Abstract

The announcement in January 2001 of the discovery of bulk superconductivity in MgB₂ at T_c ~ 39 K [1] has generated a great deal of excitement for several reasons. Most importantly, T_c is higher by nearly a factor of two in comparison to other previously known simple intermetallic superconductors (e.g. Nb₃Ge, T_c ~ 23 K). This discovery has fueled the search for other simple metallic compounds that have a comparable or even higher transition temperature than MgB₂ [2]. Indeed, an important fundamental issue that has resurfaced is determining the upper limit for T_c permitted by conventional phonon-mediated pairing (see also [3] in this regard). It is important in characterizing MgB₂ to employ techniques that probe the bulk low energy electronic states. Far-infrared spectroscopy is especially useful since the gap can be directly observed. Recently, the superconducting gap in MgB₂ has been studied using terahertz time-domain spectroscopy [4].

© 2002 Optical Society of America