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TT: Fachverband Tiefe Temperaturen

TT 41: Spintronics / Quantum Information: Materials and Methods (jointly with HL)

TT 41.2: Vortrag

Mittwoch, 13. März 2013, 15:15–15:30, H2

On the misinterpretation of the temperature dependence of T₂^* in time-resolved Faraday rotation — •Sebastian Kuhlen¹, Ralph Ledesch¹, Carla Schenk¹, Matthias Althammer², Sebastian T. B. Gönnenwein², Matthias Opel², Rudolf Gross², and Bernd Beschoten¹ — ¹II. Physikalisches Institut A, RWTH Aachen University, Aachen — ²Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Garching

Time-resolved Faraday rotation (TRFR) is a well-established optical pump probe technique to generate and to probe spin coherence in semiconductors. Spin dephasing times T₂^* can easily be determined from TRFR if their values are comparable to the available pump-probe-delay. If, however, T₂^* exceeds the laser repetition time resonant spin amplification (RSA) can equally be used to extract T₂^*. We demonstrate that in ZnO these techniques have several tripping hazards resulting in deceptive results for T₂^*. We show that the temperature dependence of the amplitude ratio of two separate spin species can easily be misinterpreted as a strongly temperature dependent T₂^* of a single spin ensemble, while the two spin species have T₂^* values which are nearly independent of temperature. Additionally, consecutive pump pulses can significantly diminish the spin polarization, which remains from previous pump pulses. While this barely affects T₂^* values extracted from delay line scans, it results in seemingly shorter T₂^* values in RSA.
Work supported by DFG through SPP 1285.