Searcharxiv⌕ Search

arXiv subjects

G. D. Gu

Publications and source records attributed to G. D. Gu.

245 records · Page 14Linked to original sources
arXiv2001

Electronic structure of the trilayer cuprate superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$

The low-energy electronic structure of the trilayer cuprate superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ near optimal doping is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface, and the superconducting d-wave gap and coherence peak are observed and compared with those of single and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with $T_c$ for various optimally doped materials. This suggests that the higher $T_c$ of the trilayer system should be attributed to parameters that simultaneously enhance phase stiffness and pairing strength.

cond-mat.supr-con↗
arXiv2001

Nature of the Electronic Excitations near the Brillouin Zone Boundary of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Based on angle resolved photoemission spectra measured on different systems at different dopings, momenta and photon energies, we show that the anomalously large spectral linewidth in the $(π,0)$ region of optimal doped and underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ has significant contributions from the bilayer splitting, and that the scattering rate in this region is considerably smaller than previously estimated. This new picture of the electronic excitation near $(π,0)$ puts additional experimental constraints on various microscopic theories and data analysis.

cond-mat.supr-con↗
arXiv2001

On the Doping and Temperature Dependence of the Mass Enhancement Observed in the Cuprate Bi2212

High-resolution photoemission is used to study the electronic structure of the cuprate superconductor, Bi2212, as a function of hole doping and temperature. A kink observed in the band dispersion in the nodal direction in the superconducting state is associated with coupling to a resonant mode observed in neutron scattering. From the measured real part of the self energy it is possible to extract a coupling constant which is largest in the underdoped regime, then decreasing continuously into the overdoped regime.

cond-mat.supr-con↗
arXiv2001

Optical studies of charge dynamics in the optimally-doped Bi2212 and the non-superconducting cobaltate single crystals

An analysis of the frequency-dependent scattering rate reveals signatures of the superconducting gap as well as the pseudogap in high-T_c cuprates. These features can be identified in the temperature-dependent spectral function W(omega), inverted from the optical data of the optimally-doped Bi2212 using an experimentally unambiguous method that shows the behavior of both the maxima and minima in the spectral function.

cond-mat.supr-con↗
arXiv2001

Resonant Spin Excitation in an Overdoped High Temperature Superconductor

An inelastic neutron scattering study of overdoped Bi_2Sr_2CaCu_2O_{8+δ} $ (T_c = 83 K) has revealed a resonant spin excitation in the superconducting state. The mode energy is E_res=38 meV, significantly lower than in optimally doped Bi_2Sr_2CaCu_2O_{8+δ} (T_c = 91 K, E_ res =43 meV). This observation, which indicates a constant ratio E_res /k_B T_c \sim 5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high-temperature superconductors.

cond-mat.supr-con↗
arXiv2000

Signature of Superfluid Density in the Single-Particle Excitation Spectrum of Bi2Sr2CaCu2O8+delta

We report that the doping and temperature dependence of photoemission spectra near the Brillouin zone boundary of Bi2Sr2CaCu2O8+delta exhibit unexpected sensitivity to the superfluid density. In the superconducting state, the photoemission peak intensity as a function of doping scales with the superfluid density and the condensation energy. As a function of temperature, the peak intensity shows an abrupt behavior near the superconducting phase transition temperature where phase coherence sets in, rather than near the temperature where the gap opens. This anomalous manifestation of collective effects in single-particle spectroscopy raises important questions concerning the mechanism of high-temperature superconductivity.

cond-mat.supr-con↗
arXiv2000

Temperature Dependent Scattering Rates at the Fermi Surface of Optimally Doped Bi 2212

For optimally doped Bi 2212, scattering rates in the normal state are found to have a linear temperature dependence over most of the Fermi surface. In the immediate vicinity of the (1,0) point, the scattering rates are nearly constant in the normal state, consistent with models in which scattering at this point determines the c-axis transport. In the superconducting state, the scattering rates away from the nodal direction appear to level off and become temperature-independent.

cond-mat↗
arXiv2000

Photoemission Studies on Bi2Sr2CaCuZnO - Electronic Structure Evolution and Temperature Dependence

An angle resolved photoelectron spectroscopy study was conducted on BiSrCaCuZnO. A small amount of Zn substitution for Cu almost completely suppresses the otherwise sharp spectral peak along the (0,0) to (pi,pi) direction in BiSrCaCuZnO, while superconductivity with Tc as high as 83K survives. This behavior contrasts markedly from that seen in cases where the impurities are located off the CuO plane, as well as when the CuO planes are underdoped. This effect is also accompanied by changes of low energy excitations at (pi,0), near the anti-node position of the d-wave pairing state. With Zn doping the size of the superconducting gap is significantly suppressed, the width of the quasiparticle peak in the superconducting state becomes wider, and the dip at higher binding energy is diminished. In addition, enhanced temperature induced spectral changes also occur. We show intriguing systematic lineshape changes with temperature that persist to a very high energy scale - a result consistent with the idea that Zn enhances the local charge inhomogeneity.

cond-mat.supr-con↗
arXiv1999

Neutron Scattering from Magnetic Excitations in Bi_2 Sr_2 Ca_2 O_8+delta

Many physical properties of the copper oxide high temperature superconductors appear to defy the conventional (one-electron) theory of metals, and the development of new theories incorporating strong electron correlations is currently at the forefront of condensed matter physics. Inelastic neutron scattering provides incisive information about collective magnetic excitations that is required to guide this effort. Such measurements have thus far proven possible for only two of the many families of high temperature superconductors, La_{2-x} Sr_x CuO_4 and YBa_2 Cu_3 O_{6+x},because suitably large single crystals of other copper oxide compounds could not be grown. While the magnetic spectra of both materials bear certain similarities, there are also pronounced differences that have hampered a unified description of the spin dynamics in the copper oxides. In particular, a sharp resonant spin excitation dominates the spectrum in the superconducting state of YBa_2 Cu_3 O_{6+x}, but is not found in La_{2-x} Sr_x CuO_4. Here we report the discovery of a magnetic resonance peak in the superconducting state of a different copper oxide system, Bi_2 Sr_2 Ca Cu_2 O_{8+δ}, made possible by the synthesis of a sizable single crystal and modern neutron optics. This provides evidence of the generality of this unusual phenomenon among the copper oxides and greatly extends the empirical basis for its theoretical description.

cond-mat.supr-con↗