Fine-structure in the low-energy excitation spectrum of a high-Tc superconductor by polarization-dependent photoemission (original) (raw)
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On single crystals of the single-layer (n = 1) high-Tc superconductor Bi2Sr2-xLaxCuO6+d at optimal doping (x = 0.4), the electron spectroscopies x-ray absorption (XAS) and high-resolution angle-resolved photoemission (ARPES) were performed. The XAS gives the intensity of the so-called prepeak of the O 1s line what is due to the unoccupied part of the Zhang–Rice (ZR) singlet band. For ARPES,
Physical Review B, 2001
We study the normal-state electronic excitations probed by angle-resolved photoemission spectroscopy ͑ARPES͒ in Bi 1.6 Pb 0.4 Sr 2 CuO 6 ͑Bi2201͒ and Bi 2 Sr 2 CaCu 2 O 8ϩ␦ ͑Bi2212͒. Our main goal is to establish explicit criteria for determining the Fermi surface from ARPES data on strongly interacting systems where sharply defined quasiparticles do not exist and the dispersion is very weak in parts of the Brillouin zone. Additional complications arise from strong matrix element variations within the zone. We present detailed results as a function of incident photon energy, and show simple experimental tests to distinguish between an intensity drop due to matrix element effects and spectral weight loss due to a Fermi crossing. We reiterate the use of polarization selection rules in disentangling the effect of umklapps due to the BiO superlattice in Bi2212. We conclude that, despite all the complications, the Fermi surface can be determined unambiguously; it is a single large hole barrel centered about (,) in both materials.
Journal of Physics and Chemistry of Solids, 1998
Evidence for charge fluctuations in diagonal stripes coupled with electrons at the Fermi surface is reported. Superconducting Bi 2 Sr 2 CaCu 2 O 8þd at optimum doping (T c ¼ 91 K) has been studied by angle-scanning photoemission spectroscopy using synchrotron radiation. The Fermi surface shows broken segments and hot spots of high spectral weight. The suppression of spectral weight in the pseudogap region near M ¼ (p,0) is shown to be due to a charge modulation with wavevector q 1 Ϸ 0.4(p,p) associated with the superlattice of one-dimensional (1D) diagonal stripes or 1D charge-density waves. These stripes coexist with collective spin and charge fluctuations in the vertical direction.
Superconducting energy gap in Bi2Sr2CaCu2O8 observed by high-resolution photoemission spectroscopy
Solid State Communications, 1993
A high-eneqy resolved low-temperature photoemission spectrometer of angleintegrated mode was constructed to study the detailed electronic structure near the Fermi level of novel materials, in particular, cuprate high-Tc superconductors. Photoemission measurement with this spectrometer on a BiSr2CaCuzOs polycrystal clearly showed a transfer of spectral weight from the vicinity of the Fermi level to the higher binding-energy region below the superconducting transition temperature, indicating opening of the superconducting gap. Numerical simulation for both normal and superconducting states showed that the superconducting gap parameter (A) of 18 meV with dxz-9 symmetry gives a most reasonable fitting.
Physical Review Letters, 2007
An undoped cuprate with apical fluorine and inner (i) and outer (o) CuO2-layers is a 60 K superconductor whose Fermi surface (FS) has large n and p-doped sheets with the SC gap on the n-sheet twice that on the p-sheet [1]. The Fermi surface is not reproduced by the LDA, but the screening must be substantially reduced due to electronic correlations, and oxygen in the o-layers must be allowed to dimple outwards. This charges the i-layers by 0.01|e|, causes an 0.4 eV Madelung-potential difference between the i and o-layers, quenches the i-o hopping, and localizes the n-sheets onto the i-layers, thus protecting their d-wave pairs from being broken by scattering on impurities in the BaF layers. The correlation-reduced screening strengthens the coupling to z-axis phonons.
Photoemission from the highT c superconductors
Journal of Low Temperature Physics, 1994
We review angle resolved photoemission spectroscopy (ARPES) results on the high Tc superconductors, focusing primarily on results obtained on the quasi-two dimensional cuprate Bi2Sr2CaCu2O8 and its single layer counterpart Bi2Sr2CuO6. The topics treated include the basics of photoemission and methodologies for analyzing spectra, normal state electronic structure including the Fermi surface, the superconducting energy gap, the normal state pseudogap, and the electron self-energy as determined from photoemission lineshapes.
