Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 58: Poster IIb

HL 58.15: Poster

Tuesday, March 8, 2005, 16:30–19:00, Poster TU F

Transition between incompressible states of different spin polarization: a half-polarized ground state? — •Karel Výborný and Daniela Pfannkuche — 1st Institute of theoretical physics, Jungiusstr. 9, University of Hamburg, 20355 Hamburg

Incompressible fractional quantum Hall states are not always fully spin polarized and even transitions between ground states of different spin (but at fixed filling factor) can be achieved by tuning the Zeeman splitting. This is also the case at ν=2/3 where the transition between a spin-singlet ground state (GS) and a fully polarized GS was observed experimentally as a huge longitudinal magnetoresistance effect. Experiments suggested that the system constitutes a quantum Hall ferromagnet [1] or that a stable half-polarized ground state in the middle of the transition occurs [2].

We study this transition using exact diagonalization with electrons on torus. For homogeneous systems we find a low excited half-polarized state around the transition which might become the GS in the thermodynamical limit. We study its structure and compare it to the singlet and polarized GS’s.

Adding magnetic inhomogeneities into the system we investigate stability of all three involved GS’s and tendency to build up domains like in conventional ferromagnets.

[1] S. Kronmüller et al., Phys. Rev. Lett., 81, 2526 (1998); J. Smet et al., Nature, 415, 281 (2002)

[2] I. V. Kukushkin et al., Phys. Rev. Lett., 82, 3665 (1999)