T. Yokoya

Electronic Spectra and Their Relation to the ( π,π) Collective Mode in High- Tc Superconductors

The photoemission line shape near (pi, 0) in Bi(2)Sr(2)CaCu(2)O(8+delta) below T(c) is characterized by a sharp peak, followed at higher energy by a dip and hump. We study the evolution of this line shape as a function of momentum, temperature, and doping. We find the hump scales with the peak and persists above T(c) in the pseudogap state. We present strong evidence that the peak-dip-hump structure arises from the interaction of electrons with a collective mode of wave vector (pi, pi). The inferred mode energy and its doping dependence agree well with a magnetic resonance observed by neutron scattering.

Superconducting Gap Anisotropy and Quasiparticle Interactions: A Doping Dependent Photoemission Study

Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d-wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple coskx 2 cosky form, which suggests an increasing importance of long range interactions as the insulator is approached.

Electronic excitations in Bi2Sr2CaCu2O8: Fermi surface, dispersion, and absence of bilayer splitting

From a detailed study, including polarization dependence, of the normal state angle-resolved photoemission spectra for Bi2Sr2CaCu2O8, We find only one CuO2 band related feature. All other spectral features can be ascribed either to unklapps from the superlattice or to shadow bands. Even though the dispersion of the peaks looks like band theory, the line shape is anomalously broad and no evidence is found for bilayer splitting. We argue that the dip feature in the spectrum below T-c arises not from bilayer splitting, but rather from many-body effects.

Evolution of the Fermi Surface with Carrier Concentration in Bi2Sr2CaCu2O8+δ

We show, by use of angle-resolved photoemission spectroscopy, that underdoped Bi2Sr2CaCu2O8+delta appears to have a large Fermi surface centered at (pi, pi), even for samples with a T-c as low as 15 K. No clear evidence of a Fermi surface pocket around (pi/2, pi/2) has been found. These conclusions are based on a determination of the minimum gap locus in the pseudogap regime T-c < T < T*, which is found to coincide with the locus of gapless excitations in momentum space (Fermi surface) determined above T*. These results suggest that the pseudogap is more likely of precursor pairing rather than magnetic origin.

Unusual Dispersion and Line Shape of the Superconducting State Spectra of Bi2Sr2CaCu2O8+δ

Photoemission spectra of Bi_2Sr_2CaCu_2O_{8+delta} below T_c show two features near the (pi,0) point of the zone: a sharp peak at low energy and a higher binding energy hump. We find that the sharp peak persists at low energy even as one moves towards (0,0), while the broad hump shows significant dispersion which correlates well with the normal state dispersion. We argue that these features are naturally explained by the mixing of electrons with a bosonic mode which appears only below T_c, and speculate that the latter may be related to the resonance seen in recent neutron data.

Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission

Particle-hole (

Determination of the Fermi surface in high-T c superconductors by angle-resolved photoemission spectroscopy

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Angle-resolved photoemission spectroscopy study of the superconducting gap anisotropy in Bi2Sr2CaCu2O8+x.

) mixing is a fundamental consequence of the existence of a pair condensate. We present direct experimental evidence for

ARPES study of the superconducting gap and pseudogap in Bi2Sr2CaCu2O8+x

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Dual Character of 5f Electrons in UPd 2Al 3 Observed by High-Resolution Photoemission Spectroscopy

mixing in the angle-resolved photoemission (ARPES) spectra in the superconducting state of