Modern Physics Letters B

We study the scattering of a Gaussian wave packet in the modified Pöschl–Teller potential well in time respect. Analytical expressions of average dwell time, phase time, and average traversal time due to Larmor-clock times are obtained, from which the average traversal time can be identified with the average dwell time. We observe that the average dwell time is appreciably longer than the phase time at low energies, but they tend to coincide in the limit of narrow momentum distribution, high energy, and large interaction region. We also find that both of them are longer than the classical scattering time in the potential. All of these times are, however, shorter than the free-particle time, demonstrating the acceleration effect of the potential in temporal aspect of the scattering.

In this paper, our focus is on ABA trilayer graphene nanoribbon (TGN), in which the middle layer is horizontally shifted from the top and bottom layers. The conductance model of TGN as a FET channel is presented based on Landauer formula. Besides the good reported agreement with experimental study lending support to our model, the presented model demonstrates that minimum conductivity increases dramatically by temperature. It also draws parallels between TGN and bilayer graphene nanoribbon, in which similar thermal behavior is observed. Maxwell–Boltzmann approximation is employed to form the conductance of TGN near the neutrality point. Analytical model in degenerate regime in comparison with reported data proves that TGN-based transistor will operate in degenerate regime like what we expect in conventional semiconductors. Moreover, our model confirms that in similar condition, the conductivity of TGN is less than bilayer graphene nanoribbon as reported in some experiments.

We report experimental results on current–voltage characteristics of Au-Ti/n-Si/Au-Ti devices made on unintentionally n-doped silicon, which depend dramatically on temperature and external magnetic field. While such devices show Ohmic behavior in the temperature range 154–300 K, space-charge effect dominates at high bias voltages in the temperature range 77–154 K. In the later case, external magnetic field may increase its breakdown voltage, thus inducing large positive magnetoresistance similar to those reported by other groups.

Structural and magnetic properties of Bi_0.5 Ca_0.5-xBa_xMnO₃ (x = 0, 0.03, 0.05, 0.07 and 0.10) samples with charge ordering (CO) state and C-type antiferromagnetic (AFM) magnetic structure have been studied systematically. With increasing Ba-doping level, both CO and AFM are weakened. From the micro-magnetic analysis, we clarify the ambiguity about the Néel temperature T_N in bismuth-based perovskite manganites. We find that the paramagnetic (PM)-CO/AFM transition temperature T_CO at high temperature is the onset temperature of the PM–AFM transition, while customarily so-called T_N at low temperature indicates the finish of the PM–AFM transition. Both the macro- and micro-magnetic data show that, in all the samples, only AFM state coexists with PM matrix below CO transition and above T_N, while AFM state coexists with ferromagnetic (FM) state and PM state at lower temperature below T_N.

In the paper, the thermodynamic parameters of the superconducting state for Calcium under the pressure at 120 GPa have been determined. The numerical analysis has been made in the framework of the Eliashberg approach. In particular, the free energy difference between the superconducting and normal state has been calculated. On the basis of the obtained results, the specific heat for the superconducting (C^S) and normal (C^N) state, as well as the thermodynamic critical field (H_C) have been determined. It has been shown that the characteristic values of the considered thermodynamic functions do not obey the BCS universal laws: ΔC(T_C)/C^N(T_C) = 2.48 and .

Research on the influence of alloy concentration and distribution on bimetallic cluster plays a key role in exploring new structural material. This paper studies the melting process of icosahedral bimetallic cluster (PdPt)₁₄₇ with different Pt concentrations and different atomic distributions by using molecular dynamics with an embedded atom method. The results indicate that the mixed Pd–Pt cluster shows an irregular phenomenon between 580 and 630 K, i.e. the atomic energy decreases with the increase of temperature. This is because the surface energy of Pd is lower than that of Pt; the decreased energy due to Pd atomic segregation is larger than the increased energy due to heating during the segregation process. In addition, the temperature of Pd atomic segregation is strongly related to Pt concentration. This leads to that Pd atoms prefer to remain on the surface even after the cluster melted.

Single-electron models are regularly used in molecular physics to obtain information on the quantum properties of many-atom systems. Examples include applications of a particle contained on a ring to benzene, and an electron on a helix to helical polymers. Here it is shown that the model of an electron on a spherical helix (a loxodrome) is also amenable to such investigation, and may be used to describe an emerging class of molecules known as "molecular apple peels". Moreover, the Schrödinger equation that arises during consideration of this model is solved exactly.

The thermodynamical properties of interacting Bose atoms in a harmonic potential are studied within the mean-field approximation. For weak interactions, the quantum statistics is equivalent to an ideal gas in an effective mean-field potential. The eigenvalue of the Gross–Pitaevskii equation is identified as the chemical potential of the ideal gas. The condensation temperature and density profile of atoms are calculated. It is found that the critical temperature T_c decreases as the interactions increase. Below the critical point, the condensation fraction exhibits a universal relation of N₀/N = 1-(T/T_c)^γ, with the index γ ≈ 2.3 independent of the interaction strength, the chemical potential, as well as the frequency of the confining potential.