[Paper] Anomalous Superfluid Density in a Disordered Charge-Density-Wave Material: Pd-Intercalated ErTe$_3$
Our new study about a rapid increase of the superfluid density in quasi-2D superconductors below the transition was published in Physical Review Letters on July 15, 2024, and selected as the Editors' Suggestion.
The superfluid density, a crucial parameter indicating the stiffness of the superconducting order parameter, typically shows a mild increase in its temperature derivative near the critical temperature $T_c$ for conventional 3D BCS(Bardeen-Cooper-Schrieffer) superconductors. Exceptionally, in 2D systems thinner than the coherence length, a sharp temperature derivative near $T_c$ is expected. Thermal fluctuations are more substantial in low-dimensional systems, reducing $T_c$ from the BCS theory value to the Berezinskii-Kosterlitz-Thouless transition temperature.
However, we observed a significant increase in this derivative near $T_c$ for quasi-2D layered superconductors Pd$_x$ErTe$_3$, suggesting the influence of quantum phase fluctuations in addition to thermal fluctuations. Using the scanning SQUID(Superconducting QUantum Interference Device) susceptometry, we examined the local superfluid responses in quasi-2D layered superconductors,Pd$_x$ErTe$_3$, materials known for their disordered charge density waves. These responses reveal a homogeneous superfluid density that markedly increases near $T_c$, deviating from the expected behavior in conventional 3D BCS superconductors. Our findings align with simulations from the quantum rotor model, indicating that quantum phase fluctuations are crucial in suppressing the critical temperature. These results underscore the utility of temperature-dependent superfluid density in exploring quantum phase fluctuations in quasi-2D superconductors.