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

Abstract

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.

A new type of charge-density-wave pinning in orthorhombic TaS$_3$ crystals with quenching defects

“…A similar picture was observed on samples with weak pinning caused by growth point defects arising under nonideal synthesis conditions [13] or isoelectronic impurities in o-TaS 3 alloys with Nb [14]. In the case of a non-uniform distribution of weak pinning centers created by In diffusion into the contact area [19], the rate of suppression of the maximum d ln R/d(1/T ) was also greater than in our (also not completely uniform) case.…”

“…An activation dependence of the In diffusion coefficient in NbSe 3 was found. In [19] In diffusion into the contact region of the o-TaS 3 sample led to changes in the photoconductance spectra, a decrease in the value of T P (∆T P ≈ 5 K) and an increase in E T about 20 %. Fig.…”

“…It was suggested that the different degree of stability of the properties of the grown crystals is due to the different content of quenching defects in them, and the effect of weakening the CDW pinning is due to their ability to move and exit the sample. This assumption is based on the analogy with the results of [18,19], devoted to the study of the kinetics of In impurities and its influence on the transport properties of the Peierls conductors 3) . In both papers, In atoms intercalated into the crystal from contacts upon heating in an inert gas flow, and then diffused into the sample.…”

“…1 along with all the above-mentioned cases of local pinning and samples with small S. And again, the change in HW HM in the case of the non-local pinning is much weaker than the local pinning cases. In [12] a considerable smearing of the Peierls transition due to irradiation of the sample was accompanied by the strong pinning [13] strong pinning [12] weak pinning [14] weak pinning [13] weak non-uniform pinning [19] weak pinning, finite size effect [26] HWHM(K) 200 220…”