7 ms·

Superconductivity Theory Under Attack

95 points by dnetesn 7y ago

asdfasdfdavid 7y ago
This looks like it could be a huge turning point for the understanding of matter at temperatures we love.
- deleted 7y ago
  [deleted]
eigenspace 7y ago
One of my great surprises coming into my masters degree in condensed matter theory working with superconductors was just how poorly we understand them. We have these incredibly seductive theoretical frameworks for thinking about superconductors which we know are deeply flawed, but it seems nobody (myself included) has the vision to see an alternate way of looking at them. The tyranny of the BCS theory of superconductors is real.
- AnimalMuppet 7y ago
  > The tyranny of the BCS theory of superconductors is real. Are you saying that the BCS theory is wrong? That it's limiting people from looking at alternate ways that could also superconduct? Or what?
  - eigenspace 7y ago
    The BCS theory does a reasonably good job of describing the properties of so called ‘conventional superconductors’ which are actually a very small class, dwarfed by the ‘unconventional superconductors’ which include almost everything high-Tc. However, BCS is built upon a pile of questionable assumptions and simplifications and there are signs that it’s not even a good theory for describing conventional superconductors. I think of BCS as something of a ‘local maximum’ in the space of theories describing superconductors and we’re all stuck trying to find ways of incrementally improving the theory when really we’re going to have to make a large leap to a quite different description before real progress is made. It’s like climbing a tree to get to the moon. You get a little closer, but to get any further you’re actually going to have to climb down and do a lot of work on earth before getting any higher.
- etaioinshrdlu 7y ago
  Do you think it's likely that the Standard Model cannot sufficiently explain superconductivity? Or alternatively, that it can be perfectly explained, but the actual analysis is just super difficult? I find this interesting because pretty much everything else in day to day life seems to have been explained by the standard model minus gravity.
  - Xcelerate 7y ago
    Like most of quantum chemistry, I imagine the Standard Model works just fine for simulating superconductivity to whatever degree of accuracy we (practically) need. The issue is finding an algorithm that can efficiently perform the calculation itself. I don't know much about condensed matter physics, but I know that for my own research in the past, something called the fermion sign problem (NP-hard) made accurate quantum chemical calculations extremely difficult.
    - acqq 7y ago
      Thanks for mentioning the term that I was able to find: https://en.wikipedia.org/wiki/Numerical_sign_problem https://en.wikipedia.org/wiki/Numerical_sign_problem https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94.170201 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94... "Computational Complexity and Fundamental Limitations to Fermionic Quantum Monte Carlo Simulations, Matthias Troyer and Uwe-Jens Wiese, Phys. Rev. Lett. 94, 170201, 4 May 2005" "Quantum Monte Carlo simulations, while being efficient for bosons, suffer from the “negative sign problem” when applied to fermions — causing an exponential increase of the computing time with the number of particles. A polynomial time solution to the sign problem is highly desired since it would provide an unbiased and numerically exact method to simulate correlated quantum systems. Here we show that such a solution is almost certainly unattainable by proving that the sign problem is nondeterministic polynomial (NP) hard, implying that a generic solution of the sign problem would also solve all problems in the complexity class NP in polynomial time." https://arxiv.org/abs/cond-mat/0408370 https://arxiv.org/abs/cond-mat/0408370
      - eigenspace 7y ago
- perlgeek 7y ago
  I only heard about high temperature superconductor theory through one seminar + lab, and I too got the impression that nobody really understood this stuff -- at least not good enough to make solid predictions, and to explain it to a physics undergrad. I'm glad somebody else shares this sentiment, and it wasn't just me being dense.
- scotradamus 7y ago
  I wouldn't so casually dismiss BCS theory. BCS contains one of only a few exactly solvable wave functions. It's used in everything from superconductivity to neutron stars. Actually, anytime there is a fermi sea instability BCS is a good starting framework. It's an triumph of modern physics.
  - eigenspace 7y ago
    There’s a reason I call the BCS theory “seductive”. It’s striking, beautiful and powerful. I also think it’s clear that BCS is far from the whole story when it comes to superconductivity and I also think the huge success of the BCS theory has cast a long shadow which makes developments in different directions more difficult.
- poelzi 7y ago
  With the fractional quantum hall effect, it should be clear at the latest, that neither the common electron nor the BCS superconductivity model can be true. I follow Stoyan Sargs "Basic Structures of Matter - Supergravitation Unified Theory" model, which has a very different understand of SC and solves most problems in physics. Due the fact that the electron is also quite different, the FQHE becomes easily explained. The Electron is a open, complexly formed, 3 body object with internal oscillations. In a superconductor environment, the overall structure disintegrates and build a train of electron shells and positrons. Same happens under certain effects that "create positrons". According to BSM, you can't create positrons, only shoot them out of their electron shell. Superconductivity is only a state of the vacuum in which the energy of the CL node is below a certain energy threshold, that sits between the parma and diamagnetic domains. Chapter 2, 3, 4 and 6 explain this in great detail. They are surely 200 pages together, so explaining the details enough for this to make sense is unfortunately outside the scope what a comment field can provide :) If you wonder, the reaction of electron + positron creates a compound particle of electron + positron mass but neutral charge as well as photons. It's relative stable and quite hard to detect.
  - eigenspace 7y ago
    > With the fractional quantum hall effect, it should be clear at the latest, that neither the common electron nor the BCS superconductivity model can be true. I don’t think you’re interpreting the outcome of the FQHE correctly. > I follow Stoyan Sargs "Basic Structures of Matter - Supergravitation Unified Theory" model, which has a very different understand of SC and solves most problems in physics. I don’t mean to be rude here, but I went and looked up this book and found that it was full of crackpot nonsense, and nearly all the reviews on the amazon page seemed to be planted fake reviews. So I’m going to be as clear as I can here in case anyone not in the field gets curious about this POV: This is nonsense.
