Periodic Coherence Peak Height Modulations in Superconducting BSCCO

In this paper we analyze, using scanning tunneling spectroscopy (STS), the local density of electronic states (LDOS) in nearly optimally doped BSCCO in zero field. We see both dispersive and non-dispersive spatial LDOS modulations as a function of energy in our samples. Moreover, a spatial map of the superconducting coherence peak heights shows the same structure as the low energy LDOS. This suggests that these non-dispersive LDOS modulations originate from an underlying charge-density modulation which interacts with superconductivity.Comment: 8 pages, 5 figures with 15 total eps file

Software tools for acoustic database management

Digital archiving of bioacoustic data provides both curatorial and scientific benefits. To realize these benefits, key system requirements must be satisfied. This report discusses these requirements, and describes the software tools developed by the WHOI bioacoustic laboratory to maintain and utilize an archive of digitized biological sounds. These tools are written in standard C code, and are designed to run on PC-compatible microcomputers. Both the usage and structure of these programs are described in relation to the SOUND database of marine animal sounds. These tools include software for analog-to-digital conversion, text header maintenance, data verification and interactive spectrographic review. Source code listings are supplied.Funding was provided by the Office of Naval Research through the Ocean Acoustics Program (code 11250) Contract N00014-88-K-0273 and Grant N00014-J-1445 with supplemental support from NOARL (code 211)

SOUND database of marine animal vocalizations : structure and operations

The SOUND database system for marine animal vocalizations has been updated to include changes in the structure and operations that have evolved with use. These include more convenient operations, greater flexibilty in analysis routines, and a revised database structure. The formats for data sorting and indexing, database structure, and analysis routines have developed into a convenient research tool. This report is a revision of the earlier operating manual for the SOUND databases (Watkins, Fristrup, and Daher 1991.) The interactive databases that comprise the SOUND system provide comprehensive means for quantitative analyses and statistical comparisons of marine animal vocalizations. These SOUND databases encompass (1) descriptive text databases cataoging the WHOI collection of underwater sound recordings of marine animals, (2) sets of files of digital sound sequences, (3) text databases organizing the digital sound cuts, and (4) software for analysis, display, playback, and export of selected sound files. The text databases index and sort the information about the sounds, and the digital sound cut files are accessed directly from the text record. From the text database, the sound cut data may be analyzed on screen, listened to, and compared or exported as desired. The objective of this work has been the development of a basic set of tools for the study of marine animal sound. The text databases for cataloging the recordings provide convenient sorting and selection of sounds of interest. Then, as specific sequences are digitized from these recordings, they become part of another database system that manages these acoustic data. Once a digital sound is part of the organized database, several tools are available for interactive spectrographic display, sound playback, statistical feature extraction, and export to other application programs.Funding was provided by the Office of Naval Research through the Ocean Acoustics Program (code 11250A) under Contract No. N00014-88-K-0273 and No. N00014-91-J-1445 with supplemental support by ORINCON/DARPA and NRL (code 211)

STM/STS Study on 4a X 4a Electronic Charge Order of Superconducting Bi2Sr2CaCu2O8+d

We performed low-bias STM measurements on underdoped Bi2212 crystals, and confirmed that a two-dimensional (2D) superstructure with a periodicity of four lattice constants (4a) is formed within the Cu-O plane at T<Tc. This 4a X 4a superstructure, oriented along the Cu-O bonding direction, is nondispersive and more intense in lightly doped samples with a zero temperature pseudogap (ZTPG) than in samples with a d-wave gap. The nondispersive 4a X 4a superstructure was clearly observed within the ZTPG or d-wave gap, while it tended to fade out outside the gaps. The present results provide a useful test for various models proposed for an electronic order hidden in the underdoped region of high-Tc cuprates.Comment: 4 pages, submitted to J. Phys. Soc. Jp

Quasiparticle interference patterns as a test for the nature of the pseudogap phase in the cuprate superconductors

Electrons, when scattered by static random disorder, form standing waves that can be imaged using scanning tunneling microscopy. Such interference patterns, observable by the recently developed technique of Fourier transform scanning tunneling spectroscopy (FT-STS), are shown to carry unique fingerprints characteristic of the electronic order present in a material. We exploit this feature of the FT-STS technique to propose a test for the nature of the enigmatic pseudogap phase in the high-$T_c$ cuprate superconductors. Through their sensitivity to the quasiparticle spectra and coherence factors, the FT-STS patterns in principle carry enough information to unambiguously determine the nature of the condensate responsible for the pseudogap phenomenon. We argue that the next generation of FT-STS experiments, currently underway, should be able to distinguish between the pseudogap dominated by the remnants of superconducting order from the pseudogap dominated by some competing order in the particle-hole channel. Using general arguments and detailed numerical calculations, we point to certain fundamental differences between the two scenarios and discuss the prospects for future experiments.Comment: 15 pages REVTeX + 9 ps figures. For related work and info visit http://www.physics.ubc.ca/~franz; version 2 to appear in IJMP

Muon-Spin Rotation and Magnetization Studies of Chemical and Hydrostatic Pressure Effects in EuFe2(As1− x P x )2

The magnetic phase diagram of EuFe2(As1−x P x )2 was investigated by means of magnetization and muon-spin rotation (μSR) studies as a function of chemical (isovalent substitution of As by P) and hydrostatic pressure. The magnetic phase diagrams of the magnetic ordering of the Eu and Fe spins with respect to P content and hydrostatic pressure are determined and discussed. The present investigations reveal that the magnetic coupling between the Eu and the Fe sublattices strongly depends on chemical and hydrostatic pressure. It is found that chemical and hydrostatic pressures have a similar effect on the Eu and Fe magnetic orde

Local edge modes in doped cuprates with checkerboard polaronic heterogeneity

We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree-Fock and a random phase approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two dimensions

The origin of the anomalously strong influence of out-of-plane disorder on high-Tc superconductivity

The electronic structure of Bi2Sr2-xRxCuOy(R=La, Eu) near the (pi,0) point of the first Brillouin zone was studied by means of angle-resolved photoemission spectroscopy (ARPES). The temperature T* above which the pseudogap structure in the ARPES spectrum disappears was found to have an R dependence that is opposite to that ofthe superconducting transition temperature Tc. This indicates that the pseudogap state is competing with high-Tc superconductivity, and the large Tc suppression observed with increasing the out-of-plane disorder is due to the stabilization of the pseudogap state.Comment: 4 pages, 4 figure