Mechanism of exchange bias for isolated nanoparticles embedded in an antiferromagnetic matrix
Valera P. Shcherbakov, Karl Fabian, and Suzanne A. McEnroe
Single magnetic nanodots, exchange coupled to an antiferromagnetic (AF) matrix, can produce large exchange bias, while superparamagnetic behavior of the nanodots is suppressed. The exchange bias originates from the formation of a (quasi)spherical domain wall inside the AF matrix when the particle mo ... [Phys. Rev. B 80, 174419 (2009)] published Fri Nov 20, 2009.
Photoinduced spin-polarized current in InSb-based structures
M. Frazier, J. G. Cates, J. A. Waugh, J. J. Heremans, M. B. Santos et al.
We demonstrate the observation of spin-polarized photocurrent in InSb films grown on GaAs and InP substrates and InSb quantum wells where a nonequilibrium spin population has been achieved by using circularly polarized radiation. The characteristics of our observations indicated that the circular ph ... [J. Appl. Phys. 106, 103513 (2009)] published Fri Nov 20, 2009.
A method for evaluating the ground state excitonic band gaps of strained InGaN/GaN quantum wells
T. K. Sharma and E. Towe
A simple method for calculating the ground state excitonic band gaps of strained wurtzite InGaN/GaN quantum wells (QWs) for the entire composition range is proposed. The modification of the electronic band structure due to strain becomes significant for high values of indium concentration. It is obs ... [J. Appl. Phys. 106, 104509 (2009)] published Fri Nov 20, 2009.
Influence of the substrate bands on the sp-levels topology of Ag films on Ge(111)
P. Moras, D. Topwal, P. M. Sheverdyaeva, L. Ferrari, J. Fujii et al.
Angle-resolved photoemission spectroscopy and first-principles calculations were employed to analyze unusual features in the electronic structure of ultrathin Ag films grown on Ge(111). The Ag sp-derived quantum well states exhibit hexagonal-like constant energy contours with different in-plane orie ... [Phys. Rev. B 80, 205418 (2009)] published Thu Nov 19, 2009.
High-temperature ferromagnetism by means of oriented nanocolumns: Co clustering in (Zn,Co)O
N. Jedrecy, H. J. von Bardeleben, and D. Demaille
In order to provide insight into the magnetic properties of semiconductors with ferromagnetic inclusions, we present a thorough quantitative analysis of (Zn,Co)O films with high Co concentration, which give rise to high saturation magnetization values (~110 kA m) at room temperature. From the orien ... [Phys. Rev. B 80, 205204 (2009)] published Thu Nov 19, 2009.
Effect of microstructure on magnetic properties and anisotropy distributions in Co/Pd thin films and nanostructures
Justin M. Shaw, Hans T. Nembach, T. J. Silva, Stephen E. Russek, Roy Geiss et al.
The structure of Co/Pd multilayers has a strong effect on the localized anisotropy distribution within a film and on the resulting switching properties of nanostructures fabricated from identical material. By varying the underlying seed layer in sputtered films, the microstructure can be controlled ... [Phys. Rev. B 80, 184419 (2009)] published Thu Nov 19, 2009.
Coherent transport in semiconductor heterostructures: A phenomenological approach
Ariel Gordon and Daniel Majer
We propose a theoretical method for describing coherent quantum transport in semiconductor heterostructures and particularly in quantum cascade lasers (QCLs). The method is an extension of standard rate-equation models to include coherence. Instead of building the model from microscopic consideratio ... [Phys. Rev. B 80, 195317 (2009)] published Wed Nov 18, 2009.
Direct measurement of auger recombination in InGaN/GaN quantum wells and its impact on the efficiency of InGaN/GaN multiple quantum well light emitting diodes
M. Zhang, P. Bhattacharya, J. Singh, and J. Hinckley
The Auger recombination coefficient in InGaN/GaN quantum wells, emitting at 407 nm has been determined from large signal modulation measurements on lasers in which these quantum wells form the gain region. A value of 1.5 x 10 cm s is determined for the Auger coefficient at room temperature, which i ... [Appl. Phys. Lett. 95, 201108 (2009)] published Wed Nov 18, 2009.
Spin mapping at the nanoscale and atomic scale
Roland Wiesendanger
The direct observation of spin structures with atomic-scale resolution, a long-time dream in condensed matter research, recently became a reality based on the development of spin-sensitive scanning probe methods, such as spin-polarized scanning-tunneling microscopy (SP-STM) and magnetic exchange for ... [Rev. Mod. Phys. 81, 1495 (2009)] published Wed Nov 18, 2009.
Nonadiabatic spin-transfer torque in (Ga,Mn)As with perpendicular anisotropy
J.-P. Adam, N. Vernier, J. Ferre, A. Thiaville, V. Jeudy et al.
Current-induced magnetic domain wall motion has been investigated in microtracks made from a ferromagnetic semiconductor (Ga,Mn)As thin film with perpendicular anisotropy. In order to reveal the nature of this motion, small fields were additionally applied. The results demonstrate that, when driven ... [Phys. Rev. B 80, 193204 (2009)] published Tue Nov 17, 2009.
Large radiation fields from nonlocal interaction between terahertz waves and quantum wells with an applied electric field
Guanghui Wang and Qi Guo
The effects of pump intensities and applied electric fields on radiation fields excited by the nonlocal interaction between terahertz waves and AlGaAs/GaAs quantum wells (QWs) are investigated. The numerical results show the resonant radiation fields are very large in the confinement direction, and ... [J. Appl. Phys. 106, 103506 (2009)] published Tue Nov 17, 2009.
