Magnetotransport study of the charged stripes in high-T_c cuprates

We present a study of the in-plane and out-of-plane magnetoresistance (MR) in heavily-underdoped, antiferromagnetic YBa_{2}Cu_{3}O_{6+x}, which reveals a variety of striking features. The in-plane MR demonstrates a "d-wave"-like anisotropy upon rotating the magnetic field H within the ab plane. With decreasing temperature below 20-25 K, the system acquires memory: exposing a crystal to the magnetic field results in a persistent in-plane resistivity anisotropy. The overall features can be explained by assuming that the CuO_2 planes contain a developed array of stripes accommodating the doped holes, and that the MR is associated with the field-induced topological ordering of the stripes.Comment: 4 pages, 5 figures, invited paper at M2S-HTSC-VI, to be published in Physics C (Proceedings of the International Conference on Materials and Mechanisms of Superconductivity, High Temperature Superconductors VI (M2S-HTSC-VI), Houston, Feb 20-25, 2000

Aureobasidin A, an antifungal cyclic depsipeptide antibiotic, is a substrate for both human MDR1 and MDR2/P-glycoproteins

AbstractThe human MDR1 gene encodes the multidrug transporter P-glycoprotein (Pgp). Although the MDR2/Pgp shares about 80% identity at the amino acid level with the MDRI/Pgp, the MDR2/Pgp cannot act as a multidrug transporter. We examined the drug sensitivity of Saccharomyces cerevisiae expressing either the human MDR1/Pgp or MDR2/Pgp. The human MDR1/Pgp conferred about 4-fold resistance to aureobasidin A, a cyclic depsipeptide antifungal antibiotic, on the drug-sensitive yeast strains. Interestingly the human MDR2/Pgp also conferred about 2.5-fold resistance to aureobasidin A. The resistance to aureobasidin A conferred by the MDR2/Pgp as well as by the MDR1/Pgp was overcome by vinblastine, verapamil, and cyclosporin A, depending on their concentrations, but not by colchicine. Aureobasidin A probably interacts directly with Pgps, because it overcame multidrug resistance of human cells and inhibited azidopine photoaffinity labeling of MDRI/Pgp in human cell membranes. These results suggest the possibility that the human MDR1 and MDR2/Pgps have conserved domain(s) for drug recognition

Large-scale Filamentary Structure around the Protocluster at Redshift z=3.1

We report the discovery of a large-scale coherent filamentary structure of Lyman alpha emitters in a redshift space at z=3.1. We carried out spectroscopic observations to map the three dimensional structure of the belt-like feature of the Lyman alpha emitters discovered by our previous narrow-band imaging observations centered on the protocluster at z=3.1. The feature was found to consist of at least three physical filaments connecting with each other. The result is in qualitative agreement with the prediction of the 'biased' galaxy-formation theories that galaxies preferentially formed in large-scale filamentary or sheet-like mass overdensities in the early Universe. We also found that the two known giant Lyman alpha emission-line nebulae showing high star-formation activities are located near the intersection of these filaments, which presumably evolves into a massive cluster of galaxies in the local Universe. This may suggest that massive galaxy formation occurs at the characteristic place in the surrounding large-scale structure at high redshift.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter

Implications for the Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst 050904 at z = 6.3

The gamma-ray burst (GRB) 050904 at z = 6.3 provides the first opportunity of probing the intergalactic medium (IGM) by GRBs at the epoch of the reionization. Here we present a spectral modeling analysis of the optical afterglow spectrum taken by the Subaru Telescope, aiming to constrain the reionization history. The spectrum shows a clear damping wing at wavelengths redward of the Lyman break, and the wing shape can be fit either by a damped Ly alpha system with a column density of log (N_HI/cm^{-2}) ~ 21.6 at a redshift close to the detected metal absorption lines (z_metal = 6.295), or by almost neutral IGM extending to a slightly higher redshift of z_{IGM,u} ~ 6.36. In the latter case, the difference from z_metal may be explained by acceleration of metal absorbing shells by the activities of the GRB or its progenitor. However, we exclude this possibility by using the light transmission feature around the Ly beta resonance, leading to a firm upper limit of z_{IGM,u} < 6.314. We then show an evidence that the IGM was largely ionized already at z=6.3, with the best-fit neutral fraction of IGM, x_HI = N_HI/N_H = 0.00, and upper limits of x_HI < 0.17 and 0.60 at 68 and 95% C.L., respectively. This is the first direct and quantitative upper limit on x_HI at z > 6. Various systematic uncertainties are examined, but none of them appears large enough to change this conclusion. To get further information on the reionization, it is important to increase the sample size of z >~ 6 GRBs, in order to find GRBs with low column densities (log N_HI <~ 20) within their host galaxies, and for statistical studies of Ly alpha line emission from host galaxies.Comment: Matches the published version in PASJ. The version with full resolution figures is available upon request to Totani or at http://www.kusastro.kyoto-u.ac.jp/~totani/up/grb050904-paper2-astroph-v3.pd

Magnetoresistance Anomalies in Antiferromagnetic YBa_2Cu_3O_{6+x}: Fingerprints of Charged Stripes

We report novel features in the in-plane magnetoresistance (MR) of heavily underdoped YBa_2Cu_3O_{6+x}, which unveil a developed ``charged stripe'' structure in this system. One of the striking features is an anisotropy of the MR with a "d-wave" symmetry upon rotating the magnetic field H within the ab plane, which is caused by the rotation of the stripes with the external field. With decreasing temperature, a hysteresis shows up below ~20 K in the MR curve as a function of H and finally below 10 K the magnetic-field application produces a persistent change in the resistivity. This "memory effect" is caused by the freezing of the directionally-ordered stripes.Comment: 4 pages, 6 figures, final version, to appear in 4 October 1999 issue of PR