Tunneling Conductance in dx2-y2+idxy Mixed Wave Superconductor Graphene Junctions

Using the extended Blonder-Tinkham-Klapwijk formalism, we investigate the conductance spectra of normal metal/d_x²-y²+id_xy mixed wave superconductor graphene junctions. It is found that the conductance spectra vary strongly with the orientation of the gap and the amplitude ratio (Δ₁/Δ₀) of two components for d_x²-y²+id_xy mixed wave. The zero bias conductance isnearly 2 and the conductance peak vanishes in doped graphene forα=0 and Δ₁/Δ₀=1. The conductance increases with increasing the amplitude ratio of two components for α=π/4 and Δ₁/Δ₀=1. The ZBCP becomesobservable wide with 1F/Δ₀<100 for α=π/4 and Δ₁/Δ₀=1. This property is different from that in normal metal/d_x²-y² wave superconductor graphenejunctions.     

Effect of Landau Zener tunneling by the varying sweeping rate of external field

We study the effect of Landau--Zener (LZ) tunneling caused by the varying sweeping rate of the external field, and solve the problem about the LZ tunneling rate among many levels. The LZ tunneling rate is essentially changed by the unsteady variation of the time-dependent sweeping field and is different from the steadily varying sweeping field, which makes the particles in lower states transit periodically to upper states within a finite time.     

Electronic structure and charge transport properties of amorphous Ta2O5 films

Amorphous Ta₂O₅ films were deposited by sputtering Ta onto silicon substrates with reactive ion beam. Electron energy loss spectroscopy measurements on the film found that the plasma oscillation energy is 23.1 eV. The refractive index and the extinction coefficient were measured with spectroscopic ellipsometry over the spectral range of 1.9–4.9 eV. The optical band gap is found to be 4.2 ± 0.05 eV. The valence band consists of three bands separated by ionic gaps. The values of electron effective masses were estimated with DFT quantum-chemical calculation. Experiments on injection of minority carriers from silicon into oxide were also conducted and we found that the electron component of conduction current governed by the electron current in the amorphous Ta₂O₅.     

磁性隧道结中的量子相干输运研究

采用散射矩阵的方法研究了铁磁/绝缘层/半导体/绝缘层/铁磁(FM/I/SM/I/FM)磁性双隧道结的量子相干输运特性.研究发现当隧穿电子平均自由程(l_p)和中间层半导体厚度(L)可比拟时双结隧道磁阻(TMR)将随L的变化产生量子振荡,当l_p远大于L时振荡拐点处出现cut-off波矢,分析表明cut-off波矢主要是来自于隧道结两边的铁磁和半导体层隧穿电子动量波矢的高度不匹配性,随着L关键词： cut-off 波矢 量子相干 振荡 隧道磁阻     

Defects and Pd growth on the reduced SnO2(1 0 0) surface

Scanning tunneling microscopy experiments on a clean, reduced SnO₂(1 0 0)-(1 × 1) surface reveal surface defects with zero-, one-, and two-dimensions. Point defects consist of missing SnO/SnO₂ units. Line defects are probably crystallographic shear planes that extend to the surface and manifest themselves as rows of atoms, shifted half a unit cell along the [0 1 0] direction. Their ends act as preferential nucleation sites for the formation of Pd clusters upon vapor deposition. Areas of a more reduced surface phase, still with a (1 × 1) structure and a half-unit cell deep, form at [0 0 1]-oriented step edges.     

Large scale atomic ordering on uncovered GaAs(0 0 1) after InAs monolayer capping: Atomic structure of the (12 × 6) reconstruction

A well ordered c(8 × 2)-InAs monolayer is grown by molecular beam epitaxy (MBE) on a GaAs(0 0 1) substrate. After slow sublimation of this monolayer up to 560 °C, a homogeneously (n × 6) reconstructed GaAs surface is obtained. This surface is studied by scanning tunneling microscopy (STM) in UHV. This shows that it is well-ordered on a large scale with 200 nm long As dimer rows along and is also locally (12 × 6) reconstructed, the cell structure is proposed. We believe that this surface organization results from the specific As/Ga (0.7) surface atomic ratio obtained after the InAs monolayer growth and sublimation cycle.     

A single h-BN layer on Pt(1 1 1)

The structure and formation of an ultrathin hexagonal boron nitride (h-BN) film on Pt(1 1 1) has been studied by a combination of scanning tunneling microscopy, low energy electron diffraction, low energy electron microscopy, X-ray absorption and high resolution core level spectroscopy. The study shows that a single boron nitride layer is formed on Pt(1 1 1), resulting in a coincidence structure. High resolution scanning tunneling microscopy (STM) images of the h-BN ultrathin film display only one of the atomic species in the unit cell. Probing the boron and nitrogen related local density of states by near edge X-ray absorption fine structure measurements we conclude that the nitrogen sublattice is visible in STM images. The growth of the single hexagonal boron nitride layer by vapourized borazine in the pressure range of 1×10^-6–1×10^-8 at 800 °C is further studied by low energy electron microscopy, and reveals that the number of nucleation sites and the perfection of the growth is strongly pressure dependent. A model for the single, hexagonal, boron nitride layer on Pt(1 1 1) is proposed.     

Transformations of C-type defects on Si(100)-2 × 1 surface at room temperature – STM/STS study

We present a scanning tunneling microscopy study of the C-type defects on the Si(100)-2 × 1 surface and their transformations into other defect forms at room temperature. A model of the C defect as a dissociated water molecule was adopted for interpretation of the observed transformations. We explained the transformations by hopping the H or OH between bonding sites on Si dimers. Newly, the most stable defect form, corresponding to the H and hydroxyl group adsorbed on the same dimer, is reported. Real time observations provided an explanation for the defect C2-C2 described earlier. A reversible transition of this defect into another form, not revealed yet, is presented. Electronic structure of the observed defects is studied by means of scanning tunneling spectroscopy. Measured spectra show semiconducting character of the C defect. Spectra of the other defect forms are discussed.     

Fermions tunneling from Reissner–Nordström black hole

Hawking tunneling radiation of spin ? 1/2 particles from the event horizon of the Reissner–Nordström black hole is studied. We introduce the Dirac equation of the charged particles. We further consider the gravitational interaction and back reaction of the emitted spin particles in the dynamical background space–time. The result shows that when the energy conservation and charge conservation are taken into account, the actual radiation spectrum of fermions also derivates from the thermal one and the tunneling rate is related to the change of Bekenstein–Hawking entropy.     

Electrical conductance properties for magnetic tunnel junctions with MgO barriers

We measured inelastic electron tunneling (IET) spectra and conductance for MgO tunneling magnetoresistance (TMR) films to obtain information on the ferromagnetic/barrier layer interface. The IET spectra showed the difference between amorphous and crystalline structures in the barrier. In the magnetic tunnel junction (MTJ) with a crystalline barrier the IET spectra indicated an Mg-O phonon peak at a low bias voltage by measurement with a parallel magnetization configuration. On the other hand, no peak was observed in the MTJ with an amorphous barrier.