Questions tagged [spin-models]
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222
questions
0
votes
1answer
17 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 ...
0
votes
1answer
30 views
Ground state magnetization of the Heisenberg XXZ chain
The Hamiltonian of the Heisenberg XXZ chain (without external field) has the form
$$
H = -J \sum_{n=1}^{N}\left(S_n^xS_{n+1}^x+ S_n^yS_{n+1}^y + \Delta S_n^zS_{n+1}^z\right).
$$
It is known that this ...
3
votes
2answers
41 views
Doping and inter plane coupling for cuprates
I'm not very familiar with high-Tc and I have naive questions on cuprates materials (CuO2). It seems common that everyone treats it as a 2D material for good reasons: in undoped system, there are two ...
0
votes
1answer
43 views
Difference between thermal hall and phonon hall effect
I know of thermal hall effect which refers to a charge-neutral excitations exhibit hall effect that transport heat: for example, a heat current along x-direction generates a temperature gradient along ...
0
votes
0answers
35 views
How to prove identity $\langle \mathbf{S} \rangle^2 + \langle \mathbf{Q} \rangle^2 = 4/3$ for any spin-1 wavefunction?
Is there an easy way to prove that for an arbitrary wavefunction of spin-one
$$\langle \mathbf{S} \rangle^2 + \langle \mathbf{Q} \rangle^2 = 4/3$$
where $\mathbf{S} = (S_x, S_y, S_z)$ for spin-1, ...
-1
votes
0answers
17 views
Spin 1/2 and Ohanian's field picture of spin
I have understood that the standard theory of electrons considers them as point particles and "intrinsic" spin must be considered mathematically.
Ohanian showed that spin can also be deduced from a ...
1
vote
0answers
30 views
Product over integral representations and steepest descents
Suppose we have a product of Dirac or Heaviside functions in the context of a spin model and we use an integral representation to express these in order to do some manipulations, more specifically ...
3
votes
3answers
298 views
What do physicists mean by solving the Ising model?
To me, an Ising model is a setting of discrete objects, that have attributes (spins) that contribute to energy based on interactions with nearby objects. With the energy function (Hamiltonian) written ...
0
votes
0answers
18 views
Spin pumping: interface between a Ferromagnetic and a normal metal
We know that at the interface $(y=0^+)$ of a ferromagnetic material (FM) with excited magnons, and a normal metal (NM), there is an injection of spin current (or spin pumping) arising from the magnons ...
0
votes
0answers
16 views
How to get algebraic PSG solutions once we got the constraints?
The question is more technical than conceptual. I've been trying to understand the classification of spin liquids as done by Prof.Wen. I have got the constraints on IGG(Invariant gauge group) elements ...
0
votes
0answers
21 views
Is the definition of gap of a Hamiltonian, i.e. difference between two distinct eigenvalues, restrictive?
The spectral gap of a quantum model or a Hamiltonian, in the context of whether it is a gapped or gapless model, is often defined as the difference between the two lowest distinct eigenvalues of the ...
3
votes
1answer
63 views
Invariants of spin chains
I consider modelling a particular physical phenomenon using a spin chain (Ising, XYZ, Potts, etc.). Once I establish the mapping from experimental data to the states of spins for, I get the values $\{...
0
votes
0answers
30 views
What are differences among chiral, helical and spiral in quantum spin context?
For chiral, as far as I know, there are vector chirality $\kappa_{ij}=\mathbf{S}_{i}\times \mathbf{S}_{j}$ which characterizes non-collinear spin arrangement and scalar chirality $\chi_{ijk}=\mathbf{S}...
0
votes
0answers
22 views
Ferromagnetic/Paramagnetic Phase Transition in a Non-Zero External Magnetic Field
I'm new to condensed matter theory, especially spin-glass systems. I understand that the Ising model exhibits a Phase Transition when there is no external magnetic field (h=0). And that at the ...
0
votes
0answers
14 views
How to understand spin-phonon coupling in any material? Differs from electron-phonon coupling?
Spin-phonon coupling is an interesting phenomena, especially, in the case of multiferroic materials. Its origin is said to be the exchange interaction of magnetic ions. In that case, any magnetic ...
3
votes
0answers
32 views
Temperature of spin-glass transition
In the literature on spin glasses I see a lot of theoretical phase diagrams and experimental plots with a definite spin-glass transition temperature $T_\mathrm{G}$. For example, in this figure from J....
2
votes
0answers
31 views
De Almeida-Thouless line and spin glass in the Hopfield network
From the SK model, the Almeida-Thouless line appears to divide the stable paramagnetic phase and unstable spin-glass phase in the presence of an external magnetic field.
However, in the case of a ...
