Charge Reservoir Research Articles

Tuning superconductivity by carrier injection

We have found that by extensive current injection along the c-axis, the superconducting properties of Bi2Sr2CaCu2O8+δ can be changed effectively. We show that critical temperature, c-axis resistivity, and critical current of intrinsic Josephson junctions can be tuned in a large range from underdoping to extreme overdoping. This effect is reversible and persistent. Our results can be explained by trapping charges in the insulating layers, which induce a change of carrier concentration in superconducting planes. This floating gate concept can be a general property of layered materials where the insulating charge reservoir layers are separated from the conducting planes.

Superconductivity in Pb-1212–Cu1−xPbxSr2Y0.6Ca0.4Cu2O7 (x = 0.5–0.9)

We report synthesis and superconductivity of Pb-1212–Cu1−xPbxSr2Y0.6Ca0.4Cu2O7 (x=0.5–0.9) compounds. These compounds were synthesized through solid-state reaction route with optimized sintering temperatures and conditions. In particular, one needs to employ reducing atmosphere conditions to achieve superconductivity in higher Pb content samples. The X-ray diffraction (XRD) patterns reveals that all the compounds are crystallized in space group P4/mmm RE-123 structure. Superconductivity at 56K (onset) is achieved for Pb content as high as 90%. Our study reveals that superconductivity and structure stabilization in Pb-based are more critical to synthesizing conditions than other cuprates. It is concluded that superconductivity can be introduced in Pb-1212 compounds by synthesizing the same in reducing atmosphere and thus the Pb in lower (<+4) valence state. This ensures the replacement of Cu–Ox chains of RE-123 by Pb–Ox sheets acting as charge reservoir carrier donating blocks.

Eletrização de dielétricos: novas propostas para resolver velhos problemas

Electrostatic phenomena were discovered long ago but their interpretation according to well-established atomic-molecular theory is still lacking. As a result, electrostatic phenomena are often irreproducible and uncontrolled, causing serious practical problems. Highly reproducible recent experimental results on electrostatic charging from this and other laboratories are reviewed in this work, together with a description of the relevant but not so usual Kelvin probe and Faraday cup techniques. These results support a new model for electrostatic charging of dielectrics and insulated metals, based on the role of moist atmosphere as a charge reservoir.

A Search for a Low Anisotropic Superconductor

In this article, we have given a review of thallium based (TlmBa2Can-1CunO2n+2) and copper based (CuBa2Can-1 CunO2n+4) high temperature superconductors. This review article is based on the methods of preparation in the form of bulk and thin films and their physical properties. We have also studied the sources of anisotropy and methods of lowering it via changing the composition of charge reservoir layer and developing a better inter-plane coupling.

Role of chemical pressure in enhancing the transition temperature (Tc) and upper critical field (Hc2) in the Y-doped Ce-oxyfluoride superconductor

Structural and superconducting properties of yttrium substituted Ce1-xYx(O/F)FeAs superconductors have been investigated for the first time. All the compounds crystallize in the tetragonal ZrCuSiAs structure type. There is a decrease in both the a and c lattice parameters on increasing yttrium substitution (with fixed F content) along with a substantial enhancement of the superconducting transition temperature (Tc) and upper critical field (Hc2) indicating the influence of chemical pressure. Interestingly the maximum Tc (~48 K) was observed for an intermediate composition (Ce0.5Y0.5O0.9F0.1FeAs) which is higher than either of the parent Y or Ce-compounds, (YO0.9F0.1FeAs (~10 K) and Ce(O/F)FeAs (~42 K)). The transition temperature was also found to be nearly independent of the electron -doping introduced by fluoride substitution (0.1 to 0.2 moles per formula unit) indicating the significance of the charge reservoir layer (Ce-O). The yttrium substituted (fluoride free) compositions of the type, Ce1-xYxOFeAs were found to be semimetallic like the parent compound CeOFeAs with the shift in the anomaly temperature towards low temperature on substitution of yttrium ions. Hall coefficient and thermopower measurements show an increase in charge carriers (electrons) through Y-doping in fluorine doped CeOFeAs.

