Heat capacity of mesoscopically inhomogeneous superconductors: theory and applications to MgB2

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

“…In this connection, the failure of the most sophisticated approaches to make any prediction of true or, at least "bare" T c , (provided that the corresponding T c -value is not known a priori) despite hundreds of existing superconductors with varying fascinating properties, forced Phillips [63] to reject all apparently first-principle continuum theories in favor of his own percolative filamentary theory of superconductivity [64][65][66][67] (see also the random attractive Hubbard model studies of superconductivity [68,69] and the analysis of competition between superconductivity and charge density waves studied in the framework of similar scenarios [70][71][72]). We totally agree with such considerations in the sense of the important role of disorder in superconductors with high T c on the verge of crystal lattice instability [73][74][75][76][77][78][79][80][81][82][83]. Nevertheless, it is questionable whether a simple one-parameter "master function" of [63,67] would be able to make quantitative and practically precise predictions of T c .…”

“…Since, instead of one, two or more well-separated superconducting energy gaps, a continuous, sometimes wide, gap distribution is often observed (see results for Nb 3 Sn in [284] and MgB 2 in [285][286][287][288][289]), the original picture of the gap multiplicity in the momentum, k, space loses its beauty, whereas the competing scenario [76,290] of the spatial (r-space) extrinsic or intrinsic gap spread becomes more adequate and predictive [77][78][79]. For the case of cuprates, it has been recently shown experimentally that the spread is really spatial, but corresponds to the pseudogap (CDW gap) rather than its superconducting counterpart, the latter most probably being a single one [291] (see also the discussion in [83] and below).…”

Enhanced paramagnetic limit of the upper critical magnetic field for superconductors with charge-density waves

“…The justification of the two gap ( nd and d ) occurrence is very interesting in the context of the more general problem dealing with the coexistence in the same spatial region of two different superconducting gaps originating from two different pieces of the FS [32,33]. This topic became a burning one because the hypothesis of two-gap superconductivity was claimed to happen in MgB 2 [34,35], though there are sound objections to such a viewpoint [36][37][38][39].…”

Bulk MgB2 Superconducting Materials: Technology, Properties, and Applications

“…Many publications have been devoted to the investigation of the various properties of MgB 2 superconductors and their theoretical considerations (e.g., [ 19 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ] and the references therein). MgB 2 ’s properties are considered more similar to metal than to those of HTS [ 28 ].…”

“…Among the dozens of studied additions to MgB 2 , the ones that are the most effective from the point of view of an increase in the critical current density are carbon, carbon-containing compounds, silicon carbide, titanium, tantalum, zirconium, and compounds containing these metals [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 ]. Relatively recently, in the literature [ …”