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Apr
15
accepted Out-of-Plane Phonons
Apr
14
comment Out-of-Plane Phonons
Im not sure I understand where $\tilde{h}$ comes into this. Whenever you have the differential equation can't you just make a substitution like I made above and get the answer? What is $\tilde{h}$ explicitly?
Apr
13
asked Out-of-Plane Phonons
Mar
5
awarded  Popular Question
Feb
8
awarded  Yearling
Aug
20
accepted Graphene's Tight Binding Hamiltonian
Aug
11
comment Graphene's Tight Binding Hamiltonian
I see. Can you always write the bilayer as a 2x2 matrix, or is it only when it is AB stacked and low energy approx?
Aug
11
comment Graphene's Tight Binding Hamiltonian
The answer below and this comment clears things up greatly - Ill accept an official answer soon. Are there are good books or papers on this? Conceptually, one thing I can't see right away, is why are the electrons predominately on these two lattice sites?
Aug
10
asked Graphene's Tight Binding Hamiltonian
Mar
31
comment Is there a mechanism for time symmetry breaking?
I'll let someone else answer but I believe magnetic fields are key here.
Mar
9
comment I don't understand what we really mean by voltage drop
(Part III) This steady state of flow is a current. And the only thing now that defines the Voltage (or voltage drop - look at my answer) is the resistance between your two probe points. Probe a wire (pretty much zero resistance), no voltage drop. Probe across a resistor you will get a finite voltage drop. I hope this is clear.
Mar
9
comment I don't understand what we really mean by voltage drop
(Part II) Energetically we could talk about an effective potential which now takes into account this new resistive element. It mightn't be a bad idea to think about voltage like this. I can't get around it - but the basis of this concept is $V=IR$ which is why my answer focused on it. Note it is the relationship between a flow, impedance and potential difference. One needs to think about the entire circuit at once, macroscopically - I don't know what happens individual electrons. Once the battery is connected, practically instantly the circuit will reach a steady state of flow.
Mar
9
awarded  Commentator
Mar
9
comment I don't understand what we really mean by voltage drop
I might need to think about this more but I've read Edit 2 a few times. Certainly a battery works by a separation of charge, but when in a circuit I think one must be careful about thinking about things in terms of "difference in number of electrons". Its all about flow (current). The Voltage is the potential difference which allows flow to occur (think gravitational potential difference allowing an object to fall from high to low). What if something impedes this motion? In our classical mechanics example we could introduce a viscous liquid or pinball maze to divert flow.
Mar
9
awarded  Enthusiast
Mar
5
awarded  Editor
Mar
5
revised I don't understand what we really mean by voltage drop
Further example
Mar
5
answered I don't understand what we really mean by voltage drop
Mar
4
comment Greens function in EM with boundary conditions confusion
I said coincidence since this was the confusing point for me - when it is physical, and when it is not. It is very intuitive for me to say: Lets build up a charge distribution from dirac deltas. Then we jump from the greens to the convolution of G and $\rho$. Thanks for the clarification though!
Feb
28
comment Greens function in EM with boundary conditions confusion
If this comes up I recommend mentioning that in an unbounded region the Greens function by coincidence (upto a normalization factor) is the potential of a point charge. So here it kind of has a physical meaning. When using it to solve problems, specifically when we consider boundaries or finite regions of space it is purely a tool. We use our conditions, jackson 1.42 and our freedom in $G$, Namely $G(x,x')=1/|x-x'|+F(x,x')$ where $F$ must satisfy the laplace equation to find the solution. (That is briefly what I got from your answers and my research). Graduate TA's would be nice to have.