Constrain on superconductivity of potassium intercalated phenanthrene

Raman-scattering measurements are performed in K${}_x$phenanthrene with the nominal value $x$ ranging from 0 to 6.0 at room temperature. Based on the Raman spectra, two phases ($x$ = 3.0 and 4.0) are observed among the K${}_x$phenanthrene, and the immediate phase ($x$ = 3.5) is produced. Only the $x$ = 3.0 phase is found to exhibit the superconducting transition at 5 K. The C-C stretching mods are observed to broaden and become disorder in K${}_x$phenanthrene (nominal value $x$ =2.0, 2.5, 6.0), indicating some molecular disorder in the metal intercalation process. This disorder is expected to influence the nonmetallic nature of these materials. The absence of metallic characteristics in those nonsuperconducting phases is provided from the calculated electronic structures based on the local density approximation.