Thermal transport of organic molecular crystals (DMe-DCNQI)2Li(1−x)Cux and observation of their super-lattice structure by means of synchrotron radiation X-ray

We have measured the thermal conductivity for organic molecular crystals (DMe-DCNQI)2Li1−xCux (x=0, 0.08, and 0.14) over a wide range of temperatures (4∼250 K). A peak can be seen near ∼20 K. The peak height decreases with decreasing x, and it completely vanishes for x=0 specimen. This peak is created by a crossover between the phonon mean free path that diverges as T−2 and the phonon specific heat that decreases as T3. In addition, we have also succeeded in observing the super-lattice patterns of 4kF and 2kF of (DMe-DCNQI)2Li1−xCux (x=0 and 0.06) accompanied by the Peierls and the spin Peierls transitions by means of the synchrotron radiation X-ray in Tsukuba's Photon Factory.