[HN Gopher] Weird new electron behaviour in stacked graphene thr...
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Weird new electron behaviour in stacked graphene thrills physicists
Author : pseudolus
Score : 40 points
Date : 2024-03-26 18:17 UTC (4 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| amelius wrote:
| How long until we can simulate configurations like this?
| itishappy wrote:
| That's the big question, aint it? We don't understand the
| mechanism here. This is only the second material demonstrating
| the fractional anomalous quantum hall effect we've discovered.
| amelius wrote:
| Yes, but perhaps by simulating at the microscopic level we
| can understand the macroscopic behavior.
| vcg3rd wrote:
| Anyone feel like explaining it to me like I'm 5? High School
| physics was over 40 years ago, and while I like reading
| "layman's" science this one only made me think about the
| discussion of diminsions in 3 Body Problem, which also confused
| me. Frankly I've never figured out why people write of dimensions
| as if Time isn't one (e.g. isn't the 2D material discussed
| actually 3D?) Is it just understood that Time is a given one
| doesn't have to name?
|
| TIA
| behringer wrote:
| Time is not a spatial dimension. It's not relavent in most
| spatial discussions.
| luxuryballs wrote:
| I'm not sure if you can measure time without employing
| something that changes spatially though can you?
| bee_rider wrote:
| I think when nanodevice engineers talk about 2D problems,
| they are talking about devices in which the interesting
| physics happen in 2D.
|
| The actual devices actually exist in the 3 spatial
| dimensions of course, and evolve in the time dimension.
| They just have physics that involve very flat sheets of
| things, or all of the interesting stuff happens on the
| surface of something.
|
| The big deal stuff about time and space both being
| dimensions is more of a relativity thing I think. IIRC in
| quantum physics time is really annoying and everybody hates
| it.
| tsimionescu wrote:
| Time is not a dimension in the same sense as the spatial
| dimensions. It's a coordinate for events, of course, but you
| can't for example cross from one side of a line on a 2D plane
| to the other without ever intersecting the line by moving in
| the time dimension like you can if you have a 3rd space
| dimension (e.g. by flying over the line).
|
| Even in relativity, the fourth time-related dimension is not of
| the same nature as the other two (the distance between two
| points counts the time dimension differently than the space
| ones).
| finally2049 wrote:
| > you can't for example cross from one side of a line on a 2D
| plane to the other without ever intersecting the line by
| moving in the time dimension
|
| Can't you though? Time travel to before the line existed,
| move over, time travel back.
| GlibMonkeyDeath wrote:
| There's quite a few layers to this onion, I'll try to go from
| simplest to what is described in the article:
|
| Coordinate definition: Current travels along x, magnetic field
| applied along z, and voltage is measured across y:
|
| Hall Effect: A transverse voltage (y) that appears along a
| conductor carrying current (along x) in the presence of a
| transverse (z) magnetic field. Basically, the magnetic field
| pushes the traveling charge to one side or the other (+/- y) as
| it moves, causing a charge separation along y, and hence
| generating an external "Hall" voltage. (BTW, this is a handy
| way to detect a magnetic field of a small permanent magnet,
| hence all the "Hall effect sensors" you can buy to measure if
| e.g. your door is closed, without need for a physical
| electrical contact...)
|
| Quantum Hall Effect: The observed voltage has quantized "Steps"
| because electrons must form orbits that follow the rules of
| quantum mechanics (so the quantum phase of the carriers must be
| an integer along the orbit) It's usually only observed at very
| low temperatures (so the carriers aren't getting their phases
| bashed around) and in "2D" materials (i.e., carriers restricted
| to the say X-Y plane, as in a MOSFET just under the oxide
| gate.) That way all the orbits have to lie in the same plane.
|
| Fractional Quantum Hall Effect: Wait, the orbits can sometimes
| be some other integer fraction (like 4/7, 2/3 etc.)? How can
| that be? Well, basically the carriers interact with the outside
| edges of the material (the orbits "bounce against" the edges,
| making it "topological" i.e. dependent on the physical shape of
| the sample.)
|
| Anomalous (Quantum or not, Fractional or not) Hall Effect:
| Rather than supplying the external magnetic field, the sample
| itself (via some spin-orbit mechanism, i.e. the little orbits
| of the electrons around the atoms) effectively supply the
| magnetic field.
|
| It isn't obvious that this material should exhibit fractional,
| anomalous quantum Hall effect behavior, so theorists are super
| excited to work on something new. And who knows? Lots of times
| things that seem boring and unimportant turn out to be
| useful...
| emporas wrote:
| Well, absolute zero temperatures (or close to it) are the usual
| way to create quantum computation. Absolute zero temperatures
| however are totally impractical economically also size of the
| machine (see MRI machines) and other reasons i cannot recall
| right now.
|
| In absolute zero temperatures, the electrons behave in a
| discreet way, like digits, they behave less unpredictably.
| Temperature is one way to control their movement, but i think
| magnetism is another one.
|
| What these two discoveries mean (MoTe2 and the graphene one),
| is that there is another way to control their movement, less
| unpredictable movement once again, in normal temperatures and
| without magnetism. They call that "fractional quantum anomalous
| Hall effect (FQAHE)".
|
| That's my take on it. Still not GPT-4 level but getting there.
|
| EDIT: Also 2d material means a material one atom thick.
| Graphene is exactly that, that's the definition of graphene:
| graphite one atom thick. The two materials they describe, are
| not 2D exactly, but they are thin enough that they consider
| them 2D. They essentially mean _sheets_ of atoms, instead of
| them being just an atom thick, a little bit more, like 5 or 10
| atoms thick.
| Izkata wrote:
| First thought: At least "thrills physicists" is a better title
| than "baffles physicists".
| PlunderBunny wrote:
| "This one weird trick with stacked graphene has physicists
| baffled..."
| pred_ wrote:
| One of the reasons people have studied FQHE has been to create
| (non-abelian) anyons and thereby a framework for topological
| quantum computing. Is that also the story here?
| pyinstallwoes wrote:
| I got downvoted to hell for providing the backstory to that.
|
| https://news.ycombinator.com/item?id=39517011
| LargoLasskhyfv wrote:
| Mehw? "In der Kurze liegt die Wurze."
| pie420 wrote:
| My response to anything graphene related is to ignore it as there
| is 100% chance it's hype or non-scalable.
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