Debye temperature in YBa2Cu3Ox as measured from the electron spin-lattice relaxation of doped Yb3+ ions

The electron spin-lattice relaxation (SLR) times T1 of Yb3+ ions were measured from the temperature dependence of electron spin resonance line width in Y0.99Yb0.01Ba2Cu3Ox with different oxygen contents. Raman relaxation processes dominate the electron SLR. Derived from the temperature dependence of the SLR rate, the Debye temperature (ΘD) increases with the critical temperature Tc and oxygen content x. This relationship between Tc and ΘD can be well understood in terms of the modified Bardeen-Cooper-Schriefer theory of phonon mechanism for a strong electron-phonon coupling