10 research outputs found
Magnetic impurities in the honeycomb Kitaev model
We study the effect of coupling magnetic impurities to the honeycomb lattice
spin-1/2 Kitaev model in its spin liquid phase. We show that a spin-S impurity
coupled to the Kitaev model is associated with an unusual Kondo effect with an
intermediate coupling unstable fixed point K_c J/S separating topologically
distinct sectors of the Kitaev model. We also show that the massless spinons in
the spin liquid mediate an interaction of the form
S_{i\alpha}^{2}S_{j\beta}^{2}/R_{ij}^{3} between distant impurities unlike the
usual dipolar RKKY interaction S_{i\alpha}S_{j\alpha}/R_{ij}^{3} noted in
various 2D impurity problems with a pseudogapped density of states of the spin
bath. Furthermore, this long-range interaction is possible only if the
impurities (a) couple to more than one neighboring spin on the host lattice and
(b) the impurity spin is not a spin-1/2.$Comment: 4 pages, 3 figures, Published versio
Noise studies of magnetization dynamics in dilute magnetic semiconductor heterostructures
We study theoretically and experimentally the frequency and temperature
dependence of resistivity noise in semiconductor heterostructures delta-doped
by Mn. The resistivity noise is observed to be non-monotonous as a function of
frequency. As a function of temperature, the noise increases by two orders of
magnitude for a resistivity increase of about 50%. We study two possible
sources of resistivity noise -- dynamic spin fluctuations and charge
fluctuations, and find that dynamic spin fluctuations are more relevant for the
observed noise data. The frequency and temperature dependence of resistivity
noise provide important information on the nature of the magnetic interactions.
In particular, we show how noise measurements can help resolve a long standing
debate on whether the Mn-doped GaAs is an p-d Zener/RKKY or double exchange
ferromagnet. Our analysis includes the effect of different kinds of disorder
such as spin-glass type of interactions and a site-dilution type of disorder.
We find that the resistivity noise in these structures is well described by a
disordered RKKY ferromagnet model dynamics with a conserved order parameter.Comment: 15 pages, 7 eps figures, published versio
Charge inhomogeneities and transport in semiconductor heterostructures with a manganese -layer
We study experimentally and theoretically the effects of disorder, nonlinear
screening, and magnetism in semiconductor heterostructures containing a
-layer of Mn, where the charge carriers are confined within a quantum
well and hence both ferromagnetism and transport are two-dimensional (2D) and
differ qualitatively from their bulk counterparts. Anomalies in the electrical
resistance observed in both metallic and insulating structures can be
interpreted as a signature of significant ferromagnetic correlations. The
insulating samples turn out to be the most interesting as they can give us
valuable insights into the mechanisms of ferromagnetism in these
heterostructures. At low charge carrier densities, we show how the interplay of
disorder and nonlinear screening can result in the organization of the carriers
in the 2D transport channel into charge droplets separated by insulating
barriers. Based on such a droplet picture and including the effect of magnetic
correlations, we analyze the transport properties of this set of droplets,
compare it with experimental data, and find a good agreement between the model
calculations and experiment. Our analysis shows that the peak or shoulder-like
features observed in temperature dependence of resistance of 2D
heterostructures -doped by Mn lie significantly below the Curie
temperature unlike the three-dimensional case, where it lies above and
close to . We also discuss the consequences of our description for
understanding the mechanisms of ferromagnetism in the heterostructures under
study.Comment: 13 pages, 12 figures, RevTe