Stripe formation in high-Tc superconductors

The non-uniform ground state of the two-dimensional three-band Hubbard model for the oxide high-Tc superconductors is investigated using a variational Monte Carlo method. We examine the effect produced by holes doped into the antiferromagnetic (AF) background in the underdoped region. It is shown that the AF state with spin modulations and stripes is stabilized du to holes travelling in the CuO plane. The structures of the modulated AF spins are dependent upon the parameters used in the model. The effect of the boundary conditions is reduced for larger systems. We show that there is a region where incommensurability is proportional to the hole density. Our results give a consistent description of stripes observed by the neutron- scattering experiments based on the three-band model for CuO plane.Comment: 8 pages, 9 figure

Locally Optimal Control of Quantum Systems with Strong Feedback

For quantum systems with high purity, we find all observables that, when continuously monitored, maximize the instantaneous reduction in the von Neumann entropy. This allows us to obtain all locally optimal feedback protocols with strong feedback, and explicit expressions for the best such protocols for systems of size N <= 4. We also show that for a qutrit the locally optimal protocol is the optimal protocol for a given range of control times, and derive an upper bound on all optimal protocols with strong feedback.Comment: 4 pages, Revtex4. v2: published version (some errors corrected

Effects of energy dependence in the quasiparticle density of states on far-infrared absorption in the pseudogap state

We derive a relationship between the optical conductivity scattering rate 1/\tau(\omega) and the electron-boson spectral function \alpha^2F(\Omega) valid for the case when the electronic density of states, N(\epsilon), cannot be taken as constant in the vicinity of the Fermi level. This relationship turned out to be useful for analyzing the experimental data in the pseudogap state of cuprate superconductors.Comment: 8 pages, RevTeX4, 1 EPS figure; final version published in PR

Ultra-High-Speed Photography and Optical Flash Measurement of Nylon Sphere Impact Phenomena

AbstractAn optical spike is sometimes observed prior to the main flash in high-velocity impact experiments. The spikes are particularly noticeable in the case of Nylon66 projectiles. In this study, we conducted experiments in which Nylon66 spheres impacted the flat surfaces of Nylon66 blocks perpendicularly at 7km s-1. We observed the impact phenomena by using an ultra-high-speed camera and high-temporal-resolution photometers to identify the cause of the spikes. High-speed photographs show that the entire projectile was shining while it was penetrating a target. Glaring light from the shock front propagating in the projectile is assumed to become diffused within the translucent projectile and then radiated from its surface. The blackbody radiation from the shock front at 3600K, which is calculated based on a one-dimensional shock model, accounts for the radiative intensities measured by the photometers. A sub-spike was observed just after the main spike in all the experiments conducted, the cause of which was not ascertained