Quantum Materials

Our research delves into the quantum realm of two-dimensional (2D) helium, a prime candidate for exploring strongly correlated quantum matter. By finely controlling atomically layered helium films on graphite substrates and delving into their properties at microkelvin temperatures, we aim to uncover novel quantum states and transitions. Our toolkit includes advanced techniques such as SQUID NMR, heat capacity, and torsional oscillator methods, enabling us to probe both fermionic and bosonic helium films with unprecedented precision. As we navigate through this quantum landscape, our investigations are set to reveal new facets of quantum criticality, superfluidity, and magnetism at the frontiers of low-dimensional systems.

Quantum Materials

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, including low frequency broadband SQUID NMR, heat capacity and torsional oscillator methods.

Graphite is atomically flat. We create a range of composite substrates by preplating the graphite surface. We can study both 3He and 4He, and 3He on a superfluid 4He film. The films are readily cooled into the microkelvin temperature régime, revealing new emergent quantum states in fermionic and bosonic systems, as their density is precisely tuned.

Prior work has demonstrated: Mott-Hubbard transition in 2D 3He [1]; frustrated magnetism on a triangular lattice [2]; heavy fermion quantum criticality [3]; intertwined superfluid and density wave order (2D super solid) [4, 5]. 

Current and future work includes the following topics: 

  • NMR evidence for solid order in 2D supersolid
  • 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 
  • studies of helium on graphene and associated technical developments 

This work is reviewed in [6,7].

References

  1. Evidence for a Mott-Hubbard transition in a two dimensional 3He fluid monolayer. A Casey, H Patel, J Nyéki, B P Cowan and J Saunders. Rev. Lett. 90, 115301 (2003) PRL 90 115301 (2003)
  2. Two-Dimensional Ferromagnetism of a 3He Film: Influence of Weak Frustration: Casey, M. Neumann, J. Saunders, N. Shannon, Phys. Rev. Lett. 111, 125302 (2013) PRL 111, 125302 (2013)
  3. Bilayer 3He: a simple two-dimensional heavy fermion system with quantum criticality. M Neumann, J Nyeki, B Cowan, J Saunders. Science 317, 1356 (2007) Science 324 601 (2009)
  4. Intertwined superfluid and density wave order in two dimensional 4He, J. Nyeki, A. Phyllis, A Ho, D. Lee, P Coleman, J Parpia, B. Cowan, J. Saunders, Nature Physics 13, 455-459 (2017). NaturePhys 13 455 (2017)
  5. On the ‘Supersolid’ Response of the Second Layer of 4He on Graphite J Nyéki, A Phillis, B Cowan, J Saunders Journal of Low Temperature Physics 187, 475-481(2017) JLTP 187 475 (2017)
  6. Atomically layered helium films at ultralow temperatures: model systems for realizing quantum materials. John Saunders, Brian Cowan, Jan Nyéki. In Special Issue: 50 years of the Journal of Low Temperature Physics (Part II) 201, 615-633 (2020) https://link.springer.com/article/10.1007/s10909-020-02448-9
  7. Realizing quantum materials with Helium: Helium films at ultralow temperatures, from strongly correlated atomically layered films to topological superfluidity, J Saunders. In Topological Phase Transitions and New Developments, p. 165-196 (2019). Ed. Lars Brink, Mike Gunn, Jorge V Jose, John Michael Kosterlitz, Kok Phoo Phua (World Scientific). http://arxiv.org/abs/1910.01058