All Questions
Tagged with spin-models solid-state-physics
19
questions
15
votes
1
answer
4k
views
What is the difference between spin glass and spin liquid?
What is the difference between spin glass and spin liquid?
Do they both originate from frustration?
8
votes
1
answer
3k
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Spin ice / spin liquid v.s. quantum spin ice / quantum spin liquid
What are the distinguishment between (1) spin ice, (2) spin liquid and (3) quantum spin ice, (4) quantum spin liquid?
Apparently the quantum effect for the later (3) and (4) becomes important. But ...
7
votes
1
answer
1k
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 ...
3
votes
2
answers
313
views
Explanation of massive Goldstone modes
I'm solving this exercise with a Heisenberg Hamiltonean in linear spin-wave theory and at some point we are asked to compute the dispersion relation at $k=0$, which leads me to finding two different ...
3
votes
2
answers
484
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Fermi "surface" at finite temperature and its measurement in the lab
As we increase the temperature, we know the sharp Fermi surface at zero temperature becomes smeared out at finite temperature $T>0$. (Just think of the Fermi-Dirac distribution, there will be no ...
2
votes
0
answers
136
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The Ising approximation - what exactly is it?
I am slightly confused about the nature of the Ising model to study ferromagnetism. Consider the Heisenberg Hamiltonian with Zeeman term:
\[H=-\frac{1}{2} \sum_{i\ne j}J_{ij} S_i\cdot S_j+g\mu_B {B}\...
2
votes
0
answers
121
views
Validity of Ising model for mean field thoery
The Heisenberg model for the Hamiltonian of a ferromagnet is given by:
$$H=-\frac{J}{2} \sum \vec{S}_i\cdot \vec{S}_j+\mu_B B \sum_i S^z_i$$
when performing mean field theory, to find $\chi$, we ...
2
votes
0
answers
333
views
The ground state of AFM Heisenberg model $H=+J\displaystyle \sum_{\langle i,j\rangle} \vec{S}_i \cdot \vec{S}_j$ on the triangular lattice?
What is the order -- the ground state of AFM Heisenberg model $H=+J\displaystyle \sum_{\langle i,j\rangle}\vec{S}_i \cdot \vec{S}_j$ on the triangular lattice, with $J>0$ and nearest neighbor ...
1
vote
2
answers
1k
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Polaron transformation in quantum optics
I'm trying to understand the so-called polaron transformation as frequently encountered in quantum optics. Take the following paper as example: "Quantum dot cavity-QED in the presence of strong ...
1
vote
1
answer
47
views
Spin polarization due to exchange? Would spin polarized ground state exist if no $e$-$e$ repulsion?
Non-relativistic no-magnetic-field many electron hamiltonian contains no spin operators. How would spin polarization happen in many electron ground state (modeled by LSDA DFT for instance)?
I often ...
1
vote
1
answer
123
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Why is the gauge group of pseudo-fermion mapping referred to as $\mathrm{SU}(2)$ and not $\mathrm U(2)$?
The representation of spin $\frac{1}{2}$ operators $\hat{S}^{a}$ by pseudo-fermions (also called Abrikosov fermions) is defined by the mapping
$$
\hat{S}^{a} = \frac{1}{2} \text{Tr}\big[ \hat{\psi}^{\...
0
votes
1
answer
130
views
What kind of spin liquids is the Herbertsmithite?
What kind of spin liquids the Herbertsmithite is? Roughly it is a spin-1/2 Heisenberg model on the Kagome lattice with a coupling $J>0$.
It seems that there are long mismatches between the theory, ...
0
votes
2
answers
55
views
Bragg-Williams microcanonical esemble
In this question Bragg-Williams theory of phase transition of the forum someone was asking for Bragg-Williams aprox. and how to calculate entropy. The answer is clear and correct, the Bragg-Williams ...
0
votes
0
answers
31
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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.
0
votes
0
answers
121
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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 $x$-...