Surface states in an external electric field

In an electric field typical for field ion microscopy, true surface states can exist. Their shift towards higher energies can be quite significant, and moreover, additional surface levels at still higher energies can appear.     

Existence of localized electronic states at interfaces

A simple self-consistent atomic model is used to show that both true localized interface states as well as interface resonances can occur at the junction between a metal and a non-metal. These results resolve a controversy of long standing over whether or not true localized states (Bardeen states) can exist when one of the electrodes is a metal. Two distinct physical situations are considered for the metal-non-metal interface showing that these interface states may or may not exist depending upon the band gap of the non-metal and the coupling strength across the interface. In addition, results are presented for the case when both electrodes are non-metals (heterojunctions).     

Low-temperature metastable states in thermal desorption of cyclic ethers

Three cyclic ethers, two dioxanes and one trioxane, exhibit unusual, low-temperature desorption states from Ru(001). For all three compounds, the peak temperature, 150–170 K, is significantly lower than that of the true multilayer state. As a function of increasing exposure, the low-temperature state always populates before the true multilayer, and disappears again as the multilayer state grows to dominance. For all three compounds, the coverage-exposure relationship is consistent with the idea that the multilayer forms by a nucleation process. For two of the three ethers, variation of heating rate indicates that the low-temperature state can undergo activated conversion to the multilayer, and so is truly metastable. These data suggest that such low-temperature states, previously observed for benzene on several metal surfaces, may exist for a variety of adsorbates. The fundamental origin of these states, however, remains unknown.     

Model studies of the Tamm-like and field-sustained surface states of germanium

The effects of varying the intensity of an applied positive electric field on the Tamm-like and field-sustained surface states of a semi-infinite 6-well model of germanium are studied. The effects of a neon image gas atom on such states are also examined. It is found that there are ranges of the field intensity for which field-sustained surface states do not exist. The localization properties of electrons in the various surface states are discussed with the help of relative probability density functions. As is well-known, electrons in Tamm-like states in the first forbidden energy gap tend to be strongly localized near the surface and inside the crystal. However those in Tamm-like states in higher gaps do not exhibit any pronounced localization. Electrons in field-sustained surface states tend to be strongly localized outside the crystal.     

Nonlinear Tamm states in layered metal–dielectric metamaterials

We study nonlinear surface modes at the edge of metal–dielectric nanostructured metamaterial with a nonlinear surface layer. We demonstrate that such semi‐infinite structures can support transverse electric (TE) polarized surface states with subwavelength localization near the surface, an optical analogue of the Tamm states, even in the cases when the surface modes do not exist in the linear regime. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Confined states and spin polarization on a topological insulator thin film modulated by an electric potential

We study the electronic structure and spin polarization of the surface states of a three-dimensional topological insulator thin film modulated by an electrical potential well. By routinely solving the low-energy surface Dirac equation for the system, we demonstrate that confined surface states exist, in which the electron density is almost localized inside the well and exponentially decayed outside in real space, and that their subband dispersions are quasilinear with respect to the propagating wavevector. Interestingly, the top and bottom surface confined states with the same density distribution have opposite spin polarizations due to the hybridization between the two surfaces. Along with the mathematical analysis, we provide an intuitive, topological understanding of the effect.     

Defect-free surface states in modulated photonic lattices

We predict that interfaces of periodically curved waveguide arrays can support a novel type of surface states which exist in a certain region of modulation parameters associated with the band flattening. Such linear surface states appear in truncated but otherwise perfect (defect-free) lattices as a direct consequence of the periodic modulation of the lattice potential. We show that the existence of these modes in different band gaps can be flexibly controlled by selecting the modulation profile, with no restrictions on Bloch-wave symmetries characteristic of Shockley states.     

Interfacial electronic states in semiconductor heterostructures

It is shown that electronic states of a new type, with energy in the band gap can exist at a heterointerface. The interfacial states may be associated with Tamm surface states in the materials forming the heterointerface, but they can appear even if there are no surface states in the initial materials. In the plane of the heterojunction, the energy spectrum of interfacial states forms a two-dimensional band. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 393–398 (25 March 1998)     

Violation of the entropic area law for fermions

We investigate the scaling of the entanglement entropy in an infinite translational invariant fermionic system of any spatial dimension. The states under consideration are ground states and excitations of tight-binding Hamiltonians with arbitrary interactions. We show that the entropy of a finite region typically scales with the area of the surface times a logarithmic correction. Thus, in contrast with analogous bosonic systems, the entropic area law is violated for fermions. The relation between the entanglement entropy and the structure of the Fermi surface is discussed, and it is proven that the presented scaling law holds whenever the Fermi surface is finite. This is, in particular, true for all ground states of Hamiltonians with finite range interactions.     

Discrete surface solitons

It is theoretically shown that discrete nonlinear surface waves are possible in waveguide lattices. These self-trapped states are located at the edge of the array and can exist only above a certain power threshold. The excitation characteristics and stability properties of these surface waves are systematically investigated.     