1
vote
0answers
72 views
Physical argument that the Ising model has no phase transition for nonzero external field
I have seen rigorous proofs on why the Ising model does not have a phase transition for $h\ne 0$ (via the Lee-Yang theorem or GHS inequality). However, these proofs don't shed much physical intuition ...
4
votes
1answer
104 views
Implementation of neural network quantum states of the anti-ferromagnetic Heisenberg model
I'm studying this Science paper "Solving the quantum many-body problem with artificial neural networks" and looking into the implementation of the Anti-ferromagnetic Heisenberg model. The Hamiltonian ...
0
votes
1answer
33 views
Anisotropy in spin chain hamiltonian
The Hamiltonian of XY Spin Chain on a lattice of N sites can be written as
$$
H = -J\sum_{i=1}^N \left(\frac{1+\gamma}{2}\sigma_i^x\sigma_{i+1}^x + \frac{1-\gamma}{2}\sigma_i^y\sigma_{i+1}^y + \lambda ...
1
vote
1answer
58 views
$Z_2$ symmetry breaking in XXZ model
I have a question about an statement that is said in the paper Entanglement and spontaneous symmetry breaking in quantum spin models (Phys. Rev. A 68, 060301(R), (2013)). It is related to the XXZ ...
2
votes
0answers
26 views
Lagrangian formulation of classical spin chains
Is there a way to construct a Lagrangian formulation of the classical dynamics of a spin chain - say a Heisenberg or XY chain? The Hamiltonians here are obvious.
1
vote
1answer
47 views
Mermin-Wagner in Second Quantization
The following link provides a detailed proof of the Mermin-Wagner Theorem for the quantum spin model. However, one thing that I don't quite understand is why the underlying Hilbert space $H_\Lambda$ ...
0
votes
0answers
46 views
Order parameter fluctuations in the mean field model for ferromagnetism (mathematical approach)
I'm a math student taking first steps into statistical mechanics and... I need help!
Consider the Curie-Weiss model (i.e. the classical mean field model for ferromagnetism). If $N$ is the number of ...
2
votes
2answers
520 views
Spin-orbit coupling Hamiltonian in tight-binding models
Consider spin-orbit coupling (of strength $\lambda_1$) on lattice, with the below Hamiltonian
$$H = i \lambda_1 \sum_{<ij>} ~\frac{E_{ij} \times R_{ij}}{|E_{ij} \times R_{ij}|} \cdot \sigma ~...
0
votes
0answers
29 views
Heisenberg Hamiltonian: Energy per site on the triangular lattice
I want to find the energy per site for the Heisenberg Model with 3D spin-vectors $\bf S_i$ on a 2D triangular lattice and nearest neighbor interactions. I have a Monte-Carlo Simulation (green +) and I'...
1
vote
0answers
58 views
Question about the Dyson-Schwinger equation for 4-point function of the SYK model
In studying the SYK model, I have no idea how to get the kernel $K(t_a,t_b,t_3,t_4)$ and $\Gamma_0(t_1,t_2,t_3,t_4)$ and also ladder diagrams in the Dyson-Schwinger equation for 4 point function of ...
0
votes
1answer
62 views
Mean field solution of the Ising Model
I try to compute the variational free energy in the Ising Model using the bogoliubov inequality: \begin{equation} \mathcal{F}(\lambda) = F_{0}(\lambda) \ + \ \langle\mathcal{H_{1}(\lambda)} \rangle_{...
3
votes
1answer
98 views
What is the Hilbert space of the SYK model?
In reading a recent preprint [1] contrasting bosonic models with local (tensor product) Hilbert spaces with SYK-like models of fermions, I realized I was confused about something. While I have a vague ...
1
vote
1answer
43 views
Existence of the Schwinger boson creation operator
Schwinger boson transformation is widely used in spin systems. It represents three Pauli matrices in the following form
$$
s^+=\frac{1}{2}\sigma^+ = a^\dagger b \, ,
$$
$$
s^-=\frac{1}{2}\sigma^- = b^\...
0
votes
3answers
90 views
Phase transition on magnetic materials
Is ferromagnetic to paramagnetic phase transition a reversible process?
If I start with a ferromagnetic material with a spontaneous magnetization below the Curie temperature, and then I start to heat ...
2
votes
0answers
57 views
$T$-duality symmetry of $SU(2)_1$ WZW model
For bosons at self-dual radius, the CFT has T-duality symmetry. My question is can we realize this symmetry on the lattice model? for example antiferromagnetic spin chain.
