With its world-leading expertise in ultra-low temperature physics, the Quantum Fluids and Solids group is pushing the limits of knowledge in topological quantum matter, low dimensional physics and mesoscopic physics.
Our current research focuses on experimentally realizing a broad range of quantum materials using two dimensional helium as a model system. Examples include: quantum spin liquid, two-dimensional Fermi liquid, two-dimensional 4He supersolid. Superfluid ³He confined on the nanoscale (topological mesoscopic superfluid 3He) is being studied as a model system for topological superconductivity.
A further new frontier is the study of quantum materials at ultralow temperatures driven by the emergence of exotic ordered states, which are highly tuneable by external control parameters such as magnetic field and strain. Electrons are cooled to below 1mK in a candidate topological superconductor, and in nanoelectronic quantum devices based on cold low dimensional electrons.
This programme is tied to extensive research on new measurement techniques, and new low temperature platforms.
Our fundamental research drives forward the development of research capacity and infrastructure beyond state-of-the-art. This is important for the coming quantum technology revolution, and for the understanding of quantum materials and their discovery. Development of new techniques directly benefits the scientific instruments industry in the short-medium term, especially those focused on cryogenics, nanoscience and superconducting technologies, widening its customer base. This is fostered by the global reach of UK industry in this sector. Collaboration with National Measurement Institutes has important societal impacts through metrology and standards.
The experiments are undertaken at Royal Holloway in the London Low Temperature Laboratory to temperatures as low as a few hundred μK. The London Low Temperature Laboratory at Royal Holloway is part of the European Microkelvin Platform (EMP), which is funded as a European Advanced Infrastructure by Horizon 2020.
- Cornell University (Jeevak Parpia)
- NIST, Wasington (Rob Ilic)
- PTB, Berlin (Thomas Schurig, Dietmar Drung)
- Northwestern University (James Sauls)
- Montana State University (Anton Vorontsov)
- Oxford University (Steve Simon)
- University of Jyvaskyla (Mikhail Silaev)
- Kyoto University and Topo-Q International Network (Norio Kawakami, Yoshiteru Maeno)
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany (Manuel Brando, Alexander Steppke, Kent Shirer, Markus Koenig).
- Physics Insitute, Goethe University (Cornelius Krellner)
- University of Cambridge (David Ritchie, Charles Smith)
We present below our current research projects. The experiments are undertaken at Royal Holloway in the London Low Temperature Laboratory to temperatures as low as a few hundred μK. The London Low Temperature Laboratory at Royal Holloway is part of the European Microkelvin Platform(EMP), which is funded as a European Advanced Infrastructure by Horizon 2020.
Topological mesoscopic superfluidity of 3He
Superfluid 3He is one of the most exciting and rich condensed matter systems we know. Over the past thirty years its intellectual impact has been felt in areas as diverse as unconventional superconductivity, cosmology and turbulence. Our recent research has taken superfluid 3He into a new regime, through its confinement on the nanoscale in well characterized nanofluidic sample chambers [1-3], exploiting new sensitive NMR techniques . The influence of confinement is profound and we expect to identify and explore new states of topological quantum matter, opening a new chapter in quantum fluids research.
Figure 1 - 3D representation of one of our typical nanofluidic confinement geometries.
In this project, we exploit superfluid 3He, known to support two distinct topological superfluid phases in bulk, establishing the new research direction of topological mesoscopic superfluidity. Under nanoscale confinement, this material provides a unique model for topological superconductivity. The subtle interplay between symmetry and topology in these materials is an open question. Our approach will be to confine 3He in precisely engineered geometries to create hybrid nanostructures, allowing a degree of control that is unprecedented. Confinement and periodic structures, with liquid pressure as a tuning parameter of Cooper pair diameter, will induce new superfluid phases, for which the order parameter symmetry will be inferred from nuclear magnetic resonance. These materials will be building blocks for hybrid mesoscopic superfluid systems.
Figure 2 - 3D schematic of hybrid mesoscopic superfluid 3He structure: nanofluidic SNS and NSN junctions
- L. V. Levitin, R. G. Bennett, A. Casey, B. Cowan, J. Saunders, D. Drung, T. Schurig and J. M. Parpia, Science 340 (6134), 841-844 (2013).
- L. V. Levitin, R. G. Bennett, E. V. Surovtsev, J. M. Parpia, B. Cowan, A. J. Casey and J. Saunders, Phys Rev Lett 111 (23), 235304 (2013).
