Making sense of Brillouin Zones - Part 2

[@souravmallick7699]

Thats what a creative person do with physics.

[@Alan655321]

This is a very clear demonstration of the aliasing effect. It seemed obscure when I first heard about it in a lecture but you've explained it well. The first video on Brillouin zones is excellent. I found the videos very helpful so cheers!

[@MinusMedley]

This is brilliant, speaks to my theory where the position of electrons are the manifestation of two superimposed waves.

[@Simply--Science]

hats off to you! Hope every physics teacher makes such efforts to make things simple!

[@lucaskywalker93]

Great video for understanding Brillouin zones, thanks Adam!

[@DeShark88]

Brilliant, this has made things A LOT clearer. The thing with the fan didn't help me much, but your diagrams were very useful. Now i just have to get my head around dispersion relations... ai ai ai!

[@junwenteh]

@micolich Additional point, discontinuities at Brilluin Zone, depending on what you are explaining, in terms of photonics, it is called VAn Hove SIngularities, where only single density of states is allowed in certain energy, or in this context, single DOS at that Brilluoin Zone

[@omoshiroi2326]

Wonderful Professor! Thank you for the much-needed demo. I just have a minor query about the analogy: in this case you're going from higher Brillouin Zones to lower, right? Because at higher time periods for the fan you are going to find yourself at the edge of higher Brillouin Zones...

[@junwenteh]

The fan demonstration well explained the aliasing effect, but what it has to do with dispersion?

[@ccsmith897]

this is some good stuff, want to come to glasgow and sit my condensed matter exam. thanks mate!

[@Ad_Mico]

I'd probably fail, it's been years since I've done an exam let alone that course. Exams are such a contrived process in many ways, demonstrate less what you know and more what you can regurgitate. Good luck with it though!

[@junwenteh]

@micolich Thank You for your effort for explaining this, I've done my dissertation on Graphene and the Brillouin Zone they were talkng about well, has nth much to do with your video (it helped alot anyway). The same quote to use here: I cant explain much in 500 characters. Make it short, I think the Brilluoin Zone in my Graphene context is about the Electronic Wavelength of the Pi orbitals between carbon atoms. I am not generalizing the use of "Brilluoin Zone" concept...

[@junwenteh]

@junwenteh but there the Brillouin Zone (BZ) can simply be used to illustrate whatever that has to do with waveform phenomena and structure. Example, I am an electrical engineer here, doing something on the photonics side, BZ give the picture of Pi orbital energy disperson, the crystaline structure, even possible light wavelength... BZ to me is a technique of giving people the picture of with the flavour of "frame or location of reference". Well, I am not at the level of...

[@muhammadhaidir2485]

Thank you from Indonesia

[@himanshugwala8455]

Awesome, I enver ever saw this type teaching prosses cardially thanking you😊

[@fidrewe99]

Very nice demonstration! Still I don't understand why the crystal periodicity leads to something like a discrete sampling. I mean the lattice isn't just defined and interacting with the electrons right at the lattice points, but also in between. Electrons "see" each other also in between and a unit cell consists of several atoms in general.

[@Ad_Mico]

+Fid Rewe That's true, the electrons see the lattice everywhere they are, but they can't escape the lattice being periodic. Basically there's two objects with periodicity here that interact, whenever you have that there's always discrete sampling effects. Can be a CCD camera taking a photo of a brick wall even; there's still going to be an interplay between two different periodicities, so we will get this effect popping out.

[@sriharshakodati]

I understand Aliasing...it is a sampling thing. How does this sampling thing relates to Brillouin Zone? Does this mean, we get the solutions of si only near the position of atom? Does that mean,we have no clue of how the si is in between the 2 lattice points? Someone please?

[@Ad_Mico]

Aliasing is an effect of a continuous wave or periodic system in a discrete period system or sampling. It relates here because you have a continuous wave, which is the electron, in a periodic discrete system, which is the lattice. You can know the solutions everywhere, that's not the implication here. The implication here is that the electron looks like a free particle at wavelengths very different from those of the periodic lattice, but at wavelengths that are integer to the periodic lattice you get substantial modifications from free particle behaviour. What I'm trying to get across in this video is the underlying reasons why an electron in a crystalline solid sometimes does and sometimes doesn't behave like a free particle.

[@junwenteh]

@junwenteh publishing my thoughts in a journel regarding the possible usage of BZ, but this is what I've read-up during my winter break (screwed-up Christmas eh). MIcolich: I don't know why you brought up the phase and group velocity issue, or even frequency/wavelength relation, may be its your way of comprehending something beyond my knowledge

[@鄭心和]

God , that fan sound almost explode.

[@anilsrivastava4257]

Great Man!

[@junwenteh]

@micolich What was my question? lol

[@hebrewhammer1000]

Thank you

[@wah7788]

i think i'm having a nightmare