The optoelectronic and transport properties of two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are highly susceptible to external perturbation, enabling precise tailoring of material function through post-synthetic modifications. Here we show that nanoscale inhomogeneities known as nanobubbles can be used for both strain and, less invasively, dielectric tuning of exciton transport in bilayer tungsten disulfide (WSe2). We use ultrasensitive spatiotemporally resolved optical scattering microscopy to directly image exciton transport, revealing that dielectric nanobubbles are surprisingly efficient at funneling and trapping excitons at room temperature, even though the energies of the bright excitons are negligibly affected. Our observations suggest that exciton funneling in dielectric inhomogeneities is driven by momentum-indirect (dark) excitons whose energies are more sensitive to dielectric perturbations than bright excitons. These results reveal a new pathway to control exciton transport in 2D semiconductors with exceptional spatial and energetic precision using dielectric engineering of dark state energetic landscapes. Main text:Two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are van der Waals materials that hold great promise for nanoscale optoelectronics thanks to their strong light-matter interactions even at the atomically-thin limit. The optoelectronic properties of 2D TMDs are in large part governed by their Coulomb-bound electron-hole pairs (excitons), with relatively large binding energies of up to hundreds of milli-electronvolts (meV) due to weak out-of-plane dielectric screening. [1][2][3][4][5][6] Unlike free charges, excitons are charge neutral and are therefore difficult to manipulate with external electric fields in electronic devices. [7][8][9] Therefore, the transport properties of excitons are largely dictated by random, diffusive motion with no long-range directionality, limiting their use as information and energy carriers. Finding new ways to manipulate exciton transport in 2D TMDs without radically altering other material properties would result in excitonic devices that combine strong light-matter interactions and precise control over energy and information flow in atomically thin materials.An attractive route to controlling the properties of 2D TMDs is to leverage their extreme sensitivity to extrinsic factors such as strain, 10-21 and dielectric screening by the environment (Figure 1a), 5,[22][23][24][25][26] enabling post-synthetic tuning of their optoelectronic and transport properties. For example, tensile strain reduces the optical transition energy of 2D TMDs; 16,18,27,28 localized strain regions thus create energy gradients that can funnel and trap excitons in nanoscale low-energy sites, a process that was leveraged to create long-lived quantum emitters. 14,[29][30][31][32][33] Strain engineering, however, is difficult to control over macroscopic scales and can introduce undesired disorder.A less invasive and in principle more contr...
To study the mutator phenotype characteristic of tumors showing widespread replication errors at simple DNA repeat sequences (RER+), we designed a selectable reporter system for the detection of such mutations in mammalian cells. A hygromycin B phosphotransferase gene was rendered out-of-frame by the insertion of a (CA)13 dinucleotide repeat tract immediately following the ATG start codon, and subcloned into a retroviral expression vector containing a G418 (neo) selectable marker. Following transduction of this construct into cultured cells, clonal neo+ cell lines were established and then tested for their ability to form colonies in hygromycin B-containing medium. Using this system, we found that the HCT116, LS174T and LS180 human colon carcinoma cell lines acquire hygromycin resistance (hygr) at a 100-fold higher frequency than the HT29, SW480, DLD-1 and HCT15 human colon carcinoma and NIH3T3 fibroblast cell lines, and at a 25-fold higher rate than the Rat 6 embyro fibroblast cell line. DNA sequence analysis indicated that frameshift mutations had occurred within the CA dinucleotide repeat tract in HCT116 cells that became hygr. Thus, the mutation rates at simple repeated sequences in mammalian cell lines can be readily determined and studied using this system.
We develop a microscopic theory for the multimode polariton dispersion in materials coupled to cavity radiation modes. Starting from a microscopic light−matter Hamiltonian, we devise a general strategy for obtaining simple matrix models of polariton dispersion curves based on the structure and spatial location of multilayered 2D materials inside the optical cavity. Our theory exposes the connections between seemingly distinct models that have been employed in the literature and resolves an ambiguity that has arisen concerning the experimental description of the polaritonic band structure. We demonstrate the applicability of our theoretical formalism by fabricating various geometries of multilayered perovskite materials coupled to cavities and demonstrating that our theoretical predictions agree with the experimental results presented here.
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