記
日時: 平成 15 年 3 月 13 日（木） 14:00~15:30
場所: 電気通信研究所 1 号館 3 階
N308
講演者: Dr. Igor Zutic (Department of Physics,
University of Maryland at College Park)
講演題目: Bipolar Spintronics
概要: We develop a theory of bipolar (electrons and holes) spin-polarized
transport in semiconductors and discuss its implications for spintronic
devices [1-3]. We focus on the inhomogeneously doped semiconductors
such as a magnetic p-n junction [1] (which could serve as a building block
for magnetic bipolar transistors) with spatially dependent spin splitting of
carrier bands, realized by magnetic doping or applied magnetic field. We
study the influence of injected nonequilibrium spin and predict several
phenomena with potential spintronic applications. For example, magnetoresistance can increase exponentially with applied magnetic field, spin
density can be amplified [2], and there is a strong coupling between the
spin and charge transport leading to the spin-voltaic effect [1]. We discuss
how the properties of spin-voltaic effect can be used to perform
all-electrical measurements of spin relaxation time [4]. In particular, we
show [1,4] that the charge current can flow even at no applied bias in the
direction which can be switched either by the reversal of the directions of
applied magnetic field or a polarization of the injected spin.
[1] I. Zutic, J. Fabian, S. Das Sarma, Phys. Rev. Lett. 88, 066603 (2002).
[2] I. Zutic, J. Fabian, S. Das Sarma, Phys. Rev. B 64, 121201 (2001).
[3] I. Zutic, J. Fabian, S. Das Sarma, Appl. Phys. Lett. 79, 1558 (2001).
[4] I. Zutic, J. Fabian, S. Das Sarma, Appl. Phys. Lett. 82, 221 (2003).
講演者: Dr. Jan Martinek (Institute of Molecular Physics,
Polish Academy of Sciences)
講演題目: Nature of the Kondo effect in the
presence of the itinerant electron magnetism
概要: We study the Kondo effect in a quantum dot (QD), which is coupled
to ferromagnetic leads, and analyze its properties. The new key questions,
which emerge are: (i) does the Kondo effect survive and how does the
spin-asymmetry affect the effect, (ii) how are the transport properties
modified, and (iii) what is the ground state of the system? We analyzed
these and related questions using scaling arguments, the equation of
motion (EOM) technique, and numerical renormalization group (NRG)
approach. Based on a poor man's scaling analysis we first show that the
strong-coupling limit can still be reached in this case if an external
magnetic field is applied. We compare the analytical results by the exact
NRG calculations, which confirm the obtained results for the equilibrium
situations. We also analyze within EOM approach the nonlinear transport
through the QD. We find that for parallel alignment of the lead
magnetizations the zero-bias anomaly is split. This splitting can be
removed by appropriately tuning the strength of an external magnetic field.
問い合わせ先: 大野研究室
松倉文礼
(内線 5555, E-mail: f-matsu@riec.tohoku.ac.jp)