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Topological superfluids under engineered nanoscale confinement: New phases and the search for Majoranas


Experiments on liquid helium-three near the absolute zero of temperature have played a key role in the development of many central concepts in condensed matter physics. The discovery of superfluid 3He gave us the first p-wave superfluid, a model for unconventional superconductivity, in which the pairing breaks the symmetry of the parent normal metal. Since that time the international programme of materials discovery has thrown up many new unconventional superconductors. And formally the phases of superfluid 3He can be regarded as quantum vacua, with parallels in particle physics and cosmology [see "The Universe in a Helium Droplet", G.E.Volovik].

Recently the topology (in momentum space) of condensed matter systems has been widely applied as a powerful scheme for their classification, alongside the concept of broken symmetry. The simple truths of topology (eg a sphere's surface cannot be continuously deformed into that of a torus) have a powerful impact when applied to complex interacting quantum systems, by pointing to phenomena that must be there, independent of microscopic details; robust protection is conferred by the inviolable constraints of topology.


In particular it is predicted that at the surface of the quantum vacuum that is the B-phase of superfluid 3He, there exist excitations that are Majorana fermions. This system is also predicted to exhibit “supersymmetry”.  Thus the unique condensed matter system that is superfluid 3He potentially unites condensed matter physics and particle physics “in the laboratory”.



(Contact Prof. John Saunders or Dr. Andrew Casey for more information)

In this project, with EPSRC support, we study the topological superfluidity of helium-three confined in regular nanofabricated geometries, as a model system to further our understanding of topological quantum matter. Our experiments exploit the recent technical breakthroughs we have made in quantum nanofluidics, and the development of sensitive NMR techniques based on the detection of the precessing magnetic signal by SQUIDs (Superconducting Quantum Interference Devices). See references below.

Confinement of superfluid 3He in a slab-like cavity of thickness of order the diameter of the Cooper pairs, has a profound effect on the superfluid order and is expected to stabilize new superfluid states of matter. The compressibility of 3He allows the pair diameter to be pressure-tuned, varying the effective confinement. Regular geometries are fabricated with well-characterized surfaces, which can be tuned in situ by plating with a helium-4 film. This exquisite geometrical control and tuneability, coupled to the ideal material qualities of superfluid 3He, and highly developed microscopic models provide a rigorous theory-experiment interface.

Phases with different topologies are expected to be stable under different conditions, and we will map the effect of our new control parameter, confinement, on these phases. We will quantify the role of disorder, arising from surface roughness, and the importance of quantum size effects. These topological superfluids support novel excitations at the faces or edges of the cavity, at domain walls and vortices. The precise character of these excitations depends on whether the superfluid ground state preserves or breaks time reversal symmetry.


At the surface of the B-phase the excitations are propagating Majorana fermions. Majorana fermions are predicted particles which are their own antiparticle, and are yet to be discovered, and we will search for these as part of the project.

This project has a strong international collaborative dimension, both experimental and theoretical, closely partnering with Cornell and Northwestern in the USA, and PTB (Berlin) in Germany, and exploiting our membership of the European Microkelvin  Platform www.emplatform.eu.  We will connect with other programmes on topological quantum matter in the UK and internationally, enhanced by the Hubbard Theory Consortium https://www.royalholloway.ac.uk/cmt/htc.aspx , through its visitors programmes and workshops.

The project is expected to lead to fundamental insights into topological quantum matter and topological superfluidity/superconductivity in particular. It will drive the innovation of new instrumentation at the new frontier combining ultra-low temperatures and nanoscience, and new SQUID NMR techniques of broad applicability.



EPSRC EP/J022004/1 £1,140,435. PI J Saunders co-Is: A Casey, B. Cowan, M. Eschrig. Topological superfluids under engineered nanofluidic confinement: new order parameters and exotic excitations

Collaborators: Northwestern University (USA), Cornell University (USA), PTB (Berlin).


References to some of our published work

Phase Diagram of the Topological Superfluid 3He Confined in a Nanoscale Slab Geometry. L. Levitin, R. Bennett, A. Casey, B. Cowan, J. Saunders, D. Drung, T. Schurig, J. Parpia Science 340, 841 (2013)

Surface Induced Order Parameter Distortion in Superfluid 3He-B Measured by Non-Linear NMR, L. Levitin, R. Bennett, E. Surovtsev, J. Parpia, B. Cowan, A. Casey, J. Saunders. Phys. Rev. Lett. 111, 235304 (2013)

Quantum transport in mesoscopic 3He films: experimental study of the interference of bulk and boundary scattering. P. Sharma, A Corcoles, RG Bennett, JM Parpia, B Cowan, A Casey, J  Saunders. Phys. Rev. Lett. 107, 196805 (2011)

Anodically bonded submicron microfluidic chambers. S Dimov, RG Bennett, A Corcoles, LV Levitin, B Ilic, SS Verbridge, J Saunders, A Casey and JM Parpia. Rev. Sci. Inst. 81, 013907 (2010)

A nuclear magnetic resonance spectrometer for operation around 1 MHz with a sub-10 mK noise temperature, based on a two stage DC SQUID sensor. LV Levitin, RG Bennett, A Casey, BP Cowan, CP Lusher, J Saunders, D Drung, Th Schürig. Applied Physics Letters 91, 262507 (2007)

Study of superfluid 3He under nanoscale confinement: A new approach to the investigation of superfluid 3He films. L. Levitin, R. Bennett, A. Casey, B. Cowan, J. Saunders, D. Drung, Th. Schurig, J. Parpia, B. Ilic, N. Zhelev.  J. Low Temp. Phys. 175, 667-680 (2014)


Former students associated with this work

Lev Levitin (PDRA RHUL)

Rob Bennett (PDRA Cornell now Isentropic Ltd)

Antonio Corcoles (PDRA Cambridge, IBM Yorktown Heights)

Helen Dyball (Managing Editor, Electronics Letters)

Former PDRAs

Junyun Li (now Oxford Instruments, China)

Andrew Casey (EPSRC Advanced Research Fellow, now Lecturer RHUL).


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