Detail High-field studies of quantum oscillations in quasi-two-dimensional organic metals Bibliografi Author: Sandhu, Pravindrajit ; Brooks, James S. (Advisor) Topik: PHYSICS; CONDENSED MATTER Bahasa: (EN )    ISBN: 0-599-10151-2     Penerbit: Boston University     Tahun Terbit: 1999     Jenis: Theses - Dissertation Fulltext: 9911913.pdf (0.0B; 0 download) Abstract The organic metals derived from the molecule BEDT-TTF (or ET for short) are important as model systems for the study of low-dimensional phenomena. These materials are molecular crystals with a low Fermi energy (10–100 meV), high mobility (∼104 cm2/Vs) and highly anisotropic Fermi surfaces. We have conducted experimental studies of ( i) the Shubnikov-de Haas (SdH) effect in pulsed fields up to 50 T and (ii) the de Haas-van Alphen (dHvA) effect in steady fields up to 33 T on α − (ET)2 MHg(SCN) 4 (where M = K, Tl and NH4) and κ − (ET)2 Cu (NCS)2. At these high fields, the wave shape as well as the temperature and field-dependence of the oscillations deviate from the behavior predicted by the standard Lifshitz-Kosevich theory. These measurements reveal the limits of the conventional theory of metals and lay the ground-work for extending the theory to low-dimensional systems. We have also performed extended Huckel tight-binding calculations to model the effects of pressure and uniaxial stress on the electronic band structure of κ − (ET)2 KHg (SCN)4 and κ − (ET)2 Cu (NCS)2. The calculated changes in the Fermi surface topology are in excellent agreement with the experimental values determined from SdH measurements. We also report predictions of the effects of uniaxial stress in the transverse directions and discuss the behavior of the effective mass and magnetic breakdown probability. Finally, we have investigated the origin of anomalous magnetic breakdown frequencies in the dHvA effect that are forbidden according to semi-classical theories. We construct a tight-binding model based on the realistic band-structure of the system, which is then solved numerically to compute the field-dependence of the magnetization. This model provides a natural description for the phenomenon of magnetic breakdown between co-existing closed and open Fermi surfaces and accounts for the anomalous frequencies that are observed experimentally. The occurrence of these frequencies in the dHvA signal is found to be a quantum mechanical effect arising from differences in field dependence of the states in the two partially occupied bands near the Fermi level. Opini Anda Klik untuk menuliskan opini Anda tentang koleksi ini! Lihat Sejarah Pengadaan  Konversi Metadata   Kembali

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