In most cases, a nuclear spin in a host material is dormant and does not influence electron transport. However in a certain case particularly in a semiconductor material with s-wave conduction band like in GaAs, the hyperfine interaction can be significantly large and the interaction between an electron and a nuclear spin degree of freedoms cannot be ignored. In fact, if all nuclear spins were fully polarized in GaAs, the magnetic field (known as Overhauser or Hyperfine field) exerted on an electron spin would be as high as -5.3 T!. Likewise, a net of electron spin polarization would generate an effective magnetic field for the nuclear spin (known as Knight field) and shift the nuclear Zeeman energy level. One can directly measure electron spin polarization by looking at the shift in the electrically-detected nuclear magnetic resonance. Furthermore, measuring how fast the nuclear spin relaxes toward thermal equilibrium provides a way to probe electron spin fluctuations. One can study a great deal of electronic states in semiconductor nanostructures by measuring the Knight shift and the nuclear spin relaxation rate.

In collaboration with Prof. Yoshiro Hirayama and Assistant Prof. Katsushi Hashimoto of Tohoku University, we are actively exploring the topic to study various spin phase transitions in fractional quantum Hall states and anomalous conductance plateau observed below the lowest subband in a quantum point contact.

See our recent review on arXiv to learn more about the subject.