October 5, John Reppy, Cornell University

in Fall 2012
June 2nd, 2012

3:00 PM in Room 210, 8 St. Mary’s Street

reppyRefreshments served at 2:45 PM

Pursuit of the Elusive Supersolid

Abstract: Thirty-five years elapsed between the predictions of a supersolid state of solid 4He by Chester (1968), Andreev and Lfschitz (1969) and Leggett (1970) and the surprising discovery of experimental evidence for its existence. In 2004 Eunsoeng Kim and Moses Chan reported on a series of torsional oscillator measurements with solid 4He. In these measurements they observed an unexpected decrease in the period of the torsional oscillator at temperatures below 250 mK. They interpreted this decrease in period as the result of a superfluid-like decoupling of a fraction of the solid helium moment of inertia from the oscillator. This discovery generated a flurry of experimental and theoretical interest that persists to this day. This initial excitement has recently been tempered by the realization that many of the early supersolid observations were contaminated by effects arising from an anomaly in the elastic properties of solid 4He that occurs over the same temperature range of the supersolid phenomenon reported by Kim and Chan. In an attempt to separate dynamic elastic effects from a true supersolid signal, we are employing torsional oscillators with two eigen frequencies and have achieved some unexpected results that calls into question the original interpretation of Kim and Chan’s original experiment.

Biography: John Reppy received a Bachelor’s degree in math and physics in 1954 at University of Connecticut and a master’s degree from the same school two years later. He completed a Ph.D at Yale University in 1962, where he spent four years as an assistant professor. Reppy joined the Cornell Physics Department in 1966, later becoming the John Wetherill Professor of Physics. He is the recipient of numerous awards and honors, including the Fritz London Memorial Prize in 1981 and the NASA Distinguished Public Service Medal for leadership and support to the NASA microgravity fundamental physics program in 2000. Reppy is also a member of the National Academy of Sciences.

 

Faculty Host: David Bishop

Student Host: Adam Moldawer

 

 

 

 

 

 

 

 

Faculty Host: David Bishop