Analysis of confinement potential fluctuation and band-gap renormalization effects on excitonic transition in GaAs/AlGaAs multiquantum wells grown on (1 0 0) and (3 1 1)A GaAs surfaces

The competition between confinement potential fluctuations and band-gap renormalization (BGR) in GaAs/Al_xGa_1−xAs$\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells grown on [1 0 0] and [3 1 1]A GaAs substrates is evaluated. The results clearly demonstrate the coexistence of the band-tail states filling related to potential fluctuations and the band-gap renormalization caused by an increase in the density of photogenerated carriers during the photoluminescence (PL) experiments. Both phenomena have strong influence on temperature dependence of the PL-peak energy (E_PL(T))$(E_{\mathit{PL}}(T))$. As the photon density increases, the E_PL can shift to either higher or lower energies, depending on the sample temperature. The temperature at which the displacement changes from a blueshift to a redshift is governed by the magnitude of the potential fluctuations and by the variation of BGR with excitation density. A simple band-tail model with a Gaussian-like distribution of the density of state was used to describe the competition between the band-tail filling and the BGR effects on E_PL(T).     

Multiple-vehicle collision induced by a sudden stop in traffic flow

We study the dynamic process of the multiple-vehicle collision when a vehicle stops suddenly in a traffic flow. We apply the optimal-velocity model to the vehicular motion. If a vehicle does not decelerate successfully, it crashes into the vehicle ahead with a residual speed. The collision criterion is presented by _vi(t)/Δ_xi(t)→∞$v_i(t)/\mathrm{\Delta }{x}_i(t)\to \infty$ if Δ_xi(t)→0$\mathrm{\Delta }{x}_i(t)\to 0$ where _vi(t)$v_i(t)$ and Δ_xi(t)$\mathrm{\Delta }{x}_i(t)$ are the speed and headway of vehicle i at time t. The number of crumpled vehicles depends on the initial velocity, the sensitivity, and the initial headway. We derive the region map (or phase diagram) for the multiple-vehicle collision.     

The anisotropic quantum spin-1/2 Heisenberg antiferromagnet in the presence of a longitudinal field on a bcc lattice

In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter (Δ)$(\Delta )$ and magnetic field (H  ), where Δ=0$\Delta =0$ and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N  =4 spins (EFT-4). The staggered _ms=(_mA−_mB)/2$m_s=(m_A-m_B)/2$ and total m=(_mA+_mB)/2$m=(m_A+m_B)/2$ magnetizations are numerically calculated, where in the limit of _ms→0$m_s\to 0$ the critical line _TN(H,Δ)$T_N(H,\Delta )$ is obtained. The phase diagram in the T−H$T-H$ plane is discussed as a function of the parameter Δ$\Delta$ for all values of H∈[0,_Hc(Δ)]$H\in [0,H_c(\Delta )]$, where _Hc(Δ)$H_c(\Delta )$ correspond the critical field (_TN=0)$(T_N=0)$. Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=_Hc(Δ)≥_Hc(Δ=1)=8J$H=H_c(\Delta )\ge H_c(\Delta =1)=8J$ in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of Δ∈[0,1]$\Delta \in [\mathrm{0,1}]$. This reentrant behavior increases with increase of the anisotropy parameter Δ$\Delta$. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values.     

Lorentz covariant nucleon self-energy decomposition of the nuclear symmetry energy

Using the Hugenholtz–Van Hove theorem, we derive analytical expressions for the nuclear symmetry energy _Esym(ρ)$E_{\mathrm{sym}}(\rho )$ and its density slope L(ρ)$L(\rho )$ in terms of the Lorentz covariant nucleon self-energies in isospin asymmetric nuclear matter. These general expressions are useful for determining the density dependence of the symmetry energy and understanding the Lorentz structure and the microscopic origin of the symmetry energy in relativistic covariant formulism. As an example, we analyze the Lorentz covariant nucleon self-energy decomposition of _Esym(ρ)$E_{\mathrm{sym}}(\rho )$ and L(ρ)$L(\rho )$ and derive the corresponding analytical expressions within the nonlinear σ–ω–ρ–δ relativistic mean field model.     

Quantum information entropies for a squared tangent potential well

The particle in a symmetrical squared tangent potential well is studied by examining its Shannon information entropy and standard deviations. The position and momentum information entropy densities _ρs(x)${\rho }_s(x)$, _ρs(p)${\rho }_s(p)$ and probability densities ρ(x)$\rho (x)$, ρ(p)$\rho (p)$ are illustrated with different potential range L and potential depth U  . We present analytical position information entropies _Sx$S_x$ for the lowest two states. We observe that the sum of position and momentum entropies _Sx$S_x$ and _Sp$S_p$ expressed by Bialynicki-Birula–Mycielski (BBM) inequality is satisfied. Some eigenstates exhibit entropy squeezing in the position. The entropy squeezing in position will be compensated by an increase in momentum entropy. We also note that the _Sx$S_x$ increases with the potential range L, while decreases with the potential depth U  . The variation of _Sp$S_p$ is contrary to that of _Sx$S_x$.     

