共查询到20条相似文献,搜索用时 78 毫秒
1.
H. Aghaie M.R. Gholami M. Monajjemi M.D. Ganji 《Physica E: Low-dimensional Systems and Nanostructures》2008,40(9):2965-2972
The electron transport characteristics of a 1,10-dimethylene-1,10-dicarba-closo-decaborane (10-vertex carborane) single molecular conductor is investigated via the density functional-based non-equilibrium Green's function (DFT-NEGF) method. We consider three configurations for the molecular wire sandwiched between two Au(1 0 0) electrodes: the hollow site, top site and bridge site positions. Our results show that the energetically favorable hollow site configuration has a higher current intensity than the other configurations.The projection of the density of states (PDOS) and the transmission coefficients T(E) of the two-probe system at zero bias are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to the higher conductance for the hollow configuration.Furthermore, the transmission coefficients of the hollow system at various external voltage biases are also investigated and it shows that the broadening of the transmission coefficient spectrum with increasing of the external voltage bias indicates a strong coupling between the molecular orbitals in the carborane and the incident states from the electrodes, and thus the current increases with increases of the bias voltage. 相似文献
2.
G.P. Pepe G. Peluso R. Scaldaferri L. Parlato C. Granata E. Esposito M. Russo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):421-425
A new fabrication process for three-terminal superconducting devices consisting of two Josephson junctions in a stacked configuration
is reported. The process is based on the deposition of the whole Nb/AlxOy/Nb-Al/AlxOy/Nb multilayer on a Si crystalline wafer without any vacuum breaking. Lift-off techniques, anodization processes and a SiO
film deposition have been adopted for patterning and insulating the two tunnel stacked junctions. Devices have been characterized
in terms of current-voltage (I-V) curves and Josephson critical current vs. the externally applied magnetic field. They show high quality factors (V
m values up to 65 mV at 4.2 K), and good current uniformity.
Received 5 June 2001 相似文献
3.
The structures, stabilities and magnetic properties of CrXn (X = Na, Rb and Cs; n up to 9) clusters are studied using density functional theory to search for the stable magnetic superatoms. The geometrical optimisations indicate the ground-state structures of CrXn evolve toward a close packed structure with an interior Cr atom surrounded by X atoms as the cluster size increase. Their stabilities are analysed by the relative energy, gain in energy (ΔE(n)) and the highest unoccupied molecular orbital and lowest unoccupied molecular orbital gaps. Furthermore, the magnetic moments of CrXn clusters show an odd–even oscillation. Here, we mainly focus on the CrX7 (X = Na, Rb and Cs) clusters due to the same valence count as the known stable magnetic superatoms VNa8, VCs8 and TiNa9. Although these clusters all have a filled electronic configuration 1S21P6 and large magnetic moment 5 μB, our studies indicate that only CrNa7 is highly stable compared to its nearest neighbours, while CrRb7 and CrCs7 clusters are less stable. This suggests that Cr-doped Na7 is most appropriate for filled electronic configuration and CrNa7 is shown to be a stable magnetic superatom. More interesting, we find CrRb8 and CrCs8 with the filled electronic configuration 1S21P6 have higher stability and large magnetic moment 6 μB in their respective series. 相似文献
4.
Li-Qin Yan Fen Wang Yuelei Zhao Tao Zou Jun Shen Young Sun 《Journal of magnetism and magnetic materials》2012
The exchange bias phenomenon has been investigated in multiferroic Eu0.75Y0.25MnO3. The material shows a weak ferromagnetism with cone spin configuration induced by external magnetic field below 30 K. Consequently, the electric polarization coming from the cycloid spin order below 30 K can be suppressed by external magnetic fields. The magnetic hysteresis loops after cooling in a magnetic field exhibit characteristics of exchange bias below the spin glassy freezing temperature (Tg)∼16 K. The exchange bias field, coercivity field, and remanent magnetization increase with increasing cooling magnetic field. The exchange bias effect is ascribed to the frozen uncompensated spins at the antiferromagnetism/weak ferromagnetism interfaces in the spin-glass like phase. 相似文献
5.
