  The recent discovery of superconductivity (SC) and charge density wave (CDW)
in kagome metals AV3Sb5 (A = K, Rb, Cs) provides an ideal playground for the
study of emergent electronic orders. Application of moderate pressure leads to
a two-dome-shaped SC phase regime in CsV3Sb5 accompanied by the destabilizing
of CDW phase; such unconventional evolution of SC may involve the
pressure-induced formation of a new stripe-like CDW order resembling that in
La-214 cuprate superconductors. Nonetheless, the nature of this pressure-tuned
SC state and its interplay with the stripe order are yet to be explored. Here,
we perform soft point-contact spectroscopy (SPCS) measurements in CsV3Sb5 to
investigate the evolution of superconducting order parameter with pressure.
Surprisingly, we find that the superconducting gap is significantly enhanced
between the two SC domes, at which the zero-resistance temperature is
suppressed and the transition is remarkably broadened. Moreover, the
temperature dependence of the SC gap in this pressure range severely deviates
from the conventional BCS behavior, evidencing for strong Cooper pair phase
fluctuations. These findings reveal the complex intertwining of the stripe-like
CDW with SC in the compressed CsV3Sb5, suggesting striking parallel to the
cuprate superconductor La2-xBaxCuO4. Our results point to the essential role of
charge degree of freedom in the development of intertwining electronic orders,
thus provides new constraints for theories.
