Top PDF Plaquette Valence Bond Theory of Cuprate High Temperature Superconductivity

Plaquette Valence Bond Theory of Cuprate High Temperature Superconductivity

Plaquette Valence Bond Theory of Cuprate High Temperature Superconductivity

After 30 years history of extremely intensive experi- mental [1–4] and theoretical [5–10] studies of the high- temperature superconductivity (HTSC) in copper oxides we are still far from understanding the basic mechanism of this fascinating phenomenon. Taking into account the enormous number of researchers involved in this field, one can assume that almost all possible ideas were ex- pressed and that the main problem is just to select the basic simple concepts from the pile of available theo- retical results. The most ambitious attempt was made by P. W. Anderson who emphasized with his resonat- ing valence bond (RVB) theory the crucial importance of strong electron correlations, the tendency to singlet
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Macroscopic Quantum System, Highly Correlated Electron State, and High Temperature Superconductivity in Iron Pnictides

Macroscopic Quantum System, Highly Correlated Electron State, and High Temperature Superconductivity in Iron Pnictides

The qualitative model of the high-temperature superconductivity suggested earlier for cuprates and based on the idea that the superconductivity is associated with delocalized π bonding be- tween ions is not only confirmed by experimental data on iron pnictides but is also improved. It is shown that the FeAs layer state is similar to that of a macroscopic quantum system characterized by a sandwich-type charge distribution in which negatively charged planes are two-dimensional electron crystals of pairs and positively charged planes are formed by positively charged ions. Superconductivity in such a system is accomplished by a two-dimensional Wigner crystal of bo- sons condensed into one and the same state. The crystal occupies a middle position with respect to charged planes in the sandwich structure, which leads to mutual compensation of all its inte- ractions with all charged planes. The model can prove useful for development of the theory of superconductivity taking into consideration the highly correlated state of all valence electrons that manifests itself in formation of electron crystals with strong Coulomb interactions between them.
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Theory and Applications of High Temperature Superconductor

Theory and Applications of High Temperature Superconductor

and Ch atoms as compared to Fe atoms, they pack themselves in edge- sharing tetrahedral. But in a cuprate superconductor, the size difference between the copper and oxygen atom is small so cuprate leads to corner- sharing octahedral packing. Due to the tetrahedral configuration, the Fe atoms in Fe based superconductor are closer to each other than the Cu atoms are in a cuprate superconductors. Both Fe and Cu occupy the same row of the periodic table. Their valence electrons occupy 3d orbital. But because of the Fe atoms closer packing, all five Fe 3d orbital contribute charge carriers. In cuprates, only Cu 3d orbital contributes. The Fe based superconductors and cuprates are different in another respect: chemical substitution. In the 1111 family, dopants can be inserted at any of four ionic positions, even into the iron layer. But the chemical manipulation of copper layer in the cuprates proved severely detrimental to their superconductivity.
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Right Hemisphere Theory and The Valence Theory: A Closer Look at How Gender Infleunces Emotional Processing

Right Hemisphere Theory and The Valence Theory: A Closer Look at How Gender Infleunces Emotional Processing

interference effect by using a block design which is a common methodology in EST studies. As opposed to our study, which presented words randomly, those that use the block methodology present the words in groups according to their valence (i.e. emotional or neutral). More recently, Phaf & Kan (2007) conducted a meta-analysis to further investigate slow interference as it pertains to the EST. Similar to McKenna & Sharma (2004) they also they also found support for this effect, in particular, this effect was strongest in studies that used a block design. Despite these results, many EST studies continue to prefer using blocked presentations because they have been found to produce greater interference effect for emotional words relative to random presentations (Holle & Neely, 1997). On the other hand, it should be emphasised that several studies have successfully used a random presentation format to demonstrate an interference effect (Foa, Feske, Murdock, Kozak & McCarthy, 1991; Mogg et al., 2000; Owens,
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Quantum Statistical Theory of Superconductivity in MgB2

Quantum Statistical Theory of Superconductivity in MgB2

We now extend our theory to include elementary fermions (electron, fluxon) as members of the c-fermion set. We can then treat the 2D superconductivity and the QHE in a unified manner. The c-boson containing one electron and one fluxon can be used to describe the principal QHE. Important pairings and effects are listed below: a) a pair of conduction electrons, superconductivity; b) c-fermions and fluxon, QHE; c) a pair of like- charge conduction electrons with two fluxons, QHE in graphene.

