Anisotropic Disorder in Superfluid 3 He: Effects of High Porosity Aerogel

1. Anisotropic Disorder in Superfluid 3He: Effects of High Porosity Aerogel on the Superfluid Phases of 3HeYoonseok Lee, University of Florida, DMR 0803516 The effect of disorder on a many particle system is one of the most important and ubiquitous problems in condensed matter physics. We study the effect of controlled disorder in otherwise the purest condensed matter system, liquid 3He by utilizing nanometer scale porous medium, silica aerogel. Especially in the low milikelvin range, we can study the influence of disorder on unconventional (p-wave) superfluid 3He. Using high frequency ultrasound, we found drastically different behavior in the transition between two superfluid phases (the A- and the B-phase) in response to applied magnetic field from the pure superfluid. Using this technique we constructed a phase diagram in pressure-field-temperature space. The key features of the phase diagram can be understood on the basis of two fundamental points: firstly, the strong coupling effect is significantly reduced in this system by impurity scattering, and secondly, the anisotropic disorder presented in the form of aerogel strands plays an important role that emulates the effect of a magnetic field. B.H. Moon et al., Phys. Rev. B 81, 134526 (2010). Phase diagram of superfluid 3He in 98% aerogel. The solid triangles represent the aerogel superfluid transition. The A-B transitions in aerogel obtained by two different methods are represented by solid circles and stars. For comparison, the constant field A-B phase boundaries for the bulk liquid are shown by the dotted lines for 0.1, 0.3, 0.5, 0.55, and 0.58 T, respectively. The numbers next to the star symbols indicate the mid-field strength.

2. Anisotropic Disorder in Superfluid 3He: Effects of High Porosity Aerogel on the Superfluid Phases of 3HeYoonseok Lee, University of Florida, DMR 0803516 Outreach In the past year, PI organized and participated in numerous outreach events: hosting recruit events and lab tours for STARS local high school students and science teachers and about 100 high school students and parents through Outstanding High School Scholars Program (OHSP). Serving as a judge for the Science Fair at Hawthorne Middle/High School (Title 1 school located in an underrepresented area) and Junior Science, Engineering and Humanities Symposium (JSEHS) is one of the annual activities since 2002. Two REU students conducted research during the summer of 2009 and 2010. One of them is a minority student. Technological Impact In the process of quantifying anisotropic property of high porosity aerogel, we observed strong optical birefringence when aerogel is uniaxially deformed. We conducted extensive measurements on this phenomena and recognized its applicability as a tunable wave plate. Based on this work, a US Utility Patent Application, “Tunable Silica Aerogel Wave Plate”, was filed in January 2010.