Silver sheds light on superconductor secrets

Dec 20, 2012
Silver sheds light on superconductor secrets

(Phys.org)—By doping a bismuth-based layered material with silver, Chinese scientists demonstrated that superconductivity is intrinsic to the new material rather than stemming from its impurities.

The first report on the chemical substitution, or doping, using silver atoms, for a new class of superconductor that was only discovered this year, is about to be published in European Physical Journal B. Chinese scientists from Institute of , , Hefei, discovered that the superconductivity is intrinsic rather than created by impurities in this material with a sandwich-style layered structure made of bismuth oxysulphide (Bi4O4S3).

Superconductors with a transition temperature (TC) above the boiling temperature of liquid nitrogen (77 kelvins or −196 °C) are called high TC superconductors. In the quest for such materials, compounds with bismuth disulphide (BiS2) layers have recently started to attract a lot of attention. Indeed, in July 2012, reported achieving a TC at around 4.5 kelvins (-268.65 °C) with the first bismuth oxysulphide superconductor.

All the superconducting samples for this new superconductor reported so far are a mixture of Bi4O4S3 and impurities. However, the pure sample without impurities is not superconducting. Scientists have therefore been wondering whether the observed superconductivity stems from the presence of impurities.

The Hefei team performed systematic measurement of the material's characteristics relying on x-ray diffraction, magnetic susceptibility, and . Using comparison of the x-ray , they found that silver atoms partially replace the bismuth sites in the bismuth oxysulphide lattice.

Further experiments involved controlling the composition of the material through various levels of silver doping. The superconductivity, the authors found, was suppressed as the silver content increases and eventually disappears above a certain doping threshold. They believe that it is the modification of electronic structure upon doping that suppresses the superconductivity. Based on these observations, they concluded that the observed superconductivity originates from the bismuth oxysulphide lattice rather than any impurities.

Explore further: Physicist pursues superconductivity mysteries

More information: 1. S. G. Tan, P. Tong, Y. Liu, W. J. Lu, L. J. Li, B. C. Zhao, Y. P. Sun (2012), Suppression of superconductivity in layered Bi4O4S3 by Ag doping, European Physical Journal B, DOI: 10.1140/epjb/e2012-30975-2

2. Mizuguchi et al. arXiv:1207.3145 [cond-mat.supr-con]

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Macksb
1.8 / 5 (4) Dec 20, 2012
This conclusion--that the superconductivity originates from the lattice (specifically, the bismuth oxysulfide lattice)- is consistent with a theory I have posted before in Physorg. My theory is that the lattice vibrations become coordinated or synchronized in a highly specific pattern. These coordinated lattice vibrations in turn organize electrons in groupings akin to Cooper pairs. This idea extends BCS theory, in which simple lattice vibrations organize electrons in simple Cooper pairs. My theory is that high temp superconductivity involves more complex (but synchronrized) lattice vibrations; and more complex (but synchronized) pairing (2 way or 4 way) of electrons.

In each case, the patterns will be one or more patterns specified by Art Winfree, circa 1967, in his law of coupled limit-cycle oscillators. Winfree, who won a MacArthur prize, was a bio-mathematician. His "law" should also apply to physics, which, as a quantum system, is comprised entirely of periodic oscillations.
Macksb
1.8 / 5 (4) Dec 20, 2012
In more colorful terms, here's the idea.

BCS or low temp superconductors: A monotonous drumbeat in the lattice causes electrons to dance in bound pairs, perfectly antisynchronous as to orbit and angular momentum (spin), both of which are periodic oscillations. Fermions become bosons.

High temp superconductors, all flavors, work as follows: the lattice vibrations of the atoms are polyphonic and harmonized. Their electrons dance rhythmically to this music, like Astaire and Rogers; or perhaps like two identical Astaire and Rogers pairs, in which case one pair is more loosely bound internally, and externally with the other pair. Fermions become bosons, at integer 1 or 2.

The complex but rhythmic motions in the lattice and in the dance of the electrons "absorb" the higher energy perfectly, maintaining precise order at temps too high for old, low-temp superconductivity. The BCS theory, generalized in this manner, can explain the high temp supers as well as the low temp supers.

johanfprins
1 / 5 (3) Dec 21, 2012
Well? If they are correct, why do they not have SC WITHOUT the silver doping?

You need localised Mott-type electron-orbitals for SC to be possible: When the spacings between the orbitals are too large, you have no superconduction. When the spacings between the orbitals become too small, an impurity band forms and again no SC.

They have not discovered anything new at all! Whether you increase the orbital-spacing by doping, by cooling, or even by applying pressure, the same principles applies: Too large inter-orbital distances=no SC. Too small inter-orbital distances=no SC. In between there is SC! You can see this for ALL SC materials EVER discovered.

