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9

Every Element/atom has a different electron configuration. This gives the valence electrons unique energy levels and arrangements. When electrons absorb energy they are excited to certain and again unique energy levels. When The energy is released it gives a photon a certain frequency which we perceive as a certain color.


5

A lot of things can affect the color of an object. As you've mentioned, absorption plays an important role in determining what part of the visible spectrum gets subtracted from the color your eyes perceive. Optical bandgap arising from the microstructure of materials determines what portion of the spectrum is absorbed. It is closely related to the electronic ...


3

In the thermodynamic limit (linear size of the system $L$ to infinity), boundary conditions don't really matter, and most physical observables will be the same for all boundary conditions. The use of periodic boundary conditions is mostly for practical reasons, in particular, translation symmetry is conserved, which really helps. One could in principle do ...


3

Well, $1/2\otimes1/2=0\oplus1$, so a system with two fermions has integer spin. But it is still a two fermion system, and therefore its wavefunction must be antisymmetric, as usual. This is not specific to Cooper pairs, but is basic Quantum Mechanics... [what is specific to Cooper pairs is that their size is $\gg a_0$, which means they are highly ...


2

When we say that a lattice has a particular symmetry we mean that the lattice is mapped onto itself by the symmetry. So if I have a (2d) material which has inversion symmetry in the bulk and which has an atom at a point $(x,y)$ then inversion symmetry tells me that there is another, identical atom at $(-x, -y)$. At the surface, however, this is no longer ...


2

The spin orbit coupling can be derived from the nonrelativistic limit of the dirac equation and is given by $$ H_{\text{s-p}} = \frac{\varepsilon_0}{2m_e^2c^2}\mathbf{\hat{s}}\cdot\left(\mathbf{E}\times\mathbf{\hat{p}} \right) $$ $\mathbf{E}$ is the total electric field acting on an electron, which consist of a microscopic electric field ...


2

I have taught myself and several other people how to understand band diagrams properly and I find that universally (myself included) there is a certain need to "unlearn" things that you may have been mistaught in classes or misunderstood. Major problems occur if one has taken a solid-state physics course which only studied band structure in infinite ...


2

The answer to nearly everything is: yes :) your intuition about it is quite right, and your picture is good, too. You have two different kinds of points, and any pair with one point from each kind would be a suitable basis. You will of course take adjacent ones in practice. You could also take more than two points as primitive cell, but it will not be a good ...


2

Exact mechanism varies with material, simple materials (non-organic) are easier to analyze. Simplest answer is if you bring them together they will join, provided size is small. For example in Cold Welding less than 10 nm wire is rejoined just by contact. The exact mechanics depends on what kind of Intermolecular force is in play. According to Grove Karl ...


1

There's not enough information to say. It looks like your model has spring-like (harmonic) potentials between neighboring atoms, but phonon scattering requires anharmonic potentials. Harmonic potentials mean that the superposition principle still holds, so the phonons just pass right through each other without scattering. Since you have harmonic ...


1

If the pressure is uniform, there is no problem, because you just multiply the pressure by the total surface area of interest. However, if the pressure is varying on the surface, pressure should be regarded as a point function of location, and the contribution to the total force on the surface at a differential element of area on the surface dA is equal to ...


1

This is my favorite graphene reference. It's more concerned with the high magnetic field behavior of graphene (quantum Hall regime), but it's introduction is still very well done. A few points: -The wavefunction is the sum of two Bloch functions (one for each sublattice of graphene). The tight binding approximation assumes that the electronic wavefunction ...


1

Things don't really have "colour". Colour is a perception that we have of light entering our eyes. We use our eyes to perceive the world, and in our eyes are a series of receptors (photoreceptors). These are the rod, and cone-shaped cells which exist in your retina. These cells send electrical signals to our brain, via the optic nerve, and it is a ...



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