The study of physical properties condensed phases of matter, including solids and liquids.
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26 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 ...
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1answer
69 views
What is the importance of the Fermi energy $E_F$ or the chem. potential $\mu$ for topological superconductors
A lot of effort is put into shifting the Fermi energy of a topological insulator to exactly zero which then provides some advantages when this TI is coupled with a superconductor.
I don't understand ...
8
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1answer
118 views
What're the relations and differences between slave-fermion and slave-boson formalism?
As we know, in condensed matter theory, especially in dealing with strongly correlated systems, physicists have constructed various "peculiar" slave-fermion and slave-boson theories. For example,
For ...
8
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2answers
395 views
What is the mathematical reason for topological edge states?
There are many free fermion systems that possess topological edge/boundary states. Examples include quantum Hall insulators and topological insulators. No matter chiral or non-chiral, 2D or 3D, ...
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1answer
71 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 ...
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2answers
99 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
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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 ...
5
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0answers
255 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), ...
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42 views
Lambda transition data points of $\require{mhchem}\ce{^4He}$
I'm looking to get some data on the lambda transition of $\require{mhchem}\ce{^4He}$. I need the data points of the specific heat vs. temperature graph, if that makes sense.
4
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1answer
74 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 ...
2
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0answers
52 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 ...
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1answer
42 views
If a balloon is continuously filled with air and stays at a constant shape and size will there be any empty space in the balloon?
If a container like a balloon but with constant volume is filled, is it possible to pack air molecules so closely together that they don't have any empty space between them? If so, what would this ...
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0answers
97 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), ...
11
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1answer
433 views
Emergent symmetries
As we know, spontaneous symmetry breaking(SSB) is a very important concept in physics. Loosely speaking, zero temprature SSB says that the Hamiltonian of a quantum system has some symmetry, but the ...
8
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1answer
116 views
What is Anderson localization? Could someone give an example worked out in detail?
What is Anderson localization, for someone with no previous knowledge on the subject?
I tried to read Anderson's original paper, but it was too terse for me. I have seen a couple of intuitive ...
2
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1answer
29 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 ...
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4answers
5k views
Practical applications for a Bose-Einstein condensate
What are the main practical applications that a Bose-Einstein condensate can have?
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2answers
136 views
Would HgTe be a topological insulator?
In "Quantum Spin Hall Insulator State in HgTe Quantum Wells", researchers observed a 2D topological insulator by sandwiching HgTe between CdTe. Is the CdTe really necessary? Would Vacuum/HgTe/Vacuum ...
2
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2answers
329 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 ...
12
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3answers
562 views
Shine a light into a superconductor
A type-I superconductor can expel almost all magnetic flux (below some critical value $H_c$) from its interior when superconducting. Light as we know is an electromagnetic wave. So what would happen ...
6
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0answers
118 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" ...
1
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1answer
88 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 we theoretical (i.e. BCS) some things just slipped ...
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0answers
23 views
What are some applications of crystal fabrication? [closed]
I have heard of some applications here or there in certain papers, but I am looking for a broader scope of examples.
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1answer
105 views
Why are topological solitons present in some phases for lattice models?
Over a spatial continuum, it is easy to see why some topological solitons like vortices and monopoles have to be stable. For similar reasons, Skyrmions also have to be stable, with a conserved ...
5
votes
2answers
158 views
A question on the existence of Dirac points in graphene?
As we know, there are two distinct Dirac points for the free electrons in graphene. Which means that the energy spectrum of the 2$\times$2 Hermitian matrix $H(k_x,k_y)$ has two degenerate points $K$ ...
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3answers
143 views
What is the mathematical justification for the quadratic approximation to the energy of a spring in a one-dimensional lattice?
It follows easily from this draw, the length $l$ of this spring as a function of the vertical distance $x$, as $l(x)=\sqrt{1+x^{2}}$
Now, $l$ can be expressed as a MacLaurin expansion:
$$l(x) = ...
1
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1answer
60 views
Calculation of the quantized Hall coefficient in the Integral Quantum Hall Effect
I have been reading about the QHE over the past couple of days. I am facing difficulty understanding a calculation in this review.
www.nimt.or.th/nimt/upload/linkfile/sys-metrology-248-434.pdf
In ...
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0answers
30 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 ...
3
votes
2answers
186 views
What limits the maximum attainable Fermi Energy for a material experimentally?
Either through doping or gating. What are some good terms to search for if I'm looking for some experimentally obtained values for particular materials? I'm particularly interested in what the limit ...
