Search for new phases of the exotic superfluid 3He under nanoconfinement

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Non-technical AbstractMost consumer items utilize technology that emerged because of advances in condensed matter research. Future advances will be enabled by the sort of “curiosity driven” exploration of new regimes accessible only in a laboratory environment. The research to be conducted in this program will examine the special properties of superfluid 3He when confined in precisely defined structures less than a thousandth of a millimeter tall, marking the transition from bulk so-called 3 dimensional behavior to a new 2 dimensional regime. Undergraduate students and a Ph.D student will build on cutting edge knowledge to design and fabricate these structures opening up a new area of quantum nano-fluidics. The surfaces will have to have a well-defined smoothness since the smoothness (alterable with a coating of helium 4) changes the scattering at the surface much like a mirrored surface is different from a frosted surface. This scattering quality (together with the confinement) can also change the types of superfluid states (“phases”) that emerge. These phases should show a property “chirality” that should have properties like a spinning top. These new phases should exhibit novel characteristics such as highly conducting “edge states” that are scientifically “exciting” and that could, in the future form the basis of new types of devices for metrology and computation. Past graduate students and undergraduates of this team have gone on to productive careers in academia, high-technology industries and the financial sector, and the planned research will prepare a new generation of students for challenging careers. Technical abstract:Superfluid 3He can inform research activity that extends across many fields in Physics. The project combines nanofluidics (intricate and precisely fabricated silicon cavities with sizes tuned to the scale of the superfluid’s coherence length) with low temperature physics, to expose new size effects. The experimental activity will probe excitations using transport (superfluid density and heat conductivity) as well as novel noise thermometry and a nanowire to act as local thermometers. Researchers expect that entirely new p-wave superfluid states can be stabilized by such confinement and the balance between the superfluid ground state that preserves (3He-B) or breaks (3He-A) time reversal symmetry will also be affected by confinement. By measuring the phase diagram of confined 3He, details of the pressure and temperature dependence of the strong coupling strength will be mapped out allowing for more reliable prediction of the phase diagrams of 3He under confinement. Confinement will also provide the means to study the surface/edge excitations emerging as a result of bulk/edge correspondence. Studies of the hysteresis in the first-order transition between the confined A and B phases (radically different from nucleation in bulk) will challenge current understanding of these quantum transitions. New geometries will explore the physics of quantum transport across single and multiple interfaces. By combining low temperatures and nano fabrication, graduate students and undergraduates will be exposed to the exciting training ground that has prepared scientists for lead roles in academia and high-technology industries. Eventually, the new superfluids that emerge under confinement might be of interest in quantum computation.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.