Superconductivity is one of the most fascinating phenomena in condensed matter physics. This session will focus on the study of the high TC superconductivity of a Y1Ba2Cu3O7 (YBCO) thin film. We will use the superconducting quantum interference device (SQUID), which consists of a ring of superconductor containing two parallel Josephson junctions. In particular, we will study the voltage-current (V-I) and voltage-flux (V-Φ) characteristics of the SQUID (Mr. SQUID from STAR Cryoelectronics). From the V-I and V-Φ curves, we can extract superconducting parameters, such as the critical current, normal resistance, transition temperature, and the amplitude of the voltage oscillation.
Ram C. Rai, Assistant Professor in the Department of Physics at Buffalo State College, has been teaching the Advanced Lab course since Fall 2007. Professor Rai gained his first research experience in condensed matter physics in 1998 as a graduate student at the University of Kentucky. His research interests include the study of electronic and magnetic materials via transport, optical, electro-optical, and magneto-optical techniques under extreme conditions (4–800 K and 0–33 Tesla). He is particularly interested in the growth and study of thin films of complex oxides with functional properties.
Professor Ram C. Rai, Buffalo State College, Department of Physics, 1300 Elmwood Avenue, Buffalo, NY 14222. Email: rairc@buffalostate.edu. Telephone: 716-878-3767
The superconducting transition of a YBCO sample can be observed in the electrical resistance versus temperature graph. For the resistance measurement, we'll build a battery-run constant current source (∼10 μA). Since a silicon diode demonstrates a linear resistive property as a function of temperature, at least down to ∼25 K, it is a very reliable temperature sensor. A silicon diode can be calibrated at room temperature (∼300 K) and liquid nitrogen temperature (∼77 K) for its use as a temperature sensor. Using these home-made devices—current source and temperature sensor—we can measure the resistance of a YBCO sample as a function of temperature, from room temperature down to the boiling temperature of liquid nitrogen (77 K). We will also study the ac Josephson effect of the SQUID and demonstrate a phase-locking mechanism leading to Shapiro steps in the V-I curve. Participants will learn to use the SQUID apparatus and to perform the resistance measurement at low temperatures.