Questions tagged [spin-models]
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194
questions
2
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1answer
73 views
What are $U(n)$ or $\mathbb{Z}_2$ quantum spin liquids?
Quantum spin liquid is a state of matter in which spins are correlated and fluctuate even at zero temperature.
My question is about these terms in general. When we say that a state or a quasi-...
0
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0answers
7 views
How to obtain Hamiltonian parameters with EPR technique
I want to ask you how to obtain the parameters of the spin Hamiltonian of a system. I’m doing simulations with the EasySpin tool to obtain these parameters such as, J, the anisotropy factors D and E, ...
0
votes
0answers
43 views
Calculating expected values $\langle S_x \rangle$ and $\langle S_y \rangle$ in the Heisenberg model
Let's say, that we are considering the basic Heisenberg model with only two spin-particles. So our Hamiltonian can be written as follows:
$$
H = \sum_{\langle i,i' \rangle} S^{(x)}_i S^{(x)}_{i'} + S^...
1
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0answers
59 views
Irrational Conformal Field Theory v.s. Non-Unitary Conformal Field Theory?
Unitary conformal field theories (CFTs) with irrational (or including the special case of rational) central charge is called irrational conformal field theory (ICFT).
Irrational conformal field ...
1
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0answers
58 views
Calculating the local energy in neural network quantum state
given a Hamiltonian of Heisenberg 1D model as following:
$$H = -J\sum_{I}\sigma_{i}^{z}\sigma_{i+1}^{z}$$
I am trying to solve it with a neural network function given by Restricted Boltzmann machine ...
0
votes
0answers
64 views
Generalised Ising models?
Are there generalised Ising models:
The underslying mesh/connectivity is completely arbitrary - non rectangular, 3D...ND, complete connectivity should be possible
The interaction potential is ...
0
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0answers
35 views
Where to find a Path Integral treatment of 1D Quantum Heisenberg model or Quantum Spin Chain?
All:
Where to find a Path Integral treatment of 1D Quantum Heisenberg model or Quantum Spin Chain?
I would like to find a detailed calculation of path amplitude in such situation. I did some google ...
1
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0answers
32 views
Heat-bath algorithm of 2D XY model
Can anyone suggest any reference where the heat-bath algorithm for the classical 2D XY model has been discussed in detail. I have found references for the 3D Heisenberg model which can be exactly ...
5
votes
2answers
103 views
Naming symmetries in quantum systems, e.g. $\mathbb{Z}_2$ or $U(1)$
I'm constantly confused by some of nomenclature that is associated with symmetries in quantum Hamiltonians and was hoping someone could set me straight.
Specifically, we often have something like a ...
0
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0answers
40 views
Quantum Monte Carlo Loop Algorithm for quantum spin: why is the freezing graph present in ferromagnetic Ising model?
I study the loop algorithm (Evertz et al).
I cannot understand, why the freezing graph type where we have to flip all 4 spins together is not present for the quantum-XY model and the anti-/...
5
votes
1answer
104 views
Gilbert original paper (1955) reference
I'm looking for the Gilbert's original paper where he derives the gyromagnetic Landau Lifshitz Gilbert (LLG) equation of motion from a variational principle.
Most of the people cite:
Gilbert, ...
1
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0answers
23 views
Why do the Binder Cumulants of different system sizes intersect at the critical point?
When Monte Carlo simulations are performed for spin models (Ising model etc.) the critical temperature can be found by simulating for different lattice sizes and plotting the Binder Cumulant for them. ...
1
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0answers
20 views
Why the geometrical frustration (spin ice model) has never been studied in superparamagnetic size range?
I'm trying to understand the effect of geometrical frustration in assembly of superparamagnetic nanoparticles but I can't find any reference. Does anyone know how magnetism can be affected by ...
1
vote
2answers
58 views
Different concepts of phase transitions in spin models
I am currently revising the lecture notes in which different spin systems
are analyzed, focussing on the occurrence (or absence) of phase transitions.
Different techniques are applied to analyze the ...
1
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0answers
25 views
Semiclassical limit $S \to\infty$ in spin model
In many literature, the limit $S \to \infty$ is considered as a semiclassical limit. My question is that when this approximation is valid? Since paticles, say electrons, have the fixed spin number $S=...
1
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0answers
56 views
Interpretation of the single particle spectral function in a spin liquid
Experimenter here (fair warning). I've had a question nagging at me for some time revolving around this paper by Tang et al. I don't have a good intuition for what the single electron spectral ...
0
votes
1answer
47 views
Spinmodel Statistics
Consider a spin model with the following energy with $ \{\sigma\} =(\sigma_1,\sigma_2,...,\sigma_N)$ where each $\sigma$ can take the values: $-s,-s+1,...,-1,0,1,...,s-1,s$ and $E(\{\sigma \}) = \mu H ...
