Charge modulation driven Fermi surface of Pb–Bi2201

2000

We present a study of the topology of the normal state Fermi surface (FS) of the high Tc superconductor Bi2Sr2CaCu2O 8−δ (Bi2212) using angle-resolved photoemission. We present FS mapping experiments, recorded using unpolarised radiation with high (E,k) resolution, and an extremely dense sampling of k-space. In addition, synchrotron radiation-based ARPES has been used to prove the energy independence of the FS as seen by photoemission. We resolve the current controversy regarding the normal state FS in Bi2212. The true picture is simple, self-consistent and robust: the FS is hole-like, with the form of rounded tubes centred on the corners of the Brillouin zone. Two further types of features are also clearly observed: shadow FSs, and diffraction replicas of the main FS caused by passage of the photoelectrons through the modulated Bi-O planes.

Physical Review B, 2006

We report the observation of a change in Fermi surface topology of Bi2Sr2CaCu2O 8+δ with doping. By collecting high statistics ARPES data from moderately and highly overdoped samples and dividing the data by the Fermi function, we answer a long standing question about the Fermi surface shape of Bi2Sr2CaCu2O 8+δ close to the (π,0) point. For moderately overdoped samples (Tc=80K) we find that both the bonding and antibonding sheets of the Fermi surface are hole-like. However for a doping level corresponding to Tc=55K we find that the antibonding sheet becomes electron-like. This change does not directly affect the critical temperature and therefore the superconductivity. However, since similar observations of the change of the topology of the Fermi surface were observed in LSCO [1, 2] and Bi2Sr2Cu2O 6+δ [3], it appears to be a generic feature of hole-doped superconductors. Because of bilayer splitting, though, this doping value is considerably lower than that for the single layer materials, which again argues that it is unrelated to Tc.

Physica C: Superconductivity, 2000

We present a study of the topology of the normal state Fermi surface (FS) of the high Tc superconductor Bi2Sr2CaCu2Os_~ (Bi2212) using angle-resolved photoemission. We present FS mapping experiments, recorded using unpolarised radiation with high (E,k) resolution, and an extremely dense sampling of k-space. In addition, synchrotron radiation-based ARPES has been used to prove the energy independence of the FS as seen by photoemission. We resolve the current controversy regarding the normal state FS in Bi2212. The true picture is simple, self-consistent and robust: the FS is hole-like, with the form of rounded tubes centred on the corners of the Brillouin zone. Two further types of features are also clearly observed: shadow FSs, and diffraction replicas of the main FS caused by passage of the photoelectrons through the modulated Bi-O planes.

Physical Review Letters, 2006

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.

Physical Review B, 2001

High resolution angle resolved photoemission data from Pb doped Bi2Sr2CaCu2O8 (Bi2212) with suppressed superstructure is presented. Improved resolution and very high momentum space sampling at various photon energies reveal the presence of two Fermi surface pieces. One has the hole-like topology, while the other one has its van Hove singularity very close to (π, 0), its topology at some photon energies resembles the electron-like piece. This result provides a unifying picture of the Fermi surface in the Bi2212 compound and reconciles the conflicting reports.

Physical Review B, 2014

Charge density modulations, recently observed in underdoped high critical-temperature (Tc) cuprate superconductors, coexist with the so-called pseudogap and compete with superconductivity. Surface sensitive techniques have suggested that bulk charge modulations could be present also around the summit of the superconducting dome (optimal doping). Using energy-resolved resonant x-ray scattering we have found evidence for such bulk charge modulations, or soft collective charge modes (soft CCMs), in optimally-doped Bi1.5Pb0.6Sr1.54CaCu2O 8+δ (Pb-Bi2212) around momentum transfer q ∼ 0.28 r.l.u. along the Cu-O bond direction. The signal is stronger at T ≃ Tc than at lower temperatures, thereby confirming a competition between charge modulations and superconductivity. These results demonstrate that soft CCMs are not constrained to the underdoped regime but extend at least up to optimal doping.

Physical Review Letters, 2011

We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission (ARPES). From detailed low-energy electron diffraction measurements and an analysis of the ARPES polarization-dependence, we show that these pockets are not intrinsic, but arise from multiple overlapping superstructure replicas of the main and shadow bands. We further demonstrate that the hole pockets reported recently from ARPES [Meng et al, Nature 462, 335 (2009)] have a similar structural origin, and are inconsistent with an intrinsic hole pocket associated with the electronic structure of a doped CuO$_2$ plane. The nature of the Fermi surface topology in the enigmatic pseudogap phase therefore remains an open question.

Physica C: Superconductivity, 2004

The single-layer high-T c superconductor (BiPb) 2 Sr 2Àx La x CuO 6þd represents an excellent possibility to study the almost undisturbed CuO 2 -plane, the substantial element of the cuprate superconductors. For this material, a new splitting of the spectral weight at E F has been observed along the Cu-O bond (p, 0) direction of the Brillouin zone. It will be shown by high-resolution angle-resolved photoemission spectroscopy that similar to the strong polarization dependence the split excitations reveal a distinct 90°asymmetry and exist only below a certain temperature which is probably the transition temperature of the pseudo-gap phase T Ã . These observations are additional hints on the onedimensionality of the electronic structure of the two-dimensional CuO 2 -plane.

