共查询到20条相似文献,搜索用时 15 毫秒
1.
Takanari Kashiwagi Masayuki Hagiwara Shojiro Kimura Hiroshi Miyazaki Isao Harada Zentaro Honda Koich Kindo 《Applied magnetic resonance》2009,36(2-4):309-316
The S = 1 quasi-one-dimensional Heisenberg antiferromagnet [Ni(C5H14N2)2N3](PF6), abbreviated as NDMAP, has been studied by electron spin resonance in a magnetic field above the critical field (H c). We studied angular and frequency dependences of spin excitations. The angular dependence of the spin excitations in the vicinity of H c is explained well by a phenomenological field theory, but the agreement between the experiment and the calculation is not satisfactory above 10 T. In high magnetic fields above 15 T, we obtained some characteristic spin excitations which are well explained by conventional antiferromagnetic resonance modes. These results suggest that the spin excitations change from a quantum state to a classical one due to the suppression of quantum fluctuations by high magnetic fields. 相似文献
2.
In their recent work on the dimensional reduction, Candelas and Weinberg considered a model which is compactified into a direct product space of the Minkowski space (M4) and an N-dimensional sphere (SN). In the present paper we investigate generalized models of their type which are compactified into M4 × SM × SN and M4 × SM × CP2. The compactification is caused by the quantum loop effect due to a large number of matter fields. The conditions for the vacuum stability are studied. Numerical computation of the loop effect is undertaken, and it is shown that some of the models of the type M4 × SM × SN admit a stable solution which has finite circumferences of both of the extra spaces and positive coupling constants of the Einstein-Yang-Mills theory in four dimensions. 相似文献
3.
The free induction decay (FID) of the transverse magnetization in a dipolar-coupled rigid lattice is a fundamental problem in magnetic resonance and in the theory of many-body systems. As it was shown earlier the FID shapes for the systems of classical magnetic moments and for quantum nuclear spin ones coincide if there are many nearly equivalent nearest neighbors n in a solid lattice. In this paper, we reduce a multispin density matrix of above system to a two-spin matrix. Then we obtain analytic expressions for the mutual information and the quantum and classical parts of correlations at the arbitrary spin quantum number S, in the high-temperature approximation. The time dependence of these functions is expressed via the derivative of the FID shape. To extract classical correlations for S > 1/2 we provide generalized POVM measurement (positive-operator-valued measure) using the basis of spin coherent states. We show that in every pair of spins the portion of quantum correlations changes from 1/2 to 1/(S + 1) when S is growing up, and quantum properties disappear completely only if S → ∞. 相似文献
4.
Nan Jia Bijun Fang Zhaorong Yang 《Applied Physics A: Materials Science & Processing》2014,116(2):839-843
The magnetism of the colossal magnetoresistance material FeCr2S4 was studied through substitution by nonmagnetic element Cd. With the increase of Cd content, the high-field magnetization measured at 5 K increases, demonstrating a ferromagnetic Cr–Cr interaction in CdCr2S4. As comparing with the anti-ferromagnetic material ZnCr2S4, it is deduced that the ferromagnetic interaction in CdCr2S4 is favored by its larger Cr–Cr distance. On the other hand, due to Cd substitution, the low-field magnetization irreversibility between zero-field-cooling and field-cooling magnetization weakens with the increase of Cd content and disappears at last when x = 1 in the Fe1?x Cd x Cr2S4 (0 ≤ x ≤ 1.0) system. By taking account of the single-ion anisotropy of the ferrous ion on the tetrahedral site, the picture of irreversible magnetic behavior induced by magnetic anisotropy is examined. 相似文献
5.
