Abstract
Manifestations of quantum interference effects in macroscopic objects are rare. Weak localization is one of the few examples of such effects showing up in the electron transport through solid state. Here we show that weak localization becomes prominent also in optical spectroscopy via detection of the electron spin dynamics. In particular, we find that weak localization controls the free electron spin relaxation in semiconductors at low temperatures and weak magnetic fields by slowing it down by almost a factor of two in $n$-doped GaAs in the metallic phase. The weak localization effect on the spin relaxation is suppressed by moderate magnetic fields of about 1 T, which destroy the interference of electron trajectories, and by increasing the temperature. The weak localization suppression causes an anomalous decrease of the longitudinal electron spin relaxation time $T_1$ with magnetic field, in stark contrast with well-known magnetic field induced increase in $T_1$. This is consistent with transport measurements which show the same variation of resistivity with magnetic field. Our discovery opens a vast playground to explore quantum magneto-transport effects optically in the spin dynamics.
Highlights
The design of future spintronic and optospintronic devices requires a detailed understanding of the correlation between the electron conductivity and spin relaxation in prospective material systems, such as semiconductors
We show that weak localization becomes prominent in optical spectroscopy via detection of the electron spin dynamics
We find that weak localization controls the free electron spin relaxation in semiconductors at low temperatures and weak magnetic fields by slowing it down by almost a factor of two in n-doped GaAs in the metallic phase
Summary
The design of future spintronic and optospintronic devices requires a detailed understanding of the correlation between the electron conductivity and spin relaxation in prospective material systems, such as semiconductors. Since the 1990s, more advanced techniques have become available, such as pump-probe methods analyzing the Kerr (or Faraday) rotation [15,16] or polarization-resolved photoluminescence [17,18,19,20], and elaborated methods like resonant spin amplification [21,22], spin noise spectroscopy [23,24,25], and spin inertia reorientation [26] Each of these tools has limitations related to the achievable time resolution, the addressable time range, or the applicable magnetic field. Using the extended pump-probe Faraday rotation technique, we study the longitudinal electron spin relaxation time T1 as a function of external magnetic field in n-doped metallic bulk GaAs. While the classical theory [37] predicts an increase of T1 with increasing field, mainly due to the cyclotron motion of the free carriers, we observe an anomalous decrease of T1 in moderate fields B ≲ 1 T. Thereby all-optical access to weak localization is provided and a tool to probe locally electron transport phenomena is developed
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