# Questions tagged [spin-models]

A mathematical model used in physics primarily to explain magnetism.

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### Time for ferromagnet to align with magnetic field

A ferromagnet is inside a solenoid. When the current in the solenoid flips its direction, the solenoid magnetic field flips. As a consequence, the ferromagnet magnetization flips. What determines the ...
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### Generating Matrix Product States from a (random) vector

I try to decomposite an arbitrary quantum state into a matrix product state. For this i follow this paper by U. Schollwöck where especially section 4.1.3 is relevant. So far I did the following: ...
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### Spinfoams and LQG

I know up to some degree how spinfoam models and LQG work, but there are some details that i still miss since i have still a naif knowledge. In the literature it as often said that an open problem is ...
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### Hamiltonians with collective quantum spins and their ground states

This feels like it could be a undergrad/grad-school quantum mechanics course level problem, or potentially something pretty interesting. I'd be happy with either answer, but I don't know which one is ...
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### Phase space of the $n$-vector model

The classical Heisenberg model is described in terms of the three-component unit vector $S_a(x)$, which is a function of position, $$H=\int d^dx\frac{1}{2}\sum_{a,i}\left(\partial_i S_a(x)\right)^2.$$ ...
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### Mathematical meaning for Algebraic Bethe Ansatz

I'm a mathematician who's trying to understand the meaning of Algebraic Bethe Ansatz. What I understood is that when dealing with quantum integrable models (like XXZ Heisenberg spin chain), one is ...
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1 vote
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### Trying to understand Kitaev's calculation of relative Majorana number in two dimension

In appendix C.4.3 of "Anyons in an exactly solved model and beyond", Kitaev provides a proof of the fact that when the Chern number is odd, a vortex in the gauge field accompanies an ...
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### Magnetization Plateau and Entanglement

In some low dimensional quantum spin systems, magnetization plateau is observed before the saturation in magnetization curve. . I have couple of questions related to this effect- It seems, ...
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### 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 ...
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### Isotropic classical model with a different phase transition than its anisotropic quantum limit

I have often heard that the isotropic ferromagnetically-coupled 2d classical Ising model and the quantum 1d transverse field Ising model have similar phases and the same universality class of their ...
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### Integrability of long range Heisenberg chain

Is the long range heisenberg spin 1/2 chain integrable? More generally, is the long range version of famous spin chain models integrable?
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