Questions tagged [spin-models]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
3
votes
1answer
273 views

R-matrix for spin chains

In algebraic Bethe ansatz procedure, one of the central objects is the R-matrix satisfying the Yang-Baxter equation, but all the papers/books give directly its expression without deriving it, so my ...
8
votes
1answer
3k views

Why we call the ground state of Kitaev model a Spin Liquid?

Now we always talk about the so-called Kitaev spin liquid. One important property of spin liquid is global spin rotation symmetry. Let $\Psi$ represents a spin ground state, if $\Psi$ has global spin ...
3
votes
1answer
3k views

What is the difference between classical and quantum Ising model?

The Ising model is defined with the Hamiltonian: $$ H = -\sum_{<i,j>}S_i^z\cdot S_j^z $$ What is the difference between quantum version and classical version? My intuition is that the ...
4
votes
3answers
7k views

Nuclear Spin of Sodium 23

I am actually calculating the nuclear spin of Sodium 23. Here we have 11 protons and 12 neutrons. Now both the nuclei are short of the magic numbers. When I use the shell model for protons and ...
6
votes
1answer
939 views

A simple model that exhibits emergent symmetry?

In a previous question Emergent symmetries I asked, Prof.Luboš Motl said that emergent symmetries are never exact. But I wonder whether the following example is an counterexample that has exact ...
4
votes
1answer
1k views

Ground state degeneracy: Spin vs Fermionic language

Let us first consider the Hamiltonian of well-known 1D periodic Ising model as $$ H = -\frac{1}{2} \sum_{j=1}^N \sigma^x_j \sigma^x_{j+1} + \frac{h}{2}\sum_{j=1}^N \sigma^z_j. $$ Now, in the ...
4
votes
1answer
470 views

Quenched systems - disorder average (SYK model)

In a system with quenched disorder one is usually looking for self-averaging quantities, i.e., quantities such that the average over the couplings produces a ``typical" configuration in the ...
1
vote
1answer
1k views

What makes an electron flip to spin-up?

The normal mode of spin for an electron is spin down: with angular momentum L pointing in the opposite direction of motion V (right) but, when a free electron approaches , say, a Helium ion it must ,...
10
votes
2answers
613 views

What new features does the Heisenberg Model have compared to the Ising Model?

Both the Ising and the Heisenberg Models describe spin lattices with interaction on first neighbors. The Hamiltonian in each case is quite similar, despite the fact of treating de spins as Ising ...
6
votes
2answers
218 views

Why is classical spin the spin-$\infty$ representation of $SO(3)$, not the spin-$1$ representation of $SO(3)$?

Given a classical spin model, $$H=\mathbf{S}_1\cdot \mathbf{S}_2\tag{1}$$ where $\mathbf{S}_i=(\sin\theta_i \cos\phi_i,\sin\theta_i \sin\phi_i,\cos\theta_i), i=1,2$ is the classical spin. Given a ...