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Molecular-field Molecular-field Study on Sn Substituted Yttrium Iron Garnet

Molecular-field Molecular-field Study on Sn Substituted Yttrium Iron Garnet

Single-phase YIG-Ca-Sn and YIG-Sn samples were prepared by using sol-gel technique. Crystal structure and magnetization of the samples were studied experimentally. The temperature dependence of the saturation magnetization of the samples was well described using molecular-field theory. Models for the distribution and valence states of the cations in these materials were derived from this study. In the molecular-field calculations, Sn atoms were assumed to reside in the d sites in both samples. In order to explain the high value of magnetization and low Curie temperature of the for YIG-Sn sample, an amount of Fe 2+ equal to that of Sn 4+ was evoked in the a sublattice.
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Computational Electromagnetics: the Past, the Present and the Future

Computational Electromagnetics: the Past, the Present and the Future

Design has to be put in the context of general trends in optimisation methods The role of multi-objective tasks is increasing as practical designs often involve conflicting requirements. Such problems may be converted into single-objective tasks with a priori application of knowledge or imposition of a decision (e.g. weighting factors), but it is argued that information can easily be lost in the process. Instead the application of Pareto Optimal Front (POF) approximation is advocated. The mathematical theory of Pareto optimisation may be somewhat complicated [44], but some basic definitions and properties are easily explained using a special case of two objective functions being minimised as shown in Fig. 13.
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A Simplified Approach to the Problems of Room Temperature Superconductivity

A Simplified Approach to the Problems of Room Temperature Superconductivity

If we consider pure carbyne chain the calculations show that carbyne has maximal intrinsic SOC, which reaches 5 meV [5]. It is more difficult to determine the SOC close to hydrogenated end of chain. Various simu- lations have shown that the terminal hydrogen atoms are positively charged, but exact charge value is unknown. Basing on data about hydrogenated graphene we can assume that the enhancement also may reach 2 - 3 orders. In this case we get SOC around 1 eV close to the end of chain, what is much more than energy of the thermal oscillations at room temperature. This is more than enough to design room-temperature TI. However single chain is almost useless: initially having quasi-1d conductor, we get geometrically quasi-0-dimensional superconduct- ing area on it. Way out of the difficulty is to use an ensemble of chains. But to assemble the proper “construction” at this level of scale is possible only with the help of self-assembling.
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Valence Illustration for Large Structure: A Fast Empritical Approach Based on Bond-Valence Method

Valence Illustration for Large Structure: A Fast Empritical Approach Based on Bond-Valence Method

Abstract: Modelling of large structures by using the quantum-mechanical approach is still not accessible, especially for many heavy atoms complexes, as these tasks require vast computational resources that are not often available. This article introduces a procedure for modelling of large structures using a structural approach usually referred to as a bond-valence method. This empirical method minimalizes the computation costs and facilitates the contruction of complex 3D images of thermally dependent electron density even for very large periodic structures. This method also provides a convenient way to visualize the carrier density, defect locations, and valence dynamics under thermal fluctuation.
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Reciprocity Relation between the Mass Constituents of the Universe and Hardy’s Quantum Entanglement Probability

Reciprocity Relation between the Mass Constituents of the Universe and Hardy’s Quantum Entanglement Probability

Ω = − + (about 73.31%). (6) Such coincidence means that both mass constituents should not be considered independent of each other. Mathematically, reciprocity is found, for instance, if one considers volume in comparison to surface, or particles in comparison to waves. Relevant topological arguments from the set theory are summarized by El Naschie [11]. However, the denominator factor of 100 in Equation (5) may be interpreted as a coupling term equal to the normed dimensions of the universe [12].

