Multivalley Superconductivity in Monolayer Transition Metal Dichalcogenides

Enhanced Backgate Tunability on Interfacial Carrier Concentration in Ionic Liquid-Gated MoS2 Devices

The periodic spatial modulation potential arising from the zig-zag distribution of ions at large gate voltage in an ionic liquid-gated device may enable functionalities in a similar way as nanopatterning and moiré engineering. However, the inherent coupling between periodic modulation potential and carrier concentration in ionic liquid devices has hindered further exploration. Here, the feasibility of decoupling manipulation on periodic modulation potential and carrier density in an ionic liquid device is demonstrated by using a conventional backgate. The backgate is found to have a tunability on carrier concentration comparable to that of ionic gating, especially at large ionic liquid gate voltage, by activating the bulk channels mediated back tunneling between the trapped bands and interfacial channel.

Unveiling the Correlation between Defects and High Mobility in MoS2 Monolayers

Defects in semiconductors play a crucial role in modifying their electronic structure and transport properties. In transition metal dichalcogenides, atomic chalcogen vacancies are a primary source of intrinsic defects. While the impact of these vacancies on electrical transport has been widely studied, their exact role remains not fully understood. In this work, we correlate optical spectroscopy, low-temperature electrical transport measurements, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations to explore the effect of chalcogen vacancies in MoS2 monolayers grown by chemical vapor deposition. We specifically highlight the role of disulfur vacancies in modulating electrical properties, showing that these defects increase the density of shallow donor states near the conduction band, which facilitates electron hopping conduction, as evidenced by low-temperature transport and STM measurements. These findings are further supported by DFT calculations, which reveal that the electronic states associated with these defects are relatively delocalized, promoting hopping conduction and inducing n-type doping. This mechanism accounts for the observed high field-effect mobility (>100 cm2 V-1s-1) in the samples. These findings highlight the potential for defect engineering as a universal approach to customizing the properties of 2D materials for various applications.

Controllable p-type doping and improved conductance of few-layer WSe2via Lewis acid

Manipulation of the electronic properties of layered transition-metal dichalcogenides (TMDs) is of fundamental significance for a wide range of electronic and optoelectronic applications. Surface charge transfer doping is considered to be a powerful technique to regulate the carrier density of TMDs. Herein, the controllable p-type surface modification of few-layer WSe2by FeCl3Lewis acid with different doping concentrations have been achieved. Effective hole doping of WSe2has been demonstrated using Raman spectra and XPS. Transport properties indicated the p-type FeCl3surface functionalization significantly increased the hole concentration with 1.2 × 1013cm-2, resulting in 6 orders of magnitude improvement for the conductance of FeCl3-modified WSe2compared with pristine WSe2. This work provides a promising approach and facilitate the further advancement of TMDs in electronic and optoelectronic applications.

Synthesis and Characterization of 2D Ternary Compound TMD Materials Ta3VSe8

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are garnering considerable scientific interest, prompting discussion regarding their prospective applications in the fields of nanoelectronics and spintronics while also fueling groundbreaking discoveries in phenomena such as the fractional quantum anomalous Hall effect (FQAHE) and exciton dynamics. The abundance of binary compound TMDs, such as MX2 (M = Mo, W; X = S, Se, Te), has unlocked myriad avenues of exploration. However, the exploration of ternary compound TMDs remains relatively limited, with notable examples being Ta2NiS5 and Ta2NiSe5. In this study, we report the synthesis of a new 2D ternary compound TMD materials, Ta3VSe8, employing the chemical vapor transport (CVT) method. The as-grown bulk crystal is shiny and can be easily exfoliated. The crystal quality and structure are verified by X-ray diffraction (XRD), while the surface morphology, stoichiometric ratio, and uniformity are determined by scanning electron microscopy (SEM). Although the phonon property is found stable at different temperatures, magneto-resistivity evolves. These findings provide a possible approach for the realization and exploration of ternary compound TMDs.

Van Hove singularity driven enhancement of superconductivity in two-dimensional tungsten monofluoride (WF)

Superconductivity in two-dimensional materials has gained significant attention in the last few years. In this work, we report phonon-mediated superconductivity investigations in monolayer Tungsten monofluoride (WF) by solving anisotropic Migdal Eliashberg equations as implemented in EPW. By employing first-principles calculations, our examination of phonon dispersion spectra suggests that WF is dynamically stable. Our results show that WF has weak electron-phonon coupling (EPC) strength (λ) of 0.49 with superconducting transition temperature (Tc) of 2.6 K. A saddle point is observed at 0.11 eV below the Fermi level (EF) of WF, which corresponds to the Van Hove singularity (VHS). On shifting the Fermi level to the VHS by hole doping (3.7 × 1014cm-2), the EPC strength increases to 0.93, which leads to an increase in theTcto 11 K. However, the superconducting transition temperature of both pristine and doped WF increases to approximately 7.2 K and 17.2 K, respectively, by applying the Full Bandwidth (FBW) anisotropic Migdal-Eliashberg equations. Our results provide a platform for the experimental realization of superconductivity in WF and enhancement of the superconducting transition temperature by adjusting the position ofEFto the VHS.