9 research outputs found
Magnetic anisotropy of epitaxial (Ga,Mn)As on (113)A GaAs
The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers
grown by molecular beam epitaxy is studied by means of superconducting quantum
interference device (SQUID) magnetometry as well as by ferromagnetic resonance
(FMR) and magnetooptical effects. Experimental results are described
considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude
of cubic and uniaxial anisotropy constants is found to be proportional to the
fourth and second power of saturation magnetization, respectively. Similarly to
the case of (001) samples, the spin reorientation transition from uniaxial
anisotropy with the easy along the [-1, 1, 0] direction at high temperatures to
the biaxial anisotropy at low temperatures is observed around 25 K. The
determined values of the anisotropy constants have been confirmed by FMR
studies. As evidenced by investigations of the polar magnetooptical Kerr
effect, the particular combination of magnetic anisotropies allows the
out-of-plane component of magnetization to be reversed by an in-plane magnetic
field. Theoretical calculations within the p-d Zener model explain the
magnitude of the out-of-plane uniaxial anisotropy constant caused by epitaxial
strain, but do not explain satisfactorily the cubic anisotropy constant. At the
same time the findings point to the presence of an additional uniaxial
anisotropy of unknown origin. Similarly to the case of (001) films, this
additional anisotropy can be explained by assuming the existence of a shear
strain. However, in contrast to the (001) samples, this additional strain has
an out-of-the-(001)-plane character.Comment: 13 pages, 9 figure
Fiber-assisted detection with photon number resolution
We report the development of a photon-number resolving detector based on a
fiber-optical setup and a pair of standard avalanche photodiodes. The detector
is capable of resolving individual photon numbers, and operates on the
well-known principle by which a single mode input state is split into a large
number (eight) of output modes. We reconstruct the photon statistics of weak
coherent input light from experimental data, and show that there is a high
probability of inferring the input photon number from a measurement of the
number of detection events on a single run.Comment: 4 pages, 2 figures; Submitted for publicatio
Hysteretic magnetoresistance and thermal bistability in a magnetic two-dimensional hole system
Colossal negative magnetoresistance and the associated field-induced
insulator-to-metal transition, the most characteristic features of magnetic
semiconductors, are observed in n-type rare earth oxides and chalcogenides,
p-type manganites, n-type and p-type diluted magnetic semiconductors (DMS) as
well as in quantum wells of n-type DMS. Here, we report on magnetostransport
studies of Mn modulation-doped InAs quantum wells, which reveal a magnetic
field driven and bias voltage dependent insulator-to-metal transition with
abrupt and hysteretic changes of resistance over several orders of magnitude.
These phenomena coexist with the quantised Hall effect in high magnetic fields.
We show that the exchange coupling between a hole and the parent Mn acceptor
produces a magnetic anisotropy barrier that shifts the spin relaxation time of
the bound hole to a 100 s range in compressively strained quantum wells. This
bistability of the individual Mn acceptors explains the hysteretic behaviour
while opening prospects for information storing and processing. At high bias
voltage another bistability, caused by the overheating of electrons10, gives
rise to abrupt resistance jumps
Disorder-averaged Binder ratio in site-diluted Heisenberg models
It is demonstrated via a numerical experiment (a Monte Carlo simulation) in
the context of three-dimensional site-diluted Heisenberg spin systems that a
functional dependence of the Binder ratio () on the order parameter
correlation length () requires a modification to the usual definition
of in disordered systems. An appropriate disorder averaging procedure is
proposed.Comment: 7 pages, 7 figure