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Effective low-energy theory of superconductivity in carbon nanotube ropes

Effective low-energy theory of superconductivity in carbon nanotube ropes

In the 1D situation encountered here, superconductiv- ity can be destroyed by phase slips [14]. A phase slip (PS) can be visualized as a process in which fluctuations locally destroy the amplitude of the superconducting or- der parameter, which effectively disconnects the 1D su- perconductor into two parts. Simultaneously, the phase, being defined only up to 2π, is allowed to “slip” by 2π across the region where the amplitude vanishes. This process then leads to finite dissipation in the supercon- ducting wire via the Josephson effect. Depending on tem- perature, phase slips can be produced either by thermal or by quantum fluctuations. In the first case, which is commonly realized very near the critical temperature, we have a thermally activated phase slip (TAPS). At lower temperature, the quantum tunneling mechanism domi- nates, and one speaks of a quantum phase slip (QPS).
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Low temperature semiconductor superconductor junctions & their optimisation

Low temperature semiconductor superconductor junctions & their optimisation

As the major cooling results of this experiment were concluded from the extrapolated region of the electron temperature calibration, there was some initial doubt regarding their veracity. I therefore applied an alternative, non-empirical calibration method that is common in experiments dealing with low temperature N-I-S devices [81]. As discussed in section 1.5.3, the experimental current-voltage data from the cooling junction is superimposed on a series of theoretical isotherm curves generated from equation 1.10 using the parameters of the device under test. Each point of intersection between the experimental data and an isotherm thus yields the electronic temperature in the semiconductor island at that particular bias. Figure 7.3 illustrates the differences between the empirical and theoretical methods of temperature. Using these two methods I was able to confirm the initial conclusions, with the calibrations agreeing to within 5 mK.
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Characterization of near-room-temperature superconductivity in yttrium superhydrides

Characterization of near-room-temperature superconductivity in yttrium superhydrides

as unconventional superconductor which is nicely matched the location of other NRT superhydrides in the Uemura plot. It is also shown the thermodynamic fluctuations of the order parameter amplitude is dominating factor which limits superconducting transition temperature in superhydrides of yttrium.

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STUDY OF DE-GENNES FACTOR AND EFFECT OF EXTERNAL MAGNETIC FIELD ON SC AND AFM IN BOROCARBIDE SUPERCONDUCTORS

STUDY OF DE-GENNES FACTOR AND EFFECT OF EXTERNAL MAGNETIC FIELD ON SC AND AFM IN BOROCARBIDE SUPERCONDUCTORS

Fig.1) vs. de Gennes factor. The phase diagram shows in Fig.2 is almost linear. Our theoretical study agrees well with similar type of de Gennes scaling which was reported earlier by Machida et al.[10]. Here, the enhancement of antiferromagnetism and the supression of superconductivity are governed by exchange interaction of conduction electrons and rare earth f- electrons.

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Superconductivity and Superfluidity Part I: The development of the science of superconductivity and superfluidity in the 20th century

Superconductivity and Superfluidity Part I: The development of the science of superconductivity and superfluidity in the 20th century

The great contribution to the development of the science of superconductors was made by brothers Fritz and Heinz London. They offered its first phenomenological theory. Before the discovery of the absolute diamagnetism of superconductors, it was thought that superconductors are absolute conductors, or in other words, just metals with zero resistance. At a first glance, there is no particulary difference in these definitions. If we consider a perfect conductor in a magnetic field, the current will be induced onto its surface and will extrude the field, i.e. diamagnetism will manifest itself. But if at first we magnetize the sample by placing it in the field, then it will be cooled, diamagnetism should not occur. However, in accordance with the Meissner-Ochsenfeld effect, the result should not depend on the sequence of the events. Inside superconductors the resistance is always:
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Correlated Electron Systems and High Temperature Superconductivity

