Measurement of the Overhauser field in a two-dimensional electron system at weak magnetic fields

Optically induced polarization of electron spins has been able to generate nuclear polarization via dynamic nuclear polarization (DNP), and control of this nuclear spin polarization has extensive application potentiality in spin-based quantum information processing and quantum computation. Here, we report optically induced DNP measurements in a two-dimensional electron gas embedded in a GaAs/AlGaAs heterostructure. We are able to obtain the Overhauser field $Bn$ and show that it is proportional to the external magnetic field $Bext$ when the latter is weak. We also show that the proportionality coefficient $k$ between $Bn$ and $Bext$ can be manipulated by varying the intensity and helicity of the pump light.