Abstract

One of the most exciting recent developments in condensed matter research has been the demonstra-
tion of superconductivity in superhydrides near room temperature but at very high pressure [1]. The
compressed superhydrides demonstrate the potential of engineering a phonon-mediated superconduct-
ing pairing mechanism towards optimal outcomes. Further gains are possible by widening the scope
towards unconventional superconductors, which harness the strong electronic interactions that are also
responsible for magnetism and that are known in some cases to reach coupling strengths equivalent to
several thousand Kelvin.
We need new superconductors with superior properties, be it transition temperature, critical current
or magnetic field, metallurgy or cost, because they can have transformative impact in applications such
as powerful magnets in MRI scanners, particle accelerators and fusion research, lightweight generators,
loss-free power transmission, microwave devices, low-power, fast electronics, and quantum computing.
Unconventional superconductivity is rare, and locating it by random search within the combinatori-
ally large material space is ineffective. Fig. 1 illustrates that it is usually confined to a narrow parameter
range close to the threshold of magnetic order [2], which in turn can be used to guide the search. Using
such heuristic guiding principles, the Quantum Matter group have found several new superconductors,
most recently the layered iron germanide YFe2Ge2, its sister compound LuFe2Ge2, and the high pres-
sure phase of CeSb2.
Materials are complicated. Numerous factors – competing interactions, disorder, structural transi-
tions, the role of orbital and charge degrees of freedom – interfere with simple guiding principles but also
represent tuning parameters that may be used to advantage. The talk will present high pressure and
quantum oscillation measurements in (Y/Lu)Fe2Ge2, CeSb2, and UTe2 [3] to illustrate opportunities and
challenges in the search for new unconventional superconductors.