No abstract available

No abstract available

[en] We investigate the current noise of three-terminal hybrid structures at arbitrary bias voltages. Our results indicate that the noise can be a useful tool to extract dynamical information in multi-terminal hybrid structures. The zero-frequency noise is sensitive to the coupling with a normal lead. As a result, the characteristic multiple-step structure of the noise Fano factor due to multiple Andreev reflection will be suppressed as we increase this coupling. In addition, the internal dynamics due to processes of Andreev reflection and multiple Andreev reflection raises rich features in the noise spectrum corresponding to the energy differences of various dynamical processes. (paper)

[en] We report the optical, electronic, vibrational and mechanical properties of a stable, anisotropic, hexagonal (4H) form of silver. First principles calculations based on density functional theory were used to simulate the phonon dispersion curves and electronic band structure of 4H-Ag. The phonon dispersion data at 0 K do not contain unstable phonon modes, thereby confirming that it is a locally stable structure. The Fermi surface of the 4H phase differs in a subtle way from that of the cubic phase. Experimental measurements indicate that, when compared to the commonly known face-centered cubic (3C) form of silver, the 4H-Ag form shows a 130-fold higher, strongly anisotropic, in-plane resistivity and a much lower optical reflectance with a pronounced surface plasmon contribution that imparts a distinctive golden hue to the material. Unlike common silver, the lower symmetry of the 4H-Ag structure allows it to be Raman active. Mechanically, 4H-Ag is harder, more brittle and less malleable. Overall, this novel, poorly metallic, anisotropic, darker and harder crystallographic modification of silver bears little resemblance to its conventional counterpart. (paper)

[en] We describe the microstructure, morphology, and dynamics of growth of a droplet of martensite nucleating in a parent austenite during a solid–solid transformation, using a Landau theory written in terms of both conventional affine elastic deformations and non-affine deformations. Non-affineness, ϕ, serves as a source of strain incompatibility and screens long-ranged elastic interactions. It is produced wherever the local stress exceeds a threshold and anneals diffusively thereafter. Using a variational calculation, we find three types of stable solution (labeled I, II, and III) for the structure of the product droplet, depending on the stress threshold and the scaled mobilities of ϕ parallel and perpendicular to the parent–product interface. The profile of the non-affine field ϕ is different in these three solutions: I is characterized by a vanishingly small ϕ, II admits large values of ϕ localized in regions of high stress within the parent–product interface, and III is a structure in which ϕ completely wets the parent–product interface. The width l and size W of the twins follow the relation l∝√W in solution I; this relation does not hold for II or III. We obtain a dynamical phase diagram featuring these solutions, and argue that they represent specific solid-state microstructures. (paper)

[en] We find an unexpected scaling in the correlation energy of artificial atoms, i.e., harmonically confined two-dimensional quantum dots. The scaling relation is found through extensive numerical examinations including Hartree–Fock, variational quantum Monte Carlo, density functional, and full configuration interaction calculations. We show that the correlation energy, i.e., the true ground-state total energy minus the Hartree–Fock total energy, follows a simple function of the Coulomb energy, confinement strength and number of electrons. We find an analytic expression for this function, as well as for the correlation energy per particle and for the ratio between the correlation and total energies. Our tests for independent diffusion Monte Carlo and coupled-cluster results for quantum dots—including open-shell data—confirm the generality of the scaling obtained. As the scaling also applies well to ≳100 electrons, our results give interesting prospects for the development of correlation functionals within density functional theory. (paper)

[en] The dynamic properties of the dipolar magnet CsGd(MoO₄)₂ have been studied. The frequency and temperature dependence of the AC susceptibility investigated in the paramagnetic region above 2 K revealed the co-existence of magnetic field induced slow and fast relaxation channels with a timescale differing by three orders of magnitude. The slow relaxation is determined by the properties of the first coordination sphere of the Gd³⁺ ion and has the character of a two-phonon Orbach process. The fast relaxation is potentially attributed to a two-phonon Raman process realized via a localized phonon mode associated with the layered crystal structure. The temperature dependence of the phonon mean free path in zero magnetic field indicates significant phonon scattering below 1 K resulting from the combined effect of magnetic correlations and the scattering of dominant phonons with energies corresponding to the crystal-field levels. (paper)

[en] An alternative model of Gaussian-type potential is suggested, which allows us to describe the transport properties of the locally gated graphene bipolar junctions in all possible charge density regimes, including a smooth transition between the regimes. Using this model we systematically study the transmission probability, the resistances, the current–voltage characteristics, and the shot noise for ballistic graphene bipolar junctions of different top gate lengths under largely varying gate voltages. Obtained results on the one hand show multifarious manifestations of the Klein tunneling and the interference effects, and on the other hand describe well typical experimental data on the junction resistances. (paper)

[en] Motivated by the existence of helical wrapping patterns in composite nanotube systems, in this work we study the effects of the helical incorporation of carbon atoms in boron nitride nanotubes. We consider the substitutional carbon atoms distributed in stripes forming helical patterns along the nanotube axis. The density of states and energy band gap were calculated adopting Green function formalism by using the Rubio-Sancho technique in order to solve the matrix Dyson equation. We report the effects of the helical atomic distribution of carbon atoms on the behaviour of the density of states and the energy band gap. In particular, we show that the electronic energy band gap displays a non-monotonical dependence on the helical pattern, oscillating as a function of the helical angle θ. (paper)

[en] EuTiO₃ is shown to exhibit novel strong spin–charge–lattice coupling deep in the paramagnetic phase. Its existence is evidenced by an, until now, unknown response of the paramagnetic susceptibility at temperatures exceeding the structural phase transition temperature T_S = 282 K. The ‘extra’ features in the susceptibility follow the rotational soft zone boundary mode temperature dependence above and below T_S. The theoretical modeling consistently reproduces this behavior and provides reasoning for the stabilization of the soft optic mode other than quantum fluctuations. (fast track communication)