Far infrared linear response and radio frequency nonlinear response of charge density wave conductors and high T/sub c/ superconductors. [(TaSe/sub 4/)/sub 2/I; La/sub 1. 85/Sr/sub 0. 15/CuO/sub 4/; La/sub 1. 85/Ca/sub 0. 15/CuO/sub 4/; ac-dc mode lock of NbSe/sub 3/]

Technical Report · Wed Jun 01 04:00:00 EDT 1988

OSTI ID:7144804

Sherwin, M S

The far-ir (FIR) linear response of the charge-density-wave (CDW) conductor (TaSe/sub 4/)/sub 2/I and polycrystalline La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ and La/sub 1.85/Ca/sub 0.15/CuO/sub 4/ was measured at 8--350 cm/sup /minus/1/ and 5 to 300K. At low T in (TaSe/sub 4/)/sub 2/I, a mode with giant oscillator strength was found at 38 cm/sup -1/. This giant FIR mode lies between the pinned mode and the Peierls gap. It is suggested that a giant FIR mode distinct from the pinned mode is a common feature of CDW conductors. At low T in the high-T/sub c/ superconductors, a reflectance edge was observed near 2.5k/sub B/T/sub c/. The BCS-like temperature-dependence of the reflectance edge is suggestive of an energy gap. However, a simple model shows that a BCS-like temperature dependence is also consistent with an interpretation of the reflectance edge as a low-frequency plasmon. It is not yet possible to deduce the energy gap from the FIR spectra. The rf nonlinear response of the CDW conductor NbSe/sub 3/ was also measured. In combined rf- and dc-electric fields, mode-locking occurs in NbSe/sub 3/. Complete mode-locking in conventional samples dramatically suppresses sliding CDW conduction fluctuations. Combined rf and dc electric fields on switching NbSe/sub 3/ induced a large amplitude /open quotes/ac switching noise/close quotes/ for rf frequencies <1 MHz, and a period-doubling route to chaos for rf-frequencies >1 MHz. The mode-locking behavior of switching and nonswitching NbSe/sub 3/ is analyzed. A model of CDW elasticity qualitatively reproduces all of the experimental anomalies for dc-, ac- and combined ac- and dc-electric fields. It is suggested that, during mode-locking, the number of degrees of freedom active in CDW transport is reduced.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 7144804
• Report Number(s): LBL-25404; ON: DE88013595
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204 -- Ceramics
Cermets
&amp; Refractories-- Physical Properties
360603* -- Materials-- Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METAL COMPOUNDS
ALTERNATING CURRENT
BCS THEORY
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CHARGE DENSITY
COPPER COMPOUNDS
COPPER OXIDES
CURRENTS
DIRECT CURRENT
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRIC FIELDS
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
FAR INFRARED RADIATION
HALOGEN COMPOUNDS
INFRARED RADIATION
INFRARED SPECTRA
IODINE COMPOUNDS
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
MODE LOCKING
NIOBIUM COMPOUNDS
NIOBIUM SELENIDES
OPTICAL PROPERTIES
OSCILLATOR STRENGTHS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PLASMONS
QUASI PARTICLES
RADIATIONS
RARE EARTH COMPOUNDS
REFLECTIVITY
REFRACTORY METAL COMPOUNDS
RF SYSTEMS
SELENIDES
SELENIUM COMPOUNDS
SPECTRA
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
SUPERCONDUCTIVITY
SURFACE PROPERTIES
TANTALUM COMPOUNDS
TANTALUM SELENIDES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS