Quantum statistical analysis of superconductivity,fractional quantum Hall effect,and aromaticity

The phenomena of superconductivity and fractional quantum Hall effect (FQHE) as well as the well‐known chemical concepts of aromaticity and antiaromaticity are analyzed on the basis of quantum statistical considerations. We suggest that the superconducting transition is caused by a first‐order interaction between the charge carriers which does not necessarily involve a second‐order coupling of the electron–phonon type. For molecular model systems it is demonstrated that the formation of superconducting Cooper pairs can lead to an attenuation of destabilizing quantum constraints of the intersite type, i.e., constraints due to the Pauli antisymmetry principle (PAP). We suggest that this attenuation is the driving force for the superconducting transition. Such a reduction of the PAP influence on the quantum ensemble is also the key element of the present explanation of the FQHE. Analogies between the superconducting transition and the plateaus in the Hall conductance are emphasized. Both phenomena can be interpreted in terms of an electronic phase transition which shifts the original fermionic (fe) system towards a hard core bosonic (hcb) boundary. hcb ensembles are characterized by on‐site anticommutativity and intersite commutativity. The collective solid‐state phenomena superconductivity and FQHE are correlated with the popular chemical concepts of aromaticity and antiaromaticity. Numerical results for the superconducting pairing are derived by the two‐parameter Hubbard Hamiltonian. In order to express physically transparent interrelations between fe and hcb ensembles, the so‐called statistical transmutation is adopted. Arguments on the basis of experimental results are summarized which support the present PAP‐driven superconducting pairing formalism. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 125–162, 2000     

对称测量法在霍尔元件测磁场中的应用

在用霍尔元件测磁场时,一般采用对称测量法以消除各种附加电压的影响,当出现某种附加电压大于霍尔电压这种特殊情况时,该测量方法更为必要．     

Hall effect measurements using low ac magnetic fields and lock-in technique on field effect transistors with molybdenum disulfide channels

Hall effect measurements conventionally rely on the use of dc magnetic fields. For electronic devices made of ultrathin semiconducting materials, such as molybdenum disulfide (MoS₂), the dc Hall effect measurements have practical difficulties. Here, we report the results of the Hall effect measurements using ac magnetic fields and a lock-in detection of the Hall voltage for field effect transistors with ultrathin MoS₂ channels. The ac Hall effect measurements have some advantages over the dc measurements. The carrier concentration and the Hall mobility were estimated as a function of gate voltage from the results of the ac Hall effect measurements. They used a magnetic field strength that was lower by two orders of magnitude than those used in prior studies on MoS₂ devices, which relied on dc magnetic fields.     

Origin of large spin Hall magnetoresistance in Fe/CuOx bilayers

We have compared the spin Hall magnetoresistance (SMR) in Fe/Pt and Fe/CuO_x (with natural oxidation) bilayers with varying the thickness of Fe layer. A larger SMR in Fe/CuO_x bilayers has been found when the thickness of Fe layer is 3 nm. Moreover, the SMR of the two bilayers decrease with increasing the thickness of Fe from 3 nm to 10 nm, but that of Fe/CuO_x drops more sharply due to shunting current effect. Through harmonic measurements, the emergent spin current is proved to be generated in the Fe/CuO_x bilayers. The mixed phase of CuO_x has been confirmed including CuO, Cu₂O and Cu, which performs strong spin-orbit coupling and produce large spin current. On the other hand, the interface-generated spin current should be ruled out. All the results have been compared with those in Fe/Al₂O₃ bilayers with negligible spin current.     

Investigation of ultra-thin and flexible Au–Ag–Au transparent conducting electrode

The performance of ultra-thin Au–Ag–Au tri-layer film deposited thermally over a flexible substrate is investigated using structural, optical, mechanical and electrical-transport measurements. The optimum total thickness of the tri-layer for high transparency and conductivity is determined to be around 8 nm using a theoretical model. The Au–Ag–Au tri-layer shows maximum transmittance (≅ 62%) at wavelength 500 nm. XRD pattern shows peak corresponding to (111) plane of Au and/or Ag. Sheet resistance (≅ 10.42 Ω/□) measured at 300 K using four probe technique is stable up to 150 °C. Hall effect measurements show high conductivity (1.34 × 10⁵ (Ω cm)⁻¹), carrier concentration (2.48 × 10²³/cm³), and mobility (3.4 cm²/Vs). Scotch tape test confirms good adhesion of the film onto PET substrate. Bending-twisting tests using an indigenous apparatus indicate high resistance-stability even after 50,000 cycles. These results imply the viability of Au–Ag–Au tri-layer film as a transparent conducting electrode worth exploring for optoelectronic applications.     

音乐厅音质设计进展述评

本文对近年来音乐厅音质设计中若干问题的进展作一述评。（1）在已建立的众多独立音质参量基础上，如何作出大厅综合评价，就需要考虑到它们的互动性和贡献权，方法学将成为关键。（2）空间感已确认由声源视在展宽度ASW和听者环绕感LEV组成，对于影响两者的诸多复杂因素有了较深入研究，这声场中的细节又将如何与大厅设计相联系亦备受关注。（3）听众及座椅吸声这个老问题有了新的研究成果，对于空、满场的声学关系已积累了更多资料，使大厅音质的估算更为精确可靠。（4）常说扩散对大厅音质很重要，但其主观效应仍然处于玄虚状态，一些新的主观试听实验结果还不足以说明问题。     

Synthesis,X‐ray data,and Hall effect measurements of Li‐doped Tl‐Ba‐Ca‐Cu‐O superconductor

Lithium‐doped Tl‐based superconductor was prepared by adding an amount of 0.3 mol.% to the Tl_1.8Ba₂Ca_2.2Cu₃O_x compound. The usual solid‐state reaction method has been applied under optimum conditions. The x‐ray data of the sample show a tetragonal structure with a high ratio of Tl‐2223 superconducting phase. The sample showed a transition at 125 K and the zero resistance was observed at 117 K. Longitudinal (transport) and transverse (Hall) resistivities were measured at different temperatures under different magnetic fields and the data were interpreted. A positive Hall coefficient was observed at normal state and a sign reversal appears at temperatures lower than the critical temperature. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

量子反常霍尔效应研究进展

在没有外加磁场的作用下就能表现出量子化霍尔电导的量子反常霍尔效应已经成为霍尔家族中的重要一员, 其物理起源是体能带反转结构和铁磁性相互作用. 量子反常霍尔效应最重要的表现是在边缘态处具有无耗散运动的手性电流, 这种性质拥有可以改变未来量子电子学的潜力, 极大推动器件小型化、 低损耗、 高速率发展. 近年来,基于理论指导, 人们在实验上已多次观察到量子反常霍尔效应. 在本文中, 从实验层面上重点回顾了量子反常霍尔效应在铬(Cr) 、钒(V) 掺杂的(Bi,Sb)2Te3 体系的研究进展, 以及目前量子反常霍尔效应在其它体系中的研究现状, 深入理解量子反常霍尔效应的起源和机理, 最后对量子反常霍尔效应进行总结和展望