Enhanced response of current-driven coupled quantum wells
Antonios Balassis and Godfrey Gumbs
We have investigated the conditions necessary to achieve stronger Cherenkov-like instability of plasma waves leading to emission in the terahertz regime for semiconductor quantum wells. The surface response function is calculated for a bilayer two-dimensional electron gas (2DEG) system in the presen ... [J. Appl. Phys. 106, 103102 (2009)] published Tue Nov 17, 2009.
Magnetically Hindered Chain Formation in Transition-Metal Break Junctions
A. Thiess, Y. Mokrousov, S. Heinze, and S. Blugel
Based on first-principles calculations, we demonstrate that magnetism impedes the formation of long chains in break junctions. We find a distinct softening of the binding energy of atomic chains due to the creation of magnetic moments that crucially reduces the probability of successful chain format ... [Phys. Rev. Lett. 103, 217201 (2009)] published Mon Nov 16, 2009.
Exciton correlations in coupled quantum wells and their luminescence blue shift
B. Laikhtman and R. Rapaport
In this paper we present a study of an exciton system where electrons and holes are confined in double quantum well structures. The dominating interaction between excitons in such systems is a dipole-dipole repulsion. We show that the tail of this interaction leads to a strong correlation between ex ... [Phys. Rev. B 80, 195313 (2009)] published Fri Nov 13, 2009.
Oscillating spin-density pattern in gold metallocene and phthalocyanine molecules
Diego Carrascal, Lucas Fernandez-Seivane, and Jaime Ferrer
We present a theoretical study of the magnetic properties of the spin-1/2 dicyclopentadienyl metallocene (MCp) and phthalocyanine molecules that contain the transition-metal atoms M=Co, Cu, and Au. We find that the spin-density pattern of gold molecules shows a fully delocalized and oscillating beha ... [Phys. Rev. B 80, 184415 (2009)] published Fri Nov 13, 2009.
Mid-infrared emission from InAs quantum dots, wells, and dots on well nanostructures grown on InP (100) by metal organic vapor phase epitaxy
Junji Kotani, Peter J. van Veldhoven, and Richard Notzel
A detailed analysis to extend the emission wavelength of InAs/InP nanostructures is presented employing InAs quantum dots (QDs), InAs quantum wells (QWs), and a combination of InAs QDs and QWs grown on InGaAsP/InP (100) by metal organic vapor phase epitaxy. First the optimized growth conditions of I ... [J. Appl. Phys. 106, 093112 (2009)] published Fri Nov 13, 2009.
Long-timescale fluctuations in zero-field magnetic vortex oscillations driven by dc spin-polarized current
V. S. Pribiag, G. Finocchio, B. J. Williams, D. C. Ralph, and R. A. Buhrman
We report time and frequency domain studies of spin-torque-driven vortex self-oscillations at zero magnetic field. We observe two types of abrupt fluctuations in the frequency and amplitude, with very long random mean lifetimes (~10 to ~10 oscillation cycles). First, we observe fluctuations between ... [Phys. Rev. B 80, 180411 (2009)] published Thu Nov 12, 2009.
Photoreflectance and Fourier transform infrared spectroscopy study of intersubband transitions of a ZnCdSe/ZnCdMgSe asymmetric coupled quantum well structure for quantum cascade laser application
J. D. Wu, C. T. Huang, Y. S. Huang, W. O. Charles, A. Shen et al.
Photoreflectance (PR) and Fourier transform infrared (FTIR) spectroscopy were used to study the intersubband (ISB) transitions of a ZnCdSe/ZnCdMgSe asymmetric coupled quantum well (ACQW) structure for quantum cascade laser (QCL) application. The PR spectrum revealed a wide range of possible optical ... [Appl. Phys. Lett. 95, 191905 (2009)] published Thu Nov 12, 2009.
Radio frequency operation of clocked quantum-dot cellular automata latch
Yong Tang, Alexei O. Orlov, Gregory L. Snider, and Patrick J. Fay
The radio frequency operation of a single-electron latch based on AlAlOAl tunnel junctions is presented. By capacitively coupling the latch to a radio frequency single electron transistor, charge switching on the microsecond timescale is demonstrated. The fast switching and high repeatability of the ... [Appl. Phys. Lett. 95, 193109 (2009)] published Thu Nov 12, 2009.
Optical spin orientation in strained Ge/SiGe quantum wells: A tight-binding approach
Michele Virgilio and Giuseppe Grosso
We present a theoretical investigation of electron-spin optical orientation in strained Ge/SiGe quantum wells. The atomistic spds nearest-neighbor tight-binding model adopted, allows us to obtain the spin polarization of the excited electrons, as a function of frequency and direction of the incident ... [Phys. Rev. B 80, 205309 (2009)] published Wed Nov 11, 2009.
Electroluminescence induced by photoluminescence excitation in GaInN/GaN light-emitting diodes
Martin F. Schubert, Qi Dai, Jiuru Xu, Jong Kyu Kim, and E. Fred Schubert
Optical emission resulting from 405 nm selective photoexcitation of carriers in the GaInN/GaN quantum well (QW) active region of a light-emitting diode reveals two recombination channels. The first recombination channel is the recombination of photoexcited carriers in the GaInN QWs. The second recom ... [Appl. Phys. Lett. 95, 191105 (2009)] published Tue Nov 10, 2009.