Correlated Electron Systems and High Temperature Superconductivity

indeed enhanced and is increased as the system size increases in the 2D Hubbard model. The enhancement ratio increases almost linearly  L as the system size is increased, which is an indication of the existence of superconductivity. Our criterion is that when the en- hancement ratio as a function of the system size L is proportional to a certain power of L , superconductivity will be developed. This ratio depends on U and is reduced as U is decreased. The dependence on the band filling shows a dome structure as a function of the electron density. In the 10 10  system, the ratio is greater than 1 in the range 0.3  n e  0.9 . Let us also mention on superconductivity at half-filling. Our results indicates the absence of superconductivity in the half-filling case because there is no enhancement of pair correlation functions
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Superconductivity in ropes of carbon nanotubes

Superconductivity in ropes of carbon nanotubes

and long mean free path [9]. These properties make them long sought-after realizations of 1D conductors. In one dimension, repulsive electron-electron interactions lead to an exotic correlated electronic state, the Luttinger liquid (LL) [10, 11]. In a LL, collective plasmon- like excitations give rise to anomalies in the single-particle density of states, and long-range order cannot survive even at zero temperature. The low-energy theory of SWNTs [12, 13] predicts a metallic SWNT to constitute a realization of a four-channel LL, with channel index a = c+, c − , s+, s − corresponding to total/relative charge/spin degrees of freedom. These arise due to the K − K ′ degeneracy and the electronic spin. The interaction strength
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A Review on Cuprate Based Superconducting Materials Including Characteristics and Applications

A Review on Cuprate Based Superconducting Materials Including Characteristics and Applications

To protect the transmission or distribution electric systems from outages caused by fault currents a special device – a fault current limiter (FCL) is installed in the transmission grid. A fault current occurs in the event of a short circuit caused by lightning, accidental contact between the lines or the ground, etc. In this case, the power current flowing through a local network can increase enormously damaging electrical equipment. Conventional line reactors widely used as FCLs have high AC losses and can produce voltage drop in the grid in the case of a fault current. The HTS technology offers a much better solution to the fault current problem and represents one of the most successful applications of the cuprate superconductors. In the HTS FCL, a basic property of a superconductor is used, which is a transition from the zero resistance superconducting state to the normal resistive state when the electric current exceeds the material’s critical
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Scanning Tunneling Spectroscopy Studies of High Temperature Cuprate Superconductors

Scanning Tunneling Spectroscopy Studies of High Temperature Cuprate Superconductors

In the lab, I have been very fortunate to have “The Magician” Nils as a colleague and, more importantly, a great friend. Not only that the scanning tunneling microscope built for this thesis research would not have been realized without his expertise in the arts of machining, but also that I would not have learned so much more about life beyond physics. I am also thankful to Ted, for the interesting exchange of ideas, information and knowledge in science and culture; to Andy, for introducing me to both the techniques of cryogenic experiments and the American lifestyle outside the lab; to Andrew, for the fruitful collaboration I enjoyed during our endeavor into the phenomenological theory and for his great help with the experiments; to Cameron, for feeding me well with all sorts of homemade pastries and for sharing his passion toward the arts of cooking; to Slobodan and Marcus, for the witty discussions that show their terrific sense of dark humor; and to every Yeh group member for the friendship and support.
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Orbital Approach to High Temperature Superconductivity

Orbital Approach to High Temperature Superconductivity

It has been proposed that a classical coordinate covalent bond, CCB, is the basic bonding responsible for superconductivity [3]. A CCB contains 2 paired electron spins (a Lewis pair ) supported by an electron pair donor (EPD) species, and an electron pair acceptor (EPA) species. When the residual electrostatic at- traction of the EPD species equals the residual electrostatic attraction of the EPA species the bonded Lewis pair is effectively suspended in free space.

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