Mohammed El Amine Monir 《哲学杂志》2020,100(19):2524-2539
ABSTRACT Based on the full-potential linearised augmented plane wave plus local orbitals (FP-L/APW?+?lo) method within the density functional theory (DFT), the structural, electronic, and magnetic calculations of the cubic oxide perovskite NdInO3 compound have been done under the generalised gradient approximation (GGA). The exchange and correlation (XC) potential is defined as GGA framework in the analyses of structural properties, while both GGA and GGA?+?U (U is the Hubbard correlation term) approximations are taken to treat the electronic and magnetic properties. It is found that ferromagnetic (FM) configuration is reported as the most stable ground state of the cubic NdInO3 material; however, the equilibrium lattice parameters such as lattice constant (a0 ), bulk modulus (B0 ), its first-pressure derivative (B’), and the minimum of total energy (E0 ) are given in paramagnetic (PM), ferromagnetic (FM), and anti-ferromagnetic (AFM) states. The spin-polarized electronic structure calculations (band structure and density of states) of the cubic oxide perovskite NdInO3 compound verify the half-metallic feature due to the spin-up case which has the metallic nature, whereas the spin-down case presents the semiconducting character. Moreover, the magnetic properties show the integer value of the total magnetic moment for the studied compound (3μB ), where it is manly contributed by Nd atoms with apparition of weak local magnetic moments in non magnetic In and O sites. 相似文献
6.
M. A. Zelikman 《Technical Physics》2009,54(2):197-203
A new approach to magnetic field profiling inside a Josephson contact is suggested. Its essence consists in analyzing continuous
variation of a current configuration leading to a decrease in the Gibbs potential. With this approach, one can find a configuration
into which the Meissner state turns when an external field slightly exceeds the upper boundary of the Meissner regime and
trace the evolution of this configuration with increasing field. Calculations show that there exists critical value I
c of the pinning parameter in the range 0.95–1.00. This critical value separates two possible conditions of magnetic field
penetration into the contact. At I > I
c, a near-boundary current configuration completely compensating for the external field inside the contact arises irrespective
of the external field strength. At I < I
c, such a situation is observed only until the external field strength exceeds certain value H
max. Higher fields penetrate into the contact indefinitely deep. In nearboundary configurations, the magnetic field drops with
increasing depth almost linearly. Its slope k has rational values, which remain constant within finite intervals of I. As I goes beyond a given interval, k rises stepwise and takes on another rational value. When an external magnetic field is switched on adiabatically, configurations
with a maximal growth rate of the magnetic field are observed. 相似文献
7.
A.J. Shields P.C. Klipstein G.W. Smith D.R.P. Guy N. Apsley 《Superlattices and Microstructures》1990,7(4)
In this study, we demonstrate how electroreflectance (ER) measurements as a function of bias, and of angle of incidence (θ0), together with bias dependent photocurrent (PC) measurements, can be used to provide understanding of the complex electric field profile and carrier transport effects in a GaAs/Al0.3Ga0.7As multiple quantum well (MQW), grown inside n+ contact layers. The PC measurements exhibit split excitonic features, the components of which change in strength with the applied bias. The effect is explained by absorption in the front of the MQW stack, with the back of the stack acting as detector. We examine the θ0-dependence of the ER lineshape, to determine the depth of the layers responsible for each feature. The ER and PC lineshapes and their bias dependence are explained by the unusual electric field profile across the stack. The field profile appears to be determined by tunnelling of the dark current. 相似文献
8.
Jinzhong Zhang Abdur Rehman Jalil Pok-Lam Tse Jonas Kölzer Daniel Rosenbach Helen Valencia Martina Luysberg Martin Mikulics Gregory Panaitov Detlev Grützmacher Zhigao Hu Jia Grace Lu Thomas Schäpers 《Annalen der Physik》2020,532(8):2000273
Nanohybrid superconducting junctions using antimony telluride (Sb2Te3) topological insulator nanoribbons and Nb superconducting electrodes are fabricated using electron beam lithography and magnetron sputtering. The effects of bias current, temperature, and magnetic field on the transport properties of the junctions in a four-terminal measurement configuration are investigated. Two features are observed. First, the formation of a Josephson weak-link junction. The junction is formed by proximity-induced areas in the nanoribbon right underneath the inner Nb electrodes which are connected by the few tens of nanometers short Sb2Te3 bridge. At 0.5 K a critical current of 0.15 µA is observed. The decrease of the supercurrent with temperature is explained in the framework of a diffusive junction. Furthermore, the Josephson supercurrent is found to decrease monotonously with the magnetic field indicating that the structure is in the small-junction limit. As a second feature, a transition is also observed in the differential resistance at larger bias currents and larger magnetic fields, which is attributed to the suppression of the proximity-induced superconductive state in the nanoribbon area underneath the Nb electrodes. 相似文献
9.
