Detection of spin polarization utilizing singlet and triplet states in a single-lead quantum dot

We propose and demonstrate a new method to probe local spin polarization in semiconductor microdevices at low and zero magnetic fields. By connecting a single-lead quantum dot to a semiconductor microdevice and monitoring electron tunneling into singlet and triplet states in the dot, we can detect the local spin polarization formed in the target device. We confirm the validity of this detection scheme utilizing spin-split quantum Hall edge states. We also observe nonzero local spin polarization at the device edge in low magnetic fields, which is not detectable with conventional macroscopic probes.