Gaps between zeros of Dedekind zeta-functions of quadratic number fields

Let K be a quadratic number field, and let ζ K ( s ) denote the Dedekind zeta-function attached to K. Using the mixed second moments of derivatives of ζ K ( 1 2 + i t ) , we prove the existence of gaps between consecutive zeros of ζ K ( s ) on the critical line which are at least 6 = 2.44949 … times the average spacing.