Spatial mapping of mobility and density of the conduction electrons in (FA)2PF6

Current density imaging by pulsed conduction electron spin resonance

In analogy with Nuclear MRI, the ESR signal phase shift of conduction electrons moving in electrical currents along controlled magnetic field gradients can be used to generate spatial electronic current density maps. First two-dimensional images of the current density distribution in quasi-one-dimensional organic conductors are presented.

Conduction-electron drift velocity measurement via electron spin resonance

In analogy with NMR, motion induced phase shift of pulsed ESR signals enables in principle the direct detection of electron drift velocity or electronic current, respectively. Overcoming the difficulties with additional magnetic field gradients induced by the current itself, we succeeded in demonstrating the detection of electron flow via ESR. Measuring the electron drift velocity in the organic conductor (fluoranthene)2PF6 the microscopic Ohmic law could be observed in a current range of more than +/-0.25 A.

Zebralike patterned organic conductor with periodic modulation of mobility and Peierls transition

We manipulated the defect concentration in a (fluoranthene)2PF6 crystal by proton irradiation through a periodic grid, resulting in a striped defect pattern. Spatially resolved pulsed X-band ESR analysis was used to quantify the resulting local defect concentrations, spin diffusion coefficients, and electron spin concentrations. The temperature dependence of the data proves that spin diffusion coefficient and Peierls transition can be tailored in a controlled way via the defect concentrations.

Functional and Highly Spatially Resolved ESR Imaging

Electron spin resonance imaging is a technique using similar principles to the established nuclear magnetic resonance imaging; however, the very fast electron-spin relaxation time constants of the former are an experimental challenge. In order to obtain T2-weighted as well as functional images spatially resolved in the micrometer range, we use temperature-dependent pulsed X-band ESR and the back-projection reconstruction method. We present here recent results of our imaging project focussing on quasi one-dimensional organic conductors, where even pulsed conduction electron-spin resonance is possible.

2-d ESR diffusion coefficient imaging with the projection reconstruction method

The static gradient spin echo (SGSE) of the conduction electron spins in a quasi-one dimensional organic conductor is analyzed by simulation and for a microstructured (fluoranthene)(2)PF(6) single crystal. It is shown that useful two-dimensional magnetic resonance images of the diffusion coefficient (mobility) D can be obtained from pixel-by-pixel analysis of the signal decay with pulse separation tau, adopting the projection reconstruction (PR) method for signal generation.

Combined k-space q-space pulsed ESR imaging: mapping of restricted diffusion in (FA)(2)PF(6)

A (FA)(2)PF(6) crystal from the family of the quasi-one-dimensional organic conductors was selectively damaged by a beam of Helium ions with a slitted mask placed in the beam's trajectory. Pulsed ESR density weighted imaging of the damaged crystal revealed the appearance of regions where the ESR signal was absent. The one-dimensional motion of the charge carriers was thus restricted to the undamaged sections. The local charge carrier spin dynamics in these restricted areas was probed by combined k-space q-space pulsed ESR imaging. The local expected appearance of the restricted pulsed gradient spin echo (PGSE) "diffusive diffraction" effect is shown. The position of the diffraction minima is compatible with the density imaging results.