Stability of π\pi junction configurations in ferromagnet-superconductor heterostructures

We investigate the stability of possible order parameter configurations in clean layered heterostructures of the $SFS...FS$ type, where $S$ is a superconductor and $F$ a ferromagnet. We find that for most reasonable values of the geometric parameters (layer thicknesses and number) and of the material parameters (such as magnetic polarization, wavevector mismatch, and oxide barrier strength) several solutions of the {\it self consistent} microscopic equations can coexist, which differ in the arrangement of the sequence of ``0'' and ``$\pi$'' junction types (that is, with either same or opposite sign of the pair potential in adjacent $S$ layers). The number of such coexisting self consistent solutions increases with the number of layers. Studying the relative stability of these configurations requires an accurate computation of the small difference in the condensation free energies of these inhomogeneous systems. We perform these calculations, starting with numerical self consistent solutions of the Bogoliubov-de Gennes equations. We present extensive results for the condensation free energies of the different possible configurations, obtained by using efficient and accurate numerical methods, and discuss their relative stabilities. Results for the experimentally measurable density of states are also given for different configurations and clear differences in the spectra are revealed. Comprehensive and systematic results as a function of the relevant parameters for systems consisting of three and seven layers (one or three junctions) are given, and the generalization to larger number of layers is discussed.Comment: 17 pages, including 14 Figures. Higher resolution figures available from the author

Reply to ``Comment on `Magnetic field effects on neutron diffraction in the antiferromagnetic phase of UPt3UPt_3'''

Fak, van Dijk and Wills (FDW) question our interpretation of elastic neutron-scattering experiments in the antiferromagnetic phase of UPt_3. They state that our analysis is incorrect because we average over magnetic structures that are disallowed by symmetry. We disagree with FDW and reply to their criticism. FDW also point out that we have mistaken the magnetic field direction in the experiment reported by N. H. van Dijk et al. [Phys. Rev. B 58, 3186 (1998)]. We correct this error and note that our previous conclusion is also valid for the correct field orientation.Comment: 3 page

Single photoeffect on helium-like ions in the non-relativistic region

We present a generalization of the pioneering results obtained for single K-shell photoionization of H-like ions by M. Stobbe [Ann. Phys. 7 (1930) 661] to the case of the helium isoelectronic sequence. The total cross section of the process is calculated, taking into account the correlation corrections to first order of the perturbation theory with respect to the electron-electron interaction. Predictions are made for the entire non-relativistic energy domain. The phenomenon of dynamical suppression of correlation effects in the ionization cross section is discussed.Comment: to be published in Physics Letters

Layered ferromagnet-superconductor structures: the π\pi state and proximity effects

We investigate clean mutilayered structures of the SFS and SFSFS type, (where the S layer is intrinsically superconducting and the F layer is ferromagnetic) through numerical solution of the self-consistent Bogoliubov-de Gennes equations for these systems. We obtain results for the pair amplitude, the local density of states, and the local magnetic moment. We find that as a function of the thickness $d_F$ of the magnetic layers separating adjacent superconductors, the ground state energy varies periodically between two stable states. The first state is an ordinary "0-state", in which the order parameter has a phase difference of zero between consecutive S layers, and the second is a "$\pi$-state", where the sign alternates, corresponding to a phase difference of $\pi$ between adjacent S layers. This behavior can be understood from simple arguments. The density of states and the local magnetic moment reflect also this periodicity.Comment: 12 pages, 10 Figure

Theory of Andreev reflection in a junction with a strongly disordered semiconductor

We study the conduction of a {\sl N~-~Sm~-~S} junction, where {\sl Sm} is a strongly disordered semiconductor. The differential conductance $dI/dV$ of this {\sl N~-~Sm~-~S} structure is predicted to have a sharp peak at $V=0$. Unlike the case of a weakly disordered system, this feature persists even in the absence of an additional (Schottky) barrier on the boundary. The zero-bias conductance of such a junction $G_{NS}$ is smaller only by a numerical factor than the conductance in the normal state $G_N$. Implications for experiments on gated heterostructures with superconducting leads are discussed.Comment: 4 pages, 2 figures, to appear in Rapid Communication section of Phys. Rev.

