Huge thermoelectric effects in ferromagnet-superconductor junctions in the presence of a spin-splitting field

We show that a huge thermoelectric effect can be observed by contacting a superconductor whose density of states is spin-split by a Zeeman field with a ferromagnet with a non-zero polarization. The resulting thermopower exceeds $k_B/e$ by a large factor, and the thermoelectric figure of merit $ZT$ can far exceed unity, leading to heat engine efficiencies close to the Carnot limit. We also show that spin-polarized currents can be generated in the superconductor by applying a temperature bias.Comment: 5 pages, 4 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

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

Possibilities of utilising green hydrogen as fuel in the heavy transport sector in Finland

Abstract. This bachelor’s thesis presents one possibility of utilising green hydrogen as fuel in the heavy transport sector in Finland. The work is a literature review that includes calculations to estimate the potential hydrogen demand of heavy transportation. The topic is relevant because of the increasing concerns about climate change, and the urgent need to reduce greenhouse gas emissions asks for environment-friendly solutions in all fields including transportation. Green hydrogen has been recognised as a potential zero-emission fuel in future heavy transportation. However, the technologies that are required for this utilisation are still under development and need improvement before the usage could be possible. The thesis introduces the EU’s and Finland’s composed strategies to attain carbon neutrality, the EU in 2050 and Finland in 2035. These strategies spell out targets and guidelines for achieving decarbonisation in various fields, such as heating, electrification, industry, and transport. The strategies also predict the future of the hydrogen economy and provide a picture of the potential scale of hydrogen production and use. The study examines the current state of the sector, the feasibility of implementing green hydrogen as a fuel, and the potential benefits and challenges of its adaptation into the Finnish fuel chain. The required hydrogen demand and electricity need for this utilisation are calculated by using the exemplary consumption of an ICE hydrogen engine developed by the company Cummins Inc and collected data on Finland’s traffic performances from Statistics Finland. The calculation shows that the required demand per year would be 350 000 tonnes of hydrogen and more than 17.5 TWh of electricity would be needed to satisfy this demand. Theoretically, this electricity demand could be achieved with the current renewable electricity capacity of 36.9 TWh (2021). Although it wouldn’t be possible in practise as the total electricity demand is 69.3 TWh, without renewable hydrogen production. The electrical efficiency of electrolyser technology is, however, expected to improve by about 12.5% in the future. With this improvement, the annual electricity needed for green hydrogen production for heavy transportation would decrease to 15.3 TWh