Abstract
The electrical phase transition in van der Waals (vdW) layered materials such as transition-metal dichalcogenides and Bi2Sr2CaCu2O8+x (Bi-2212) high-temperature superconductor has been explored using various techniques, including scanning tunneling and photoemission spectroscopies, and measurements of electrical resistance as a function of temperature. In this study, we develop one useful method to elucidate the electrical phases in vdW layered materials: indium (In)-contacted vdW tunneling spectroscopy for 1T-TaS2, Bi-2212 and 2H-MoS2. We utilized the vdW gap formed at an In/vdW material interface as a tunnel barrier for tunneling spectroscopy. For strongly correlated electron systems such as 1T-TaS2 and Bi-2212, pronounced gap features corresponding to the Mott and superconducting gaps were respectively observed at T = 4 K. We observed a gate dependence of the amplitude of the superconducting gap, which has potential applications in a gate-tunable superconducting device with a SiO2/Si substrate. For In/10 nm-thick 2H-MoS2 devices, differential conductance shoulders at bias voltages of approximately ± 0.45 V were observed, which were attributed to the semiconducting gap. These results show that In-contacted vdW gap tunneling spectroscopy in a fashion of field-effect transistor provides feasible and reliable ways to investigate electronic structures of vdW materials.
Highlights
The electrical phase transition in van der Waals layered materials such as transition-metal dichalcogenides and Bi2Sr2CaCu2O8+x (Bi-2212) high-temperature superconductor has been explored using various techniques, including scanning tunneling and photoemission spectroscopies, and measurements of electrical resistance as a function of temperature
Van der Waals layered materials such as two-dimensional (2D) transition-metal dichalcogenides (TMDCs) and B i2Sr2CaCu2O8+x (Bi-2212) have shown various electronic phases that emerge from many-body features such as a charge density wave (CDW) or superconductivity, depending on the temperature and carrier density[1,2,3,4,5,6,7,8,9]
We carried out In-contacted van der Waals (vdW) gap tunneling spectroscopy for 1T-TaS2, Bi-2212, and 2H-MoS2 using an field-effect transistor (FET) geometry
Summary
The electrical phase transition in van der Waals (vdW) layered materials such as transition-metal dichalcogenides and Bi2Sr2CaCu2O8+x (Bi-2212) high-temperature superconductor has been explored using various techniques, including scanning tunneling and photoemission spectroscopies, and measurements of electrical resistance as a function of temperature. For In/10 nm-thick 2H-MoS2 devices, differential conductance shoulders at bias voltages of approximately ± 0.45 V were observed, which were attributed to the semiconducting gap These results show that In-contacted vdW gap tunneling spectroscopy in a fashion of field-effect transistor provides feasible and reliable ways to investigate electronic structures of vdW materials. VdW gap tunneling spectroscopy based on a field-effect transistor (FET) design with carbon nanotubes (CNTs) with In metal contacts was demonstrated, r ecently[16,17] In this previous work, the local conductance peaks observed in the conductance vs bias voltage plot were shown to originate from the van Hove singularities corresponding to the sub-band structures of semiconducting and metallic CNTs. In the present study, we apply a type of FET with In contacts for various vdW layered materials (i.e., 1T-TaS2, Bi-2212, and 2H-MoS2) to demonstrate that In-contacted vdW gap tunneling spectroscopy is a feasible method to investigate the electrical DOS of vdW layered materials. The differential conductance obtained from the tunnel current at a cryogenic temperature reflects the DOS of the vdW material
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