Magneto-optical studies of high-temperature superconductors using Sagnac interferometry
- While discovered in 1986, high-temperature superconductivity in cuprates remains theoretically not understood yet. In this thesis I will describe new physical properties of the normal state properties of cuprates from which the superconducting state evolves. In particular we study the symmetries of the normal state because of the central role symmetries play in any natural phenomena. We use a high-resolution zero-area loop Sagnac interferometer to measure magneto-optic Kerr effect (P-MOKE) on high-temperature superconductors. In this measurement the polarization of normal-incidence-light reflected from the surface of a material will be analyzed against the polarization of the initial beam. Non-zero Kerr effect has usually been observed in association with magnetism, and thus interpreted as a signature for broken time-reversal symmetry. However, it was recently recognized that gyrotropic materials, that is, materials that breaks spatial inversion and all mirror symmetries can also exhibit P-MOKE signal in the presence of absorption. Our results for single crystals of several high-temperature superconductors provide further evidence to the uniqueness of the electronic state in the normal state of the cuprates. First we show that the inability to train the Kerr signal with an applied magnetic field while cooling the sample through the Kerr effect onset temperature. Second we show that when measured on parallel, opposite surfaces of the same sample, the Kerr signal shows the same onset temperature, similar magnitude and the same sign. Arguing that for all measured crystals the Kerr signal also coincides with some form of charge ordering, we propose that the high-temperature superconductors posses a ``gyrotropic'' order in the normal state.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Applied Physics.
|Statement of responsibility
|Submitted to the Department of Applied Physics.
|Thesis (Ph.D.)--Stanford University, 2013.
- © 2013 by Hovnatan Karapetyan
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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