3he in Confinement

Superfluid 3He is a known topological material that is expected to host Andreev-Majorana fermionic excitations in the form of quasiparticle surface bound states, a subject central to the field of quantum information. The proposal, 3He in Confinement, is a platform for basic research on this topic. Importantly, the 3He order parameter and its symmetry is well-established for the bulk forms of the A and B superfluid phases. The same spectroscopic and thermodynamic experimental techniques used to study the bulk can be exploited to explore the topological character of new superfluid phases induced by confinement and determine the behavior of these novel bound states. For the present proposal these tools include nuclear magnetic resonance and transverse acoustics. Engineered anisotropic quasiparticle scattering through confinement of 3He in anisotropic environments, such as aerogels, slabs and pores will be used to stabilize topological phases characterized by chiral symmetry or time reversal symmetry. This work has implications for better understanding superconducting materials with unconventional symmetries. Intellectual Merit: Highly porous silica aerogel samples will be grown and processed to produce a globally uniform anisotropic environment for superfluid 3He having positive or negative uniaxial strain. It has been established that new superfluid states can be created in this way. Most notable is the recent discovery of a critical field that appears with competing interactions between magnetic field and negative strain, but surprisingly not for positive strain. To elucidate this discovery, measurements will be performed to establish the pressure-field-temperature phase diagrams and to determine the order parameter amplitudes and their symmetries as a function of pressure and strain. Variation of pressure is a means to control the coherence length and the pairing interaction and the effects of strong-coupling. The latter is proportional to the ratio of the superfluid transition temperature to the Fermi temperature. Proposed work in ~ 100 nm diameter, well-defined cylindrical pores, is motivated by recent theoretical calculations showing that new topological phases of superfluid 3He can be stabilized in this way. A new tool will be developed to study the behavior of transverse acoustics in superfluid 3He confined in a thin resonant cavity for which the path length can be varied in situ. This approach will allow the clear separation of bulk and surface contributions to acoustic attenuation, and an unambiguous confirmation of the existence and spectroscopy of Majorana excitations at the surface of 3He-B. With the variable path acoustic cavity technique, a search will be made for the transverse zero sound mode predicted by Landau many years ago. Broader Impacts: The American Physical Society recognizes the importance of broader impacts of scientific research, stating that it encourages its members to take advantage of opportunities for civic engagement, whether through public or government service, by providing advice and information to government officials, or by contributing to public debate. In this regard, work in this proposal informs both the PI and his students for engagement in these important forums. The PI will exercise these responsibilities in his administrative roles as chair of the division of condensed matter physics, the March meeting of the American Physical Society (the largest physics conference in the world), and as secretary, and eventual chair, of the commission for low temperature physics in