Alexander D. Popov 《Letters in Mathematical Physics》2008,84(2-3):139-148
We consider U(n + 1) Yang–Mills instantons on the space Σ × S 2, where Σ is a compact Riemann surface of genus g. Using an SU(2)-equivariant dimensional reduction, we show that the U(n + 1) instanton equations on Σ × S 2 are equivalent to non-Abelian vortex equations on Σ. Solutions to these equations are given by pairs (A,?), where A is a gauge potential of the group U(n) and ? is a Higgs field in the fundamental representation of the group U(n). We briefly compare this model with other non-Abelian Higgs models considered recently. Afterwards we show that for g > 1, when Σ × S 2 becomes a gravitational instanton, the non-Abelian vortex equations are the compatibility conditions of two linear equations (Lax pair) and therefore the standard methods of integrable systems can be applied for constructing their solutions. 相似文献
6.
A method is introduced for constructing lattice discretizations of large classes of integrable quantum field theories. The method proceeds in two steps: The quantum algebraic structure underlying the integrability of the model is determined from the algebra of the interaction terms in the light-cone representation. The representation theory of the relevant quantum algebra is then used to construct the basic ingredients of the quantum inverse scattering method, the lattice Lax matrices and R-matrices. This method is illustrated with four examples: The sinh-Gordon model, the affine sl(3) Toda model, a model called the fermionic sl(2|1) Toda theory, and the N=2 supersymmetric sine-Gordon model. These models are all related to sigma models in various ways. The N=2 supersymmetric sine-Gordon model, in particular, describes the Pohlmeyer reduction of string theory on AdS2×S2, and is dual to a supersymmetric non-linear sigma model with a sausage-shaped target space. 相似文献
7.
《Physics letters. A》2002,298(4):236-237
The ground state of a class of Ising models with site dependent arbitrary spin quantum number is shown to be restricted to ±SiMAX state where SiMAX is the spin quantum number at the site i. 相似文献
8.
J. O. González S. Shaji D. Avellaneda G. A. Castillo T. K. Das Roy B. Krishnan 《Applied Physics A: Materials Science & Processing》2014,116(4):2095-2105
Photovoltaic structures were prepared using AgSb(S x Se1?x )2 as absorber and CdS as window layer at various conditions via a hybrid technique of chemical bath deposition and thermal evaporation followed by heat treatments. Silver antimony sulfo selenide thin films [AgSb(S x Se1?x )2] were prepared by heating multilayers of sequentially deposited Sb2S3/Ag dipped in Na2SeSO3 solution, glass/Sb2S3/Ag/Se. For this, Sb2S3 thin films were deposited from a chemical bath containing SbCl3 and Na2S2O3. Then, Ag thin films were thermally evaporated on glass/Sb2S3, followed by selenization by dipping in an acidic solution of Na2SeSO3. The duration of dipping was varied as 3, 4 and 5 h. Two different heat treatments, one at 350 °C for 20 min in vacuum followed by a post-heat treatment at 325 °C for 2 h in Ar, and the other at 350 °C for 1 h in Ar, were applied to the multilayers of different configurations. X-ray diffraction results showed the formation of AgSb(S x Se1?x )2 thin films as the primary phase and AgSb(S,Se)2 and Sb2S3 as secondary phases. Morphology and elemental detection were done by scanning electron microscopy and energy dispersive X-ray analysis. X-ray photoelectron spectroscopic studies showed the depthwise composition of the films. Optical properties were determined by UV–vis–IR transmittance and reflection spectral analysis. AgSb(S x Se1?x )2 formed at different conditions was incorporated in PV structures glass/FTO/CdS/AgSb(S x Se1?x )2/C/Ag. Chemically deposited post-annealed CdS thin films of various thicknesses were used as window layer. J–V characteristics of the cells were measured under dark and AM1.5 illumination. Analysis of the J–V characteristics resulted in the best solar cell parameters of V oc = 520 mV, J sc = 9.70 mA cm?2, FF = 0.50 and η = 2.7 %. 相似文献
9.
