J. Phys. I France
Volume 2, Numéro 1, January 1992
Page(s) 111 - 120
DOI: 10.1051/jp1:1992127
J. Phys. I France 2 (1992) 111-120

Mesoscopic behaviour of the threshold voltage in ultra-small specimens of o-TaS $_{\bf 3}$

S. V. Zaitsev-Zotov1, V. Ya. Pokrovskii1 and J. C. Gill2

1  Institute of Radio Engineering and Electronics, Academy of Sciences of the USSR, Marx Avenue 18, 103907 Moscow, U.S.S.R.
2  H. H. Wills Physics Laboratory, University of Bristol, Royal Fort, Tyndall Avenue, Bristol BS8 1TL, G.B.

(Received 1 August 1991, accepted 17 September 1991)

In very small ( $\sim10^{-14}$ cm 3) specimens of o-TaS 3, the threshold voltage $V_{\rm T}$ for the onset of Frohlich conduction is found to vary irregularly with the temperature T. This behaviour is attributed to rearrangement of the charge-density wave (CDW) with respect to the pinning, as its wave-vector varies with T. It is consistent with weak, but not with strong, pinning by impurities. In sufficiently short ( $<10~\mu$m) specimens the variation of $V_{\rm T}$ relative to its mean $\langle V_{\rm T}\rangle$ is substantially independent of specimen volume, as is expected when the dimensionality of the weak pinning is effectively zero. However, the value $0.15\pm 0.05$ found for $\delta V_{\rm T^/}\langle V_{\rm T}\rangle$, where $\delta V_{\rm T}$ is the rms deviation of $V_{\rm T}$ from $\langle V_{\rm T}\rangle$, is smaller than for a rigid CDW whose coupling to impurities varies sinusoidally with phase. Possible causes of the discrepancy are an approach to strong pinning through local elastic distortion near pinning sites, a departure from zero-dimensional behaviour due to imperfect phase coherence in one transverse direction, and the pinning of widely-separated defects (dislocations) in the CDW structure.

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