共查询到20条相似文献,搜索用时 15 毫秒
1.
E. Khosravi S. Kurth G. Stefanucci E. K. U. Gross 《Applied Physics A: Materials Science & Processing》2008,93(2):355-364
Charge transport through a nanoscale junction coupled to two macroscopic electrodes is investigated for the situation when
bound states are present. We provide numerical evidence that bound states give rise to persistent, non-decaying current oscillations
in the junction. We also show that the amplitude of these oscillations can exhibit a strong dependence on the history of the
applied potential as well as on the initial equilibrium configuration. Our simulations allow for a quantitative investigation
of several transient features. We also discuss the existence of different timescales and address their microscopic origin. 相似文献
2.
A charge-current switch manipulated by the macroscopic quantum coherence of a single-molecule magnet
B. Chang J.-Q. Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(4):515-522
We report a theoretical analysis of electron transport
through a quantum dot with an embedded biaxial single-molecule
magnet, which is coupled to ferromagnetic electrodes of parallel and
antiparallel magnet-configurations. For the antiparallel
configuration of complete polarization it is shown that the
originally prohibited electron transport can be opened up by the
macroscopic quantum coherence of the molecular magnet, which
provides a spin-flipping mechanism. The charge-current and
differential conductance are controllable by variation of the
magnitude and orientation of an external magnetic field, which in
turn manipulates the macroscopic quantum coherence of the molecular
magnet. Moreover, the transport can be switched off at particular
values of the magnetic field, where the tunnel splitting is quenched
by the quantum phase interference of tunnel paths.The transport
current and differential conductance as functions of the
electrode-polarization and magnetic field are extensively studied,
which may be useful in practical applications. A new transport
channel is found in the completely polarized parallel-configuration
induced by the tunnel splitting of molecular magnet and
resonance-peak splits of the conductance are observed in
non-completely polarized configurations. 75.50.Xx Molecular magnets 相似文献
3.
M. Bryushinin V. Golubev Y. Kumzerov D. Kurdyukov I. Sokolov 《Applied physics. B, Lasers and optics》2009,95(3):489-495
We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous
glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created
by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal
amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 (λ=442 nm, I
0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 (λ=532 nm, I
0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L
D=0.18 μm. 相似文献
4.
Fabrizio Nesti 《The European Physical Journal C - Particles and Fields》2009,59(3):723-729
It is shown how the Lorentz and standard-model gauge groups can be unified by using algebraic spinors of the standard four-dimensional
Clifford algebra, in left–right symmetric fashion. This defines a framework of unification with gravity and generates exactly
a standard-model family of fermions, while a Pati–Salam unification group emerges, at the Planck scale, where (chiral) gravity
decouples. We show that this low-energy broken phase emerges from the VEV of extended vierbein fields, which at this stage
are assumed to be dynamically generated from a theory in the fully symmetric phase valid beyond the Planck scale (and whose
consistency and dynamics is thus yet to be assessed) providing thus a geometrical and group-theoretical framework for the
unification and breaking. At low energy, on the other hand, it is intriguing to find, as a remnant of this unification, new
isospin-triplet spin-two particles that may naturally lie at the weak scale, providing a striking signal at the LHC. 相似文献
5.
L. S. Ewe I. Hamadneh H. Salama N. A. Hamid S. A. Halim R. Abd-Shukor 《Applied Physics A: Materials Science & Processing》2009,95(2):457-463
The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature
in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T
IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T
IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T
IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region
and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E
F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The
ρ–T
2 curves are nearly linear in the metallic regime, but the ρ–T
2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data
well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers.
MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling
effect. 相似文献
6.
7.
Y. Liu T. P. Chen H. W. Lau L. Ding M. Yang J. I. Wong S. Zhang Y. B. Li 《Applied Physics A: Materials Science & Processing》2008,93(2):483-487
Conduction switching, i.e., a sharp change in the conduction from a lower-conductance state to a higher-conductance state
or vice versa in aluminum nitride thin films embedded with Al nanocrystals (nc–Al) has been observed in the ramped-voltage and ramped-current current–voltage (I–V) measurements and the time-domain current measurement as well. Each state is well defined and its I–V characteristic follows a power law. It is observed that the conductance decreases (or increases) with charging (or discharging)
in the nc–Al. It is shown that the conduction switching is due to the charging and discharging in the nc–Al at certain strategic sites. With the connecting (or breaking) of some conductive tunneling paths formed by the uncharged
nc–Al due to the discharging (or charging) in the nc–Al at the strategic sites, a conduction switching occurs. 相似文献
8.