BCS can NEVER explain this. So please STOP being so utterly stupid to assume that pair-formation is the reason for superconduction: IT IS NOT!

Minich
1 / 5 (1) Dec 21, 2012
To Macksb
Never mind. There are only "stupid" opponents to
so called "Mott" bulshitted superconductors doped by johanfprins's asshole.

Though any insulatosrs can be parent for HTSC, Mott is not neсessary condition. Neсessary condition is pozitive Hall coefficient at Fermi surface for electron in some direction. This condition is always satisfied for a little bit hole doped insulators. But that condition is not sufficient. It depends on energy momentun dispersion relations in ALL electron spectrum in conductance band (after doping) and some masses of all ions in solid.
Minich
1 / 5 (1) Dec 21, 2012
It is Chapnik well established rule (experimental!).
johanfprins
1 / 5 (2) Dec 21, 2012
@Minich,

I know you are an asshole! How much do you want to bet that localized Mott-type electron-orbitals are not required for superconduction? Can I take you on for $1,000,000. Let us see whether you are willing to put your money where your stupid mouth is! Just accept the fact that you are a disgrace to humanity!

I already told you that you are "bad rubbish" I want to get "rid off".

Minich
1 / 5 (1) Dec 22, 2012
"localized Mott-type electron-orbitals" is of cause possible fo superconductivity, as we see in cuprates.

But in MgB2 where is Mott-type? hehehe
Or in "conventional" superconductors?
Or in neutron star "earth-star"quake?
Or in superfluid He3 liquid?

Take it easy. There are many "theorists" to crow "true theory". You are one of them. Your crow is one of the sequence that die out :(

"I want" is your want. What of it.
johanfprins
1 / 5 (1) Dec 23, 2012
"localized Mott-type electron-orbitals" is of cause possible fo superconductivity, as we see in cuprates.


All materials with gaps in their electronic-energy spectrum, can form localised orbitals.

But in MgB2 where is Mott-type? hehehe
If there are not localised orbitals which can hop by quantum fluctuations there will be no superconduction.
Or in "conventional" superconductors?
Wigner already deduced in about 1935 that in non-ideal metals, which are exactly the ones that superconduct, localised orbitals MUST form at low temperatures.

Or in neutron star "earth-star"quake?
Or in superfluid He3 liquid?
These are neutral fluids, NOT CHARGED carriers. Only a complete fool who tampers with the scaling of order parameters, will believe that superfluids are the same as superconductors.

Take it easy. There are many "theorists" to crow "true theory". You are one of them.
YOU are the one doing this without giving any quantitative proof.
Tausch
1 / 5 (1) Dec 23, 2012
Does predicting a combinatorial of elements... a compound that super-conducts at room temperatures settle whos' theory is correct?

Why not just present such a compound to the rest of the community with the claim it will super-conduct at room temperatures?

johanfprins
1 / 5 (1) Dec 23, 2012
Does predicting a combinatorial of elements... a compound that super-conducts at room temperatures settle whos' theory is correct?


ANY material which has an energy gap in its electronic spectrum, within which there are localised states at an energy (delta)E below the edge of the gap, will superconduct when the density of the orbitals are such that an orbital can "borrow" energy (delta)E to be free and to move to the next orbital and replace it. The energy that is allowed by Heisenberg's relationship for energy and time must be enough to overcome (delta)E and have enough kinetic energy to move to the next site within the allowed time-interval (delta)t. If the energy is too high or the inter-orbital distances are too large, you will never have superconduction. The allowed energy-gaps and densities that will allow SC at a temperature can be easily calculated from a SIMPLE qunadratic formula (which is given in my book) and which I have tried to publish during the past 10 years.
johanfprins
1 / 5 (1) Dec 23, 2012
Thus any insulating material or semi-insulating material (like the semi-metals) can be superconductors if you can match the energy (delta)E with the density of localised orbitals.

It is not question of predicting which compound will superconduct. Rather choose the simplest insulating material and modify its electronic energy spectrum so that there is a suitable energy gap and suitable localised orbitals.

The larger you can make the energy gap (delta)E, and the denser the localised orbitals the higher the critical temperature becomes. This is why the ceramics have higher critical temperatures than the metals. The highest density of localised orbitals in the semi-metals are too low for a high Tc. The ceramics seems to be at their limit at about 250 K; but there are ways in which the localised orbitals might be modified to borrow more energy and thus to have higher Tc's. Since you want a high density of orbitals you require small inter-orbital spacings.

