arXiv:cond-mat/0312575v1 [cond-mat.supr-con] 22 Dec 2003 Effects of next-nearest-neighbor hopping t ′ on the electronic structure of cuprates K. Tanaka, T. Yoshida, A. Fujimori, D.H. Lu † , Z.-X. Shen † , X.-J. Zhou †∗ , H. Eisaki † , Z. Hussain ∗ , S. Uchida, Y. Aiura ♭ , K. Ono ♯ , T. Sugaya ‡ , T. Mizuno ‡ , and I. Terasaki ‡ Department of Physics and Department of Complexity Science and Engineering, University of Tokyo, Tokyo, 113-0033, Japan † Department of Applied Physics and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA ∗ Advanced Light Source, Lawrence Berkely National Lab, Berkeley, CA 94720, USA ♭ National Institute for Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8568, Japan ♯ Photon Factory, IMSS, High Energy Accelerator Research Organization, Tsukuba, 305-0801, Japan ‡ Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan (Dated: February 6, 2008) Photoemission spectra of underdoped and lightly-doped Bi2−z Pbz Sr2Ca1−xRxCu2O8+y (R = Pr, Er) (BSCCO) have been measured and compared with those of La2−xSrxCuO4 (LSCO). The lower-Hubbard band of the insulating BSCCO, like Ca2CuO2Cl2, shows a stronger dispersion than La2CuO4 from k ∼(π/2,π/2) to ∼(π, 0). The flat band at k ∼(π, 0) is found generally deeper in BSCCO. These observations together with the Fermi-surface shapes and the chemical potential shifts indicate that the next-nearest-neighbor hopping |t ′ | of the single-band model is larger in BSCCO than in LSCO and that |t ′ | rather than the super-exchange J influences the pseudogap energy scale. PACS numbers: 74.72.Hs, 79.60.-i, 71.28.+d Since the discovery of the high-temperature supercon- ductivity in La 2−x Ba x CuO 4 , many families of high-T c cuprates have been synthesized. Common features are that they have the two-dimensional CuO 2 planes and a similar phase diagram as a function of hole doping. This has naturally lead most of studies to emphasize the com- mon features of the cuprate electronic structures rather than emphasizing differences among them. On the other hand, there are differences among the different families of cuprates such as the significant variation in the mag- nitude of the superconducting gap and the critical tem- perature (T c ) at optimal doping, T c,max . A systematic investigation of the differences between the different fam- ilies of cuprates may enable us to understand the origin of the different T c,max ’s and eventually the mechanism of superconductivity. So far, some studies have focused on the material dependence from empirical points of view. In an early work, Ohta et al. [1] proposed the differences in the position of the apical oxygen and the resulting dif- ferences in the Madelung potentials as the origin of the different T c,max ’s. Feiner et al. [2] proposed that the p z orbital of the apical oxygen hybridizing with the d 3z 2 −r 2 orbital of Cu and the p x,y orbitals of the in-plane oxygen affects the next-nearest-neighbor hopping parameter t ′ in the single-band model description of the CuO 2 plane, and thereby T c,max in the context of the van Hove singularity scenario [3]. Those differences between the cuprate fami- lies may affect the stability of the Zhang-Rice singlet [1], instability toward charge stripes [4] and so on, and hence T c,max . Recently, Pavarini et al. [5] have demonstrated the correlation between t ′ (of the bonding band for multi- layer cuprates) and T c,max from their tight-binding model analysis of the first-principles band structures of numer- ous high-T c cuprates. For the differences in T c,max , the various degrees of disorder has also been considered im- portant [6]. In the present work, on the basis of photoemission data, we focus on differences in the electronic struc- ture of the cuprates such as the band dispersion of the parent insulator and the doped compounds as well as the Fermi surface shape between La 2−x Sr x CuO 4 (LSCO) and Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO). We have found that lightly-doped and underdoped BSCCO show a stronger band dispersion along the “underlying Fermi surface” than its counter part in LSCO. Given that J does not change much between the two families (J LSCO ∼ 139 meV and J BSCCO ∼ 127 meV from two-magnon Raman scat- tering [7, 8, 9] and magnetic neutron scattering [10]), we attribute the observed differences to the variation in t ′ , a finding consistent with the band structure estimates of t ′ [5] and the t-J model calculation on the impact of t ′ on the electronic structure around k ∼(π, 0) [11]. So far, photoemission studies of LSCO have covered a wide composition range from the lightly-doped to over- doped regions and systematic data are available for the evolution of the pseudogap [12], Fermi surface [13, 14, 15], band dispersion [14, 16] and chemical potential shift [17]. Although BSCCO has been extensively studied by angle- resolved photoemission spectroscopy (ARPES) owing to its stable cleavage surfaces in an ultra high vacuum, the available range of hole concentration has been largely lim- ited to δ =0.10-0.17. Recently, high quality single crys- tals of heavily underdoped BSCCO were synthesized by rare-earth (R) substitution for Ca and the doping depen- dence of thermodynamic and transport properties have been systematically studied [18, 19, 20]. The present study was made possible by the availability of such deeply underdoped BSCCO samples. Single crystals of Bi 1.2 Pb 0.8 Sr 2 ErCu 2 O 8 and Bi 2 Sr 2 Ca 1−x R x Cu 2 O 8+y (R = Pr, Er) were grown