Low Dimensional Organic Conductors

Organic conductors represent a class of materials, where the Coulomb correlations are strong, and their effect is further enhanced by the low-dimensionality of their crystal and electronic structures. Furthermore, subtle changes in the structure (e.g. a slight rotation of a methyl-group) results in a radical modification of the electronic ground state (e.g. from semiconductor to a superconductor). The fragile balance of the weak and strong interactions gives the whole richness of the physical properties of these compounds. It is characteristic for these materials that the application of hydrostatic pressure strongly alters their properties.

A compound which nicely illustrates the richness of organic compounds is shown below:

 

The (EDT-TTF-CONH2)6[Re6Se8(CN)6] has a kagomé topology where the interplay of interactions and frustration is studied by means of  transport measurements and ESR under temperature and pressure  variations.(Courtesy P. Batail)

 

Sketch of the band structure of a system with kagomé   geometry. One of the pecularities is the Dirac point in the dispersion relation. (Courtesy E. Tutis)

The (EDT-TTF-CONH2)6[Re6Se8(CN)6] has a kagomé topology where the interplay of interactions and frustration is studied by means of transport measurements and Electron Spin Resonance under temperature and pressure  variations. The pecularity of this system is the metallic resistivity with a room temperature value of 1 Ohmcm at 300 K. A low pressure of 0.5 GPa, conterintuitively changes the positive metallic slope into a non-mettalic one.

 

References:
[1] J. Jaćimović, D. Djokić et al., Direct evidencies for metalicity in (EDT-TTF-CONH2)6[Re6Se8(CN)6], in preparation.
[2] B. Nafradi et al., Continuous-wave far-infrared ESR spectrometer for high-pressure measurements, Journal of Magnetic Resonance, 195, 206-210 (2008).
[3] K. Nagy et al., Multifrequency ESR in ET2 MnCu[N(CN)2]4: A radical cation salt with quasi-two-dimensional magnetic layers in a three-dimensional polymeric structure, Physical Review B80, 104407 (2009).