All Questions
Tagged with spin-models quantum-spin
86
questions
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218
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How do boundary conditions change during a spin transformation?
I am currently reading the following review paper:
(1) Two Dimensional Model as a Soluble Problem for Many Fermions by Schultz et. al.
Equation (3.2), which is reproduced below, introduces the Jordan-...
user261609
1
vote
1
answer
280
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Spin hamiltonian matrix representation
To preface, I'm an applied mathematician trying to parse the meaning of physics notation I've come across in a paper. My goal is to understand the setting in terms of matrices and vectors so that I ...
- 133
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2
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131
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Why the entropy of non-zero nuclear spin is zero at $T = 0$?
When reading Concepts in Thermal Physics (second edition) by Stephen and Katherine about the concepts of the third law, I met with such a problem. The text reads as follows:
Consider a perfect ...
- 15
2
votes
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604
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If a spin $\frac{1}{2}$ particle flips its sign after a 360° rotation, why don't theorists just say it rotated by 180°?
Usually, when a wave or wave-like object or system goes through a $180^{\circ}$ twist or turn or whatever, we say it is opposite to how it was oriented before, and if it came across its former self ...
- 4,509
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1
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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
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39
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How is two-level optical transition in a spin 1 system affected by the third level?
Suppose you have a spin-1 system. Let us resonantly drive the transition between any 2 levels (say 0 1 transition). How would the the presence of the third level (-1) state affect this transition?
We ...
- 21
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votes
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336
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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
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What is helical Dirac nature?
A concept in Spintronics which can not be found on Wikipedia. The picture is from a review of Spintronics of 2016 by Fert.
- 1
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Is it possible to construct an operator for $z$-component of spin for a 2D system?
Let's say we have an arrangement of spins in 2D space (as given in the below picture).
Assume that the $z$-axis is out of the plane and a spin (circled in red) makes an angle $\theta$ with the $x$-...
- 1,335
1
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Writing down a Hamiltonian that couples spin and phonons
I am studying spin dynamics and am trying to write down a Hamiltonian that couples the spins with the phonons. I have the following interacting spin Hamiltonian
$$H_{s}=\sum h_{i}S_{i}+H_{\text{...
- 21
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69
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Time evolution of spin with Anti-symmetric (Dzyaloshinkii-Moriya) interaction
I am trying to simulate the time evolution of a spin in spin chain interacting via Dzyaloshinkii-Moriya interaction. The Hamiltonian is of the form
$$H_{A}=J_{A}\sum_{i}(S^{x}_{i}S_{i+1}^{y}-S^{x}_{i+...
- 21
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0
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487
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Commutator of Hamiltonian and the spin sum
For a 1-D Heisenberg quantum spin chain the Hamiltonian is given by:
$$H=-\sum_{j=0}^{N-1} J_{i,i+1}\boldsymbol{\sigma}_j^i \cdot\boldsymbol{\sigma}_{j+1}^i -\sum_{j=0}^{N}h_j\sigma_j^z$$
where $\...
- 11
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votes
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answer
307
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Describing a subspace of a Hilbert space of $N$ spins 1/2
Consider having $N$ spins $1/2$, so the overall state of $N$ particles can be described by the total spin value $S=0 \ldots N/2$ (let us set $N$ to be even for simplicity), and the projection of the ...
- 133
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Finding coupling between crystal sites related by symmetry
Say I have a crystal and the coupling between sites is described by the following local, model Hamiltonian (a spin 1/2 system):
$$
\hat{H}_{i,j} = J \bf{S}_i\cdot\bf{S}_j+\bf{d}\cdot\left[\bf{S}_i\...
- 130
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61
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Indistinguishability in Spin-1/2-system
In terms of statistical physics I thought the microcanonical partition function can be interpreted as summing over all possible quantum numbers. Neglecting indistinguishability in the case of two ...
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