Superconductors pressure-induced

Kimura S, Suzuki FI, Maejima T, Mori H, Yamaura J, Kakiuchi T, Sawa H, Moriyama H (2006) Checkerboard-type charge-ordered state of a pressure-induced superconductor, j8-(OTe5 o-DMBEDT-TTF)2PF6. J Am Chem Soc 128 1456-1457... 

Takimiya K, Kodani M, NiUiara N, Aso Y, Otsubo T, Bando Y, Kawamoto T, Mori T (2004) Pressure-induced superconductivity in (MDT-TS)(Aul2)o.44i [MDT-TS = 5H-2-(l,3-diselenol-2-ylidene)-l,3,4,6-tetrathiapentalene] anew organic superconductor possessing an incommensurate anion lattice. Chem Mater 16 5120-5123... 

As in polycrystalline pressed at-(BEDT-TTF)2l3, in pressed samples of Pp-(BEDT-l lF)2l3 a pressure-induced structural phase transition plays an important role. As a consequence of the structural phase transition in pp-(BEDT-TTF)2l3, the superconducting transition temperature is increas. This behavior re-emphasizes that organic superconductors might also be of interest for industrial applications, since polyciystalline materials are easier to use than single crystals. In addition, the discovery of bulk superconductivity in large pressed samples of crystallites of organic metals, of the typical diameter of 1 p.m and below, indicates that the observation of superconductivity in conducting polymers should be possible as well. 

Figure 10.1 shows the corresponding section of the periodic table. Pressure-induced superconductors are marked by a solid triangle. One may notice that instead of La the last rare earth metal Lu appears below Y in the third column. This is different from standard representations of the periodic system. The reason for this exchange will be given in section 3.3. 

It is instructive to compare the transition temperatures of La, Lu and Y with the TcS of the d-transition metals at normal pressure. In fig. 10.16 the Tc s of La, Lu and Y are shown for a pressure of 150 kbar. Such a comparison seems to be justified since the pressure dependence of Tc for the transition metals with ela 4 is very weak (e.g. Smith, 1972). It is seen that the Tc of the 5d-period metals is generally lower than the Tc for the corresponding member in the 4d period. The rule only breaks down toward the end of the 4d period at the element ruthenium.t Interestingly enough, the pair of pressure-induced superconductors, Lu and Y, obeys this rule, since the Tc of Lu is smaller than for Y. Hence Lu behaves as a real 5d-transition metal from a systematic point of view. On the other hand, the Tc of La is an order of magnitude too high to be a plain 5d-band metal. 

Recently, much attention has been paid to the so-called anisotropic gap state superconductor. At T = 0, Cs(0)/yT<- exhibits (T/T ) temperature dependence in the case of gap function with point node, while (T/T<-) temperature dependence is observed in the case of gap function with line node. As low-energy excitation is possible, one can observe the power law T dependence at the low temperature in specific heat for p and d wave superconductors. The measurements of specific heat give extremely fruitful information about the superconducting gap complementary with other measurements, such as NMR. Even if a superconductor is not bulk, zero resistance may be observed when there is a continuous superconducting current path inside the sample. By using specific heat measurements, it is possible to determine whether superconducting behavior occurs in the bulk or not. We note that it is extremely important to check the bulk nature of pressure-induced SC by specific heat measurements imder pressure. 

Tateiwa et al. (2006) studied the pressure-induced superconductor CeIrSis with the non-centrosymmetric tetragonal structure under high pressure by means of the electrical resistivity and ac heat capacity Cac in the same run for the same sample as shown in Figure 33. The critical pressure was... 

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