Muon spin relaxation as a probe of electron motion in conducting polymers

Abstract

The use of implanted muons to probe the dynamics of electronic excitations in conducting polymers is reviewed. Early work on polyacetylene showed evidence for mobile solitons performing one-dimensional diffusion in the trans isomer and localized spins in the cis isomer. Subsequent muon studies on a range of conducting polymers have shown evidence for mobile polaronic excitations and microscopic transport properties for these polarons have been derived from the measurements. A theoretical framework was developed by Risch and Kehr to describe the intermittent hyperfine coupling between a static muon and an electron diffusing randomly through a chain of sites. This theory predicts a specific form for both the muon spin relaxation function and the field dependence of the relaxation rate. The experimental data are found to be described well by this model. Intrachain diffusion rates can be extracted from the data; in several cases an interchain diffusion rate can also be measured. The anisotropy of diffusion rates can be as high as 104 at low temperatures, reducing typically to 102 or less at room temperature. The importance of molecular vibrational modes in controlling the electronic motion in the polymer has been shown.

Enhancement of Electron Movement in Cytochrome c protein with Water Hydration

“…In order to make further clear, let us take a schematic diagram as shown in Fig. 4 [15,16] where D ⊥ represents inter-chain diffusion rate of electron. Inter-molecular and intra-molecular diffusion of electron can be considered as three-dimensional diffusion and one-dimensional transfer of electron in such macromolecules, respectively.…”

“…We can clearly see that cut off field (B c ) is higher for wet sample than that of dry sample. Using temporal proposal by Pratt et al [15], the inter-chain diffusion rate (D^) can be expressed as a function of cut off field ad, D^= γ e B c where γ e is gyromatnetic ratio. From Fig.…”

Probing Quantum Critical Spin Liquids with μSR

“…In a 1D system this takes a characteristic B LF -1/2 dependence. For a 2D system the spectral density of fluctuations corresponding to diffusion takes a different form, with S() scaling approximately as log(D 2D /) where D 2D is the 2D diffusion rate for the spins [8][9][10]. A more accurate representation of S() is obtained from Fourier transformation of the spin autocorrelation function for a 2D random walk [8].…”

Importance of intramolecular electron spin relaxation in small molecule semiconductors

“…The muons can either thermalize as diamagnetic positively charged species or form a hydrogenlike muonium. [18][19][20][21] Due to unsaturated bonds that are present in the molecules, this muonium can react with a molecule creating a paramagnetic molecule. In a "longitudinal field" experiment a magnetic field is applied parallel to the muon's initial spin direction.…”