| 1. |
- Agterberg, Daniel F., et al.
(författare)
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Microscopic prediction of skyrmion lattice state in clean interface superconductors
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:6, s. 064509-
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Tidskriftsartikel (refereegranskat)abstract
- When an in-plane field is applied to a clean interface superconductor, a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like phase is stabilized. This phase has a U(1)xU(1) symmetry and, in principle, this symmetry allows for flux carrying topological excitations different from Abrikosov vortices (which are the simplest defects associated with S-1 --> S-1 maps). However, in practice, largely due to electromagnetic and other intercomponent interactions, such topological excitations are very rare in superconducting systems. Here, we demonstrate that a realistic microscopic theory for interface superconductors, such as SrTiO3/LaAlO3, predicts an unconventional magnetic response where the flux-carrying objects are skyrmions, characterized by homotopy invariants of S-2 --> S-2 maps. Additionally, we show that this microscopic theory predicts that stable fractional vortices form near the boundary of these superconductors. It also predicts the appearance of type-1.5 superconductivity for some range of parameters. Central to these results is the assumption that the Rashba spin-orbit coupling is much larger than the superconducting gap.
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| 2. |
- Babaev, Egor, et al.
(författare)
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A superconductor to superfluid phase transition in liquid metallic hydrogen
- 2004
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 431:7009, s. 666-668
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Tidskriftsartikel (refereegranskat)abstract
- Although hydrogen is the simplest of atoms, it does not form the simplest of solids or liquids. Quantum effects in these phases are considerable (a consequence of the light proton mass) and they have a demonstrable and often puzzling influence on many physical properties(1), including spatial order. To date, the structure of dense hydrogen remains experimentally elusive(2). Recent studies of the melting curve of hydrogen(3,4) indicate that at high (but experimentally accessible) pressures, compressed hydrogen will adopt a liquid state, even at low temperatures. In reaching this phase, hydrogen is also projected to pass through an insulator-to-metal transition. This raises the possibility of new state of matter: a near ground-state liquid metal, and its ordered states in the quantum domain. Ordered quantum fluids are traditionally categorized as superconductors or superfluids; these respective systems feature dissipationless electrical currents or mass flow. Here we report a topological analysis of the projected phase of liquid metallic hydrogen, finding that it may represent a new type of ordered quantum fluid. Specifically, we show that liquid metallic hydrogen cannot be categorized exclusively as a superconductor or superfluid. We predict that, in the presence of a magnetic field, liquid metallic hydrogen will exhibit several phase transitions to ordered states, ranging from superconductors to superfluids.
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| 3. |
- Babaev, Egor
(författare)
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Andreev-Bashkin effect and knot solitons in an interacting mixture of a charged and a neutral superfluid with possible relevance for neutron stars
- 2004
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Ingår i: Physical Review D. Particles and fields. - 0556-2821 .- 1089-4918. ; 70:4
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Tidskriftsartikel (refereegranskat)abstract
- We discuss a mixture of interacting neutral and charged Bose condensates, which is supposed being realized in the interior of neutron stars in the form of a coexistent neutron superfluid and protonic superconductor. We show that in this system, besides ordinary vortices of the S-1-->S-1 map, the neutron condensate also allows for (meta)stable finite-length knotted solitons, which are characterized by a nontrivial Hopf invariant and in some circumstances may be stabilized by a Faddeev-Skyrme term induced by the drag effect. We also consider a helical protonic flux tube in this system and show that, in contrast, it does not induce a Faddeev-Skyrme term.
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| 4. |
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| 5. |
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| 6. |
- Babaev, Egor, et al.
(författare)
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Comment on "Ginzburg-Landau theory of two-band superconductors : Absence of type-1.5 superconductivity"
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:1, s. 016501-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The recent paper by V. G. Kogan and J. Schmalian [Phys. Rev. B 83, 054515 (2011)] argues that the widely used two-component Ginzburg-Landau (GL) models are not correct, and further concludes that in the regime which is described by a GL theory there could be no disparity in the coherence lengths of two superconducting components. This would in particular imply that [in contrast to U(1) x U(1) superconductors] there could be no "type-1.5" superconducting regime in U(1) multiband systems for any finite interband coupling strength. We point out that these claims are incorrect and based on an erroneous scheme of reduction of a two-component GL theory.
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| 7. |
- Babaev, Egor
(författare)
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Dual neutral variables and knot solitons in triplet superconductors
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 88, s. 177002-
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Tidskriftsartikel (refereegranskat)abstract
- We derive a dual presentation of a free energy functional for spin-triplet superconductors in terms of gauge-invariant variables. The resulting equivalent model in ferromagnetic phase has a form of a version of the Faddeev model. This allows one, in particular, to conclude that spin-triplet superconductors allow formation of stable finite-length closed vortices (knotted solitons).
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| 8. |
- Babaev, Egor
(författare)
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Fractional-flux vortices and spin superfluidity in triplet superconductors
- 2005
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 94:13
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Tidskriftsartikel (refereegranskat)abstract
- We discuss a novel type of fractional-flux vortices along with integer flux vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We show that under certain conditions a spin-triplet superconductor should exhibit a novel state of spin superfluidity without superconductivity.
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| 9. |
- Babaev, Egor
(författare)
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From exotic superconductivity to QCD and back again searching things in common
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted largely to two new features which Particle Physics and Condensed Matter theory have in common. The first part of the thesis is a discussion of formation of phases precursory to the chiral phase transition in relativistic models with four-fermion interactions, considered as toy models for QCD. This discussion is based on analogy with the novel pseudogap concept in strong-coupling and low carrier density superconductors. In the second part we discuss a condensed mater realizations of knotted solitions, which were discussed earlier by Faddeev and Niemi. We argue that these defects can exist in superconducting liquid metallic hydrogen and deuterium and two-band superconductors. The knotted solitions is a novel for condensed matter concept and thus it is of great academic interest in this field. The macroscopic quantum origin of topological defects in superfluids implies its rather direct observability. This possibility to actually observe these objects, their properties, stability and interactions may result in a 'feedback" for understanding its role in the infrared limit of Yang-Mills theory complementing ongoing numerical simulations. In the third part of the thesis we study the effect of Coulumb interaction on formation of charged vortices in the Abelian Higgs model in the presence of a uniform compensating background field. This study is also of interdisciplinary interest. The description of granular superconductors and Josephson junction arrays usually includes Coulomb terms which accounts for the presence of the cristal lattice. Also it may be relevant for extreme strong coupling or low carrier density superconductors which may have vortices which r-ores are not filled by decomposed Cooper pairs. This study also allows to estimate characteristic length scales of a charged vortices which should be of interests for the studies of knotted solitons formed by two complex scalar fields with Coulomb interaction discussed by Faddeev and Niemi.
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| 10. |
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