Temperature dependence of photoconductivity and persistent photoconductivity of single ZnO nanowires 总被引:1,自引:0,他引:1
Zhi-Min Liao Yi Lu Jun Xu Jing-Min Zhang Da-Peng Yu 《Applied Physics A: Materials Science & Processing》2009,95(2):363-366
Photoelectrical properties of single ZnO nanowires have been investigated using photocurrent–voltage characteristics measurements
varying with excitation photon energy and temperature. It is found that persistent photoconductivity (PPC) exists, and the
PPC decreases with decreasing temperature. The temperature dependence of the PPC effect indicates that thermally activated
return of electrons from shallow traps is responsible for the PPC phenomenon. The photosensitivity is found to be linear with
the applied voltage, and it increases with decreasing temperature. A temperature dependence of photoconductivity gain was
introduced to explain the experimental results. 相似文献
9.
Toluene laser-induced fluorescence (LIF) emission spectra were acquired in an optical engine with excitation at 248 nm. Toluene
was homogeneously seeded in pure nitrogen and air which were used as intake gases. Data were acquired during the compression
phase without ignition leading to simultaneous increases in temperature and pressure from 20°C and 1 bar to 500°C and 23.6 bar.
Compared to LIF emission spectra at high temperature and atmospheric pressure reported in the literature, the toluene-LIF
emission signal shifts to longer wavelengths when temperature and pressure increase simultaneously, whereas the spectrally
integrated emission intensity is slightly affected by the pressure level. 相似文献
10.
Sofia Selvanathan Maike V. Peters Jutta Schwarz Stefan Hecht Leonhard Grill 《Applied Physics A: Materials Science & Processing》2008,93(2):247-252
Azobenzene derivatives were deposited onto a Au(111) surface and studied by scanning tunneling microscopy. The symmetry of
the parent azobenzene was broken by introducing tert-butyl groups which are known to decouple the molecular core from the substrate, on the one end, and carboxylic acid groups
which direct and stabilize the supramolecular assembly structure on the surface by intermolecular hydrogen bonding, on the
other end. As a consequence of the interacting COOH groups, the molecules assemble on the surface either in extended, polymeric
chains and/or in discrete, hexameric rosettes. The high stability of the rosette structure is proven experimentally by controlled
lateral displacement on the surface without breaking the non-covalent interactions. Although switching attempts were not successful,
the approach herein should facilitate the construction of well-defined multi-switch arrays.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
11.
We introduce a full interaction Hamiltonian method to the generalized quantum chemical approach and apply it to investigate the electron tunneling properties of 1,3-benzenedithiol molecular device. The weak gate effect we calculate is consistent with the experiment. The asymmetric current character mainly comes from the asymmetry of the molecule and the nonlinear responding to the gate electric field. 相似文献
12.
Z.?Radovi? V.?Paltoglou N.?Lazarides N.?Flytzanis 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(2):229-236
We study the Josephson effect in ballistic double-barrier SINIS planar junctions, consisting of bulk superconductors (S),
a clean normal metal or semiconductor (N), and insulating interfaces (I) modeled as a δ-function potential-energy barriers.
We solve the scattering problem based on the Bogoliubov-de Gennes equations and derive a general expression for the dc Josephson
current, valid for arbitrary interfacial transparency, the Fermi wave vectors mismatch, and for different effective band masses.
The effect of transmission resonances on the Josephson current and on the normal conductance is analyzed for short junctions.
Curvature of the temperature dependence of the critical Josephson current is related to the presence of resonances at the
Fermi level and to the interfacial transparency. For thin semiconductor layers with negative effective masses of the carriers,
finite interfacial transparency and large Fermi wave vectors mismatch we find that an unusual and significant enhancement
of both the normal conductance and the critical Josephson current occurs at low temperatures due to the presence of an evanescent
mode localized at interfaces. 相似文献
13.
Effects of Contact Atomic Structure on Electronic Transport in Molecular Junction 总被引:1,自引:0,他引:1 下载免费PDF全文
Based on nonequilibrium Green's function and first-principles calculations, we investigate the change in molecular conductance caused by different adsorption sites with the presence of additional Au atom around the metal- molecule contact in the system that benzene sandwiched between two Au(111) leads. The motivation is the variable situations that may arise in break junction experiments. Numerical results show that the enhancement of conductance induced by the presence of additional Au is dependent on the adsorption sites of anchoring atom. When molecule is located on top site with the presence of additional Au atoms, it can increase molecular conductance remarkably and present negative differential resistance under applied bias which cannot be found in bridge and hollow sites. Furthermore, the effects of different distance between additional Au and sulfur atoms in these three adsorption sites are also discussed. 相似文献
14.