    - poelzi 7y ago
      I studied philosophy and physics in my youth and I can distinguish between a genius and a "crackpot" very well. Details are what counts, you can get every model to fit roughly if you don't care about the number of constants involved. If the model is correct, it also works for extreme situation. FQHE is the extrem situation that breaks the electron and SC model. I have not heard any "crackpot" to distinguish between classical logic and mathematical one, because this is something only well studied people with background in logic and philosophy of science do. This was on of the hints that made me realize this guy is good, really good. Science is always 80 years ahead of current discussion: https://www.pnas.org/content/112/24/7426 https://www.pnas.org/content/112/24/7426 We are talking about interdisciplinary physics here, it's the top rank. It took me a year to really understand Stoyans Model. Now I'm in a paradox free, consistent world view with the fewest possible assumptions you can possible make. For me galaxies and the the universe as a whole, is the logical and deterministic consequence from the lowest number of fundamental particles you can have. The world became a very complex, deterministic machine of utter beauty. I understand the fine structure constant, 137, relativity (I only can smile on your implementation of it), time, Newtonian mass, magnetic fields, planetary fields (origin), gravity, electron orbit conditions, the periodic table in it's fullest (why), quasars, pulsars, globular clusters, periodicity of the redshift, lyman alpha forest, black holes, super-massive black holes (totally different object), photons, beta-particles, ... the list goes on. I understand the internal discrepancies inside the standard model, I know for a fact, that most parts of it are in fact falsified. If you bring up a error in the math equations or a logical error in the theory of his, I would be glad to discuss this in detail. So far, I have not found a problem and in fact, came to the conclusion that this is the first model I can remotely accept as true, because it is complex and not complicated. Just some weeks ago, another confirmation from a different model with quite close values was presented at a physics conference I attended. His was ~10^27 N/m² and in BSM its 1.3 * 10^26 N/m² of Vacuum pressure, a hidden variable in the standard model.
sgt101 7y ago
So what scale of QC would be needed to do this work?
jl2718 7y ago
I really wish physics articles would talk about the actual measurements. It sounds like they are using shrunken gnomes to observe electrons. Is it spectroscopy? Simulation? I think the truth would be a lot less exciting than what the article claims, but if you’re going to lie, might as well just write science fiction. Science journalism has never been great, but now it’s intentionally misleading.
- FreeFull 7y ago
  The article says they use UV photons to kick electrons off the surface, and then measure the trajectories of the electrons
- djaque 7y ago
  That would be angle resolved photoemission spectroscopy (ARPES). Read about it here: https://arpes.stanford.edu/research/tool-development/angle-resolved-photoemission-spectroscopy https://arpes.stanford.edu/research/tool-development/angle-r... The TL;DR is that you can kick electrons out of a material with light. You can study what comes off and work back to what the electrons were doing in the sample. At the most basic level it tells you "this many electrons were moving in this direction with this energy".
spectramax 7y ago
Why use a strong violent word - "Attack"? This kind of journalism bothers me. "New research questions Superconductivity Theory" should be sufficient. "Attack" is a poor word choice IMHO.
- pera 7y ago
  "attacking" a theory is a very common expression used in many scientific literature.
travisoneill1 7y ago
Why would you need a quantum computer to simulate behavior that has to do with quantum mechanics?
- tempsolution 7y ago
  Probably two things. On one hand, our theoretical understanding of quantum effects may not have come far enough to write a traditional simulation program. Or doing so would take years or even millions of years, or both. Quantum computers can simulate things that are not possible with traditional computers. These problems are in the complexity class BQP. I want to point out though, that this is very likely a result of our limited understanding, and not something that is theoretically impossible.
  - fooker 7y ago
    How do you know the quantum simulation will match the actual phenomenon. There seems to be a leap of logic there.
    - pixl97 7y ago
      How do we know that classical numerical simulation will match the phenomena... by experimentation.
      - fooker 7y ago
        Experimentation in the quantum world has this nasty habit of changing what you are trying to observe.
- cryptonector 7y ago
  That's... the whole point of quantum computing, and why Feynman [co-]invented the field. Classical computer simulations of quantum systems cannot scale. Quantum computer simulations of quantum systems can. That means that if you want to simulate a quantum system, you need a quantum computer. Or you can simply observe the quantum system and attempt to infer details of how it works from the observations. Or you could choose not to understand some quantum system, but that's not what scientists and engineers would choose.
sfink 7y ago
Interesting to see this alongside "Physicists Have Identified a Metal That Conducts Electricity But Not Heat" which is talking about another material where electrons exhibit collective behavior, "moving as a fluid". Perhaps there are a number of situations where electrons coordinate within a metallic lattice, but something additional is required to produce superconductivity. Cooper pairs could be degenerate (or at least very simple) forms of this collective behavior. Or maybe vanadium oxide is a room temperature superconductor, it's just that any amount of current destroys the effect unless it's really cold, cold enough for everything to stay put.
dspillett 7y ago
> ... at 4.2 Kelvin (4.5 degrees above absolute zero, ...) Is my understanding wrong (or out of date) or the article bad at this point? I thought the Kelvin scale was designed such that its base is absolute zero so 4.2 Kelvin would be 4.2 degrees above not 4.5? EDIT: Actually, looking at the num-pad on my keyboard, I'm now assuming that the "4.5" is simply a slip-of-the-finger typo rather than a mistake in understanding.
- lgats 7y ago
  also, 4.2 K = -452.11 F = -268.95 C

