6 ms·

Physicists Puzzle over Emergence of Electron Aggregates

105 points by westurner 2y ago

yummypaint 2y ago
The behavior of electrons in a material depend on the material. Crystals and sheets of graphene are special because of their periodicity, i.e. the inability to distinguish one location in the lattice from another over long distances. The wavefuntions of electrons are to first order due to this periodic potential. Crystals are also interesting mathematically because there is a finite number of possible lattices that can exist, and it isn't even that many. All the useful and interesting effects of doping semiconductors is the result of throwing some contaminants in to disrupt the perfect periodicity of the silicon crystal and therebey make junctions that can ultimately be used for computation etc. "Holes" are sort of emergent quasiparticles with charge +1. I think a key term in the article is "moire". When two regular patterns are overlayed and then twisted or offset, they interfere to produce a new emergent pattern, sometimes with radically different periodicity than the original. The electrons must now inhabit this very artificial pattern of pottentials that is neither a crystal or a doped crystal and may not occur in nature at all. Plus there are probably effects caused by the material being nearly 2d. Very exciting stuff, emergent complexity seems to be a major theme in physics so far this century.
- westurner 2y ago
  "Catalog of topological phonon materials" (2024) https://www.science.org/doi/10.1126/science.adf8458 https://www.science.org/doi/10.1126/science.adf8458 "Non-trivial quantum geometry and the strength of electron–phonon coupling" (2024) https://www.nature.com/articles/s41567-024-02486-0 https://www.nature.com/articles/s41567-024-02486-0 : > Here, we devise a theory that incorporates the quantum geometry of the electron bands into the electron–phonon coupling, demonstrating the crucial contributions of the Fubini–Study metric or its orbital selective version to the dimensionless electron–phonon coupling constant. We apply the theory to two materials, that is, graphene and MgB2, where the geometric contributions account for approximately 50% and 90% of the total electron–phonon coupling constant, respectively. The quantum geometric contributions in the two systems are further bounded from below by topological contributions > Here, we devise a theory that incorporates the quantum geometry of the electron bands into the electron–phonon coupling, demonstrating the crucial contributions of the Fubini–Study metric or its orbital selective version to the dimensionless electron–phonon coupling constant. We apply the theory to two materials, that is, graphene and MgB2, where the geometric contributions account for approximately 50% and 90% of the total electron–phonon coupling constant, respectively. The quantum geometric contributions in the two systems are further bounded from below by topological contributions There is emergence in complex fluid attractor systems. Superhydrodynamics models fluid attractor systems; for example with vorticity in "Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity." (2015) https://hal.science/hal-01248015/ https://hal.science/hal-01248015/ .. https://news.ycombinator.com/item?id=38871054 https://news.ycombinator.com/item?id=38871054 Vorticity in Electron-Electron interactions: https://news.ycombinator.com/item?id=40360691 https://news.ycombinator.com/item?id=40360691 Is there emergence from just vorticity?
pmayrgundter 2y ago
I wonder if the moire materials can tuned as a dynamic metamaterial to absorb or dump a lot of charge, based on their rotational geometry. That charge plateau seems like a quite powerful trick
johncarlosbaez 2y ago
I've never seen a good clear explanation of "fractionalization" - the way that that systems can contain excitations that act like particles with charges that are a fraction of the electron charge. A typical non-explanation: https://scitechdaily.com/quantum-revolution-redefining-physics-with-fractional-charges/ https://scitechdaily.com/quantum-revolution-redefining-physi...
- dustingetz 2y ago
  do fractional electrons when perturbed radiate fractional photons?
- boothby 2y ago
  I'm no physics expert but I do make programmable crystals for a living. One of my favorite applications of adiabatic quantum computers is the simulation of physical materials such as [1] wherein we see emergent phenomena like fractional magnetization. My contribution to this paper was to find the configuration of qubits equivalent to the material in question. What's really cool about experiments like this is that you can directly observe the spin configurations that give rise to the fractional states -- if you're sufficiently motivated, you could reproduce the experiment and paw through the data yourself (disclaimer: that may require you to pay my employer for QPU access). For the less motivated, see figure 3. [1, lay coverage] https://csmd.ornl.gov/highlight/quantum-computing-enables-simulations-unravel-mysteries-magnetic-materials-0 https://csmd.ornl.gov/highlight/quantum-computing-enables-si... [1, free PDF] https://arxiv.org/pdf/2003.01019 https://arxiv.org/pdf/2003.01019
- octonion137 2y ago
  Couldn't an effective theory/mean-field theory have almost any emergent behavior depending on the underlying configuration space/system? Kind of like how one can build a domain-specific language out of an expressive enough underlying language it's implemented in
  - johncarlosbaez 2y ago
    Maybe, but getting fractional charges out of a system with charges that are integer multiples of the electron charge is no mean feat, and I want to understand the math behind this in detail. Someone knows, but I haven't found any clear explanations.
mensetmanusman 2y ago
“ The potential of non-abelian anyons for quantum computing has driven decades of research in academia and industry.” I love sentences like these. Reminds me that the world is far more complicated than a human can grasp in their lifetime. Great work!
- visarga 2y ago
  > the world is far more complicated than a human can grasp in their lifetime Language plays a big part in this "grasping" process. Without language we would not have been able to build upon past experience and get to where we are now. It now preserves more knowledge than any one human can ever learn. We often think intelligence is an individual trait, but it is made of concepts and methods discovered by a social process based on language. A single human can't bootstrap to that level on his own.

