Modern Physics Letters B

I propose that the phase of an electron's wavefunction changes by π when the electron goes around a loop maintaining phase coherence. Equivalently, that the minimum orbital angular momentum of an electron in a ring is ℏ/2 rather than zero as generally assumed, hence, that the electron in a ring has azimuthal zero point motion. This proposal implies that a spin current exists in the ground state of aromatic ring molecules and suggests an explanation for the ubiquitousness of persistent currents observed in mesoscopic rings.

Recent efforts in measuring magnetic properties of ferromagnets in their transient states created by the illumination of intensive femtosecond laser pulses are critically re-analyzed. It is concluded that, although various pump-probe architectures can provide certain information about the magnetic properties of disturbed ferromagnets in their transient states, these schemes measured neither coercivity nor remanence defined in the conventional sense. One of the popular experimental schemes cannot even be used to define the working definitions of coercivity and remanence becuase they depend on the details of pumping pulses.

We investigate the structure of the electromagnetic current density for the pseudorelativistic massless spinor effective model for graphene. It is shown that the pseudorelativistic planar massless Dirac theory in the presence of a constant homogeneous electric field actually leads to the recently measured value for the minimum quantum conductivity.

The spin dynamics of ultracold bosonic atoms in a double well at finite temperatures is studied in terms of the spin structure factor within the two-site Bose–Hubbard model. The spin structure factor for positive frequencies reveals spin excitations at two frequencies corresponding two transitions among the eigenstates of the Hamiltonian. It has been found that the temperature effect is quite substantial. At zero temperature, only spin excitations at the low frequency survive, while the spectral weights at the two frequencies become approximately equal at high temperatures. As temperature increases, the spectral weight shifts from the low frequency to the high frequency.

We have calculated the fifth-order nonlinear optical response at experimentally relevant field strengths within the model of massless Dirac fermions by coupling the massless Dirac fermions to the time-dependent electric field quantum mechanically. It demonstrates that the fifth-order nonlinear optical response plays an important role in the contribution to the optical conductivity of pristine single-layer graphene in the low frequency part of the terahertz regime. The nonlinear effect can enhance the optical activity of single-layer graphene in the terahertz regime and significantly decreases the transmittance of graphene in the regime of frequencies from 0.1 to 0.5 THz. These properties of graphene may be used for photonic and optoelectronic device in the terahertz regime.

Electronic and thermoelectric properties of pure In₂O₃ and In_1.5T_0.5O₃ (T=Sc, Y) alloys including the band gap, the electrical and thermal conductivity, Seebeck coefficient and figure of merit have been investigated using semi-classical Boltzmann transport theory. The calculated results indicated that substituting indium atoms by these dopants have a significant influence on the electronic properties of alloyed In₂O₃ crystals. Substitution of Sc and Y atoms for In atoms increases the band gaps and Seebeck coefficient. The intrinsic relations between electronic structures and the transport performances of In₂O₃ and its alloys with Sc and Y are also discussed.

In this letter, self-absorption is discussed using the concept of escape factor. The calculation method of the escape factor for spherical geometry plasma is discussed. For the spherical geometry, the escape factors Λ(r) at any position r in a spherical geometry plasma (with the radius R) for Lorentzian and Holtsmarkian profiles are calculated, and a general expression is obtained. As an example, for the sodium 330.3 nm resonance line, the total radiance and the real radiance are calculated, and the self-absorption for the resonance line is discussed. This discussion will be useful for the study of the relationship of escape factor and the self-absorption of spectral lines for any geometries.

Ni substituted Li–Zn ferrites with compositional formulas Li_0.4-0.5xZn_0.2Ni_xFe_2.4-0.5xO₄, where x = 0.02 ≤ x ≤ 0.1 in steps of 0.02, is synthesized by a chemical method using citrate precursors. The prepared ferrites are investigated for their structural, electrical and magnetic properties. Ni substitution significantly changes the characteristic properties of Li–Zn ferrites. There is an increase in grain growth as determined from SEM measurements. An increase in the room temperature DC resistivity is observed with the addition of Ni. The room temperature initial permeability shows an overall decrease with Ni concentration, which is explained with respect to saturation magnetization and supplemented by nuclear hyperfine field obtained from Mössbauer analysis. The variation of the complex permeability with frequency is measured over the frequency range of 100 Hz–1 MHz and dispersion is found. A possible mechanism contributing to the above process is discussed.

The effects of oxidation on the weight change (D_W) and modulus change (D_E) of an uncoated C/SiBC were investigated in 600–1000°C. The results show that larger D_W does not mean larger damage. D_E is more sensitive to the oxidation process than D_W. At lower temperatures, a small D_W can result in a large D_E. The results result from the different oxidation rates of carbon fibers and pyrocarbon interphase.