共查询到20条相似文献,搜索用时 31 毫秒
1.
The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases. 相似文献
2.
3.
A. Henstra 《Molecular physics》2013,111(7):859-871
Nuclear orientation via electron spin locking (NOVEL) is a technique to orient nuclear spins embedded in a solid. Like other methods of dynamic nuclear polarization (DNP) it employs a small amount of unpaired electron spins and uses a microwave field to transfer the polarization of these unpaired electron spins to the nuclear spins. Traditional DNP uses CW microwave fields, but NOVEL uses pulsed electron spin resonance (ESR) techniques: a 90 degree pulse–90 degree phase shift–locking pulse sequence is applied and during the locking pulse the polarization transfer is assured by satisfying the Hartmann–Hahn condition. The transfer is coherent and similar to coherence transfer between nuclear spins. However, NOVEL requires an extension of the existing theory to many, inequivalent nuclear spins and to arbitrary, i.e. high electron and nuclear spin polarization. In this paper both extensions are presented. The theory is applied to the system naphthalene doped with pentacene, where the proton spins are polarized using the photo-excited triplet states of the pentacene molecules and found to show excellent agreement with the experimentally observed evolution of the polarization transfer during the locking pulse. 相似文献
4.
Shaojun Zhang Zhaobing Tian Qingpu Wang Xin Yin Shichen Li 《Optics & Laser Technology》2007,39(3):507-509
With the polarization plane gyration and the electro-optic effect existing simultaneously in an optical activity crystal, the theory on interaction of optical activity and electro-optic effect on the arbitrary linearly polarized light propagating through the crystal along the optical axis is studied. The electro-optical Q-switch is designed successfully. With the conclusion of the theory, the optimal length of optical activity crystal using as electro-optical Q-switch at a given wavelength is calculated. 相似文献
5.
Souma S Kosaka K Sato T Komatsu M Takayama A Takahashi T Kriener M Segawa K Ando Y 《Physical review letters》2011,106(21):216803
We have performed spin- and angle-resolved photoemission spectroscopy of Bi(2)Te(3) and present the first direct evidence for the existence of the out-of-plane spin component on the surface state of a topological insulator. We found that the magnitude of the out-of-plane spin polarization on a hexagonally deformed Fermi surface of Bi(2)Te(3) reaches maximally 25% of the in-plane counterpart, while such a sizable out-of-plane spin component does not exist in the more circular Fermi surface of TlBiSe(2), indicating that the hexagonal deformation of the Fermi surface is responsible for the deviation from the ideal helical spin texture. The observed out-of-plane polarization is much smaller than that expected from the existing theory, suggesting that an additional ingredient is necessary for correctly understanding the surface spin polarization in Bi(2)Te(3). 相似文献
6.
M. A. Osipov M. V. Gorkunov H. F. Gleeson S. Jaradat 《The European physical journal. E, Soft matter》2008,26(4):395-404
A molecular theory of the ferroelectric smectic C* phase has been developed using the simple model of a chiral molecule composed
of a uniaxial core and a pair of off-center nonparallel dipoles which determine molecular chirality and polarity. The interaction
between uniaxial cores is modeled by a rather general effective potential which can be used to describe smectic materials
with both conventional and anomalously weak layer contraction in the smectic C* phase. Spontaneous polarization, tilt, and
layer spacing are calculated numerically as functions of temperature, and it is shown that the variation of the polarization
generally deviates from that of the tilt angle. It is shown that this deviation is more pronounced in smectic materials tilting
with low layer contraction which corresponds to existing experimental data. The model has been used to reproduce qualitatively
the experimental data for polarization, tilt and layer spacing for two similar mixtures exhibiting conventional and anomalously
weak layer contraction. The polarization and the tilt are also calculated in the case when the smectic A-smectic C* transition
is characterized by the biaxial primary order parameter. 相似文献
7.
The interatomic potentials in a system of an excited Na or K atom and an inert gas atom are calculated on the basis of the
effective pseudopotential method, using a new form of the polarization interaction potential obtained by calculating the most
important polarization diagrams of perturbation theory in the Thomas-Fermi approximation. The results of a calculation, on
its basis, of the intermolecular terms of this van der Waals system are given, refining the existing data; some of the results
have been obtained for the first time. A comparison is made with the available experimental and theoretical data.
Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 32–35, September,
1996. 相似文献
8.
Particle sizing and velocity measurement of microspheres from the analysis of polarization of the scattered light 总被引:1,自引:0,他引:1
X.Q. HuangV. Lepiller Y. Bailly F. GuermeurP. Hervé 《Optics and Lasers in Engineering》2012,50(1):57-63
A brief review of the existing particle sizing methods is presented. An optical method under development is introduced from the analysis of the polarization ratio of the light scattered by the particles based on Lorenz-Mie theory. The theoretical background is summarized with the numerical calculation presented. A photogrammteric system has been set up to perform the measurements. Calibration of the experimental setup has been carried out on polystyrene microspheres of different size. The experimental values of the polarization ratio have been obtained by analyzing the particle images taken by the CCD to render the particle size under investigation. Several experiments and their results are demonstrated to illustrate the application fields of the optical method presented in the current study. 相似文献
9.
