Large isotope effect on Tc in cuprates despite a small electron-phonon coupling

R. ZEYHER AND A. GRECO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 2009 vol. 80 p. 645191 - 645197

0163-1829

We calculate the isotope coefficients
and

for the superconducting critical temperature Tc and thepseudogap temperature T
in a mean-field treatment of the t-J model including phonons. The pseudogap phaseis identified with the d-charge-density wave
d-CDW phase in this model. Using the small electron-phononcoupling constant d0.02 obtained previously in local-density approximation calculations in YBa2Cu3O7,

is negative but negligibly small, whereas
increases from about 0.03 at optimal doping to values around 1 atsmall dopings, in agreement with the general trend observed in many cuprates. Using a simple phase fluctuationmodel where the d-CDW has only short-range correlations, it is shown that the large increase of
at lowdopings is rather universal and does not depend on the existence of sharp peaks in the density of states in thepseudogap state or on specific values of the phonon cutoff. Rather, it is caused by the large depletion of spectralweight at low frequencies by the d-CDW and thus should also occur in other realizations of the pseudogap.