NMR study of carrier doping effects on spin gaps in the spin ladder Sr_14-xA_xCu₂₄O₄₁(A=Ca, Y, and La)

Ken-ichi Kumagai, S.Tsuji , M.Kato ^(*) , Y. Koike ^(*)

Dept. of Phys., Hokkaido Univ., Sapporo, Japan

^{(*)Dept. of Applied Phys. , Tohoku Univ., Sendai, Japan}

Physical Review Letter vol 78 No. 10 1992-5 ( 1997 )

Abstruct.

Carrier doping effects on spin dynamics in Sr_14-xA_xCu₂₄O₄₁ (A=Ca, Y, and La) are investigated by Cu NMR and NQR. The energy gaps in the spin excitation spectra (spin gap) are confirmed to be Delta =140 K for the CuO₂ chain and Delta =470 K for the Cu₂O₃ ladder in Sr₁₄Cu₂₄O₄₁. The spin for the ladder increases with the Y and La substitutions for Sr (up to x=3), while it decreases with increasing x in Sr_14-xCa_xCu₂₄O₄₁ and seems to collapse around x=13 of the Ca substitution. Hole-doping effects on the spin gaps for the ladder configuration are interpreted in terms of magnon and hole-depairing excitations for the spin S= 1/2 ladder.