《Nuclear Physics B》1996,473(3):469-508
We approach the study of non-integrable models of two-dimensional quantum field theory as perturbations of the integrable ones. By exploiting the knowledge of the exact S-matrix and form factors of the integrable field theories we obtain the first-order corrections to the mass ratios, the vacuum energy density and the S-matrix of the non-integrable theories. As interesting applications of the formalism, we study the scaling region of the Ising model in an external magnetic field at T ∼ Tc and the scaling region around the minimal model M2,7. For these models, a remarkable agreement is observed between the theoretical predictions and the data extracted by a numerical diagonalisation of their Hamiltonian. 相似文献
10.
The quantum anisotropic antiferromagnetic Heisenberg model with single ion anisotropy, spin S=1 and up to the next-next-nearest neighbor coupling (the J1–J2–J3 model) on a square lattice, is studied using the bond-operator formalism in a mean field approximation. The quantum phase transitions at zero temperature are obtained. The model features a complex T=0 phase diagram, whose ordering vector is subject to quantum corrections with respect to the classical limit. The phase diagram shows a quantum paramagnetic phase situated among Neél, spiral and collinear states. 相似文献
11.
Erik?Rosenbaum Magnus?Sellstedt Fredrik?Almqvist Lennart?B.-A.?Johansson 《Journal of fluorescence》2010,20(6):1249-1253
UV-VIS absorption and fluorescence spectroscopic properties of six related polyaromatic 2-pyridones have been studied. Excitation of the lowest and rather weak and structure-less transition [ε max (430 nm)?≈?3,000 mol?1dm3cm?1] gives rise to a broad fluorescence band in the visible region, for these compounds. These S 0 ? S 1 transitions are compatible with symmetrically forbidden transitions, promoted by intensity borrowing, as is revealed by fluorescence depolarisation data. With one exception, all compounds exhibit strong fluorescence, with quantum yields in glycerol varying between 40% and 70%. The corresponding fluorescence lifetimes range from 11 ns to 17 ns, while the radiative lifetimes are very similar (≈26 ns), for all compounds. Interestingly and rarely observed, the calculated radiative lifetimes for the weak absorption band are significantly longer, i.e. between 37 and 40 ns. 相似文献
12.
Freddy Muñoz Paulina Valenzuela William Gacitúa 《Applied Physics A: Materials Science & Processing》2012,108(4):1007-1014
In this study, Eucalyptus nitens species was nano-characterized to determine variability in nanomechanical properties within the cellular ultra-structure between the bark and wood fibers. Three factors, including site (2 levels), family (2 levels) and fiber type (bark and wood) were analyzed using three response variables, including the elastic modulus (E), hardness (H) and ductility ratio (E/H) in the middle lamella (ML) and the cell wall within the S2 layer. The results indicated significant differences for E S2 and H S2 when comparing fiber types: E S2≈12.52 GPa and H S2≈0.31 GPa for wood fiber and E S2≈10.81 GPa and H S2≈0.26 GPa for bark fiber. There is not statistically significant difference in ductility ratio (E/H) in S2 and ML between fiber types. These results indicate that bark and wood fibers can be used together or separately in the development of new composite materials and engineering products. 相似文献
13.
Hidekatsu Nemura 《Few-Body Systems》2013,54(7-10):1223-1226
We present our recent study on ΛN and ΣN (isospin I = 3/2) interactions by measuring Nambu–Bethe–Salpeter wave functions on the Lattice QCD. The lattice QCD calculation is performed by using the N f = 2 + 1 gauge configurations generated by PACS-CS collaboration together with employing an improved method to obtain potentials in lattice QCD simulations. For the 1 S 0 channel, the central ΣN (I = 3/2) potential and the central ΛN (1 S 0) potential are found to be very similar. For the spin triplet (3 S 1?3 D 1) channels, the central ΛN(3 S 1?3 D 1) potential is attractive while the central ΣN(I = 3/2, 3 S 1?3 D 1) potentials is repulsive. Tensor potentials, on the other hand, are rather weak in both ΛN and ΣN(I = 3/2) systems. 相似文献
14.
