Measuring the Josephson plasma resonance in Bi_2Sr_2CaCu_2O_8 using intense coherent THz synchrotron radiation

摘要

Infrared (IR) spectroscopy has been employed to investigate the c axis reflectivity of Bi_2Sr_2CaCu_2O_8 in the sub-THz frequency region. In order to reach this challenging frequency range a synchrotron source has been employed. Working in a special low-momentum compaction mode of operation where the electron bunch shape is significantly shortened and distorted, stable broadband coherent (superradiant) very far-infrared radiation is produced with orders of magnitude more intensity than conventional thermal and synchrotron sources. Using this source for reflectivity measurements we have been able to observe the Josephson plasma resonance (JPR) in optimally doped Bi_2Sr_2CaCu_2O_8. Evidence is found for an inhomogenous distribution of superfluid density within the sample. This source allows us to investigate charge dynamics in this extremely anisotropic superconductor, and opens up the possibility to study other highly correlated systems in this critical low-energy region.