IANAP, but I thought that quantum field theory (which isn't incredibly controversial) already treats particles as merely emergent convenient ways to describe common excitations of the fields. I'm surprised it isn't mentioned here at all.
> A regular particle isn't really emergent, it corresponds 1:1 to the excitation of the field
Maybe 'emergent' was the wrong word here. I meant that particles are convenient ways of describing behavior of the fields in many (but not all) cases, with the fields themselves considered to be the (more) fundamental description of reality.
Quantization exists because of the waves though. It's a consequence of standing waves being produced when an excitation is confined. It's not AFAIK an axiom of QFT, more an emergent result.
Theoretical condensed matter here (though not an expert on strange metals specifically).
The idea is that in a quantum many-body system, a (low-energy) state can often be represented as a set of independent excitations of the field, which are called quasiparticles. The "particle" picture for the Fermi liquid already operates in a framework of quantum fields. "No quasiparticles" means that there is no such representation, i.e., you can't say something like "these two states differ by an addition of a particle with such-and-such properties."
I would assume that's mostly a function of this being for a general audience. Yes, you absolutely can talk about quasiparticles using techniques adapted from QFT. I don't know if Landau originally conceived of it that way, but there were definitely a bunch of Soviet physicists shortly after him who did.
QFT is perfect for a single particle, but it gets harder to describe the behavior of particles en masse. It's super hard to find simplifications that reveal emergent behavior.
Great read! One fascinating to me is how the article frames the field as progressing once again now that researchers are getting over the quasi particle model.
Reminds me of the elephant and rope adage: young elephants are trained with small chains, which as they mature they outsized and could easily break but don't.
Though to give credit to researchers, those new experiments of "listening" for electron perturbations seem amazing. That's just a brilliant idea. Theorists often like to pretend they're better than the experimentalists, but without proper data the theorists get stuck in dead ends. ;)
The article says that resisivity in normal metals follows a quadratic curve, but the article also says that it follows an exponential curve. Does anyone know which it right?
Typically, the behavior of any given metal is a mix of mechanisms so the measured behavior is fit to a curve where you fit n. So for metals the exponent is typically a decimal between 2 and 5.
But the specific word they were looking for is "quintic". (And the corresponding word for 4th-degree, in case anyone is curious, is "quartic"; one sometimes sees "biquadratic", which unfortunately is also sometimes used to describe a particular subset of quartics.)
Oh right, silly me. Wow, my own vocabulary deserted me there, huh?
Yeah I think generally "sextic" is the highest you see before people stop doing that, and that one's somewhat uncommon I'd say. ("Quintic" is actually fairly common, contrary to what I said earlier, oops.) The fact that seventh-degree would be "septic" might be one reason stop with the words at that point!
I'm pretty sure that more than half the times I've seen "quintic" are in one single context: talking about the fact that while you can solve polynomial equations of degree 1-4 by doing arithmetic and taking n'th roots, this stops being possible once you get as far as quintic equations. (The "insolubility of the quintic".)
No. Exponential growth or decay is much faster than quadratic growth or decay. You may be mixing up exponential functions, of the form x maps to ab^x, with power functions, of the form x maps to ax^b. These are very different!
Annoyingly, people often use "exponential" colloquially to mean anything faster than linear, but in fact lots of things are faster than linear.
From the other responses, it sounds like "none of the above". It's more like a "polynomial curve" that is only sometimes quadratic. Is "polynomial curve" a thing? "Power curve" / "power function"?
So superconductivity is a laminar flow of electron goop?
Ok, it's different in that liquid flows through pipes and electrons flow through crystal lattices or whatever, so electrons go between and around the material while liquid is bounded by it.
It makes me speculate that electron flow through a metal is sort of like liquid flowing through a compressible boundary tube, whereas flow through a non-metal has rigid walls. Non-metals reject the electrons, metals allow them to play Spiderman and hitch a temporary ride (if you'll forgive the overly particle-centric analogy.)