Michael L. Baker Marzio Rancan Floriana Tuna Grigore A. Timco David Collison Hannu Mutka Hans-Ulrich Güdel Robin J. Pritchard Richard E. P. Winpenny Eric J. L. McInnes 《Applied magnetic resonance》2010,37(1-4):685-692
The synthesis, magnetic and electron paramagnetic resonance (EPR) characterisation of isolated, discrete, {Cr n III } antiferromagnetically coupled chain complexes is reported for n = 6 and 7. Previous studies had reported supramolecular linked {Cr n III } x species. For n = 6, the lowest lying total spin state is diamagnetic with S = 1 and 2 first and second excited states, respectively; for n = 7, the lowest lying total spin state is S = 3/2 with S = 1/2 and 5/2 first and second excited states, respectively. The zero-field splittings of these states are well defined by low-temperature, multi-frequency EPR spectroscopy. 相似文献
15.
Hironori Yamaguchi Shojiro Kimura Masayuki Hagiwara Yusuke Nambu Satoru Nakatsuji Yoshiteru Maeno Koichi Kindo 《Applied magnetic resonance》2009,36(2-4):285-289
We report the experimental results of electron spin resonance in high magnetic fields up to about 53 T on the quasi-two-dimensional triangular lattice antiferromagnet NiGa2S4. The temperature dependence of the resonance field at 584.8 GHz shows a steep change below about 30 K, indicating a development of the short-range correlation. The frequency dependence of the resonance field at the lowest temperature for H∥c is explained by one of the helical resonance modes. These experimental results suggest that the short-range order is well developed at low temperatures, and the resonance mode is described by a conventional spin wave theory. 相似文献
16.
J.P. Jay-Gerin 《Journal of Physics and Chemistry of Solids》1974,35(1):81-87
A study is made of the effect of the quantization of the electron energy levels in a strong magnetic field on the ‘electron-diffusion’ contribution, Se, of the transverse thermoelectric power of a high-purity isotropic semiconductor (n-type gallium arsenide GaAs) in the extreme quantum limit, when all the carriers in the conduction band are in the lowest Landau level. A theoretical expression for Se is derived, taking into account of spin splitting. The sign of Se is either positive or negative, depending on the sign of the conducting carriers. The transition to nondegeneracy, which takes place when the lowest Landau level is driven through the Fermi level, has a large effect on the variation of Se with magnetic field. This effect is characterized by a large and rapid increase in |Se|. Spin splitting effects, even with a small effective mass (, where m0 is the free-electron mass) and a very small g-factor (g ≈ 0·32), greatly modify and reduce |Se| a a function of field. For large fields, |Se| increases monotonically with H. Calculations are carried out for n-type GaAs at T = 0·5°K with N = 1·2 × 1016cm?3 carriers. 相似文献
17.
O. N. Prudnikov A. V. Taichenachev V. I. Yudin E. M. Rasel 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(12):1420-1428
The possible deep laser cooling of 24Mg atoms in a deep optical lattice in the presence of an additional pumping field resonant to the narrow 3s3s1S0 → 3s3p3P1 (λ = 457 nm) optical transition is studied. Two quantum models of the laser cooling of atoms in the optical trap are compared. One is based on the direct numerical solution to the kinetic quantum equation for an atomic density matrix; it considers both optical pumping and quantum recoil effects during interaction between the atoms and field photons. The second, simplified model is based on decomposing the states of the atoms over the levels of vibration in the optical trap and analyzing the evolution of these states. The comparison allows derivation of optical field parameters (pumping field intensity and detuning) that ensure cooling of the atoms to minimal energies. The conditions for fast laser cooling in an optical trap are found. 相似文献
18.
