Experimental Determination of the Pairing State of the High Temperature Superconductors

The discovery of high temperature superconductors in 1987 set off a wave of scientific activity aimed at understanding the mechanism for supercondunctivity in these materials and exploring their potential for technological applications. Recently, theoretical calculations have suggested the exciting possibility that the cuprates may exhibit a novel superconducting mechanism characterized by a highly anisotropic energy gap. This symmetry, known as d-wave pairing, would open up a wide range of interesting theoretical and experimental studies involving the behavior of d-wave superconductors, and would have important implications for the development of technological applications incorporating the high temperature superconductors. Ultimately, experiments must resolve this issue, and preliminary results do support this state, with the most direct evidence being provided by a recent experiment carried out by their group in collaboration with other researchers at the University of Illinois.

Professor Van Harlingen and his team propose a series of experiments designed to determine unambiguously the symmetry of the pairing state of the high temperature superconducting cuprates and to elucidate the nature of the pairing mechanism. They have identified three investigations that they consider to be the most interesting and important and in which they believe they can make a significant impact. The first would be to extend the present experiment to other high temperature superconductors to determine which materials exhibit the d-wave pairing and which have the conventional s-wave symmetry. Second, they propose to adapt their experiment to thin film samples in order to measure simultaneously both the magnitude and phase of the energy gap in the superconductors. Finally, they plan direct magnetic field detection of circulating currents that are expected if the pairing has d-wave symmetry. Together, these experiments should contribute to a complete description of the pairing state in the high temperature superconductors and open the door to further technological development of these materials.