paper

Ferromagnetic insulator-based superconducting junctions as sensitive electron thermometers

arXiv:1502.07548 · doi:10.1103/PhysRevApplied.4.044016

Abstract

We present an exhaustive theoretical analysis of charge and thermoelectric transport in a normal metal-ferromagnetic insulator-superconductor (NFIS) junction, and explore the possibility of its use as a sensitive thermometer. We investigated the transfer functions and the intrinsic noise performance for different measurement configurations. A common feature of all configurations is that the best temperature noise performance is obtained in the non-linear temperature regime for a structure based on an europium chalcogenide ferromagnetic insulator in contact with a superconducting Al film structure. For an open-circuit configuration, although the maximal intrinsic temperature sensitivity can achieve nKHz, a realistic amplifying chain will reduce the sensitivity up to KHz. To overcome this limitation we propose a measurement scheme in a closed-circuit configuration based on state-of-art SQUID detection technology in an inductive setup. In such a case we show that temperature noise can be as low as nKHz. We also discuss a temperature-to-frequency converter where the obtained thermo-voltage developed over a Josephson junction operated in the dissipative regime is converted into a high-frequency signal. We predict that the structure can generate frequencies up to GHz, and transfer functions up to GHz/K at around K. If operated as electron thermometer, the device may provide temperature noise lower than nKHz thereby being potentially attractive for radiation sensing applications.

11 pages, 10 color figures

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