CAREER: Nature of Pure and Dirty Liquid 3He-Fundamental Investigations and Educational Activities

University Of Florida, Gainesville FL

Investigators

Abstract

This low temperature physics CAREER project will investigate the fundamental nature of pure and dirty superfluid 3He using ultrasound spectroscopic techniques. The effect of strong magnetic fields (up to 15 T) on the dirty p-wave superfluid in the presence of magnetic and non-magnetic impurities will be investigated. This work will provide important information on the phase diagram of this relatively new system and has the potential to reveal new phenomena near the critical pressure. The critical pressure is related to quantum phase transitions, which are of great current interest in a range of condensed matter systems. Using a transverse sound spectroscopic technique, direct evidence of a sub-dominant f-wave pairing interaction in the B-phase will be investigated. This novel spectroscopic technique is believed to be superior to the conventional technique in searching for the new collective modes whose existence is guaranteed only by the f-wave pairing interaction. The observation of the new mode would be the first experimental confirmation of the collective modes generated by the subdominant pairing interaction in a more general class of superfluids. Fluctuation effects above the transition will be studied using zero sound. The known background contribution and an extremely high resolution in the zero sound velocity measurements will facilitate the direct measurement of the coherence length. This low temperature physics CAREER project will investigate fundamental properties of pure and so-called dirty superfluid 3He using ultrasound spectroscopic techniques. Dirty superfluid refers to superfluid samples in the presence of very low-density porous solids, such as an aerogel. The research, near the absolute zero of temperature, is relevant not only to the quantum fluids community, scientists who investigate the properties of 3He and 4He, but to many other areas of condensed matter physics. Recently, many interesting phenomena related to quantum phase transitions have been discovered and studied extensively in various condensed matter systems. Unlike conventional (classical) transitions, which occur at finite temperatures such as melting of solids, quantum phase transitions are triggered from purely quantum mechanical origins and accordingly can occur at absolute zero temperature. The dirty superfluid system is an excellent system to study this quantum phase transitions especially near the critical pressure. The effect of strong magnetic fields on the phase diagram of disordered superfluid 3He will be investigated. In other work, the detailed microscopic origin of superfluidity in pure superfluid 3He will be investigated via a search for a new excited state of the Cooper pairs (of 3He atoms) using a novel transverse sound spectroscopic technique. The incipient superfluidity above, but near, the transition temperature will be studied by conducting high resolution sound velocity measurements. The incipient superfluidity is caused by the thermally driven fluctuations of Cooper pairs with a short lifetime. The research involves extensive participation of both graduate and undergraduate students, who will be provided a wide range of rigorous laboratory experience and training for later career opportunities in academe, industry or government. The research project includes an important integral component directed toward improving local high school science education.