The gap amplification at a "shape resonance" in a superlattice of quantum stripes: a mechanism for high Tc

The amplification of the superconducting critical temperature Tc from the low temperature range in homogeneous 2D planes (Tc<23 K) to the high temperature range (23 K<Tc<150 K) in an artificial heterostructure of quantum stripes is calculated. The high Tc is obtained by tuning the chemical potential near the bottom of the nth subband at a "shape resonance", in a range, whithin the energy cutoff for the pairing interaction. The resonance for the gap at the nth "shape resonance" is studied for a free electron gas in the BCS approximation as a function of the stripe width L, and of the number of electrons {\rho} per unit surface. An amplification factor for coupling 0.1<{\lambda}<0.3 is obtained at the third shape resonance raising the critical temperature in the high Tc range.Comment: 9 pages 6 figure

Role of the Ce valence in the coexistence of superconductivity and ferromagnetism of CeO1−x_{1-x}Fx_{x}BiS2_{2} revealed by Ce L3L_3-edge x-ray absorption spectroscopy

We have performed Ce $L_3$-edge x-ray absorption spectroscopy (XAS) measurements on CeO$_{1-x}$F$_x$BiS$_2$, in which the superconductivity of the BiS$_2$ layer and the ferromagnetism of the CeO$_{1-x}$F$_x$ layer are induced by the F-doping, in order to investigate the impact of the F-doping on the local electronic and lattice structures. The Ce $L_3$-edge XAS spectrum of CeOBiS$_2$ exhibits coexistence of $4f^1$ (Ce$^{3+}$) and $4f^0$ (Ce$^{4+}$) state transitions revealing Ce mixed valency in this system. The spectral weight of the $4f^0$ state decreases with the F-doping and completely disappears for $x>0.4$ where the system shows the superconductivity and the ferromagnetism. The results suggest that suppression of Ce-S-Bi coupling channel by the F-doping appears to drive the system from the valence fluctuation regime to the Kondo-like regime, leading to the coexistence of the superconducting BiS$_2$ layer and the ferromagnetic CeO$_{1-x}$F$_x$ layer.Comment: 5 pages, 5 figure

Anomalous momentum dependence of the multiband electronic structure of FeSe_1-xTe_x superconductors induced by atomic disorder

When periodicity of crystal is disturbed by atomic disorder, its electronic state becomes inhomogeneous and band dispersion is obscured. In case of Fe-based superconductors, disorder of chalcogen/pnictogen height causes disorder of Fe 3d level splitting. Here, we report an angle-resolved photoemission spectroscopy study on FeSe_1-xTe_x with the chalcogen height disorder, showing that the disorder affects the Fe 3d band dispersions in an orbital-selective way instead of simple obscuring effect. The reverse of the Fe 3d level splitting due to the chalcogen height difference causes the splitting of the hole band with Fe 3d x^2-y^2 character around the Gamma point.Comment: 5 pages, 4 figure

Superconductivity of a striped phase at the atomic limit

Abstract The resonant amplification of the superconducting critical temperature, the isotope effect, the change of the chemical potential in a particular 2D striped phase formed by superconducting stripes of width L alternated by separating stripes of width W with a period l at the atomic limit is studied. The critical temperature shows a &apos;shape resonance&apos; by tuning the p charge density where the chemical potential m is in the range E -m -E q &quot; v , where E is the bottom of the nth n n 0 n superlattice subband for n ) 2, and &quot; v is the energy cutoff for the pairing interaction. The maximum critical 0 superconducting temperature is reached at the cross-over from 2D to 1D behavior. The particular properties of this electronic phase and its similarities with the normal and superconducting properties of doped cuprate perovskites are discussed. q 1998 Elsevier Science B.V

Local lattice instability and stripes in the CuO 2 plane of the La 1.85 Sr 0.15 CuO 4 system by polarized XANES and EXAFS

Temperature-dependent polarized Cu K-edge x-ray absorption has been used to investigate local structural distortions in the ${\mathrm{CuO}}_{2}$ plane of the ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ system. The Cu-O pair distribution shows the presence of a minority phase containing ${\mathrm{CuO}}_{6}$ octahedra characterized by a shorter Cu-O(apical) bond (\ensuremath{\Delta}R\ensuremath{\sim}-0.1 \AA{}) and two longer Cu-O(planar) bonds (\ensuremath{\Delta}R\ensuremath{\sim}+0.08 \AA{}) and a tilting angle of 16\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}. The temperature-dependent distortions show a maximum around T (\ensuremath{\sim}1.${6\mathrm{T}}_{\mathrm{c}}$) and a minimum at ${\mathrm{T}}_{\mathrm{c}}$ (\ensuremath{\sim}35 K). The data show the coexistence of two types of doped charges in different stripes in the superconducting phase

