Download Anomalous Magnetoresistance in Dirty Magnetic Quantum Wells

Anomalous Magnetoresistance in Dirty Magnetic Quantum Wells
J. Jaroszyńskiab , T. Andrearczykba , G. Karczewskib, T. Wojtowiczb , J. Wróbelb , Dragana Popovića, and
T. Dietlbc
a
National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
Institute of Physics, Polish Academy of Science, 02-668 Warszawa, Poland
c
Institute of Theoretical Physics, Warsaw University, 00-681 Warszawa, Poland
b
A giant Zeeman splitting in (Cd,Mn)Te quantum wells brings Landau levels into coincidence and gives
rise to the formation of the Quantum Hall Ferromagnets (QHFM) at selected fields B c [1].
Here we report on new findings at the low-B limit. Since spin- polarization increases as B decreases
magnetoresistance oscillation originated from the QHFM formation are clearly observed down to B =
0.3 T and up to T = 1.5 K, despite very low mobility µ < 500 cm2 /Vs. At the same time transport
becomes strongly nonlinear. Moreover, while at B = 0 and high excitation currents I exc the apparent
metal to insulator transition is observed, for a low Iexc a strong increase (3 orders of magnitude) of R
takes place. Under these circumstances a collosal negative magnetoresistance is observed in a parallel
B. However, it does not scale with Mn magnetization, contrary to a positive MR observed at high T or
Iexc , as well as for the lowest electron densities ns < 1.65 · 1011 cm−2 where Shklovskii-Efros-like hopping
behavior shows-up. We attribute these findings to a possible Wigner glass formation [2].
[1] J. Jaroszyński et al., Phys. Rev. Lett. 89, 266802 (2002).
[2] S. Chakravarty et al., Philos. Mag. B79, 859 (1999).
Sorting category: Db Conducting electrons in condensed matter
Keywords: Spin Dependent Transport, Quantum Hall Effect, Magnetic Semiconductors
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