Europhysics Letters (EPL), 2004
PACS. 74.72.-h -Cuprate superconductors. PACS. 74.72.Hs -Bi-based cuprates. PACS. 79.60.-i -Photoemission and photoelectron spectra. PACS. 71.10.Hf -Non-Fermi-liquid ground states. Abstract. -Recently observed splitting in angular resolved photoemission spectroscopy (ARPES) on Bi2Sr2−xLaxCuO 6+δ high-temperature superconductor (Janowitz C. et al., Europhys. Lett., 60 (2002) 615) is interpreted within the phenomenological Luttinger-liquid framework, in which both the non-Fermi liquid scaling exponent of the spectral function and the spin-charge separation are introduced. The anomalous Green function with adjustable parameters fits very well to the Fermi edge and the low-energy part of ARPES along the Γ − M line in the Brillouin zone.
Journal of the Physical Society of Japan, 2010
Electronic structure of heavily over-doped Bi 1:72 Pb 0:38 Sr 1:88 CuO 6þ (Bi2201) superconductor was investigated by using the angle-resolved photoemission spectroscopy with soft x-ray as the incident photon source (SX-ARPES), which is known as one of the best bulk sensitive experimental techniques to investigate the electronic structure. By using the Cu 2p-3d resonance condition, we succeeded in determining the energy-momentum dispersion near the Fermi level and the Fermi surface. It is clearly shown that both SX-and VUV-ARPES are capable of determining the energy-momentum dispersion near " F at least for the homologous series of Bi 2 Sr 2 Ca n Cu nþ1 O 6þ2nþ cuprate superconductors, and that the combinational use of SX-and VUV-ARPES is one of the best experimental methods to determine the electronic structure of bulk materials.
Universal features in the photoemission spectroscopy of high-temperature superconductors
Proceedings of the National Academy of Sciences, 2013
The energy gap for electronic excitations is one of the most important characteristics of the superconducting state, as it directly reflects the pairing of electrons. In the copper-oxide high temperature superconductors (HTSCs), a strongly anisotropic energy gap, which vanishes along high symmetry directions, is a clear manifestation of the d-wave symmetry of the pairing. There is, however, a dramatic change in the form of the gap anisotropy with reduced carrier concentration (underdoping). Although the vanishing of the gap along the diagonal to the square Cu-O bond directions is robust, the doping dependence of the large gap along the Cu-O directions suggests that its origin might be different from pairing. It is thus tempting to associate the large gap with a second order parameter distinct from superconductivity. We use angle-resolved photoemission spectroscopy (ARPES) to show that the two-gap behavior, and the destruction of well defined electronic excitations, are not universal features of HTSCs, and depend sensitively on how the underdoped materials are prepared. Depending on cation substitution, underdoped samples either show two-gap behavior or not. In contrast, many other characteristics of HTSCs, such as the domelike dependence of Tc on doping, long-lived excitations along the diagonals to the Cu-O bonds, energy gap at the antinode (crossing of the underlying Fermi surface and the (π, 0)-(π, π) line) decreasing monotonically with doping, while persisting above Tc (the pseudogap), are present in all samples, irrespective of whether they exhibit two-gap behavior or not. Our results imply that universal aspects of high Tc superconductivity are relatively insensitive to differences in the electronic states along the Cu-O bond directions.
Physical Review B, 2000
We address the question as to whether the topology of the normal state Fermi surface of Bi2Sr2CaCu2O 8+δ -as seen in angle resolved photoemission -depends on the photon energy used to measure it. High resolution photoemission spectra and Fermi surface maps from pristine and Pbdoped Bi2Sr2CaCu2O 8+δ are presented, recorded using both polarised and unpolarised radiation of differing energies. The data show clearly that no main band crosses the Fermi surface along the ΓM Z direction in reciprocal space, even for a photon energy of 32 eV, thus ruling out the existence of a Γ-centred, electron-like Fermi surface in this archetypal high TC superconductor. The true topology of the normal state Fermi surface remains that of hole-like barrels centred at the X,Y points of the Brillouin zone.