# Linear Scaling of the Superfluid Density with the Critical Temperature in the Layered Superconductor 2H-NbSe_2

## TL;DR

This study shows that in the layered superconductor 2H-NbSe_2, the superfluid density scales linearly with the critical temperature under pressure, revealing an intrinsic unconventional superconductivity characteristic in transition metal dichalcogenides.

## Contribution

It demonstrates that the linear scaling between superfluid density and T_c is an intrinsic property of transition metal dichalcogenides, expanding understanding beyond cuprates.

## Key findings

- Superfluid density increases with pressure in 2H-NbSe_2.
- Superfluid density scales linearly with T_c.
- Superconducting gaps are unaffected by charge density wave suppression.

## Abstract

We report on high-pressure (p_max = 2.1 GPa) muon spin rotation experiments probing the temperature-dependent magnetic penetration depth in the layered superconductor 2H-NbSe_2. Upon increasing the pressure, we observe a substantial increase of the superfluid density n_s, which we find to scale linearly with T_c. This linear scaling is considered a hallmark feature of unconventional superconductivity, especially in high-temperature cuprate superconductors. Our current results, along with our earlier findings on 1T'-MoTe_2 (Z. Guguchia et. al., Nature Communications 8, 1082 (2017)), demonstrate that this linear relation is also an intrinsic property of the superconductivity in transition metal dichalcogenides, whereas the ratio T_c/T_F is approximately a factor of 20 lower than the ratio observed in hole-doped cuprates. We, furthermore, find that the values of the superconducting gaps are insensitive to the suppression of the quasi-two-dimensional CDW state, indicating that the CDW ordering and the superconductivity in 2H-NbSe_2 are independent of each other.