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  1. Abstract Engineering the properties of quantum materials via strong light-matter coupling is a compelling research direction with a multiplicity of modern applications. Those range from modifying charge transport in organic molecules, steering particle correlation and interactions, and even controlling chemical reactions. Here, we study the modification of the material properties via strong coupling and demonstrate an effective inversion of the excitonic band-ordering in a monolayer of WSe 2 with spin-forbidden, optically dark ground state. In our experiments, we harness the strong light-matter coupling between cavity photon and the high energy, spin-allowed bright exciton, and thus creating two bright polaritonic modesmore »in the optical bandgap with the lower polariton mode pushed below the WSe 2 dark state. We demonstrate that in this regime the commonly observed luminescence quenching stemming from the fast relaxation to the dark ground state is prevented, which results in the brightening of this intrinsically dark material. We probe this effective brightening by temperature-dependent photoluminescence, and we find an excellent agreement with a theoretical model accounting for the inversion of the band ordering and phonon-assisted polariton relaxation.« less
    Free, publicly-accessible full text available December 1, 2023
  2. Abstract Chemical vapor deposition (CVD)-grown monolayer (ML) molybdenum disulfide (MoS 2 ) is a promising material for next-generation integrated electronic systems due to its capability of high-throughput synthesis and compatibility with wafer-scale fabrication. Several studies have described the importance of Schottky barriers in analyzing the transport properties and electrical characteristics of MoS 2 field-effect-transistors (FETs) with metal contacts. However, the analysis is typically limited to single devices constructed from exfoliated flakes and should be verified for large-area fabrication methods. In this paper, CVD-grown ML MoS 2 was utilized to fabricate large-area (1 cm × 1 cm) FET arrays. Two differentmore »types of metal contacts (i.e. Cr/Au and Ti/Au) were used to analyze the temperature-dependent electrical characteristics of ML MoS 2 FETs and their corresponding Schottky barrier characteristics. Statistical analysis provides new insight about the properties of metal contacts on CVD-grown MoS 2 compared to exfoliated samples. Reduced Schottky barrier heights (SBH) are obtained compared to exfoliated flakes, attributed to a defect-induced enhancement in metallization of CVD-grown samples. Moreover, the dependence of SBH on metal work function indicates a reduction in Fermi level pinning compared to exfoliated flakes, moving towards the Schottky–Mott limit. Optical characterization reveals higher defect concentrations in CVD-grown samples supporting a defect-induced metallization enhancement effect consistent with the electrical SBH experiments.« less
    Free, publicly-accessible full text available March 8, 2023
  3. While MAX phases offer an exotic combination of ceramic and metallic properties, rendering them a unique class of materials, their applications remain virtually hypothetical. To overcome this shortcoming, a sol–gel based route is introduced that allows access to microwires in the range of tens of micrometers. Thorough structural characterization through XRD, SEM, EDS, and AFM demonstrates a successful synthesis of carbonaceous Cr 2 GaC wires, and advanced low temperature electronic transport measurements revealed resistivity behavior dominated by amorphous carbon. The tunability of electronic behavior of the obtained microwires is shown by a halide post-synthesis treatment, allowing purposeful engineering of themore »microwires’ electrical conductivity. Raman studies revealed the polyanionic nature of the intercalated halides and a slow decrease in halide concentration was concluded from time-dependent conductivity measurements. Based on these findings, the process is considered a viable candidate for fabricating chemiresistive halogen gas sensors.« less
    Free, publicly-accessible full text available January 20, 2023
  4. Free, publicly-accessible full text available February 1, 2023
  5. Abstract Heterobilayers of transition metal dichalcogenides (TMDCs) can form a moiré superlattice with flat minibands, which enables strong electron interaction and leads to various fascinating correlated states. These heterobilayers also host interlayer excitons in a type-II band alignment, in which optically excited electrons and holes reside on different layers but remain bound by the Coulomb interaction. Here we explore the unique setting of interlayer excitons interacting with strongly correlated electrons, and we show that the photoluminescence (PL) of interlayer excitons sensitively signals the onset of various correlated insulating states as the band filling is varied. When the system is inmore »one of such states, the PL of interlayer excitons is relatively amplified at increased optical excitation power due to reduced mobility, and the valley polarization of interlayer excitons is enhanced. The moiré superlattice of the TMDC heterobilayer presents an exciting platform to engineer interlayer excitons through the periodic correlated electron states.« less
    Free, publicly-accessible full text available December 1, 2022
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  7. Free, publicly-accessible full text available September 30, 2022
  8. Abstract Interlayer excitons in layered materials constitute a novel platform to study many-body phenomena arising from long-range interactions between quantum particles. Long-lived excitons are required to achieve high particle densities, to mediate thermalisation, and to allow for spatially and temporally correlated phases. Additionally, the ability to confine them in periodic arrays is key to building a solid-state analogue to atoms in optical lattices. Here, we demonstrate interlayer excitons with lifetime approaching 0.2 ms in a layered-material heterostructure made from WS 2 and WSe 2 monolayers. We show that interlayer excitons can be localised in an array using a nano-patterned substrate. Thesemore »confined excitons exhibit microsecond-lifetime, enhanced emission rate, and optical selection rules inherited from the host material. The combination of a permanent dipole, deterministic spatial confinement and long lifetime places interlayer excitons in a regime that satisfies one of the requirements for simulating quantum Ising models in optically resolvable lattices.« less
    Free, publicly-accessible full text available December 1, 2022