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1.
Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this review is dedicated to the use of ultrathin films of insulating oxides as barriers for tunnel junctions. In addition to dielectric non-magnetic epitaxial barriers, which can produce tunneling magnetoresistances in excess of a few hundred percent, we pay special attention to the possibility of exploiting the multifunctional character of some oxides in order to realize ‘active’ tunnel barriers. In these, the conductance across the barrier is not only controlled by the bias voltage and/or the electrodes magnetic state, but also depends on the barrier ferroic state. Some examples include spin-filtering effects using ferro- and ferrimagnetic oxides, and the possibility of realizing hysteretic, multi-state junctions using ferroelectric barriers. The second part of this review is devoted to novel states appearing at oxide interfaces. Often completely different from those of the corresponding bulk materials, they bring about novel functionalities to be exploited in spintronics and electronics architectures. We review the main mechanisms responsible for these new properties (such as magnetic coupling, charge transfer and proximity effects) and summarize some of the most paradigmatic phenomena. These include the formation of high-mobility two-dimensional electron gases at the interface between insulators, the emergence of superconductivity (or ferromagnetism) at the interface between non-superconducting (or non-ferromagnetic) materials, the observation of magnetoelectric effects at magnetic/ferroelectric interfaces or the effects of the interplay and competing interactions at all-oxide ferromagnetic/superconducting interfaces. Finally, we link up the two reviewed research fields and emphasize that the tunneling geometry is particularly suited to probe novel interface effects at oxide barrier/electrode interfaces. We close by giving some directions toward tunneling devices exploiting novel oxide interfacial phenomena. 相似文献
2.
I. Shigeta Y. Tanaka F. Ichikawa Y. Asano 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):141-149
We propose a new approach of smearing origins of a zero-bias
conductance peak (ZBCP) in high-Tc superconductor tunnel
junctions through the analysis based on the circuit theory for a
d-wave pairing symmetry.
The circuit theory has been recently developed from conventional
superconductors to unconventional superconductors.
The ZBCP frequently appears in line shapes for this theory, in which the
total resistance was constructed by taking account of the effects
between a d-wave superconductor and a diffusive normal metal (DN) at a
junction interface, including the midgap Andreev resonant states (MARS),
the coherent Andreev reflection (CAR) and the proximity effect.
Therefore, we have analyzed experimental spectra with the ZBCP of
Ag-SiO-Bi2Sr2CaCu2O8+δ (Bi-2212) planar tunnel
junctions for the {110}-oriented direction by using a simplified
formula of the circuit theory for d-wave superconductors.
The fitting results reveal that the spectral features of the ZBCP are
well explained by the circuit theory not only excluding the Dynes's
broadening factor but also considering only the MARS and the DN
resistance.
Thus, the ZBCP behaviors are understood to be consistent with those of
recent studies on the circuit theory extended to the systems containing
d-wave superconductor tunnel junctions. 相似文献
3.
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
4.
C. Benjamin T. Jonckheere A. Zazunov T. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):279-289
We consider a model for a single molecule with a large frozen spin
sandwiched in between two BCS superconductors at equilibrium, and
show that this system has a π junction behavior at low
temperature. The π shift can be reversed by varying the other
parameters of the system, e.g., temperature or the position of the
quantum dot level, implying a controllable π junction with
novel application as a Josephson current switch. We show that the mechanism
leading to the π shift can be explained simply in terms of the contributions
of the Andreev bound states and of the continuum of states above the superconducting gap.
The free energy for certain configuration of parameters shows a
bistable nature, which is a necessary pre-condition for
achievement of a qubit. 相似文献
5.
W. Ihra M. Leadbeater J.L. Vega K. Richter 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):425-435
We study the effect on the density of states in mesoscopic ballistic billiards to which a superconducting lead is attached.
The expression for the density of states is derived in the semiclassical S-matrix formalism shedding light onto the origin of the differences between the semiclassical theory and the corresponding
result derived from random matrix models. Applications to a square billiard geometry and billiards with boundary roughness
are discussed. The saturation of the quasiparticle excitation spectrum is related to the classical dynamics of the billiard.
The influence of weak magnetic fields on the proximity effect in rough Andreev billiards is discussed and an analytical formula
is derived. The semiclassical theory provides an interpretation for the suppression of the proximity effect in the presence
of magnetic fields as a coherence effect of time reversed trajectories. It is shown to be in good agreement with quantum mechanical
calculations.
Received 21 August 1999 and Received in final form 21 March 2001 相似文献
6.
We review the methods and use of random quantum states with particular emphasis on recent theoretical developments and applications in various fields. The guiding principle of the review is the idea that random quantum states can be understood as classical probability distributions in the Hilbert space of the associated quantum system. We show how this central concept connects questions of physical interest that cover different fields such as quantum statistical physics, quantum chaos, mesoscopic systems of both non-interacting and interacting particles, including superconducting and spin–orbit phenomena, and stochastic Schrödinger equations describing open quantum systems. 相似文献
7.
