Fermi surface of Bi2Sr2CaCu2O8

We study the Fermi surface of Bi2Sr2CaCu2O8 using angle resolved photoemission spectroscopy (ARPES) with a momentum resolution of approximately 0.01 of the Brillouin zone. We show that, contrary to recent suggestions, the ARPES derived Fermi surface is a large hole barrel centered at (pi,pi), independent of the incident photon energy. We caution that the photon energy and k dependence of the matrix elements, if not properly accounted for, can lead to misinterpretation of ARPES intensities.     

Electronic structure and Fermi surface of Bi2Sr2CaCu2O8

Applying angle-resolved photoemission spectroscopy of high angular and energy resolution we have measured the electronic structure of single crystals of Bi₂Sr₂CaCu₂O₈ near the Fermi energy. Along the high symmetry direction X a band is observed to disperse upwards and to cross the Fermi level, whose unoccupied part constitutes the hole-like carriers responsible for the superconductivity. From spectra along the M direction we find evidence for an electron pocket around the M point. The measured band widths appear to be drastically reduced compared with band structure calculations indicating strong electronic correlation effects. From the observation of Fermi-Dirac-like cut-offs in the spectra due to band crossings through the Fermi level we can confirm the existence and, in particular, the shape of the Fermi surface as calculated by band structure calculations.     

Anisotropy of magnetic properties of textured superconductor Bi2Sr2CaCu2O8+δ

The values of the penetration depths and their temperature dependences were measured for differentc-axis orientations of a textured 2.2.1.2. sample. The remanent magnetic flux was studied. The giant mobility of the trapped vortex structure was found above 40 K.     

Macroscopic quantum tunneling in a d-wave high-TC Bi2Sr2CaCu2O8 + delta superconductor

While Josephson-junction-like structures intrinsic to the layered cuprate high temperature superconductors offer an attractive stage for exploiting possible applications to new quantum technologies, the low energy quasiparticle excitations characteristically present in these d-wave superconductors may easily destroy the coherence required. Here we demonstrate for the first time the feasibility of macroscopic quantum tunneling in the intrinsic Josephson junctions of a high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8 + delta), and find it to be characterized by a high classic-to-quantum crossover temperature and a relatively weak quasiparticle dissipation.     

Identification of a new form of electron coupling in the Bi2Sr2CaCu2O8 superconductor by laser-based angle-resolved photoemission spectroscopy

Laser-based angle-resolved photoemission measurements with superhigh resolution have been carried out on an optimally doped Bi(2)Sr(2)CaCu(2)O(8) high temperature superconductor. New high energy features at approximately 115 meV and approximately 150 meV, in addition to the prominent approximately 70 meV one, are found to develop in the nodal electron self-energy in the superconducting state. These high energy features, which cannot be attributed to electron coupling with single phonon or magnetic resonance mode, point to the existence of a new form of electron coupling in high temperature superconductors.     

Spin-density wave near the vortex cores in the high-temperature superconductor Bi2Sr2CaCu2O8+y

Competition with magnetism is at the heart of high-temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism we have developed a spatially resolved probe based upon NMR spin-lattice-relaxation spectroscopy. With this approach we have found a spin-density wave associated with the vortex core in Bi(2)Sr(2)CaCu(2)O(8+y), similar to checkerboard patterns in the local density of electronic states reported from scanning tunneling microscope experiments. We have determined both the spin-modulation amplitude and decay length from the vortex core in fields up to H=30 T.     

The analysis of tunneling characteristics measured on Bi2Sr2CaCu2O8 surface

Cleaved in air a-b surface of Bi₂Sr₂CaCu₂O₈ (BSCCO-2212) was measured by means of STM and STS at 4.2 K in liquid hellium bath. From fitting experimental conductivity curves by Dynes' function two superconductivity parameters (gap value) and (smearing parameter) were obtained. The shape of gap structure superimposed on dI/dV characteristics depends on tip-sample distance, what is expressed by the increase of and decrease of with shortening of s. The phenomenon of becoming gap structure more distinct when approaching the tunneling tip to the surface is explained by us as the non-vacuum tunneling, where the surface contamination layer on non-metallic BiO top-surface layer strongly influences the tunneling process. Only for s short enough tunneling electrons penetrate to deeper situated CuO layers and reflect their superconducting behaviour. Non-vacuum STM images are therefore sensitive to the tip-sample distance adjustment. The dependence of gap parameters on lateral position of the tip above the sample can also occur. In such cases STS enables to state which elements of the image belong to the topography of the surface and which to its electron density of states.     

Transverse Seebeck effect in Bi2Sr2CaCu2O8

2 Cu₃O₇ has been observed in “off-c-axis” grown Bi₂Sr₂CaCu₂O₈ films. The films were prepared by pulsed laser deposition from Bi₂Sr₂CaCu₂O₈ targets and grown with a tilt angle of 10 degrees between the film c-axis and the film surface on off-axis cut SrTiO₃ substrates. From the thermoelectric response upon laser irradiation the anisotropy of the thermopower is estimated. Received: 15 April 1996/ Accepted:19 November 1996     

Correlating off-stoichiometric doping and nanoscale electronic inhomogeneity in the high-Tc superconductor Bi2Sr2CaCu2O8+delta

A microscopic theory is presented for the observed electronic disorder in superconducting Bi2Sr2CaCu2O8+delta. The essential phenomenology is shown to be consistent with the existence of two types of interstitial oxygen dopants: those serving primarily as charge reservoirs and those close to the apical plane contributing both carriers and electrostatic potential to the CuO2 plane. The nonlinear screening of the latter produces nanoscale variations in the doped hole concentration, leading to electronic inhomogeneity. Based on an unrestricted Gutzwiller approximation of the extended t-J model, we provide a consistent explanation of the correlation between the observed dopant location and the pairing gap and its spatial evolutions. We show that the oxygen dopants are the primary cause of both the pairing gap disorder and the quasiparticle interference pattern.