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Arthur T Knackerbracket has processed the following story:

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.”

[...] 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.

[...] 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.

[...] 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.

[...] “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

Original Submission