Anisotropy of Magnetoresistance Hysteresis around the ν=2/3 Quantum Hall State in Tilted Magnetic Field

Abstract

We present an anisotropy of the hysteretic transport around the spin transition point at the Landau level filling factor ν = 2/3 in a tilted magnetic field. When the direction of the in-plane component of the magnetic field B is normal to the probe current I, a strong hysteretic transport due to the current-induced nuclear spin polarization occurs. When B is parallel to I, on the other hand, the hysteresis almost disappears. We also demonstrate that the nuclear spin-lattice relaxation rate T −1 1 at the transition point increases with decreasing angle between the directions of B and I. These results suggest that the morphology of electron spin domains around ν = 2/3 is affected by the current direction.KEYWORDs: two-dimensional electron system, fractional quantum Hall effect, phase transition, domain structure, nuclear spin system, hyperfine interaction, nuclear spin-lattice relaxation rate An incompressible quantum liquid state of the fractional quantum Hall (QH) effect occurs as a consequence of strong electron-electron interactions in high magnetic field and has continued to be one of the most absorbing subjects in solid state physics.1) In addition, the spin degree of freedom provides a rich variety of quantum phenomena in fractional QH states. Because of the small Zeeman energy of electrons in GaAs, ground states with spin configurations other than the fully polarized one are possible, and transitions between different spin states have been observed at various fractional filling factors ν. 2-4)At the spin transition point of ν = 2/3, an anomalous magnetoresistance R xx peak with hysteretic transport has been observed. [4][5][6][7][8][9] Resistively -detected nuclear magnetic resonance measurements have shown the involvement of the nuclear spin polarization in the origin of the R xx peak.5, 7-9) At the transition point, two fractional QH states with different spin configurations degenerate energetically and an electronic domain structure is formed.9, 10) Because the domain wall between the two fractional QH states connects the edge channels with opposite current direction, the backscattering of electrons through the domain wall increases R xx . 11)In addition, it is believed that when a current passes across a domain boundary, electron spins flip-flop scatter nuclear spins, inducing nuclear spin polarization. 7-9)The current-induced nuclear spin polarization reacts on the electronic domain structure through the hyperfine interaction and changes the properties of the domain structure. This mutual interplay between the domain structure and the current-induced nuclear spin polar- * E-mail address: iwata@tfu-mail.tfu.ac.jp ization causes a long-time variation of R xx in proportion to the nuclear polarization.5, 7) Moreover, hysteresis in R xx , taken with upward and downward field sweeps, has been observed around the transition point, indicating that the degree of nuclear spin polarization depends on the sweep direction.4, 8, 9) However, despite intensive works, details of the domain structure and the mechanism ...

Phase Transition to Insulating State from Quantum Hall State by Current-Induced Nuclear Spin Polarization

“…10,11) In addition, an anisotropy of the hysteretic transport for the angle between current direction and in-plane magnetic field around the transition point in a tilted magnetic field was found. 12) This suggests that the dynamics of electron spin domains is affected by the current direction for the in-plane field. However, details of the domain structure are still unclear, and the real cause of the magnetoresistance enhancement remains a riddle even now.…”

“…A previous experiment has shown that the resistanceenhanced state (RES) is not stable and decays over roughly several hundred seconds. 12) In this work, the measurement of the resistance is performed much faster than the decay time of RES. In order to avoid the heating effect due to the current, we change the measuring current to a sufficiently small value.…”