High magnetic field studies of BEDT-TTF organic conductors

This Thesis gives a detailed account of the high magnetic field properties of #alpha#-phase BEDT-TTF charge-transfer salts, with particular focus on the salts #alpha#-(BEDT-TTF)_2KHg(SCN)_4 and #alpha#-(BEDT-TTF)_2TlHg(SCN)_4. The existence of the bulk quantum Hall effect and its eventual destruction in the high-field limit is shown by a variety of experimental means, including magnetoresistance, magnetisation and Hall potential oscillation studies; the latter are based on a new technique specifically developed for this purpose. Chapter 1 introduces the concept of organic conductors and emphasises their potential as prototype systems of reduced dimensionality; in Chapter 2, the necessary physics and experimental techniques for their investigation are outlined. Following model calculations which suggested the possibility of the quantum Hall effect in #alpha#-phase BEDT-TTF salts, measurements of the Hall resistivity were carried out on #alpha#-(BEDT-TTF)_2TlHg(SCN)_4 (described in Chapter 3). These exhibit a series of plateaux and represent the direct observation of the quantum Hall effect in a bulk material. Chapter 4 reports the discovery of an anomalous magnetotransport mode in the interplane resistance of #alpha#-(BEDT-TTF)_2KHg(SCN)_4 which involves the suppression and phase inversion of the Shubnikov-de Haas oscillations at low temperatures. This is interpreted as the action of a two-dimensional chiral Fermi liquid formed from the current-carrying edge states of each quantum Hall layer. Chapter 5 reports the first observation of magnetic breakdown in the high-field phase of #alpha#-(BEDT-TTF)_2KHg(SCN)_4, allowing an improved description of the high-field Fermi surface topology. These results are used to develop a new model for the nested low-field Fermi surface which can explain experimental evidence previously unaccounted for. Studies of the limiting behaviour of Hall potential oscillations in Chapter 6 show that the quantum Hall effect is destroyed at the highest fields. This is suggested to be a consequence of the change in the density of states caused by the onset of magnetic breakdown (also Chapter 7). Finally, in Chapter 7, a comprehensive mapping of the occurrence of the quantum Hall regime in #alpha#-(BEDT-TTF)_2MHg(SCN)_4 (M K, Tl) is carried out as a function of field, temperature, rotation angle and sample quality. This has implications for the interpretation of the high-field phase diagram. (author)Available from British Library Document Supply Centre-DSC:D207389 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo