All Questions
15
questions
2
votes
1
answer
80
views
Product of Majorana operators after a orthogonal transformation
The question I want to ask is the following:
There are $N$ Majorana fermion modes: $\gamma_1, \gamma_2, \dots, \gamma_N$, and they satisfy the anti-commutation relation:
$\{ \gamma_i, \gamma_j \} = 2\...
- 1,181
0
votes
0
answers
60
views
Breaking a classical ground state degeneracy by a quantum term and order-by-disorder
Let’s assume we have a Hamiltonian for spin-1/2 particles with two terms, a classical interaction term and a “quantum” (non-diagonal) term. For simplicity, let’s assume that the quantum term is a ...
- 29
3
votes
1
answer
237
views
Neel ordering on the square lattice vs mean-field AFM Heisenberg model
Question:
It seems like the Neel order of the AFM Heisenberg model on the square lattice is actually stronger than the (bipartite) fully-connected case. This seems counterintuitive. Am I simply wrong ...
- 321
3
votes
1
answer
559
views
Static spin structure factor VS equal-time spin structure factor
It looks like many papers (maybe all papers containing "static spin structure factor") use the terminology, static spin structure factor, to refer to the equal-time spin structure factor ...
- 123
4
votes
0
answers
89
views
Operator inequality between the Heisenberg Hamiltonian and the total spin
Consider a collection of $N$ spin-1/2 particles (qubits) with total spin
$$\vec{S} = \frac{1}{2}\sum_{n=1}^N \vec{\sigma}_n$$
and a Heisenberg Hamiltonian
$$H = -J \sum_{\langle n,m\rangle} \vec{\...
- 3,684
1
vote
0
answers
109
views
Bogoliubov-Valatin transformation generalisation
Considering the following Heisenberg Hamiltonian (with spin $S$ , and $J<0$ for the case of an antiferromagnet) when we only consider interactions between first neighbors in a square lattice in the ...
- 1,124
2
votes
1
answer
153
views
Spin Glass Hamiltonian
Why do Edwards and Anderson use the hamiltonian
$$
H = \sum_{i,j} J_{ij} \mathbf{s}_i \cdot \mathbf{s}_j
$$
to describe the interactions in a spin glass?
Naively I would think that from the ...
- 754
3
votes
1
answer
336
views
Conserved charge in Density Matrix Renormalization Group (DMRG)
Currently I am facing a problem which relates to the conserved quantities in DMRG. I use old-fashioned DMRG (Steven White approach) to compute the ground state of certain models. However, the ground ...
- 413
2
votes
1
answer
53
views
Why is $\sum_{i=0}^N S_i^z S_{i+1}^z |\uparrow ... \downarrow_n ... \uparrow \rangle = \frac{1}{4}(N-4)$?
I am following these (http://edu.itp.phys.ethz.ch/fs13/int/SpinChains.pdf) lecture notes and I can't understand why given the following XXX Heisenberg hamiltonian
$$
\mathcal{H}=\frac{J N}{4}-J \sum_{...
- 1,544
0
votes
1
answer
75
views
Antiferromagnetic chain from Altland/Simons book (p.81)
In Condensed Matter Field Theory (2nd edition) by Altland/Simons there considered antiferromagnetic chain with Hamiltonian:
$$H = J\sum_{<n,m>} S_nS_m = J\sum_{<n,m>}[S^{z}_n S^{z}_m + \...
- 341
3
votes
1
answer
436
views
Are all gapless acoustic magnon modes essentially Goldstone modes?
We know gapless Goldstone mode appears when the system exhibits spontaneously symmetry broken. Does this means whenever we observe gapless acoustic modes it is Goldstone mode i.e. spontaneous symmetry ...
- 33
1
vote
1
answer
37
views
Macroscopic properties of individual spins in a material (magnet) - and their behavior under rotations
I am wondering
(A) about the influence of individual spins on the behavior of a macroscopic object
(B) and about the influence of rotating the macroscopic object on the internal spins
To approach ...
user257090
1
vote
0
answers
35
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 ...
- 11
1
vote
0
answers
494
views
Practical/experimental difference between (quantum) Heisenberg and (classical) Ising model
I have read a few discussions about the difference between the Heisenberg model (using quantum spin operators) and Ising model (with spins $\pm 1$), notably this one or this Quora post.
All the ...
- 119
2
votes
0
answers
43
views
How do phonons and spinwaves interact? [closed]
What governs the coupling of acoustic phonons to transverse and longitudinal spinwaves? Is there a simple picture?
- 117