Internal dynamics and "superfluidity" in small helium and hydrogen clusters

• Applicant: Professor Dr. Leonid Surin
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2008 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 74729024

• Final Report Year: 2014

Final Report Abstract

Small clusters counting a few to several tens of helium atoms or hydrogen molecules doped with a probe molecule were investigated by millimeter-wave and microwave spectroscopy addressing fundamental questions related to the microscopic nature of superfluidity, namely, what number of helium atoms is required for the onset of superfluidity and whether hydrogen can be made superfluid? Effective moments of inertia determined from rotational spectra of jet-cooled clusters feature non-trivial dependence on the system size, with a pronounced turnaround due to decoupling of part of the helium density from the rotational motion of the doped molecule. A big step forward in answering the initial questions is observation of helium decoupling in Hen–CO clusters starting already at four He atoms (for (pH2)n–CO clusters at six H2 molecules). To provide a deeper insight into relation of the observed effect to superfluidity in the bulk helium further experimental spectroscopic investigations of clusters involving fermionic particles, i.e., 3Hen–molecule and (HD)n–molecule are needed. We made already a first step observing binary complexes containing 3He and HD. Comparison to clusters involving bosonic particles, i.e., 4Hen–molecule and (H2)n–molecule will help to clarify the relationship between ‘‘microscopic’’ and ‘‘macroscopic’’ superfluidity.

Publications

• Rotational Study of Carbon Monoxide Solvated with Helium Atoms. Phys. Rev. Lett. 101, 233401 (2008)
  L.A. Surin, A.V. Potapov, B.S. Dumesh, S. Schlemmer, Y. Xu, P.L. Raston, W. Jäger
  
• Millimeter-wave spectroscopy of weakly bound molecular complexes: isotopologues of He–CO. Opt. Spectrosc. 106, 183-189 (2009)
  A.V. Potapov, L.A. Surin, V.A. Panfilov, and B.S. Dumesh
  
• Rotational spectroscopy of the CO–paraH2 molecular complex. Astrophys. J. 703, 2108-2112 (2009)
  A.V. Potapov, L.A. Surin, V.A. Panfilov, B.S. Dumesh, T.F. Giesen, S. Schlemmer, P.L. Raston, W. Jäger
  
• Spectroscopy of small helium clusters and “nanoscopic” superfluidity: HeN–CO, N = 2-20... Advances in Physical Sciences 52, 294 (2009)
  B.S. Dumesh, A.V. Potapov, L.A. Surin
  
• Rotational study of carbon monoxide isotopologues in small 4He clusters. Phys. Chem. Chem. Phys. 12, 8260-8267 (2010)
  P.L. Raston, Y. Xu, W. Jäger, A.V. Potapov, L.A. Surin, B.S. Dumesh, and S. Schlemmer
  
• The problem of the structure (state of helium) in small HeN–CO clusters. JETP, 111 (5), 770-775 (2010)
  A.V. Potapov, V.A. Panfilov, L.A. Surin, and B.S. Dumesh
  
• Millimeter-wave study of the CH4–CO complex: new measurements with OROTRON spectrometer. J. Mol. Spectrosc. 268, 112-114 (2011)
  A.V. Potapov, A.A. Dolgov, V.A. Panfilov, L.A. Surin, and S. Schlemmer
  
• Submillimeter-wave spectroscopy of the K = 2–1 subband of the Ne–CO complex. J. Mol. Spectrosc. 270, 116-119 (2011)
  A.V. Potapov, L.A. Surin, S. Schlemmer, and T.F. Giesen
  
• A comprehensive experimental and theoretical study of H2–CO spectra. J. Chem. Phys. 138, 084307 (2013)
  P. Jankowski, L. Surin, A. Potapov, S. Schlemmer, A.R.W. McKellar, and K. Szalewicz
  
• Nonclassical rotations of single molecules in small helium and hydrogen clusters: of manifestation of “microscopic superfluidity”. JETP Lett. 97 (1), 57-65 (2013)
  L.A. Surin