Questions tagged [spin-models]
A mathematical model used in physics primarily to explain magnetism.
440
questions
4
votes
0
answers
37
views
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 ...
- 5,687
2
votes
0
answers
36
views
Gap of Ferromagnet in a magnetic field
There are numerous known results concerning the absence of a spectral gap in ferromagnets in their thermodynamic limit and various bounds on the value of the spectral gap in finite size realizations. ...
- 131
1
vote
1
answer
46
views
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}...
1
vote
2
answers
70
views
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 ...
0
votes
0
answers
35
views
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 ...
- 1
0
votes
1
answer
23
views
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 ...
2
votes
0
answers
22
views
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}^{...
- 165
2
votes
0
answers
33
views
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 ...
- 325
0
votes
1
answer
34
views
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 $...
- 2,282
2
votes
2
answers
107
views
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 ...
- 49
3
votes
0
answers
44
views
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^...
- 2,282
0
votes
1
answer
53
views
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:
$$H = -\frac{1}{2}|J| \sum_{i,\vec{\delta}} \left[\frac{1}{2}(S_i^+S^-_{i+\vec{\delta}} + S_i^-S^+_{i+\vec{\delta}})...
- 665
1
vote
0
answers
22
views
Any quantum Monte-Carlo algorithm for calculating the lowest eigenenergy in each symmetry sector?
Suppose we have a hamiltonian which has the parity symmetry (e.g., the Heisenberg model with the open boundary condition). Is there any quantum Monte-Carlo algorithm which can be used to calculate the ...
- 1,947
1
vote
0
answers
45
views
Constructing a gapped family of Hamiltonians in the trivial paramagnet
Consider the trivial paramagnet, which has the Hamiltonian $$H = - \sum_i \sigma^x_i$$ Now let's say I have two different Hamiltonians $$H_0 = H + 2\sigma^x_{i_0} \qquad H_1 = H + 2\sigma^x_{i_1}$$ ...
- 737
3
votes
1
answer
147
views
What is the signal of a spin wave?
From what I understand, for example in the Ising model, we can probe the correlation function via neutron scattering, and the correlation function gives the magnetic susceptibility for the system. Is ...
- 700