0
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0answers
25 views
What is the critical temperature for a BKT transition in the 2D quantum XY model with $S=1$ (not $S=1/2$)?
What is the critical temperature for a BKT transition in the 2D quantum XY model with $S=1$ (not $S=1/2$)? For instance, the classical XY model has KTc/J = 0.898 and the quantum XY model with S=1/2 ...
0
votes
1answer
37 views
Swap operation with the Heisenberg Hamiltonian
According to REF 1 equation 3, a SWAP operation can be achieved via the Heisenberg Hamiltonian for spins $H=J(t)\mathbf{S}_1\mathbf{S_2}$
$U^{1/2}_{SWAP}=e^{-i\frac{\pi}{8}}\exp\left(i\frac{\pi}{2}\...
1
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0answers
18 views
Is it possible to implement the Invaded Cluster Algorithm on a network of Ising spins rather than a lattice?
My main concern is how to know if a cluster has percolated the network. For a periodic square lattice it is easy to determine if the cluster percolates by looking at the size of the cluster (as given ...
0
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0answers
47 views
Troubles with Haldane Shastry Spin Chain
I'm actually reading the article of Shastry "Exact solution of an S= 1/2 Heisenberg Antiferromagnetic Chain with Long-rnaged interactions", Phys.
Rev. Lett. 60, 639 (1988)"
The articles ...
1
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0answers
35 views
Cavity method pedagogic references
I am looking for pedagogic references (textbook, review/expository articles, lecture notes, etc.) explaining the cavity method in detail.
I am talking specifically about this:
https://link.springer....
5
votes
1answer
154 views
Symmetry transformations that are self-inverse and global symmetries of the Hamiltonian
I have the simplified Ising model. The Hamiltonian is given by
$$
\mathcal{H} = -\mathrm{J}\sum_{<ij,i' j'>} \sigma_{ij} \sigma_{i'j'}.
$$
Where the sum over $<ij,i'j'>$ means just the ...
5
votes
1answer
91 views
Integrability of a non-integrable quantum spin model at critical point
Is it right, that non-integrable quantum spin models in one dimension become integrable at their critical points? Or do they stay nonintegrable at the critical point also? Are there any examples known?...
2
votes
0answers
63 views
Textbooks about spin-glasses for beginners
I am a Ph.D. student in Physics attending my second year. I would like to ask you whether you know any good textbook about spin-glasses (and physics of complex systems in general) for beginners. ...
0
votes
1answer
78 views
Bose-Einstein distribution and magnons
I have some doubt about the Bose-Einstein distribution for magnons/spin-waves.
A one-dimensional ferromagnet placed in an external magnetic field $\mathbf{B} = B\, \hat{z}$ obeys the Hamiltonian
$$H ...
8
votes
2answers
223 views
Lagrange multiplier in spin liquid mean-field theory (Paper by X.G. Wen)
My question is about a step in this paper: PhysRevB.65.165113 (X.G. Wen) page 6
Or alternatively: PhysRevB.90.174417 page 3. All the papers concerning spin liquids and the projective symmetry group ...
0
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0answers
71 views
Why the correlation function of 2D classical XY model is written so?
2D classical XY model $$H = -J\cos(\theta_{i}-\theta_{j})%$$ is famous for Berezinskii-Kosterlitz-Thouless phase transition. This is because of the difference of correlation function between hot and ...
1
vote
1answer
176 views
Two spin-1 system and the projector onto total spin 2 subspace [closed]
I am having trouble grasping the projection operators in the context of composite spins system, e.g. with two spin-1. First off, a projector $P$ is said to be an operator that squares to itself, $P^2=...
1
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0answers
16 views
In spin systems, a mean field with nonzero Chern number after Gutzwiller projection changed into trivial state?
The mean field is nontrivial because of nonzero Chern number. The gauge symmetry is Z2. Under Gutzwiller projection, I calculate the ground state degeneracy(GSD) and find that the GSD is one(trivial ...
0
votes
1answer
555 views
What is the Kitaev Model and why it became so popular? [closed]
I am seeing Kitaev Model everywhere. It feels like the spin-glass model of our time. How the Kitaev model differ from spin-glass and why it can be used everywhere? Looking at equation 1 here suggests ...
1
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0answers
37 views
How can I compute the spin texture for a $SU(2)$ gauge model?
I am trying to determine the helicity of 4 Dirac cones in my model, and one way I want to approach it is by plotting the spin-texture. However, I am unsure of how one would calculate the spin-texture ...
0
votes
0answers
90 views
spinless and time reversal symmetry breaking of p-wave pairing in topological superconductors
In the context of Majorana zero modes, I often hear that the p-wave pairing is effectively 'spinless' and time reversal symmetry broken.
