The study of physical properties condensed phases of matter, including solids and liquids.
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2answers
84 views
Are electronic wavefunctions in band gap insulators localized? is a single-particle picture sufficient in this case?
I am having trouble understanding the physics of band gap insulators.
Usually in undergrad solid state physics one looks at non-interacting electrons in a periodic potential, with no disorder.
Then, ...
1
vote
1answer
111 views
Does anyone know the difference and relation between $k\cdot p$ method and tight binding (TB) method?
Among the methods of calculating energy bands for crystals, first-principles method is the most accurate. Besides first principles, two commonly used modeling methods are the $k\cdot p$ method and ...
3
votes
1answer
35 views
Imposing anti-commutation relations on fermionic quasi-particles
In many theories of CMT, we assume the nature of quasi-particles (without giving proper justifications). For example, we assume nature of quasi-particles to be fermionic in case of a interacting ...
3
votes
1answer
117 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), ...
1
vote
1answer
29 views
The relation between spectral function and band structure
I am confused by the wavevector in spectral function A(k,w). How to understand this k for a periodic structure? And how is it related to the k (in first Brillouin Zone) we use in the band structure? ...
4
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0answers
46 views
The critical point of Bose-Hubbard model
The Hamiltonian of Bose-Hubbard model reads as
$$H=-t\sum\limits_{<i,j>}b_i^{\dagger}b_j+h.c.+\frac{U}{2}\sum\limits_{i}n_i(n_i-1)-\mu\sum\limits_in_i$$.
In the limit $t\ll U$, the ground ...
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0answers
51 views
Toward the establishment of non-equilibrium (quasi-equilibrium) magnon BEC theory
In 2006, Demokritov et al have reported that they have achieved the observation of quasi-equilibrium magnon Bose-Einstein condensation (BEC) in YIG at finite (room) temperature by using the method ...
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0answers
17 views
penetration of a solid body in a liquid
A solid (for example a steel ball) is moving with a certain constant velocity U toward a liquid in a container; I can write the equations of motion of the solid when it has a little part of it in the ...
2
votes
1answer
303 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 ...
3
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0answers
46 views
Renormalization group equation of 1D charge susceptibility
I am readng the famous book Quantum Physics in One Dimension by Thierry Giamarchi ,where I have a subtle question about the Renormalization group equation of 1D charge susceptibility at the end of ...
4
votes
2answers
156 views
How to cut a stone on on a White Dwarf
I've heard that white dwarfs are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?
3
votes
1answer
98 views
How does phonon cause two electrons to attract each other?
We know that like charges repel each other. But my professor claimed that two electrons can attract each other as well. What he said was that due to screening an electron traveling at some speed wont ...
3
votes
1answer
40 views
Differences between spin waves and spin density waves
Roughly speaking, in condensed matter systems, spin waves and spin density waves are both low-energy states with spin that varies spatially. What precisely are their differences?
11
votes
2answers
285 views
Is there a way to directly observe the spin texture of the surface states of topological insulators?
Is there a way to directly, here I means in real space, observe the interaction of the surface states of 3D topological insulators with defects (dopings and adatoms)? How to observe the spin texture ...
1
vote
2answers
42 views
How would a diffraction pattern change if the atoms were triangular instead of spheres?
On a related note, what's a good book/source that would answer questions that go very in depth with these kinds of "what if" questions because I am also asked the same if the atoms were long cylinders ...
3
votes
2answers
225 views
Why does a superconductor obey particle-hole symmetry?
We normally solve the Bogoliubov-de Gennes (BdG) equations in order to compute the energy spectrum of a superconductor. The Nambu spinor is a common object that is used in formulating these equations. ...
5
votes
1answer
358 views
How can one localize the massless fermions in Dirac materials?
I noticed that finite electric potential cannot localize the low energy excitations in a graphene sheet. Is it possible to localize the massless fermions in the surface band of topological insulators ...