Sushil K. Misra S. I. Andronenko A. Punnoose Dmitry Tipikin J. H. Freed 《Applied magnetic resonance》2009,36(2-4):291-295
High-frequency (236 GHz) electron paramagnetic resonance (EPR) studies of Fe3+ ions at 255 K are reported in a Sn1?x Fe x O2 powder with x = 0.005, which is a ferromagnetic semiconductor at room temperature. The observed EPR spectrum can be simulated reasonably well as the overlap of spectra due to four magnetically inequivalent high-spin (HS) Fe3+ ions (S = 5/2). The spectrum intensity is calculated, using the overlap I(BL) + (I(HS1) + I(HS2) + I(HS3) + I(HS4)) × exp(?0.00001B), where B is the magnetic field intensity in Gauss, I represents the intensity of an EPR line (HS1, HS2, HS3, HS4), and BL stands for the baseline (the exponential factor, as found by fitting to the experimental spectrum, is related to the Boltzmann population distribution of energy levels at 255 K, which is the temperature of the sample in the spectrometer). These high-frequency EPR results are significantly different from those at X-band. The large values of the zero-field splitting parameter (D) observed here for the four centers at the high frequency of 236 GHz are beyond the capability of X-band, which can only record spectra of ions with much smaller D values than those reported here. 相似文献
19.
Joseph Ben Geloun 《Communications in Mathematical Physics》2014,332(1):117-188
Classes of renormalizable models in the Tensorial Group Field Theory framework are investigated. The rank d tensor fields are defined over d copies of a group manifold \({G_D=U(1)^D}\) or \({G_D= SU(2)^D}\) with no symmetry and no gauge invariance assumed on the fields. In particular, we explore the space of renormalizable models endowed with a kinetic term corresponding to a sum of momenta of the form \({p^{2a}, a\in (0,1]}\) . This study is tailored for models equipped with Laplacian dynamics on G D (case a = 1) but also for more exotic nonlocal models in quantum topology (case 0 < a < 1). A generic model can be written \({(_{\dim G_D}\Phi^{k}_{d}, a)}\) , where k is the maximal valence of its interactions. Using a multi-scale analysis for the generic situation, we identify several classes of renormalizable actions, including matrix model actions. In this specific instance, we find a tower of renormalizable matrix models parametrized by \({k \geq 4}\) . In a second part of this work, we study the UV behavior of the models up to maximal valence of interaction k = 6. All rank \({d \geq 3}\) tensor models proved renormalizable are asymptotically free in the UV. All matrix models with k = 4 have a vanishing β-function at one-loop and, very likely, reproduce the same feature of the Grosse–Wulkenhaar model (Commun Math Phys 256:305, 2005). 相似文献
20.
S. Uetake A. Yamaguchi D. Hashimoto Y. Takahashi 《Applied physics. B, Lasers and optics》2008,93(2-3):409-414
We have successfully observed high-resolution spectra of spin-forbidden electric quadrupole transition (1 S 0→3 D 2) in ytterbium (174Yb) atoms. The differential light shifts between the 1 S 0 and the 3 D 2 states in a far-off resonant trap at 532 nm are also measured. For the spectroscopy, we developed simple, narrow-linewidth, and long-term frequency stabilized violet diode laser systems. Long-term drifts of the excitation laser (404 nm) is suppressed by locking the laser to a length stabilized optical cavity. The optical path length of the cavity is stabilized to another diode laser whose frequency is locked to a strong 1 S 0→1 P 1 transition (399 nm) of Yb. Both lasers are standard extended-cavity diode lasers (ECDLs) in the Littrow configuration. Since the linewidth of a violet ECDL (~10 MHz) is broader than a typical value of a red or near infra-red ECDL (<1 MHz), we employ optical feedback from a narrow-band Fabry–Perot cavity to reduce the linewidth. The linewidth is expected to be <20 kHz for 1 ms averaging time, and the long-term frequency stability is estimated to be ~200 kHz/h. 相似文献