Superconductivity is current flow without electrical resistance. Theoretical and experimental physicists are working to discover and explain the underlying fundamental mechanisms of superconductivity. Intensive research on superconductivity is driven by the possibility of new applications in energy and motor technology.
Of particular interest is the material strontium ruthenate. In this compound, superconductivity is accompanied by spontaneous ring currents which, unlike normal currents in metal wires or supercurrents in conventional superconductors, occur as a property of the ground state—comparable to the electron motion in atomic orbitals, but in a superconductor, it is caused by the collective motion of many electrons. Since this special type of superconductivity with spontaneous currents is also relevant for quantum computing, strontium ruthenate could also be significant for future applications of superconductivity.
In a paper just published in the journal Nature Physics, subatomic particles called muons were used as probes to experimentally detect these subtle electric currents in superconducting strontium ruthenate using the resulting magnetic fields. When strontium ruthenate is subjected to uniaxial pressure, the spontaneous currents start at a lower temperature than superconductivity. In other words, the transition splits into two regions: first superconductivity, then spontaneous currents. Such a split with symmetry-breaking pressure has never been demonstrated in any other material, requiring a new view of previous theoretical models.
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