Studies of crystalline organic molecular materials under extreme conditions

Thesis

This thesis describes investigations into the properties of -phase BEDT-TTF charge transfer salts. Charge transfer salts are mainly studied as they are very useful test beds for fundamental physics due to the tuneability of their proper- ties and ground states. The effects of temperature and pressure on such systems have been studied, as these allow access to a wide range of different states and properties. Transport properties of these systems have been studied to obtain information about the Fermi surface and effective mass, and the effect of deuter- ation and also change of pressure media will be discussed. The interaction of infrared radiation with these systems has also been investigated and simultaneous pressure and temperature measurements will be presented, something not greatly studied due to the large technical challenges. The techniques and approaches for overcoming these are also discussed.

Chapter 1 provides an introduction to the organic materials themselves with particular emphasis on the actual compounds studied.

Chapter 2 provides the necessary theoretical background for studying organic charge transfer salts using magnetic quantum oscillations and their infrared re- ectivity.

Chapter 3 covers the experimental techniques and also discusses some of the challenges encountered and their solutions to aid others working in this area. Chapter 4 describes an investigation into the transport properties of - (ET)2Cu(SCN)2 by studying Shubnikov-de Haas oscillations using both deuter- ated and normal samples and using two different pressure media, and comparing it to work done using a third.

Chapter 5 presents an investigation into the pressure dependence of selected phonon modes in -(ET)2Cu(SCN)2 using infrared radiation on a deuterated sam- ple.

Chapter 6 presents what is believed to be the first pressure and temperature dependent infrared study of an organic molecular material. In this case the or- ganic molecular material is d8--(ET)2Cu[N(CN)2]Br, but the techniques should be readily transferable to other materials.

Authors: Biggs, TJ

• Publication date: 2006
• DOI: 10.5287/ora-o8nejovy9
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: piston cylinder cell; phonon modes; high pressure; IR; low temperature; Shubnikov-de Haas; quasi 2D Fermi surface; extended Drude model; Fourier transform spectrometer; TMTSF2PF6; magnetoresistance; diamond anvil pressure cell; charge transfer salts; organic supercondutor; infrared reflectivity; helium gas pressure cell; FFT spectrometer; BEDT-TTF; deuterated kappa phase BEDT-TTF copperthiocyanate
• Subjects: Physical Sciences; Condensed Matter Physics