity (field and angular dependences) is mainly determined by resonance scattering of phonons at the first quasi-doublet of the electron spectrum of Tb3+ ion.

Changes in the magnetic structure of (La0.25Pr0.75)0.7Ca0.3MnO3 upon the isotopic substitution of 18O for 16O

A giant isotope effect, wherein the low-temperature metallic state is replaced by an insulator state, was recently observed when 18O was substituted for 16O in (La0.25Pr0.75)0.7Ca0.3MnO3 [N. A. Babushkina, L. M. Belova, O. Yu. Gorbenko et al., Nature (London) 391, 159 (1998)]. In the present work, the temperature evolution of the magnetic structure of two samples of this compound is studied by neutron diffraction. One sample contained a natural mixture of oxygen isotopes, 99.7% 16O, while the other was enriched to 75% with the isotope 18O. It is established that the samples are crystallographically identical at room temperature. As the temperature decreases, the sample with 16O undergoes successive antiferromagnetic (TAFM=5150 K) and ferromagnetic (TFM=110 K) transitions, which lead to the establishment of a noncollinear ferromagnetic structure, while a purely antiferromagnetic (TAFM=150 K) order arises in the sample with 18O. The temperature dependences of the intensities of the diffraction peaks associated with the charge ordering differ substantially in samples with 16O and 18O, and they correlate with the behavior of their electric resistance and magnetic structure.

Effect of dispersion on the phonon focusing and anisotropy of thermal conductivity of silicon single crystals in the boundary scattering regime

The effect of dispersion on the focusing of thermal phonons and on the thermal conductivity of silicon single crystals in the boundary scattering regime has been investigated. Analysis of the spectra of acoustic modes obtained for silicon single crystals from inelastic neutron scattering data has demonstrated that, upon transition from long-wavelength phonons to short-wavelength phonons, the directions of their focusing change. With an increase in temperature, this leads to a change in the anisotropy of thermal conductivity of phonons with different polarizations and, consequently, to a change in the anisotropy of the total thermal conductivity. Analysis of the temperature dependence of the thermal conductivity has revealed that the presence of extended flattened sections in the spectrum of short-wavelength transverse phonons indicates anomalously low values of the group velocity and, accordingly, a significant decrease in the contribution from these phonons to the thermal conductivity with increasing temperature. The contribution from longitudinal phonons to the thermal conductivity also significantly increases even at temperatures higher than 110 K and becomes dominant.

17O NMR IN HIGH-TC SUPERCONDUCTOR TL2BA2CACU2OY

Abstract 17 O NMR measurements have been performed between 10 and 400 K on an overdoped sample of Tl 2 Ba 2 CaCu 2 O y ( T c = 103 K). The electric field gradient parameters were deduced for all the oxygen sites. The temperature dependence of the magnetic hyperfine shift was measured for all these sites. No thermal variation of the shift was detected down to T c for oxygen in the TlO reservoir plane. As for oxygen in the CuO 2 plane the temperature dependence of the shift is similar to that for 205 Tl NMR line from thallium defects in the Ca layer measured in the same powder sample. This similarity is consistent with the single spin fluid model. The spin contribution to 17 K iso ( T ) and magnetic hyperfine constant 17 A iso were deduced.

Thermal conductivity of layered superconductors

Abstract The thermal conductivity K(T) of the superconducting 90-KYBCO, 60-KYBCO, BSCCO (2212) and non-superconducting Pr2CuO4, PrBa2Cu3O7−x, Bi2Sr2YCu2O8 single crystals have been measured. All investigated superconducting crystals demonstrate an upturn in K(T) at the superconducting critical temperature Tc. The thermal conductivity of the non-superconducting oxides varies strongly from a common dielectric-like behavior (Pr2CuO4) to a glassy-like temperature dependence (BSYCO).

Stimulated Raman scattering-active isotopically pure 12С and 13С diamond crystals: A milestone in the development of diamond photonics

Isotopically pure 12С and 13С diamonds are synthesized by chemical vapor deposition and impulsive stimulated Raman scattering in these crystals is investigated. The thermal conductivity of 12С isotopically pure damond and natC diamond with natural isotopic composition is measured. Phonon-nondegenerate Stokes lasing based on the χ(3) nonlinearity in the 12С, 13С, and natC diamond “triad” is attained, which opens a new stage in the development of diamond photonics.