Letters to Nature

Nature 395, 360-362 (24 September 1998) | doi:10.1038/26439; Received 13 March 1998; Accepted 29 June 1998

Global and local measures of the intrinsic Josephson coupling in Tl2Ba2CuO6 as a test of the interlayer tunnelling model

A. A. Tsvetkov1,2, D. van der Marel1, K. A. Moler3, J. R. Kirtley4, J. L. de Boer1, A. Meetsma1, Z. F. Ren5, N. Koleshnikov6, D. Dulic1, A. Damascelli1, M. Grüninger1, J. Schützmann1, J. W. van der Eb1, H. S. Somal1 & J. H. Wang5

  1. Materials Science Centre, University of Groningen, 9747 AG Groningen, The Netherlands
  2. P. N. Lebedev Physical Institute, 117924 Moscow, Russia
  3. Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
  4. IBM T. J. Watson Research Center, PO Box 218, Yorktown Heights, New York 10598, USA
  5. Department of Chemistry, SUNY at Buffalo, Buffalo, New York 14260-3000, USA
  6. Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Russia

Correspondence to: D. van der Marel1 Correspondence and requests for materials should be addressed to D.v.d.M. (e-mail: Email: D.van.der.marel@phys.rug.nl).

One leading candidate theory of high-temperature superconductivity in the copper oxide systems is the interlayer tunnelling (ILT) mechanism1. In this model, superconductivity is created by tunnelling of electron pairs between the copper oxide planes — contrasting with other models in which superconductivity first arises by electron pairing within each plane. The ILT model predicts that the superconducting condensation energy is approximately equal to the gain in kinetic energy of the electron pairs due to tunnelling. Both these energies can be determined independently2, 3, 4, providing a quantitative test of the model. The gain in kinetic energy of the electron pairs is related to the interlayer plasma frequency, omegaJ, of electron pair oscillations, which can be measured using infrared spectroscopy. Direct imaging of magnetic flux vortices also provides a test5, which is performed here on the same samples. In the high-temperature superconductor Tl2Ba2CuO6, both the sample-averaging optical probe and the local vortex imaging give a consistent value of omegaJ approximately 28 cm-1 which, when combined with the condensation energy, produces a discrepancy of at least an order of magnitude with deductions based on the ILT model.