6 votes
Accepted

How do liquid crystals rotate the plane of polarized light (electric field of light) which is used in LCD displays?

The liquid crystal “state” can be thought of as being between the solid (molecules fixed in both position and orientation) and liquid (molecules with both random position and orientation) state. In ...
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6 votes

How do liquid crystals rotate the plane of polarized light (electric field of light) which is used in LCD displays?

The key physics is that liquid crystals shown in your diagram are birefringent material. This means that the polarization (orientation) of the light changes the effective index it sees. In the case ...
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3 votes
Accepted

Why is electronic specific heat divided by $V$ rather than $M$?

Start with the definition of (extensive) specific heat: $$C_v=\frac{dE}{dT}$$ from there, you can define three different intenstive quantities: massic : $\displaystyle c_v=\frac{C_v}{m}$ in J/K/kg ...
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  • 2,256
2 votes
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How can NO charge carriers exist in the depletion region?

Never take a physical model to represent perfection. We speak of insulators and conductors, but insulators conduct (small) currents, and conductors present (small) resistance to current. For most ...
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  • 4,123
2 votes

Which electron shells make up the electron gas?

The abstract idea of a Fermi gas is simply that of a bunch of fermions that are free to move in space. In this abstract framework, fermions (electrons) are not bound to an atom, and hence the usual ...
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  • 1,606
2 votes

Intrinsic carrier concentration in doped semiconductors

In heavily-doped semiconductors, acceptor and donor energy levels (which are close to the valence and conduction band edges, respectively) form energy bands, effectively moving the valence and ...
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  • 7,634
2 votes
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Why do not all the semimetals turn into the excitonic insulators?

When the binding energy of the exciton, Eb, overcomes the band gap, the system becomes the excitonic insulator. What is meant here is the direct gap, i.e., the gap between the conduction and valence ...
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2 votes

Reading a graph for dispersion relation of normal modes in 3D lattice

Take a look at a Brillouin zone for zinc blende crystals. You’ll see that it’s a polyhedron. The “high-symmetry” points are just points such as the center of the polyhedron ($\Gamma$) or corners or ...
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1 vote

Partition function for $H=-\vec \mu \cdot \vec B$

The calculation of the microcanonical ensemble involves integrating over all possible energetic microstates, which in this case translate to all possible spin (or magnetic dipole) orientations. You ...
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  • 165
1 vote

Is charge carrier density an intrinsic property of a material and is thus constant?

No, the carrier density will depend on the material, and for metals you might argue that it is a property of the material, but it will still depend on the details. If you look at it from a condensed ...
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  • 619
1 vote

On reciprocal lattice properties

You can define a “maximal” family of regularly spaced family of parallel lattice planes by the equation: $$ R_n\cdot G_m \in 2\pi\mathbb Z $$ for a certain $G_m$ in the dual lattice. The problem with ...
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  • 1,657
1 vote
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On reciprocal lattice properties

Each reciprocal lattice vector $\mathbf{G}$ defines a set of equally-spaced, parallel planes via $$ \mathbf{G}\cdot\mathbf{R}=2\pi m\,, $$ one for every integer $m$. Nearest-neighbor planes have $|\...
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  • 4,062
1 vote
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Meaning of spectral functions for a non-interacting electron system at $T \to 0$

At T = 0 the system is in its ground state where all energy levels up to the Fermi level have full occupation and all of the energy levels above the Fermi level are completely unoccupied. The spectral ...
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How do experimentalists measure the exciton binding energy?

One can measure light absorption in a semiconductor. Peaks in absorption could appear corresponding to the photon -> exciton transition. They appear bellow optical gap
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