共查询到20条相似文献,搜索用时 9 毫秒
1.
The Becker-Döring equation of classical nucleation theory is derived in the framework of spin-flip dynamics of the Ising model. The derivation is based on a microscopic analysis of droplet geometry at low temperature. 相似文献
2.
量子电容在半导体纳米材料和器件中是一个日趋重要的参数,测量和提取石墨烯的量子电容,不仅可以得到石墨烯的重要物理性质,而且对石墨烯晶体管的尺寸缩减行为具有重要指导意义.文章中采用简单工艺在石墨烯上制备出均匀超薄的高质量Y2O3栅介质,其等效栅氧厚度(EOT)可缩减至1.5nm,通过控制栅介质厚度的变化,精确测量并提取了石墨烯量子电容,其电容值在远离狄拉克点时与理论计算相符合;在此基础上,文章作者提出了基于电势涨落的量子电容微观模型,通过采用单一参数——电势涨落δV,可以定量地描述Dirac点附近的量子电容行为,从而在全能量范围内实现对石墨烯量子电容测量值的完美拟合,并得到了石墨烯的相关重要参数.进而,作者从量子电容的角度,探索了石墨烯晶体管的性能极限,并比较其相对于Ⅲ-Ⅴ族场效应晶体管的潜在优势. 相似文献
3.
Starting from microscopic mechanics, we derive thermodynamic relations for heat conducting nonequilibrium steady states. The extended Clausius relation enables one to experimentally determine nonequilibrium entropy to the second order in the heat current. The associated Shannon-like microscopic expression of the entropy is suggestive. When the heat current is fixed, the extended Gibbs relation provides a unified treatment of thermodynamic forces in the linear nonequilibrium regime. 相似文献
4.
This paper is devoted to the study of the Young equation, which gives a connection between surface tensions and contact angle. We derive the generalized form of this equation for anisotropic models using thermodynamic considerations. In two dimensions with SOS-like approximations of the interface, we prove that the surface tension may be computed explicitly as a simple integral, which of course depends upon the orientation of the interface. This allows a complete study of the wetting transition when a constant wall attraction is taken into account within the SOS and Gaussian models. We therefore give a complete analysis of the variation of the contact angle with the temperature for those models. It is found that for certain values of the parameters, two wetting transitions may successively appear, one at low temperature and one at high temperature, giving the following states: film—droplet—film. This study rests upon the generalized Young equation, the validity of which is proved for the Gaussian model with a constant wall attraction, using microscopic considerations.On leave from Faculté des Sciences, Université de l'Etat, 7000-Mons, Belgium. 相似文献
5.
We consider mixed crystals of the form(MY)
x
(MX)
1–x
, whereY is an active component which drives a structural phase transition, while the componentX has no active internal degree of freedom. We describe this system by a compressible Ising model, including the dilution of the spinsY and the elastic strain fields caused by the componentX. We derive a Landau expansion of the free energy for this system, within molecular field theory. The coefficients of this expansion depend on temperature, pressure, spin concentrationx and the strain fields. This simple model exhibits a rich phase diagram. At sufficiently high concentrationsx, the phase transition is first order. Decreasingx, the transition passes through a tricritical point and eventually becomes second order. For lowx or high strain fields, no transition occurs. 相似文献
6.
G. Caginalp 《Journal of statistical physics》1990,59(3-4):869-884
Macroscopic free boundary problems involving phase transitions (e.g., the classical Stefan problem or its modifications) are derived in a unified way from a Hamiltonian based on a general set of microscopic interactions. A Hamiltonian of the form +
x,x
J(x–x)(x)(x) leads to differential equations as a result of Fourier transforms. Expanding the Fourier transform ofJ in powers ofq (the wave number), one can truncate the series at anarbitrary orderM, and thereby obtainMth-order differential equations. An asymptotic analysis of these equations in various scalings of the physical parameters then implies limits which are the standard macroscopic models for the dynamics of phase boundaries. 相似文献
7.
Detlef Lehmann 《Communications in Mathematical Physics》1995,173(1):155-174
The propagator for a noninteracting many electron system in a constant magnetic field in three space time dimensions is computed. This formula and the results of [FT1,2] are used to give a microscopic derivation of a BCS-equation with magnetic field. It is shown that this equation has no solution if the magnetic field is sufficiently large. Perturbation theory in the interaction around the magnetic field propagator is discussed. 相似文献
8.
