Noise Enhanced Stability Phenomenon in Electron Spin Dynamics

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Possible utilization of the electron spin as an information carrier in electronic devices is an engaging challenge for future spin-based electronics. Inthese new devices, the information stored in a system of polarized electron spins, is transferred byapplying an external electric field and finally detected. However, each initial non-equilibrium magnetization decays both in time and distance duringthe transport. Because of increasing miniaturization, to avoid too much intense electric fields,which could lead the system to exhibit a stronglynonlinear physical behavior, applied voltages arevery low. Low voltages are subjected to the background noise; hence, it is mandatory to understandthe influence of fluctuations on the spin depolarization process in order to guarantee a reliable manipulation, control and detection of information inspin-based devices.The presence of noise is generally considered adisturbance, since strong fluctuations affect theperformance of the devices. In the last decade,however, an increasing interest has been directedtowards possible constructive aspects of noise in the dynamical response of non-linear systems.Interesting theoretical works on the possibility toimprove the ultra-fast magnetization dynamics ofmagnetic spin systems by including random fieldshave been recently published. Instead, at thebest of our knowledge, the investigation of the roleof noise on the electron spin dynamics in semiconductors is still beginning. Preliminary findingsshow that in semiconductor crystals a fluctuatingelectric field can strongly modify the spin depolarization length, an essential design parameter inspin-based electronic devices.In this contribution, we investigate the effects of different types of external source of noise on thespin relaxation process in low-doped n-type GaAscrystals. The electron transport is simulated by aMonte Carlo procedure which takes into accountall the possible scattering phenomena of hot electrons in the medium and includes the evolution ofthe spin polarization vector. The effects causedby the addition of external fluctuations are investigated by analyzing the modification of the spindepolarization length. In the presence of a correlated source of noise and for electric field amplitudes greater than the Gunn field, an increase ofthe spin relaxation length up to 20% is found. This result can be considered a NoiseEnhanced Stability (NES) consequence and can beexplained in terms of a decrease of the occupationof the L-valleys, where the strength of spin-orbitcoupling felt by electrons is at least one order ofmagnitude greater than that present in the lowest energy valley. If the random component of thedriving electric field is modeled with a dichotomous stochastic process (Random telegraph noise) characterized by two discrete levels, the spin depolarization process changes, in a way that critically depends on the jump rate of the stochastic process.We investigate on a possible relationship betweenthe semiconductor characteristic time scales andthe noise characteristic time in order to find themost favorable condition for the transmission of information by electron spin.
Original languageEnglish
Number of pages1
Publication statusPublished - 2012


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