Search results for "conduct"

Field dependence of the vortex-core sizes in dirty two-band superconductors

2019

We study the structure of Abrikosov vortices in two-band superconductors for different external magnetic fields and different parameters of the bands. The vortex core size determined by the coherence lengths are found to have qualitatively different behaviour from that determined by the quasiparticle density of states spatial variation. These different vortex core length scales coincide near the upper critical field, while the discrepancy between them becomes quite significant at lower fields. Within the diffusive approximation we demonstrate several generic regimes in the field dependence of the vortex core sizes determined by the disparity of diffusion constants in the two bands.

Time-dependent quantum transport in nanosystems : a nonequilibrium Green's function approach

2016

A time-dependent extension to the Landauer–Büttiker approach to study transient quantum transport in arbitrary junctions composed of leads and conducting devices is developed. The nonequilibrium Green’s function approach is employed for describing the charge and heat transport dynamics. The importance of the developed method is that it provides a closed formula for the time-dependent density matrix in both electronic and phononic systems. In the electronic case the nonequilibrium conditions are due to a switch-on of a bias voltage in the leads or a perturbation in the junction whereas in the phononic case the central region of interest is coupled to reservoirs of di erent temperatures. In b…

Development of niobium-based superconducting junctions

2012

This thesis presents a review of publications which mainly focuses on the fabrication and performance of Nb-based normal metal-insulator-superconductor (NIS) tunnel junctions and superconductor-normal metal-superconductor (SNS) Josephson junctions at low temperatures. The Cu/AlOx-Al/Nb based NIS double tunnel junctions were successfully fabricated using conventional electron beam lithography combined with multi-angle thermal evaporation of metals in ultra high vacuum. The subgap characteristics of these junctions showed expected temperature dependence from 0.2 K to 5 K with a good thermometry sensitivity 0.2-0.3 mV/K. Signatures of small electronic cooling effects were observed near the Nb …

Chirality selective spin interactions mediated by the moving superconducting condensate

2018

We show that superconducting correlations in the presence of nonzero condensate velocity can mediate the peculiar interaction between localized spins that breaks the global inversion symmetry of magnetic moments. The proposed interaction mechanism is capable of removing fundamental degeneracies between topologically distinct magnetic textures. For the generic system of three magnetic impurities in the current-carrying superconductor, we find the energy term proportional to spin chirality. In realistic superconductor/ferromagnetic/superconductor setups we reveal significant energy differences between various magnetic textures with opposite chiralities. We calculate Josephson energies of junc…

Comparison of the Richardson and BCS models of superconductivity based on calculations of ground state energies

2017

Suprajohtavuuden Richardsonin ja BCS mallien vertailu perustilojen laskettujen energioiden perusteella. Suprajohtavuus on edelleen aktiivinen tutkimuksen alue, koska sen tarjoamista mahdollisuuksista huolimatta sitä ei vielä ymmärretä kokonaisvaltaisesti. Tässä pro gradu -tutkielmassa käyn läpi perusteet kahdelle suprajohtavuuden mallille, Richardsonin ja BCS malleille. BCS teoria on ensimmäinen ja käytetyin mikroskooppinen suprajohtavuuden teoria. Richardsonin malli on harvemmin käytetty malli, josta saadaan redusoidun BCS Hamiltonin operaattorin tarkat ominaistilat. Lasken molempien mallien perustilojen energiat sekä redusoidulle että täydelle BCS Hamiltonin operaattorille. Sama lasketaan…

Electron-phonon interaction in flat-band superconductivity

2017

Parhaiten tunnettu suprajohtavuuden syntymekanismi perustuu fononien välittämään vetovoimaan elektronien välillä. Tässä tutkielmassa tutkin fononien välittämää suprajohtavuutta systeemeissä, jossa elektronivyöt ovat tasomaisia. Tasovyöllä elektronien dispersio on erittäin heikko, jolloin tilatiheys on tavanomaista suurempi. Tämän takia suprajohtavuus tasovyöllä on tavanomaista voimakkaampi silloin kun elektronien välinen vetovoima on heikko. Eliashbergin teoria on elektroni–fononi-suprajohtavuuden teoria, joka ottaa luonnollisella tavalla fononien äärellisen nopeuden huomioon elektronien välisessä vuorovaikutuksessa. Pohjustuksena tasovyösuprajohtavuuteen perehdyn Eliashbergin teoriaan ensi…

Normal-Metal–Insulator–Superconductor Tunnel Junction With Atomic-Layer-Deposited Titanium Nitride as Superconductor

2015

Vibrational properties of semiconductor nanowires and nanowire heterostructures: ensembles and single nanowires

2013

Phonon Deformation Potentials from Raman Measurements on Semiconductor Membranes

1997

Associations Between Sympathetic Nervous System Synchrony, Movement Synchrony, and Speech in Couple Therapy

2022

Background: Research on interpersonal synchrony has mostly focused on a single modality, and hence little is known about the connections between different types of social attunement. In this study, the relationship between sympathetic nervous system synchrony, movement synchrony, and the amount of speech were studied in couple therapy. Methods: Data comprised 12 couple therapy cases (24 clients and 10 therapists working in pairs as co-therapists). Synchrony in electrodermal activity, head and body movement, and the amount of speech and simultaneous speech during the sessions were analyzed in 12 sessions at the start of couple therapy (all 72 dyads) and eight sessions at the end of therapy (…