Evidence of the charge-density wave state in polypyrrole nanotubes

Abstract

We present a detailed investigation of the low-frequency dielectric and conductivity properties of conducting polymer nanowires. Our results, obtained by connecting ∼ 10 7 nanowires in parallel, show that these polypyrrole nanowires behave like conventional charge density wave (CDW) materials, in their nonlinear and dynamic response, together with scaling of relaxation time and conductivity. The observed Arrhenius law for both these quantities gives a CDW-gap of 3.5 meV in the regime of temperature (∼ 40 K) in which the CDW state survives. We find good agreement with a theory of weakly pinned CDW, screened by thermally excited carriers across the CDW gap.The identification of polymer nanowires as CDW provides us a model system to investigate charge ordering owing to electrostatic interaction, relevant to a variety of systems from dusty plasma to molecular biology.

Evidence of density waves in single-crystalline nanowires of pyrochlore iridates

“…3D. Similar behaviour for the dielectric relaxation at high temperatures (where there is no switching and no hysteresis) in CDW's (and SDW's) has also been seen earlier in K 0.3 MoO 3 [37,38], (TaSe 4 ) 2 I [39], polypyrole nanotubes [40] and Sr 14 Cu 24 O 41 ladder compounds [41].…”

“…4D, that ω p (T ) ∝ σ 0 (T ). This is a consequence of the longitudinal damped collective charge oscillations in a CDW (polarization built up at the vicinity of the pinning sites), being screened by thermally excited 'normal' quasi-particles [40][41][42]. In fact, we find that ω p /σ 0 ≈ 0.98 × 10 4 Hz Ω cm, and using the relation for the low frequency longitudinal response which yields ω p /σ 0 ≈ 4π vacuum /( 0 − ∞ ) [41], we obtain the relative dielectric constant of YBIO to be 0 ≈ 1.4 × 10 10 ( ∞ 0 ) which is consistent with the numbers obtained from the ac data fit using Eq.…”

Optical Tuning of Wigner Lattice in Conducting Polymer Nanowires

“…In Figure 5b, we have shown the variation of extracted CDW energy‐gap (Δ) obtained from Arrhenius fittings of the τ ( T ) and σ ( T ) values shown in Figure 4. The energy‐gap value obtained without photoexcitation is consistent with earlier value, [ 15 ] and then, the CDW gap reduces linearly with an increase in laser power. An increase in laser power increases doping density ( ρ ) and, hence, WL parameter ( a = 1/ρ ).…”

“…The generalized form of frequency response of a disordered system is given by the following equations [ 15,26–28 ] …”

“…[ 10,11,14 ] The CDW energy‐gap of these PPY nanowires was found to be 3.04 meV from conductivity and dielectric measurements. [ 15 ] Here, we have shown that the effective CDW energy‐gap in these polymer nanowires can be tuned with optical illumination that enhances the charge‐carrier density in the PPY nanowires. The formation of CDW state in the organic materials opens up possibility of having colossal [ 9 ] dielectric constant ( ε ) on the order of 10 5 in the general area of flexible nanodielectric materials (FNDMs) [ 16–18 ] having wide range of applicability.…”