105 points by westurner 2y ago

The behavior of electrons in a material depend on the material. Crystals and sheets of graphene are special because of their periodicity, i.e. the inability to distinguish one location in the lattice from another over long distances. The wavefuntions of electrons are to first order due to this periodic potential. Crystals are also interesting mathematically because there is a finite number of possible lattices that can exist, and it isn't even that many. All the useful and interesting effects of doping semiconductors is the result of throwing some contaminants in to disrupt the perfect periodicity of the silicon crystal and therebey make junctions that can ultimately be used for computation etc. "Holes" are sort of emergent quasiparticles with charge +1. I think a key term in the article is "moire". When two regular patterns are overlayed and then twisted or offset, they interfere to produce a new emergent pattern, sometimes with radically different periodicity than the original. The electrons must now inhabit this very artificial pattern of pottentials that is neither a crystal or a doped crystal and may not occur in nature at all. Plus there are probably effects caused by the material being nearly 2d. Very exciting stuff, emergent complexity seems to be a major theme in physics so far this century.

westurner 2y ago
"Catalog of topological phonon materials" (2024) https://www.science.org/doi/10.1126/science.adf8458 https://www.science.org/doi/10.1126/science.adf8458 "Non-trivial quantum geometry and the strength of electron–phonon coupling" (2024) https://www.nature.com/articles/s41567-024-02486-0 https://www.nature.com/articles/s41567-024-02486-0 : > Here, we devise a theory that incorporates the quantum geometry of the electron bands into the electron–phonon coupling, demonstrating the crucial contributions of the Fubini–Study metric or its orbital selective version to the dimensionless electron–phonon coupling constant. We apply the theory to two materials, that is, graphene and MgB2, where the geometric contributions account for approximately 50% and 90% of the total electron–phonon coupling constant, respectively. The quantum geometric contributions in the two systems are further bounded from below by topological contributions > Here, we devise a theory that incorporates the quantum geometry of the electron bands into the electron–phonon coupling, demonstrating the crucial contributions of the Fubini–Study metric or its orbital selective version to the dimensionless electron–phonon coupling constant. We apply the theory to two materials, that is, graphene and MgB2, where the geometric contributions account for approximately 50% and 90% of the total electron–phonon coupling constant, respectively. The quantum geometric contributions in the two systems are further bounded from below by topological contributions There is emergence in complex fluid attractor systems. Superhydrodynamics models fluid attractor systems; for example with vorticity in "Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity." (2015) https://hal.science/hal-01248015/ https://hal.science/hal-01248015/ .. https://news.ycombinator.com/item?id=38871054 https://news.ycombinator.com/item?id=38871054 Vorticity in Electron-Electron interactions: https://news.ycombinator.com/item?id=40360691 https://news.ycombinator.com/item?id=40360691 Is there emergence from just vorticity?

pmayrgundter 2y ago

I wonder if the moire materials can tuned as a dynamic metamaterial to absorb or dump a lot of charge, based on their rotational geometry. That charge plateau seems like a quite powerful trick

johncarlosbaez 2y ago

I've never seen a good clear explanation of "fractionalization" - the way that that systems can contain excitations that act like particles with charges that are a fraction of the electron charge. A typical non-explanation: https://scitechdaily.com/quantum-revolution-redefining-physics-with-fractional-charges/ https://scitechdaily.com/quantum-revolution-redefining-physi...

dustingetz 2y ago
do fractional electrons when perturbed radiate fractional photons?
boothby 2y ago
I'm no physics expert but I do make programmable crystals for a living. One of my favorite applications of adiabatic quantum computers is the simulation of physical materials such as [1] wherein we see emergent phenomena like fractional magnetization. My contribution to this paper was to find the configuration of qubits equivalent to the material in question. What's really cool about experiments like this is that you can directly observe the spin configurations that give rise to the fractional states -- if you're sufficiently motivated, you could reproduce the experiment and paw through the data yourself (disclaimer: that may require you to pay my employer for QPU access). For the less motivated, see figure 3. [1, lay coverage] https://csmd.ornl.gov/highlight/quantum-computing-enables-simulations-unravel-mysteries-magnetic-materials-0 https://csmd.ornl.gov/highlight/quantum-computing-enables-si... [1, free PDF] https://arxiv.org/pdf/2003.01019 https://arxiv.org/pdf/2003.01019
octonion137 2y ago
Couldn't an effective theory/mean-field theory have almost any emergent behavior depending on the underlying configuration space/system? Kind of like how one can build a domain-specific language out of an expressive enough underlying language it's implemented in
- johncarlosbaez 2y ago
  Maybe, but getting fractional charges out of a system with charges that are integer multiples of the electron charge is no mean feat, and I want to understand the math behind this in detail. Someone knows, but I haven't found any clear explanations.

mensetmanusman 2y ago

“ The potential of non-abelian anyons for quantum computing has driven decades of research in academia and industry.” I love sentences like these. Reminds me that the world is far more complicated than a human can grasp in their lifetime. Great work!

visarga 2y ago
> the world is far more complicated than a human can grasp in their lifetime Language plays a big part in this "grasping" process. Without language we would not have been able to build upon past experience and get to where we are now. It now preserves more knowledge than any one human can ever learn. We often think intelligence is an individual trait, but it is made of concepts and methods discovered by a social process based on language. A single human can't bootstrap to that level on his own.