Modern Physics Letters B

A survey of recent Raman scattering studies on the interstitial hydrogen molecule (H₂) in Si and GaAs is presented. It is shown that properties of H₂ strongly depend on the nuclear spin state I. In either material, para-H₂ (I=0) is unstable against irradiation with band gap light. In the case of Si, para-H₂ also preferentially disappears from the Raman spectra in the course of storage at room temperature in the dark. Possible explanations for this surprising behavior are discussed and compared with the latest infrared absorption studies.

The isotropic rigid and non-rigid rotators in the framework of Tsallis statistics are studied in the high and low temperature limits. The generalized partition functions, internal energies and heat capacities are calculated. Classical results of the Boltzmann–Gibbs statistics have been recovered as non-extensivity parameter approaches to 1. It has also been observed that non-extensivity parameter q behaves like a scale parameter in the low temperature regime of the rigid rotator model.

Quantum dynamics time evolution of a molecular magnet Fe₈ interacting with an electron nuclear spin is studied by solving the time-dependent Schrödinger equations. It is found that the variation of Fe₈ magnetization and the nuclear spin crucially depends on the interaction strength. The time evolution of the entanglement between the injecting electron and Fe₈ is evaluated. It is observed that the entanglement oscillates in time and is tightly related to the spin variation of the injecting electron. From these characteristics, the technique for the reversing and read-out of Fe₈ spin states is suggested.

The effect of Co–Ga paired substitution on the superconducting properties of YBa₂Cu₃O_7-δ (Y-123) has been investigated by X-ray diffraction, ac susceptibility, dc resistivity and oxygen content measurements. We report in this paper the results of our studies on the paired substitution of a magnetic and non-magnetic ion at Cu site in Y-123, while keeping the total dopant concentration fixed. The simultaneous substitution of Co and Ga at Cu site shows variation in the transition temperature (T_c), oxygen content and hole concentration as a function of change in the balance of magnetic (Co) and non-magnetic (Ga) concentration. Orthorhombicity (D), given as (b-a)/a, also varies as a function of increasing dopant concentration. The variation in T_c due to Co–Ga substitution is discussed in the light of dopant valency and hole filling mechanism.

We have derived the five-variable generating functions for the numbers of pyramid and staircase polyhedra on the cubic lattice with given values of width, depth, height, area and volume.

The Fermi level for a multiwalled carbon nanotube is determined analytically by using the Fermi velocity obtained from the particle-in-a-box model. Fermi energy is found to be quantized so that the corresponding quantum number coincides with the wall number. In addition, the classical limit is discussed.