The study of physical properties condensed phases of matter, including solids and liquids.
9
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142 views
Lagrangian for Goldstone mode + topological excitation
The XY-model Hamiltonian is the following,
$${\cal H}~=~-J\sum_{\langle i,j\rangle} \cos (\theta_i -\theta_j).$$
The Goldstone mode corresponds to term $(\nabla \theta)^2$ in the effective ...
7
votes
0answers
188 views
How to determine if an emergent gauge theory is deconfined or not?
2+1D lattice gauge theory can emerge in a spin system through fractionalization. Usually if the gauge structure is broken down to $\mathbb{Z}_N$, it is believed that the fractionalized spinons are ...
6
votes
0answers
104 views
Some questions about anyons?
(1) As we know, we have theories of second quantization for both bosons and fermions. That is, let $W_N$ be the $N$ identical particle Hilbert space of bosons or fermions, then the "many particle" ...
5
votes
0answers
118 views
How does Haldane conjecture follow from the topological $\Theta$ term
The one dimensional SU(2) Heisenberg quantum spin chain is known to be described by the 1+1d O(3) nonlinear $\sigma$ model with a $\Theta$ term, following the action
...
5
votes
0answers
233 views
Do EM waves transmit spin polarization?
Suppose you have a normal dipole antennae (transmitter and receiver) . Spin polarized current (as opposed to normal current) is sent into the transmitter, it emits an EM wave and the Receiver receives ...
5
votes
0answers
254 views
Is the “particle number” of “electrons” well defined in Wen's string-net theory of elementary particles?
According to professor Wen's string-net theory(Colloquium: Photons and electrons as emergent phenomena, Levin and Wen, Rev. Mod. Phys. 77, 871(2005), see e.g. http://arxiv.org/abs/cond-mat/0407140), ...
5
votes
0answers
180 views
Griffiths phase
What are Griffiths effects in the context of condensed matter physics?
From a cursory examination of the literature I've gathered the following: it seems that ordered systems have a "clean" critical ...
5
votes
0answers
144 views
Can I integrate out the fermion field that is not gapped?
This piece of argument has been repeated again and again by experts, that is
Since the fermions are gapped, then I can integrate it out.
but I have no idea of what will happen if the fermions ...
5
votes
0answers
167 views
Quasi 1D insulators with strong spin-orbital interaction
We know that the spin-1 chain realizes the Haldane phase which is an example of
symmetry protected topological (SPT) phases (ie short-range entangled phases with symmetry). The Haldane phase is ...
5
votes
0answers
151 views
What is the energy functional for v=5/2 Moore-Read state?
I am trying to do some Monte Carlo simulations for Pfaffian state from Fractional Quantum Hall effect. I am wondering what is the energy functional for v=5/2 Moore-Read state?
4
votes
0answers
49 views
How to understand Modular transformation in topological order?
Topological order in (2+1)D is described by its ground state degeneracy and the braiding statistics and topological spins of excitations. People believe that these information is all encoded in ground ...
4
votes
0answers
54 views
What is Resonance Width? Why we use it to distinguish different Regimes of the Anderson Model
The single inpurity Anderson Hamiltonian is
...
4
votes
0answers
130 views
What is the mass of the emergent magnetic monopoles in spin ice and how is the mass of an emergent particle determined?
In solid state physics emergent particles are very common.
How one determines if they are gap-less excitations?
Do the defects in spin ice called magnetic monopoles have mass?
What is the mass of ...
4
votes
0answers
181 views
Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?
There is a claim often made about cold fusion, that it is excluded theoretically. The main theoretical argument is that electronic energies are too low to overcome the Coulomb barrier, since d-d ...
4
votes
0answers
152 views
Significance of Dirac cones in condensed matter physics
In condensed matter physics, Dirac cones can be found in graphene, topological insulators, cuprates, and iron-pnictides. This means that electrons behave as massless particles near the Dirac points.
...
4
votes
0answers
126 views
What happens to a Luttinger liquid under time reversal?
Suppose you a have an ordinary Luttinger liquid with
$$ H = \int dx \sum _{\eta= \pm 1 , \sigma =\uparrow,\downarrow } \psi^\dagger_{\eta, \sigma} (x) (-i v \eta \partial _x) \psi _{\eta,\sigma} (x). ...
