NER: Terahertz Detection of Electron Spin Precession

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This proposal was received in response to the Nanoscale Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NER category. The overall effort focuses on direct detection of electron spin dynamics by sensing the emission of terahertz radiation mediated by the magnetic dipole of a population of electrons precessing in an applied magnetic field. The goal of this initial exploratory project is to determine if measurable terahertz radiation is produced from an optically excited population of spin-oriented electrons in n-doped GaAs and possibly semimagnetics such a CdMnTe. A superconducting split-coil magnet will be used to apply fields upto 6.5 Tesla. Detection of the radiated intensity of the terahertz will be done by using a liquid helium cooled bolometer to avoid the alignment difficulties presented by electrooptic or photoconductive detection. The population of spin-oriented electrons will be generated by optical excitation with circularly-polarized femtosecond pulses. To obtain populations that are sufficient large to generate a detectable signal, either amplified pulses, or "spin amplification" by excitation that is resonant with the spin precession will be used. Based on measurement of the intensity alone, the optimum configuration can be determined and saturation characteristics studied. These results will complement prior studies made using Faraday rotation and provide the background for using more sophisticated detection of the terahertz radiation to measure the emitted electric field, which reflects the spin dynamics. This will provide a direct probe of the electron spin dynamics without the ambiguities present in the currently used indirect optical probes such as Faraday or Kerr rotation. Such a direct probe will answer important basic questions about spin dynamics for larger spin densities than can be probed with current techniques. The results will provide important fundamental knowledge necessary for the development of nanotechnology devices based on the manipulation of electron spins. In addition, they could provide the basis for a source of terahertz radiation based on advances in spin manipulation using nanotechnology.