HIGH PRESSURE ELECTRICAL TRANSPORT STUDIES ON SEVERAL ORGANIC CHARGE TRANSFER SALTS (HMTSF-TCNQ, PEIERLS TRANSITION, HMTTF-TCNQ, TMTSF-TCNQ)

This thesis reports on the high pressure electrical transport measurements of three organic one-dimensional charge transfer complexes, HMTSF-TCNQ, HMTTF-TCNQ, and TMTSF-TCNQ. A technique using the diamond anvil cell has been developed which permits the study of electrical resistivity of these brittle single crystals to hydrostatic pressures of 6 GPa and temperatures as low as 30 mK. This has allowed us to explore the behavior of these materials under conditions not previously accessible.;There is also evidence that the charge transfer changes in a systematic manner with increasing pressure for the series of salts TTF-TCNQ, TSF-TCNQ, and TMTSF-TCNQ. This, in turn, has been used to predict a pressure (4 to 5 GPa) at which the charge transfer for HMTSF-TCNQ should reach a gap in the allowed values of the charge transfer. Theory predicts that a discontinuous jump to a value of one should occur at this point and result in an inverse Mott-Hubbard transition. To the accessible hydrostatic pressure of 6 GPa, no definitive evidence is found for such a transition. However, there is Raman scattering data and the occurence of a plateau in the pressure dependent resistivity data (both at a pressure of 4.5 GPa) may indicate the onset of the gap.;Three models are discussed to account for the low temperature behavior of HMTTF-TCNQ and HMTSF-TCNQ, which, for pressures greater than 1.4 GPa, show maximums in their temperature dependent resistance data at 14K and 4K, respectively.