Investigating the Nature of Excitations in Superfluid 3He Using MEMS Oscillators

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Non-technical Description:More than 50 years ago, a distinguished theoretical physicist and a science writer George Gamow said that only number theory and topology had no application to physics. Nonetheless, physicists started to understand the significant role of topology in physics since 1980's, and new types of materials called topological quantum matter are being discovered. These materials possess unexpected properties which not only expand our knowledge but also functionality of the materials. In general, these topological materials are composed of multiple elements with complex structures. However, a form of helium, called helium-three isotope, becomes a topological matter when it is cooled down to a liquid form at extremely low temperature close to absolute zero. At such conditions it forms a new state of matter called a superfluid that exhibits fascinating quantum phenomena. In this project, the PI's research group investigates the nature of superfluid helium-three using a unique experimental technique employing small mechanical oscillators. This project will expand our understanding on these unique properties of helium-three. The research group is composed of graduate and undergraduate students working as a team. They will be trained not only in the field of low-temperature physics but also in silicon nanofabrication technology from design to fabrication of specialized devices that have proliferated our modern world through their widespread use as sensors and actuators.Technical Description: Growing interest in the surface Andreev bound states in p-wave superfluid 3He arises from the fact that it is arguably the most complete platform available to investigate the nature of topological excitations. The PI's group has developed a versatile and powerful experimental probe based on Micro-Electro-Mechanical System (MEMS) technology to study the surface Andreev bound states in this system. The major activities are: (i) Investigation of the topological surface states on a specular boundary for comprehensive understanding of the nature such as experimental evidence for Dirac fermions and a possible field-driven topological transition. (ii) Investigation of the interactions between two surface states in close proximity. (iii) Development of a sensitive quasiparticle flux sensor with a spatially resolved detection capability in the form of MEMS arrays. This project, in close collaboration with theorists, will certainly expand our understanding of these unique excitations in a pristine topological superfluid. Confirmation of the theoretically predicted topological transition induced by a small magnetic field would be one of the most convincing manifestation of a symmetry-protected topological superfluid and Majorana fermions in this system. The successful development of MEMS arrays will provide unprecedented opportunities to achieve spatially-resolved detection in 3He and 4He with many foreseeable applications: visualization of vortices and angle-resolved detection of quasiparticles in 3He, and momentum resolved roton-phonon detection and quantum turbulence study in He-II.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.