Posted on 02/16/2021 6:23:28 AM PST by Red Badger
Levitation of a magnet on top of a superconductor. Credit: Jubobroff, Fbouquet, LPS CC BY-SA 3.0
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A new theory that could explain how unconventional superconductivity arises in a diverse set of compounds might never have happened if physicists Qimiao Si and Emilian Nica had chosen a different name for their 2017 model of orbital-selective superconductivity.
In a study published last month in npj Quantum Materials, Si of Rice University and Nica of Arizona State University argue that unconventional superconductivity in some iron-based and heavy-fermion materials arises from a general phenomenon called “multiorbital singlet pairing.”
In superconductors, electrons form pairs and flow without resistance. Physicists cannot fully explain how pairs form in unconventional superconductors, where quantum forces give rise to strange behavior. Heavy fermions, another quantum material, feature electrons that appear to be thousands of times more massive than ordinary electrons.
Si and Nica proposed the idea of selective pairing within atomic orbitals in 2017 to explain unconventional superconductivity in alkaline iron selenides. The following year, they applied the orbital-selective model to the heavy fermion material in which unconventional superconductivity was first demonstrated in 1979.
They considered naming the model after a related mathematical expression made famous by quantum pioneer Wolfgang Pauli, but opted to call it d+d. The name refers to mathematical wave functions that describe quantum states.
“It’s like you have a pair of electrons that dance with each other,” said Si, Rice’s Harry C. and Olga K. Wiess Professor of Physics and Astronomy. “You can characterize that dance by s- wave, p-wave and d-wave channels, and d+d refers to two different kinds of d-waves that fuse together into one.”
In the year after publishing the d+d model, Si gave many lectures about the work and found audience members frequently got the name confused with “d+id,” the name of another pairing state that physicists have discussed for more than a quarter century.
“People would approach me after a lecture and say, ‘Your theory of d+id is really interesting,’ and they meant it as a compliment, but it happened so often it got annoying,” said Si, who also directs the Rice Center for Quantum Materials (RCQM).
In mid-2019, Si and Nica met over lunch while visiting Los Alamos National Laboratory, and began sharing stories about the d+d versus d+id confusion.
“That led to a discussion of whether d+d might be connected with d+id in a meaningful way, and we realized it was not a joke,” Nica said.
The connection involved d+d pairing states and those made famous by the Nobel Prize-winning discovery of helium-3 superfluidity.
“There are two types of superfluid pairing states of liquid helium-3, one called the B phase and the other the A phase,” Nica said. “Empirically, the B phase is similar to our d+d, while the A phase is almost like a d+id.”
The analogy got more intriguing when they discussed mathematics. Physicists use matrix calculations to describe quantum pairing states in helium-3, and that is also the case for the d+d model.
“You have a number of different ways of organizing that matrix, and we realized our d+d matrix for the orbital space was like a different form of the d+id matrix that describes helium-3 pairing in spin space,” Nica said.
Si said the associations with superfluid helium-3 pairing states have helped him and Nica advance a more complete description of pairing states in both iron-based and heavy-fermion superconductors.
“As Emil and I talked more, we realized the periodic table for superconducting pairing was incomplete,” Si said, referring to the chart physicists use to organize superconducting pairing states.
“We use symmetries — like lattice or spin arrangements, or whether time moving forward versus backward is equivalent, which is time-reversal symmetry — to organize possible pairing states,” he said. “Our revelation was that d+id can be found in the existing list. You can use the periodic table to construct it. But d+d, you cannot. It’s beyond the periodic table, because the table doesn’t include orbitals.”
Si said orbitals are important for describing the behavior of materials like iron-based superconductors and heavy fermions, where “very strong electron-electron correlations play a crucial role.”
“Based on our work, the table needs to be expanded to include orbital indices,” Si said.
Reference: “Multiorbital singlet pairing and d + d superconductivity” by Emilian M. Nica and Qimiao Si, 5 January 2021, npj Quantum Materials. DOI: 10.1038/s41535-020-00304-3
The research was supported by a startup grant from Arizona State University, the Department of Energy (DE-SC0018197), the Welch Foundation (C-1411) and the National Science Foundation (PHY-1607611).
RCQM is a multidisciplinary research effort that leverages the strengths and global partnerships of more than 20 Rice research groups.
Slight correction, the ones with opposite spin ( +1/2, -1/2) pair off. The pair together then has a net spin of zero, like a photon ( a boson), which do not obey the Pauli exclusion principle. This allows the electrons to flow without resistance.
Okay, they are gender neutral electrons....................
See post #21 for ‘slight correction’ to my oversimplified explanation, from takebackaustin......................
Silly me....here I thought this was a physics discussion of superconductors......
Now I will have to get a bag of Cheetos and a six-pack of Jolt cola and head to my basement computer to ponder......
OK, off topic tip. If anyone is lookin for strong magnets 🧲 Heard it on yojtube, haven’t tried it out yet to see if true r not though. Supposedly the old hdd’s have “rare earth magnets 🧲 in them. Supposed to be pretty powerful. Not sure where they located. But shouldn’t b hard to find if they are there.
J9ust look up first to see if true though. I haven’t had time, but will do so I. A few minutes
I know, right? Any third grade student knows that 😆
Tiny..........................
ok, If that helps you ... I would think of happily married couples having fewer interruptions on the dance floor, if we are going there. :)
Not gender neutral....each has an opposite spin but when combined they are neutral per post #21.
That would make them heterosexual.....Two different combining as one to superconduct......
These are very naughty electrons!😏
They looked an ok size on the following sire that shows how to get at them they look to be about 3 inches long or so, but are pretty powerful. I will make a knife sharpening jig which will use one to secure the knife to the ret to hold it steady while sharpening *(plus have a backrest to keep the knife j. Position too). The 3 inch magn e t should be perfed ft size for that
Here’s a ,ink if you wanna see how to remove them
https://www.instructables.com/Rare-Earth-Magnets-From-Old-Hard-Drives/
How old of a hard drive?
My old hard drive is barely 3 inches total!..............
Ah, it s gotta be the old larger ones, can’t remember the size now, but over 5 inches I beleive, the old PC hdds. Not laptop ones, though those might have them too, but smaller. If you have a computer repair shop nearby, you could prolly get some real cheap, ask for junk ones. I got a few that way. But also have 4 or so left over fro pre sdd days
The link shows the size, though they do show smaller ones next to it in first photo too, so they likely have magnets too
“But, sometimes, electrons that spin is the same direction will ‘stick together’ and sync their spins.
Get enough of these electrons to sync up and they will superconduct.”
Wait around long enough, and particle science always circles back to “spinning vortices in the ether”, even if they use different terms each time they head back in that direction.
Everything is waves. And 2 waves can combine in a semi-permanent traveling standing wave.
*taakes a bow*
Poor choice of example on your part. Eigen is the German word translating roughly to "own" or "characteristic of" which is what an Eigenvalue is.
Diagonalize the matrix representation of a quantum mechanical operator and the values down the diagonal, the eigenvalues, are the allowed values of that operator; if they are strictly real (non-imaginary) they correspond to the physical measurements. Also, such matrices are Hermitian -- their transpose is equal to their complex conjugate; which for diagonal elements requires them to be real.
(Memory from 30+ years ago.)
+1. More concise than my explanation, thank you.
Too Much Information.™ :-D
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