Angular dependence of Jc for YBCO coated conductors at low temperature and very high magnetic fields

We present very high field angle dependent critical current density(Jc) data for threerecently obtained YBa2Cu3O7−x (YBCO) coated conductors used in the construction of highfield solenoids. We find that strongly correlated pins, such asBaZrO3 (BZO) nanorods,while yielding strong c-axis peaks at 77 K, produce almost no measurable contribution at 4 K. Raising the field from<5 to 30 T at 4 K causes a marked transition from a Ginzburg–Landau-likeJc(θ) at low fields to a marked cusp-like behavior at high fields. Transmissionelectron micrographs show that all samples contain a high density ofstacking faults which strengthen the plane correlated pinning parallel to theab planes producedby the intrinsic ab-plane pinning of the Cu–O charge reservoir layers.

Effect of Cation Substitution on the Lattice Vibration and Crystal Structure of Magnetic RuSr1.9A0.1GdCu2O8(A = Ca, Sr, and Ba) Superconductors

The lattice vibration and crystal structure of alkaline earth metal-substituted RuSr 1.9 A 0.1 GdCu 2 O 8 (A= Ca, Sr, and Ba) have been investigated with micro-Raman spectroscopy. The present RuSr 1.9 A 0.1 GdCu 2 O 8 materials show not only several weak Raman peaks corresponding to the vibrations of O Cu and O Ru but also strong characteristic phonon lines related to O Sr vibration mode. A comparison between the frequency of O Sr vibration and the bond distances of (Ru―O Sr ) and (Cu―O Sr ) in the present ruthenocuprates reveals that the vibration energy of O Sr is mainly dependent on the bond distance of (Ru-O Sr ). The peak splitting of the O Sr phonon lines was observed for the unsubstituted RuSr 2 GdCu 2 O 8 , suggesting the existence of two different (Ru-O Sr ) bond distances. Such a peak splitting caused by the appearance of low-energy shoulder reflects the presence of internal charge transfer pathway from the RuO 2 plane to the superconductive CuO 2 one. After the substitution of Sr with Ca or Ba, the low-energy shoulder peak of O Sr vibration becomes suppressed, underscoring the depression of internal charge transfer between the RuO 2 and CuO 2 planes. The weakened role of RuO 2 layer as charge reservoir in the RuSr 1.9 Ao 0.1 GdCu 2 O 8 (A = Ca, Ba) would be responsible for the depression of T c upon the Ca/Ba substitution.

Petroleum system analysis of the Mishrif reservoir in the Ratawi, Zubair, North and South Rumaila oil fields, southern Iraq

ABSTRACT Five oil samples reservoired in the Cretaceous Mishrif Formation from the Ratawi, Zubair, Rumaila North and Rumaila South fields have been analysed using Gas Chromatography – Mass Spectroscopy (GC-MS). In addition, fifteen core samples from the Mishrif Formation and 81 core samples from the Lower Cretaceous and Upper Jurassic have been subjected to source rock analysis and palynological and petrographic description. These observations have been integrated with electric wireline log response. The reservoirs of the Mishrif Formation show measured porosities up to 28% and the oils are interpreted as being sourced from: (1) Type II carbonate rocks interbedded with shales and deposited in a reducing marine environment with low salinity based on biomarkers and isotopic analysis; (2) Upper Jurassic to Lower Cretaceous age based on sterane ratios, analysis of isoprenoids and isotopes, and biomarkers, and (3) Thermally mature source rocks, based on the biomarker analysis. The geochemical analysis suggests that the Mishrif oils may have been sourced from the Upper Jurassic Najma or Sargelu formations or the Lower Cretaceous Sulaiy Formation. Visual kerogen assessment and source rock analysis show the Sulaiy Formation to be a good quality source rock with high total organic carbon (up to 8 wt% TOC) and rich in amorphogen. The Lower Cretaceous source rocks were deposited in a suboxic-anoxic basin and show good hydrogen indices. They are buried at depths in excess of 5,000 m and are likely to have charged Mishrif reservoirs during the Miocene. The migration from the source rock is likely to be largely vertical and possibly along faults before reaching the vuggy, highly permeable reservoirs of the Mishrif Formation. Structural traps in the Mishrif Formation reservoir are likely to have formed in the Late Cretaceous.

