Dependence of the gap parameter on the number of CuO_2 layers in a unit cell of optimally doped BSCCO, TBCCO, HBCCo and HSCCO

摘要

We have measured the superconducting gap DELTAs in optimally doped samples of Bi_2Sr_2Ca_n-1Cu_nO_2n+4, Tl_2Ba_2Ca_n-1Cu_nO_2n+4, HgBa_2Cu_nO_2n+2 and HgSr_2Ca_2Cu_3O_8 by Andreev and tunnelling spectroscopy and by ARPES. We have found that the low-temperature value of DELTAs within experimetnal errors is linearly increasing with the number n of CuO_2 layers in the unit cell of the investigated HTSC-families (n<=3). The variation of the critical temperature Tc max with n does not obey this simple relation. For a given n the values of DELTAs at T=4.2 K for the Tl- and Hg-families practically conicide but systematically exceed that in the Bi-family.