Skyrmionic Excitations of Composite Fermions

D.R. Leadley1, R.J. Nicholas2, D.K. Maude3, J.C. Portal3, A.N. Utjuzh4, J.J. Harris5 and C.T. Foxon6

  1. Department of Physics, University of Warwick, Coventry CV4 7AL
  2. Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU
  3. Grenoble High Magnetic Field Laboratory, MPI-CNRS, BP 166, 38042 Grenoble Cedex 9, France
  4. Russian Academy of Sciences, Institute of High Pressure Physics, 142092 Troitsk, Russia
  5. Department of Electronic and Electrical Enginering, University College, London, WC1E 7JE, UK
  6. Department of Physics, Nottingham University, University Park, Nottingham, NG7 2RD, UK

Two recent discoveries in the quantum Hall effect (QHE) of 2D electrons have introduced new quasi-particles into condensed matter physics known as composite Fermions and Skyrmions. In this work we present experimental evidence for the combination of these -- skyrmionic excitations of the composite Fermions or in short a composite Skyrmion.

The fractional QHE ground state at filling factor v=1/3 is spin polarised consisting of one completely full composite Fermion Landau level and so is analogous to the v=1 integer QHE state. That state is ferromagnetic and the excitations out of it are determined by competition between the Zeeman energy and exchange correlations. At vanishingly small Zeeman energy the excitations are Skyrmions with a non-trivial spin order and smaller energy than the spin waves seen otherwise.

In these experiments Skyrmion formation is encouraged by reducing the magnitude of the g-factor with hydrostatic pressures of up to 22 kbar. As |g| gets smaller the energy gap at 1/3 also reduces and shows a minimum at 18 kbar where g=0. At higher pressure the gap opens up again as g takes the opposite sign. From the rate of change of energy gap with Zeeman energy we conclude that the excitation contains ~3 reversed spins, consistent with calculations for composite Skyrmions. Meanwhile the energy gap at 2/5 shows two distinct regimes which we interpret as a change from a spin polarised to an unpolarised ground state.

Presented at: Institute of Physics, Condensed Matter and Materials Physics Conference, Exeter 1997