1
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1answer
133 views
Calculation of number density from material density
Material density is given by $ \rho =m/V$, where $m$ is mass and $V$ is volume.
Again number density given by $n=N/V$, where $N$ is the total number of particle. How can I calculate number density $n$ ...
0
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1answer
42 views
Influence of the temperature on the ionization energies for impurities in silicon
Is there any dependence of the impurities ionization energy on temperature in silicon? I mean if there are any interactions between localized electron and phonons which leads to renormalization of ...
0
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1answer
150 views
Photon Absorption and Emission: Conductors v. Semiconductors
I'm having a hard time understanding how photon absorption and emission in metals (conductors) compares to semiconductors. Obviously, in SCs, absorbed photons lead to electron-hole pairs and emitted ...
2
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2answers
129 views
What's the differences among the concepts: binding energy, cohesive energy and formation energy?
In the papers about first principles (or ab initio) calculations, there are three energies which are often calculated: "binding energy", "cohesive energy" and "formation energy". Their meanings are ...
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3answers
330 views
Introduction to Anderson localization [closed]
I find Anderson's original paper too terse. I am looking for something that introduces me gently to the subject so that I can understand Anderson's paper and other literature. What references are out ...
7
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1answer
91 views
Phase transition water
The water-gas phase transition is said to be similar to the ferromagnetic-paramagnetic phase transition (same set of critical exponents = same universality class). In the former case the order ...
3
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1answer
76 views
Electrical energy storage in superconductors
I am a first year A-level student and I am doing a project about the possibility of storing electrical energy in a superconductor. I have researched and I am aware of the critical current density and ...
5
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0answers
234 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 ...
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4answers
724 views
Bose-Einstein condensate in 1D
I've read that for a Bose-Einstein gas in 1D there's no condensation. Why this happenes? How can I prove that?
5
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1answer
153 views
A question on the doped Kitaev-Heisenberg model?
Recently, some groups have studied the effects of doping the Kitaev model on honeycomb lattice(e.g.,http://arxiv.org/abs/1109.6681 and http://arxiv.org/abs/1109.4155) and their calculations show the ...
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2answers
138 views
Graphene +1 extra carbon bond
I'm not a physicist just a curious mind, so please go easy!
I was just watching a BBC Horizon Documentary that featured a piece on the recently discovered material Graphene. One of the facts ...
7
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1answer
3k views
Kubo Formula for Quantum Hall Effect
I'm trying to understand the Kubo Formula for the electrical conductivity in the context of the Quantum Hall Effect.
My problem is that several papers, for instance the famous TKNN (1982) paper, or ...
6
votes
2answers
413 views
The difference between the Wannier function and atomic orbit in a tight binding model
In a tight binding model, we usually start from the atomic orbits and linearly combine them to get the wave function of the crystal energy band.
My questions are:
Since this kind of tight binding ...
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1answer
52 views
Conceptual questions about Fermi surface
So I am wondering what kind of two dimensional Fermi surface is called quasi one dimensional, what is its character? Also, when there are orbital hybridization taking place in lattice site, what are ...
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0answers
91 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 ...
2
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1answer
155 views
Specific heat capacity of a 2D free electron gas
I have got so far the 2D density of states as $g(\epsilon)=\frac{Am}{\pi\hbar^2}$ where $A$ is the area of the "square" and $m$ is the the electron mass. Then I have found an expression for the the ...
1
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2answers
99 views
Eigenfunctions in periodic potential
For Hamiltonian $\operatorname H$ and lattice translation operator $\operatorname T$, if
$$\operatorname H\psi=E\psi, \qquad \operatorname T\psi=e^{ik\cdot R}\psi,$$
and
$$\operatorname ...
5
votes
0answers
120 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
...
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1answer
78 views
What states are satisfying an entropic area law and why do they satisfy it? More specificly why do matrix product states satisfy it?
I am currently reading some papers concerning the question why the density matrix renormalization group (DMRG) method is working well for simulating one dimensional systems and bad for higher ...
3
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1answer
97 views
Fermi level with Landau levels
So my question is regarding where the Fermi energy is when you have 2D electron gas in an applied magnetic field. My book explains that, using the Landau gauge, you find that the 2D density of states ...
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1answer
103 views
Calculation of Number Density
Number density equation is given by
$ n= \dfrac{(N_A)\rho}{M} $
where
$ N_A =6.023\times10^{23} mol^{-1} $
$ \rho=8.02\ g/cm^3 $(at 1500 degree celsius.)
$M=63.546*1.6605\times10^{-24} g$
Whats ...
