Microwave Hall effect in a quasi-one-dimensional system: Tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ)

We have measured the Hall mobility at room temperature in three samples of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ), using a Faraday-rotation technique at 9.3 GHz, with the magnetic field normal to the $a-b$ plane of the crystals. The Hall mobility, expressed as the drift mobility in the $a$ direction multiplied by an enhancement factor $\eta$, is observed to be positive, and $\eta$ is measured to be between 5 and 10. We compute this enhancement for a model in which transport across chains is diffusive, while transport along chains is metallic; we adopt a triangular lattice as a model. The phase interference in the presence of a magnetic field arises from two competing processes for charge transfer and leads to a further enhancement of the Hall mobility. The sign of the Hall mobility is interpreted as indicating that the carriers in the TCNQ chain relax more rapidly. Microwave measurements on the conductivity along both the $a$ and $b$ axes are also reported.