Dimensional reduction and ionic gating induced enhancement of superconductivity in atomically thin crystals of 2H-TaSe₂

Abstract

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.