Magnetic skyrmion lattices in heavy fermion superconductor UPt3

Topological analysis of nearly SO(3)_{spin} symmetric Ginzburg--Landau theory, proposed for UPt$_{3}$ by Machida et al, shows that there exists a new class of solutions carrying two units of magnetic flux: the magnetic skyrmion. These solutions do not have singular core like Abrikosov vortices and at low magnetic fields they become lighter for strongly type II superconductors. Magnetic skyrmions repel each other as $1/r$ at distances much larger then the magnetic penetration depth $\lambda$, forming a relatively robust triangular lattice. The magnetic induction near $H_{c1}$ is found to increase as $(H-H_{c1})^{2}$. This behavior agrees well with experiments.Comment: 4 pages, 2 figures, 2 column format; v2:misprint in the title is correcte

Magnetic skyrmions and their lattices in triplet superconductors

Complete topological classification of solutions in SO(3) symmetric Ginzburg-Landau free energy has been performed and a new class of solutions in weak external magnetic field carrying two units of magnetic flux has been identified. These solutions, magnetic skyrmions, do not have singular core like Abrikosov vortices and at low magnetic field become lighter for strongly type II superconductors. As a consequence, the lower critical magnetic field Hc1 is reduced by a factor of log(kappa). Magnetic skyrmions repel each other as 1/r at distances much larger then magnetic penetration depth forming relatively robust triangular lattice. Magnetic induction near Hc1 increases gradually as (H-Hc1)^2. This agrees very well with experiments on heavy fermion superconductor UPt3. Newly discovered Ru based compounds Sr2RuO4 and Sr2YRu(1-x)Cu(x)O6 are other possible candidates to possess skyrmion lattices. Deviations from exact SO(3) symmetry are also studied.Comment: 23 pages, 10 eps figure

Microtubules in Bacteria: Ancient Tubulins Build a Five-Protofilament Homolog of the Eukaryotic Cytoskeleton

Microtubules play crucial roles in cytokinesis, transport, and motility, and are therefore superb targets for anti-cancer drugs. All tubulins evolved from a common ancestor they share with the distantly related bacterial cell division protein FtsZ, but while eukaryotic tubulins evolved into highly conserved microtubule-forming heterodimers, bacterial FtsZ presumably continued to function as single homopolymeric protofilaments as it does today. Microtubules have not previously been found in bacteria, and we lack insight into their evolution from the tubulin/FtsZ ancestor. Using electron cryomicroscopy, here we show that the tubulin homologs BtubA and BtubB form microtubules in bacteria and suggest these be referred to as “bacterial microtubules” (bMTs). bMTs share important features with their eukaryotic counterparts, such as straight protofilaments and similar protofilament interactions. bMTs are composed of only five protofilaments, however, instead of the 13 typical in eukaryotes. These and other results suggest that rather than being derived from modern eukaryotic tubulin, BtubA and BtubB arose from early tubulin intermediates that formed small microtubules. Since we show that bacterial microtubules can be produced in abundance in vitro without chaperones, they should be useful tools for tubulin research and drug screening

Inhomogeneous magnetism induced in a superconductor at superconductor-ferromagnet interface

We study a magnetic proximity effect at superconductor (S) - ferromagnet (F) interface. It is shown that due to an exchange of electrons between the F and S metals ferromagnetic correlations extend into the superconductor, being dependent on interface parameters. We show that ferromagnetic exchange field pair breaking effect leads to a formation of subgap bands in the S layer local density of states, that accommodate only one spin-polarized quasiparticles. Equilibrium magnetization leakage into the S layer as function of SF interface quality and a value of ferromagnetic interaction have also been calculated. We show that a damped-oscillatory behavior versus distance from SF interface is a distinguished feature of the exchange-induced magnetization of the S layer.Comment: 10 pages, 7 Postscript figure

Symmetries of Pairing Correlations in Superconductor-Ferromagnet Nanostructures

Using selection rules imposed by the Pauli principle, we classify pairing correlations according to their symmetry properties with respect to spin, momentum, and energy. We observe that inhomogeneity always leads to mixing of even- and odd-energy pairing components. We investigate the superconducting pairing correlations present near interfaces between superconductors and ferromagnets, with focus on clean systems consisting of singlet superconductors and either weak or half-metallic ferromagnets. Spin-active scattering in the interface region induces all of the possible symmetry components. In particular, the long-range equal-spin pairing correlations have odd-frequency s-wave and even-frequency p-wave components of comparable magnitudes. We also analyze the Josephson current through a half-metal. We find analytic expressions and an interesting universality in the temperature dependence of the critical current in the tunneling limit.Comment: 20 pages, 5 figures, added citations, corrected typo