6
votes
1answer
176 views
Chiral coupling in string-nets
In Xiao-Gang Wen's review of topological order http://arxiv.org/abs/1210.1281 , he states in footnote 52 that string-nets are so far unable to produce the chiral coupling between the SU(2) gauge boson ...
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0answers
146 views
Are there any good reading materials for variational approach in many-body theory? [closed]
I need something like a summary of existing results, including the treatment of BCS Hamiltonian and Hubbard model. Auerbach's book is a good one but I still hope to get more comprehensive review. My ...
6
votes
1answer
322 views
Realization of Witten-type topological quantum field theory in condensed matter physics
It is well-known that some exotic phases in condensed matter physics are described by Schwarz-type TQFTs, such as Chern-Simons theory of quantum Hall states. My question is whether there are condensed ...
2
votes
1answer
78 views
Self-consistent field approximation and uniform field approximation?
Can anyone give me explanation of self-consistent field approximation and uniform field approximation? I know self-consistent as when we write the Schrödinger equation as
$$[ -\frac{\hbar^2}{2m} ...
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vote
0answers
53 views
How to solve Boltzmann equation using monte carlo methods? [closed]
I'm trying to solve for electron and hole distribution function using Boltzmann equation with various scattering mechanisms. Since I land up with an integro-differential equation, analytical soln. is ...
1
vote
1answer
91 views
Schrödinger equation for many body systems
$$H_{tot}=\sum \dfrac{p_i^2}{2m}+\sum\dfrac{p_I^2}{2M_I}+\sum V_{nucl}(r_i)+\dfrac{1}{2}\sum_{i\ne j} \dfrac{e^2}{|r_i-r_j|}+\dfrac{1}{2}\sum_{I\ne J}\dfrac{z_Iz_Je^2}{|R_I-R_J|} $$
with:
...
0
votes
1answer
74 views
Momentum change in colisions (Drude Model)
A particle suffers elastic colisions with scattering centers with a probability of colision per unit time $\lambda$. After a colision the particle is in a direction caracterized by a solid angle ...
1
vote
1answer
43 views
Origin of Charge Neutrality
What is the origin of the "charge neutrality" requirement in solids? Why do we require the bulk to be charge neutral, yet the surface can have a net charge?
5
votes
2answers
110 views
Toric Code and Random Bond Ising Model
It was established by Dennis, Kitaev et al. that the 2D Toric Code
can be mapped to a 2D Random Bond Ising Model. The original derivation
was given in the paper "Topological quantum memory" which ...
4
votes
1answer
84 views
Simple uncertaintly calculation of the center coordinates of a Landau Level
I am reading the following review paper on the Quantum Hall Effect. I am sorry for the extremely stupid question, but I have been stuck on this very easy equation for long.
In equation 2.39, the ...
4
votes
1answer
144 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 ...
2
votes
1answer
47 views
Difference between Wigner crystal state and fractional quantum Hall (FQH) state
Wigner crystal and FQH effect are both due to strong electron-electron interaction under magnetic field. As we know, Landau's symmetry-breaking cannot be used to describe FQH state. But can it be used ...
9
votes
1answer
439 views
Is ultradense deuterium real?
I've found several articles discussing experimental evidence of a deuterium state of densities over $140 \textrm{ kg}/\textrm{cm}^3$:
F. Winterberg. Ultradense Deuterium. arXiv.
Shahriar Badiei, ...
2
votes
2answers
357 views
Exact diagonalization of graphene's tight binding Hamiltonian
While directly diagonalize graphene's tight binding Hamiltonian, which is numerical. We have to use a finite-sized graphene.
So how to deal with boundary conditions? The usual solutions are zigzag or ...
4
votes
1answer
93 views
Clarification of Landauer approach
I am trying to understand the Landauer approach. Consider the setup: (left contact)-(conductor)-(right contact). For simplicity, the conductor is a 1d wire (the transverse part is not relevant for ...