LING-FENG MAO 《Pramana》2013,81(2):309-317
The quantum capacitance, an important parameter in the design of nanoscale devices, is derived for armchair-edge single-layer graphene nanoribbon with semiconducting property. The quantum capacitance oscillations are found and these capacitance oscillations originate from the lateral quantum confinement in graphene nanoribbon. Detailed studies of the capacitance oscillations demonstrate that the local channel electrostatic potential at the capacitance peak, the height and the number of the capacitance peak strongly depend on the width, especially a few nanometres, of the armchair-edge graphene nanoribbon. It implies that the capacitance oscillations observed in the experiments can be utilized to measure the width of graphene nanoribbon. The results also show that the capacitance oscillations are not seen when the width is larger than 30 nm. 相似文献
9.
L. S. Garcia-Colin 《Journal of statistical physics》1979,20(1):19-24
Alternative results derived on a microscopic basis for the mode-mode coupling kinetic equations are shown to be identical. It is also emphasized that nonlinear kinetic equations for the gross variables describing the system are only suggested but not implied by the corresponding equations obeyed by their dynamical variables. Finally an equivalent closed form for the renormalized transport coefficients is shown to hold in mode-mode coupling theory.Miembro del Colegio Nacional. On sabbatical leave from UAM—Iztapalapa, Mexico. 相似文献
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Alexey V Melkikh 《理论物理通讯》2020,72(1):15101-47
The consideration of measuring instruments as macroscopic bodies leads to neglect of the microscopic processes that occur during measurements. This disregard is not justified in general cases. As an example of measurements using microscopic instruments, the scattering of a photon by an electron with electron interference at two slits(Compton effect) was used. The amount of information that can be obtained in such a process is inversely proportional to the wavelength of the incident photon. At large photon wavelengths(soft measurements), the pure state of the electron can be disrupted by an arbitrarily small extent; accordingly, the amount of information extracted in such an experiment is also arbitrarily small. It is shown that the energy price for a bit obtained in such a measurement tends toward a constant value for increasing the photon wavelength. Microscopic instruments can be used in situations where energy costs for measurements are important. 相似文献
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Silicene and related buckled materials are distinct from both the conventional two dimensional electron gas and the famous graphene due to strong spin orbit coupling and the buckled structure. These materials have potential to overcome limitations encountered for graphene, in particular the zero band gap and weak spin orbit coupling. We present a theoretical realization of quantum capacitance which has advantages over the scattering problems of traditional transport measurements. We derive and discuss quantum capacitance as a function of the Fermi energy and temperature taking into account electron–hole puddles through a Gaussian broadening distribution. Our predicted results are very exciting and pave the way for future spintronic and valleytronic devices. 相似文献
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We discuss a possible experimental realization of fast quantum gates with high fidelity with ions confined in microscopic traps. The original proposal of this physical system for quantum computation comes from Cirac and Zoller (Nature 404, 579 (2000)). In this paper we analyse a sensitivity of the ion-trap quantum gate on various experimental parameters which was omitted in the original proposal. We address imprecision of laser pulses, impact of photon scattering, nonzero temperature effects and influence of laser intensity fluctuations on the total fidelity of the two-qubit phase gate. 相似文献
18.
We reinterpret the microcanonical conditions in the quantum domain as constraints for the interaction of the "gas subsystem" under consideration and its environment ("container"). The time average of a purity measure is found to equal the average over the respective path in Hilbert space. We then show that for typical (degenerate or nondegenerate) thermodynamical systems almost all states within the allowed region of Hilbert space have a local von Neumann entropy S close to the maximum and a purity P close to its minimum, respectively. Typically, thermodynamical systems should obey the second law. 相似文献
19.
Landauer–Buttiker formalism with the assumption of semi-infinite electrodes as reservoirs has been the standard approach in modeling steady electron transport through nanoscale devices. However, modeling dynamic electron transport properties, especially nanoscale capacitance, is a challenging problem because of dynamic contributions from electrodes, which is neglectable in modeling macroscopic capacitance and mesoscopic conductance. We implement a self-consistent quantum tight-binding model to calculate capacitance of a nano-gap system consisting of an electrode capacitance and an effective capacitance of the middle device. From the calculations on a nano-gap made of carbon nanotube with a buckyball therein, we show that when the electrode length increases, the electrode capacitance moves up while the effective capacitance converges to a value which is much smaller than the electrode capacitance . Our results reveal the importance of electrodes in modeling nanoscale ac circuits, and indicate that the concepts of semi-infinite electrodes and reservoirs well-accepted in the steady electron transport theory may be not applicable in modeling dynamic transport properties. 相似文献
20.
P. Grangier J.-P. Poizat 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):99-105
By generalizing recently obtained results we calculate the excess noise factor (Petermann factor) for a laser system with
non-orthogonal eigenmodes. The quantum consistency of the calculation is shown through the explicit conservation of input-output
commutation rules. As a result of the calculation, the excess noise in the lasing mode is shown to depend on the laser gain
below threshold, and on the noise analysis frequency below and above threshold.
Received: 27 October 1998 / Received in final form: 11 March 1999 相似文献