J. Carvalho C. Furtado F. Moraes 《The European Physical Journal C - Particles and Fields》2008,58(2):331-335
We study the problem of electromagnetic self-interaction of line sources in the presence of an array of parallel cosmic strings
akin to the von Kármán vortex street configuration. Keeping in mind possible applications in condensed matter physics we consider
also a mixed array where both deficit angle and excess angle cosmic strings appear. We obtain explicit expressions for both
the electric and magnetic self-energies for the cases studied and demonstrate that these results reproduce the known self-energies
in the single-string limit. 相似文献
15.
Kourosh Nozari S. Davood Sadatian 《The European Physical Journal C - Particles and Fields》2008,58(3):499-510
We consider two alternative dark-energy models: a Lorentz-invariance preserving model with a non-minimally coupled scalar
field and a Lorentz-invariance violating model with a minimally coupled scalar field. We study accelerated expansion and the
dynamics of the equation of state parameter in these scenarios. While a minimally coupled scalar field does not have the capability
to be a successful dark-energy candidate with line crossing of the cosmological constant, a non-minimally coupled scalar field
in the presence of Lorentz invariance or a minimally coupled scalar field with Lorentz-invariance violation have this capability.
In the latter case, accelerated expansion and phantom divide line crossing are the results of the interactive nature of this
Lorentz-violating scenario. 相似文献
16.
M. Aoki K. Miwa T. Noritake N. Ohba M. Matsumoto H.-W. Li Y. Nakamori S. Towata S. Orimo 《Applied Physics A: Materials Science & Processing》2008,92(3):601-605
We have investigated the structural and dehydriding properties of Ca(BH4)2. It was found that Ca(BH4)2 undergoes a structural phase transformation from an orthorhombic low-temperature (LT) modification into a tetragonal high-temperature
(HT) modification between 433 K and 523 K. The amount of hydrogen desorbed from Ca(BH4)2 during the pressure–composition (p–c) isotherm measurement was 5.9 mass%. This hydrogen desorption is caused by the partial dehydrogenation of Ca(BH4)2 accompanied by the formation of CaH2 and orthorhombic intermediate phases. 相似文献
17.
D.?Koudela A.-M.?Uimonen H.?H?kkinen 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):111-117
We study the dependence of the intrinsic conductance of a nanocontact on its shape by using the recursion-transfer-matrix
method. Hour-glass, torus, and spherical shapes are defined through analytic potentials, the latter two serving as rough models
for ring-like and spherical molecules, respectively. The sensitivity of the conductance to geometric details is analyzed and
discussed. Strong resonance effects are found for a spherical contact weakly coupled to electron reservoirs. 相似文献
18.
M. C. B. Abdalla M. E. X. Guimarães J. M. Hoff da Silva 《The European Physical Journal C - Particles and Fields》2008,57(4):791-796
We obtain, via the Gauss–Codazzi formalism, the expression of the effective Einstein–Brans–Dicke projected equations in a
non-ℤ2 symmetric braneworld scenario which presents hybrid compactification. It is shown that the functional form of such equations
resembles the one in the Einstein case, except for the fact that they bring about extra information in the context of exotic
compactifications. 相似文献
19.
A. Saffarzadeh M. Ghorbani Asl 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):239-244
Using the tight-binding approximation and the nonequilibrium Green’s function approach, we investigate the coherent spin-dependent
transport in planar magnetic junctions consisting of two ferromagnetic (FM) electrodes separated by a graphene flake (GF)
with zigzag or armchair interfaces. It is found that the electron conduction strongly depends on the geometry of contact between
the GF and the FM electrodes. In the case of zigzag interfaces, the junction demonstrates a spin-valve effect with high magnetoresistance
(MR) ratios and shows negative differential resistance features for a single spin channel at positive gate voltage. In the
case of armchair interfaces, the current-voltage characteristics behave linearly at low bias voltages and hence, both spin
channels are in on state with low MR ratios. 相似文献
20.
Radek Zeipl Jarmila Walachová Martin Pavelka Miroslav Jelínek Václav Studnička Tomáš Kocourek 《Applied Physics A: Materials Science & Processing》2008,93(3):663-667
Room temperature conductivity and the Seebeck coefficient of thin layers prepared by laser ablation from Bi2Te3 target were explored. The power factor was calculated for samples prepared at substrate temperature of 360°C with the density
of the laser beam 5 J cm−2 and at substrate temperature of 410°C with the density of the laser beam 2 J cm−2 during the deposition. Oscillations of the conductivity and the power factor with the layer thickness were observed at room
temperature. The oscillations of conductivity were also verified at the temperature of 77 K. The period of oscillations depends
on the preparation conditions. This behavior has been theoretically explained by the quantum size effect in the layers containing
different phases and in addition, it was demonstrated by the X-ray Diffraction measurement.
The behavior of the power factor of the layers is compared to the behavior of the figure of merit of the layers published
earlier. 相似文献