M. Ciszek K. Rogacki K. Oganisian N. D. Zhigadlo J. Karpinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(3):359-365
The DC magnetization and AC complex magnetic
susceptibilities were measured for MgB2 single crystals, unsubstituted
and carbon substituted with the composition of
Mg(B0.94C0.05)2. The measurements were performed in AC and DC
magnetic fields oriented parallel to the c-axis of the crystals. From the DC
magnetization loops and the AC susceptibility measurements, critical current
densities (J
c were derived as a function of temperature and the DC and
AC magnetic fields. Results show that the substitution with carbon decreases
J
c
) at low magnetic fields, opposite to the well known effect of an
increase of J
c
at higher fields. AC magnetic losses were derived from
the AC susceptibility data as a function of amplitude and the DC bias
magnetic field. The AC losses were determined for temperatures of 0.6 and
0.7 of the transition temperature T
c
, so close to the boiling points of
LH2 and LNe, potential cooling media for magnesium diboride based
composites. The results are analyzed and discussed in the context of the
critical state model. 相似文献
10.
M. J. Ma M. B. A. Jalil S. G. Tan D. E. Koh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,82(1):37-46
We theoretically study the spin-polarized transport
through double barrier magnetic tunnel junction (DBMTJ) consisting
of the quantum dot sandwiched by two ferromagnetic (FM) leads. The
tunneling current through the DBMTJ is evaluated based on the
Keldysh nonequilibrium Green’s function approach. The self-energy
and Green’s function of the dot are analytically obtained via the
equation of motion method, by systematically incorporating two
spin-flip phenomena, namely, intra-dot spin-flip, and spin-flip
coupling between the lead and the central dot region. The effects of
both spin-flip processes on the spectral functions, tunneling
current and tunnel magnetoresistance (TMR) are analyzed. The
spin-flip effects result in spin mixing, thus contributing to the
spectral function of the off-diagonal Green’s function components ( Gs[`(s)] r )\left( {G_{\sigma \bar \sigma }^r } \right). Interestingly, the spin-flip coupling
between the lead and dot enhances both the tunneling current and the
TMR for applied bias above the threshold voltage V
th
. On the
other hand, the intra-dot spin-flip results in an additional step in
the I-V characteristics near V
th
. Additionally, it
suppresses the tunneling current but enhances the TMR. The opposing
effects of the two types of spin-flip on the tunneling current means
that one spin-flip mechanism can be engineered to counteract the
other, so as to maintain the tunneling current without reducing the
TMR. Their additive effect on the TMR enables the DBMTJ to attain a
large tunneling current and high TMR for above threshold bias
values. 相似文献
11.
《Superlattices and Microstructures》1995,18(4):259
We propose a new artificial neural cell based on the dynamical properties of superconducting Wheatstone bridges loaded with a transmission line across their transverse junction. The current through the load line of the bridge switches (via magnetic coupling) to a non-zero voltage state an array of double-junction superconducting quantum interference devices (2J-SQUIDs) composing the synaptic circuit. It is shown that the current flowing to the postsynaptic neural cell can be controlled digitally by switching the bias current of the 2J-SQUIDs from zero (OFF state) to 90% of 2 Ic (ON state), where Ic is the critical supercurrent in each junction of the 2J-SQUIDs. Potential applications of the neural cell are briefly discussed. 相似文献
12.
M. A. Zelikman 《Technical Physics》2010,55(3):337-346
The current configurations and the profile of the magnetic field penetrating into a 3D ordered Josephson medium are calculated
for I < I
C
. The calculation algorithm (modified for finite-length samples) is based on analyzing the continuous variation of the configuration
toward a decrease in the Gibbs potential. This algorithm makes it possible to find a configuration into which the Meissner
state passes when I < I
C
and an external field slightly exceeds H
max and trace the evolution of this configuration with a further rise in the field. At H > H
max, the magnetic field penetrates into the sample as a quasi-uniform sequence of plane vortices. When H is roughly equal to H
0/2, where H
0 is the outer field at which one fluxoid Φ0 passes through each cell, the plane vortices disintegrate into linear ones centered in cells neighboring along the diagonal.
As the field grows, the vortex pattern condenses: zero-fluxoid cells are gradually “filled” starting from the boundary. When
the field approaches H
0, a sequence of plane vortices centered in adjacent rows arises near the boundary. With a further increase in the field, sequences
of linear vortices with a double fluxoid form at the boundary. Then, such a scenario is periodically repeated with a period
H
0 in the external field. 相似文献
13.
The semi-analytical method, previously used to construct model double-null and single-null diverted tokamak equi- libria (Bingren Shi, Plasma Phys. Control Fusion 50 (2008) 085006, 51 (2009) 105008, Nucl. Fusion 51 (2011) 023004), is extended to describe diverted tokamak equilibria with nonzero edge current, including the Pfirsch–Schlüter(PS) cur- rent. The PS current density is expressed in a way suitable to describe a diverted tokamak configuration in the near separatrix region. The model equilibrium is expressed by only two terms of the exact separable solutions of the Grad– Shafranov equation, one of which is governed by a homogeneous ordinary differential equation, and the other by an inhomogeneous one. The particular merits of such a model configuration are that the internal region inside the separa- trix and a suitable scrape-off layer can be simultaneously described by this exact solution. To investigate the physics in the region near the X-point, the magnetic surfaces can be satisfactorily described by approximate hyperbolic curves. 相似文献
14.
M. A. Zelikman 《Technical Physics》2010,55(11):1588-1595
The Meissner state of a 3D Josephson medium is analyzed for stability against small fluctuations of phase discontinuities
at contacts. For any form of fluctuations, there exists value I
0 of pinning parameter I such that the Meissner configuration remains stable if I < I
0. Reasons why the configuration remains stable at small I are considered. Instability arises when the quadratic form of the second variation of Gibbs potential G is not a positively definite quantity. At small I, the contribution of the Josephson energy to G is small. The second variation of the magnetic energy, the other component of G, is always a positively definite quadratic form. Therefore, instability may arise only if I has a finite value. This statement holds true not only for the Meissner but also for any equilibrium configuration. At I < I
0, stability persists up to the boundary of the Meissner state. Then, a sequence of plane vortices parallel to the boundary
appears throughout the sample. Thus, vortices appearing at I < I
0 are plane vortices rather than linear. The configurations of currents and the magnetic field profile inside the sample are
calculated for I < I
0. Calculation is based on analyzing the continuous variation of the current configuration toward a decrease in the Gibbs potential. 相似文献
15.
L. Alff S. Kleefisch U. Schoop M. Zittartz T. Kemen T. Bauch A. Marx R. Gross 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):423-438
Andreev bound states at the surface of superconductors are expected for any pair potential showing a sign change in different
k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report
on the observation of Andreev bound states in high temperature superconductors (HTS) employing tunneling spectroscopy on bicrystal
grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic
field. The tunneling spectra of GBJ formed by YBa2Cu3O (YBCO), Bi2Sr2CaCu2O(BSCCO), and La1.85Sr0.15CuO4 (LSCO) show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy
that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS Nd1.85Ce0.15CuO4-y (NCCO) no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero
to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev
bound states are discussed and experimental evidence for anomalous Meissner currents is presented.
Received: 17 February 1998 / Revised: 27 April 1998 / Accepted: 23 June 1998 相似文献
16.
ABDELALI DAOUDI MOHAMED FILALI BABA SOUAD ELKHATTABI FRANÇOIS ROGEMOND HENRY CHERMETTE 《Molecular physics》2013,111(19):2929-2951
The electronic structure of the ScN and ScP molecules is a subject of controversy and turns out to be a challenging problem in quantum chemistry. We show that the ground-state electronic structure for both molecules depends critically on the choice of methods used which incorporate different ways of accounting for electron correlation. A parallel ab initio, DFT and TD-DFT study is performed for this purpose and uses sufficiently flexible basis sets able to reproduce accurate electronic structures, as well as correct spectroscopic constants. In the ab initio methodology, results have been obtained with methods such as Hartree-Fock (HF), M?ller-Plesset perturbation theory (MPn), direct configuration interaction (CI), quadratic configuration interaction (QC), coupled cluster configuration interaction (CC), complete active space self-consistent field (CASSCF) and multireference configuration interaction (CIPSI) methods. In the DFT methodology, various ‘pure’ and ‘hybrid’ density functionals are used and the corresponding results are compared to sophisticated ab initio methods and to available experimental data. All the methods used show that the ground state of both molecules is 1Σ+, but two electronic structure natures, 1Σ+ open-shell or 1Σ+ closed-shell, are competitive and depend on the method employed. All the ab initio methods based on a single determinant wavefunction suffer seriously in predicting clearly the exact nature of the ground state or its correct structural and spectroscopic parameters. However, the ab initio methods based on a multiconfigurational wavefunction appear to be successful in describing correctly, within one shot, the electronic structure and the molecular spectroscopic constants. The ground state, particularly for the ScN molecule, presents an unusual electronic structure: the presence of degenerate determinants, quasidegeneracy with other states and one avoided crossing in the region around the equilibrium distances. The bonding of the ground state is a two open-shell 1Σ+ state described as a π double bond and a Σ dative bond; the real triple bond 1Σ+ state, i.e. closed-shell state, is found to lie higher in energy. The potential energy curves of the lowlying electronic states, the derived electronic structures and various molecular spectroscopic constants are presented and discussed for each method employed. 相似文献
17.
18.
M. A. Zelikman 《Technical Physics》2009,54(12):1742-1748
The configurations of currents and the profile of a magnetic field penetrating into a finite-length contact at I < I
C
are calculated. The computational method is based on analyzing the continuous variation of the current structure leading
to a decrease in the Gibbs potential. Such an approach makes it possible to find a configuration that sets in when an external
field slightly exceeds H
max and trace the evolution of this configuration with increasing field. It is shown that at H > H
max boundary structures turn into quasi-uniform sequences of vortices the spacing between which oscillates about a mean value
decreasing with increasing H. At some values of H, vortices with a number of fluxoids Φ0 larger by unity start penetrating into the contact in the form of boundary sequences. As the field grows, they produce quasi-uniform
sequences, etc. Vortices with the number of fluxoids Φ0 differing by more than unity can fall into the contact at no field. The penetration of vortices with (k + 1)Φ0 into a contact each cell of which contains kΦ0 is fully identical to the penetration of vortices with one Φ0 into the Meissner configuration. This statement is supported by the almost strict periodicity of mean induction b in the contact versus external field h dependence with a period of 1 along both axes and also by the form of the dependences of the magnetic field in the cells
on the cell-boundary distance. 相似文献
19.
We have studied the effect of the internal circumferential magnetic field HB created by the dc bias current IB on longitudinal and off-diagonal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that by changing the dc current IB it is possible to considerably change the MI dependencies. The bias current applied to such microwire transforms the symmetric and hysteretic MI curve to asymmetrical and anhysteretic. The minimum of longitudinal MI curve shifts from the zero-field point. Reversing the bias current causes reversal of the bias field direction and results in a mirroring of the MI curves. It is proposed to apply a cross-checking of two MI curves with IB of different polarity for magnetic field sensing. In particular, this method allows to overcome the drawbacks usually associated with longitudinal MI—namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. Moreover, the operating range of the longitudinal MI sensor, in contrast to the off-diagonal one, can be much extended as it exhibits a quite high sensitivity in the field range up to one order of magnitude higher than the anisotropy field. 相似文献
20.
At an extremely low temperature of 20 mK, we measured loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φf) and the small dc-SQUID (Φfcjj), respectively, the potential shape of the system can be fully controlled in situ. Variations of transition step and overlap size in switching current with the barrier flux bias are analyzed, from which we can obtain some relevant device parameters and built up a model to explain the experimental phenomenon. 相似文献