Low-temperature superconductors

Superconductivity The physical state in which all resistance to the flow of direct-current electricity disappears is defined as superconductivity. The Bardeen-Cooper-Schriefer (BCS) theoiy has been reasonably successful in accounting for most of the basic features observed of the superconducting state for low-temperature superconductors (LTS) operating below 23 K. The advent of the ceramic high-temperature superconductors (HTS) by Bednorz and Miller (Z. Phys. B64, 189, 1989) has called for modifications to existing theories which have not been finahzed to date. The massive interest in the new superconductors that can be cooled with liquid nitrogen is just now beginning to make its way into new applications. 

Superconductivity is the loss of all electrical resistance when a substance is cooled below a certain characteristic transition temperature (Ts). It is thought that the low temperatures are required to reduce the effect of the vibrations of the atoms in their crystalline lattice. Superconductivity was first observed in 1911 in mercury, for which Ts = 4 K. Over the years, many other metallic superconductors were identified, some having transition temperatures as high as 23 K. However, low-temperature superconductors need to be cooled with liquid helium, which is very expensive. To use superconducting devices on a large scale, higher transition temperatures would be required. 

Low temperature superconductors (LTS), 23 828-836. See also Low temperature superconductivity LTS Josephson devices... 

See also Josephson entries Low temperature superconductors (LTS) Lube basestocks, dewaxing of, 16 844 Lube oil additives, maleic anhydride derivatives as, 15 512. See also Lubricant (lube) additives Lube oil sulfonates... 

Since alkali metal doped fullerenes are conductors, and low-temperature superconductors, one wonders if the curved polynuclear hydrocarbons might exhibit a similar behavior. 

The appearance of reflections in the diffraction pattern due to anharmonicity of thermal motion is not limited to the diamond-type structures, and is observed, for example, for the A 15-type structure of the low-temperature superconductor V3Si (Borie 1981), and for zinc (Merisalo et al. 1978). It has been described as thermal excitation of reflections, though no excitation in the spectroscopic sense of the word is involved. 

Figure 9 Voltage vs current and onset of resistance above the critical current for (A) "ideal case", (B) premature thermal runaway, (C) damaged sample, and (D) inadequate current transfer length between voltage and current taps as discussed for low temperature superconductors. Ref. 26.

Figure 11 Voltage (in percent of full scale) vs current at 7 Tesla magnetic field for a commercial low temperature superconductor using a voltage criterion of different values to indicate the importance of specifying the criterion. Ref. 30.

All these exciting developments are discussed, but we begin by looking at the properties of the low temperature superconductors that were discovered nearly a century ago. 

Then, from fig.lc it is seen that SC transition onset points Tconset(H)(= Tk(H)) are at the Bloch-Gruneisen curve (dashed curve). On the other hand, such a picture is characteristic for low temperature superconductors described by s-wave BCS theory. From this analogy it may be concluded that in the cuprates the SC order parameter is of s-wave symmetry, also. Moreover, as seen from magnetic phase H-T diagram, the... 

The function of a current lead is to improve the efficiency of liquid helium-cooled superconducting electromagnets. The current is fed to the coils in three stages. The first comprises cooled copper leads (the resistivity of a metal falls with falling temperature) which are joined to the HTS leads, connected in turn to the low temperature superconductor (e.g. Nb3Sn). The heat management is such... 

It is known that many bulk, low-temperature superconductors have dramatically enhanced (sometimes by several orders of magnitude) superconductive transition temperatures, Tc, when they are rendered into a disordered or granular state. Even more striking is the fact that several other systems whose constituents usually have no, or unmeasurably low, Tc s, have been shown to have measurable, and sometimes, even reasonably high... 

The advent of the new low-temperature superconductors, however, has whetted a lot of appetites for the repulsive EDS system, the one that uses superconducting magnets. This system seems to have advantages that could more than offset its higher start-up costs—if and when magnets of the new oxides come into practical use. Larry Johnson listed the benefits ... 

Since 1911, superconductivity research has gone through two stages slow and steady progress (prior 1986) and explosive progress (after 1986). Accordingly, the superconductors are simply classified into low temperature superconductors < 30 K), which... 

The Synthesis and Fabrication of Ceramics for Special Application 261 17.3.10. Preparation of Superconductive Ceramics 17.3.10.1. Low Temperature Superconductors... 

Owing to the large volume of information on low temperature superconductivity already available in the books and excellent reviews, and the high cost of refrigeration required for using the low temperature superconductors, we describe briefly the preparation of a few low temperature superconductors and then focus on the preparation of high temperature superconducting copper oxides. 

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