Raman scattering from the superconductor niobium diselenide

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1980

OSTI ID:5585142

Sooryakumar, R

At 33 K 2H-NbSe/sub 2/ distorts into an incommensurate charge density wave (CDW) state. The Raman spectrum shows amplitude modes of A and E symmetry near 40 cm/sup -1/ induced by the CDW. At 7 K this material becomes superconducting, and at 2 K additional Raman peaks near 20 cm/sup -1/ were observed, 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, ad 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/sub 2/ that have their CDW transition suppressed by non-magnetic impurities but still retain their superconducting properties.

• Research Organization: Illinois Univ., Urbana (USA)
• OSTI ID: 5585142
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
CHALCOGENIDES
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
INFRARED SPECTRA
NIOBIUM COMPOUNDS
NIOBIUM SELENIDES
PHYSICAL PROPERTIES
RAMAN EFFECT
SELENIDES
SELENIUM COMPOUNDS
SPECTRA
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS