Thermalization of hot electrons via interfacial electron-magnon interaction

Recent work on layered structures of superconductors (S) or normal metals (N) in contact with ferromagnetic insulators (FI) has shown how the properties of the previous can be strongly affected by the magnetic proximity effect due to the static FI magnetization. Here we show that such structures can also exhibit a new electron thermalization mechanism due to the coupling of electrons with the dynamic magnetization, i.e., magnons in FI. We here study the heat flow between the two systems and find that in thin films the heat conductance due to the interfacial electron-magnon collisions can dominate over the well-known electron-phonon coupling below a certain characteristic temperature that can be straightforwardly reached with present-day experiments. We also study the role of the magnon band gap and the induced spin-splitting field induced in S on the resulting heat conductance and show that heat balance experiments can reveal information about such quantities in a way quite different from typical magnon spectroscopy experiments

Cyclostationary measurement of low-frequency odd moments of current fluctuations

Measurement of odd moments of current fluctuations is difficult due to strict requirements for band-pass filtering. We propose how these requirements can be overcome using cyclostationary driving of the measured signal and indicate how the measurement accuracy can be tested through the phase dependence of the moments of the fluctuations. We consider two schemes, the mixing scheme and the statistics scheme, where the current statistics can be accessed. We also address the limitations of the schemes, due to excess noise and due to the effects of the environment, and, finally, discuss the required measurement times for typical setups.Comment: 13 pages, 3 figure

Thermopower induced by a supercurrent in superconductor-normal-metal structures

We examine the thermopower Q of a mesoscopic normal-metal (N) wire in contact to superconducting (S) segments and show that even with electron-hole symmetry, Q may become finite due to the presence of supercurrents. Moreover, we show how the dominant part of Q can be directly related to the equilibrium supercurrents in the structure. In general, a finite thermopower appears both between the N reservoirs and the superconductors, and between the N reservoirs themselves. The latter, however, strongly depends on the geometrical symmetry of the structure.Comment: 4 pages, 4 figures; text compacted and material adde

