Bilayer Splitting in the Electronic Structure of Heavily OverdopedBi2Sr2CaCu2

Abstract

The electronic structure of heavily overdoped Bi2Sr2CaCu2O 8+δ is investigated by angle-resolved photoemission spectroscopy. The long-sought bilayer band splitting in this two-plane system is observed in both normal and superconducting states, which qualitatively agrees with the bilayer Hubbard model calculations. The maximum bilayer energy splitting is about 88 meV for the normal state feature, while it is only about 20 meV for the superconducting peak. This anomalous behavior cannot be reconciled with the quasiparticle picture.PACS numbers: 71.18.+y, 74.72.Hs, 79.60.Bm High temperature superconductors (HTSC's), as doped Mott insulators, show strong doping dependent behavior. The underdoped regime of the HTSC's is characterized by its unconventional properties, such as the pseudogap and non-Fermi liquid transport behavior. On the other hand, the overdoped regime is considered to be more "normal", partly because of the absence of a pseudogap and more Fermi liquid-like behavior. It is very challenging and important for HTSC theories to be able to explain the phenomenology in both regimes. Angle resolved photoemission spectroscopy (ARPES), one of the most direct probes of the electronic structure, has contributed greatly to the understanding of the electronic structure of the HTSC's. However, most systems studied by ARPES have either low T c 's (below 40K for La 2−x Sr x CuO 4+δ (LSCO), and Bi 2 Sr 2 CuO 6+δ (Bi2201)), or doping limitations (only up to slightly overdoping for Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) and YBa 2 Cu 3 O 7−y (YBCO)). For a complete understanding, it is very important to study the heavily overdoped systems, especially Bi2212, which is the most studied system by ARPES.Recent advances in high pressure annealing techniques have made it possible to synthesize heavily overdoped Bi2212. In this paper, we report ARPES measurements of the electronic structure of heavily overdoped Bi2212. We show that the long-sought bilayer band splitting (BBS) exists for both normal and superconducting states of this material over large fraction of the Brillouin zone. The detection of the BBS, which has been predicted by band structure calculations [1,2], but not observed in earlier ARPES data [3], enables us to address several important issues. First, it provides a very detailed test for the theoretical calculations, with our experimental results favoring the bilayer Hubbard model [4] over LDA calculations [1,2]. Second, it shows the novel result that the bilayer splitting energy in the superconducting state is only about 23% of the normal state splitting. Third, it provides an explanation for the detection of a "peak-diphump" structure in the normal state of heavily overdoped samples [5,6].Heavily overdoped Bi2212 samples (T C (onset) = 65 K, ∆T C (10% ∼ 90%) = 3 K, denoted as OD65) were synthesized by annealing floating-zone-grown single crystals under oxygen pressure P O2 = 300 atm at 300• C for two weeks, and characterized by various techniques. Magnetic susceptibility measurements show that the presence of a s...

Effect of the magnetic resonance on the electronic spectra ofhigh−Tcsuperconductors

“…This is consistent with the data of Ref. 65. The onset of strong fermionic damping should be independent of the band index, as it is given by scattering to the nodes, and thus occurs at the fixed energy Ω res .…”

Theoretical investigation of the quasiparticle dispersion of bilayer high-Tcsuperconductors

“…Eventually, only the BB peak can be seen near (0.2π, π). These features are in good agreement with ARPES experiments [17]. However, the lineshape caused by the phonon-coupling displays a striking contrast to those shown in Fig.3(a) and in experiments [17] , namely, the peak is far below the dip and the dip is below the hump [ Fig.3(b)].…”

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