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Title:Raman Scattering From the Superconductor Niobium-Diselenide
Author(s):Sooryakumar, Ratnasingham
Department / Program:Physics
Discipline:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Physics, Condensed Matter
Abstract:At 33 K 2H-NbSe(,2) distorts into an incommensurate charge density wave (CDW) state. The Raman spectrum shows amplitude modes of A and E symmetry near 40 cm('-1) induced by the CDW. At 7 K this material becomes superconducting, and at 2 K we observe additional Raman peaks near 20 cm('-1), one each of A and E symmetry. These are close in energy to the energy gap 2(DELTA), as measured by far infrared transmission. The Raman activity of the gap excitations is believed to be caused by coupling to the Raman active CDW phonon modes. Such coupling is shown directly by the changes in the Raman spectra at 2 K due to an applied magnetic field. The zero field results can be explained by a model (by C. A. Balseiro and L. M. Falicov) in which the optical CDW phonon modes couple to superconducting electrons, and the resulting phonon self energy is calculated using the BCS theory for the electrons.
Extensions of the zero field theory to include lifetime broadening effects and consequences of changing the electron-phonon coupling are presented. The results in an external magnetic field are explained in terms of a complex gap parameter.
These results are confirmed by experiments on samples of 2H-NbSe(,2) that have their CDW transition suppressed by non-magnetic impurities but still retain their superconducting properties.
Issue Date:1980
Type:Text
Language:English
Description:164 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
URI:http://hdl.handle.net/2142/77197
Other Identifier(s):(UMI)AAI8108670
Date Available in IDEALS:2015-05-13
Date Deposited:1980


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