3
votes
0answers
55 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?
3
votes
0answers
55 views
Two-fluid description of superfluidity
I'm trying to teach myself about superfluidity and I'm slightly confused on the ''two-fluid'' description. From what I understand, the superfluid is considered to be a mixture of two fluids, a ...
3
votes
0answers
295 views
Goldstone modes and Heisenberg model
The ideia is to show that, because of Goldstone modes, 2d systems are quite different from 3d ones. So, considering the Heisenberg model, I'll post here what I'm asked to and my current thoughts on ...
3
votes
0answers
83 views
Qualitative argument to determine energy of defects
In a book of "LES HOUCHES - Critical Phenomena, Random systems, Gauge theories" the author Frolich says that:
2D
In two dimensions, the mean energy of an isolated point defect in a square area of ...
3
votes
0answers
106 views
Nonlinear anomalous Hall effect
Has there been any research on anomalous Hall effect which would observe or predict a non-constant dependence of the AHE conductivity on the applied electric field?
3
votes
0answers
171 views
Descent equation and anomaly polynomial
I am just reading Ryu, Moore and Ludwig's paper on classifications of topological insulators and quantum anomaly(arXiv:1010.0936v1). They are trying to relate the quantum anomaly as a signal of the ...
2
votes
0answers
26 views
Is there a critical order of the Abelian gauge theory in (2+1)D
In (2+1)D spacetime, it is known that the $U(1)$ gauge theory is always confined (according to Polyakov), while the $\mathbb{Z}_2$ gauge theory can support a deconfined phase. Now consider a generic ...
2
votes
0answers
35 views
Is this 2D structure triclinic?
The only rotation axis obvious to me is rotation by 360 degrees, the identity. Vertical mirror planes I've been dicing and cutting it through several planes and I still see none. Yet, the structure ...
2
votes
0answers
59 views
A general wavefunction in a square lattice
Suppose we have a square lattice with periodic condition in both $x$ and $y$ direction with four atoms per unit cell, the configuration of the four atoms has $C_4$ symmetry. What will be a general ...
2
votes
0answers
49 views
Is it possible to have topological degeneracy in 1D ?
I mean to have q-fold degenerate ground states on a ring which could not be lifted by local perturbation.
If the answer is no, then what is the physical (or mathematical) reason against having such ...
2
votes
0answers
90 views
How to define the mirror symmetry operator for Kane-Mele model?
Let us take the famous Kane-Mele(KM) model(http://prl.aps.org/abstract/PRL/v95/i22/e226801 and http://prl.aps.org/abstract/PRL/v95/i14/e146802) as our starting point.
Due to the time-reversal(TR), ...
2
votes
0answers
57 views
Why do Fermi liquids have T^2 resistivity?
I have often read that metals that are Fermi liquids should have a resistivity that varies with temperature like $\rho(T) = \rho(0) + a T^2 $.
I guess the $T^2$ part is the resistance due to ...
2
votes
0answers
64 views
Electron Relaxation/Polarization for and n-type Semiconductor
Please help me understand the following (general) statement, referring to electrons in a full valence band of an n-type semiconductor:
"An electron filling up the last empty state in the valence band ...
2
votes
0answers
30 views
Why the peak of spectrum gets vague when the dimension is lower?
In a many-body system, we can know the spectrum function at a particular temperature from Green function. It means density of states. A peak of spectrum represents one mode. My question is that in the ...
2
votes
0answers
47 views
Will Anderson's Poor Man's Scaling loose its effect when band width is small?
The s-d interaction Hamiltonian is as fellows
$H_I=Js.S$, J is the coupling strength.
We focus on the antiferromagnetic case, where $J>0$.
According Anderson's poor man's scaling, the ...
2
votes
0answers
173 views
Simple model of edge states for a two-dimensional topological insulator
Quantum spin Hall states or, topological insulators are novel states of matter that have insulating bulk and gapless edge states. Are there any simple models that show these features?
See e.g. the ...
2
votes
0answers
69 views
Inelastic Scattering and coherent scatterng
Another Scattering Question
So I have this Bravais Lattice of sites R vibrating with some normal mode with a small displacement amplitude $u_o$, some wave vector k and some frequency $\omega$. We can ...
2
votes
0answers
105 views
Are the electrons in a quantum hall edge state entangled?
