Biography

I received my PhD in 2011 from Université Pierre et Marie Curie (Paris 6), France. As a PhD student, I worked under the supervision of Sébastien Balibar at Laboratoire de Physique Statistique, Ecole Normale Supérieure, on the topic: Supersolidity and Quantum Plasticity. During my thesis, I developed a technique for growing very high quality and ultrapure helium single crystals with a defined orientation. I developed innovative low-temperature acoustic techniques to measure these crystals with extremely small mechanical stress. The main result of my thesis was to demonstrate the existence of a giant plasticity in helium crystals, caused by a large mobility of crystalline defects (i.e. dislocations) at low temperature. This exotic property is now understood as caused by the large quantum fluctuations (or zero-point motion of atoms) in solid helium. This thesis work has allowed us to make significant progress on the question of the possible existence of a supersolid state in solid helium, a state of matter defined by the coexistence of a superfluid and a solid state. In particular, we demonstrated that, supersolidity had not yet been observed in solid helium experiments, and that the results of previous experiments was actually misinterpreted due to the presence of the unexpected giant plasticity that we measured.

After my PhD, I joined John Davis group at University of Alberta as a Postdoctoral Research Fellow. My research project was to develop new acoustic techniques for the study of quantum fluids (i.e liquid helium) at low temperature in nanofluidic devices. Some highlights from my postdoctoral research include the development of an acoustic analogy of the well-known Fabry-Pé́rot optical interferometer to measure the first-sound of liquid helium 4 confined in nanofluidic geometries. Another highlight is the development of a superfluid nanomechanical resonator for the detection of finite-size effects in the superfluid fraction of liquid helium 4 at the superfluid transition.

In 2015, I joined John Saunders group at Royal Holloway University of London as a Postdoctoral Research Fellow. My research project was on the topological superfluidity of helium 3 confined in nanofabricated geometries, as a model system to further our understanding of topological quantum matter. To tackle this problem, I have developed new designs for acoustic and thermal sensors compatible at ultra-low temperature.

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Dr Xavier Rojas

Academic Positions

• 2016-PresentRoyal Society Univ. Research Fellow

  Department of Physics
  Royal Holloway University of London, UK

• 2015-2016Postdoctoral Research Fellow

  Department of Physics
  Royal Holloway University of London, UK

• 2012-2015Postdoctoral Research Fellow

  Department of Physics
  University of Alberta, Canada

• 2008-2011Doctorate

  Department of Physics
  Ecole Normale Supérieure, France