- L. V. Levitin, R. G. Bennett, A. Casey, B. Cowan, J. Saunders, D. Drung, T. Schurig, J. M. Parpia, B. Ilic and N. Zhelev, Journal of Low Temperature Physics 175 (5-6), 667-680 (2014).
- L. V. Levitin, R. G. Bennett, A. Casey, B. P. Cowan, C. P. Lusher, J. Saunders, D. Drung and T. Schurig, Applied Physics Letters 91 (26), 262507 (2007).
Realizing quantum materials with atomically layered helium films
Historically the study of helium has played a central role in condensed matter physics: the establishment of the Landau theory of Fermi liquids; the first unconventional “superconductor” with p-wave pairing breaking the high symmetry of the normal state; the demonstration of atomic ring exchange and frustrated magnetism in solid 3He; superfluidity and BEC in an interacting bosonic system; phase transitions mediated by topological defects (the 2D Kosterlitz-Thouless superfluid transition).
In this project helium in two-dimensions (2D) is investigated as a model system to tackle important questions in the field of strongly correlated quantum matter. Our approach in this proposal is to manipulate atomically layered thin films of helium on graphite, and study these films at ultralow temperatures with diverse techniques.
Prior work has demonstrated: Mott-Hubbard transition in 2D 3He ; frustrated magnetism on a triangular lattice ; heavy fermion quantum criticality ; intertwined superfluid and density wave order (2D super solid) [4, 5].
Current and future work includes the following topics:
- survival of Fermi liquids in a strictly 2D strongly correlated system
- interacting coupled 2D fermion-boson system
- realization of a model quantum spin liquid in 2D 3He
- intertwined superfluid and density wave order
- studies of helium on graphene and associated technical developments
- A. Casey, H. Patel, J. Nyeki, B. P. Cowan and J. Saunders, Phys Rev Lett 90 (11), 115301 (2003).
- A. Casey, M. Neumann, B. Cowan, J. Saunders and N. Shannon, Phys Rev Lett 111 (12), 125302 (2013).
- M. Neumann, J. Nyeki, B. Cowan and J. Saunders, Science 317 (5843), 1356-1359 (2007).
- J. Nyéki, A. Phillis, A. Ho, D. Lee, P. Coleman, J. Parpia, B. Cowan and J. Saunders, Nature Physics 13 (5), 455-459 (2017).
- J. Nyéki, A. Phillis, B. Cowan and J. Saunders, Journal of Low Temperature Physics 187 (5-6), 475-481 (2017). ￼
Heavy fermion superconductivity
YbRh2Si2 is a canonical heavy fermion metal with a field tuned quantum critical point. In recent work we have developed transport measurements on high quality single crystal samples which show it to be a superconductor below 10 mK. We also determine the phase diagram in a magnetic field.
This new superconductor has numerous interesting features, and is a candidate for spin-triplet topological superconductivity.
There is an interplay between coexisting, possibly intertwined, magnetism and superconductivity, with nuclear magnetism playing a role. The onset of superconductivity is anisotropic, and there is evidence for multiple superconducting phases.
The target of this project is to firmly identify the nature of the superconducting order in this system, and to exploit it in devices. This will involve: transport measurements in samples micro-structured by focussed ion beam (FIB); the development of new techniques for measurements into the microkelvin regime; exploitation of via nuclear magnetism (through by Yb isotope enrichment), strain, magnetic field and temperature.
The increased accessibility of low temperatures through cryogen-free technology opens the door to technological applications of relatively fragile exotic ordered states appearing as a result of electron correlations in a range of quantum materials and mesoscopic devices. In this regime competition between interactions allows systems to be relatively easily fine-tuned by external control parameters, such as magnetic field, strain and structured geometry.
In our laboratory we have developed techniques to both cool and measure diverse electron systems to below 1mK, with ultra-sensitive SQUID magnetometers playing a key role in low dissipation measurements. Two-dimensional electrons in semiconductor heterostructures have been cooled to close to 1 mK in an 3He immersion cell, employing a cooling-through-the-leads strategy, and requiring the identification and elimination of important sources of heat input.
Future work will centre on the study of gate-tuned nanoelectronic devices, cooled into this ultralow temperature regime, in which new correlated, spin ordered states are predicted. Cooling low dimensional electron systems in high magnetic fields will be possible on ND3, enabling the study of the exotic Fractional Quantum Hall Effect states.