Spatial inhomogeneity and chiral symmetry of the lattice incommensurate supermodulation in high temperature superconductor Bi2Sr2CaCu2O8+y

Using scanning micro X-ray diffraction we report a mixed real and reciprocal space visualization of the spatial heterogeneity of the lattice incommensurate supermodulation in single crystal of Bi2Sr2CaCu2O8+y with Tc=84 K. The mapping shows an amplitude distribution of the supermodulation with large lattice fluctuations at microscale with about 50% amplitude variation. The angular distribution of the supermodulation amplitude in the a-b plane shows a lattice chiral symmetry, forming a left-handed oriented striped pattern. The spatial correlation of the supermodulation is well described by a compressed exponential with an exponent of 1.5 and a correlation length of about 50 {\mu}m, showing the intrinsic lattice disorder in high temperature superconductors.Comment: 12 pages, 3 figures; Physical Review B Rapid Communications 201

Effect of ultra-high pressure on small animals, tardigrades and Artemia

This research shows that small animals, tardigrades (Milnesium tardigradum) in tun (dehydrated) state and Artemia salina cists (dried eggs) can tolerate the very high hydrostatic pressure of 7.5 GPa. It was really surprising that living organisms can survive after exposure to such a high pressure. We extended these studies to the extremely high pressure of 20 GPa by using a Kawai-type octahedral anvil press. After exposure to this pressure for 30 min, the tardigrades were soaked in pure water and investigated under a microscope. Their bodies regained metabolic state and no serious injury could be seen. But they were not alive. A few of Artemia eggs went part of the way to hatching after soaked in sea water, but they never grew any further. Comparing with the case of blue-green alga, these animals are weaker under ultra-high pressure

Rapid and sensitive XAFS using a tunable X-ray undulator at BL10XU of SPring-8

The design and performance of the high-brilliance XAFS facility at BL10XU of SPring-8, aimed at rapid and sensitive measurement of X-ray absorption fine structure (XAFS), is reported. Both undulator gap and double-crystal monochromator have been successfully controlled covering a wide energy range (5-30 keV). A versatile goniometer system, consisting of two independent high-precision goniometers. is capable of polarized XAFS in fluorescence mode and surface-sensitive experiments using a grazing-incidence geometry. By sharing major components, i.e. a monolithic Ge 100-pixel array detector and a closed-cycle He cryostat, both polarized XAFS and X-ray standing wave (XSW) experiments can be performed at low temperature (15-300 K). The performance of the spectrometer has been evaluated by recording XAFS spectra in transmission mode

A novel one-dimensional electronic state at IrTe2 Surface

Highly one-dimensional (1D) Fermi sheets are realized at the surface of a layered Ir telluride IrTe2 which exhibits a stripe-type charge and orbital order below ∼280 K. The 1D Fermi sheets appear in the low temperature range where the stripe order is well established. The 1D Fermi sheets are truncated by the bulk Fermi surfaces, and the spectral weight suppression at the Fermi level deviates from the typical Tomonaga–Luttinger behavior. The 1D band runs along the stripe and is accompanied by several branches which can be derived from the quantization in the perpendicular direction

Pressure tolerance of Artemia cysts compressed in water medium

The high pressure tolerance of cysts of Artemia salina was investigated up to several GPa in water. No survival was observed after exposure to 1.0 GPa for 15 min. After exposure to 2.0 GPa for the same time duration, the hatching rate had recovered to 33%, but decreased to 8% following compression at 7.5 GPa. This contrasts with results using Fluorinert™ as the pressure-transmitting medium where 80–88% recovery was observed. The lower survival rate in water is accompanied by swelling of the eggs, indicating that liquid H2O close to the ice-VI crystallization pressure penetrated inside the eggs. This pressure exceeds the stability limit for proteins and other key biomolecules components within the embryos that could not be resuscitated. Rehydration takes several minutes and so was not completed for all samples compressed to higher pressures, prior to ice-VI formation, resulting in renewed survival. However H2O penetration inside the shell resulted in increased mortalit