Structural Transition in the Quasi‐Two‐Dimensional Organic Superconductor κ‐(ET)₂Cu[N(CN)₂]Br Studied by¹³C MAS NMR

What influence does the non-centrosymmetric anion ordering have on the low-temperature electronic properties of superconducting charge transfer salts such as the title compound? To answer this question, high resolution 13C magic angle spinning (MAS) NMR measurements were made in the temperature range 170–300 K. Following determination of the spin densities on central carbon sites at room temperature, evidence is presented for a possible small monoclinic distortion at low temperatures and an incommensurate transition at 170 K.