Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [quantum-spin]

Fundamental characteristic property of particles which together with orbital angular momentum acts as the generator of rotations and which doesn't have a classical equivalent but is sometimes compared to and contrasted with classical intrinsic angular momentum.

0
votes
0answers
26 views

What's the relation between the Lorenztz group and spin of particles?

I know that particles are defined in terms of irreducible representations of the Poincaré group, and that the state of a massive particle is defined by its mass and spin, which are the eigenvalues of ...
0
votes
0answers
33 views

Spin for Dirac fermions proof $\Sigma_{i}=\frac{1}{2} \gamma_{5} \gamma_{0} \gamma_{i}$

The spin for Dirac fermions is defined as: $$\Sigma_{i} \equiv \frac{1}{4}\epsilon_{ijk}\sigma_{jk}$$ Without using an explicit representation for the matrices, I would like to show that the spin ...
2
votes
3answers
129 views

Are superposition quantum systems really in two pure states at once?

I know that quantum systems can have properties of waves as well as those of particles. Also, I know that the mathematical description of quantum states is probabilistic, i.e. $$\Psi = \frac{1}{\sqrt{...
1
vote
1answer
69 views

Spin of elementary particles

Going by the explanation given by Stephen Hawking (as given in Brief History of Time) , the spin of a particle is no. of rotation you give to that particle so that it looks the same. Like you give ...
2
votes
1answer
87 views

Quantum Mechanics - How do we know that the observed locations of electrons are random? [duplicate]

How do we know that the observed location of a electron (or any quantum object) is purely random (there is no way to predict it) within the probability-function instead of normal randomness (we don't ...
2
votes
1answer
38 views

Why do some protons align against the magnetic field?

I was learning about proton NMR (Nuclear Magnetic Resonance Spectroscopy) which is where protons (with their own spins) are subjected to an external magnetic field and a radio frequency is applied to ...
1
vote
1answer
40 views

Possible spins and parities of $^{38}_{17}Cl$

In my introductory nuclear physics course, the following question came up: Consider the odd-odd nucleus $^{38}_{17}Cl$, which has 17 protons and 21 neutrons. Its 17th proton sits in the $1d_{3/2}$ ...
1
vote
1answer
29 views

Notation - angular momentum for composite systems

In the discussion for the addition of angular momentum for composite systems, my lecturer uses the following notation in his notes when referring to a composite system of two spin-half particles: $ ...
0
votes
1answer
35 views

What is this angular momentum coupling notation? $\langle \ell 2 m_\ell 0|\ell 2\ell' m'_\ell\rangle \langle \ell 2 0 0|\ell 2\ell' 0\rangle$

I'm reading this unsigned powerpoint presentation of the Nilsson model in nuclear structure physics. On p. 15, they have this: $$\langle \ell'm'_\ell|Y_{20}|\ell m_\ell\rangle = i^{\ell-\ell'}\sqrt{\...
0
votes
0answers
37 views

Beam separation distance of silver atoms in Stern gerlach experiment

The Sge experiment is well known and the principle is well understood. I am asked the question to find the distance $d$ between the 2 beams after they are separated at the end of the magnets in the in....
1
vote
0answers
25 views

Is there a real proof that Stern-Gerlach Interferometer is behaving like it wasn't there, exactly the same spin direction at output as input?

Have you heard of, know or performed an experiment with a Stern-Gerlach Interferometer (SGI) that would prove that it is really behaving like it wasn't there. We obtained exactly the same spin ...
5
votes
2answers
962 views

There's only time, no space in Quantum Mechanics

In this lecture (44:23) Nathan Seiberg: Topics in 2+1 Dimensional Quantum Field Theories 2. Nathan Seiberg says there's no space in QM and therefore fermions have spin 0. This sounds pretty revolting ...
1
vote
1answer
45 views

Constructing singlet state in second quantization formalism

I am trying to understand the second quantization formalism. Let's say we have a system of fermions (e.g. electrons) with spin in an array of quantum dots. The creation and annihilation operators $c^{\...
6
votes
3answers
143 views

Are quasi-particles really particles?

In my understanding, quasi-particles were just some real world particle (like electrons) but in different environment i.e. an electron in a crystal. But Recently, I have started studying Spintronics/...
0
votes
1answer
71 views

Rotation of a Point Particle

I wonder if there is a meaning of rotation for a point particle. Does a point particle have angular momentum and does he reply to torque?
6
votes
5answers
767 views

Alternative classical explanation of the Stern-Gerlach Experiment?