将磁光效应和光纤非线性效应作为微扰,采用导波光耦合理论分析了高非线性光纤中导波光发生磁光四波混频的机理;实验测试了磁场对四波混频偏振依赖性的影响,理论分析与实验结果符合.研究表明,当输入的探测光和抽运光为相互正交的线偏振光时,四波混频的磁控效果最为明显,输出的闲频光功率随磁光耦合系数振荡变化,施加适当的外加磁场可使四波混频效率得到进一步提高.选择适当费尔德常数的光纤材料,利用磁光效应对四波混频偏振依赖性的影响,可实现不同范围的磁场测量. 相似文献
10.
A. V. Glushkov A. F. Kivganov V. N. Khokhlov T. V. Buyadzhi L. A. Vitavetskaya V. P. Borovskaya V. N. Polishchuk 《Russian Physics Journal》1998,41(3):223-226
The interatomic potentials in a system formed by an ion of an inert gas in the ground state and an atom of an inert gas (e.g.,
Ne+, Ar+-Ne, Ar, Kr, Xe) are calculated on the basis of a calculation of the most important polarization diagrams of perturbation
theory in the Thomas-Fermi approximation. The calculation employs the effective pseudopotential method using a new form of
the polarization interaction potential. Results are presented from a calculation of the quasimolecular terms of particular
van der Waals systems that improve existing data; some of the data were obtained in earlier studies.
Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 36–40, March,
1998. 相似文献
11.
N. Auerbach 《Nuclear Physics A》1974,229(3):447-460
A systematic study of the core polarization correction to Coulomb displacement energies is carried out. A zero range density independent and density dependent force is used to calculate this correction in the A = 16, A = 40, and A = 208 regions. It is found that the core polarization correction does not increase the Coulomb displacement energies and, therefore, cannot resolve the existing discrepancy between theory and experiment. Moreover, when the mean square radius of the excess neutron distribution is decreased the core polarization correction to the Coulomb energy becomes attractive and cancels the gain resulting from the direct Coulomb term. Hence, it is concluded that the discrepancy cannot be resolved even when the excess neutron distribution has an anomalously small radius. It is also pointed out that when the core polarization term is added the discrepancy is almost equal in mirror nuclei with a single hole in the N = Z core and those with a single particle outside the same core. Evidently, additional charge asymmetric corrections are required to resolve the discrepancies in Coulomb displacement energies. 相似文献
12.
Biesheuvel PM 《The European physical journal. E, Soft matter》2005,16(4):353-359
We consider the problem of polyelectrolyte molecules adsorbing on oppositely charged interfaces. For sufficiently long chains, the ground-state dominance approximation can be used which results in a (semi-)analytical solution of the self-consistent field equations (aSCF). Whereas existing aSCF theory assumes a low polyelectrolyte density, here the required electrostatic corrections for a high polymer density are implemented. Adsorbed polymer excludes volume for the solvent and small ions, a volume effect that also leads to a reduced dielectric permittivity and a resulting polarization term in the exchange potential. Calculations show the influence of volume exclusion on the polymer density profile. 相似文献
13.
Based on the many-particle theory, a general approach to the stimulated polarization effects in a strong periodic field is formulated. A relation to the perturbation theory is demonstrated and forms of the effective polarization potentials for isolated atoms and ions and for ions in plasma are presented. The state of the art of the theory of stimulated polarization bremsstrahlung effect is analyzed, and some prospects for further experimental and analytical investigations are outlined. 相似文献
14.
We demonstrate, for the first time to our knowledge, optical parametric oscillation based on four-wave mixing in microstructure fiber. The measured wavelength-tunability range of the device (40 nm) and the threshold-pump peak power (34.4 W) are in good agreement with the theory of four-wave mixing in optical fibers. The ellipticity of the fiber's polarization modes allows the device to be implemented in a relatively simple Fabry-Perot configuration. Spectral peaks that are due to cascaded-mixing processes are easily observed in our setup, which may provide a way to extend the tunability range of existing high-power lasers. 相似文献
15.
A design concept of a wire-grid polarizer, which is based on the effective-medium theory, has been proposed. The effective indices of a wire-grid grating are evaluated with the effective-medium theory. The results show that, the wire-grid grating acts as a metal for TE polarization, but it behaves like a dielectric material for TM polarization. According to the different effective optical properties of the wire-grid grating for the different polarizations, a wire-grid polarizer with a high polarization ratio can be obtained by enhancing both the transmission for TM polarization and the reflection for TE polarization. 相似文献
16.
17.
本文通过计入异核偶极相互作用的非久期项对交叉极化弛豫速率的影响而推广交叉极化理论。自旋系统内部的快运动可以使得异核偶极相互作用的非久期项对交叉弛豫的贡献变得可观。本文给出了交叉弛豫速率的一般公式,并讨论了本理论在交叉极化实验中的应用。 相似文献
18.
We describe a new algorithm in a cost effective polarization division multiplexing (PDM) system. Without modifying the existing transmitter, receiver electronics, or softwares, we use a special optical scheme to demultiplex the signal multiplexed and improve it with a conjugated gradient algorithm. We experimentally resume the polarization state with a deviation under 5% and the power loss less than 20 dB which proves the feasibility of the polarization control algorithm in the new polarization multiplexing system. 相似文献
19.
We present experimental measurements of the polarization dependence of two-photon absorption in silicon photodiodes at 1550 nm, and we offer a simple theory that explains our observations. Based on this theory, we propose and demonstrate that it is possible to construct an optical cross-correlation system that is polarization insensitive, provided that one of the two input polarization states can be controlled. 相似文献