If resistivity is determined by the equivalent of turbulence, though, I've no idea what the graph against temperature should be. Do electrons travel faster when there's less resistance?
Turbulence on a small scale acts like increased viscosity on a large scale, because they're both forms of momentum diffusion. However, current doesn't have any momentum diffusion terms, the momentum is lost to the conductor.
AFAIK nothing stops an electron from existing in the same space as a proton or neutron - they don't have to go around. Indeed that's required for certain kinds of radioactive decay to occur. Not all electron orbitals overlap the nucleus, but some do.
TL;DR: the analogy is helpful at a high level, but has limitations when you look closely.
> Ok, it's different in that liquid flows through pipes and electrons flow through crystal lattices or whatever, so electrons go between and around the material while liquid is bounded by it.
This is not perfect, but it works at a high level.
The main difference with e.g. water flows is that what restricts electron flux is traps. Electrons are not limited by walls that prevents them from going outside channels, instead they are held in place by atoms’ nuclei.
In a conductor, the “force” holding them is effectively zero, so when an electron comes in on one side, another one comes out of the other.
In a semiconductor. An electron needs some energy to get out of its trap before it can move. Then, “freed” electrons hop from trap to trap and the current is the overall effect of this. Electrons do not have to move far to create a current, there just needs to be enough of them. There is no real macroscopic analogy for this.
In an insulator, electrons just don’t get out of their traps because the energy required is too large.
This ignores a lot of details and quantum effects, but it is still a useful way to think about this.
> It makes me speculate that electron flow through a metal is sort of like liquid flowing through a compressible boundary tube, whereas flow through a non-metal has rigid walls.
Not really. Electrons moving in a metal are slowed down by a lot of different phenomena but this cannot really be considered as a compressible fluid. The effect is more similar to viscosity than compressibility.
In non-metals, electrons just don’t move unless they are made available, for example by doping or with a source of energy.
> Non-metals reject the electrons, metals allow them to play Spiderman and hitch a temporary ride
The general model is that metals let electrons flow and non-metals hold on to them.
> If resistivity is determined by the equivalent of turbulence, though, I've no idea what the graph against temperature should be. Do electrons travel faster when there's less resistance?
The analogy kind of breaks down here. There are competing effects and conductivity as a function of time is often highly non-trivial. In general, the number of electrons available increases with temperature, but scattering by other electrons, vibrations and defects also increases. Overall, resistivity tends to increase with temperature in metals and decrease in semiconductors, but there are exceptions.
How should we visualize what pushes the electron goop forward? If it's like water pressure, that would make the hindmost goop bunch up with the foremost goop.
Presumably electricity has something to do with positive charge at the back of the 'pipe' and negative charge at the 'front' (or have I got those backward?), perhaps a better visualization would be that they're all rolling down an inclined plane together?
Current flows due to a difference in electric potential, which is called voltage. This is similar to the difference in gravitational potential that causes a ball to roll downhill. If imagining electricity like water, then voltage is lifting up one end of the pipe (or water going over a waterfall of a certain height).
“The violation of the standard theory of solids in these strange metals is so dramatic—it’s in your face,” says Qimiao Si, a physicist at Rice University who collaborates with Paschen.
One of the properties of electrons is spin. The stern-gerlach expt demonstrated spin on a macrosopic scale. Does spin play a role in the change of conductivity? In other words, does an externally applied magnetic field change the temperature at which superconductivity occurs or perhaps the slope of rising resistivity?
Progress is seeing the cloud from the particles I reckon. I am excited to see practical uses of measuring entanglement to push forward materials research. I’m curious about what other materials have linear changes related to temperature or other inputs, seems uncommon.
so electrons are just like photons being a wave/particle?
The article seems to suggest in strange metals
their particle properties are absent and only 'electron field' gradients move,
like if electrons exhanged their 'charge'.
Electrons are not just like photons. It's tempting to say that, but there are some significant differences that can lead you in error if you think in this picture.
