Magnetic shape-memory effects in La2-xSrxCuO4 crystals

The magnetic field affects the motion of electrons and the orientation of spins in solids, but it is believed to have little impact on the crystal structure. This common perception has been challenged recently by ferromagnetic shape-memory alloys, where the spin-lattice coupling is so strong that crystallographic axes even in a fixed sample are forced to rotate, following the direction of moments. One would, however, least expect any structural change to be induced in antiferromagnets where spins are antiparallel and give no net moment. Here we report on such unexpected magnetic shape-memory effects that take place ironically in one of the best-studied 2D antiferromagnets, La2-xSrxCuO4 (LSCO). We find that lightly-doped LSCO crystals tend to align their b axis along the magnetic field, and if the crystal orientation is fixed, this alignment occurs through the generation and motion of crystallographic twin boundaries. Both resistivity and magnetic susceptibility exhibit curious switching and memory effects induced by the crystal-axes rotation; moreover, clear kinks moving over the crystal surfaces allow one to watch the crystal rearrangement directly with a microscope or even bare eyes.Comment: 3 pages, 4 figures; shortend version of this paper has been published in Nature as a Brief Communicatio

Ando, Lavrov, and Segawa Reply

Authors' Reply to the Comment by Janossy et al. [cond-mat/0005275] on our article, "Magnetoresistance Anomalies in Antiferromagnetic YBa_{2}Cu_{3}O_{6+x}: Fingerprints of Charged Stripes" [cond-mat/9905071, Phys. Rev. Lett. 83, 2813 (1999)].Comment: 1 page, 1 figure, accepted for publication in PR

Two mechanisms of pseudogap formation in Bi-2201: Evidence from the c-axis magnetoresistance

Measurements of the c-axis resistivity and magnetoresistance have been used to investigate the pseudogap (PG) behavior in Bi_{2+z}Sr_{2-x-z}La_xCuO_y (Bi-2201) crystals at various hole densities. While the PG opening temperature T* increases with decreasing hole doping, the magnetic-field sensitivity of the PG is found to have a very different trend: it appears at lower temperatures in more underdoped samples and vanishes in non-superconducting samples. These data suggest that besides the field-insensitive pseudogap emerging at T*, a distinct one is formed above T_c as a precursor to superconductivity.Comment: 7 pages, 6 figures, accepted for publication in Europhysics Letters (initially submitted to PRL on 14 June 2000

The Discovery of Two Lymanα\alpha Emitters Beyond Redshift 6 in the Subaru Deep Field

We have performed a deep optical imaging survey using a narrowband filter ($NB921$) centered at $\lambda =$ 9196 \AA ~ together with $i^\prime$ and $z^\prime$ broadband filters covering an 814 arcmin$^2$ area of the Subaru Deep Field. We obtained a sample of 73 strong $NB921$-excess objects based on the following two color criteria; $z^\prime - NB921 > 1$ and $i^\prime - z^\prime > 1.3$. We then obtained optical spectroscopy of nine objects in our $NB921$-excess sample, and identified at least two Ly$\alpha$ emitters at$z=6.541 \pm 0.002$ and $z=6.578 \pm 0.002$, each of which shows the characteristic sharp cutoff together with the continuum depression at wavelengths shortward of the line peak. The latter object is more distant than HCM-6A at $z=6.56$ and thus this is the most distant known object found so far. These new data allow us to estimate the first meaningful lower limit of the star formation rate density beyond redshift 6; $\rho_{\rm SFR} \sim 5.2 \times 10^{-4} M_\odot$ yr$^{-1}$ Mpc$^{-3}$. Since it is expected that the actual density is higher by a factor of several than this value, our new observation reveals that a moderately high level of star formation activity already occurred at $z \sim$ 6.6.Comment: 13 pages, 3 figures. PASJ (Letters), 55, vol.2, in pres

Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals

We report the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane resistivity and the Hall angle, we demonstrate that the nature of the low-temperature normal state in the Zn-doped samples is significantly altered from that in the pristine samples under high magnetic fields. In particular, we observe nearly-isotropic negative magnetoresistance as well as an increase in the Hall coefficient at very low temperatures in non-superconducting Zn-doped samples, which we propose to be caused by the Kondo scattering from the local moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in Phys. Rev.

Low-temperature nodal-quasiparticle transport in lightly doped YBa_{2}Cu_{3}O_{y} near the edge of the superconducting doping regime

In-plane transport properties of nonsuperconducting YBa_{2}Cu_{3}O_{y} (y = 6.35) are measured using high-quality untwinned single crystals. We find that both the a- and b-axis resistivities show log(1/T) divergence down to 80 mK, and accordingly the thermal conductivity data indicate that the nodal quasiparticles are progressively localized with lowering temperature. Hence, both the charge and heat transport data do not support the existence of a "thermal metal" in nonsuperconducting YBa_{2}Cu_{3}O_{y}, as opposed to a recent report by Sutherland {\it et al.} [Phys. Rev. Lett. {\bf 94}, 147004 (2005)]. Besides, the present data demonstrate that the peculiar log(1/T) resistivity divergence of cuprate is {\it not} a property associated with high-magnetic fields.Comment: 4 pages, 3 figures. Our previous main claim that the pseudogap state of cuprates is inherently insulating was found to be erroneous and has been retracted; the paper now focuses on the log(1/T) resistivity divergence and its implication

Coherence and superconductivity in coupled one-dimensional chains: a case study of YBa2_{2}Cu3_{3}Oy_{y}

We report the infrared (IR) response of Cu-O chains in the high-$T_{c}$ superconductor YBa$_{2}$Cu$_{3}$O$_{y}$ over the doping range spanning $y=6.28-6.75$. We find evidence for a power law scaling at mid-IR frequencies consistent with predictions for Tomonaga-Luttinger liquid, thus supporting the notion of one-dimensional transport in the chains. We analyze the role of coupling to the CuO$_{2}$ planes in establishing metallicity and superconductivity in disordered chain fragments.Comment: 4 pages, 3 figure