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/]
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
- Resource Relation:
- Other Information: Thesis (Ph.D.). Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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