I am reading the paper on Quantum Energy Teleportation by Yusa, Izumida and Hotta(This article), and it seems that they are assuming that the quantum hall edge state is a quantum correlated state, ...
2
votes
0answers
246 views
Helicity and Pseudospin in Graphene
The Hamiltonian for graphene at $\vec{k}$ away from the $K$ point is proportional to
$$
\vec{\sigma} \cdot \vec{k} =\begin{pmatrix}
0 & k_x - i k_y \\
k_x + i k_y & 0 \\
\end{pmatrix}
=
k ...
2
votes
0answers
72 views
Factorization of fermionic scattering integral in 2d momentum rep
the scattering integrals for fermions involves both momentum ($k$) and energy ($k^2$) conservation and a nonlinear phase space factor of a distribution function $f(k)$.
$$\begin{multline}I(k) = ...
2
votes
0answers
308 views
A question about Dirac operator
The Dirac operator at 2 dimension can be written as
$$
D=\sum_{k=1,2}\sigma^{k}D_{k}=\left( \begin{array}{cc}
0 & \partial_{x}-i\partial_{y}-i(A_x-iA_y)\\
...
1
vote
0answers
44 views
Why do some things break when twisted?
Explain at the atomic level why twisting something, like a thin tree branch or arm, will break from twisting, but something else, such as a bowling ball or cinder block, will not break from twisting.
1
vote
0answers
64 views
Fermi level for the bulk of topological insulator
"Fermi level" is the term used to describe the top of the collection of electron energy levels at absolute zero temperature. Why does the Fermi level for the bulk of topological insulator fall within ...
1
vote
0answers
28 views
How to understand topological order at finite temperature?
I have heard that in 2+1D, there are no topological order in finite temperature. Topological entanglement entropy $\gamma$ is zero except in zero temperature. However, we still observe some features ...
1
vote
0answers
25 views
Wavefunction in first Brillouin zone
We know that with symmetry, Brillouin zone is nothing but copies of its irreducible zone, so can we conclude that we can find all possible wavefunctions in its irreducible zone? What about ...
1
vote
0answers
29 views
Neutron scattering for a critical magnetic-ordering system : what about critical opalescence?
Liquid-gas transition critical point is believed to share the same universality class as the 3D Ising model.
We know that the liquid-gas transition is characterized by a phenomenon called critical ...
1
vote
0answers
90 views
In what direction does a frustrated magnetic moment get aligned?
Consider 3 layers of Ferromagnetic materials stacked on top of each other with appropriate spacer layers in between. Let the top and bottom layers be pinned to layers of Anti Ferromagnets adjacent to ...
1
vote
0answers
81 views
guage invariance in Laughlin's argument
In Laughlin's gedanken experiment which aims to explain quantization of Hall conductance, one takes the adiabatic derivative of the Hamiltonian with respect to vector potential. Now it seems that it ...
1
vote
0answers
70 views
Asking for references on the variational treatment of spin wave
My idea is the following:
We have a system with Hamiltonian $H$, and we know that there is spin wave in this system by some symmetry-breaking arguments. Now we start from the ground state ...
1
vote
0answers
65 views
How to derive the divergence leading to Kohn anomalies?
I'm trying to understand the mathematical derivation given in the book "A Quantum Approach to Condensed Matter Physics" on page 215 (see 1), for explaining how the phonon-energy perturbed by ...
1
vote
0answers
38 views
Why the dangling bonds at the edge terminated by hydrogen atoms give no contribution to the electronic states near the Fermi level
How about changing H atom to other kinds of atoms?
1
vote
0answers
39 views
Understanding Resonance States in Condensed Matter
What exactly is a resonance state?
My understanding so far is that a resonant state appears as a large spike in the DOS of a material due to an adsorbed impurity or vacancy in the lattice and that ...
1
vote
0answers
34 views
In heterojunction problem, how to align the energy band in presence of bias voltage
For example, SiO$_2$ barrier embeded between Fe magnet and 2-dimensional-electron-gas such as Si.
How to align the energy bands of the three materials when an electric field is perpendicular to the ...
1
vote
0answers
211 views
Calculating conductivity from Green's functions
I am trying to calculate the conductivity in the linear response regime of a disordered electron gas. (or eventually of a mean field Heavy fermion system with known one particle green's functions).
I ...
