The exploration of unconventional superconductivity has entered a new frontier with
the emergence of exotic phases in quantum materials—from moiré superlattices to
topological semimetals. Probing the superfluid properties and pairing symmetry in
these systems is essential to understanding their unconventional behavior, yet
traditional techniques often falter when applied to atomically thin materials or those
with extremely low critical temperatures. Here, we present a novel approach that
“listens to the sound of superfluid” by probing the kinetic inductance of
superconductors through microwave resonant cavities. Variations in superfluid
stiffness perturb the cavity resonance frequency, enabling precise measurements of
the London penetration depth with parts-per-million sensitivity. This technique
provides unprecedented access to the superfluid response in fragile and low-
temperature superconductors. Applied to magic-angle twisted trilayer graphene and
the Weyl semimetal MoTe₂, our measurements uncover compelling signatures of
nodal superconductivity. In twisted trilayer graphene, we observe a linear
temperature dependence of the superfluid stiffness and a zero-temperature stiffness
that scales linearly with the critical temperature—echoing Uemura’s relation in
cuprates. In MoTe₂, the penetration depth exhibits a T 2 dependence down to
millikelvin temperatures. Most strikingly, both systems display the anomalous
nonlinear Meissner effect, where the superfluid response becomes current-
dependent—a hallmark of nodal quasiparticles.
These results offer strong evidence for unconventional pairing in both moiré and
topological superconductors, demonstrating how “listening” to the subtle resonances
of quantum fluids can illuminate the hidden symmetries of correlated electron matter.
Ref.: A. Banerjee, et. al., Nature 638, 93 (2025).