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.
Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset
Moritz Brehm, Francesco Montalenti, Martyna Grydlik, Guglielmo Vastola, Herbert Lichtenberger et al.
The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer (WL) of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understan ... [Phys. Rev. B 80, 205321 (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.
Excitation dynamics in polymer-coated semiconductor quantum dots with integrated dye molecules: The role of reabsorption
Tobias Niebling, Feng Zhang, Zulqurnain Ali, Wolfgang J. Parak, and Wolfram Heimbrodt
Inorganic CdSe/ZnS core-shell quantum dots have been coated with amphiphilic polymers in order to enable their transfer to aqueous solutions. Additionally, ATTO-dye molecules have been embedded in the polymer shell. In this geometry ATTO dye acts as acceptor of the quantum dot donors' excitation. Th ... [J. Appl. Phys. 106, 104701 (2009)] published Thu Nov 19, 2009.
Phonon-assisted transitions from quantum dot excitons to cavity photons
Ulrich Hohenester, Arne Laucht, Michael Kaniber, Norman Hauke, Andre Neumann et al.
For a single semiconductor quantum dot embedded in a microcavity, we theoretically and experimentally investigate phonon-assisted transitions between excitons and the cavity mode. Within the framework of the independent boson model we find that such transitions can be very efficient, even for relati ... [Phys. Rev. B 80, 201311 (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.
Hyperfine-induced valley mixing and the spin-valley blockade in carbon-based quantum dots
Andras Palyi and Guido Burkard
Hyperfine interaction (HFI) in carbon nanotube and graphene quantum dots is due to the presence of C atoms. We theoretically show that in these structures the short-range nature of the HFI gives rise to a coupling between the valley degree of freedom of the electron and the nuclear spin, in addition ... [Phys. Rev. B 80, 201404 (2009)] published Tue Nov 17, 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.
Phonon-induced dephasing of singlet-triplet superpositions in double quantum dots without spin-orbit coupling
K. Roszak and P. Machnikowski
We show that singlet-triplet superpositions of two-electron spin states in a double quantum dot undergo a phonon-induced pure dephasing which relies only on the tunnel coupling between the dots and on the Pauli-exclusion principle. As such, this dephasing process is independent of spin-orbit couplin ... [Phys. Rev. B 80, 195315 (2009)] published Tue Nov 17, 2009.
Light absorption in silicon quantum dots embedded in silica
S. Mirabella, R. Agosta, G. Franzo, I. Crupi, M. Miritello et al.
The photon absorption in Si quantum dots (QDs) embedded in SiO has been systematically investigated by varying several parameters of the QD synthesis. Plasma-enhanced chemical vapor deposition (PECVD) or magnetron cosputtering (MS) have been used to deposit, upon quartz substrates, single layer, or ... [J. Appl. Phys. 106, 103505 (2009)] published Tue Nov 17, 2009.
Formation of InAs/InGaAsP quantum-dashes on InP(001)
A. Lenz, F. Genz, H. Eisele, L. Ivanova, R. Timm et al.
Self-assembled InAs/InGaAsP/InP(001) nanostructures are investigated using cross-sectional scanning tunneling microscopy. Atomically resolved images at both the (110) and the ([overline 1]10) cleavage surface show InAs quantum dashes with almost binary composition and a truncated pyramidal shape. Th ... [Appl. Phys. Lett. 95, 203105 (2009)] published Mon Nov 16, 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.
Radiative lifetimes in undoped and p-doped InAs/GaAs quantum dots
Edmund Harbord, Peter Spencer, Edmund Clarke, and Ray Murray
We investigate the effect of p doping on the luminescence properties of InAs/GaAs self-assembled quantum dots (QDs). Continuous-wave and time-resolved photoluminescence measurements are obtained as a function of temperature and used to extract the radiative lifetime of the QD ground state. We find t ... [Phys. Rev. B 80, 195312 (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.
g-factor and exchange energy in a few-electron lateral InGaAs quantum dot
M. Larsson, H. A. Nilsson, H. Hardtdegen, and H. Q. Xu
We report on the measurements of the g-factor and the exchange interaction of electrons in a few-electron lateral quantum dot formed in an InGaAs/InP semiconductor heterostructure. The spin filling sequence of the electron states in the dot is determined by magnetotransport measurements and parallel ... [Appl. Phys. Lett. 95, 192112 (2009)] published Fri Nov 13, 2009.
Temperature dependence of the spectral band shape of CdSe nanodots and nanorods
J. I. Climente, J. Planelles, and F. Rajadell
We study theoretically the effect of thermal population on the emission spectrum of single CdSe nanocrystals. Quantum confinement leads to nonsimple emission band shapes, which have different characteristics for excitons, biexcitons, positive, and negative trions. These effects are particularly pron ... [Phys. Rev. B 80, 205312 (2009)] published Thu Nov 12, 2009.
Internal electronic structure and fine structure of multiexcitons in semiconductor quantum dots
Vladan Mlinar and Alex Zunger
We perform a detailed theoretical study of the characteristic internal electronic structure of various multiexcitons (N,N), where N is number of holes and N is the number of electrons in the self-assembled semiconductor quantum dots (QDs). For each of the leading (N,N) excitonic complexes we start f ... [Phys. Rev. B 80, 205311 (2009)] published Thu Nov 12, 2009.
Quantum criticality near the Stoner transition in a system of two tunnel-coupled quantum dots with spin-orbit coupling
Oleksandr Zelyak and Ganpathy Murthy
We study a system of two tunnel-coupled quantum dots with the first dot containing interacting electrons (described by the universal Hamiltonian) not subject to spin-orbit coupling whereas the second contains noninteracting electrons subject to spin-orbit coupling. We focus on describing the behavio ... [Phys. Rev. B 80, 205310 (2009)] published Thu Nov 12, 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.
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.