Many questions have been asked on this site about the Stern-Gerlach experiment, but as far as I can tell this one hasn't. Does the following classical explanation of the SG experiment work? Model ...
0
votes
0answers
12 views

Hund's Rule Coupling in an Effective Hamiltonian/Lagrangian

I am reading a book on Skyrmions, and I am at the part where the interaction of skyrmions with electrons is discussed. The chapter speaks of Spin-Transfer Torque (STT) and makes the following ...
0
votes
0answers
37 views

Troubles with Haldane Shastry Spin Chain

I'm actually reading the article of Shastry "Exact solution of an S= 1/2 Heisenberg Antiferromagnetic Chain with Long-rnaged interactions", Phys. Rev. Lett. 60, 639 (1988)" The articles ...
1
vote
3answers
90 views
0
votes
0answers
82 views

Why aren't gravitons spin 1?

Expressing the metric as $g_{\mu \nu} = \eta_{\mu \nu} + h_{\mu \nu}$, assuming $h_{mu \nu} \ll 1$ we can write the Einstein Hilbert action to leading order in $h_{\mu \nu}$ and quantize the ...
1
vote
1answer
28 views

Can free electrons in a cathode ray pair up?

I read Wikipedia articles "Cooper pair" and "Electron pair" among others. In an atom electrons can be in the same orbital only if they have a different spin (Pauli exclusion principle). In Cooper ...
0
votes
1answer
15 views

Resource recommendation for spintronics

What are some good beginner level books to understand spintronics. I am looking for some sources in which basic mathematics of spintronics is properly explained.
2
votes
0answers
28 views

Can an arbitrary spin state be written uniquely in a Dicke state basis?

Consider a system of e.g. $N=3$ spin-1/2 particles. The state of the system $\vert\psi\rangle$ lives in a Hilbert space of dimension $2^N=8$. Now, consider the collective spin operator $$\mathbf{J} = ...
0
votes
0answers
19 views

Spin and Symmetry of SM Particles

I am reading about Quantum Field theory and I cannot understand how do physicists assign spin to particles. Is there a systematic way to assign spin to particles without knowing it first through ...
1
vote
1answer
61 views

What is the systematic way to determine the spin of lowest-lying states of baryons like $uuu$, $ssd$, $uds$ etc?

I learned that for the lowest lying states, $uuu$, $sss$, $ddd$ can only have $J=\frac{3}{2}$ $uus$, $ddu$, $ddu$, $ssu$ etc can only have $J=\frac{1}{2},\frac{3}{2}$ $uds$ can have $J=\frac{1}{2}, \...
0
votes
0answers
10 views

Resources for spin-stabilized magnets

I will be carrying out an experiment investigating the factors that effect the speed of a spin stabilized magnet. Can someone provide resources or articles that talk about/ have formulas related to ...
1
vote
1answer
29 views

Spin 0 boson interaction

I have a question regarding the interaction of two spin 0 bosons in a shared harmonic oscillator. What would their first excited state be? I'm thinking that the total state has to be symmetric so ...
0
votes
1answer
39 views

Precise value of spin in Nms?

What is the exact value of the spin of a particle with a 'spin' of 'one'? In units of Nms (Newton-meter-second)? And does a boson really have a spin of exactly one, or has that been 'normalized'? ...
4
votes
2answers
120 views

Why should spin “degeneracy” of electron not be infinite?

When we calculate the density of states for an electron, in the standard way as done in statistical mechanics textbooks ( by integrating once over space, then integrating over $\theta$ and $\phi$ of ...
1
vote
1answer
58 views

In the ground state of helium what's the differing quantum number?

In the ground state of the helium atom, both the electrons have the same quantum numbers $(n,l,m)$ equal to $(1,0,0)$. By Pauli's exclusion principle, the fourth quantum number must be different. What ...
4
votes
3answers
98 views

Can the Pauli equation be used to derive the usual $\mathbf L\cdot \mathbf S$ spin-orbit coupling? If not, what's the simplest way?

Can the Pauli equation, $$ \left[{\frac {1}{2m}}({\boldsymbol {\sigma }}\cdot (\mathbf {p} -q\mathbf {A} ))^{2}+q\phi \right]|\psi \rangle =i\hbar {\frac {\partial }{\partial t}}|\psi \rangle, $$ be ...
0
votes
2answers
62 views

Fermion Superposition [closed]

In case of superposition of identical particles, we usually just add their amplitudes. For example, if we have several particles having the amplitudes of being in a particular quantum state $\psi_1, \...
0
votes
1answer
55 views

Reverse Clesbch Gordan coefficients

I'm quite unsatisfied with this answer, so I'm hoping to get an adequate one. I'm trying to understand how to compute the reverse CB coefficents. I'll provide the simplest example. If I have a $l =...
0
votes
0answers
26 views

Introducing Spin operator in QM

What was the experimental facts used in the construction of spins in Quantum Mechanics? What forced W.pauli to invent the idea of spins ? Can there be other internal degrees of freedom yet to be ...
3
votes
1answer
180 views

Second order relativistic corrections to Pauli equation from Dirac equation

I'm trying to derive the full and correct Hamiltonian for spin$\frac{1}{2}$ particles from Dirac equation up to second order in $v/c$. For a potential and magnetic field constant in time. In ...
5
votes
2answers
1k views

Can I feed enough spin up electrons to a black hole to affect its angular momentum?

