Questions tagged [spin-models]
A mathematical model used in physics primarily to explain magnetism.
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What is the physical meaning of the average value of the long product of spin operators
For the quantum one-dimensional XYZ Heisenberg model with $N$ spins $1/2$, consider the following average values of the products of successive operators $\hat{\sigma}^x$ in the ground state
$$
C_j(n) =...
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Ising Model magnetisation
I am simulating the 2D Ising Model and specifically looking at the time evolution of magnetisation $m$. Now, in the non-equilibrium state, magnetisation will grow as a power law with time $t$, if ...
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Are Landau-Lifshitz equations equivalent to Hamilton's equations for classical spins?
Let $\boldsymbol{s}_1$ describe a "classical spin", i.e. a point on the surface of a unit sphere embedded in $\mathbb{R}^3$. It can be parametrized, for example, as
$$ \boldsymbol{s}_1 = \...
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Are strong correlations of boundary spins possible in the absence of long-range order in the bulk?
Question about one-dimensional models with short range interaction of quantum spins, such as transverse Ising and Heisenberg models. Are there any examples when, in the ground state of the system, the ...
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Hubbard-Stratonovich (HS) transform (or similar) for higher order-interactions
I have a question about a generalization of the Hubbard-Stratonovich (HS) transformation to decouple two-body interactions. When dealing with Hamiltonians of the kind
\begin{equation}
H = -\sum_{a}...
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Photo of an actual piece of spin glass?
I can't find any picture anywhere of a physical spin-glass, such as the Copper-Manganese alloy (CuMn) with 1 a.t.%, or the AuFe. Can someone post an image of physical spin glasses? I am just confused ...
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Mean energy measurement in an arbitrary quantum state
I've gone through many papers looking for a way to measure a mean energy in an arbitrary state $\langle \psi | H | \psi \rangle$. I am interested in a theoretical protocol or an exemplary experimental ...
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What's the relations between Quantum spin liquid and Quantum magnetism? [closed]
I am a fourth years undergraduate student. Recently, I am seeking that my research direction for my upcoming graduate program, and I found that my tutor is working that direction (as shown in the ...
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The energy for nonzero total spin of 1-dimensional XY model
I want to compute the energies and eigenstates for non-zero total spin of the 1-dimensional XY model.
The Hamiltonian for the 1-dimensional XY model is given by:
\begin{align*}
H = -J \sum_{i=1}^{...
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Mean-field self-consistency and thermodynamic limit
Is the mean-field self-consistent-equation approach used to study, e.g., the magnetization of an Ising model able to take into account finite-size effects, or is it written, so to say, directly in the ...
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Is there a good definition of free energy of a subsystem?
Consider the $L$ by $L$ 2d Ising model with $\beta H = -K \sum_{\langle i j \rangle} \sigma_i \sigma_j$. I'm interested in the canonical ensemble.
I can define the free energy of the whole system as $...
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Expressing the spin-1/2 operators in terms of the quantum rotor variables
In this paper, a spin-1/2 Hamiltonian is introduced on a cubic lattice [Eq. (12)]:
$$
H_c = -J \sum_{\Box} (S_1^+ S_2^-S_3^+S_4^- + \text{H.c.}),
$$
where the sum runs over all plaquettes of the cubic ...
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What $(2+0)d$ classical model becomes the $(1+1)d$ Heisenberg model?
The $(1+1)d$ transverse-field Ising chain is closely related to the $(2+0)d$ Ising model. In particular, the $(2+0)d$ classical Ising model has a transfer matrix that can be written suggestively as $e^...
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Showing that the ground state of the Heisenberg ferromagnet is an eigenstate of the Hamiltonian
The Hamiltonian of a Heisenberg ferromagnet in terms of $S^+, S^-, S^z$ is given by:
$$H = -\frac{1}{2}|J| \sum_{i,\vec{\delta}} \left[\frac{1}{2}(S_i^+S^-_{i+\vec{\delta}} + S_i^-S^+_{i+\vec{\delta}})...
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Any quantum Monte-Carlo algorithm for calculating the lowest eigenenergy in each symmetry sector?
Suppose we have a hamiltonian which has the parity symmetry (e.g., the Heisenberg model with the open boundary condition). Is there any quantum Monte-Carlo algorithm which can be used to calculate the ...
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