Full Counting Statistics of Charge Transfer in Coulomb Blockade Systems

Full counting statistics (FCS) of charge transfer in mesoscopic systems has recently become a subject of significant interest, since it proves to reveal an important information about the system which can be hardly assessed by other means. While the previous research mostly addressed the FCS of non- interacting systems, the present paper deals with the FCS in the limit of strong interaction. In this Coulomb blockade limit the electron dynamics is known to be governed by a master equation. We develop a general scheme to evaluate the FCS in such case, this being the main result of the work presented. We illustrate the scheme, by applying it to concrete systems. For generic case of a single resonant level we establish the equivalence of scattering and master equation approach to FCS. Further we study a single Coulomb blockade island with two and three leads attached and compare the FCS in this case with our recent results concerning an open dot either with two and three terminals. We demonstrate that Coulomb interaction suppresses the relative probabilities of large current fluctuations.Comment: 17 pages, 16 figure

Quantum Disorder and Quantum Chaos in Andreev Billiards

We investigate the crossover from the semiclassical to the quantum description of electron energy states in a chaotic metal grain connected to a superconductor. We consider the influence of scattering off point impurities (quantum disorder) and of quantum diffraction (quantum chaos) on the electron density of states. We show that both the quantum disorder and the quantum chaos open a gap near the Fermi energy. The size of the gap is determined by the mean free time in disordered systems and by the Ehrenfest time in clean chaotic systems. Particularly, if both times become infinitely large, the density of states is gapless, and if either of these times becomes shorter than the electron escape time, the density of states is described by random matrix theory. Using the Usadel equation, we also study the density of states in a grain connected to a superconductor by a diffusive contact.Comment: 20 pages, 10 figure

Физика газового разряда и ее современные приложения: учебное пособие

Курс лекций по физике газового разряда предназначен для студентов первого года обучения в магистратуре, обладающих знаниями по физике и математике в объеме программы бакалавриата факультета физико-математических наук РУДН. Он направлен на углубленное изучение кинетических процессов, протекающих в плазменных средах, основных типов устройств, реализующих газовый разряд, явлений, возникающих в приэлектродных областях, плазмохимических процессов применительно к современным технологиям. Учебное пособие выполнено в рамках инновационной образовательной программы Российского университета дружбы народов, комплекс экспортоориентированных инновационных образовательных программ по приоритетным направлениям науки и технологий

Phase separation in the two-dimensional electron liquid in MOSFETs

We show that the existence of an intermediate phase between the Fermi liquid and the Wigner crystal phases is a generic property of the two-dimensional pure electron liqd in MOSFET's at zero temperature. The physical reason for the existence of these phases is a partial separation of the uniform phases. We discuss properties of these phases and a possible explanation of experimental results on transport properties of low density electron gas in Si MOSFET's. We also argue that in certain range of parameters the partial phase separation corresponds to a supersolid phas e discussed in [AndreevLifshitz].Comment: 11 pages, 3 figure

Magnetic fluctuations in 2D metals close to the Stoner instability

We consider the effect of potential disorder on magnetic properties of a two-dimensional metallic system (with conductance $g\gg 1$) when interaction in the triplet channel is so strong that the system is close to the threshold of the Stoner instability. We show, that under these conditions there is an exponentially small probability for the system to form local spin droplets which are local regions with non zero spin density. Using a non-local version of the optimal fluctuation method we find analytically the probability distribution and the typical spin of a local spin droplet (LSD). In particular, we show that both the probability to form a LSD and its typical spin are independent of the size of the droplet (within the exponential accuracy). The LSDs manifest themselves in temperature dependence of observable quantities. We show, that below certain cross-over temperature the paramagnetic susceptibility acquires the Curie-like temperature dependence, while the dephasing time (extracted from magneto-resistance measurements) saturates.Comment: 15 pages, 4 figure