Surface states of cobalt nanoislands on Cu111

The electronic structure of thin Co nanoislands on Cu(111) has been investigated below and above the Fermi level (E(F)) by scanning tunneling spectroscopy at low temperature. Two surface related electronic states are found: a strong localized peak 0.31 eV below E(F) and a mainly unoccupied dispersive state, giving rise to quantum interference patterns of standing electron waves on the Co surface. Ab initio calculations reveal that the electronic states are spin polarized, originating from d3(z(2)-r(2))-minority and sp-majority bands, respectively.     

Nuclear spin cooling using Overhauser-field selective coherent population trapping

We show that a quantum interference effect in optical absorption from two electronic spin states of a solid-state emitter can be used to prepare the surrounding environment of nuclear spins in well-defined states, thereby suppressing electronic spin dephasing. The coupled electron-nuclei system evolves into a coherent population trapping state by optical-excitation-induced nuclear-spin diffusion for a broad range of initial optical detunings. The spectroscopic signature of this evolution where the single-electron strongly modifies its environment is a drastic broadening of the dark resonance in optical absorption experiments. The large difference in electronic and nuclear time scales allows us to verify the preparation of nuclear spins in the desired state.     

电子散斑干涉条纹骨架线提取的新方法

电子散斑干涉条纹的强噪声特性使其信噪比过低，常用的图像二值化、细化等算法对散斑干涉条纹的骨架提取都存在一定的不足，文章在对散斑条纹图像平滑去噪、对比度增强的预处理基础上，对其进行边缘提取、填充、细化，从而得到干涉条纹的中心骨架线，提出一种基于MATLAB的散班图像自动处理算法。结果表明：文中提出的干涉条纹的细化方法可以准确地找到骨架线，为获得面内位移场的等位移线图提供了一种新方法。     

Rashba interferometers: Spin-dependent single- and two-electron interference

Quantum transport in semiconductor nanostructures can be described theoretically in terms of the propagation and scattering of electron probability waves. Within this approach, elements of a phase-coherent electric circuit play a role similar to quantum-optical devices that can be characterised by scattering matrices. Electronic analogues of well-know optical interferometers have been fabricated and used to study special features of charge carriers in solids. We present results from our theoretical investigation into the interplay between spin precession and quantum interference in an electronic Mach-Zehnder interferometer with spin-orbit coupling of the Rashba type. Intriguing spin-dependent transport effects occur, which can be the basis for novel spintronic devices such as a magnet-less spin-controlled field-effect transistor and a variety of single-qubit gates. Their functionality arises entirely from spin-dependent interference of each single-input electron with itself. We have also studied two-electron interference effects for the spin-dependent Mach-Zehnder interferometer, obtaining analytical expressions for its two-fermion-state scattering matrix. Using this result, we consider ways to generate two-electron output states for which the Rashba spin-subband quantum number and the output arm index are entangled. Combining spin-dependent interference in our proposed Mach-Zehnder interferometer with a projective charge measurement at the output enables entanglement generation. As our particular scheme involves tuneable spin precession, electric-field control of entanglement production can be achieved.     

Quasiparticle interference around a magnetic impurity on a surface with strong spin-orbit coupling

On surfaces with strong spin-orbit coupling, backscattering is forbidden since it requires flipping of the spin of the electron. It has been proposed that the forbidden scattering channels in such systems can be activated if time reversal symmetry is locally broken, for example, by a magnetic scattering center. Scanning tunneling spectroscopic maps of quasiparticle interference patterns around a single magnetic MnPc molecule on a Bi(110) surface reveal only spin-conserving scattering events. Simulations based on the Green's functions approach confirm that the charge-density interference patterns are unaffected by the magnetic state of the impurity. A fingerprint of backscattering processes appears, however, in the magnetization patterns, suggesting that only spin-polarized measurements can access this information.     

Implementation of Full Spin-State Interferometer

Matter-wave interferometers with spin quantum states are attractive in quantum manipulation and precision measurements. Here, five spatial interference patterns corresponding to the full spin states are observed in each run of the experiment, by the combination of the Majorana transition according to the exponential modulation of the magnetic field pulse decline curve and radio frequency coupling among multiple magnetic sub-states.Compared to the realization of two Majorana transitions, the interference fringe for the magnetic field insensitive state also has a higher contrast. After spatially overlapping the full magnetic sub-state interference patterns dozens of times in consecutive experimental measurements, clear fringes are still observed, indicating the great stability of the relative phases of different components. This indicates the potential to achieve an interferometer with multiple spin clocks.     