Bulk and local magnetic susceptibility in CeAl2 and CeB6

A comprehensive and high-precision magnetoresistance (MR) Δρ/ρ(H,T)$\mathrm{\Delta }\rho /\rho (H,T)$ and magnetization M(H,T) measurements have been carried out for two well known and archetypal magnetic strongly correlated electron systems—CeAl₂ and CeB₆. It was shown that the main Brillouin-type component of MR in these magnetic heavy fermion compounds can be consistently interpreted in the frameworks of a simple relation between resistivity and magnetization—Δρ/ρ∼M²$\mathrm{\Delta }\rho /\rho \sim M^2$ obtained by Yosida [Phys. Rev. 107 (1957) 396]. A local magnetic susceptibility _χloc(T,H)=(1/H^*(d(Δρ/ρ)/dH))^1/2${\chi }_{\mathrm{loc}}(T,H)=(1/H^{*}(\mathrm{d}(\mathrm{\Delta }\rho /\rho )/\mathrm{d}H){)}^{1/2}$ was deduced directly from this part of MR and compared in details with the data of bulk susceptibility χ(T,H) measurements. Two additional contributions to MR have been also deduced for CeAl₂ ((i) linear (∼H) and (ii) nanoscale ferromagnetic components) and applied for a characterization of spin polarons in this magnetic material. The dependencies χ_loc(T,H) and χ(T,H) obtained in this study for CeB₆ and CeAl₂ allow us to analyze the H–T magnetic phase diagram in these magnetic heavy fermion compounds.     

On the propensity of magnetism in 3d transition-metal-MgCNi3 alloys

The effects of disorder and incipient magnetism in MgC(_Ni1-xTx)3$\mathrm{MgC}({\mathrm{Ni}}_{1-x}{\mathrm{T}}_x{)}_3$ (T≡Fe$\mathrm{T}\equiv \mathrm{Fe}$, Co or Cu) alloys are studied using coherent-potential approximation and Ginzburg–Landau coefficients. The first-principles, local-density-functional-based calculations for substitutionally disordered Fe and Co impurities in the Ni sub-lattice of MgCNi₃, in low concentrations, show that incipient magnetism resides in these materials. The overestimation of the calculated magnetic properties points to the limitations of the local-density approximation. However, using a phenomenological approach based on Ginzburg–Landau coefficients and the fixed-spin moment method, we show that MgC(_Ni1-xTx)3$\mathrm{MgC}({\mathrm{Ni}}_{1-x}{\mathrm{T}}_x{)}_3$ alloys remain paramagnetic. At expanded volumes, we also find the possibility of a ferromagnetic state for MgC(_{Ni0.95Fe0.05)3}$\mathrm{MgC}({\mathrm{Ni}}_{0.95}{\mathrm{Fe}}_{0.05}{)}_3$ and MgC(_{Ni0.90Co0.10)3}$\mathrm{MgC}({\mathrm{Ni}}_{0.90}{\mathrm{Co}}_{0.10}{)}_3$ alloys.     

Effect of external magnetic field on superconducting and spin density wave gaps of high-Tc superconductors

A theoretical model is addressed here to study the interplay of the superconductivity (SC) and the spin density wave (SDW) long range orders in underdoped region in the vicinity of on-set of superconductivity in presence of an external magnetic field. The order parameters are calculated by using Zubarev’s technique of Green’s functions and determined numerically self-consistently. The gap parameters are found to be strongly coupled to each other through their coupling constants. The interplay displays BCS type two gaps in the quasi-particle density of states (DOS) which resemble the tunneling conductance of STM experiments. The gap edges in the DOS appear at ±(z+z₁)$\pm (z+z_1)$ and ±(z-z₁)$\pm (z-z_1)$. The applied magnetic field further induces Zeeman splitting which is explained on the basis of spin-filter effect of tunneling experiment.     

On hydrogen transport in the first wall material of fusion devices in the presence of a broadband distribution of traps over the trapping energy

The dynamics of hydrogen dissolved in a sample with continuous distribution of traps over trapping energy φ(ε)∝exp(−αε)$\phi (\epsilon )\propto \exp (-\alpha \epsilon )$ (ε=E/T$\epsilon =E/T$ is the ratio of trapping energy E to the sample's temperature T  ) is considered. Assuming that the hydrogen density is smaller than the trap density and the most of hydrogen is trapped, we found that the dynamics of hydrogen transport can be described by either sub-diffusion or non-linear diffusion equations. Analysis of the outgassing of the sample homogeneously loaded with hydrogen gives, in the most important cases, both power-law, _ΓH∝t^−p${\Gamma }_{\mathrm{H}}\propto t^{-p}$ (p≥1/2$p\ge 1/2$) and exponential, ln(_ΓH)∝−t^α$\ln ({\Gamma }_{\mathrm{H}})\propto -t^{\alpha }$, time dependencies of the outgassing flux, _ΓH(t)${\Gamma }_{\mathrm{H}}(t)$.     