An X-ray absorption study of the electric field effect mechanism in “123” cuprates

X-ray absorption spectroscopy in the presence of an electric field has been used to study the doping mechanism of the CuO2 planes in Nd1+xBa2-xCu3O7 compounds. The electric field effect doping is well-known as a method to modify the electrical properties of a thin film using an external gate voltage and in the copper based high critical temperature superconductors (HTS), it has been used to shift the critical temperature and even to induce phase transitions. Field effect experiments in ultra-thin HTS are usually interpreted by supposing that the induced charges develop into carriers in the CuO2 conducting planes, thus changing the filling of the Zhang-Rice (ZR) band. Here we show that the polarization charges in both insulating and superconducting films, are mainly confined in the charge reservoir, and in particular in the CuO chains. The characteristics of the charge reservoir layer determine the doping of the CuO2 planes, achieved by transfer of a fraction of the total injected charges. Moreover we found that holes injection in the CuO2 planes is reduced in oxygen deficient NdBCO films.

Superconducting properties of Cd doped Cu 0.5Tl 0.5Ba 2Ca 3Cu 4− yCd yO 12− δ ( y = 0, 0.25, 0.5, 0.75, 1.0) superconductors

Cadmium doped Cu 0.5Tl 0.5Ba 2Ca 3Cu 4− y Cd y O 12− δ ( y = 0, 0.25, 0.5, 0.75, 1.0) samples have been synthesized and their superconducting properties are studied using X-ray diffraction (XRD), resistivity, ac-susceptibility and Fourier Transform Infrared (FTIR) absorption measurements. These samples have shown tetragonal structure, their unit cell volume is decreased with the increased Cd doping. The zero resistivity critical temperature [ T c( R = 0)] decreases and the magnitude of diamagnetism is suppressed with the increased concentration of Cd in superconductors. The T c( R = 0) and the magnitude of diamagnetism in these compounds are improved after post-annealing in oxygen atmosphere. It is most likely that the increased concentration of oxygen in Cu 0.5Tl 0.5Ba 2O 4− δ charge reservoir layer optimizes the density of carriers in the conducting planes to the desired level consequently increasing superconductivity in the final compound. Changes in the shape of FTIR absorption spectra after Cd doping have shown incorporation of Cd in the unit cell of the final compounds. The FTIR absorption measurements of these samples have shown hardening of apical oxygen modes of type Cu(1)–O A–Cu(2)/Cd y ( y = 0, 0.25, 0.5, 0.75, 1.0) with increased Cd doping. It is most likely that hardening of apical oxygen modes of vibration are associated with the damped harmonic oscillations of heavier Cd atoms in the CuO 2 planes which suppress the phonons population from a desired level reducing the magnitude of superconductivity in the final compound.

Superconductivity in Co doped Cu 0.5Tl 0.5Ba 2(CaM)Cu 2.95Co 0.05O 10− δ (M = Mg, Be) samples

We have investigated the possible source of suppression of superconductivity in Cu 0.5Tl 0.5Ba 2Ca 2Cu 2.95Co 0.05O 10− δ samples. We substituted Mg ( r = 0.65 Å) and Be ( r = 0.31 Å) at Ca ( r = 0.99 Å) sites in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ (M = Mg, Be) superconductor to enhance inter-planar coupling and Li in the charge reservoir layer (Cu 0.5Tl 0.25Li 0.25)Ba 2O 4− δ to supply extra carriers to CuO 2 planes. It was observed that zero resistivity critical temperature is decreased after Mg and Be substitution in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ samples. However, the c-axis lattice parameter is increased in both samples in spite of smaller ionic radius of Mg and Be as compared to Ca. However, in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ (M = Mg, Be) samples we have achieved enhanced superconductivity by Li doping. It was observed from these studies that cobalt doped in the conducting CuO 2 planes somehow localizes the carriers at Co 3+ sites and decrease the density of mobile carriers. But Li in Cu 0.5Tl 0.5Ba 2O 4− δ charge reservoir layer supplies the required number of carriers to the CuO 2 planes; therefore, the critical temperature is increased in Li doped samples.