NEMS, Nano-electro-mechanical Systems at ULT
Nano-Electro-Mechanical Systems (NEMS) represent a new key disruptive technology providing potential solutions for research and industry across a wide range of sectors, from Quantum Information processing through physical sensors to biological sensor applications. As the dimensions of devices and structures reduce, new technologies and approaches are required.
NEMs offer a new candidate system for probing the properties of quantum fluids. They can be nanofabricated with dimensions on the order of the size of the superfluid 3He cooper pair, resulting in resonant frequencies spanning a range from 0.1-100 MHz for beams and even higher frequencies for surface modes. To exploit these properties at low temperatures the motion of the NEMs needs to be read-out with a low dissipation measurement technique.
In prior work we have coupled NEMs devices to an extremely sensitive SQUID, Superconducting Quantum Interference Device, developed by our partners at PTB. We performed measurements in the temperature range 10 mK to 8 K on resonators with quality factors of 1-100 million with a resonant frequency of order of 1 MHz . This work revealed a strong interplay between the motion of the beam and the state of the readout SQUID2.
In this project the aims are to:
- Probe the nature of superfluid 3He by incorporating NEMs as local probes for topological mesoscopic superfluidity.
- To cool a sub 100 MHz NEMs device into the quantum regime, to achieve a long coherence time quantum state.
To achieve these aims NEMS can be optimised using advanced fabrication techniques and new materials. The project will investigate new materials such as graphene and SiN, as well as metallic NEMS resonators. These low frequency and high Q resonators should produce states with a long coherence time, but will require ultralow temperatures to enter the quantum regime.
Figure 1: An example of a 300 µm long silicon nitride string resonator (100 x 250 nm cross section), coated with a 30 nm thick Aluminium layer, provided by Eddy Colin (CNRS)
Figure 2: An example of a 40 µm long silicon nitride string resonator (50 x 50 nm cross section), coated with a niobium layer, provided by Jeevak Parpia (Cornell).
This project is based in the London Low Temperature Laboratory, Royal Holloway, which is part of the European Microkelvin Platform.
Cornell University (Jeevak Parpia)
Institut Néel, CNRS, Grenoble (Eddy Collin)
Lancaster University (Kunal Lulla)
PTB, Berlin (Dietmar Drung, Thomas Schurig).
Rupert Mellor (2018), Nano-Electro-Mechanical Systems at Ultra Low Temperatures as Probes for Quantum Fluids with Superconducting Quantum Interference Device Transduction. (Doctoral Thesis)
Cooling a NEMs device with a SQUID, paper in preparation.
Ultralow temperature engineering and technology
Currently, one can’t buy a thermometer that works from 10 to 1 millikelvin or a refrigerator to get to this temperature. The thermometry situation has been described “Like selling a BMW without a speedometer.” Technology developed for studying the behaviour of matter at mK has led to partnerships with Oxford Instruments and National Measurement Institutions to develop a new kind of refrigerator to reach sub mK and use the associated temperature measurement technology to define the Kelvin (the unit of temperature measurement). The impact of this development is on manufacturing-- in the leading cryogenics industry in the UK, and on metrology—in the international definition of the unit of temperature (Kelvin), and on commercial quantum computing—the primary market for ultra-low temperatures. The work was highlighted by the Institute of Physics in their document “Inspirational physics for a modern economy” https://www.iop.org/publications/iop/2015/file_65903.pdf, following on from REF2014.
The solution to the problem of ultralow temperature thermometry has been the development of a current sensing noise thermometer [1-3] within the LLTL. This device is currently being used to establish a methodology to achieve measurements of thermodynamic temperature, to be encoded in the Mise en Pratique of the new definition of the Kelvin1.
A major advance of the group to open the ultralow temperature regime to a wider scientific community was through combining cryogen-free dilution refrigerators with nuclear demagnetisation, in partnership with Oxford Instruments Nanoscience. In this work sub millikelvin temperatures in a cryogen-free environment were achieved for the first time .
In this project the aim is to produce a new generation of cryogenic heat exchanger materials through developing an understanding of the Kapitza boundary resistance. Here we can exploit the properties of the current sensing noise thermometer to measure the thermal boundary resistance between candidate materials and helium. Ultimately leading to both more efficient cryostats and enhanced cooling of mesoscopic samples.
Figure 1: Redefinition of the SI base units, links K directly to the Boltzmann constant.
Figure 2: Nuclear Demagnetisation Cryostat with SQUID based Kapitza boundary resistance cell.