Triple quantum dots as charge rectifiers

We theoretically analyze electronic spin transport through a triple quantum dot in series, attached to electrical contacts, where the drain contact is coupled to the central dot. We show that current rectification is observed in the device due to current blockade. The current blocking mechanism is originated by a destructive interference of the electronic wavefunction at the drain dot. There, the electrons are coherently trapped in a singlet two-electron dark state, which is a coherent superposition of the electronic wavefunction in the source dot and in the dot isolated from the contacts. Its formation gives rise to zero current and current rectification as the voltage is swept. We analyze this behavior analytically and numerically for both zero and finite magnetic dc fields. On top of that, we include phenomenologically a finite spin relaxation rate and calculate the current numerically. Our results show that triple dots in series can be designed to behave as quantum charge rectifiers.     

SPIN POLARIZATION IN A MODEL QUANTUM WIRE WITH A CROSS-SECTION

Numerical investigation of the electronic structure of a small closed quantum system fabricated on the two-dimensional electron gas forming on the interference between GaAs and Al_xGa_1-xAs is reported. The Kohn-Sham spin-density-fun ctional theory is applied. Self-consistent results show that the quantum system assumes unequal numbers of electrons for spin up and spin down because of the existence of bound states. The profiles of effective potential energies for spin up and spin down electrons are then found to be very different, which will result in different transmission coefficients. It is notable that this spin polarization is caused by the geometry of the nanostructure.     

Spontaneous macroscopic spin polarization in independent spinor Bose-Einstein condensates

We present experimental evidence for the spontaneous formation of a macroscopic spin polarization in overlapping regions of two independent Bose-Einstein condensates produced in different hyperfine states of 87Rb. The condensates are independent in the sense that we do not explicitly introduce a relative phase between them. A single "spin-tip" pulse maps the transverse spin polarization into longitudinal spin polarization, and the atomic density distributions are measured with a Stern-Gerlach imaging method. The resulting matter-wave interference patterns are anticorrelated.     

石墨烯纳米片大自旋特性第一性原理研究

通过基于密度泛函理论的全电子数值轨道第一性原理电子结构计算,研究了各种形状有限石墨烯片段(石墨烯纳米片, GNF)的磁特性,证明GNF的自旋磁有序来源于由其形状决定的π键拓扑挫折(topological frustration)作用.锯齿形边缘的三角形GNF的净自旋不为零,如同一个人造铁磁性原子团,总自旋随尺度线性增加.根据拓扑挫折原理,可以在GNF中引入较大的净自旋和独特的自旋分布,如由三角形GNF单元构成的复杂分形结构,总自旋随分形级数呈指数上升.通过刻蚀技术制作具有一定拓扑结构的GNF可以实现可控自旋电子纳米材料和器件应用.     

Electron-spin motion: a new tool to study ferromagnetic films and surfaces

When electrons are interacting with a ferromagnetic material, their spin-polarization vector is expected to move. This spin motion, comprising an azimuthal precession and a polar rotation about the magnetization direction of the ferromagnet, has been studied in spin-polarized electron scattering experiments both in transmission and reflection geometry. In this review we show that electron-spin motion can be considered as a new tool to study ferromagnetic films and surfaces and we discuss its application to a number of different problems: (a) the transmission of spin-polarized electrons across ferromagnetic films, (b) the influence of spin-dependent gaps in the electronic band structure on the spin motion in reflection geometry, (c) interference experiments with spin-polarized electrons and (d) the influence of lattice relaxations in ferromagnetic films on the spin motion.     

Defects in heavy-fermion materials: unveiling strong correlations in real space

Defects provide important insight into the complex electronic and magnetic structure of heavy-fermion materials by inducing qualitatively different real-space perturbations in the electronic and magnetic correlations of the system. These perturbations possess direct experimental signatures in the local density of states, such as an impurity bound state, and the nonlocal spin susceptibility. Moreover, highly nonlinear quantum interference between defect-induced perturbations can drive the system through a first-order phase transition to a novel inhomogeneous ground state.     

Coherence of an optically illuminated single nuclear spin qubit

We investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt, Science 316, 1312 (2007)10.1126/science.1139831] when a proximal electronic spin associated with a nitrogen-vacancy (N-V) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment.     

