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Fourier Transform Scanning Tunneling Spectroscopy: A New Window on the Electronic Structure of Bi_2Sr_2CaCu_2O_{8+δ}

100%

Davis J.

Acta Physica Polonica A

2003

vol. 104

issue 3-4

193-204

Scanning tunneling spectroscopy is used to study the dispersive wave vectors of the local-density-of-states modulations in near-optimal Bi_2Sr_2CaCu_2O_{8+δ}. Atomic-resolution energy-resolved spectroscopic images are acquired in a 650Å field of view on the BiO cleave surface of these crystals at 4.2 K. Fourier transforms are used to measure the wave vectors of spatial modulations in the local density of states. At sub-gap energies, up to 16 inequivalent sets of dispersive wave vectors are observed. When analyzed within a model of quasiparticle scattering-induced interference between a characteristic "octet" of states in momentum-space, they yield an estimate of the Fermi-surface location and the energy gap |Δ(k)| in agreement with angle-resolved photoemission spectroscopy. At energies approaching the gap-maximum, the local-density-of-states modulations become intense, commensurate with the crystal, and localized by the apparent nanoscale domains. This may indicate that the lifetimes of the k=(π/a_0,0) quasiparticles are determined by nanoscale disorder scattering.

Characterization of the Liquid Crystal Display Modulation. Optimization for Some Applications

39%

Campos J., Márquez A., Nicolás J., Moreno I., Iemmi C., Davis J., Yzuel M.

Acta Physica Polonica A

2002

vol. 101

issue 1

189-200

In this paper we revise recent results of our team in the optimization of twisted nematic liquid crystal displays to be used as spatial light modulators for image processing and diffractive optics. In general two kind of responses are desired for the mentioned applications: amplitude-only and phase-only modulations. However, it is not a trivial task to find the polarization configurations for which these responses are obtained. We show that a reverse-engineering approach is needed to optimize the liquid crystal display response. According to this reverse-engineering approach the modulation characteristics can be calibrated by evaluating the modulation response in a few polarization configurations. These results are used to fit the liquid crystal display behavior to a simplified physical model, which uses two modulation parameters. We demonstrate that the degree of accuracy of this model is very high, thus enabling the prediction of the modulation behavior of the display at other polarization configurations. Therefore, we can perform computer searches for the optimum orientation of the polarizing elements to obtain the required optical transmission. We demonstrate the need to use short wavelengths and the need to insert wave plates in front and behind the liquid crystal displays to obtain either amplitude-only or phase-only regime.

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2 Acta Physica Polonica A

1 2003

1 2002

2 Davis J.

1 Campos J.

1 Iemmi C.

1 Moreno I.

1 Márquez A.

1 Nicolás J.

1 Yzuel M.

Search results

Fourier Transform Scanning Tunneling Spectroscopy: A New Window on the Electronic Structure of Bi_2Sr_2CaCu_2O_{8+δ}

Characterization of the Liquid Crystal Display Modulation. Optimization for Some Applications