The relaxation time study by Shubnikov-De Haas effect in Pb0.82Sn0.18 Te narrow band-gap semiconductors

The nature of broadening of the Landau levels in Pb_0.82Sn_0.18Te on the basis of recent experimental data is discussed. One needs to take into account the dependence of the monotonic part of magnetoresistance on the magnetic field H to determine the Dingle temperature on the Shubnikov-de Haas data. The Dingle temperature in solid solutions of Pb_0.82Sn_0.18Te is large (T_D=2.2?24.8 K) and depends on H. The T_D(H) dependence is explained of the transition to quantum limit. In this case the relaxation time _D=?(πkT_D)^?1 is increased with rising of the magnetic field, which is in accordance with the theory of Abrikosov. The _D/₀ dependence on carriers concentration can explain scattering on short range potential supposing the total scattering cross-section to be $\text{S}{}_{\mathrm{T}}\text{～?}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$. It was shown that the presence of random fluctuations of crystal potential in the solid solution is the most possible reason of broadening of the quantum levels. The experiment supports the dependence T_D ～ √n obtaining theoretically. cally.     

Critical behavior of electron spin resonance in La0.8Sr0.2MnO3 — a material with colossal magnetoresistance

High-frequency absorption in the colossal magnetoresistance material La_0.8Sr_0.2MnO₃ is investigated near the critical temperature in a magnetic field. The temperature dependences of the width, position, and intensity of the ESR line are studied in the near-critical region. Pis’fma Zh. éksp. Teor. Fiz. 67, No. 12, 1000–1004 (25 June 1998)     

Van der Waals Gaps in Sm1+x Ba2−x Cu3O y and Their Effect on Superconductivity

We have used electron–positron annihilation to study superconducting cuprates Sm_1+x Ba_2–x Cu₃O _y . We have determined the average radii for oxygen ions in Sm_1+x Ba_2–x Cu₃O _y . Taking into account the ion coordinates and their radii, we have constructed a geometric model for the arrangement of copper and oxygen ions in CuO₂ layers in the [b, c] plane, responsible for the superconductivity. From these data, we have determined the length of the ionic/covalent bonds and the width of the interionic gaps. We have established the effect of the features of the atomic structure of Sm_1+x Ba_2–x Cu₃O _y on the superconducting transition temperature T _c and we have shown that T _c increases as X inceases.