Browsing by Author "Voo, KK"

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An alternative interpretation of the magnetic penetration depth data on Pr2-xCexCuO4-y and La2-xCexCuO4-y
(2005-01-01)
Voo, KK
;
Wu, WC
;
電子物理學系
;
Department of Electrophysics
We have revisited the magnetic penetration depth data on the electron-doped cuprates, Pr2-xCexCuO4-y and La2-xCexCuO4-y. It is proposed that the transition between nodal-gap-like and nodeless-gap-like behavior upon electron-doping [e.g., see M. Kim et al., Phys. Rev. Lett. 91 (2003) 87001] can be due to a scattering of the quasiparticles in the d-wave superconducting state by an incipient or weak antiferromagnetic spin-density-wave. This conjecture is supported by the inelastic neutron scattering and angle-resolved photoemission experiments on some closely related electron-doped cuprates. (C) 2004 Elsevier B.V. All rights reserved.
Connecting wave functions at a three-leg junction of one-dimensional channels
(2006-01-01)
Voo, KK
;
Chen, SC
;
Tang, CS
;
Chu, CS
;
電子物理學系
We propose a scheme to connect the wave functions on different one-dimensional branches of a three-leg junction (Y junction). Our scheme differs from that due to Griffith [Trans. Faraday Soc. 49, 345 (1953)] in the respect that ours can model the difference in the widths of the quasi-one-dimensional channels in different systems. We test our scheme by comparing results from a doubly connected one-dimensional system and a related quasi-one-dimensional system, and we find a good agreement. Therefore our scheme may be useful in the construction of one-dimensional effective models out of (multiply connected) quasi-one-dimensional systems.
Fano resonance in transport through a mesoscopic two-lead ring
(2005-10-01)
Voo, KK
;
Chu, CS
;
電子物理學系
;
Department of Electrophysics
The ballistic transport through a one-dimensional two-lead ring at zero magnetic field is studied. We have focused on the case in which the potential in the ring does not define closed cavities or dots. Even in the absence of well-defined quasibound states, we find Fano profiles in the transmission probability. Those Fano profiles appear at energies corresponding to the standing-wave states in the ring, but their occurrence depends sensitively on the commensurability of the system parameters. When the system parameters are commensurate, the widths of the profiles at some energies are infinitesimally small. These findings suggest that the conventional understanding of the Fano profiles as a result of the interference effect of the transition through resonant states and nonresonant continuum of states, might not account for all the Fano profiles seen in the transport measurements. Moreover, the sensitivity and tunability of the resonance with respect to the system parameters may be usable in the fabrication of electrical nanodevices.
Local density of states modulation and scanning tunneling microscopy in cuprate superconductors: Effect of gap anisotropy
(2005-06-01)
Wu, WC
;
Voo, KK
;
電子物理學系
;
Department of Electrophysics
Recent low-temperature Fourier-transformed scanning tunneling microscopy (FT-STM) data on optimally- and over-doped superconducting Bi2Sr2CaCu2O8 was shown to be an excellent manifestation of good quasiparticles in these samples. Along this line, we extend to study how the gap anisotropy effect can be investigated in the FT-STM images. The case of d(x2-y2)+s-wave gap, which may be relevant to YBa2Cu3O7-delta, is examined in details.