RatRace : Nuorten aktivointitapahtuma

Opinnäytetyön aiheena on Haapavedellä liikuntahallilla järjestettävä RatRace 2014 nuorten aktivointitapahtuma. Päävastuu tapahtuman järjestämisestä on vapaa-aikatoimella. Opinnäytetyön yhtenä tavoitteena on selvittää, koetaanko tapahtuma tärkeäksi ja hyödylliseksi. Onko tapahtumalla positiivisia vaikutuksia nuorten osallisuuteen sekä aktivoiko tapahtuma nuoria vapaa-ajalla tai koulutusvalinnoissa. Tapahtuma on järjestetty vuonna 2012 ensimmäisen kerran. Opinnäytetyömme on perehdytys vastaavan tapahtuman järjestämiseen, sekä myös arvio tapahtuman toteutumisesta. Toivomme, että opinnäytetyötä voidaan tulevaisuudessa hyödyntää samanlaisten tapahtumien järjestämisessä, sekä markkinoinnissa muille kunnille. Toteutimme kyselytutkimuksen webropol-kyselynä yläkouluikäisille nuorille sekä tapahtumaan osallistuville näytteilleasettajille. RatRace tapahtuma koostuu kahdesta osiosta. Päivätapahtuma klo. 12–16 toteutetaan messuluonteisena. Esillä on kattavasti alueen harrastus-, järjestö- ja koulutusmahdollisuuksia, viranomaistoimintaa sekä päihde- ja valistustyötä. Tapahtumassa mukana on elämyksellisiä aktiviteetteja sekä monenlaista hyvinvointiin liittyvää tekemistä. Tapahtuman tarkoituksena on tuottaa iloa ja elämyksiä nuorille ja heidän perheille. Punaisena lankana on vahvasti yhteisöllisyys ja nuorten osallisuus sekä tulevaisuuteen suuntautuva ote arjesta. Tapahtuma on ensisijaisesti suunnattu yläkouluikäisille, jotka osallistuvat tapahtumaan luokittain. Tapahtuma on avoin kaikenikäisille ja enenevissä määrin alakouluikäiset sekä perheet ovat ottaneet osaa tapahtumaan. Parhaaksi toteuttamisajankohdaksi on katsottu toisen asteen oppilaitosten yhteishaun aikaan. Ajankohdalla varmistamme oppilaitosten hyödyn markkinoinnista sekä nuorten tietoisuuden koulutustarjonnasta. Iltaohjelmassa klo. 18–23 on esiintynyt nuorison suosikkiartisteja Vuoden 2014 RatRace tapahtuman jälkeen lähetimme laatimamme kyselylomakkeet tapahtumasta 8. ja 9. luokkalaisille nuorille sekä näytteilleasettajille. Kyselytutkimusten perusteella saimme nuorilta tietoa tapahtuman onnistumisesta. Näytteilleasettajilta saatiin tieto siitä, kuinka tapahtumaa voidaan kehittää vielä paremmaksi kokonaisuudeksi. Tutkimme tapahtumaa näytteilleasettajien näkökulmasta, että hyötyvätkö he tapahtumaan osallistumisesta. Saimmekin hyviä vinkkejä toimijoilta sekä kannanottoja nuorilta tapahtuman jatkoa ajatellen. Kyselyn ja havainnoinnin kautta hankitut tutkimustulokset eivät ole suoraan yleistettäviä, mutta suuntaa antavia.This thesis description is about the RatRace youth activation day. This thesis was ordered by the city of Haapavesi. Job purpose is to serve special youth work. One main task of this thesis is to familiarise new employees into the event. It can also be used to market the event in neighboring cities. The activation day is in two parts; day event is between 12-16 hours and the evening program starts at 18 hours and last about until 22. The RatRace activation day is built at the sports hall. All the local col-leges and schools in the neighboring areas, clubs and organisations present their work. Our aim is to give young people lots of information and so help to choose the suitable place of study, hobby or some other activities in their lives. The event is for A-clinic nurse, mental health nurse, social worker, cura-tor, the school nurse, youth worker and outreach youth worker just to mention a few. Their mission is to educate youngsters on current issues. All exhibitions have a functional score. Young people can actually experiment in different types of sports or other hobbies. Colleges and their different lines of study are also featured operationally. Young people can cut boards, drill, fix the car, take pictures or explore the sectors of tourism. Visitor will receive brochures, (leaflets) and other giveaways. The event is intended to raise young people’s wellbeing in the city of Haapavesi. It would be great to help everyone to find their place in their free-time, education or professionally. Prevention of social exclusion is one of the major aims. Topics may be serious, but the events itself aim at being happy.The evening event is purely for fun. Performers in the evening are popular domestic artists. During the previous years they have been Jukka Poika, JVG and Justimus. Children under 12 years will come with their parents to the event. We wanted to give the families a possibility to spend time together. Young people were listening to good music, dancing and having fun in safe and controlled manners. The event is completely substance-free. RatRace has been organised already for three times. Because of the positive feedback, we will continue the tradition of RatRace

Photon heat transport in low-dimensional nanostructures

At low temperatures when the phonon modes are effectively frozen, photon transport is the dominating mechanism of thermal relaxation in metallic systems. Starting from a microscopic many-body Hamiltonian, we develop a nonequilibrium Green's function method to study energy transport by photons in nanostructures. A formally exact expression for the energy current between a metallic island and a one-dimensional electromagnetic field is obtained. From this expression we derive the quantized thermal conductance as well as show how the results can be generalized to nonequilibrium situations. Generally, the frequency-dependent current noise of the island electrons determines the energy transfer rate.Comment: 4 pages, 3 Fig

Thermal, electric and spin transport in superconductor/ferromagnetic-insulator structures

A ferromagnetic insulator (FI) attached to a conventional superconductor (S) changes drastically the properties of the latter. Specifically, the exchange field at the FI/S interface leads to a splitting of the superconducting density of states. If S is a superconducting film, thinner than the superconducting coherence length, the modification of the density of states occurs over the whole sample. The co-existence of the exchange splitting and superconducting correlations in S/FI structures leads to striking transport phenomena that are of interest for applications in thermoelectricity, superconducting spintronics and radiation sensors. Here we review the most recent progress in understanding the transport properties of FI/S structures by presenting a complete theoretical framework based on the quasiclassical kinetic equations. We discuss the coupling between the electronic degrees of freedom, charge, spin and energy, under non-equilibrium conditions and its manifestation in thermoelectricity and spin-dependent transport.Comment: 117 pages, 33 figures. arXiv admin note: substantial text overlap with arXiv:1706.0824