Journal of Experimental and Theoretical Physics最新文献

The sputtering yields of a tungsten target by hydrogen isotopes in the energy range of bombarding particles from 50 eV to 100 eV, as well as the dependence of the sputtering yields on the angle of incidence of the beam on the target and the energy and angular distributions of sputtered particles are obtained by the code developed by us. The strong influence of the type of surface barrier on the results of calculation of the sputtering yield, as well as on the characteristics of sputtered particles is demonstrated. The results obtained make it possible to more accurately assess the tungsten impurity inflow into the hot plasma zone of tokamak.

A detailed investigation of contributions to the magnetization of nonmagnetic YB₆, LaB₆, and YbB₆ hexaboride single crystals has been performed, and a procedure for their separation has been proposed. It has been shown that a low value of electronic susceptibility χ_e(T) in YB₆ and LaB₆ hexaborides seems to be associated with a small effective mass of band carriers, m* ~ 0.5m₀. As a result of this, the Pauli component and Landau diamagnetism cancel each other. It has been found that χ_e(T) varies in the intervals T < T* (T* ~ 50  K) and T > 150 K, which are attributed to an order–disorder transition below T* and a carriers-related contribution due to the Jahn–Teller structural instability of the boron frame work.

The behavior of fine-grained YBa₂Cu₃O_6.92 HTSCs during cooling in a weak magnetic field is investigated. The magnetization of samples, the crystallite sizes is which are comparable with the magnetic field penetration depth, is comprehensively analyzed in the range below the superconducting transition temperature. When the crystallite size is smaller than 0.5 μm, vortices are shown not to be fixed to pinning centers, and the temperature dependence of magnetization is completely determined by the screening of crystallites and the temperature of appearance of intercrystallite superconducting currents.

We have considered the high-order harmonic generation in plane graphene quantum dots of hexagonal shape by the independent quasiparticle approximation-tight binding model. We have investigated how such a nonlinear effect is affected by a strong optical wave field, quantum dot typical band gap and lateral size, and dephasing processes. The equation of motion for the density matrix is solved by performing the time integration with the eight-order Runge–Kutta algorithm. If the optical wave frequency is much less than the quantum dot intrinsic band gap, the main aspects of multiphoton high harmonic emission in quantum dots are revealed. In such case dependence of the cutoff photon energy on the strength of the optical pump wave is almost linear. But when the wave frequency is comparable to the bandgap of the quantum dot, the cutoff photon energy shows saturation behavior with an increase in the wave field strength.

Silicon is indispensable in semiconductor industry. Understanding its high-temperature thermodynamic properties is essential both for theory and applications. However, first-principle description of high-temperature thermodynamic properties of silicon (thermal expansion coefficient and specific heat) is still incomplete. Strong deviation of its specific heat at high temperatures from the Dulong–Petit law suggests substantial contribution of anharmonicity effects. We demonstrate, that anharmonicity is mostly due to two transverse phonon modes, propagating in (111) and (100) directions, and can be quantitatively described with formation of the certain type of nanostructured planar defects of the crystal structure. Calculation of these defects' formation energy enabled us to determine their input into the specific heat and thermal expansion coefficient. This contribution turns out to be significantly greater than the one calculated in quasi-harmonic approximation.

Transport characteristics of superconducting MoN strips with a single side cut near one of the superconductor edges in zero and weak magnetic fields are studied experimentally and theoretically. The presence of the cut makes it possible to observe regimes with one and several simultaneously moving Abrikosov vortices, the number of which is controlled by the value of the applied current. A change in the number of vortices is accompanied with the emergence of a “kink” on the current–voltage characteristic, which can be clearly distinguished in the dependence of the differential resistance on the current. This makes it possible to find average velocity ({bar {v}}) of vortices (including a single vortex) and the current/voltage ranges with the known number of moving vortices. The vortex velocity determined in this way for our superconducting strips turns out to be weakly depending on the current and is close to maximal value ({{{bar {v}}}_{{max }}}) ≈ 3 km/s, for which a superconductor transition to the normal state occurs. The maximal velocity value is comparable with the known values for superconductors of types Nb, NbN as well as, and YBCO, but is several times smaller than for superconductors of types MoSi, NbC, and Pb. The fact that difference in the maximal velocities of vortices is associated with different times of variation of the superconducting order parameter magnitude in different superconducting materials is considered.

The expression for the conductance of a 1D channel, which has been obtained using the well-known exact solution, is analyzed. It is shown that in the case of strong electron—electron interaction, the slowest (linear in frequency) asymptotics of the conductance is determined by the behavior of electron—electron interaction in the region of transition from 1D to 3D motion realized near the impurity.

The second harmonic radiation of a single-pass free electron laser (FEL) and its dependence on the second harmonic of the undulator field are investigated. In analysis of properties of materials, the nonlinear generation of the second harmonic as a response to radiation is an important effect. In this context, the second harmonic generation of the radiation source (FEL) is undesirable since it masks the signal being analyzed. Conversely, in other cases, the second harmonic radiation of the FEL can be useful as radiation with a higher frequency. We investigate the possibility of suppression (or, conversely, enhancement) of the FEL second harmonic power depending on the phase and strength of the second harmonic of the FEL undulator field. The proposed approach is independent in principle of the radiation frequency. We consider examples of LCLS and PAL-XFEL in the X-ray range and SPARC and LEUTL in the visible range. The more effective influence of the undulator field harmonic in operation with narrow electron beams is demonstrated.

The luminescence excitation spectra of the D₁ resonance line of atoms K, Rb, and Cs in gas mixtures with CF₄ are found to contain satellite transitions, which correspond to the transition of an atom to the states (n – 1)d ²D_3/2,5/2 and (n + 1)s ²S_1/2, where n = 4, 5, and 6 for K, Rb, and Cs, respectively, with the simultaneous excitation of CF₄ molecule vibrations at the IR active mode frequency ν₃ with a quantum energy of 1283 cm^–1. These satellite transitions are A(ns ²S_1/2) + CF₄(ν₃ = 0) + hν → A((n – 1)d ²D_3/2,5/2) + CF₄(ν₃ = 1) and A(ns ²S_1/2) + CF₄(ν₃ = 0) + hν → A((n + 1)s ²S_1/2) + CF₄(ν₃ = 1), where A = K, Rb, and Cs. The appearance of an optical coupling between the upper and lower states of these asymptotically (at ({{R}_{{{text{A}} - {text{C}}{{{text{F}}}_{4}}}}}) → ∞) forbidden transitions is shown to be caused by the interaction of the dipole moment of the ν₃ = 1 ↔ ν₃ = 0 vibrational transition in the CF₄ molecule with the dipole moments of the electronic transitions np ²P_1/2,3/2 ↔ (n – 1)d ²D_3/2,5/2 and np ²P_1/2,3/2 ↔ (n + 1)s ²S_1/2 in an alkali metal atom; as a result of this interaction, the upper state of the satellite transition acquires admixtures of the A(np ²P_1/2,3/2)CF₄(ν₃ = 0) resonance states.