Superconductivity at 2.2 K in the layered oxypnictideLa3Ni4P4O2

We report the observation of superconductivity in ${\text{La}}_{3}{\text{Ni}}_{4}{\text{P}}_{4}{\text{O}}_{2}$ at 2.2 K. The layer stacking in this compound results in an asymmetric distribution of charge reservoir layers around the ${\text{Ni}}_{2}{\text{P}}_{2}$ planes. The estimated Wilson ratio, ${R}_{W}\ensuremath{\approx}5$, indicates the presence of strongly enhanced normal-state susceptibility, but many of the basic superconducting characteristics are conventional. The estimated electronic contribution to the specific heat, $\ensuremath{\gamma}\ensuremath{\approx}6.2\text{ }\text{mJ}\text{ }{\text{mol-Ni}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$, is about 2/3 of that found in layered nickel borocarbide superconductors.

The (Cu 0.5Tl 0.5)Ba 2O 4−δ charge reservoir layer as an efficient source of carriers to the CuO 2 planes: Doping of Bi in (Cu 0.5Tl 0.5)Ba 2Ca 2Cu 3O 10−δ superconductors

In order to study the higher carrier’s doping efficiency of (Cu 0.5Tl 0.5)Ba 2O 4− δ charge reservoir layer to the conducting CuO 2 planes we have incorporated Bi in (Cu 0.5Tl 0.5)Ba 2Ca 2Cu 3O 10− δ superconductors; the presence of Bi in the charge reservoir layer promotes highest anisotropy to these compounds. For such studies, we have successfully synthesized (Cu 0.25Tl 0.5Bi 0.25)Ba 2Ca 2Cu 3O 10− δ , (Bi 0.5Tl 0.5)Ba 2Ca 2Cu 3O 10− δ , (Cu 0.25Tl 0.25Bi 0.25Li 0.25)Ba 2Ca 2Cu 3O 10− δ and (Cu 0.25Tl 0.25Bi 0.25Li 0.25)Ba 2Ca 2− y Be y Cu 3O 10− δ superconductors at normal pressure and studied their superconducting properties. These studies have shown that incorporation of Bi at the charge reservoir layer promoted a decrease in the density of carriers in the conducting CuO 2 planes which in turn suppressed the magnitude of diamagnetism of final compound. The decreased density of the carriers in the CuO 2 planes, which most likely promotes inferior superconducting properties, was replenished by doping of Li in the charge reservoir layer and optimizing their number by post-annealing in oxygen atmosphere. It is observed that Bi doping in (Cu 0.5Tl 0.5)Ba 2O 4− δ charge reservoir layer promotes an increase in the c-axis length which in turn increase the anisotropy and decrease the Fermi-vector [ k F = (3 π 2 N/ V) 1/3] and Fermi-velocity [ v F = ( π ε c Δ / ℏ ) ] of the carriers. We have decreased the c-axis length of Bi doped compounds by doping Be at the Ca sites in (Cu 0.25Tl 0.25Bi 0.25Li 0.25)Ba 2Ca 2− y Be y Cu 3O 10− δ superconductors. It is observed from these experiments that Beryllium doping of y = 0.5 has produced excellent superconducting properties in terms of enhancement of T c( R = 0) and magnitude of diamagnetism in this compound. A maximum decrease in the unit cell volume is observed with this Be doping concentration, which enhance k F, v F and superconducting order parameter of the carriers and hence promote the enhancement of superconducting properties. These studies have also shown that the role of density of the carriers in CuO 2 planes is pivotal in the mechanism of superconductivity in these compounds and Bi doping significantly affects them due to its presence in the charge reservoir layer.