This project is based in the London Low Temperature Laboratory, Royal Holloway, which is part of the European Microkelvin Platform.
PTB, Berlin (Jost Engert, Alexander Kirste, Dietmar Drung, Thomas Schurig)
NPL, UK (Graham Machin)
Oxford Instruments (Michael Cuthbert)
Magnicon (Henry J. Barthelmess)
New Evaluation of T- T2000 from 0.02 K to 1 K by Independent Thermodynamic Methods, Engert, J., Kirste, A., Shibahara, A., Casey, A., Levitin, L. V., Saunders, J., Hahtela, O., Kemppinen, A., Mykkänen, E., Prunnila, M., Gunnarsson, D., Roschier, L., Meschke, M. & Pekola, J., Int J Thermophys. 37, 125 (2016), doi: http://dx.doi.org/10.1007/s10765-016-2123-4
Primary current sensing noise thermometry in the millikelvin regime, A. Shibahara, O. Hahtela, J. Engert, H.van der Vliet, L. V. Levitin, B.Yager, A.Casey, C. P. Lusher, J. Saunders, D.Drung and Th. Schurig- - Philosophical Transactions A, (2016), doi: http://dx.doi.org/10.1098/rsta.2015.0054
Current Sensing Noise Thermometry: A Fast Practical Solution to Low Temperature Measurement, A.Casey, Arnold, F., Levitin, L. V., Lusher, C. P., Nyeki, J., Saunders, J., Shibahara, A., van der Vliet, H., Yager, B., Drung, D., Schurig, T., Batey, G., Cuthbert, M. N. & Matthews, A. J., J. Low Temp. Phys. 175, 764-775 (2014), doi: http://dx.doi.org/10.1007/s10909-014-1147-z
A microkelvin cryogen-free experimental platform with integrated noise thermometry, Batey, G., Casey,A., Cuthbert, M., Matthews, A., Saunders, J. & Shibahara, A., New J. Phys. 15, 113034 (2013), doi: http://dx.doi.org/10.1088/1367-2630/15/11/113034
|Professor John Saunders||Professor|
|Professor Brian Cowan||Professor|
|Dr Andrew Casey||Reader|
|Dr Chris Lusher||Senior Lecturer|
|Dr Xavier Rojas||Royal Society University Research Fellow|
|Dr Jan Nyeki||Senior Research Officer|
|Dr Lev Levitin||Senior Research Officer|
|Dr Petri Heikkinen||Postdoctoral Research Fellow|
|Mr Marijn Lucas||Postdoctoral Research Fellow|
|Dr Om Prakash||Postdoctoral Research Fellow (Marie Curie Fellow)|
|Dr Angadjit Singh||Postdoctoral Research Fellow|
- Superconducting Sweet-Spot in Microcrystalline Graphite Revealed by Point-Contact Spectroscopy
Arnold, F., Nyeki, J. & Saunders, J.
JETP Lett. 107, 9, p. 577-578 (2018)
- Charge Density Waves in Graphite: Towards the Magnetic Ultraquantum Limit
Arnold, F., Isidori, A., Kampert, E., Yager, B., Eschrig, M. & Saunders, J.
Physical Review Letters. 119, 136601 (2017)
- The A-B transition in superfluid helium-3 under confinement in a thin slab geometry
Zhelev, N., Abhilash, T. S., Smith, E. N., Bennett, R., Rojas, X., Levitin, L., Parpia, J., Saunders, J.
Nature Communications. 8, 15963 (2017)
- Intertwined superfluid and density wave order in two dimensional 4He
Nyeki, J., Phillis, A., Ho, A., Lee, D., Coleman, P., Cowan, B. & Saunders, J.
Nature Physics 13, 5 (2017)
- Phase Diagram of the Topological Superfluid 3He Confined in a Nanoscale Slab Geometry
Levitin, L.V., Bennett, R. G., Casey, A., Cowan, B., Saunders, J., Drung, D., Schurig, T. & Parpia, J. M.
Science 340, 6134, (2013)
For more publications from the group click here.
Recent PhD student thesis:
- Nano-Electro-Mechanical Systems at Ultra Low Temperatures as Probes for Quantum Fluids With Superconducting Quantum Interference Device Transduction
Mellor, R., 2018, (Unpublished)
- Platforms for new quantum technologies - addressing the challenges in cooling and exploring the properties of strongly correlated electron system
van der Vliet, H., 2018, (Unpublished)