Magnetic anisotropy switching in (Ga,Mn)As with increasing hole concentration

We study a possible mechanism of the switching of the magnetic easy axis as a function of hole concentration in (Ga,Mn)As epilayers. In-plane uniaxial magnetic anisotropy along [110] is found to exceed intrinsic cubic magnetocrystalline anisotropy above a hole concentration of p = 1.5 * 10^21 cm^-3 at 4 K. This anisotropy switching can also be realized by post-growth annealing, and the temperature-dependent ac susceptibility is significantly changed with increasing annealing time. On the basis of our recent scenario [Phys. Rev. Lett. 94, 147203 (2005); Phys. Rev. B 73, 155204 (2006).], we deduce that the growth of highly hole-concentrated cluster regions with [110] uniaxial anisotropy is likely the predominant cause of the enhancement in [110] uniaxial anisotropy at the high hole concentration regime. We can clearly rule out anisotropic lattice strain as a possible origin of the switching of the magnetic anisotropy.Comment: 5 pages, 4 figures, to appear in Phys. Rev.

Electrical control of Kondo effect and superconducting transport in a side-gated InAs quantum dot Josephson junction

We measure the non-dissipative supercurrent in a single InAs self-assembled quantum dot (QD) coupled to superconducting leads. The QD occupation is both tuned by a back-gate electrode and lateral side-gate. The geometry of the side-gate allows tuning of the QD-lead tunnel coupling in a region of constant electron number with appropriate orbital state. Using the side-gate effect we study the competition between Kondo correlations and superconducting pairing on the QD, observing a decrease in the supercurrent when the Kondo temperature is reduced below the superconducting energy gap in qualitative agreement with theoretical predictions

Propagating Coherent Acoustic Phonon Wavepackets in InMnAs/GaSb

We observe pronounced oscillations in the differential reflectivity of a ferromagnetic InMnAs/GaSb heterostructure using two-color pump-probe spectroscopy. Although originally thought to be associated with the ferromagnetism, our studies show that the oscillations instead result from changes in the position and frequency-dependent dielectric function due to the generation of coherent acoustic phonons in the ferromagnetic InMnAs layer and their subsequent propagation into the GaSb. Our theory accurately predicts the experimentally measured oscillation period and decay time as a function of probe wavelength.Comment: 4 pages, 4 figure

Rashba spin-orbit interaction in a Mg_xZn_(1−x)O/ZnO two-dimensional electron gas studied by electrically detected electron spin resonance

We report the experimental determination of Rashba spin-orbit interaction (SOI) strength in two-dimensional electrons in a MgZnO/ZnO heterostructure using electrically detected electron spin resonance. The Rashba parameter is determined to be 7.0 × 10⁻¹⁴ eV m, which is the second smallest value among prevalent semiconductor heterostructures, following Si/SiGe. A long transverse spin relaxation time was derived to show a maximum value of 27 ns, owing to weak SOI. Our study demonstrates that the ZnO heterostructure is a promising candidate for spintronic devices utilizing long spin coherence

ValueGuard: Protection of Native Applications against Data-Only Buffer Overflows

Code injection attacks that target the control-data of an application have been prevalent amongst exploit writers for over 20 years. Today however, these attacks are getting increasingly harder for attackers to successfully exploit due to numerous countermeasures that are deployed by modern operating systems. We believe that this fact will drive exploit writers away from classic control-data attacks and towards data-only attacks. In data-only attacks, the attacker changes key data structures that are used by the program’s logic and thus forces the control flow into existing parts of the program that would be otherwise unreachable, e.g. overflowing into a boolean variable that states whether the current user is an administrator or not and setting it to “true” thereby gaining access to the administrative functions of the program. In this paper we present ValueGuard, a canary-based defense mechanism to protect applications against data-only buffer overflow attacks. ValueGuard inserts canary values in front of all variables and verifies their integrity whenever these variables are used. In this way, if a buffer overflow has occurred that changed the contents of a variable, ValueGuard will detect it since the variable’s canary will have also been changed. The countermeasure itself can be used either as a testing tool for applications before their final deployment or it can be applied selectively to legacy or high-risk parts of programs that we want to protect at run-time, without incurring extra time-penalties to the rest of the applications.status: publishe