95 points by dnetesn 7y ago

asdfasdfdavid 7y ago

This looks like it could be a huge turning point for the understanding of matter at temperatures we love.

deleted 7y ago
[deleted]

eigenspace 7y ago

One of my great surprises coming into my masters degree in condensed matter theory working with superconductors was just how poorly we understand them. We have these incredibly seductive theoretical frameworks for thinking about superconductors which we know are deeply flawed, but it seems nobody (myself included) has the vision to see an alternate way of looking at them. The tyranny of the BCS theory of superconductors is real.

AnimalMuppet 7y ago
> The tyranny of the BCS theory of superconductors is real. Are you saying that the BCS theory is wrong? That it's limiting people from looking at alternate ways that could also superconduct? Or what?
- eigenspace 7y ago
  The BCS theory does a reasonably good job of describing the properties of so called ‘conventional superconductors’ which are actually a very small class, dwarfed by the ‘unconventional superconductors’ which include almost everything high-Tc. However, BCS is built upon a pile of questionable assumptions and simplifications and there are signs that it’s not even a good theory for describing conventional superconductors. I think of BCS as something of a ‘local maximum’ in the space of theories describing superconductors and we’re all stuck trying to find ways of incrementally improving the theory when really we’re going to have to make a large leap to a quite different description before real progress is made. It’s like climbing a tree to get to the moon. You get a little closer, but to get any further you’re actually going to have to climb down and do a lot of work on earth before getting any higher.
etaioinshrdlu 7y ago
Do you think it's likely that the Standard Model cannot sufficiently explain superconductivity? Or alternatively, that it can be perfectly explained, but the actual analysis is just super difficult? I find this interesting because pretty much everything else in day to day life seems to have been explained by the standard model minus gravity.
- Xcelerate 7y ago
  Like most of quantum chemistry, I imagine the Standard Model works just fine for simulating superconductivity to whatever degree of accuracy we (practically) need. The issue is finding an algorithm that can efficiently perform the calculation itself. I don't know much about condensed matter physics, but I know that for my own research in the past, something called the fermion sign problem (NP-hard) made accurate quantum chemical calculations extremely difficult.
  - acqq 7y ago
    Thanks for mentioning the term that I was able to find: https://en.wikipedia.org/wiki/Numerical_sign_problem https://en.wikipedia.org/wiki/Numerical_sign_problem https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94.170201 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94... "Computational Complexity and Fundamental Limitations to Fermionic Quantum Monte Carlo Simulations, Matthias Troyer and Uwe-Jens Wiese, Phys. Rev. Lett. 94, 170201, 4 May 2005" "Quantum Monte Carlo simulations, while being efficient for bosons, suffer from the “negative sign problem” when applied to fermions — causing an exponential increase of the computing time with the number of particles. A polynomial time solution to the sign problem is highly desired since it would provide an unbiased and numerically exact method to simulate correlated quantum systems. Here we show that such a solution is almost certainly unattainable by proving that the sign problem is nondeterministic polynomial (NP) hard, implying that a generic solution of the sign problem would also solve all problems in the complexity class NP in polynomial time." https://arxiv.org/abs/cond-mat/0408370 https://arxiv.org/abs/cond-mat/0408370
    - eigenspace 7y ago
perlgeek 7y ago
I only heard about high temperature superconductor theory through one seminar + lab, and I too got the impression that nobody really understood this stuff -- at least not good enough to make solid predictions, and to explain it to a physics undergrad. I'm glad somebody else shares this sentiment, and it wasn't just me being dense.
scotradamus 7y ago
I wouldn't so casually dismiss BCS theory. BCS contains one of only a few exactly solvable wave functions. It's used in everything from superconductivity to neutron stars. Actually, anytime there is a fermi sea instability BCS is a good starting framework. It's an triumph of modern physics.
- eigenspace 7y ago
