5 ms·
'Strange metals' point to a whole new way to understand electricity
- baerrie 1y agoProgress 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.
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- dinfinity 1y agoIANAP, 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.
- tux3 1y agoA 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
- dinfinity 1y ago> 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.
- colechristensen 1y agoEh, 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.
- dinfinity 1y agoWhat? QFT doesn't preclude quantization at all. You're attacking a weird straw man here.
- soulofmischief 1y agoAnd wave particle duality isn't some kind of scientific debate with camps on both sides.
- rcxdude 1y agoQuantization 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.
- jfengel 1y agoQFT 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.
- bkcooper 1y agoI 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.
- EvgeniyZh 1y agoTheoretical 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."
- countWSS 1y agoso 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'.
- toast0 1y agoYeah, electrons are waves and experience quantum tunneling which we see in high density electronics and specifically apply in flash memories.
- ChrisClark 1y agoYeah, everything is just like photons, everything is a wave/particle
- rnhmjoj 1y agoElectrons 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.
- whatshisface 1y agoWhy don't photons have a position operator?
- kens 1y agoThe 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?
- fwip 1y agoIf 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_conductivity#Metals https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...
- VygmraMGVl 1y agoTypically, 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.
- fwip 1y agoThanks, I appreciate the explanation. :)
- Sniffnoy 1y agoYou would normally just say "5th degree" or "5th power".
- gjm11 1y agoBut 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.)
- Sniffnoy 1y agoOh 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!
- sfink 1y agoSo 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?
- whatshisface 1y agoTurbulence 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.
- kergonath 1y agoTL;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.
- elcritch 1y agoGreat 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. ;)
- afsdef3f3wafew 1y ago[dead]
- est 1y agoAfter 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
- nonelog 1y agoTo 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.”
- bawana 1y agoOne 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?