New Particles Lurking in High-T Superconductors?
One of the greatest unsolved problems in condensed matter physics is explaining how electrons pair up in the copper-oxide materials that superconduct at temperatures above 100 K. Some theorists believe that the place to start in straightening out this mystery is to understand better how the cuprates behave at normal temperatures, long before they become superconducting.
Professors Philip Phillips and Rob Leigh suggest that the solution might be the existence of a previously overlooked doubly charged particle, one that mediates interactions among electrons lying in planes filled with copper and oxygen atoms. This particle would be distinct from a Cooper pair, the charge carrier in a superconductor. The new particle, a boson that carries twice the charge of an electron but is not made out of elementary excitations, arises from the strong repulsive interactions between electrons in the normal state. (Read the paper)
“When this 2e boson binds with a hole, the result is a new electronic state that has a charge of e,” Phillips said. “In this case, the electron is a combination of this new state and the standard, low-energy state. Electrons are not as simple as we thought.”
The figure shows (a) Spectral function for filling n = 0.9 along the nodal direction. The intensity is indicated by the color scheme. Clearly shown is the bifurcation of the electron dispersion below the chemical potential. Such substructure to the electron dispersion indicates that the electron at low energies is in a linear superposition of two excitations. One of these excitations arises from the charge 2e boson predicted by this theory. (b) Location of the low and high energy kinks as indicated by the change in the slope of the electron dispersion. (c) The energy bands that give rise to the bifurcation of the electron dispersion. Click on the figure for a higher-resolution image.