First of all, if you think of a photon as some small ball, not that's not what it is. Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
Unlike photons, electrons have a position operator, so in principle you can measure and say where one electron is. The same is impossible for photons. Also electrons have a mass, but photon are massless. This means you can have motionless electrons, but this is impossible for photons: they always move at the speed of light. Electrons have a non-relativistic classical limit, while photon do not.
W. E. Lamb used to say that people should be required a license for the use of the word "photon", because it can be very misleading.
Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Since it lives and dies in the same instant, it can't have a position—because the moment it exists and the moment it doesn't is exactly the same time.
It takes time—even for light—to get from point A to point B. However, the measurement of any positions—relative to the photon itself—will always be the same. It's related to that property of quantum physics that allows two particles to exists in two different places at the same time.
> > > Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
> Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Would an appropriate analogy be a "glider" from Conway's Game of Life? "Lives and dies in the same instant" isn't exactly the same, but I'm thinking of how no parts of the glider move while the glider as a whole "moves" across the board.
Not just like photons. For one thing, they can travel slower than light. But many experiments on photons can also be done on electrons, such as diffraction. You can perform a double-slit experiment with electrons. Also, they're fermions, but photons are bosons.
IANAP, but I thought that quantum field theory (which isn't incredibly controversial) already treats particles as merely emergent convenient ways to describe common excitations of the fields. I'm surprised it isn't mentioned here at all.
A regular particle isn't really emergent, it corresponds 1:1 to the excitation of the field
Quasiparticles arise out of a collection of particles, that's why they're emergent
> A regular particle isn't really emergent, it corresponds 1:1 to the excitation of the field
Maybe 'emergent' was the wrong word here. I meant that particles are convenient ways of describing behavior of the fields in many (but not all) cases, with the fields themselves considered to be the (more) fundamental description of reality.
Eh, in the wave-particle duality wars you may have been swayed a bit too strongly into the wave camp.
Quantization exists and isn't just a convenience.
Quantization exists because of the waves though. It's a consequence of standing waves being produced when an excitation is confined. It's not AFAIK an axiom of QFT, more an emergent result.
What? QFT doesn't preclude quantization at all. You're attacking a weird straw man here.
And wave particle duality isn't some kind of scientific debate with camps on both sides.
Theoretical condensed matter here (though not an expert on strange metals specifically). The idea is that in a quantum many-body system, a (low-energy) state can often be represented as a set of independent excitations of the field, which are called quasiparticles. The "particle" picture for the Fermi liquid already operates in a framework of quantum fields. "No quasiparticles" means that there is no such representation, i.e., you can't say something like "these two states differ by an addition of a particle with such-and-such properties."
I would assume that's mostly a function of this being for a general audience. Yes, you absolutely can talk about quasiparticles using techniques adapted from QFT. I don't know if Landau originally conceived of it that way, but there were definitely a bunch of Soviet physicists shortly after him who did.
QFT is perfect for a single particle, but it gets harder to describe the behavior of particles en masse. It's super hard to find simplifications that reveal emergent behavior.
Great read! One fascinating to me is how the article frames the field as progressing once again now that researchers are getting over the quasi particle model.
Reminds me of the elephant and rope adage: young elephants are trained with small chains, which as they mature they outsized and could easily break but don't.
Though to give credit to researchers, those new experiments of "listening" for electron perturbations seem amazing. That's just a brilliant idea. Theorists often like to pretend they're better than the experimentalists, but without proper data the theorists get stuck in dead ends. ;)
The article says that resisivity in normal metals follows a quadratic curve, but the article also says that it follows an exponential curve. Does anyone know which it right?
If I'm reading Wikipedia correctly, the formula is quadratic for some metals, and cubic or quintuplic(?) for others: https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...
Typically, the behavior of any given metal is a mix of mechanisms so the measured behavior is fit to a curve where you fit n. So for metals the exponent is typically a decimal between 2 and 5.
Thanks, I appreciate the explanation. :)
You would normally just say "5th degree" or "5th power".
But the specific word they were looking for is "quintic". (And the corresponding word for 4th-degree, in case anyone is curious, is "quartic"; one sometimes sees "biquadratic", which unfortunately is also sometimes used to describe a particular subset of quartics.)