  There’s a reason I call the BCS theory “seductive”. It’s striking, beautiful and powerful. I also think it’s clear that BCS is far from the whole story when it comes to superconductivity and I also think the huge success of the BCS theory has cast a long shadow which makes developments in different directions more difficult.
poelzi 7y ago
With the fractional quantum hall effect, it should be clear at the latest, that neither the common electron nor the BCS superconductivity model can be true. I follow Stoyan Sargs "Basic Structures of Matter - Supergravitation Unified Theory" model, which has a very different understand of SC and solves most problems in physics. Due the fact that the electron is also quite different, the FQHE becomes easily explained. The Electron is a open, complexly formed, 3 body object with internal oscillations. In a superconductor environment, the overall structure disintegrates and build a train of electron shells and positrons. Same happens under certain effects that "create positrons". According to BSM, you can't create positrons, only shoot them out of their electron shell. Superconductivity is only a state of the vacuum in which the energy of the CL node is below a certain energy threshold, that sits between the parma and diamagnetic domains. Chapter 2, 3, 4 and 6 explain this in great detail. They are surely 200 pages together, so explaining the details enough for this to make sense is unfortunately outside the scope what a comment field can provide :) If you wonder, the reaction of electron + positron creates a compound particle of electron + positron mass but neutral charge as well as photons. It's relative stable and quite hard to detect.
- eigenspace 7y ago
  > With the fractional quantum hall effect, it should be clear at the latest, that neither the common electron nor the BCS superconductivity model can be true. I don’t think you’re interpreting the outcome of the FQHE correctly. > I follow Stoyan Sargs "Basic Structures of Matter - Supergravitation Unified Theory" model, which has a very different understand of SC and solves most problems in physics. I don’t mean to be rude here, but I went and looked up this book and found that it was full of crackpot nonsense, and nearly all the reviews on the amazon page seemed to be planted fake reviews. So I’m going to be as clear as I can here in case anyone not in the field gets curious about this POV: This is nonsense.
  - poelzi 7y ago
    I studied philosophy and physics in my youth and I can distinguish between a genius and a "crackpot" very well. Details are what counts, you can get every model to fit roughly if you don't care about the number of constants involved. If the model is correct, it also works for extreme situation. FQHE is the extrem situation that breaks the electron and SC model. I have not heard any "crackpot" to distinguish between classical logic and mathematical one, because this is something only well studied people with background in logic and philosophy of science do. This was on of the hints that made me realize this guy is good, really good. Science is always 80 years ahead of current discussion: https://www.pnas.org/content/112/24/7426 https://www.pnas.org/content/112/24/7426 We are talking about interdisciplinary physics here, it's the top rank. It took me a year to really understand Stoyans Model. Now I'm in a paradox free, consistent world view with the fewest possible assumptions you can possible make. For me galaxies and the the universe as a whole, is the logical and deterministic consequence from the lowest number of fundamental particles you can have. The world became a very complex, deterministic machine of utter beauty. I understand the fine structure constant, 137, relativity (I only can smile on your implementation of it), time, Newtonian mass, magnetic fields, planetary fields (origin), gravity, electron orbit conditions, the periodic table in it's fullest (why), quasars, pulsars, globular clusters, periodicity of the redshift, lyman alpha forest, black holes, super-massive black holes (totally different object), photons, beta-particles, ... the list goes on. I understand the internal discrepancies inside the standard model, I know for a fact, that most parts of it are in fact falsified. If you bring up a error in the math equations or a logical error in the theory of his, I would be glad to discuss this in detail. So far, I have not found a problem and in fact, came to the conclusion that this is the first model I can remotely accept as true, because it is complex and not complicated. Just some weeks ago, another confirmation from a different model with quite close values was presented at a physics conference I attended. His was ~10^27 N/m² and in BSM its 1.3 * 10^26 N/m² of Vacuum pressure, a hidden variable in the standard model.

