Tagged Questions
2
votes
1answer
58 views
NP-completeness of non-planar Ising model versus polynomial time eigenvalue algorithms
From the papers by Barahona and Istrail I understand that a combinatorial approach is followed to prove the NP-completeness of non-planar Ising models. Basic idea is non-planarity here. On the other ...
1
vote
1answer
68 views
What is the interface tension between ordered and disordered phases of the Potts model?
I read in these papers(1,2) the concept of interface tension. I can't understand its definition. I can hardly imagine there is some tension in a model. Any help will be appreciated.
0
votes
0answers
39 views
Lambda transition data points of $\require{mhchem}\ce{^4He}$
I'm looking to get some data on the lambda transition of $\require{mhchem}\ce{^4He}$. I need the data points of the specific heat vs. temperature graph, if that makes sense.
1
vote
0answers
29 views
Neutron scattering for a critical magnetic-ordering system : what about critical opalescence?
Liquid-gas transition critical point is believed to share the same universality class as the 3D Ising model.
We know that the liquid-gas transition is characterized by a phenomenon called critical ...
2
votes
1answer
96 views
How to define the order parameter of the q-state Potts model?
The order parameter of Ising model can be defined as $m=\frac{N_1-N_2}{N}$, if $N$ is the total number of lattice points, $N_1$ and $N_2$ is the number of lattice points spin up and down respectively, ...
0
votes
0answers
90 views
Ground and first excited state of non interacting spin system Hamiltonian
For a non interacting spin system containing two $\frac{1}{2}$ spin particles I am trying to determine its Hamiltonian. If the energy of a up spin is $+\mu {\bf B}$ and a down spin is $-\mu {\bf B}$, ...
0
votes
1answer
86 views
Ground states of the Hamiltonian of a two spin system
For the spin system shown in this graph (http://i.stack.imgur.com/3lg1R.png), the Hamiltonian is $$S^{(1)}_z\cdot S^{(1)}_z=\frac{1}{4}\begin{pmatrix}
1 & 0 &0 &0 \\
0&-1 &0 ...
1
vote
1answer
112 views
Hamiltonian of a simple graph
I have a spin system:
As shown in the picture, there are two spins S1 and S2, and a pair of interactions between them. One is a ferromagnetic interaction and the other is anti ferromagnetic ...
5
votes
0answers
254 views
Is the “particle number” of “electrons” well defined in Wen's string-net theory of elementary particles?
According to professor Wen's string-net theory(Colloquium: Photons and electrons as emergent phenomena, Levin and Wen, Rev. Mod. Phys. 77, 871(2005), see e.g. http://arxiv.org/abs/cond-mat/0407140), ...
4
votes
3answers
163 views
Partition function of a gas of $N$ identical classical particles
Partition function of a gas of $N$ identical classical particles is given by
$$ Z~=~\frac {1}{N! h^{3N}} \int \exp[-\beta H(p_1.......p_n, x_1....x_n)]d^3p_1...d^3p_n,d^3x_1...d^3x_n $$
in this ...
0
votes
0answers
18 views
Rice Allnatt distribution function
Can anyone give me an article of which explains Rice Allnatt distribution function or can you explain the function here?
1
vote
2answers
209 views
Why should the Fermi level of a n-doped semiconductor be below the one of a p-doped?
In a pn-junction, the difference in Fermi level between the p doped and the n doped regions causes the apparition of a built-in electric field at equilibrium. This electric field goes from the n to ...
3
votes
2answers
277 views
Can a first order phase transition have an order parameter?
Order parameter is used to describe second order phase transition. It seems that in some papers it is used in the first order phase transitions. Can first order phase transition have an order ...
8
votes
1answer
99 views
Why are topological solitons present in some phases for lattice models?
Over a spatial continuum, it is easy to see why some topological solitons like vortices and monopoles have to be stable. For similar reasons, Skyrmions also have to be stable, with a conserved ...
0
votes
2answers
116 views
What is the origin of nonconservative force?
