INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 14 (2002) 6675–6688 PII: S0953-8984(02)32963-1 Polarized XANES study of the importance of inter-block vis-` a-vis intra-block coupling in evolution of T c in halide-molecule-intercalated Bi 2 Sr 2 CaCu 2 O 8-δ single crystals R K Singhal 1,6 , N L Saini 2 , B Dalela 1 , S Dalela 1 , J H Choy 3 , D Chaturvedi 1 , B R Sekhar 4 , D C Jain 1 , K B Garg 1 , Hong-Ji Lin 5 , T Y Hou 5 and C T Chen 5 1 Department of Physics, University of Rajasthan, Jaipur-302004, India 2 INFN, Universitat de Roma, Roma 00185, Italy 3 Chemistry Department, Seoul National University, Seoul 151-742, Korea 4 Institute of Physics, Bhubaneshwar 751002, Orissa, India 5 Synchrotron Radiation Research Centre, Hsinchu 30077, Taiwan E-mail: krish35@sancharnet.in (K B Garg) Received 23 January 2002, in final form 2 May 2002 Published 21 June 2002 Online at stacks.iop.org/JPhysCM/14/6675 Abstract In addition to doping in the lattice that affects the intra-block coupling, intercalated molecules sit in between the consecutive basal planes, thereby increasing the effective length of the c-axis. This, in turn, must lead to a decrease in inter-block coupling. Both the doping and intercalation have been reported to affect the evolution of T c in a system, implying the inherent importance of both types of coupling. In the latter case, the resulting depression of T c is ascribed to transfer of charge between the intercalate and the host CuO 2 plane. Most interesting studies in this regard pertain to use of I 2 , HgI 2 and HgBr 2 molecules as intercalates for the Bi 2 Sr 2 CaCu 2 O 8+y system. Earlier reports mostly claim that the host CuO 2 plane in Bi 2 Sr 2 CaCu 2 O 8+y invariably becomes overdoped whichever the intercalate, thereby leading to a fall in T c . In this paper, we examine these claims in the case of Bi 2 Sr 2 CaCu 2 O 8+y single crystals by measuring the number of itinerant holes before and after intercalation by making polarization-dependent soft-x-ray absorption measurements at the O K and the Cu L 3 edges. Our results do support the earlier claims on overdoing of the CuO 2 plane in the case of iodine intercalate but are not in agreement with those in the case of the HgI 2 intercalate. 6 Author to whom any correspondence should be addressed. 0953-8984/02/266675+14$30.00 © 2002 IOP Publishing Ltd Printed in the UK 6675