Oh right, silly me. Wow, my own vocabulary deserted me there, huh?
Yeah I think generally "sextic" is the highest you see before people stop doing that, and that one's somewhat uncommon I'd say. ("Quintic" is actually fairly common, contrary to what I said earlier, oops.) The fact that seventh-degree would be "septic" might be one reason stop with the words at that point!
I'm pretty sure that more than half the times I've seen "quintic" are in one single context: talking about the fact that while you can solve polynomial equations of degree 1-4 by doing arithmetic and taking n'th roots, this stops being possible once you get as far as quintic equations. (The "insolubility of the quintic".)
afaiu quadratic is a subtype of exponential, so they are not mutually exlusive
No. Exponential growth or decay is much faster than quadratic growth or decay. You may be mixing up exponential functions, of the form x maps to ab^x, with power functions, of the form x maps to ax^b. These are very different!
Annoyingly, people often use "exponential" colloquially to mean anything faster than linear, but in fact lots of things are faster than linear.
Ouch, not a good look for a technical article.
From the other responses, it sounds like "none of the above". It's more like a "polynomial curve" that is only sometimes quadratic. Is "polynomial curve" a thing? "Power curve" / "power function"?
So superconductivity is a laminar flow of electron goop?
Ok, it's different in that liquid flows through pipes and electrons flow through crystal lattices or whatever, so electrons go between and around the material while liquid is bounded by it.
It makes me speculate that electron flow through a metal is sort of like liquid flowing through a compressible boundary tube, whereas flow through a non-metal has rigid walls. Non-metals reject the electrons, metals allow them to play Spiderman and hitch a temporary ride (if you'll forgive the overly particle-centric analogy.)
If resistivity is determined by the equivalent of turbulence, though, I've no idea what the graph against temperature should be. Do electrons travel faster when there's less resistance?
Turbulence on a small scale acts like increased viscosity on a large scale, because they're both forms of momentum diffusion. However, current doesn't have any momentum diffusion terms, the momentum is lost to the conductor.
AFAIK nothing stops an electron from existing in the same space as a proton or neutron - they don't have to go around. Indeed that's required for certain kinds of radioactive decay to occur. Not all electron orbitals overlap the nucleus, but some do.
TL;DR: the analogy is helpful at a high level, but has limitations when you look closely.
> Ok, it's different in that liquid flows through pipes and electrons flow through crystal lattices or whatever, so electrons go between and around the material while liquid is bounded by it.
This is not perfect, but it works at a high level.
The main difference with e.g. water flows is that what restricts electron flux is traps. Electrons are not limited by walls that prevents them from going outside channels, instead they are held in place by atoms’ nuclei.
In a conductor, the “force” holding them is effectively zero, so when an electron comes in on one side, another one comes out of the other.
In a semiconductor. An electron needs some energy to get out of its trap before it can move. Then, “freed” electrons hop from trap to trap and the current is the overall effect of this. Electrons do not have to move far to create a current, there just needs to be enough of them. There is no real macroscopic analogy for this.
In an insulator, electrons just don’t get out of their traps because the energy required is too large.
This ignores a lot of details and quantum effects, but it is still a useful way to think about this.
> It makes me speculate that electron flow through a metal is sort of like liquid flowing through a compressible boundary tube, whereas flow through a non-metal has rigid walls.
Not really. Electrons moving in a metal are slowed down by a lot of different phenomena but this cannot really be considered as a compressible fluid. The effect is more similar to viscosity than compressibility.
In non-metals, electrons just don’t move unless they are made available, for example by doping or with a source of energy.
> Non-metals reject the electrons, metals allow them to play Spiderman and hitch a temporary ride
The general model is that metals let electrons flow and non-metals hold on to them.
> If resistivity is determined by the equivalent of turbulence, though, I've no idea what the graph against temperature should be. Do electrons travel faster when there's less resistance?
