Results 1 - 10 of 3828
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[en] The problem of states of an electron system interacting with impurities that have a spin of 1/2 is considered. It is shown that in the calculation of the energy of the system, the electron spin-flip processes and the formation of electron–hole–impurity flip spin (hole against the background of electrons with another spin projection) play the major role. Such complexes are accumulated in the system (a sort of Bose condensate of complexes is formed); this reduces the energy of the system, which is a linear function of the initial interaction of an electron with the impurity spin (in contrast, for example, to the result obtained in perturbation theory). The hole-type excitation and the spin excitation have a gap in the spectrum. Small parameters of the problem are the interaction of electrons with impurity spins and the number of impurities. The electron–electron interaction is not taken into account. Impurities are assumed to be distributed at random, and calculations are performed using the known averaging over the positions of impurities.
[en] We have performed Monte Carlo simulations of interacting dipoles that relax through quantum tunneling. We aim to mimic tunneling experiments on crystals of magnetic clusters, such as Fe8 , at very low temperatures. Accordingly, we allow spin flips only if the corresponding energy change is less than some 2 delta hhf . Time evolutions of the dipolar field distribution Pt(H) are studied. As in experiments, a ''hole'' develops in Pt(H) . The half-width W of incipient holes of weakly polarized systems are, under certain conditions, simply related to delta hhf . For kBT∼<0.5 delta hhf and delta hhf smaller than approximately 1/10 of the half-width of the dipolar field distributions of disordered systems, W≅0.75deltahhf
[en] Inspired by recent feats in exchange coupling antiferromagnets to an adjacent material, we demonstrate the possibility of employing them for inducing spin-splitting in a superconductor, thereby avoiding the parasitic effects of ferromagnets employed to this end. We derive the Gor'kov equation for the matrix Green's function in the superconducting layer, considering a microscopic model for its disordered interface with a two-sublattice magnetic insulator. We find that an antiferromagnetic insulator with effectively uncompensated interface induces a large, disorder-resistant spin-splitting in the adjacent superconductor, thereby addressing the feasibility of a wide range of devices involving spin-split superconductors. In addition, we find contributions to the self-energy stemming from the interfacial disorder. Within our model, these mimic impurity and spin-flip scattering, while another breaks the symmetries in particle-hole and spin spaces. The latter contribution, however, vanishes in the quasi-classical approximation and thus, does not significantly affect the superconducting state. Our results illustrate the potential of antiferromagnets for superconducting spintronics avoiding stray fields usually accompanying ferromagnets.
[en] We introduce a kinetically constrained spin model with a local softness parameter, such that spin flips can violate the kinetic constraint with an (annealed) site-dependent rate. We show that adding MC swap moves to this model can dramatically accelerate structural relaxation. We discuss the connection of this observation with the fact that swap moves are also able to accelerate relaxation in structural glasses. We analyse the rates of relaxation in the model. We also show that the extent of dynamical heterogeneity is strongly suppressed by the swap moves. (ucgp7)
[en] Surface spin-flop transition is investigated for smooth and rough uncompensated surfaces of a semi-infinite, two-sublattice, collinear antiferromagnet. The influence of size effects arising in the flat antiferromagnetic layer on the spin-flop and spin-flip transitions is considered for smooth and rough surfaces. A principal difference is demonstrated between how the spin-flop transition proceeds in the layer areas with an odd and even number of atomic planes. (reviews of topical problems)
[en] Graphical abstract: Adiabatic singlet-triplet gap of the oxyallyl diradical has been studied by multireference coupled cluster methods. The results demonstrate the necessity to account for connected triexcitations and to employ a size-extensive method. The best result obtained at the MkCCSD(Tu)/cc-pVQZ level is in an excellent agreement both with experiment and with recent spin-flip EOMCCSD(dT) calculations. Highlights: ► This paper reports a MRCC study of the adiabatic singlet-triplet gap of the oxyallyl diradical.B. ► To get correct results, connected triples and size-extensive MRCC method are needed. ► The best result obtained at the MkCCSD(Tu)/cc-pVQZ level is in an excellent agreement with experiment. - Adiabatic singlet–triplet gap of the oxyallyl diradical has been studied by multireference Brillouin–Wigner and Mukherjee’s coupled cluster methods (BWCC and MkCC). The results demonstrate the necessity to include connected triples excitations, as well as employing a size-extensive MRCC method. The best result, calculated at the MkCCSD(Tu)/cc-pVQZ level, is in an excellent agreement with both experiment and recent spin-flip EOMCCSD(dT) calculations.
[en] In the present paper we calculate the cross–section of radiation from axially channeled polarized electrons. We consider two types of transitions: with and without electron spin flip. It is shown that channeling radiation from polarized electron without spin flip is 2–3 times greater than one with electron spin flip
[en] The purpose of this contribution is to present the ideas which are contained in the spin observables of the nucleon able to filter and eliminate, at least partially, the dominant VDM. It is shown than the measurements have to be done for two different transverse/longitudinal ratios implying electroproduction around 15 to 20 GeV at two Q2 values. The status of simulations, with a new Φ-meson generator which have been developed, is presented defining the feasibility criteria for the experimental device. The present contribution is limited to the case of a proton target. (author)
[en] It was shown in Augusiak et al. [Phys. Rev. A 77, 030301(R) (2008)] that discrimination between entanglement and separability in a two-qubit state can be achieved by a measurement of a single observable on four copies of it. Moreover, a pseudoentanglement monotone π was proposed to quantify entanglement in such states. The main goal of this Brief Report is to show that the close relationship between π and concurrence reported there is a result of sharing the same underlying construction of a spin-flipped matrix. We also show that monogamy of entanglement can be rephrased in terms of π and prove the factorization law for π.