Maciej M. Maśka

The Fulde-Ferrell-Larkin-Ovchinnikov phase in the presence of pair hopping interaction

The recent experimental support for the presence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in CeCoIn(5) directed attention towards the mechanisms responsible for this type of superconductivity. We investigate the FFLO state in a model where on-site/inter-site pairing coexists with the repulsive pair hopping interaction. The latter interaction is interesting in that it leads to pairing with non-zero momentum of the Cooper pairs even in the absence of the external magnetic field (the so-called η pairing). It turns out that, depending on the strength of the pair hopping interaction, the magnetic field can induce one of two types of the FFLO phase with different spatial modulations of the order parameter. It is argued that the properties of the FFLO phase may give information about the magnitude of the pair hopping interaction. We also show that η pairing and d-wave superconductivity may coexist in the FFLO state. It holds true also for superconductors which, in the absence of magnetic field, are of pure d-wave type.

Wave function engineering in quantum dot–ring nanostructures

Modern nanotechnology allows the production of, depending on the application, various quantum nanostructures with selected properties. These properties are strongly influenced by the confinement potential which can be modified e.g. by electrical gating. In this paper, we analyze a nanostructure composed of a quantum dot surrounded by a quantum ring. We show that, depending on the details of the confining potential, the electron wave functions can be located in different parts of the structure. Since many properties of such a nanostructure strongly depend on the distribution of the wave functions, by varying the applied gate voltage one can easily control them. In particular, we illustrate the high controllability of the nanostructure by demonstrating how its coherent, optical and conducting properties can be drastically changed by a small modification of the confining potential.

Inhomogeneity-induced enhancement of the pairing interaction in cuprate superconductors.

Scanning tunneling spectroscopy has recently discovered a positive correlation between the magnitude of the superconducting gap and positions of dopant oxygen atoms in Bi-based cuprates. We propose a microscopic mechanism that could be responsible for this effect. In particular, we demonstrate that the dopant-induced spatial variation of the atomic levels always enhances the superexchange interaction.

Spin relaxation in semiconductor quantum rings and dots?a comparative study

We calculate spin relaxation times due to spin-orbit-mediated electron-phonon interactions for experimentally accessible semiconductor quantum ring and dot architectures. We elucidate the differences between the two systems due to different confinement. The estimated relaxation times (at B = 1 T) are in the range between a few milliseconds to a few seconds. This high stability of spin in a quantum ring allows us to test it as a spin qubit. A brief discussion of quantum state manipulations with such a qubit is presented.The implementation of a spin qubit in a quantum ring occupied by one or a few electrons is proposed. Quantum bit involves the Zeeman sublevels of the highest occupied orbital. Such a qubit can be initialized, addressed, manipulated, read out and coherently coupled to other quantum rings. An extensive discussion of relaxation and decoherence is presented. By analogy with quantum dots, the spin relaxation times due to spin-orbit interaction for experimentally accessible quantum ring architectures are calculated. The conditions are formulated under which qubits build on quantum rings can have long relaxation times of the order of seconds. Rapidly improving nanofabrication technology have made such ring devices experimentally feasible and thus promising for quantum state engineering. PACS numbers: 73.21.La 85.30.De 72.25.Rb 71.70.Ej Semiconductor quantum ring 2

Superconductivity ofLa3Co4Sn13andLa3Rh4Sn13: A comparative study

We report the electric transport and thermodynamic properties of the skutterudite-related La

Coexistence of superconductivity and incommensurate magnetic order

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Improving the efficiency of ultracold dipolar molecule formation by first loading onto an optical lattice

Co

Pattern formation in mixtures of ultracold atoms in optical lattices.

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Upward curvature of the upper critical field in the boson-fermion model

Sn

Upper critical field for anisotropic superconductivity: A tight-binding approach

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