Conduction-Electron Drift Velocity Measurement via Electron Spin Resonance

Abstract

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.

Current density imaging by pulsed conduction electron spin resonance

“…The experimental data is in good agreement with this prediction and shows the expected linear slope for À115 mA 6 I 6 115 mA. The slope, which is determined by the charge carrier density n, compares well with the theoretically predicted value, thus acknowledges the reliability of this newly introduced method [23]. Compared with an earlier examined crystal, the present phase shift is larger by a factor of two [23], indicating a smaller cross-section.…”

“…For small I values one expects a linear dependence, with a straight line through the origin. Only for higher currents, in combination with the presence of nonuniform current distribution, one may expect a deviation from the proportional dependence [23]. The experimental data is in good agreement with this prediction and shows the expected linear slope for À115 mA 6 I 6 115 mA.…”

“…Whereas the spatially varying, but low density of defects barely influences the conduction electron spin density in the metallic phase, it modulates the conduction electron relaxation rates and mobility and causes inhomogeneous current distribution of a crystal contacted at both ends. The uninterrupted conducting FA stacks-in the 1% range for typical (FA) 2 PF 6 crystals [5,23]-predominate in the electrical current. In the present context, the quasi-one-dimensional behavior helps to minimize yet another possible complication caused by the existence of Hall forces expected to influence the motion of the moving charge carriers in magnetic fields.…”

“…The solid line represents a linear fit, valid for small I values and describing the experimental data very well. See[23] for details.…”

Longitudinal and transverse diffusion of conduction-electron spins on stacks of fluoranthene radical cations

“…[29][30][31] It has been shown recently that indeed the electric current in ͑FA͒ 2 PF 6 can be detected by ESR via the motion of the spins in a magnetic field gradient. 32 Thus the experimental techniques established earlier for the derivation of the spin diffusion coefficient D͑T͒, its anisotropy D͑͒, and the spatial restriction of spin diffusion due to broken chains or exchange interaction with paramagnetic defects, l ʈ ͑T͒, can be adopted. [29][30][31][33][34][35][36][37][38][39][40][41][42][43] This is exploited here for different ͑FA͒ 2 PF 6 single crystals with controlled content of defects, allowing extrapolation to the behavior of ideal ͑FA͒ 2 PF 6 crystals.…”