Destruction of superconductivity through phase fluctuations in ultrathin <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>a</mml:mi></mml:math>-MoGe films
Soumyajit Mandal, Surajit Dutta, Somak Basistha, Indranil Roy, John Jesudasan, Vivas Bagwe, Lara Benfatto, A. Thamizhavel, Pratap Raychaudhuri
Abstract
Superconductivity occurs in metals when attractive interactions between electrons promote the formation of Cooper pairs which get locked in a phase-coherent state, leading to superfluid behavior. In situations where the phase stiffness falls below the pairing energy, the superconducting transition temperature ${T}_{c}$ is driven by phase fluctuations and pairing can continue to survive above ${T}_{c}$. Such a behavior has long been thought of as the hallmark of unconventional superconductivity. Here we combine sub-K scanning tunneling spectroscopy, magnetic penetration depth measurements, and magnetotransport measurements to show that in ultrathin amorphous MoGe ($a$-MoGe) films the superfluid density is strongly suppressed by quantum phase fluctuations at low temperatures for thickness below 5 nm. This is associated with a rapid decrease in the superconducting transition temperature ${T}_{c}$ and the emergence of a pronounced pseudogap above ${T}_{c}$. These observations suggest that even in conventional superconductors strong disorder and low dimensionality will ultimately trigger a Bosonic route for the destruction of superconductivity.