sgt101 7y ago

So what scale of QC would be needed to do this work?

jl2718 7y ago

I really wish physics articles would talk about the actual measurements. It sounds like they are using shrunken gnomes to observe electrons. Is it spectroscopy? Simulation? I think the truth would be a lot less exciting than what the article claims, but if you’re going to lie, might as well just write science fiction. Science journalism has never been great, but now it’s intentionally misleading.

FreeFull 7y ago
The article says they use UV photons to kick electrons off the surface, and then measure the trajectories of the electrons
djaque 7y ago
That would be angle resolved photoemission spectroscopy (ARPES). Read about it here: https://arpes.stanford.edu/research/tool-development/angle-resolved-photoemission-spectroscopy https://arpes.stanford.edu/research/tool-development/angle-r... The TL;DR is that you can kick electrons out of a material with light. You can study what comes off and work back to what the electrons were doing in the sample. At the most basic level it tells you "this many electrons were moving in this direction with this energy".

spectramax 7y ago

Why use a strong violent word - "Attack"? This kind of journalism bothers me. "New research questions Superconductivity Theory" should be sufficient. "Attack" is a poor word choice IMHO.

pera 7y ago
"attacking" a theory is a very common expression used in many scientific literature.

travisoneill1 7y ago

Why would you need a quantum computer to simulate behavior that has to do with quantum mechanics?

tempsolution 7y ago
Probably two things. On one hand, our theoretical understanding of quantum effects may not have come far enough to write a traditional simulation program. Or doing so would take years or even millions of years, or both. Quantum computers can simulate things that are not possible with traditional computers. These problems are in the complexity class BQP. I want to point out though, that this is very likely a result of our limited understanding, and not something that is theoretically impossible.
- fooker 7y ago
  How do you know the quantum simulation will match the actual phenomenon. There seems to be a leap of logic there.
  - pixl97 7y ago
    How do we know that classical numerical simulation will match the phenomena... by experimentation.
    - fooker 7y ago
      Experimentation in the quantum world has this nasty habit of changing what you are trying to observe.
cryptonector 7y ago
That's... the whole point of quantum computing, and why Feynman [co-]invented the field. Classical computer simulations of quantum systems cannot scale. Quantum computer simulations of quantum systems can. That means that if you want to simulate a quantum system, you need a quantum computer. Or you can simply observe the quantum system and attempt to infer details of how it works from the observations. Or you could choose not to understand some quantum system, but that's not what scientists and engineers would choose.

sfink 7y ago

Interesting to see this alongside "Physicists Have Identified a Metal That Conducts Electricity But Not Heat" which is talking about another material where electrons exhibit collective behavior, "moving as a fluid". Perhaps there are a number of situations where electrons coordinate within a metallic lattice, but something additional is required to produce superconductivity. Cooper pairs could be degenerate (or at least very simple) forms of this collective behavior. Or maybe vanadium oxide is a room temperature superconductor, it's just that any amount of current destroys the effect unless it's really cold, cold enough for everything to stay put.

dspillett 7y ago

> ... at 4.2 Kelvin (4.5 degrees above absolute zero, ...) Is my understanding wrong (or out of date) or the article bad at this point? I thought the Kelvin scale was designed such that its base is absolute zero so 4.2 Kelvin would be 4.2 degrees above not 4.5? EDIT: Actually, looking at the num-pad on my keyboard, I'm now assuming that the "4.5" is simply a slip-of-the-finger typo rather than a mistake in understanding.

lgats 7y ago
also, 4.2 K = -452.11 F = -268.95 C