铁磁/铁磁/超导结中的量子干涉效应对准粒子输运的影响

通过求解Bogoliubov-deGennes方程,利用推广的Bonder-Tinklam-Klapwijk方法,计算铁磁/绝缘层/铁磁/绝缘层/超导结构中的微分电导(G)和散粒噪声(S)。研究发现系统中的微分电导和散粒噪声都随中间铁磁层厚度作两种不同周斯的振荡,其中通过增强铁磁材料中的交换劈裂和铁磁/超导界面的势垒强度,短周期分量可从长周期中分离出来,反之通过降低铁磁层中的交换劈裂和铁磁/超导界面的势垒强度,长周期分量可从短周期中分离出来,这一结果表明G和S中的两种不同周期的振荡分量分别来自入射电子与铁磁/超导界面处的Andreev反射和正常电子反射的量子干涉效应。     

Tunneling Conductance and Magnetoresistance in Ferromagnet/Ferromagnet/d-Wave Superconductor Double Tunnel Junctions

The tunneling conductance and tunneling magnetoresistance (TMR) are investigated in ferromagnet/insulator/ferromagnet/insulator/d-wave superconductor (FM/I/FM/I/d-wave SC) structures by applying an extended Blonder-Tinkham-Klapwijk (BTK) approach. We study the effects of the exchange splitting in the FM, the magnetic impurity scattering in the thin insulator interface of FM/I/FM, and noncollinear magnetizations in adjacent magnetic layers on the TMR. It is shown (1) that the tunneling conductance and TMR exhibit amplitude-varying oscillating behavior with exchange splitting, (2) that with the presence of spin-flip scattering in insulator interface of FM/I/FM, the TMR can be dramatically enhanced, and (3) that the TMR depends strongly on the angle between the magnetization of two FMs.     

Ultrafast Spin Dynamics in the Iron Borate Easy-Plane Weak Ferromagnet

Journal of Experimental and Theoretical Physics - Ultrafast processes of the spin dynamics in iron borate FeBO3 are considered theoretically; the mechanisms responsible for excitation of...     

Interfacial Ferromagnetism in a Co/CdTe Ferromagnet/Semiconductor Quantum Well Hybrid Structure

The magnetization properties of a ferromagnet-semiconductor Co/CdMgTe/CdTe quantum well hybrid structure are investigated by several techniques. Exploiting the proximity effect between acceptor bound holes and magnetic ions we detect the magnetization curves by measuring the circular polarization of photoluminescence in an out-of-plane magnetic field. We show that magnetization originates from interfacial ferromagnet on Co-CdMgTe interface and the proximity effect is caused by magnetization of interfacial Co-CdMgTe ferromagnetic layer whose magnetic properties are very different from Co.     

Bias Dependence in Spin-Polarized Tunneling of Ferromagnet/Ferromagnetic Insulator (Semiconductor)/Ferromagnet Junctions

Based on the nearly-free-electron approximation, the bias dependencies of electron transport properties of ferromagnet/ferromagnetic insulator (semiconductor)/ferromagnet junctions have been studied. Resonances appear in electron transmission probability. These resonances cause oscillations in the zero-temperature tunnel current and the resonances occur in tunnel conductance. Tunnel magnetoresistance (TMR) is an oscillatory function of bias. The TMR can reach a value as high as 100%. The bins dependencies of electron transport properties relate to the magnetic configurations of the junctions.     

Semi-Classical Dynamics in Quantum Spin Systems

We consider two limiting regimes, the large-spin and the mean-field limit, for the dynamical evolution of quantum spin systems. We prove that, in these limits, the time evolution of a class of quantum spin systems is determined by a corresponding Hamiltonian dynamics of classical spins. This result can be viewed as a Egorov-type theorem. We extend our results to the thermodynamic limit of lattice spin systems and continuum domains of infinite size, and we study the time evolution of coherent spin states in these limiting regimes.     