Physical review. B, Condensed matter, 1995

P b 0.4 Bi 1.6 Sr 2 CaCu 2 O 8+x (Bi(P b)−2212) single crystal samples were studied using transmission electron microscopy (TEM), ab−plane (ρ ab ) and c−axis (ρ c ) resistivity, and high resolution angle-resolved ultraviolet photoemission spectroscopy (ARUPS). TEM reveals that the modulation in the b−axis for P b(0.4)−doped Bi(P b)−2212 is dominantly of P b−type that is not sensitive to the oxygen content of the system, and the system clearly shows a structure of orthorhombic symmetry. Oxygen annealed samples exhibit a much lower c−axis resistivity and a resistivity minimum at 80 − 130K. He-annealed samples exhibit a much higher c−axis resistivity and dρ c /dT < 0 behavior below 300K. The Fermi surface (FS) of oxygen annealed Bi(P b)−2212 mapped out by ARUPS has a pocket in the FS around theM point and exhibits orthorhombic symmetry. There are flat, parallel sections of the FS, about 60%

Electronic structure and Fermi surfaces of Bi 2 Sr 2 CaCu 2 O 8+δ δ δ δ observed from high resolution ARPES S11-III A. Bansil First principles simulations of angle-resolved photointensities High-T c 's

Physical Review Letters, 2000

We study the Fermi surface of Bi2Sr2CaCu2O8 (Bi2212) using angle resolved photoemission (ARPES) with a momentum resolution of ∼ 0.01 of the Brillouin zone. We show that, contrary to recent suggestions, the Fermi surface is a large hole barrel centered at (π, π), independent of the incident photon energy.

The Journal of Physical Chemistry C

Defects introduced to the surface of Bi(111) break the translational symmetry and modify the surface states locally. We present a theoretical and experimental study of the 2D defects on the surface of Bi(111) and the states that they induce. Bi crystals cleaved in ultrahigh vacuum (UHV) at low temperature (110 K) and the resulting ion-etched surface are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) as well as spectroscopy (STS) techniques in combination with density functional theory (DFT) calculations. STS measurements of cleaved Bi(111) reveal that a commonly observed bilayer step edge has a lower density of states (DOS) around the Fermi level as compared to the atomic-flat terrace. Following ion bombardment, the Bi(111) surface reveals anomalous behavior at both 110 and 300 K: Surface periodicity is observed by LEED, and a significant increase in the number of bilayer step edges and energetically unfavorable monolayer steps is observed by STM. It is suggested that the newly exposed monolayer steps and the type A bilayer step edges result in an increase to the surface Fermi density as evidenced by UPS measurements and the Kohn−Sham DOS. These states appear to be thermodynamically stable under UHV conditions.

Journal of …, 2002

We present a comprehensive study performed with high-resolution angle-resolved photoemission spectroscopy on triple-layered Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ single crystals. By measurements above T C the Fermi surface topology defined by the Fermi level crossings of the CuO 2 -derived band was determined. A hole-like Fermi surface as for single and double-CuO 2 layered Bi-based cuprates is found, giving new input to the current debate of the general Fermi surface topology of the high T C superconductors. Furthermore, we present measurements of the superconducting gap of Bi-2223 and show that there are clear indications for a strong anisotropy of the superconducting gap.

1999

We present a re-examination of the electronic structure and Fermi Surface (FS) of Bi-Sr-Ca-Cu-O (BSCCO) as obtained from angle-resolved photoemission experiments. By applying a stricter set of FS crossing criteria as well as by varying the incident photon energy outside the usual range, we have found very different behavior from that previously observed. In particular we have found an electron-like FS centered around the Gamma point, and the flat bands at E_F near the M point of the zone are absent. These results are robust over a large range of dopings and from single to double layer samples.

Physical Review B, 2004

The structure of Bi 1.7 Pb 0.4 Sr 2 Ca 0.9 Cu 2 O 8 ͑T c =93 K͒ was refined from x-ray single crystal diffraction data in space group A2aa, a = 5.3852͑9͒ Å, b = 5.4286͑9͒ Å, c = 30.997͑6͒ Å. For this composition, the crystal structure is free from the structural modulation connected with the presence of additional oxygen atoms in the BiO layers. The c-axis lattice parameter is slightly larger in (Bi,Pb)-2212 crystals than in Pb-free Bi-2212 crystals, but the complete structural refinement revealed an inhomogeneous redistribution of the inter-planar distances. In particular, the distance between the two neighboring BiO layers has significantly decreased in the modulation-free phase as compared to the Pb-free phase. We believe that this is a key point in understanding the widely observed reduction of the anisotropy in Bi-2212 by Pb-doping. The irreversibility line as well as the onset of the second magnetization peak in modulation-free (Bi,Pb)-2212 crystals were studied. Because of the strongly reduced value of the anisotropy, the 2D-3D crossover field value, H cr , is significantly higher in (Bi,Pb)-2212 crsystals than in Bi-2212 crystals. As a direct consequence of the structural modifications induced by the removal of the modulation, the nature of the inter-layer coupling changes from electromagnetic in modulated Bi-2212 to Josephson in modulation-free (Bi,Pb)-2212. Annealing the (Bi,Pb)-2212 crystals under oxygen reintroduced the structural modulation.