arXiv subjects

T. Mochiku

Publications and source records attributed to T. Mochiku.

24 records · Page 2Linked to original sources

arXiv1997

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

In this paper, we review some of our ARPES results on the superconducting and pseudo gaps in Bi2Sr2CaCu2O8+x. We find that optimally and overdoped samples exhibit a d-wave gap, which closes at the same temperature, Tc, for all k points. In underdoped samples, a leading edge gap is found up to a temperature T* > Tc. We find that T* scales with the maximum low temperature gap, increasing as the doping is reduced. The momentum dependence of the pseudogap is similar to that of the superconducting gap; however, the pseudogap closes at different temperatures for different k points.

cond-mat.supr-con↗

arXiv1997

Bosonic Mode Mixing in the Superconducting State Spectral Function of Bi_2Sr_2CaCu_2O_{8+delta}

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.

cond-mat.supr-con↗

arXiv1996

Evolution of the Fermi surface with carrier concentration in Bi_2Sr_2CaCu_2O_{8+δ}

We show, by use of angle-resolved photoemission spectroscopy, that underdoped Bi_2Sr_2CaCu_2O_{8+δ} appears to have a large Fermi surface centered at (π,π), even for samples with a T_c as low as 15 K. No clear evidence of a Fermi surface pocket around (π/2,π/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.

cond-mat.supr-con↗

arXiv1996

ARPES Study of the Superconducting Gap Anisotropy in Bi_2Sr_2CaCu_2O_8+x

We report measurements of the momentum dependence of the superconducting gap in Bi_2Sr_2CaCu_2O_{8+x} (Bi2212) with angle-resolved photoemission spectroscopy using a dense sampling of the Brillouin zone in the vicinity of the Fermi surface. In the Y quadrant of the zone, where there are no complications from ghost bands caused by the superlattice, we find a gap function consistent within error bars to the form cos(k_x)-cos(k_y) expected for a d-wave order parameter. Similar results are found in the X quadrant with the photon polarization chosen to enhance main band emission over that due to ghost bands.

cond-mat↗

arXiv1996

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

Particle-hole (p-h) mixing is a fundamental consequence of the existence of a pair condensate. We present direct experimental evidence for p-h mixing in the angle-resolved photoemission (ARPES) spectra in the superconducting state of Bi_2Sr_2CaCu_2O_{8+δ}. In addition to its pedagogical importance, this establishes unambiguously that the gap observed in ARPES is associated with superconductivity.

cond-mat↗

arXiv1995

Electronic excitations in Bi$_2$Sr$_2$CaCu$_2$O$_8$ : Fermi surface, dispersion, and absence of bilayer splitting

From a detailed study, including polarization dependence, of the normal state angle-resolved photoemission spectra for Bi$_2$Sr$_2$CaCu$_2$O$_8$, we find only one CuO$_2$ band related feature. All other spectral features can be ascribed either to umklapps from the superlattice or to ``shadow bands''. Even though the dispersion of the peaks looks like band theory, the lineshape 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.

cond-mat↗