Dimensional reduction and ionic gating induced enhancement of superconductivity in atomically thin crystals of...

The effects of dimensional reduction and ion intercalation on superconductivity (SC) in the presence of charge density waves (CDWs) in two-dimensional crystals of 2H-TaSe₂ were characterized. We prepared atomically thin crystals by mechanical exfoliation and performed electrical transport measurements on devices made by photolithography. The superconducting transition temperature (T _c ^SC ) was found to increase monotonically as the thickness decreased, changing from 0.14 K in the bulk to higher than 1.4 K for a 3-nm-thick crystal. The temperature dependence of upper critical field was found to be anomalous. The CDW transition temperature (T _c ^CDW ) was found to decrease, but to a less extent than T _c ^SC , from 120 K in the bulk to around 113 K for the 3-nm-thick crystal. In addition, ion intercalation was found to increase T _c ^SC and suppress T _c ^CDW in an atomically thin crystal of 2H-TaSe₂. The implications of these findings are discussed. We suggest that dimensional reduction and ion intercalation are potentially effective ways to engineer material properties for layered transition metal chalcogenides.