I understand that s-wave and p-wave refer to the spin portion ...
2
votes
0answers
39 views
How to quantify frustration for spin models with long range interactions?
Consider the following Hamiltonian:
$$
H=-\sum_{i\neq j}J_{ij}S_iS_j-\sum_i H_iS_i
$$
where $S_i\in\{-1,1\}$, and the summed pair $i,j$ can be any two distinct indices (not necessary adjacent spins)....
1
vote
1answer
104 views
One-dimensional $SU(3)$ Heisenberg Model, the non-linear sigma model, $\theta$-term
Let's consider a one dimensional $SU(N)$ antiferromagnetic Heisenberg Model with an irreducible representation and its conjugate on alternating sites, such that they correspond to a Young tableaux ...
2
votes
1answer
134 views
What is the order parameter of 2D generalized $XY$ model?
I'm now studying the phase transition of 2D generalized XY model. This model considered here has a mixture with ferromagnetic and nematic-like interactions,
$$\mathcal{H}=-\sum_{\langle i j\rangle}\...
1
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0answers
82 views
How to find groundstate energy of a simple Hamiltonian at $N/L$-filling using Jordan-Wigner (JW) transformation?
$\underline{\textbf{Model:}}$
Let we have the $t-V$ model for spinless fermions on a 1D lattice, which is defined in second quantization operators as follows:
$$H_1 = -t\sum_i \big(c_i^\dagger c_{i+...
0
votes
1answer
78 views
What are exactly “norms” in spin networks? Are there any non-quantum spin networks?
Roger Penrose proposed a series of networks from which, fundamentally, space-time would emerge, called spin networks
(https://en.wikipedia.org/wiki/Spin_network)
In this article, it is said:
...
10
votes
2answers
162 views
What is the intuition behind the statement that non-equilibrium systems with static disorder are self-averaging?
In this paper(1) by C. De Dominics, he makes the argument that in a dynamical statistical mechanics system, one doesn't need to apply the replica trick and can directly disorder average the generating ...
0
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0answers
22 views
Exchange stiffness for HCP
I am studying the exchange interaction, which can be described with the Heisenberg Hamiltonian:
$\hat{H} = -\sum_{i,j}J_{ij}\hat{\mathbf{S_i}}\cdot \hat{\mathbf{S_j}}$
In the framework of constant ...
2
votes
0answers
36 views
$p$-spin spherical spin glass
Consider the $p$-spin spherical spin glass model with Hamiltonian $$H_{N,p}(\sigma)=\frac{1}{{N}^{\frac{(p-1)}{2}}} \sum \limits_{i_1,...i_p} J_{i_1,...i_p} \sigma_{i_1} \sigma_{i_2} .. \sigma_{i_p} $$...
0
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0answers
41 views
Which phenomenon is related to the spin of photons? [duplicate]
The phenomenon of the deflection of a moving electron in a magnetic field is related to the electrons spin. From which phenomenon it is concluded, that photons have a spin?
3
votes
1answer
65 views
Why is the projective symmetry group a group?
I am reading the paper from X. Wen about quantum orders and symmetric spin liquids. It can be found here: https://arxiv.org/abs/cond-mat/0107071
The Hamiltonian he is writing about looks like this:
\...
0
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1answer
171 views
Relation between spin and polarization of photon? [duplicate]
What is the possible spin configuration of photon?
And does spin has any relation with polarization?
1
vote
1answer
50 views
A dreidel on a spinning table
In the spirit of the holidays.
Let's assume that a dreidel is spinning counter-clockwise at frequency $f$ on a table.
From external point of view, what will I see if I rotate the table clockwise at ...
0
votes
1answer
70 views
Average entropy of a subsystem
In this paper by Don Page, https://arxiv.org/pdf/gr-qc/9305007.pdf, He conjectures average entropy of a substem of dimension m with Hilbert space dimension mn, $m \leq n$. to be :
$ S_{mn} = \sum_{n+...
0
votes
2answers
270 views
Pauli matrices as measurement operators versus spin probability
Pauli matrices tell us what the spin of a particle is along a certain axis.
Let's say I want to measure the spin along the z-axis then the pauli operator
$$\sigma_z = \begin{bmatrix}1&&0\\0&...
1
vote
2answers
453 views
Finding the Eigenvalues and Eigenvectors of the Hamiltonian for three spin-1/2 particles coupled antiferromagnetically
Problem
Given three spin-1/2 particles with the total spin operator $\vec{S}=\sum\limits_{i=1}^3 \vec{S}_i$ and its $z$ projection $S_z=\sum\limits_{i=1}^3 S_{z,i}$, and the Hamiltonian
$$H = J\sum\...
