Calculation of the field and temperature dependence of the c-axis plasmon in Bi2Sr2Ca2Cu2O8+delta

We calculate the c-axis Josephson plasmon frequency omega(pl)(B,T) versus t emperature T and magnetic induction B in Bi2Sr2Ca2Cu2O8 + delta, treating t he order parameter fluctuations in the lowest Landau level (LLL) approximat ion. The calculation agrees qualitatively with recent field-cooled measurem ents of Matsuda et al. assuming a c-axis dielectric constant epsilon(0)simi lar to 20-50. For any given B, omega(pl) falls monotonically with increasin g T, remains finite in the flux liquid state, and varies continuously acros s the solid-liquid transition when disorder is included. We also obtain an expression for omega(pl) which is valid everywhere in the flux liquid state and is not restricted to the LLL approximation. This expression leads to o mega(pl)similar to 1/root B in the flux liquid state, in agreement with exp eriment. [S0163-1829(99)03705-4].