DETERMINATION OF THE ANGULAR-DEPENDENCE OF HC2 IN HIGH-TC SINGLE-CRYSTALS BY A MICROWAVE TECHNIQUE

It is shown that using an ESR spectrometer with magnetic field modulation and sweeping the temperature across T(c) (at a constant and a very low magnetic field), is equivalent to temperature modulation. The signal intensity obtained when crossing T(c) is proportional to 1/(partial-H(c2)/partial-T) at T = T(c). Using the WHH relation H(c2)(T = 0) = 0.7 T(c)(partial-H(c2)/partial-T)(T = Tc) it enabled the measurement of the relative angular variation of H(c2) in single crystals of YBaCuO with T(c) approximately 85K. The data fit the Ginzberg-Landau theory. This very sensitive technique can be used to characterize properties of high T(c) superconducting materials. Results on thin films will also be presented.