# Questions tagged [spin-models]

The tag has no usage guidance.

229 questions
Filter by
Sorted by
Tagged with
50 views

### What if we used “Schwinger Fermions” to study spin waves?

When studying spin waves excitations in the Heisenberg Hamiltonian people often use Schwinger Bosons representation or Holstein-Primakoff which is a specific case of Schwinger Bosons. This leads you ...
49 views

### Is the Aubry-André-Harper (AAH) model renormalizable？

We know the Aubry-André-Harper (AAH) model can have a local/delocal phase transition at $\Delta/J=2$, but can this phase transition point be obtained by RG procedure? Or can this local/delocal phase ...
32 views

### Partition function for 4 spins

I was reading some notes by John Chalker on order by disorder and encountered a classical spins partition function calculation. I could not follow the integration, i.e. obtaining eqn. (1.7) from (1.5) ...
35 views

15 views

### Meaning of elastic energy formulation

In Chaikin's Principles of Condensed Matter Physics, in chapter 6 ("Generalized Elasticity"), on pg. 290, there is a formulation of what he refers to as an elastic energy associated with gradients of ...
49 views

### Valence Bond Solid order paramter

I'm confused about the valence bond solid (VBS) in condensed matter literature. The idea is a lattice is covered by spin singlets and thus spin rotational invariant. It seems that it's commonly ...
32 views

### What are Skyrmion bubbles?

what exactly is the difference between a skyrmion and a skyrmion bubble? Thanks.
20 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 ...
52 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 ...
57 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 ...
49 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 ...
38 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, ...
31 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 ...
306 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 ...
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 ...
18 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 ...
37 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 ...
64 views

24 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 ...
16 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 ...
34 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....
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 ...
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 ...
106 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 ...
34 views

35 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'...
63 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 ...
66 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_{...
114 views

### What is the Hilbert space of the SYK model?

In reading a recent preprint  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 ...
46 views

87 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 ...
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 ...