We perform absorption and photoluminescence spectroscopy of trions in hBN-encapsulated WSe2, WS2, MoSe2, and MoS2 monolayers, depending on temperature. The different trends for W-and Mo-based materials are excellently reproduced considering a Fermi-Dirac distribution of bright and dark trions. We find a dark trion, 19 meV below the lowest bright trion, in WSe2 and WS2. In MoSe2, lies 6 meV above , while and almost coincide in MoS2. Our results agree with GW-BSE ab-initio calculations and quantitatively explain the optical response of doped monolayers with temperature.
We demonstrate the back-end integration of optically broadband, high-NA GaN micro-lenses by micro-assembly onto non-native semiconductor substrates. We developed a highly parallel process flow to fabricate and suspend micron scale plano-convex lens platelets from 6" Si growth wafers and show their subsequent transfer-printing integration. A growth process targeted at producing unbowed epitaxial wafers was combined with optimisation of the etching volume in order to produce flat devices for printing. Lens structures were fabricated with 6 − 11 µm diameter, 2 µm height and root-mean-squared surface roughness below 2 nm. The lenses were printed in a vertically coupled geometry on a single crystalline diamond substrate and with µm-precise placement on a horizontally coupled photonic integrated circuit waveguide facet. Optical performance analysis shows that these lenses could be used to couple to diamond nitrogen vacancy centres at micron scale depths and demonstrates their potential for visible to infrared light-coupling applications.
instance spin, orbital, and valley magnetic moments) band structure of a material. [2][3][4][5][6][7] Therefore, FR spectroscopy (FRS) is a powerful method in physics, chemistry, and biology. Some notable examples include the magnetic response and domain structures of solids, [2,8] optically detected nuclear magnetic resonances in fluids, [9,10] sensitive detection of paramagnetic molecules in gas mixtures, [11] biochemical and for biomolecular detection, [12] spin coherence probing in cold atoms, [13,14] investigation of quantum spin fluctuations, [15] and laser-frequency stabilization. [16] It is also used to perform Zeeman spectroscopy of many-body quasiparticles in solids, such as neutral and charged excitons. [2,17] As such, it is of fundamental importance to investigate the magnetic response of materials as a function of the photon energy. [18] It is because their characteristic band structures have energy-dependent spin-polarized density of states and van Hove singularities which possess prominent magnetic responses. [18,19] FRS provides this information with high sensitivity, under magnetic field (B) strengths of the order of 1 T or less, which are also suitable for device applications. [2] With the recent advancements in the area of 2D semiconductors and magnets, [17,[20][21][22][23][24][25][26] FRS naturally emerges as a method for studying their magnetic-field-dependent band structures.A major challenge while performing temperature-dependent (typically liquid He temperature up to room temperature) A Faraday rotation spectroscopy (FRS) technique is presented for measurements on the micrometer scale. Spectral acquisition speeds of about two orders of magnitude faster than state-of-the-art modulation spectroscopy setups are demonstrated. The experimental method is based on charge-coupled-device detection, avoiding speed-limiting components, such as polarization modulators with lock-in amplifiers. At the same time, FRS spectra are obtained with a sensitivity of 20 µrad (0.001°°) over a broad spectral range (525-800 nm), which is on par with state-of-the-art polarization-modulation techniques. The new measurement and analysis technique also automatically cancels unwanted Faraday rotation backgrounds. Using the setup, Faraday rotation spectroscopy of excitons is performed in a hexagonal boron nitride-encapsulated atomically thin semiconductor WS 2 under magnetic fields of up to 1.4 T at room temperature and liquid helium temperature. An exciton g-factor of −4.4 ± 0.3 is determined at room temperature, and −4.2 ± 0.2 at liquid helium temperature. In addition, FRS and hysteresis loop measurements are performed on a 20 nm thick film of an amorphous magnetic Tb 20 Fe 80 alloy.
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