3
votes
1answer
98 views
Flow of supercurrent in a superconductor
I have two questions one practical and one theoretical. Even though I have a decent understanding of superconductivity both phenomenological as well as theoretical (i.e. BCS), some things just slipped ...
2
votes
1answer
159 views
Why we call the ground state of Kitaev model a Spin Liquid?
Now we always talk about the so-called Kitaev spin liquid. One important property of spin liquid is global spin rotation symmetry. Let $\Psi$ represents a spin ground state, if $\Psi$ has global spin ...
9
votes
1answer
212 views
What is the “BCS Cooper pair condensation” as a physical phenomenon in terms of experiments?
"Thought" experiments and "numerical" experiments are allowed.
This question is motivated by the question Has BCS Cooper pair condensate been observed in experiment? ,
and by our recent research on ...
1
vote
1answer
61 views
What does the wavevector $\textbf{k}$ mean?
In Ashcroft, Mermin Solid State Physics, Eq. 17.43 is
$$
\epsilon(\textbf{k}) = \frac{\hbar^2 k^2}{2m} - e\phi(\textbf{r})
$$
where $\textbf{k}$ is the wavevector and all other symbols have their ...
2
votes
1answer
181 views
$J_1$-$J_2$ Heisenberg antiferromagnet
In this paper, the authors solve for the excitation spectrum in a $J_1$-$J_2$ Heisenberg antiferromagnet using the modified spin-wave theory in the Dyson-Maleev representation. As an intermediate ...
6
votes
1answer
115 views
Precise statement of Mermin–Wagner theorem
Roughly speaking, Mermin-Wagner theorem states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions ...
2
votes
1answer
42 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 ...
9
votes
1answer
179 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 ...
3
votes
1answer
80 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 ...
4
votes
2answers
68 views
How are X-rays focused? Specifically in XRD. Well do they even focus X-rays in XRD?
I read in a government website that reflecting an x-ray from a parabolic mirror followed by a reflection from a hyperbolic mirror results in focusing the x-ray, but this was for astronomical purposes. ...
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votes
0answers
30 views
Why is planar geometry preferred to observe ordinary Hall effect?
In the Physics Today article by Avron et.al. "A Topological Look at the Quantum Hall Effect" Physics Today (2003) it is suggested that to observe ordinary Hall effect, planar geometry is preferred to ...
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votes
0answers
55 views
Some questions about the edge states for time-reversal invariant topological superconductors?
Stimulated by my some recent calculations on edge states(ES) for time-reversal invariant(TRI) topological superconductors(TS) as well as many questions concerning the "edge states" in Physics ...
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0answers
52 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.
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votes
0answers
23 views
Kinetic and Thermodynamic Dopant Solubility
I've read that both the "kinetic" and "thermodynamic" solubility of impurities limit substitutional dopant concentrations. Unfortunately, I haven't found a clear explanation of the two types and the ...
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vote
2answers
45 views
Free spin (Curie) Paramagnetism
I'm working through a derivation for Curie paramagnetism and hope someone could help clarify a couple of steps. The way that makes sense to me (although now I have seen the wikipedia derivation below ...
2
votes
1answer
77 views
NP-completeness of non-planar Ising model versus polynomial time eigenvalue algorithms
From the papers by Barahona and Istrail I understand that a combinatorial approach is followed to prove the NP-completeness of non-planar Ising models. Basic idea is non-planarity here. On the other ...
8
votes
2answers
186 views
Ferromagnetism with mobile spins
How can electron spins in Iron at room temperature have ferromagnetic order even though they are travelling at very high speeds?
One could argue that spin and motion are completely uncorrelated and ...
2
votes
1answer
29 views
Origin of interaction in inelastic neutron scatting
In solid state physics, inelastic neutron scattering is a commonly-used experimental technique for probing the energy spectrum of phonon and magnon excitations. This technique relies on the ...