The Free Energy of the Quantum Heisenberg Ferromagnet at Large Spin

We consider the spin-S ferromagnetic Heisenberg model in three dimensions, in the absence of an external field. Spin wave theory suggests that in a suitable temperature regime the system behaves effectively as a system of non-interacting bosons (magnons). We prove this fact at the level of the specific free energy: if S???? and the inverse temperature ????0 in such a way that ??S stays constant, we rigorously show that the free energy per unit volume converges to the one suggested by spin wave theory. The proof is based on the localization of the system in small boxes and on upper and lower bounds on the local free energy, and it also provides explicit error bounds on the remainder.     

GaAlAs／GaAs量子阱结构的实验研究

利用分子束外延生长法生长出了ＧａＡｌＡｓ／ＧａＡｓ梯度折射率分别限制单量子阱结构材料，对样品进行了光荧光谱、双晶Ｘ射线衍射和电化学电容－电压分布测量。实验结果表明，样品质量达到了设计要求，利用该材料制作的激光二极管获得了初步结果。     

Spin-Triplet Andreev Reflection in Ferromagnet/Ferromangnet/s-Wave Superconductor Junctions

Four-component Bogoliubov-de Gennes equations are applied to study the tunnelling conductance spectra G（ E） of half-metallic ferromagnet/ferromagnet/s-wave superconductor tunnel junctions. It is found that only for noncollinear magnetizations, there exists nonzero G（ E） structure within the energy gap, which is a signature of appearance of the novel Andreev reflection and spin-triplet pairing correlations.     

Carrier Dynamics in Quantum Well Lasers

A fully microscopic theory is used to perform an analysis of carrier–carrier and carrier-LO phonon scattering in semiconductor quantum wells, focussing on the high-density case relevant for laser structures. A large variance of scattering times is observed depending on the material parameters, apparently contradicting popular belief in some cases. For instance, carrier–carrier scattering may slow down when the carrier density is increased. Electron-hole scattering times are found to be on the same order of magnitude as carrier-phonon scattering, making the introduction of a separate electron and hole temperature necessary. Heating by optical pumping is investigated and plasma cooling is shown to be possible by optical pumping of the laser structure.     

Two-Dimensional GaAs/AlGaAs Multiple Quantum Well Spatial Light Modulators

Multiple quantum well spatial light modulators with 128x128 array in 38μm pitch are fabricated using two pproaches, one with an attachment of an optical substrate and another one without. These two fabrication processes are described and compared.     

dc Josephson Effect in s-Wave Superconductor/Ferromagnet Insulator/p-Wave Superconductor Junctions

The Josephson currents in s-wave superconductor/ferromagnet insulator/p-wave superconductor（s/FI/p） junctions are calculated as a function of temperature and the phase taking into account the roughness scattering effect at interface. The phase dependence of the Josephson current I （φ） between s-wave and px-wave superconductor is predicted to be sin（2φ）. The ferromagnet scattering effect, the barrier strength, and the roughness strength at interface suppress the dc currents in s/FI/p junction.     

Dynamics of Einstein-Podolsky-Rosen Steering in Quantum Spin Environment

We explore the dynamics of Einstein-Podolsky-Rosen steering (EPR), measured by steering robustness, for two spin-qubits coupled to a general XY spin chain environment. The evolution process is numerically investigated in the vicinity of critical point for the spin environment. The results show an obvious suppression of steering robustness when the environment undergoes a quantum phase transition. The scaling behavior for the dynamics of EPR steering is also revealed and analyzed around the critical point. Furthermore, we find that steering robustness power (i.e. the average value of steering robustness within a certain time) can indicate the quantum criticality of the environment directly.

     

Two-Dimensional Semimetal HgTe in 14-nm-Thick Quantum Wells

JETP Letters - A two-dimensional semimetal is discovered in the (013) HgTe quantum well with a thickness of d = 14 nm, which is much smaller than those previously studied. It is found that such...