Low frequency surface waves in the presence of an external high frequency electric field

The problem of surface sound propagation in the presence of external high frequency dipole electric field is investigated using Vlasov-Poisson equations. The structure of the electric field of these surface waves is also determined. It has been found that the ion sound waves that exist in the presence of external high frequency waves are true surface waves while those without the external field are quasi-surface waves as the former waves decay within one wavelength away from the surface.     

Influence of electron correlation on surface states of nonmetallic solids

In this note the method of Mott and Littleton is adopted to construct the position dependent correlation potential for energy bands in a non-metallic solid. One specifically studies the case of a solid with a surface. The principle result is that the effect of electronic correlation is to inhibit the effect of formation of true localized surface states in the region of the band gaps.     

Zero-energy Andreev surface bound states in the lattice model

The conditions for zero-energy Andreev surface bound states to exist are found for the lattice model of a d-wave superconductor with arbitrary surface orientation. Both nearest-neighbors and next-nearest-neighbors models are considered. It is shown that the results are very sensitive to the surface orientation. In particular, for a half-filled (hl0)-surface, zero-energy Andreev surface states only appear under the condition that h and l are odd simultaneously.     

AlxGa1-xAs(100)表面性质的研究

用紫外光电子能谱研究了Al_0.7Ga_0.3As的表面态结构,观察到Al_0.7Ga_0.3As在价带中的两个表面态结构。在1500L原子氢吸附后消失。研究了这两个表面态结构在热退火消除表面损伤过程中的变化。结合LEED和XPS的实验结果,确定在450℃左右的热退火可以有效地消除损伤,获得一个完整的Al_0.7Ga_0.3As(100)表面。 关键词：     

Low energy Auger and loss electron spectra from magnesium and its oxide

Data have been obtained from Auger and energy loss processes in clean metallic Mg, Mg during stages of oxidation, and UHV cleaved MgO(100) surfaces. Particular attention has been paid to twenty features below 200 eV in the Auger spectra from these surfaces. A comparison of spectra from the metal, oxidised metal surface, and single crystal MgO has enabled estimates to be made of surface charging effects, and the MgO steady state surface potential is found to be near + 10 V above ground. All the Auger features are given assignments, two of which are interfacial processes involving ionic initial states and metallic final states. Several features in the low energy Auger spectrum are attributed to diffraction of true secondary electrons.     

Hydrodynamic flow patterns and synchronization of beating cilia

We calculate the hydrodynamic flow field generated far from a cilium which is attached to a surface and beats periodically. In the case of two beating cilia, hydrodynamic interactions can lead to synchronization of the cilia, which are nonlinear oscillators. We present a state diagram where synchronized states occur as a function of the distance of cilia and the relative orientation of their beat. Synchronized states occur with different relative phases. In addition, asynchronous solutions exist. Our work could be relevant for the synchronized motion of cilia generating hydrodynamic flows on the surface of cells.     

BiOCl{001}表面原子与电子结构的第一性原理研究

基于密度泛函理论的第一性原理方法研究了BiOCl{001}的三种不同终端面({001}-1Cl, {001}-BiO 和{001}-2Cl)的表面弛豫、能带结构、电子态密度和表面能. 计算结果表明: {001}-1Cl, {001}-BiO和{001}-2Cl表面均发生明显弛豫, 而在双Cl原子层处的层间距变化较大, 但未出现振荡弛豫现象, 其中{001}-1Cl表面弛豫较小. 与体相BiOCl电子结构相比, BiOCl{001}面具有较窄的带隙宽度, 并呈现较强局域性:对于{001}-BiO表面, 其导带与价带均往低能方向发生较大移动, 并且在导带底部出现表面态; 而{001}-2Cl表面的表面态主要出现在价带顶; {001}-1Cl表面的带隙中则无表面态产生; 表面态的出现导致{001}-BiO面和{001}-2Cl面带隙明显减小. BiOCl{001}三种终端表面的表面能分析结果表明, {001}-1Cl表面的表面能最小(0.09206 J·m^-2), 结构最稳定, 而{001}-BiO表面和{001}-2Cl表面的表面能分别为2.392和2.461 J·m^-2. 理论预测{001}-BiO表面和{001}-2Cl表面具有较高的活性, 但在BiOCl晶体生长过程中不易暴露. 本文计算结果为实验获得BiOCl高活性面{001}给予了基础理论解释, 进一步为BiOCl新型光催化材料的应用研究提供理论指导. 关键词： BiOCl{001}表面 表面弛豫 表面能 第一性原理     

Analytical study of surface states caused by the edge decoration

Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional (1D) model and zigzag edged graphene (ZEG) are presented by means of transfer matrix method, in the frame of which the conditions for the existence of edge states are determined. For 1D model, the zero-energy surface state occurs regardless of whether the decorations exist or not, while the non-zero-energy surface states can be induced and manipulated through adjusting the edge decoration. On the other hand, the case for the semi-infinite ZEG model with nearest-neighbour interaction is discussed in the analogous way. The non-zero-energy surface states can be induced by the edge decoration and moreover, the ratio between the edge hopping and the bulk hopping amplitudes should be within a certain threshold.