My understanding about conservative force is a force that its work is independent of path such that we can construct another form of the work called potential to make our life easier.
For friction, ...
4
votes
3answers
816 views
Why is the canonical ($NVT$) ensemble often used for (classical) molecular dynamics (MD) simulations?
Molecular dynamics (MD) simulation is a common approach to the (classical) many-body problem. It relies on integration of Newton's equations of motion to simulate the trajectories of many (e.g., ...
5
votes
2answers
153 views
Effect of boundary conditions on partition functions
While computing partition functions in statistical mechanics models (say) on a 2d lattice one usually makes use of "circular boundary conditions" which thus gives the lattice topology of a torus. It ...
4
votes
1answer
342 views
Hit a bottle of beer on the top with another causes the first to spit all the gas, why?
So, on the other day me and my colleges were discussing the following phenomena:
Pick two open bottles of beer. With the bottom of the first, hit the second on the bottleneck, in the following way: ...
3
votes
0answers
83 views
Qualitative argument to determine energy of defects
In a book of "LES HOUCHES - Critical Phenomena, Random systems, Gauge theories" the author Frolich says that:
2D
In two dimensions, the mean energy of an isolated point defect in a square area of ...
3
votes
1answer
114 views
How is the dynamic equilibrium nature of fermi-dirac distribution of particles facilitated?
I read this in Kittel: Introduction to Solid State Physics about deriving that product of electron and hole concentration as independent at a given temperature by the law of mass action.
For this ...
2
votes
0answers
72 views
Factorization of fermionic scattering integral in 2d momentum rep
the scattering integrals for fermions involves both momentum ($k$) and energy ($k^2$) conservation and a nonlinear phase space factor of a distribution function $f(k)$.
$$\begin{multline}I(k) = ...
6
votes
1answer
157 views
Thermodynamic limit “vs” the method of steepest descent
Let me use this lecture note as the reference.
I would like to know how in the above the expression (14) was obtained from expression (12).
In some sense it makes intuitive sense but I would ...
3
votes
1answer
124 views
From spectrum/dispersion relation to the partition function
I know the spectrum/dispersion relation for a bosonic system.
$$E \left( \mathbf{k} \right) = \cdots$$
Is there a general method for writing down the partition function when the spectrum of the ...
9
votes
1answer
360 views
What are some predictions from string theory that say some crystalline materials “will end up in one of many lowest-energy ground states?”
I am referring to this recent "news feature" by Zeeya Merali from Nature magazine www.nature.com/uidfinder/10.1038/478302a. Here is the specific quote:
"To make matters worse, some of the testable ...
7
votes
1answer
49 views
Canonical averages in a Fermi gas aka generalized Fermi-Dirac distribution
I am in the process of applying Beenakker's tunneling master equation theory of quantum dots (with some generalizations) to some problems of non-adiabatic charge pumping. As a part of this work I ...
1
vote
1answer
98 views
Heuristic argument for the temeprature dependence of specific heat in the “low” temperature regimes
Here by "low temperature" I meant it in the scale of the characteristic $\hbar \omega$ of the system.
One can calculate and show that in the low temperature regime $C_V$ of phonons goes like $T^3$ ...
2
votes
2answers
291 views
Identifying a critical phenomena?
I have a system with a number of measurables (in time). Some measurables are discrete some are continuous (within the measurement accuracy). How can I determine whether my system experiences ...
3
votes
1answer
712 views
Chemical potential interpretation
Something that has bothered me for a while regards the interpretation of chemical potential for different statistics. While I understand its meaning in metals (and its relation with the Fermi ...
9
votes
2answers
917 views
trying to understand Bose-Einstein Condensate (BEC)
I am a computer scientist interested in network theory. I have come across the Bose-Einstein Condensate (BEC) because of its connections to complex networks. What I know about condensation is the ...
10
votes
2answers
289 views
What is known about some massive Gaussian models on a lattice?
Recently I started to play with some massive Gaussian models on a lattice. Motivation being that I work on massless models and want to understand the massive case because it seems easier to handle ...