Towards the MSSM from F-theory

We study the MSSM in F-theory. Its group is the commutant to a structure group SU(5)×UY₍₁₎$\mathit{SU}(5)\times U{(1)}_Y$ of a gauge bundle in E₈$E_8$. The spectrum contains three generations of quarks and leptons plus vectorlike electroweak and colored Higgses. The minimal MSSM Yukawa couplings with matter parity is obtained at the renormalizable level.     

The influence of 3d-impurities on magnetic and transport properties of CoSiB metallic glasses

Temperature dependencies of magnetic susceptibility and electric resistivity of Co-based metallic glasses (MGs) of the general composition _Co(72-x)Mex(Si,B₎₂₈${\mathrm{Co}}_{(72-x)}{\mathrm{Me}}_x(\mathrm{Si},\mathrm{B}{)}_{28}$(Me=Fe,Cr,Si:B=18:10)$(\mathrm{Me}=\mathrm{Fe},\mathrm{Cr},\mathrm{Si}:\mathrm{B}=18:10)$ have been studied up to 950 K. The studied MGs were found to be ferromagnets at the room temperature and their Curie point _TC$T_{\mathrm{C}}$ ranges within 260–560 K depending on the dopant contents. At the temperatures higher than _TC$T_{\mathrm{C}}$, a wide paramagnetic region exists. The regularities of magnetic moment variation upon Cr doping evidence a formation of antiferromagnetic clusters, which determine the anomalous behavior of resistivity.     

First-principles materials design of CuInSe2-based high-efficiency photovoltaic solar cells

Based on ab initio   electronic structure calculations by self-interaction-corrected local-density-approximation (SIC-LDA) with the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA), we propose a materials design for high efficiency photovoltaic solar cells (PVSCs). It is shown that (i) the concentration dependence of the mixing energy of CuIn_1−xGa_xSe₂${\mathrm{CuIn}}_{1-x}{\mathrm{Ga}}_x{\mathrm{Se}}_2$ shows upward convexity, thus this system favors phase separation. Due to the type II band alignment between CuInSe₂${\mathrm{CuInSe}}_2$ and CuGaSe₂${\mathrm{CuGaSe}}_2$, efficient electron–hole separation is realized in decomposed phase of this system. (ii) CuIn_1−xZn_0.5xSn_0.5xSe₂${\mathrm{CuIn}}_{1-x}{\mathrm{Zn}}_{0.5x}{\mathrm{Sn}}_{0.5x}{\mathrm{Se}}_2$ has a direct band gap and no impurity state appears in the gap. Therefore, cost reduction is possible by using Zn and Sn instead of In. (iii) n-type CuAl_1−xSn_xS₂${\mathrm{CuAl}}_{1-x}{\mathrm{Sn}}_x{\mathrm{S}}_2$ and p-type Cu_1−xV_CuxAlS₂${\mathrm{Cu}}_{1-x}{\mathrm{V}}_{\mathrm{Cu}x}{\mathrm{AlS}}_2$ have negative activation energy for doped impurities and are expected to be low-resistive transparent conducting sulfides, which should be useful for CuInSe₂${\mathrm{CuInSe}}_2$-based PVSCs.     

Investigations of half-metallic ferromagnetism and thermoelectric properties of cubic XCrO3 (X = Ca,Sr,Ba) compounds via first-principles approaches

In this paper, the physical aspects of the cubic phase XCrO₃ ($\mathrm{X}=\mathrm{Ca},\mathrm{Sr},\mathrm{Ba}$) perovskites are studied by employing full-potential linearized augmented plane wave plus local orbital ($\text{FP-LAPW}+\mathit{lo}$) method. These compounds have been found stable in ferromagnetic (FM) phase since they possess lower energy in FM phase compared to non-FM phase and their stability is also confirmed by calculating the enthalpy of formation (ΔH). The electronic structures of these compounds are analyzed with Trans and Blaha modified Becke–Johnson potential (TB-mBJ) for both spin up and spin down channels, which indicate their half-metallic characters. Analysis of density of states (DOS) shows major contributions of O-2p states in the valence band and Cr 3d-state in conduction band. A comparative analysis of crystal field effect ($\mathrm{\Delta }{\mathrm{E}}_{\mathrm{crystal}}$) and the exchange energies (direct ${\mathrm{\Delta }}_x(d)$ and indirect ${\mathrm{\Delta }}_x(pd)$) tells about the main part of electronic spin in ferromagnetic character. The calculated magnetic moments make these compounds favorable for spintronic applications. In the end, thermoelectric parameters are computed for 200 K–800 K temperature range to explore potential of these compounds for applications in renewable energy devices.