Magneto-Tunable Thermal Diode Based on Bulk Superconductor

Thermal diode is a growing technology and important for active thermal flow control. Since the theoretical designing of thermal diode in 2004, various kinds of solid-state thermal diodes have been theoretically and experimentally investigated. Here, we report on the observation of thermal rectification in bulk-size superconductor-normal metal junctions. High-purity (5N) wires of Pb and Al are soldered, and thermal conductivity (\k{appa}) of the junctions is measured in two different directions of the heat flow, forward (\k{appa}F) and reverse (\k{appa}R) directions. Thermal rectification ratio (\k{appa}F / \k{appa}R) of 1.75 is obtained at T ~ 5.2 K with H = 400 Oe. The merit of the Pb-Al junction is a large difference of \k{appa} in an order of several hundred W m-1 K-1 and magneto-tunability of the working temperature.