Kavli Affiliate: Ke Wang
| First 5 Authors: Ke Wang, Ke Wang, , ,
| Summary:
Pair-density-wave (PDW) states — exotic superconductors with spatially
modulated order — are a long-sought-after phase of quantum materials, with the
potential to unravel the mysteries of high-$T_c$ cuprates and other strongly
correlated superconductors. Yet, surprisingly, a key signature of stable
superconductivity, namely the positivity of the superfluid density, $n_s(T)$,
has not yet been demonstrated. Here, we address this central issue by
calculating $n_s(T)$, for a generic model two-dimensional PDW superconductor.
We uncover a surprisingly large region of intrinsic instability, associated
with negative $n_s(T)$, revealing that a significant portion of the parameter
space thought to be physical cannot support superconducting order. This
instability is driven by the large pairing momentum required to form the PDW
state. In the remaining stable regime, we predict two striking and observable
fingerprints: an anomalously small longitudinal superfluid response that is
vulnerable to thermal fluctuations, and an unusual temperature dependence for
$n_s(T)$ arising from the unique gapless excitation spectrum of the PDW state.
These generally model independent, as well as experimentally relevant findings
suggest that the fragility of the superfluid density poses a significant
problem for the formation of stable, finite temperature PDW superconductivity.
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