Raising Bi-O Bands above the Fermi Energy Level of Hole-DopedBi2Sr2CaCu2O8+δand Other Cuprate Superconductors

Abstract

The Fermi surface (FS) of Bi2Sr2CaCu2O 8+δ (Bi2212) predicted by band theory displays Birelated pockets around the (π, 0) point, which have never been observed experimentally. We show that when the effects of hole doping either by substituting Pb for Bi or by adding excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi energy (EF ) and the resulting first-principles FS is in remarkable accord with measurements. With decreasing hole-doping the Bi-O bands drop below EF and the system self-dopes below a critical hole concentration. Computations on other Bias well as Tl-and Hg-based compounds indicate that lifting of the cation-derived band with hole doping is a general property of the electronic structures of the cuprates.PACS numbers: 74.72. Hs,74.25.Jb,71.18.+y, First-principles band theory computations on the cuprates have become a widely accepted tool for gaining insight into their electronic structures, spectral properties, Fermi surfaces (FS's), and as a starting point for constructing theoretical models for incorporating strong correlation effects beyond the framework of the local-density approximation (LDA) underlying such calculations 1,2,3,4 . For example, in the double layer Bicompound Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) − perhaps the most widely investigated cuprate − the LDA generated band structure 5,6 is commonly invoked to describe the doped metallic state of the system. Band theory however clearly predicts the FS of Bi2212 to contain a FS pocket around the antinodal point M (π, 0) as a Bi-O band drops below the Fermi energy (E F ), but such FS pockets have never been observed experimentally 7 . This 'Bi-O pocket problem' is quite pervasive and occurs in other Bi-compounds. 8 Similarly, Tl-and Hg-compounds display cation-derived FS pockets, presenting a fundamental challenge for addressing on a first-principles basis issues related to the doping dependencies of the electronic structures of the cuprates.In this Letter, we show how the cation-derived band responsible for the aforemenentioned FS pockets is lifted above E F when hole doping effects are properly included in the computations. Detailed results for the case of Bi2212 are presented, where hole doping is generated either by substituting Pb for Bi or by adding excess oxygen in the Bi-O planes. With 20% Pb doping in the orthorhombic crystal structure, the Bi-O band lies ≈ 1 eV above E F and the remaining bonding and antibonding FS sheets are in remarkable accord with the angleresolved photoemission (ARPES) measurements on an overdoped Bi2212 single crystal 9 . Below a critical hole doping level, the Bi-O band falls below E F and, as a result of this self-doping effect, further reduction in the hole doping level no longer reduces the number of holes in the CuO 2 layers. We argue that the underlying mechanism at play here is that hole doping reduces the effective positive charge in the Bi-O donor layers, which then reduces the tendency of the electrons to 'flow back' and self-dope the material. We have also carried out computatio...

Spectral decomposition and matrix element effects in scanning tunneling spectroscopy ofBi2Sr2CaCu2O8+Nieminen1, Suominen2, Markiewicz3 et al. 2009Phys. Rev. BSelf Cite362460View full textAdd to dashboardCite

“…This choice is also supported by calculations of Ref. 25, which show the sensitivity of the position of the Bi-band with respect to impurities and doping. The absence of the bottom of the BiO band in the STS spectra may also be due to a voltage gradient across the insulating filter layers (BiO and SrO layers) when applying a bias voltage between the tip and the sample.…”

“…While the tight-binding band structure is in reasonable agreement with the LDA band structure of Ref. 25, in order to carry out spectroscopic computations, one must additionally make sure that the underlying wavefunctions are described correctly including their symmetries. Our procedure based on the the use of Koster-Slater matrix elements not only fits the band stuctures, but the symmetries and phases of the associated wavefunctions are also described correctly.…”

Scanning tunneling spectroscopy of high-temperature superconductors

“…Singh and Pickett ͑1995͒ found that in Bi2201 the calculated Bi-O bands move upward by ϳ400 meV when the distortion of the BiO planes is taken into account. Very recently, Lin et al ͑2006͒ found that a similar shift occurs in Bi2212 when lead or oxygen doping is introduced in the calculation.…”

Predictions of highest transition-temperature for electron–phonon superconductors

“…The highest T c is about 130 K for cuprate superconductors close to the range. From the Fig.4, there are larger vertex corrections at higher Ω P and larger λ, however the T c doesn't changes significantly because the band-width of CuO 2 plane for cuprate superconductors such as Bi2212 is not too small about 4 eV, and the Fermi-energy E F is at least 1 eV [29,30].…”