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5

Conclusion: The particles are, in-fact, magnetic This is doubtful. There are two possibilities here: If the objects used to grind (let's call them grinders) the dust grains were made of a ferromagnetic material like iron/steel and/or nickel, then it is possible that the grinders deposited some material onto the dust. There is no reason to think that ...


0

No way, amount of dark matter is estimated to be 4 times the amount of normal matter. Even if we ignore all other arguments, it still does not restore the symmetry. Dark matter (if there is such a thing), is actually transparent matter (we can not see it) and cold matter (it does not absorb/emit any heat/radiation). That also means that you can not measure ...


4

No, we know enough of the "bulk properties" of antimatter to rule this out. Antimatter interacts with the electromagnetic field in exactly the same way as regular matter, just with the opposite charge. Therefore, antimatter should be detectable using most of the techniques we use to detect regular matter in astronomy. This works even if the antimatter is a ...


2

I think we can pretty safely say this is not the case. The main reason is that we have a pretty good idea of where dark matter is--to some degree, it can be reconstructed from the gravitational influence it has on surrounding matter. The dark matter appears to be distributed evenly throughout the galaxy. Thing is, a galaxy is pretty "dirty," as far as space ...


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One reason is that the volume of your third BZ is twice the volume of your first BZ. To see it another way, notice that the black dot on the far right (the middle of the three vertical dots) is a BZ center, a $\Gamma$ point. The black dot directly above that one (far upper right corner) is also a $\Gamma$ point, but it must be in the next BZ. Half-way ...


0

You're right, the usual language of band theory doesn't apply in the out-of-plane direction. The system really becomes a quantum well in that direction, so you will have a discrete spectrum of energy levels and there won't be any dispersion with $k_z$ ($dE/dk_z = 0$) if $z$ is out of the plane. The relevant tunneling processes in that paper are basically ...


2

For wave mechanics there is the phase velocity and group velocity. For the energy $E~=~\hbar\omega$ the phase velocity is $$ v_p~=~\frac{\omega}{k}~=~\frac{\hbar}{2m}(k~+~ck^3). $$ This is the velocity of a wave front, or where the phase of the wave is constant. There is also the group velocity that is $$ v_g~=~\frac{\partial\omega}{\partial k}~=~\frac{\hbar}...


1

Your question is really broad. As correctly pointed out by @John Rennie there can be so many signals that can pass from the solids. It must be noted that even if the signal can pass through solid it will experience certain losses. Mechanical waves such as sound took advantage of elasticity of the material. The sound oscillations are transferred through ...


1

Remember that $\eta^{q}$ are Fermionic operators, therefore $\eta^{2}_{q}=0=\eta^{\dagger 2}_{q}$.


-2

Most objects are porous and allow the elector-magnetic signal through. Little electrons can pass through what appears to be solid material like photons through glass. Some are still trapped in the atoms. Denser metals like lead do not have enough space between the atoms to allow the electromagnetic waves through. Certain wavelengths can pass through certain ...


1

One way to do this is to start by solving for the allowed $\mathbf{k}$ values for an $L \ \times \ L \ \times L$ crystal using the usual procedure found in any book on solid state physics (if you're unfamiliar, see A & M pg. 430-432). The allowed $| \mathbf{k} |$ values are integer multiples of $\frac{2 \pi}{L}$. The corresponding density of k-states is ...


0

There is one relevant gap in semiconductor physics: the gap between the highest fully occupied energy band (valence band) and the lowest unoccupied band (conduction band). But there are also gaps between other energy bands. The thing is just that they are not very relevant for the semiconducting effect. Between full bands they have no effect because there is ...


2

The fractional quantum Hall effect (FQHE) is a physical phenomenon in which the Hall conductance of 2D electrons shows precisely quantised plateaus at fractional values of e^2/h . It is a property of a collective state in which electrons bind magnetic flux lines to make new quasiparticles, and excitations have a fractional elementary charge and possibly ...


1

In Solar Cell Device Physics, the author Stephen Fonash makes a distinction between "electrostatic (electric) fields" and "effective fields", and you have stumbled upon an example that needs the distinction. Electrostatic fields arise from a real electric charge density, which would be caused,for example, by uncompensated donor atoms. In your schematic as ...


0

The dielectric constant, $\epsilon$, is also called the relative permittivity of a material. If we take the word literally, it can be seen as how much the material "permits" an electric field to come in. This basically translates to how much a material will allow itself to be polarized. Consequently, a perfect electrical conductor (PEC) would have $ \epsilon ...


0

The three-dimensional nature of a crystalline solid leads to a directional electron population. If a valence band maximum and conduction band minimum do not occur in the same electron-momentum direction, light absorption that would otherwise occur at the bandgap energy will be very unlikely. This is because the electron that hops up in energy (taking up ...


