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We demonstrate that the exciton energy of a monolayer of tungsten diselenide on an SiO2/Si substrate can be tuned by an applied in-plane electric field for two samples with different dielectric capping materials. The exciton energy can be either red- or blue-shifted by up to 20 meV based on the polarity of the applied electric field. We argue that a piezoelectric effect creates a large internal electric field, which is either partially aligned or partially antialigned with the external electric field. Additionally, optical hysteresis is observed on cycling of the external electric field due to trapped charges. [ABSTRACT FROM AUTHOR]

Abstract Single atomic layers of two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for integration of optical and electronic circuits due to their extraordinary optical oscillator strength and large exciton binding energy. Customizing the exciton energy of the TMDs is a direct way to control the light-matter interaction. Here we demonstrate that the electronic band gap of tungsten diselenide WSe 2 can be tuned continuously with the application of the uniaxial tensile strain. The energy is redshifted with a rate of ∼62.5 meV/% strain for exciton A, determined by photoluminescence spectroscopy along with Finite Element Method modeling using the commercial software ANSYS. The uniaxial bandgap deformation potential (DP) of the electronic bandgap of monolayer WSe 2 can be computed directly from our measurements and is about −6.3 ± 0.5 eV. Our results agree well with first-principles calculations. The ability to control the renormalization of the bandgap in 2D materials with strain could be used in flexible electronics or optoelectronic devices such as a TMDs based microcavity. Highlights • The electronic band gap of WSe 2 can be tuned continuously with the application of the uniaxial tensile strain. • The uniaxial bandgap ADP of the electronic bandgap of monolayer WSe 2 can be computed directly from our measurements. • Our results agree well with first-principles calculations. • Modifying the bandgap in 2D materials with strain could be used in flexible electronics or optoelectronic devices. [ABSTRACT FROM AUTHOR]

In non-Hermitian open quantum systems, such as polariton condensates, the local tailoring of gains and losses opens up an interesting possibility to realize functional optical elements. Here, we demonstrate that deliberately introducing losses via a photonic defect, realized by reducing the quality factor of a DBR mirror locally within an ultrahigh-quality microcavity, may be utilized to create directed polariton currents towards the defect. We discuss the role of polariton–polariton interactions in the process and how to tailor the effective decay time of a polariton condensate by coupling it to the defect. Our results highlight the far-reaching potential of non-Hermitian physics in polaritonics. [ABSTRACT FROM AUTHOR]

Phase fluctuations determine the low-energy properties of quantum condensates. However, at the condensation threshold, both density and phase fluctuations are relevant. While strong emphasis has been given to the investigation of phase fluctuations, which dominate the physics of the quantum system away from the critical point, number fluctuations have been much less explored even in thermal equilibrium. In this work, we report experimental observation and theoretical description of fluctuations in a circularly confined nonequilibrium Bose-Einstein condensate of polaritons near the condensation threshold. We observe critical fluctuations, which combine the number fluctuations of a single-mode condensate state and competition between different states. The latter is analogous to mode hopping in photon lasers. Our theoretical analysis indicates that this phenomenon is of a quantum character, while classical noise of the pump is not sufficient to explain the experiments. The manifestation of a critical quantum state competition unlocks possibilities for the study of condensate formation while linking to practical realizations in photonic lasers. [ABSTRACT FROM AUTHOR]