Abstract
Understanding the coexistence, competition and/or cooperation between superconductivity and charge density waves (CDWs) in the transition metal dichalcogenides (TMDs) is an elusive goal which, when realized, promises to reveal fundamental information on this important class of materials. Here, we use four-terminal current-voltage measurements to study the Van der Waals interface between freshly exfoliated flakes of the high-Tc superconductor, Bi-2212, and the CDW-dominated TMD layered material, 1T-TaS2. For highly transparent barriers, there is a pronounced Andreev reflection feature providing evidence for proximity-induced high-Tc superconductivity in 1T-TaS2 with a surprisingly large energy gap (~20 meV) equal to half that of intrinsic Bi-2212 (~40 meV). Our systematic study using conductance spectroscopy of junctions with different transparencies also reveals the presence of two separate boson modes, each associated with a “dip-hump” structure. We infer that the proximity-induced high-Tc superconductivity in the 1T-TaS2 is driven by coupling to the metastable metallic phase coexisting within the Mott commensurate CDW (CCDW) phase and associated with a concomitant change of the CCDW order parameter in the interfacial region.
Highlights
In the past few decades, the study of interfaces between novel materials including metals, semiconductors, superconductors, topological insulators and layered materials harboring charge density waves (CDWs) has generated the emergence of unexpected phenomena
For even lower transparency interfaces, such as Junction-5 with BTK parameter Z = 2.5 shown in Fig. 5(b), any remnants of a superconducting proximity effect with markers at Δp and Δa have disappeared
From the linear DC I–V characteristics (seen in Figs 2(a) and S.5(a,b)), the normalized zero-bias conductance (NZBC) for Junction-1 with Z = 0.25 divided by the conductance at 100 K is calculated and shown in Fig. 6(a) as a function of temperature for the cooling cycle
Summary
In the past few decades, the study of interfaces between novel materials including metals, semiconductors, superconductors, topological insulators and layered materials harboring charge density waves (CDWs) has generated the emergence of unexpected phenomena. These discoveries require a new understanding of underlying mechanisms which in turn may well lead to promising new technologies. We find evidence for proximity-induced high-Tc superconductivity in the topmost layers of pristine 1T-TaS2 at the interface of Van der Waals bonded Bi-2212/1T-TaS2 junctions, where pristine Bi-2212 is the high-Tc superconductor Bi2Sr2CaCu2O8+δ with a transition temperature Tc = 85 K and intrinsic energy gap Δ0 = 40 meV. The proximity induced gap Δa in the 1T-TaS2 is found to be a surprisingly large 20 meV, thereby implying a strong coupling limit (2Δsc/kBTc ~ 5.8)
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