Current-induced modification of spin wave mode interference

We have studied the effect of adiabatic spin-transfer torque on mode interference of spin waves. The mode interference generates amplitude-localized spots at special positions which do not move with time. When applying current, the wavevector of spin wave is modified, resulting in current-dependent displacement of amplitude-localized spots. This current-dependent change in the mode interference may allow to probe current-induced spin wave Doppler shift in space-domain. In favorable situations, it can be used to estimate the intrinsic properties of magnetic materials such as spin polarization.     

Continual deformation analysis with scanning phase method and time sequence phase method in temporal speckle pattern interferometry

If a laser beam illuminates a continual deformation object surface, it will lead to a temporal speckle pattern on the observation plane. Recording this time-dependent speckle pattern the deformation of the surface of an object can be obtained. Two methods, scanning phase method (SPM) and time sequence phase method (TSPM), have been introduced for measuring the displacement caused by the deformation in temporal speckle pattern interferometry (TSPI). Their principle is that by capturing a series of speckle interference patterns related to the object deformations, the fluctuations in the intensity of the interference patterns can be obtained. Through scanning these fluctuations and estimating both the average intensity and modulation of the temporal speckle interference patterns, the phase maps for whole-field displacements are calculated. In this way one is capable of quantitatively measuring continual displacements simply using a conventional electronic speckle pattern interferometry (ESPI) system without phase shifting or a carrier. The elaboration on the new methods is given in this paper and experiments are performed to demonstrate their performance with a conventional ESPI system.     

Combinatorial methods in ESR spectroscopy

Combinatorial methods based on the Pólya theory of counting and multinominal expansions are applied to the prediction of the number of hyperfine lines and their intensity patterns arising from the electronic spin and nuclear spin couplings. It is shown that these methods are very useful for predicting the ESR spectral patterns of radicals containing a large number of multinuclear spins.     

Spin Thermoelectric Effects in a Three-Terminal Double-Dot Interferometer

We theoretically investigate the thermoelectric properties of a three-terminal double-dot interferometer with Rashba spin-orbit interaction. It is found that with some temperature distributions a thermal spin current can even be produced without the help of magnetic flux and by tuning the spin interference effect in the system, a pure spin or fully spin-polarized current can be driven by temperature differences. For the cases that two of the terminals are held at the same temperature, the charge (spin) thermopower and the charge (spin) figure of merit are defined and calculated in the linear response regime. With some choices of the system parameters the calculated spin and charge thermopowers are of the same order of magnitude and the charge figure of merit can exceed 1.     

Excitation of spin remagnetization waves in systems with spin-orbit coupling

Elementary excitations of a new type in paramagnetic materials with spin-orbit interaction are predicted theoretically within the Rashba model and named the spin remagnetization waves. These normal modes arise from rotation of the spin magnetic moment in a medium where the electric field contains a constant component and a traveling wave component. A method is proposed for exciting these vibrations by illuminating the sample with an oscillating interference pattern. The spin remagnetization waves can be experimentally detected by measuring the dependence of the current through the sample on the oscillation frequency and wave vector of the interference pattern.     

Half-metallic silicon nanowires: first-principles calculations

From first-principles calculations, we predict that specific transition metal (TM) atom-adsorbed silicon nanowires have a half-metallic ground state. They are insulators for one spin direction, but show metallic properties for the opposite spin direction. At high coverage of TM atoms, ferromagnetic silicon nanowires become metallic for both spin directions with high magnetic moment and may have also significant spin polarization at the Fermi level. The spin-dependent electronic properties can be engineered by changing the type of adsorbed TM atoms, as well as the diameter of the nanowire. Present results are not only of scientific interest, but also can initiate new research on spintronic applications of silicon nanowires.     

Electronic transport through tetrahedron-structured DNA-like system

We theoretically investigate the electronic transport properties of a multi-terminal tetrahedronstructured DNA under a uniform magnetic field. Based on a tight-binding model, the current and nonlocal resistance are calculated under different situations by employing the Landauer–Büttiker formula. Our results indicate that the current displays a clear sign of interference in the presence of the magnetic field and can be mainly divided into three patterns, as demonstrated by the Fourier transformation. Furthermore, the tetrahedron-structured DNA can be used as a molecular switch. The underlying physical mechanisms are analyzed for the various phenomena observed in this threedimensional DNA interferometer.