Superconductivity critical pressure

In passing, it would be worth mentioning the corresponding situation in condensed matter physics. Magnetism and superconductivity (SC) have been two major concepts in condensed matter physics and their interplay has been repeatedly discussed [14], Very recently some materials have been observed to exhibit the coexistence phase of FM and SC, which properties have not been fully understood yet itinerant electrons are responsible to both phenomena in these materials and one of the important features is both phases cease at the same critical pressure [15]. In our case we shall see somewhat different features, but the similar aspects as well. 

Fig. 9. Correlation of superconducting critical temperature, Tc, vs. N, the number of naturally-occurring stable isotopes. The shaded curves should be considered only as showing the trend and the possibility of separating into two groups. The Tc data are obtained from Properties of Selected Superconductive Materials Natl. Bureau of Stand. Technical Note (1972). The number, N, is obtained from American Institute of Physics Handbook (McGraw-Hill Book Company, 1972. () - superconducting only under high pressure, - radioactive, and - represents more than one Tc for the same element under different physical environment.

Table 12.3 Superconducting Critical Temperatures Tc(Kelvin, at 1 bar) or Tc (Kelvin) at Applied Pressure P(kbar) for Selected Organic, Intercalated Graphite, (SN)X, and Fulleride Superconductors3...

The investigation of transport properties under pressure has shown that the SDW ground state can be suppressed above a critical pressure of 25 kbar [160]. (TMTTF)2Br was thus found to retain a strong metallic character down to 1.2 K. Furthermore, some samples showed a slight drop of the resistance down to a nonzero value near 3.5 K which was ascribed to a possible signature of superconductivity [160]. 

Important further illuminations of the relationships between the structural and transport properties is provided by crystallographic studies under pressure. As yet, very limited information is available. However, from studies of (TMTSF)2PF6, the volume compressibility is estimated to be 0.5% kbar-1 (49). It, therefore, requires 6 kbar to compress (TMTSF)2PF6 into the same volume as (TMTSF)2C104, which is in rough agreement with the critical pressure for superconductivity in the PF6 compound. 

The common pressure dependence of the (TMTSF)2X salts is illustrated in Fig. 20. Below the critical pressure Pc the electronic ground state is an insulator of either the spin density wave type or the anion-assisted Peierls type. Above Pc the ground state is superconducting. The critical pressure Pc varies monotonically with the anion volume discussed above but the transition temperature at ambient pressure and the type of low-pressure ground state depend specifically on the... 

Table 3. Superconducting critical temperatures (/Kelvin, at 1 bar) or (/Kelvin, at applied pressure P/kbar) for organic, intercalated graphite, (SN),, and fulleride superconductors (updated from [71] TCE is 1,1,2-trichloroethylene BCDE is 1-bromo-1,2-dichloroethylene BDCE is 2-bromo-l,l-dichloroethylene DBCE is 1,2-dibromo-1-chloroethylene, TBE is 1,1,2-tribromoethylene).

The critical pressure, at which superconductivity begins (i.e. 7, = OK), is consistent with the Zspi values for these three metals. That is, the Pc of lutetium and yttrium are about the same, but significantly lower than that of scandium (fig. 12a), and 2jpj for yttrium and lutetium are nearly the same and about 3 to 4 times lower than 2spi for scandium. This supports the above analysis that the absence of superconductivity in lutetium, scandium and yttrium is due to spin fluctuations in these metals. 

Coexistence of FM order and superconductivity under pressure The experimental phase diagram of FM collapse under pressure and simultaneous appearance of superconductivity is shown in fig. 43. The critical pressure for disappearance of FM order is pc2 = 16-17 kbar. The SC phase appears between pc = 10 kbar and pc2 = 16 kbar which is also the critical pressure for the FM-PM transition. The critical temperature Tx p) of the jc-phase hits the maximum of Tdp) at the optimum pressure pm = 12.5 kbar. As mentioned before the nature of the order parameter in the jc-phase remains elusive. The coincidence of maximum Tc with vanishing jc-phase order parameter suggests that the collective bosonic excitations of the X-phase which supposedly become soft at pm mediate superconductivity and not quantum critical FM spin fluctuations which are absent due to the persisting large FM... 

Electrical resistivity ps Temperature coefficient Pressure coefficient Electrical resistivity pi Superconducting critical temperature T tit Superconducting critical field Hait Hall coefficient R Thermoelectric coefficient Electronic work function Thermal work function Molar magnetic susceptibility /mol, solid (SI)... 

Electrical resistivity ps Temperature coefficient Pressure coefficient Electrical resistivity pi Resistivity ratio Superconducting critical temperature Tent Superconducting critical field Hctii... 

Superconducting only in thin films or under high pressure in a crystal modification not normally stable. Critical temperatures for those elements from [32, Chapter 12]. 

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. 

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