This is why I choose diamond!
winthrom
not rated yet Dec 24, 2012
try testing theories using quantum dots as pseudo elements
johanfprins
1 / 5 (1) Dec 24, 2012
try testing theories using quantum dots as pseudo elements


WHY? Quantum dots cannot hop by means of quantum fluctuations (delta)E*(delta)t=g*(hbar) where the value of g is determined by the localised orbital. The latter motion causes superconduction:

Not idiotic models based on Cooper pairs which can be accelerated. If you accelerate to generate the motion of the charge-carriers, you do work in order to create the kinetic energy required for motion. Kinetic energy dissipates by increasing the entropy: ergo RESISTIVE MOTION.

Superconduction does NOT increase the entropy! If it did you would not be able to sustain a perpetual current around a ring.

ValeriaT
1 / 5 (1) Dec 24, 2012
Article preprint Bi4O4S3 is composed of a stacking of Bi4O4(SO4) spacer layers and two BiS2 layers, which are supposed to be the source of holes as the CuO2 layer in cuprates or the Fe2An2 layer in oxypnictides. The addition of silver just kills the superconductivity monotonously.
johanfprins
1 / 5 (1) Dec 24, 2012
Adding dopants can have two effects: It can act as n- or p-type donors or it can compensate donors (or acceptors) already present. In most of the ceramics, if not all, donor-centers within the crystallographic layers donate electrons to form localised states between the layers which, when they reach a high enough density, can superconduct and when reaching too high a density cannot superconduct anymore.

You thus have competing conduction mechanims: 1. holes in the CL's, 2. localised thermal hopping by n-type orbitals between the CL's and 3. SC when the density of the orbitals between the layers falls within the interval at which these localised states can hop by means of quantum fluctuations.

ALL phase diagrams of ALL the ceramic materials can be easily interpreted in terms of these competing conduction mecahnisms. The so called "energy gaps" occurs when one of these conducting mechanims becomes more prominent than the others.
Minich
1 / 5 (1) Dec 24, 2012
Does predicting a combinatorial of elements... a compound that super-conducts at room temperatures settle whos' theory is correct?

Why not just present such a compound to the rest of the community with the claim it will super-conduct at room temperatures?


It is the best method. I see 4 methods to do this. But i present it in my letter to President Putin first. And after to all interested, if my work won't be classified.
ValeriaT
1 / 5 (1) Dec 24, 2012
Adding dopants can have two effects
This is general blurb and it doesn't explain, why pure Bi4O4S3 is superconductive and why addition of silver destroys the superconductivity.
johanfprins
1 / 5 (1) Dec 25, 2012
Why not just present such a compound to the rest of the community with the claim it will super-conduct at room temperatures?


It is the best method. I see 4 methods to do this. But i present it in my letter to President Putin first. And after to all interested, if my work won't be classified.


LOL: Your methods will NOT WORK! They are based on the BS of order parameters.
johanfprins
1 / 5 (1) Dec 25, 2012
Adding dopants can have two effects
This is general blurb and it doesn't explain, why pure Bi4O4S3 is superconductive and why addition of silver destroys the superconductivity.


It does! Except when you are too stupid to understand the basic electronic mechanisms in all materials. You have proved time and again on this forum that you are confusing real physics with ducks and bubbles!

Obviously the addition of silver compensates and reduces the density of the localized orbitals which are responsible for superconduction. QED!
ValeriaT
1 / 5 (1) Dec 25, 2012
I could say, the addition of silver compensates and reduces the density of the Cooper pairs which are responsible for superconduction. BCS!
johanfprins
1 / 5 (1) Dec 25, 2012
I could say, the addition of silver compensates and reduces the density of the Cooper pairs which are responsible for superconduction. BCS!


I know you can say it because it is in your nature to say bullshit!

You DO NOT require Cooper Pairs for superconduction to occur: Furthermore it is just as unlikely that they will form as it is that a Higgs boson is required for mass-energy to manifest.

Even if Cooper pairs could form, they would only be able to transfer a current by being accelerated; so that there MUST then be a voltage drop! And when there is a voltage drop, there CANNOT be superconduction.
ValeriaT
1 / 5 (1) Dec 26, 2012
it is just as unlikely that they will form as it is that a Higgs boson is required for mass-energy to manifest
Please explain this line of reasoning. Cooper pairs indeed don't form in the empty vacuum, the lattice quantum vibrations (phonons) are required for their formation.
if Cooper pairs could form, they would only be able to transfer a current by being accelerated
The vibrations of lattice maintain the necessary energy by itself. For example, inside of these tiny metallic rings the current is maintained even without any external voltage. In this sense, they're superconductive at short distance.
Minich
1 / 5 (1) Dec 27, 2012
1. In some sense superconducting electrons are electrons in "diod" states. There is only ONE state in some ENERGY region and there is NO "opposite momentum" state at all.
2. Those superconducting states diminish full energy, at special cases of "hole" orbitals at fermi level. When diminished energy prevail over enhanced energy of nonsuperconducting electrons there becomes superconductivity.

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