اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديد2D nano-granularity of the oxygen chains in the YBa2Cu3O6.33 superconductor
384
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The organization of dopants in high temperature superconductors provides complex topological geometries that controls superconducting properties. This makes the study of dopants spatial distribution of fundamental importance. The mobile oxygen ions, y, in the CuO2 plane of YBa2Cu3O6+y (0.33<y<0.67) form ordered chains which greatly affect the transport properties of the material. Here we visualize and characterize the 2D spatial organization of these oxygen chains using scanning micro X-ray diffraction measurements in transmission mode on a thin single crystal slab with y=0.33 (Tc=7 K) near the critical doping for the insulator-to-metal transition. We show the typical landscape of percolation made of a granular spatial pattern due the oxygen chains segregating in quasi-one-dimensional needles of Ortho II (O-II) phase embedded in an insulating matrix with low density of disordered oxygen interstitials
قيم البحث
اقرأ أيضاً
Oxygen chain fragments are known to appear at the insulator to superconductor transition (SIT) in YBa2Cu3O6+y. However the self organization and the size distribution of oxygen chain fragments is not known. Here we contribute to fill this gap, using
scanning micro X ray diffraction which is a novel imaging method based on advances in focusing synchrotron radiation beam. This novel approach allows us to probe both real-space and k-space of a high-quality YBa2Cu3O6.33 single crystals with Tc=7K. We report compelling evidence for nanoscale striped puddles, with Ortho-II structure, made of chain fragments in the basal Cu(1) plane with local oxygen concentration 0.5. The size of the Ortho-II puddles spans a range between 2 and 9 nanometers. The real space imaging of Ortho-II puddles granular network shows that superconductivity, at low hole-doping regime, occurs in a network of nanoscale oxygen ordered patches, interspersed with oxygen depleted regions. The manipulation by thermal treatments of the striped Ortho II puddles has been investigated focusing on the spontaneous symmetry breaking near the order to disorder phase transition at 350 K.
In two dimensions there is a direct superconductor-to-insulator quantum phase transition driven by increasing disorder. We elucidate, using a combination of inhomogeneous mean field theory and quantum Monte Carlo techniques, the nature of the phases
and the mechanism of the transition. We make several testable predictions specifically for local spectroscopic probes. With increasing disorder, the system forms superconducting blobs on the scale of the coherence length embedded in an insulating matrix. In the superconducting state, the phases on the different blobs are coherent across the system whereas in the insulator long range phase coherence is disrupted by quantum fluctuations. As a consequence of this emergent granularity, we show that the single-particle energy gap in the density of states survives across the transition, but coherence peaks exist only in the superconductor. A characteristic pseudogap persists above the critical disorder and critical temperature, in contrast to conventional theories. Surprisingly, the insulator has a two-particle gap scale that vanishes at the SIT, despite a robust single-particle gap.
The superconductor-insulator transition of ultrathin films of bismuth, grown on liquid helium cooled substrates, has been studied. The transition was tuned by changing both film thickness and perpendicular magnetic field. Assuming that the transition
is controlled by a T=0 critical point, a finite size scaling analysis was carried out to determine the correlation length exponent v and the dynamical critical exponent z. The phase diagram and the critical resistance have been studied as a function of film thickness and magnetic field. The results are discussed in terms of bosonic models of the superconductor-insulator transition, as well as the percolation models which predict finite dissipation at T=0.
The new rare-earth arsenate superconductors are layered, low carrier density compounds with many similarities to the high-Tc cuprates. An important question is whether they also exhibit weak-coupling across randomly oriented grain-boundaries. In this
work we show considerable evidence for such weak-coupling by study of the dependence of magnetization in bulk and powdered samples. Bulk sample magnetization curves show very little hysteresis while remanent magnetization shows almost no sample size dependence, even after powdering. We conclude that these samples exhibit substantial electromagnetic granularity on a scale approximating the grain size, though we cannot yet determine whether this is intrinsic or extrinsic.
We report the impact of silver addition on granularity of NdFeAsO0.8F0.2 superconductor. The ac susceptibility and electrical resistivity under magnetic field are measured to study the improvement in weak links of NdFeAsO0.8F0.2 with addition of Ag.
The Ag free NdFeAsO0.8F0.2 compound shows superconductivity at around 51.8K. Typical two step superconducting transitions due to the inter and intra grain contributions, induced from the combined effect of superconducting grains and the inter-granular weak-coupled medium respectively are clearly seen in susceptibility plots. In comparison to the pure NdFeAsO0.8F0.2 compound, the coupling between the superconducting grains is significantly improved for 20Ag silver doped sample, and the same is deteriorated for higher Ag content i.e., for 30wt Ag sample. The magneto transport measurements R(T)H of polycrystalline 20Ag doped NdFeAsO0.8F0.2, exhibited the upper critical filed [Hc2(0)] of up to 334Tesla, which is slightly higher than the one observed for pure NdFeAsO0.8F0.2. The flux flow activation energy varies from 7143.38K to 454.77K with magnetic field ranging from 0Tesla to 14Tesla for 20wtAg doped NdFeAsO0.8F0.2. In this investigation, our results show that limited addition of Ag improves the granular coupling of superconducting grains of NdFeAsO0.8F0.2 compound.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