1
vote
0answers
58 views
Massive Thirring model as continuum limit of Heisenberg model
The massive Thirring model
$S = \int d^2 x \left[ \bar{\psi} \gamma^\mu \partial_{\mu} \psi - m \bar{\psi} \psi - \frac{g}{2} \left( \bar{\psi} \gamma_\mu \psi \right) \left(\bar{\psi} \gamma^\mu \...
1
vote
0answers
52 views
Reference for Onsager’s solution of the 2D Ising model
I am interested in Onsager‘s famous paper “Crystal statistics I” where he derives the solution of the 2D Ising model.
I am reading the original paper, but I search some supplementary material (blog, ...
1
vote
0answers
131 views
What is the Haldane phase?
I'm trying to look up what is the Haldane phase, but the only thing I find is examples of physical systems that "realize" the Haldane phase, such as the AKLT model, but no clear definition of what ...
0
votes
0answers
8 views
What are some good sources to learn Spin Glass theory?
I am looking for some self study and reference books or similar material to learn Random Fields and Spin Glass Theory. Would really appreciate any suggestions.
1
vote
1answer
93 views
What is breathing Kagome lattice?
I know what kagome lattice is. While reading some article I came to know the term breathing kagome lattice. Looked up the web didn't found any definitions of it.
My suspicion is that when hopping ...
3
votes
1answer
119 views
What are $U(n)$ or $\mathbb{Z}_2$ quantum spin liquids?
Quantum spin liquid is a state of matter in which spins are correlated and fluctuate even at zero temperature.
My question is about these terms in general. When we say that a state or a quasi-...
0
votes
0answers
11 views
How to obtain Hamiltonian parameters with EPR technique
I want to ask you how to obtain the parameters of the spin Hamiltonian of a system. I’m doing simulations with the EasySpin tool to obtain these parameters such as, J, the anisotropy factors D and E, ...
0
votes
0answers
71 views
Calculating expected values $\langle S_x \rangle$ and $\langle S_y \rangle$ in the Heisenberg model
Let's say, that we are considering the basic Heisenberg model with only two spin-particles. So our Hamiltonian can be written as follows:
$$
H = \sum_{\langle i,i' \rangle} S^{(x)}_i S^{(x)}_{i'} + S^...
1
vote
0answers
78 views
Irrational Conformal Field Theory v.s. Non-Unitary Conformal Field Theory?
Unitary conformal field theories (CFTs) with irrational (or including the special case of rational) central charge is called irrational conformal field theory (ICFT).
Irrational conformal field ...
2
votes
1answer
88 views
Calculating the local energy in neural network quantum state
given a Hamiltonian of Heisenberg 1D model as following:
$$H = -J\sum_{I}\sigma_{i}^{z}\sigma_{i+1}^{z}$$
I am trying to solve it with a neural network function given by Restricted Boltzmann machine ...
0
votes
0answers
68 views
Generalised Ising models?
Are there generalised Ising models:
The underslying mesh/connectivity is completely arbitrary - non rectangular, 3D...ND, complete connectivity should be possible
The interaction potential is ...
0
votes
0answers
47 views
Where to find a Path Integral treatment of 1D Quantum Heisenberg model or Quantum Spin Chain?
All:
Where to find a Path Integral treatment of 1D Quantum Heisenberg model or Quantum Spin Chain?
I would like to find a detailed calculation of path amplitude in such situation. I did some google ...
1
vote
0answers
55 views
Heat-bath algorithm of 2D XY model
Can anyone suggest any reference where the heat-bath algorithm for the classical 2D XY model has been discussed in detail. I have found references for the 3D Heisenberg model which can be exactly ...
5
votes
2answers
117 views
Naming symmetries in quantum systems, e.g. $\mathbb{Z}_2$ or $U(1)$
I'm constantly confused by some of nomenclature that is associated with symmetries in quantum Hamiltonians and was hoping someone could set me straight.
Specifically, we often have something like a ...
0
votes
0answers
49 views
Quantum Monte Carlo Loop Algorithm for quantum spin: why is the freezing graph present in ferromagnetic Ising model?
I study the loop algorithm (Evertz et al).
I cannot understand, why the freezing graph type where we have to flip all 4 spins together is not present for the quantum-XY model and the anti-/...
1
vote
0answers
36 views
Why do the Binder Cumulants of different system sizes intersect at the critical point?
When Monte Carlo simulations are performed for spin models (Ising model etc.) the critical temperature can be found by simulating for different lattice sizes and plotting the Binder Cumulant for them. ...
1
vote
0answers
23 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 ...
2
votes
2answers
81 views
Different concepts of phase transitions in spin models
I am currently revising the lecture notes in which different spin systems
are analyzed, focussing on the occurrence (or absence) of phase transitions.
Different techniques are applied to analyze the ...