Study of the onset of superconductivity in underdoped La2−xSrxCuO4

The origin of the appearance of superconductivity in the high-transition-temperature (high-Tc) copper oxides has remained a subject of active inquiry. In order to address this issue, we chose La2−xSrxCuO4 as a model system and succeeded in fine controlling the hole concentration around the composition where Tc appears. Tc did not emerge smoothly at a critical hole concentration, xc. Tc and the absolute value of the Meissner signal below Tc increased progressively with Sr content x>xc. Measurements of magnetization versus temperature under hydrostatic pressure (P) are also reported for La2−xSrxCuO4, which has no charge reservoir. A dTc/dP> 0 found in 0.05 <x< 0.22 peaks out at x≈0.07. Comparison between these results and predictions from existing models for the high-Tc superconductivity has been made.

Hole redistribution across interfaces in superconducting cuprate superlattices

With the aim of disentangling the role of the constituent blocks in the high-${T}_{c}$ cuprate superconductors we have measured x-ray absorption spectra at the $\text{Cu}\text{ }{L}_{3}$ edge on $({\text{Cu}}_{1\ensuremath{-}\ensuremath{\delta}}{\text{C}}_{\ensuremath{\delta}}){\text{Ba}}_{2}\phantom{\rule{0.1em}{0ex}}\text{Cu}{\text{O}}_{x}$ (BCO), ${\text{CaCuO}}_{2}$ (CCO), and BCO/CCO superconducting superlattices obtained by stacking in a sequence the two blocks. By observing the polarization dependence we could discriminate between the in-plane and out-of-plane hole densities. The results strongly indicate that charge is redistributed across the interfaces from the BCO charge reservoir block to the CCO infinite layer block. In the superconducting samples a relatively high density of out-of-plane holes is still present, whereas when the CCO layer thickness is excessive the holes appear to have preferential in-plane orientation and superconductivity is suppressed.

The superconductivity at 18 K in LiFeAs system

The recent discovery of superconductivity in iron arsenide compounds RFeAsO (R=rare earth) or AFe 2As 2 (A=alkaline earth) has attracted great attention due to the unexpected high T c in the system containing ferromagnetic elements like Fe. Similar to high T c cuprates, the superconductivity in iron arsenide is related to a layered structure. Searching for new superconductors with [FeAs] layer, but of simpler structure will be of scientific significance either to build up new multilayered superconductors that may reach higher T c or to study the mysterious underlined superconducting mechanism in iron arsenide compounds. Here we report that a new superconducting iron arsenide system LiFeAs was found. The compound crystallizes into a structure containing [FeAs] conducting layer that is interlaced with Li charge reservoir. Superconductivity was observed with T c up to 18 K in the compounds.

Enhanced superconductivity by Na doping in (Cu 0.5Tl 0.25Na 0.25)Ba 2Ca 2Cu 3O 10− δ

We have studied for the first time, the reproducible method of doping the CuO 2 planes in (Cu 0.5Tl 0.5)Ba 2Ca 2Cu 3O 10− δ superconductor with the intercalation of Na at Cu 0.5Tl 0.5Ba 2O 4− δ charge reservoir layer. The zero resistivity critical temperature T c ( R = 0) and magnitude of diamagnetism are increased with Na doping. However, Na containing sample doped with Mg and Be, the T c ( R = 0) and quantity of diamagnetism are suppressed. When these results are coupled with X-ray diffraction studies, it is seen that the decrease c-axes length with Mg and Be enhances the inter-plane coupling to such an extent that repulsion starts among the carriers, which possibly suppress the superconductivity parameters. The self-doping of Na-doped samples have shown enhanced superconductivity parameters, which is most likely accomplished through the optimization of carriers in the conducting CuO 2 planes.

