Photoconduction in CDW conductors

Minakova

2015

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The results of photoconduction study of the Peierls conductors are reviewed. The studied materials are quasi-onedimensional conductors with the charge-density wave: K 0.3 MoO 3 , both monoclinic and orthorhombic TaS 3 and also a semiconducting phase of NbS 3 (phase I). Experimental methods, relaxation times, effects of illumination on linear and nonlinear charge transport, the electric-field effect on photoconduction and results of the spectral studies are described. We demonstrate, in particular, that a simple model of modulated energy gap slightly smoothed by fluctuations fits the available spectral data fairly well. The level of the fluctuations is surprisingly small and does not exceed a few percent of the optical energy gap value.

“…5 shows the best fit of the experimental results (Ref. [9]) with the 1D+2 DOS similar to one shown in Fig. 4(c).…”

Section: Fundamental Edge and Van Hove Singularitiessupporting

confidence: 66%

Section: Experimental Methodsmentioning

confidence: 99%

Section: Impurities Defects and Various Excitationsmentioning

confidence: 99%

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Charge-density waves physics revealed by photoconduction

Minakova

2015

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“…One possibility is the imperfect nesting [10,11] resulting in order parameter modulation in k-space and indirect gap 2∆ i with phonon-assisted transitions at 2∆ i < ω < 2∆ eV. The other contribution may arise from self-trapped states typical for q-1D systems [12]. In addition, Tüttö and Zawadowski obtained [3] that impurities in q-1D conductor in the weak-pinning limit would cause the region inside the gap to be filled by states if the distance between impurities is smaller than CDW amplitude coherence length ξ 0 .…”

Section: Photoconduction Spectramentioning

confidence: 99%

Indium doping-induced change in the photoconduction spectra of o-TaS3

Yakimov

2015

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Impurities and defects are known to affect the properties of the charge density wave (CDW) state but the influence of impurities on the density of states inside the Peierls gap remains largely unexplored. Here we present an experimental study of the effect of indium impurities on photoconduction spectra of CDW compound orthorhombic TaS 3 . We use the temperature diffusion method to introduce indium into a sample from preliminary attached In contacts. The concentration of In after 23 hours of diffusion is found to be nonuniform and strongly dependent on the distance to the contacts. The diffusion affects the spectral range 0.15-0.25 eV, increasing the photoconduction amplitude linearly with diffusion time. The optical gap value obtained from the measurements is 2∆ = 0.25 eV and the tail of states below 2∆ is associated with the impurities in agreement with the Tüttö-Zawadowski theory. Diffusion-induced modification of current-voltage characteristics and decrease of the Peierls temperature are also observed. Neither changes in photoconduction spectra nor in the Peierls transition temperature of the control sample with Au contacts are found.

“…The common photoconduction features of m-TaS 3 and o-TaS 3 [8,12] are the following: 1) Photoconduction is detected only at T T P /2.…”

Section: Temperature Dependences Of the Ohmic Conductance And Of The mentioning

confidence: 99%

Photoconduction in the Peierls conductor monoclinic TaS3

Minakova

2015

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Photoconduction in the monoclinic phase of quasi-one-dimensional conductor TaS 3 has been observed at T < 70 K. It was studied jointly with low-temperature ohmic and non-linear dark conduction. The strong sample quality dependence of both photoconduction and dark conduction at this temperature region has been observed. Together with a similarity of the main features of the photoconduction characteristic of both monoclinic (m-TaS 3 ) and orthorhombic (o-TaS 3 ) samples the following new peculiarities of photoconduction in m-TaS 3 were found: 1) the dependence of the activation energy of photoconduction on temperature, T , 2) the change of the recombination mechanism from the linear type to the collisional one at low T with a sample quality growth, 3) the existence of a fine structure of the electric-field dependence of photoconduction. Spectral study gives the Peierls energy gap value 2∆ * = 0.18 eV.