The Kondo effect and the Andreev reflection tunneling through a normal (ferromagnet)-double quantum dots-superconductor hybrid system is examined in the low temperature by using the nonequilibrium Green's function technique in combination with the slave-boson mean-field theory. The interplay of the Kondo physics and the Andreev bound state physics can be controlled by varying the interdot hopping strength. The Andreev differential conductance is mainly determined by the competition between Kondo states and Andreev states. The spin-polarization of the ferromagnetic electrode increases the zero-bias Kondo peak. The spin-flip scattering influences the Kondo effect and the Andreev reflection in a nontrivial way. For the ferromagnetic electrode with sufficiently large spin polarization, the negative Andreev differential conductance is found when the spin flip strength in the double quantum dots is sufficiently strong. 相似文献
8.
M. Vélez J.I. Martín J.E. Villegas A. Hoffmann E.M. González J.L. Vicent Ivan K. Schuller 《Journal of magnetism and magnetic materials》2008
This review is dedicated to summarizing the recent research on vortex dynamics and pinning effects in superconducting films with artificial magnetic structures. The fabrication of hybrid superconducting/magnetic systems is presented together with the wide variety of properties that arise from the interaction between the superconducting vortex lattice and the artificial magnetic nanostructures. Specifically, we review the role that the most important parameters in the vortex dynamics of films with regular array of dots play. In particular, we discuss the phenomena that appear when the symmetry of a regular dot array is distorted from regularity towards complete disorder including rectangular, asymmetric, and aperiodic arrays. The interesting phenomena that appear include vortex-lattice reconfigurations, anisotropic dynamics, channeling, and guided motion as well as ratchet effects. The different regimes are summarized in a phase diagram indicating the transitions that take place as the characteristic distances of the array are modified respect to the superconducting coherence length. Future directions are sketched out indicating the vast open area of research in this field. 相似文献
9.
Memory effects are ubiquitous in nature and are particularly relevant at the nanoscale where the dynamical properties of electrons and ions strongly depend on the history of the system, at least within certain time scales. We review here the memory properties of various materials and systems which appear most strikingly in their non-trivial, time-dependent resistive, capacitative and inductive characteristics. We describe these characteristics within the framework of memristors, memcapacitors and meminductors, namely memory-circuit elements with properties that depend on the history and state of the system. We examine basic issues related to such systems and critically report on both theoretical and experimental progress in understanding their functionalities. We also discuss possible applications of memory effects in various areas of science and technology ranging from digital to analog electronics, biologically inspired circuits and learning. We finally discuss future research opportunities in the field. 相似文献
10.
11.
Ju Peng 《Physics letters. A》2008,372(21):3878-3881
We theoretically report a nonlocal Andreev reflection in an Aharonov-Bohm interferometer, which is a three-terminal normal metal/superconductor (NS) mesoscopic hybrid system. It is found that this nonlocal Andreev reflection is sensitive to the systematic parameters, such as the bias voltages, the quantum dot levels, and the external magnetic flux. If we set the chemical potential of one normal metal lead equal to zero, the electronic current in the lead results from two competing processes: the quasiparticle transmission and nonlocal Andreev reflection. The appearance of zero electronic current signals unambiguously the existence of this nonlocal Andreev reflection. 相似文献
12.
J. Schefer T. Woike M. Imlau B. Delley 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):349-352
The metastable states of sodiumnitroprusside are extremely stable at temperatures below 200 K. It is possible to allocate structural changes measured by neutron diffraction
to measured spectroscopic parameters, but the amount of the structural change is relatively small for a reaction co-ordinate
as the metastable states have an extremely long lifetime. New hypotheses for related systems try to explain such a phenomena
in two ways: The first way is a bending of the NO-bond in the metastable state, the second one an exchange of the oxygen and nitrogen atoms in the NO-bond
(which can be regarded as an bending). As such changes would be possible also from our density functional calculations, we re-investigated our neutron
diffraction data using the new models. However, our results are not compatible with one of these models. On the contrary,
the neutron diffraction data show partially opposite tendencies. We compare both models with EXAFS measurements, with vibrational
spectroscopic results and the data found by M?ssbauer spectroscopy. We propose a potential scheme for all three states (GS,
and ) extracted from absorption and thermodynamic data to explain the electronic and energetic rearrangement, and the population
dynamics.
Received: 23 June 1997 / Accepted: 13 October 1997 相似文献
13.
