High-quality MgB2 films on boron crystals with onset Tc of 41.7 K

The simple binary compound, MgB2, has created enormous excitement, due to its remarkably high T-c (39 K), its exotic electronic and phononic structure, as well as its potential technological application. However, contrary to the initial expectation, worldwide efforts to enhance the T-c of this material by means of chemical doping and applying hydrostatic pressure have failed. Investigations of other diborides or related materials have also resulted in finding of lower T-c's. In this letter we report a slight, but significant enhancement of T-c in MgB2 films grown on boron crystals, which may stem from tensile-type strain. This finding opens up a new possibility for further optimizing T-c in MgB2 and perhaps in related materials. (C) 2001 American Institute of Physics.