李萨如图形的计算机模拟--大学物理CAI软件开发实例

利用计算机绘制动态演示图形，观察、分析、研究李萨如图形的规律．     

Electric gating of the multichannel conduction in LaAlO_3/SrTiO_3 superlattices

The electric gating on the transport properties of two-dimensional electron gas(2DEG) at the interface of LaAlO₃/SrTiO₃(LAO/STO) heterostructure has attracted great research interest due to its potential application in fieldeffect devices. Most of previous works of gate effect were focused on the LAO/STO heterostructure containing only one conductive interface. Here, we systematically investigated the gate effect on high-quality LAO/STO superlattices(SLs)fabricated on the TiO₂-terminated(001) STO substrates. In addition to the good metallicity of all SLs, we found that there are two types of charge carriers, the majority carriers and the minority carriers, coexisting in the SLs. The sheet resistance of the SLs with a fixed thickness of the LAO layer increases monotonically as the thickness of the STO layer increases. This is derived from the dependence of the minority carrier density on the thickness of STO. Unlike the LAO/STO heterostructure in which minority and majority carriers are simultaneously modulated by the gate effect, the minority carriers in the SLs can be tuned more significantly by the electric gating while the density of majority carriers is almost invariable. Thus, we consider that the minority carriers may mainly exist in the first interface near the STO substrate that is more sensitive to the back-gate voltage, and the majority carriers exist in the post-deposited STO layers. The SL structure provides the space separation for the multichannel conduction in the 2 DEG, which opens an avenue for the design of field-effect devices based on LAO/STO heterostructure.     

Abundant photoelectronic behaviors of La_(0.67)Sr_(0.33)MnO_3/Nb:SrTiO_3 junctions

Temperature dependence on rectifying and photoelectronic properties of La_(0.67)Sr_(0.33)MnO_3/Nb:SrTiO_3(LSMO/STON) junctions with the thickness values of LSMO film varying from 1 nm to 54 nm are systematically studied. As shown experimentally, the junctions exhibit good rectifying properties. The significant differences in photoemission property among the LSMO/STON junctions are observed. For the junction in a thicker LSMO film, the photocurrent shows a monotonic growth when temperature decreases from 300 K to 13 K. While for the junction in an ultrathin LSMO film, the behaviors of photocurrent are more complicated. The photocurrent increases rapidly to a maximum and then smoothly decreases with the decrease of temperature. The unusual phenomenon can be elucidated by the diffusion and recombination model of the photocarrier.     

Entanglement Entropy Signature of Quantum Phase Transitions in a Multiple Spin Interactions Model

Through the Jordan-Wigner transformation, the entanglement entropy and ground state phase diagrams of exactly solvable spin model with alternating and multiple spin exchange interactions are investigated by means of Green's function theory. In the absence of four-spin interactions, the ground state presents plentiful quantum phases due to the multiple spin interactions and magnetic fields. It is shown that the two-site entanglement entropy is a good indicator of quantum phase transition (QPT). In addition, the alternating interactions can destroy the magnetization plateau and wash out the spin-gap of low-lying excitations. However, in the presence of four-spin interactions, apart from the second order QPTs, the system manifests the first order QPT at the tricritical point and an additional new phase called ``spin waves', which is due to the collapse of the continuous tower-like low-lying excitations modulated by the four-spin interactions for large three-spin couplings.     

预制带肋底板混凝土双向叠合板等效各向同性板的弹性计算方法

结合预制带肋底板混凝土双向叠合板(简称双向叠合板)的正交构造异性特征,分析了当前实际工程设计中存在的问题。直接从双向叠合板的挠曲面基本微分方程出发,依据正交各向异性板理论,推导了双向叠合板与各向同性板挠度和内力的等效关系。由此等效关系,引入等效跨度比,修正双向叠合板的预制底板板肋平行、垂直方向边长,将其等效为相应的各向同性板来计算。最后,列举一边固支三边简支边界条件的双向叠合板算例,利用已有的各向同性板弹性计算系数表,直接按照等效跨度比进行插值计算,将所得结果同按照挠度和弯矩计算式计算结果进行比较。结果表明:计算结果吻合良好,各项弹性计算系数均满足双向叠合板与各向同性板挠度和内力的等效关系,说明本文提出的弹性计算方法是正确的。