2

Ordinary silica glass really is amorphous. You can study the short range order of a material by measuring its radial distribution function. That is, take any atom and plot the density as a function of distance from that atom. This is easily measured using X-ray or neutron scattering. In a crystal the RDF is just a function of the crystal structure and is ...


0

Assuming that you are working in Bragg geometry you will see one peak corresponding to one angle, from which you can get the spacing between crystal planes from Bragg reflection condition. $$2d\sin\theta=n\lambda$$ and $$\lambda=\frac{h}{\sqrt{2mE}}$$ where $E$ is the energy of the electron. Now you should gather the information about different peaks ...


1

This depends upon how you want light to solid. If you want light to be solid in the way the "Star Wars" movies have light sabers, I would say no. There are however materials that trap photons so they have zero velocity. Photons are in a sense trapped, and these are sometimes called artificial black holes. The energy of the photons then contribute a tiny ...


6

No because solid is a state of matter. Light cannot be considered matter since it is made up of particles which have no mass and I'm pretty sure occupy no space (i.e. photons have no volume). Edit: Since photons are at the quantum level, we can't actually fathom what it would mean for them to occupy space. But on this thread someone pointed out that there ...


0

I have never heard that the non intrinsic greek-written points (mainly $\Gamma$, $\Delta$, $\Lambda$ and $\Sigma$) has been written or spoken as the corresponding greek letters. Might this be a sub-community thing?


1

In general, or as far as I'm aware, the band diagrams and Density of States shown in your question are electronic band structures. You can also see this from the graph's legend which shows that you're dealing with d and p orbitals belonging to W and S. However, looking at the numbers in your question, I can see where the confusion comes from. The direct ...


5

In general the wavenumber is a vector. That is, $e^{i(\vec{k}\cdot\vec{x}-\omega t)}$ is a solution to the wave equation in 3 (or any number) dimensions. We say this solution is a plane wave propagating in the $\hat{k}$ direction with wavenumber $|\vec{k}|$ or wavelength $\lambda = 2\pi/|\vec{k}|$. So properly the de Broglie relation is $\vec{p} = \hbar \...


2

Mostly kinetic energy. The kinetic energy of a free particle is not quantized. It becomes so when the particle is closed in a box. But even in this case the energy levels are often so closely spaced that the spectrum is almost continuous. In fact, if you solve the Schroedinger equation for a particle in a 1D infinite square well you will find the following ...


4

The result $\omega^2=\frac{c_1+c_2}{M} \pm \frac{1}{M}\sqrt{c_1^2+c_2^2+2c_1c_2 \cos ka}$ leads to two real solutions for $\omega^2$, since $ -1 \lt \cos ka \lt 1$ and the square root lies between $|c_1 - c_2|$ (for $\cos ka = -1$) and $c_1 + c_2$ (for $\cos ka = +1$), so that $\omega^2$ is always positive. The frequency $\omega$ is taken as a positive ...


2

This is a general property of square potential wells. De broglie wavelength of the ground state is approximatly twice the well width. For this reason wider wells have smaller wave-numbers ($k=\frac{2 \pi}{\lambda}$) of the groundstate. Hence the lower energy of the ground state (and others) (since $E=\frac{\hbar^2 k^2}{2 m}$).


0

There is a lot of experimental evidence showing that only a tiny fraction of the electrons close to the Fermi surface participate in the physical properties of a metal. One of them is the specific heat due to electronic degrees of freedom : at a certain temperature $T$, only electrons within a typical energy of $k T$ around the Fermi level can be excited by ...


0

The main confusion was coming from the $x$ and $y$ axes of the phonon dispersion curves diagram having the same units (cm$^{-1}$), because of the choice of the natural unit system. However, two axes obviously have different meanings. The $x$ axis in the phonon dispersion diagram represents the momenta of phonons, while the $y$ axis represents the energy of ...


1

The fluctuation-dissipation theorem is a relation between the symmetrized and retarded correlation functions $$ G_s(\omega,k)=\coth\left(\frac{\omega}{2T}\right) \,{\rm Im}\, G_R(\omega,k). $$ I would not say that it is due to the "$i\epsilon$" terms. The $i\epsilon$ simply reflects the different analyticity properties of $G_{R,A}$ etc. Physically, the ...


1

Luttinger liquids are a case of bosonization. Two fermions $\psi$ and $\psi'$ are written according to a boson field $\phi$ $$ \psi^\dagger\psi' = exp(i\phi), \psi'^\dagger\psi = exp(-i\phi^\dagger), $$ where the "field" $\phi$ serves as a phase and is real valued. For the fermion operator $c_j$ the number operator $n_j = c_j^\dagger c_j$ permits us to ...



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