
Paradoxical Crystal Baffles Physicists - andrewflnr
https://www.quantamagazine.org/20150702-paradoxical-crystal-baffles-physicists/
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Xcelerate
Hyperbolic journalism aside, this is certainly an interesting material.
Surprisingly, from a cursory literature search, it appears that no one has
attempted to perform electronic structure calculations on SmB6, although the
compound seems to have only started gathering interest around 2013. DFT of
course wouldn't work for something with high electron correlation, but
considering the simplicity of the molecule, I imagine QMC could tackle this
fairly readily to provide some insight as to what's going on.

~~~
raverbashing
Discrete Fourier transform and quantum Monte Carlo?

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danarlow
"Density Functional Theory" and "Quantum Monte Carlo", two ways of calculating
electronic structures (the former tends to be more approximate and the latter
tends to be more computationally expensive)

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100ideas
The opening sentence makes it sound like scientists have discovered
"semiconductors" for the first time - yet they were never mentioned in the
article. I feel like I would have gained a better understanding of samarium
hexaboride's unexpected properties if the author had contrasted them with a
concept that is conceptually (?) similar.

    
    
        > "In a deceptively drab black crystal, physicists have stumbled upon a baffling behavior, one that appears to blur the line between the properties of metals, in which electrons flow freely, and those of insulators, in which electrons are effectively stuck in place. The crystal exhibits hallmarks of both simultaneously."

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wyager
> Calling to mind the famous wave-particle duality of quantum mechanics

Come on, quanta. You of all science news publications should know not to throw
this misleading metaphor around willy-nilly. Not everything that seems
contradictory ought to be compared to wave-particle duality, especially when
so many people have the wrong idea about it.

~~~
danharaj
It's not _that_ misleading. Pure waves and pure particles are dual to each
other in the mathematical formalism, though actual physical phenomena are
neither.

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spacehome
> One promising approach models the material as a higher-dimensional black
> hole.

That's certainly not going to be misreported in the media.

~~~
conistonwater
But why? Isn't it big news that string theory has finally been proven?

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duaneb
Nothing about string theory is provable. If you throw a stone in a physics
class you'll hit a new theory working with higher dimensions. A really
simplified explanation might be "there's a qualitative attribute that means
something special about how forces work with it".

~~~
conistonwater
Sure, I know.

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jansenv
>Amazingly, the observed deviation from the Lifshitz-Kosevich formula was
presaged in 2010 by Sean Hartnoll and Diego Hofman, both then at Harvard
University, in a paper that recast strongly correlated materials as higher-
dimensional black holes, those infinitely steep curves in space-time predicted
by Albert Einstein.

This is boggling to me. Higher dimensional black holes!?

~~~
dzdt
I think it is bad journalism, intended to boggle not enlighten.

The paper mentioned is
[http://arxiv.org/pdf/0912.0008](http://arxiv.org/pdf/0912.0008), and does not
itself make mention of black holes.

Presumably the "higher-dimensional" aspect is coming from Hartnoll and
Hofman's "large number of degrees of freedom" analysis.

I don't know anything about this area to guess whether there is really a black
hole analogy.

But I am confident it isn't a useful analogy to make anything more clear!

~~~
zokier
That paper does not directly mention black holes, but holographic
correspondence (which is even in the title!) does seem to have strong
connection to black holes and higher dimensions, which is further spelled out
in the references. As far as I can tell (which admittedly isn't much), the
black hole connection goes deeper than just an analogy. Overall, I don't feel
like Quantas short reference there is bad journalism, the subject matter being
truly quite mind-boggling.

Here is another article from the same reporter about this holographic stuff:

[https://www.quantamagazine.org/20130701-signs-of-a-
stranger-...](https://www.quantamagazine.org/20130701-signs-of-a-stranger-
deeper-side-to-natures-building-blocks/)

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smegel
> But while samarium hexaboride does conduct electricity at room temperature,
> things get strange as it cools.

So maybe the magnetic field undoes some of the effects of low temperatures? Or
is that too un-sensational an explanation for modern physics?

~~~
aisofteng
When you suggest that "the magnetic field undoes some of the effects of low
temperature", what do you mean? How could a magnetic field "undo" effects of
low temperature? And which effects?

This sounds like a comment from the all too common armchair physicist that has
no real rigorous background in physics.

~~~
smegel
Did you read the article? It's all there.

> Sebastian and her collaborators observed electrons traversing orbits
> millions of atoms in diameter inside the crystal in response to a magnetic
> field

If cooling the material down turns it from a conductor into an insulator, and
then a magnetic field is observed to make it conduct again, then maybe the
magnetic field reversed whatever effect the cooling had. Seems a lot more
believable than "black holes".

~~~
aisofteng
I am mostly replying to your initial comment of

>Or is that too un-sensational an explanation for modern physics?

which has the frankly pretentious air of "I see an easy explanation you don't,
why didn't you see it?"

This is a common phenomenon where someone reads a pop sci article and decides
they know better than experts in the field. So I asked a couple basic
questions to see whether you have any real idea what you're commenting on, or
whether you're stringing together concepts you have no real understanding of
and then being snide.

What is an insulator, and what is a conductor? What are the quantum mechanical
properties of a material the determine whether it is one or the other, or
potentially some sort of mixture? How would or could a magnetic field
influence conductance of a material?

How does a material transition from a conductor to an insulator, and how does
on recognize that transition?

For that matter, what are the known laws of magnetic interaction that one
would have in mind when trying to model such an interaction?

Or have your comments had no real content?

~~~
mf2hd
Related video, Feynman can't explain magnets:
[https://www.youtube.com/watch?v=MO0r930Sn_8](https://www.youtube.com/watch?v=MO0r930Sn_8)

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klodolph
It always amazes me how much we still have to learn about condensed matter
physics.

~~~
astrodust
It always amazes me how much we still have to learn about physics.

~~~
runeks
It always amazes me how much we still have to learn.

~~~
Natsu
It always amazes me how much we have learned.

~~~
echelon
Please do not turn HN into Reddit. The signal:noise ratio is a very important
thing to maintain. If it begins to slip too much, it might turn into a
monotonically decreasing slide.