Enhanced Superconductivity in (Cu0.5Tl0.25Cs0.25)Ba2Ca2Cu3O10−δ by Cs Doping

The self doping of carriers in CuO2 planes (accomplished through post annealing in air, N2 and O2 atmospheres in previous studies) is replaced by a more efficient alkali metal dopant such as Cs. The doping of Cs in the Cu0.5Tl0.5Ba2O4−δ charge reservoir of Cu0.5Tl0.5Ba2Ca2Cu3O10−δ superconductors has been found to enhance its superconducting properties. Enhanced superconductivity parameters, such as Tc, Hc and Jc, most likely arise from the enhanced doping efficiency of Cu0.5Tl0.25Cs0.25Ba2O4−δ charge reservoir layer; since the alkali metals are known to lose their outermost “s-orbital” electron, which could be supplied to conducting CuO2 planes. The distance between efficiently doped CuO2 planes is reduced by Be and Mg doping at the Ca Sites. The quantity of diamagnetism and zero resistivity critical temperature [Tc(R=0)] are suppressed by these substitutions. The post-annealing of the Cs doped samples further enhances their superconducting properties; oxygen doping most likely promotes the optimum holes concentration in the superconducting state in the Cs doped samples. These observations have also shown that the free carrier density plays a significant role in the mechanism of superconductivity which was accomplished by synthesizing (Cu0.5Tl0.25Cs0.25)Ba2Ca2Cu3O10−δ superconductors.

Frequency dependent dielectric properties of Cu0.5Tl0.5Ba2Ca2Cu3−yZnyO10−δ (y=, 1.0, 1.5,2.0, 2.5) superconductors

We have studied the dielectric properties of Cu0.5Tl0.5Ba2Ca2Cu3−yZnyO10−δ (y=0, 1.0, 1.5, 2.0, 2.5) superconductors to investigate the effects of Zn atoms and specifically their role in modifying dielectric properties, such as dielectric loss (tan δ) and ac-conductivity (σac). These dielectric properties have been investigated in the normal state of the samples at room temperature and in their superconducting state. From these analyses, we have determined the excess conductivity in the superconducting state (lower energy state) of the system and suggested its possible role in the mechanism of superconductivity. The lower thermal agitation at 79 K may enhance the polarizability of atoms and hence their dielectric constants (ε′, ε″). A comparison with the dielectric properties of Tl2Ba2Ca2Cu2Ox has shown that our Cu0.5Tl0.5Ba2Ca2Cu3−yZnyO10−δ material has lower losses and higher ac-conductivity at 290 and 79 K. The decreased dielectric loss with increased Zn doping strongly suggested that the polarization is most likely arising due to the separation of charges between Cu0.5Tl0.5Ba2O4−δ charge reservoir layer and mobile carriers in the conducting CuO2/ZnO2 planes since the charge reservoir layer has localized charges at Ba+2, Tl+3, and Cu+2 sites, whereas CuO2/ZnO2 planes contain mobile charge carriers, which are displaced from their equilibrium position by an external frequency. A possibility of the use of this material in practical applications is also discussed.

Charge transfer in the living matrix

The living matrix is defined as the continuous molecular fabric of the organism, consisting of fascia, the other connective tissues, extracellular matrices, integrins, cytoskeletons, nuclear matrices and DNA. The extracellular, cellular and nuclear biopolymers or ground substances constitute a body-wide reservoir of charge that can maintain electrical homeostasis and "inflammatory preparedness" throughout the organism. Recent research has emphasized the significance of charge transfer in relation to the scavenging or neutralization of free radicals delivered to sites of injury during and after the oxidative burst. Evidence comes from studies of the role of electrons in mitigating the consequences of inflammation when living systems are connected to the earth (earthing). The phenomenon helps explain how bodywork and movement therapies can facilitate the resolution of acute or chronic injuries, and how patients with inflammatory conditions may "deplete" a therapist during hands-on treatments. It is suggested that barefoot contact with the earth as well as hands-on and hands-off therapies facilitate healing by stimulating the migration of charges into sites of acute or chronic inflammation. One hypothesis to explain the effects of earthing is that charges from the ground substance reservoir prevent "collateral damage" to healthy tissues in the vicinity of an injury. A second hypothesis is that earthing allows electrons to replenish charge in the ground substance reservoirs, making electrons available throughout the body.