The analogy kind of breaks down here. There are competing effects and conductivity as a function of time is often highly non-trivial. In general, the number of electrons available increases with temperature, but scattering by other electrons, vibrations and defects also increases. Overall, resistivity tends to increase with temperature in metals and decrease in semiconductors, but there are exceptions.
How should we visualize what pushes the electron goop forward? If it's like water pressure, that would make the hindmost goop bunch up with the foremost goop.
Presumably electricity has something to do with positive charge at the back of the 'pipe' and negative charge at the 'front' (or have I got those backward?), perhaps a better visualization would be that they're all rolling down an inclined plane together?
Current flows due to a difference in electric potential, which is called voltage. This is similar to the difference in gravitational potential that causes a ball to roll downhill. If imagining electricity like water, then voltage is lifting up one end of the pipe (or water going over a waterfall of a certain height).
To sum it up:
“The violation of the standard theory of solids in these strange metals is so dramatic—it’s in your face,” says Qimiao Si, a physicist at Rice University who collaborates with Paschen.
“There’s no question there’s new physics.”
One of the properties of electrons is spin. The stern-gerlach expt demonstrated spin on a macrosopic scale. Does spin play a role in the change of conductivity? In other words, does an externally applied magnetic field change the temperature at which superconductivity occurs or perhaps the slope of rising resistivity?
Progress is seeing the cloud from the particles I reckon. I am excited to see practical uses of measuring entanglement to push forward materials research. I’m curious about what other materials have linear changes related to temperature or other inputs, seems uncommon.
After reading this all I can think of is Newton's cradle.
Electron goes into one side, another electron shoot out from the other side.
It didn't went through, but acting like one. "quasi" particle maybe?
I have no idea what's going on, correct me if I am wrong
so electrons are just like photons being a wave/particle? The article seems to suggest in strange metals their particle properties are absent and only 'electron field' gradients move, like if electrons exhanged their 'charge'.
Electrons are not just like photons. It's tempting to say that, but there are some significant differences that can lead you in error if you think in this picture.
First of all, if you think of a photon as some small ball, not that's not what it is. Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
Unlike photons, electrons have a position operator, so in principle you can measure and say where one electron is. The same is impossible for photons. Also electrons have a mass, but photon are massless. This means you can have motionless electrons, but this is impossible for photons: they always move at the speed of light. Electrons have a non-relativistic classical limit, while photon do not.
W. E. Lamb used to say that people should be required a license for the use of the word "photon", because it can be very misleading.
Why don't photons have a position operator?
It’s really not accurate to say that a photon has no position at all. How would a photodiode work? You have to be careful with this stuff. https://physics.stackexchange.com/questions/492711/whats-the...
Photons certainly appear to have a real physical location with 1e9 FPS imaging capabilities:
"Visualizing video at the speed of light — one trillion frames per second" (2012) https://youtube.com/watch?v=EtsXgODHMWk&
But is there an identity function for a photon(s), and is "time-polarization" necessary for defining an identity function for photons?
Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Since it lives and dies in the same instant, it can't have a position—because the moment it exists and the moment it doesn't is exactly the same time.
It takes time—even for light—to get from point A to point B. However, the measurement of any positions—relative to the photon itself—will always be the same. It's related to that property of quantum physics that allows two particles to exists in two different places at the same time.
> > > Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
> Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Would an appropriate analogy be a "glider" from Conway's Game of Life? "Lives and dies in the same instant" isn't exactly the same, but I'm thinking of how no parts of the glider move while the glider as a whole "moves" across the board.
Yeah, electrons are waves and experience quantum tunneling which we see in high density electronics and specifically apply in flash memories.
Not just like photons. For one thing, they can travel slower than light. But many experiments on photons can also be done on electrons, such as diffraction. You can perform a double-slit experiment with electrons. Also, they're fermions, but photons are bosons.
All matter is wavelike. Even some molecules comprised of multiple particles have been empirically proven to exhibit wavelike behavior.
https://en.wikipedia.org/wiki/Matter_wave
Yeah, everything is just like photons, everything is a wave/particle
[dead]