Superconductivity phenomena

After the initial attempt to prepare alloy and interstitial superconductors, several ceramists, chemists, and materials scientists joined the group of physicists and metallurgists in search of other superconducting materials. These scientists turned to ternary compounds and to more complex systems. From the mid-60 s to the mid-70 s, several new "inorganic materials" were found to exhibit the superconducting phenomenon. 

Superconductivity occurs as a low temperature phenomenon. So far no superconductivity phenomenon has been found above 100° K. 

Two things, then, had to be done before there could be any major application of the newfound superconducting phenomenon. One was that new materials with higher transition temperatures had to be found. These materials would superconduct in ranges that were considered techni-... 

LCO has been actively studied as a model system for elucidating the nature of the superconduction phenomenon in cuprate systems because of the relative simplicity of its chemical composition and structure. The HTSC studies of the effects of oxygen... 

At the outset, it must be emphasised that the definition of low temperature is arbitrary. A life scientist would normally equate low temperature with subzero Celsius temperature , whereas to a physicist, perhaps studying superconductivity phenomenon, the term signifies temperatures in the neighbourhood of 1 Kelvin. The reason why low temperature is often equated with freezing is probably because the freezing point of ordinary water lies near the centre (measured in degree Celsius) of the temperature range —40 to - -40°C, which we associate with life processes on this planet. 

The superconductivity phenomenon has been satisfactorily explained by means of a rather involved theory. In essence, the superconductive state results from attractive interactions between pairs of conducting electrons the motions of these paired electrons become coordinated such that scattering by thermal vibrations and impurity atoms is... 

This suggestion theoretically explains the metal and intermetallic compound superconductivity phenomenon (J. Bardin, L.N. Cooper and R. Schrieffer, Nobel Prize 1972), discovered earlier by H. Kamerling-Onnes (Nobel Prize, 1913). This phenomenon occurs only at very low temperatures (—20 K). However, superconductivity has been discovered in nonmetalhc, oxide-type chemical compounds with critical points of superconductivity up to ==140 K (in hquid nitrogen region) (so-called high-temperature super conductors, HTSC) (J.G. Bednorz and K.A. Muller, Nobel Prize, 1987). Intensive attempts to synthesize new materials of this kind are in progress. 

Of course, condensed phases also exliibit interesting physical properties such as electronic, magnetic, and mechanical phenomena that are not observed in the gas or liquid phase. Conductivity issues are generally not studied in isolated molecular species, but are actively examined in solids. Recent work in solids has focused on dramatic conductivity changes in superconducting solids. Superconducting solids have resistivities that are identically zero below some transition temperature [1, 9, 10]. These systems caimot be characterized by interactions over a few atomic species. Rather, the phenomenon involves a collective mode characterized by a phase representative of the entire solid. 

Nonstoichiometry is relatively common among mixed metal oxides, in which more than one metal is present. In 1986 it was discovered that certain compounds of this type showed the phenomenon of superconductivity on cooling to about 100 K, their electrical resistance drops to zero (Figure 20.9). A typical formula here is YBa2Cu30 where x varies from 6.5 to 7.2, depending on the method of preparation of the solid. 

The theory foresees the possibility of coulomb blockade phenomenon in such junctions. Averim and Likharev had investigated the conditions of vanishing for the Josephson tunneling and demonstrated the possibility of having normal electrodes in the junction. That is, no superconducting electrodes are necessary, and, therefore, coulomb blockade is possible to observe, in principle, even at room temperature. 

While on the topic on electrical conduction and resistance offered by an electrically conducting medium it is usual to extend to a phenomenon called superconductivity this has now been recognized as having a profound impact on the electrical field. Exciting possibilities exist. The phenomenon is exhibited by certain types of matter and is characterized by two fundamental properties ... 

Stereoisomers Diastereoisomers related to each other by the inversion of any number of chiral centres. Superconduction Conduction of electric current with zero resistance. This phenomenon occurs at liquid helium temperature and has made possible the construction of the very high powered magnets that we see in today s spectrometers. 

Materials that exhibit the phenomenon of superconductivity enter into a new state below a critical temperature Tc (see Table 8.11). 

Superconductivity provides an illustration of the Higgs mechanism. It is the property of materials that show no electrical resistance, usually at low temperatures. Such materials are capable to carry persistent currents. These currents effectively screen out magnetic flux, which is therefore zero in a superconductor (the Meisner effect). Another way of describing the Meisner effect is to say that the photons are effectively massive, as in the Higgs phenomenon. These conclusions can be shown to follow from the Lagrangian (46). In this instance it is sufficient to consider a static situation, i.e. d4 = 0, etc, leading to the Lagrangian... 

The temperature dependence of the pairing gap for the homogeneous, LOFF and DFS superconducting phases shows the phenomenon of reentrance the superconducting state is revived at finite temperatures. There exist two critical temperatures corresponding to phase transitions from the normal to the superconducting state and back as the temperature is increased from zero to finite values. 

The phenomenon of superconductivity was discovered at the beginning of the twentieth century by the Dutch physicist H. Kamerlingh Onnes, during the first attempts to liquefy helium (which at atmospheric pressure boils at 4.2 K). After refining the technique of helium liquefaction, in 1911, Onnes attempted to measure the electrical resistance of metals at these extraordinary low temperatures, and realized that at 4 K the resistance of mercury, as well as that of other metals indicated in Figure 1, became too low to be measured. This change in electrical property became the indication of the new superconductive physical state. The temperature below which materials become superconducting is defined as the critical temperature, Tc. 

As this phenomenon proceeds, it will automatically trigger the inverse of the initial process. The psilocybin, superconductively charged by mind, will harmonically cancel the ESR resonance of the harmine within the brain. The energy of the harmine-psilocybin complex ESR will be absorbed instantly into the matrix of the mushroom. This will cause those molecules metabolizing within the body and bonded to the neural DNA to instantly drop to absolute zero. Clearly this harmine-psilocybin-DNA complex must immediately separate itself from the cellular matrix. There is great danger... 

The same phenomenon that produces harmonic overtones can be used to still the movements of molecules. In very localized areas, perhaps only a few thousand angstroms across, one can produce low temperatures with audio cancellation. Molecular motion is a type of vibration and in the presence of just the right audio input such molecular motion will cease. Operationally speaking, when molecular motion ceases the molecule has reached a temperature of absolute zero, and superconductivity becomes possible. 

After more than ten years of extensive experimental and theoretical studies of the phenomenon of the high Tc superconductivity (HTSC) [1], we still do not know a microscopic mechanism responsible for this phenomenon. Numerous theories of pairing, which lead to high Tc values, are based on models [2-9] and cannot connect a specific chemical composition of HTSC ceramics with the value of the transition temperature Tc. For creating a quantitative theory of the HTSC phenomenon further comparative studies of the electronic structure and their relative properties of SC and non-SC ceramics are needed. In this paper, we confine ourselves to calculations of the electronic structure of the SC yttrium ceramics. 

---