I was reading classical spin vs quantum field spin. I know spin in quantum mechanics is just a quantum number. But what happens if I try to intentionally feed many electrons all in the same spin state ...
0
votes
3answers
36 views

Symmetry of the spin function and T0 and S states

$|T_0\rangle = \frac{1}{\sqrt{2}}(|\uparrow \downarrow\rangle + | \downarrow\uparrow\rangle )$ is a triplet state, whose spin function has to be symmetric. $|S \rangle = \frac{1}{\sqrt{2}}(|\...
0
votes
2answers
53 views

Why, precisely, do three elements in a row (iron, cobalt, nickel) show ferromagnetism, but not the elements below them on the table?

The same is true for Neodymium, Promethium and Samarium, right? But like the first three, they are consecutive, not above and below each other. Somehow only elements in those two ferromagnetic 'hot-...
5
votes
0answers
103 views

About the rigour of replacing spins by hardcore Bosons

In literature one sometimes find that spins are replaced by hardcore bosons. Formally one replaces spin operators $\sigma^- \leftrightarrow a$, $\sigma^+ \leftrightarrow a^\dagger$, $\sigma_z \...
1
vote
1answer
27 views

Quantum Numbers/state multiplicity - specifically concerned with the differences between $L$, $l$ and $S$, $s$

To put this into context, I will write out exactly what was on the lecture slide that confused me (I've also attached a picture, but I appreciate that text is preferred on here for search engine ...
0
votes
0answers
20 views

Can we change the spin of electron by applying electric field from ↑ to ↓ configuration?

I read in this forum a similary question with magnetic field. But is it possibile change the alignment of the spin with a electric field (DC or pulsant current) in a layer of metal? Probably the ...
0
votes
1answer
101 views

Second quantization notation - Hamiltonian on triplet state

So I'm struggling quite a bit with dirac notation and second quantization and it seems like no one wants to really do calculations step-by-step to at least get the notation right. We were given the ...
1
vote
0answers
13 views

effect of Jahn-Tellar distortion in energy bands

Is orbital degeneracy same as electronic degeneracy? When we mean bands are degenerate, is it like the bands are doubled or single? After Jahn-Tellar distortion what will happen to the energy bands?
-1
votes
1answer
88 views

Difference between angular momentum $L$ and $J$ in quantum mechanics

what is the difference between angular momentum L and generalized angular momentum J and their components?
1
vote
0answers
23 views

Numerical method to find the roots of the expected value of a spin 2j state

Currently I am working with finding the solutions for the following problem: I have a unit sphere in which I have n points defined by their polar and azimuthal angles: $\theta_n , \phi_n$. I then do ...
0
votes
0answers
27 views

Expand Helmholtz energy to fourth order in m (magnetisation)

The energy of a system of spins is given by: $$H=\frac{1}2\sum_{i,j=1}(J\sigma_i\sigma_j-h\sum\sigma_i)$$ I found that we can rewrite in terms of magnetisation, $m=\sum\sigma_i/N$: $$E=-N(\frac{Jm^2}...
5
votes
2answers
89 views

How did Goudsmit and Uhlenbeck figure out the electron has spin $\frac{\hbar}{2}$?

Most stuff I read online says that to explain the Anomalous Zeeman Effect they had to assume the electron's gyromagnetic ratio is $\frac{-e}{m}$ instead of the classical $\frac{-e}{2m}$. But, since ...
1
vote
0answers
18 views

Can we define Spin-Chern number for original QAHE Haldane model?

In Haldane's original paper [5], he discusses the quantum anomalous Hall effect as being characterized by the so-called Chern number that is the surface integral of Berry curvature over the entire ...
1
vote
1answer
49 views

Intuitive “story” explaining how orientation of spin axis affects up/down observation?

Is there a "convenient fiction" that explains why the angle of an electron's spin axis affects the probability of it being observed in a spin up or spin down state? By "convenient fiction", I mean a ...
1
vote
0answers
48 views

Is there a weak hypercharge : spin-3/2 analogy?

So I was not trained as a particle physicist, but I left a table of particles on a post on Hacker News based on what little I do understand about the conservation of weak hypercharge and weak isospin. ...