Impurity band Mott insulators: a new route to highT_csuperconductivity

Abstract

Last century witnessed the birth of semiconductor electronics and nanotechnology. The physics behind these revolutionary developments is certain quantum mechanical behaviour of 'impurity state electrons' in crystalline 'band insulators', such as Si, Ge, GaAs and GaN, arising from intentionally added (doped) impurities. The present article proposes that certain collective quantum behaviour of these impurity state electrons, arising from Coulomb repulsions, could lead to superconductivity in a parent band insulator, in a way not suspected before. Impurity band resonating valence bond theory of superconductivity in boron doped diamond, recently proposed by us, suggests possibility of superconductivity emerging from impurity band Mott insulators. We use certain key ideas and insights from the field of high-temperature superconductivity in cuprates and organics. Our suggestion also offers new possibilities in the field of semiconductor electronics and nanotechnology. The current level of sophistication in solid state technology and combinatorial materials science is very well capable of realizing our proposal and discover new superconductors.

Superconductivity in covalent semiconductors

“…In practice, the opposite happens -temperature is fixed and the tip is moved while measuring the I-V curves. Such maps might reveal spatial differences [24] interpreted as spatial inhomogeneity of superconductivity [25]. However, they could simply reflect spatial variation of the surface contamination, as no assessment of the latter is usually provided.…”

“…1) suggests that there are such forms. This "excess boron" was tentatively assigned to interstitial boron [25] and complexes of substitutional boron with hydrogen or another boron (B-H or B-B) [44]. Boron interstitial related complexes were indeed identified in electron-irradiated, lightly boron-doped diamond [45], but not in heavily doped as-grown diamond.…”

“…The first one is the resonating valence bond model by G. Baskaran, based on the Mott theory of insulator-metal transition and transport through an impurity band. It however requires relatively low carrier density and is therefore hardly applicable to the superconducting diamond samples studied so far, as recently admitted by the author himself [25]. The second model by J. J.…”

“…The last model is the phonon-mediated pairing mechanism by Bardeen, Cooper and Schrieffer (BCS), advocated by M. Cardona and others [43]. Recent detailed measurements of T shift upon 11 B/ 10 B or 13 C/ 12 C substitutions [27] might favor the BCS model; however, both Mares [22] and Baskaran [25] argue this result is inconclusive. Fig.…”

Superconductivity in Nanostructured Boron-doped Diamond and its Application to Device Fabrication

“…At present there are three competing theories to explain its origin but any serious experimental evidence is missing to date. The three competing theories are: i) phonon mediated pairing-driven conventional BCS theory, 14 ii) correlated impurity band theory 15 and iii) weak localization of spin-flipdriven hole pairs close to the Fermi level. 16 Some recent studies on the isotopic shift of the transition temperature upon isotopic substitution of boron and carbon atoms point to conventional BCS theory, 17 but more experimental studies are required before a conclusion on the origin of superconductivity can be drawn.…”