Electrically controlled nuclear spin polarization and relaxation by quantum-Hall states

Area of Science:

• Condensed Matter Physics
• Quantum Hall Effect
• Spintronics

Background:

• Investigating electron and nuclear spin interactions is crucial for understanding quantum phenomena.
• The resistance (Rxx) peak near Landau-level filling factor nu = 2/3 serves as a sensitive probe for these interactions.

Purpose of the Study:

• To probe the memory effects of nuclear spins on electron behavior.
• To understand the role of Skyrmions in depolarizing nuclear spins.
• To investigate the nature of composite fermions at fractional fillings.

Main Methods:

• Utilized the resistance (Rxx) peak near nu = 2/3 as a probe for electron-nuclear spin interactions.
• Temporarily tuned the filling factor (nu) to different values using a gate.
• Analyzed the regeneration and relaxation of the Rxx peak after depletion and near nu(temp) = 1.

Main Results:

• The Rxx peak at nu = 2/3 regenerates even after complete depletion (nu(temp) = 0), indicating a memorized state.
• Rapid relaxation of the Rxx peak occurs on either side of nu(temp) = 1, suggesting nuclear spin depolarization by Skyrmions.
• Enhanced nuclear spin relaxation near nu = 1/2 and 3/2 points to a Fermi sea of partially polarized composite fermions.

Conclusions:

• Nuclear spins exhibit a memory effect related to the nu = 2/3 domain morphology.
• Skyrmions play a significant role in the rapid depolarization of these nuclear spins.
• The findings suggest the existence of a composite fermion Fermi sea at fractional fillings.