Paradoxical Crystal Baffles Physicists(wired.com)

75 pointsby zw123456vor 11 Jahren13 comments

http://www.wired.com/2015/07/paradoxical-crystal-baffles-physicists/

4 comments

leni536vor 11 Jahren

I assume those "quantum oscillation" measurements were electron cyclotron resonance measurements[1].

Also there is an other type of non-conventional insulator which is considered to be well understood: the Mott-insulator[2]. It really doesn't fit in here as a candidate since one wouldn't expect cyclotron resonance from this model in the insulating regime. However it's a good learning example of strongly correlated electrons in materials.

[1]https://en.wikipedia.org/wiki/Electron_cyclotron_resonance#I... [2]https://en.wikipedia.org/wiki/Mott_insulator

dsfsdfdvor 11 Jahren

Perhaps it's a topological insulator, so that the bulk conducts but you'd never know it because the surface doesn't.

I'm a total noob, so if that is correct it's a miracle.

morganvachonvor 11 Jahren

The article touches on that:

"But this is no garden-variety insulator. Not only does its insulating behavior arise from strong correlations between its electrons, but in the past five years, mounting evidence has suggested that it is a “topological insulator” at low temperatures, a material that resists the flow of electricity through its three-dimensional bulk, while conducting electricity along its two-dimensional surfaces."

kabousengvor 11 Jahren

All conductors only conduct along their surface...unless I'm mistaken.

dalkevor 11 Jahren

You are somewhat mistaken. You are thinking of the skin effect. In DC power, current flow is proportional to the cross section. As the frequency increases, the effective resistance in the interior increases relative to the surface. At high enough frequencies, conductors effectively conduct only along the surface.

See https://en.wikipedia.org/wiki/Skin_effect and https://en.wikipedia.org/wiki/Litz_wire .

kabousengvor 11 Jahren

Thank you, looks like I was mistaken :D

morganvachonvor 11 Jahren

No, generally a thicker cable is a better conductor because its resistance is lower. If it were merely a matter of surface conductivity this wouldn't necessarily be true. However, internal conductivity and surface conductivity can be affected by magnetic fields:

http://faculty.wwu.edu/vawter/physicsnet/Topics/Gauss/IdealC...

ameliusvor 11 Jahren

There is also a tendency for currents to creep towards the surface of the conductor at high frequencies, see [1], although this is ultimately also caused by internally generated electromagnetic fields.

[1] https://en.wikipedia.org/wiki/Skin_effect

chriswarbovor 11 Jahren

For static charges, all of the charge on a conductor will be at its surface:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gausur.h...

That doesn't apply to moving charge though (ie. an electric current)

techdragonvor 11 Jahren

You may be thinking of the skin effect associated with alternating current systems. https://en.m.wikipedia.org/wiki/Skin_effect

gjm11vor 11 Jahren

"...And yet, SMB6 does not neatly fit that category either."

[deleted]vor 11 Jahren

seneqvor 11 Jahren

This could have applications on quantum computers & new type of transistors ! HYPE :) !

tzakrajsvor 11 Jahren

"Charcoal briquette cracks 8192-bit RSA keys in seconds!"