New Forms of Superconductivity
Flat band superconductivity in strained Dirac materials and transport properties of superconductors with a spin-splitting field are studied in this thesis. Flat band superconductivity is a route to high temperature superconductivity. Strain induced flat band in Dirac materials provides a new mechanism to the flat band superconductivity. Superconductors with a spin-splitting field reveal novel features which do not exist or very small in non spin-split superconductors, for example, longrange spin accumulation and thermoelectric effects. Exploring other effects is beneficial for understanding the transport phenomena in such systems. For the flat band superconductivity in strained Dirac materials, the Bogoliubov-de Gennes equation is used to study the properties of the strained Dirac materials in the superconducting state, including the inhomogeneous pair potential, local density of states and a finite supercurrent. For the superconductors with a spin-splitting field, quasiclassical Green’s function method is used to study the transport properties of such systems. The properties studied in this thesis include those in equilibrium and out of equilibrium. The noncollinearity of the spin-splitting fields between two spin-split superconductors introduces new features to the tunnelling conductance and gives rise to a finite Josephson current in the absence of external voltage. In the presence of a supercurrent, the shortrange charge imbalance is converted to long-range spin accumulation in the presence of a homogeneous spin-splitting field. The inhomogeneous spin-splitting field alters many physical observables, such as the spin current density, domain wall size, and density of states. As a precursor to the domain wall motion in a superconductor with an inhomogeneous spin-splitting field, the domain wall motion in a diffusive weak ferromagnet reveals characteristic features like time dependent domain wall velocity for the force much larger than the torque, and occurring of the intrinsic pinning eventually for the torque much larger then the force. The study on flat band superconductivity in strained Dirac materials show how this model results an inhomogeneous superconductivity, including its various properties. The study on the transport properties of superconductors with a spin-splitting field, by considering the effect of supercurrent, noncollinearity and inhomogeneity of the spin-splitting fields, fill many gaps in the previous research. ...
Julkaisuun sisältyy osajulkaisuja
- Artikkeli I: Kauppila, V. J.; Aikebaier, Faluke; Heikkilä, Tero (2016). Flat-band superconductivity in strained Dirac materials. Physical Review B, 93 (21), 214505. DOI: 10.1103/PhysRevB.93.214505. JYX: jyx.jyu.fi/handle/123456789/50656.
- Artikkeli II: Rouco, Mikel; Chakraborty, Subrata; Aikebaier, Faluke; Golovach, Vitaly N.; Strambini, Elia; Moodera, Jagadeesh S.; Giazotto, Francesco; Heikkilä, Tero T.; Bergeret, F. Sebastian (2019). Charge transport through spin-polarized tunnel junction between two spin-split superconductors. Physical Review B, 100 (18), 184501. DOI: 10.1103/PhysRevB.100.184501. JYX: jyx.jyu.fi/handle/123456789/66321.
- Artikkeli III: Aikebaier, F., Silaev, M., & Heikkilä, T. (2018). Supercurrent-induced charge-spin conversion in spin-split superconductors. Physical Review B, 98 (2), 024516. DOI: 10.1103/physrevb.98.024516. JYX: jyx.jyu.fi/handle/123456789/59196.
- Artikkeli IV: Aikebaier, F., Virtanen, P., & Heikkilä, T. (2019). Superconductivity near a magnetic domain wall. Physical Review B, 99 (10), 104504. DOI: 10.1103/PhysRevB.99.104504
- Artikkeli V: Aikebaier, Faluke; Heikkilä, Tero T. (2020). Domain wall motion in a diffusive weak ferromagnet. Physical Review B, 101 (15), 155423. DOI: 10.1103/PhysRevB.101.155423 JYX: jyx.jyu.fi/handle/123456789/68733.
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Fabrication, electrical characterization and 1/f noise study of submicron-sized superconducting tunnel junctions Julin, Juhani (University of Jyväskylä, 2016)
Large enhancement of spin pumping due to the surface bound states in normal metal–superconductor structures Silaev, Mikhail (American Physical Society (APS), 2020)We show that the spin pumping from ferromagnetic insulator into the adjacent metallic spin sink can be strongly stimulated by the superconducting correlations. The key physical mechanism responsible for this effect is the ...
Golovchanskiy, I.A.; Abramov N.N.; Stolyarov, V.S.; Chichkov, V.I.; Silaev, M.; Shchetinin, I.V.; Golubov, A.A.; Ryazanov, V.V.; Ustinov, A.V.; Kupriyanov, M.Yu. (American Physical Society (APS), 2020)In this work, magnetization dynamics is studied in superconductor-ferromagnet-superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement ...
Garaud, Julien; Corticelli, Alberto; Silaev, Mikhail; Babaev, Egor (American Physical Society, 2018)In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. For example, a dirty two-band ...
Virtanen, P.; Braggio, A.; Giazotto, F. (American Physical Society, 2019)We consider the effects of an externally applied electrostatic field on superconductivity, self-consistently within a BCS mean-field model, for a clean three-dimensional (3D) metal thin film. The electrostatic change in ...