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Communication Dans Un Congrès Année : 2013

An experimental approach to some electronic phase transitions in diamond

Résumé

After a short historical summary of the early days of diamond superconductivity, a review of the main features of the growth, doping and physical properties of the "insulating" and metallic states of boron-doped diamond close to the insulator to metal transition will be presented, as well as an experimental determination of the relevant critical exponents of the MIT (1) brought about by chemical doping in micrometer-thick single crystal epilayers. Some characteristics specific to the metallic (normal) state will then be described (2), with various indications of electronic disorder (weak localization of the free holes, plasmon overdamping, mean free path lmfp ≈ 1-5 nm) despite a Valence Band structure which remained apparently unaffected by doping, and a conventional Fermi surface centered on the  point with an average Fermi momentum kF. The presence of disorder was confirmed by a first estimate of the Ioffe-Regel parameter kFlfmp between 5 and 2 which dropped below 1 when the doping decreased closer to the critical doping value. Another chemical doping-induced transition occured at low temperatures, where the metallic normal state becomes superconductor (3), the NST occurring at a critical temperature TC (in the 0.2 to 10 K range) which depends on the growth conditions and on the doping level in a way that is not yet fully understood. Local Scanning Tunnel Spectroscopy, as well as isotopic substitution and optical phonon softening around the  point, all pointed to a conventional BCS behavior (4) with a phonon-mediated pairing mechanism, while H vs T phase diagrams of this type II superconductor yielded coherence lengths in the 10-30 nm range and a slope at TC(0) close to -1 T/K. Fabrication of SQUIDs and SNS junctions based boron-doped and taking advantage of the relatively high critical fields of this superconductor in the dirty limit will then be briefly mentioned. Finally, preliminary results of our recent attempts to bring about similar phase transitions by "electrostatic" double layer doping using ionic liquids will be briefly presented. If time allows, a discussion of the influence of disorder and dimensionality on these transitions, as well as on the possible occurrence of a superconducting to insulator transition in this system (5), will be proposed to the participants of the workshop.
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Dates et versions

hal-00967956 , version 1 (31-03-2014)

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  • HAL Id : hal-00967956 , version 1

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Etienne Bustarret, Jessica Bousquet, C. Marcenat, Shimpei Ono, Thierry Klein. An experimental approach to some electronic phase transitions in diamond. French-German Workshop on tuning superconductivity in doped semiconductors, Sep 2013, Bremen, Germany. ⟨hal-00967956⟩
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