Presentation Information
[PC6-06-INV]Development of thermal management technology based on superconductors
*Yoshikazu Mizuguchi1 (1. Tokyo Metropolitan University (Japan))
Keywords:
thermal conductivity,magneto-thermal switching,flux trapping,thermal diode
Thermal management technologies including heat storage, thermoelectric conversion, thermal switching, and thermal rectification are crucial for improvement of device performance [1]. At cryogenic temperatures, cryogenic electronic devices also require thermal management for a better performance, and superconductors can be used for cryogenic thermal managements. For example, in Ref. 2, fabrication of magneto-thermal switching (MTS) device using a bulk Pb has been demonstrated. In superconducting states, carrier thermal conductivity (k) is suppressed by the formation of Cooper pairs, and the resulting thermal conductivity in the superconducting states is lower than the normal states. Although the MTS in superconductors have been well known, nonvolatility, which is important for further development of effective MTS, had not been achieved. However, nonvolatile MTS has been achieved with commercial Sn-Pb solders [3]. The mechanism of nonvolatile MTS in Sn-Pb solders is explained by magnetic flux trapping in Sn regions of the solder (Fig. 1a-1c); Sn-Pb solders are phase-separated alloys (Fig. 1d). In superconducting states, k is low (Fig. 1a), and at H larger than Hc, k becomes high in the normal states. After magnetic field experience, with trapped magnetic fluxes in the Sn regions, the bulkiness of superconductivity of the Sn regions are suppressed, and high k is maintained (Fig. 1e-1h). In the talk, we will introduce various examples of nonvolatile MTS in phase-separate superconductors.More recently, we observed thermal diode effect (thermal rectification) in bulk-superconductor-based materials. After the theoretical proposal of superconductor-normal junction for achieving efficient thermal diode at low temperatures [4], various studies on superconductor nano junctions have been performed using simulation. However, experimental realization of bulk-scale superconductor-based thermal diode was lacking. We fabricated Pb-Al junction using high-purity (99.999 percent) wires, and observed thermal rectification ration (TRR), which is defined by the ratio of effective thermal conductivity measured along the forward and reverse directions, of TRR = 1.75 [5]. The emergence of thermal rectification can be explained by the sharp suppression of carrier thermal conductivity at Tc under magnetic field parallel to the wire direction. In the talk, we will deeply discuss the rectification properties and the mechanisms. In addition, we will show the method of fabrication of jointless thermal diode using bulk superconducting materials.