共查询到20条相似文献,搜索用时 0 毫秒
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P.H. Keyes 《Physics letters. A》1978,67(2):132-134
It is argued on the basis of a reexamination of the Landau-de Gennes theory and with reference to experimental data that the isotropic-nematic transition exhibits pretransitional fluctuations characteristics of a tricritical point. 相似文献
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We discuss 2D systems with Ising symmetry and competing interactions at different scales. In the framework of the renormalization group, we study the effect of relevant quartic interactions. In addition to the usual constant interaction term, we analyze the effect of quadrupole interactions in the self-consistent Hartree approximation. We show that in the case of a repulsive quadrupole interaction, there is a first-order phase transition to a stripe phase in agreement with the well-known Brazovskii result. However, in the case of attractive quadrupole interactions there is an isotropic-nematic second-order transition with higher critical temperature. 相似文献
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The effect of Holstein electron-phonon interaction on a Hubbard model close to a Mott-Hubbard transition at half filling is investigated by means of dynamical mean-field theory. We observe a reduction of the effective mass that we interpret in terms of a reduced effective repulsion. When the repulsion is rescaled to take into account this effect, the quasiparticle low-energy features are unaffected by the electron-phonon interaction. Phonon features are only observed within the high-energy Hubbard bands. The lack of electron-phonon fingerprints in the quasiparticle physics can be explained interpreting the quasiparticle motion in terms of rare fast processes. 相似文献
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We develop a free-energy functional for an inhomogeneous system that contains both symmetry conserved and symmetry broken parts of the direct pair correlation function. These correlation functions are found by solving the Ornstein-Zernike equation with the Percus-Yevick closure relation. The method developed here gives the pair correlation functions in the ordered phase with features that agree well with the results found by computer simulations. The theory predicts accurately the isotropic-nematic transition in a system of anisotropic molecules and can be extended to study other ordered phases such as smectics and crystalline solids. 相似文献
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The flow curves, viz. the curves of stationary stress under steady shearing, are obtained close to the glass transition in
dense colloidal dispersions using asymptotic expansions in the schematic -model of mode coupling theory. The shear thinning of the viscosity in fluid states and the yielding of glassy states is
discussed. At the transition between fluid and shear-molten glass, simple and generalized Herschel-Bulkley laws are derived
with power law exponents that can be computed for different particle interactions from the equilibrium structure factor. 相似文献
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The effects of range and geometry of a simple attractive square-well on the phase diagram of hard ellipsoids and hard spherocylinders is systematically studied using a simple van der Waals type theory. The orientational single particle distribution function is approximated using the Onsager trial function. The quantitative errors introduced by this are thought to be considerably smaller than the use of the van der Waals approximation, which has been shown to give qualitatively correct phase diagrams for similar models. The phase diagrams obtained for hard ellipsoids and hard spherocylinders of aspect ratios ranging between 3 and 10 with a variety of square-well attractions are found to fall into three general types. The first type shows liquid-vapour coexistence and an isotropic-nematic transition, which meet at a liquid-vapour-nematic triple point. The second type shows a marked widening of the isotropic-nematic biphasic region which pre-empts the liquid-vapour coexistence. The final phase diagram shows a strong destabilization of the nematic phase with respect to the isotropic, which results in a shift of the phase transition to higher densities and pressures as the temperature is lowered. 相似文献
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Sacépé B Chapelier C Baturina TI Vinokur VM Baklanov MR Sanquer M 《Physical review letters》2008,101(15):157006
Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Delta in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in Delta, and growth of the Delta/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition. 相似文献
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V.M. Filyov 《Physics letters. A》1981,84(8):430-432
The tricritical behaviour of the isotropic-nematic phase transition is studied. The presence of two independent sixth-order terms in the free energy expansion breaks the conventional tricritical behaviour and eliminates the tricritical restriction for the deviation from the mean-field approximation. 相似文献
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Levin Y 《Physical review letters》2007,99(22):228903; author reply 228904
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Murtaza Bohra Shiva Prasad N. Venketaramani Naresh Kumar S.C. Sahoo R. Krishnan 《Journal of magnetism and magnetic materials》2009,321(22):3738-3741
Temperature dependence of the magnetic properties of magnetite thin film across the Verwey transition has been investigated. As the temperature is decreased, the magnetization of the film in a fixed field showed a sharp decrease close to the Verwey transition temperature (Tv). The M–H loops of the film have been recorded at various temperatures below and above Tv. It is found that film does not saturate at any temperature and saturation becomes more difficult below Tv. While cooling through Tv, the extrapolated value of magnetization to infinite field (Q), calculated from the numerical fit 4πM=Q [1−(H*/H)1/2], does not show a drop, but the coefficient indicating difficulty in saturation (H*) shows a sharp rise as does the coercivity. 相似文献
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Capone M Sangiovanni G Castellani C Di Castro C Grilli M 《Physical review letters》2004,92(10):106401
The density-driven Mott transition is studied by means of dynamical mean-field theory in the Hubbard-Holstein model, where the Hubbard term leading to the Mott transition is supplemented by an electron-phonon (e-ph) term. We show that an intermediate e-ph coupling leads to a first-order transition at T=0, which is accompanied by a phase separation between a metal and an insulator. The compressibility in the metallic phase is substantially enhanced. At quite larger values of the coupling, a polaronic phase emerges coexisting with a nonpolaronic metal. 相似文献
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F. Fujara B. Geil H. Sillescu G. Fleischer 《Zeitschrift für Physik B Condensed Matter》1992,88(2):195-204
Self diffusion coefficients in supercooled orthoterphenyl (OTP) have been determined down toD
t
=3·10–14 m2s–1 using a1H-NMR technique applying static field gradients up to 53T m–1 In a range of more than two decades theD
t
values agree with those of photochromic tracer molecules of the same size determined by forced Rayleigh scattering down to the glass transition temperatureT
g
. A change of mechanism is found for translational diffusion atT
c
1.2T
g
whereD
t
is proportional to the inverse shear viscosity
–1 atT>T
c
butD
t
with =0.75 atT<T
c
. Rotational correlation times determined by2H-NMR stimulated echo techniques in deuterated OTP remain proportinal to
–1 down toT
g
. Our results are discussed in relation with mode coupling theory and with models of cooperative motion at the glass transition. 相似文献