Superfluid (3)He is an intensively investigated and well characterized p-wave superfluid. In the bulk Balian-Werthamer state, which is commonly called the (3)He B phase, the superfluid gap is opened isotropically but near a flat boundary such as a wall of a container it can harbor interesting quasi-particle states inside the gap. These states are called surface Andreev bound states, and have not been experimentally explored in detail. Transverse acoustic impedance measurement has revealed their existence and provided spectroscopic details of the dispersion of the bound states. Recent theoretical arguments claim that the surface Andreev bound states of the superfluid (3)He B phase can be recognized as the edge states of the topological superfluid and be regarded as a Majorana fermion, a fancy particle which has not been confirmed in elementary particle physics. In this review, we present up-to-date knowledge on the surface Andreev bound states of the (3)He B phase revealed by acoustic spectroscopy and the possible realization of a Majorana fermion, along with related studies on this topic. 相似文献
14.
R. F. Rodríguez H. Híjar 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):105-110
We use a fluctuating hydrodynamic approach to calculate the orientation
fluctuations correlation functions of a thermotropic nematic liquid crystal
in a nonequilibrium state induced by a stationary heat flux. Since in this
nonequilibrium stationary state the hydrodynamic fluctuations evolve on
three widely separated times scales, we use a time-scale perturbation
procedure in order to partially diagonalize the hydrodynamic matrix. The
wave number and frequency dependence of these orientation correlation
functions is evaluated and their explicit functional form on position is
also calculated analytically in and out of equilibrium. We show that for
both states these correlations are long-ranged. This result shows that
indeed, even in equilibrium there is long-range orientational order in the
nematic, consistently with the well known properties of these systems.We
also calculate the dynamic structure of the fluid in both states for a
geometry consistent with light scattering experiments. We find that as with
isotropic simple fluids, the external temperature gradient introduces an
asymmetry in the spectrum shifting its maximum by an amount proportional to
the magnitude of the gradient. This effect may be of the order of 7 per
cent. Also, the width at half height may decrease by a factor of about 10
per cent. Since to our knowledge there are no experimental results available
in the literature to compare with, the predictions of our model calculation
remains to be assessed. 相似文献
15.
M.M. Kuklja 《Applied Physics A: Materials Science & Processing》2003,76(3):359-366
In this article we briefly review the results of theoretical simulations for the initiation of chemistry processes in high-explosive
crystals from a solid-state-physics viewpoint. We analyze the possibility of initiation of chemical reactions from excited
electronic states. In other words, we look for conditions that facilitate electronic excitations in the crystal. Specifically,
we describe modifications to the electronic structure of RDX (cyclotrimethylene trinitramine) induced by lattice defects and
by a shock wave traversing the solid. Our approach is based on ab initio Hartree–Fock band-structure calculations with electronic
correlation corrections. An excitonic mechanism and a hole model, suggested earlier, are discussed in connection with the
most recent experimental and theoretical advances in ultrafast optical techniques. We also consider here possible new avenues
in the development of detonation theory.
Received: 3 December 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +1-301/744-4451, E-mail: KuklaMM@ih.navy.mil 相似文献
16.
Synchronization processes in populations of locally interacting elements are the focus of intense research in physical, biological, chemical, technological and social systems. The many efforts devoted to understanding synchronization phenomena in natural systems now take advantage of the recent theory of complex networks. In this review, we report the advances in the comprehension of synchronization phenomena when oscillating elements are constrained to interact in a complex network topology. We also take an overview of the new emergent features coming out from the interplay between the structure and the function of the underlying patterns of connections. Extensive numerical work as well as analytical approaches to the problem are presented. Finally, we review several applications of synchronization in complex networks to different disciplines: biological systems and neuroscience, engineering and computer science, and economy and social sciences. 相似文献
17.
We extend the circuit theory of superconductivity to cover transport and proximity effect in mesoscopic systems that contain unconventional superconductor junctions. The approach fully accounts for zero-energy Andreev bound states forming at the surface of unconventional superconductors. As a simple application, we investigate the transport properties of a diffusive normal metal in series with a d-wave superconductor junction. We reveal the competition between the formation of Andreev bound states and proximity effect that depends on the crystal orientation of the junction interface. 相似文献
18.
19.
A. Nittke P. Esquinazi H.-C. Semmelhack A.L. Burin A.Z. Patashinskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):19-30
We have measured the low-temperature (K) specific heat and heat release of small amorphous and crystalline SiO2 particles embedded in Teflon and of Vycor. The temperature and time dependence of these properties have been interpreted
in terms of the tunneling model. We found that the particle size influences the density of states of tunneling systems of
the composite. The smaller the size of the particles the larger is the density of states of tunneling systems P0. Quartz grains with dimensions in the micrometer range show similar glass-like properties as vitreous silica. In comparison
with bulk vitreous silica, Vycor shows a much larger P0 in agreement with the behavior we found for small SiO2 particles. We discuss the implication of our results on the origin of the universal low-temperature properties of glasses.
Received 9 April 1998 相似文献