Low-noise THz MgB2 Josephson mixer

• Published in: Applied physics letters 2016-09, Vol.109 (11)
• Main Authors: Cunnane, Daniel, Kawamura, Jonathan H., Acharya, Narendra, Wolak, Matthäus A., Xi, X. X., Karasik, Boris S.
• Format: Article
• Language: English
• Subjects: Applied physics; Borides; Chemical vapor deposition; Digital electronics; Epitaxial growth; Extraterrestrial radiation; Josephson effect; Magnesium compounds; Mixers; Noise; Noise temperature; Organic chemistry; Parameter sensitivity; Physical vapor deposition; Spiral antennas; Substrates
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4962634

The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The I c R n product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.