Observation of multiple Andreev-reflection assisted cooling effects in nano superconducting Josephson junctions

SHUNG-KANG KOH^1*, Pei-Yuan Li¹, Ching-Ping Lee¹, IoChun Hoi², Yen-Hsiang Lin¹, Chung-Yu Mou¹, Dah-Chin Ling³, Yung-Fu Chen⁴, Cen-Shawn Wu⁵, Jeng-Chung Chen¹

¹Physics, National Tsing Hua University, Hsinchu, Taiwan
²Physics, City University of Hong Kong, Kowloon, Hong Kong
³Physics, Tamkang University, New Taipei City, Taiwan
⁴Physics, National Central University, Jhongli, Taiwan
⁵Physics, National Changhua University of Education, Changhua, Taiwan

* Presenter:SHUNG-KANG KOH, email:kenkoh190@gmail.com

We demonstrate the cooling effect induced by multiple Andreev-reflection (MAR) in the thermal hysteresis of superconducting constrictions near clean and short limit. We measure the current- voltage (I − V ) characteristics of single constriction and micro-SQUID devices, and observe the voltage-step jumps above the critical current (I_c) and below the gap (∆). Our analysis shows that the voltage-steps are signs of the enhancement of superconductivity driven by excess I; in particular, a MAR-assisted cooling effect taken place at V ≤ ∆/e. To demonstrate the cooling effect, we show the co-existence of MAR and supper-current interference in the retrapping currents in a micro-SQUID device. Our findings provide a unified picture to understanding nonequilibrium superconductivity, and have strong implications in developing superconducting ballistics devices.

Keywords: multiple Andreev-reflection, disequilibrium of superconductivity, Josephson junction