Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality crystal symmetry. The family of semiconducting is an especially promising platform for fundamental studies two-dimensional (2D) systems, with potential applications in optoelectronics valleytronics due to direct band gap the limit highly efficient light-matter coupling. A lattice broken inversion symmetry combined...

We show that the light-matter interaction in monolayer WSe_{2} is strongly enhanced when incoming electromagnetic wave resonance with energy of exciton states Coulomb bound electron-hole pairs below electronic band gap. perform second harmonic generation (SHG) spectroscopy as a function laser and polarization at T=4 K. At energies we record an enhancement by up to 3 orders magnitude SHG efficiency, due unusual combination electric dipole magnetic transitions. The parity showing strong...

The strong light matter interaction and the valley selective optical selection rules make monolayer (ML) MoS2 an exciting 2D material for fundamental physics optoelectronics applications. But so far transition linewidths even at low temperature are typically as large a few tens of meV contain homogenous inhomogeneous contributions. This prevented in-depth studies, in contrast to better-characterized ML materials MoSe2 WSe2. In this work we show that encapsulation hexagonal boron nitride can...

We use micro-Raman and photoluminescence (PL) spectroscopy at 300K to investigate the influence of uniaxial tensile strain on vibrational optoelectronic properties monolayer bilayer MoS2 a flexible substrate. The initially degenerate E^1_{2g} Raman mode is split into doublet as direct consequence applied through Van der Waals coupling sample-substrate interface. observe strong shift band gap 48meV/(% strain) for 46meV/% bilayer, whose indirect shifts by 86meV/%. find decrease PL polarization...

We report polarization resolved photoluminescence from monolayer ${\mathrm{MoS}}_{2}$, a two-dimensional, noncentrosymmetric crystal with direct energy gaps at two different valleys in momentum space. The inherent chiral optical selectivity allows exciting one of these valleys, and close to 90$%$ polarized emission 4 K is observed 40$%$ remaining 300 K. high degree the remains unchanged transverse magnetic fields up 9 T indicating robust, selective valley excitation.

We have investigated the exciton dynamics in transition metal dichalcogenide mono-layers using time-resolved photoluminescence experiments performed with optimized time-resolution. For MoSe2 monolayers, we measure $\tau_{rad}=1.8\pm0.2$ ps that interpret as intrinsic radiative recombination time. Similar values are found for WSe2 mono-layers. Our detailed analysis suggests following scenario: at low temperature (T $\leq$ 50 K), oscillator strength is so large entire light can be emitted...

Optical interband transitions in monolayer transition metal dichalcogenides such as WSe2 and MoS2 are governed by chiral selection rules. This allows efficient optical initialization of an electron a specific K-valley momentum space. Here we probe the valley dynamics monitoring emission polarization well separated neutral excitons (bound hole pairs) charged (trions) photoluminescence. The exciton photoluminescence intensity decay time is about 4ps, whereas trion occurs over several tens ps....

In monolayer MoS2, optical transitions across the direct band gap are governed by chiral selection rules, allowing valley initialization. time-resolved photoluminescence (PL) experiments, we find that both polarization and emission dynamics do not change from 4 to 300 K within our time resolution. We measure a high show under pulsed excitation significantly decreases with increasing laser power. fast exciton decay on order of ps. The absence clear PL resolution suggests initially injected...

The mesoscopic spin system formed by the 10E4-10E6 nuclear spins in a semiconductor quantum dot offers unique setting for study of many-body physics condensed matter. dynamics this and its coupling to electron is fundamentally different from bulk counter-part as well that atoms due increased fluctuations result reduced dimensions. In recent years, interest studying systems their confined has been fueled direct implication possible applications such information processing fascinating...

The optical selection rules for interband transitions in WSe2, WS2, and MoSe2 transition metal dichalcogenide monolayers are investigated by polarization-resolved photoluminescence experiments with a signal collection from the sample edge. These measurements reveal strong polarization dependence of emission lines. We see clear signatures emitted light electric field oriented perpendicular to monolayer plane, corresponding an forbidden at normal incidence used standard spectroscopy...

We study the neutral exciton energy spectrum fine structure and its spin dephasing in transition metal dichalcogenides such as MoS$_2$. The interaction of mechanical with macroscopic longitudinal electric field is taken into account. splitting between transverse excitons calculated by means both electrodynamical approach $\mathbf k \cdot \mathbf p$ perturbation theory. This long-range exchange can induce valley polarization decay. estimated time picosecond range, agreement available...

We have experimentally studied the pump-probe Kerr rotation dynamics in WSe$_2$ monolayers. This yields a direct measurement of exciton valley depolarization time $\tau_v$. At T=4K, we find $\tau_v\approx 6$ps, fast relaxation resulting from strong electron-hole Coulomb exchange interaction bright excitons. The decreases significantly when lattice temperature increases with $\tau_v$ being as short 1.5ps at 125K. dependence is well explained by developed theory taking into account and...

The optical properties of transition metal dichalcogenide monolayers such as the two-dimensional semiconductors MoS$_2$ and WSe$_2$ are dominated by excitons, Coulomb bound electron-hole pairs. light emission yield depends on whether transitions optically allowed (bright) or forbidden (dark). By solving Bethe Salpeter Equation top $GW$ wave functions in density functional theory calculations, we determine sign amplitude splitting between bright dark exciton states. We evaluate influence...

Charged excitons, or X$^{\pm}$-trions, in monolayer transition metal dichalcogenides have binding energies of several tens meV. Together with the neutral exciton X$^0$ they dominate emission spectrum at low and elevated temperatures. We use charge tunable devices based on WSe$_2$ monolayers encapsulated hexagonal boron nitride, to investigate difference energy between X$^+$ X$^-$ fine structure. find regime, accompanied lower by a strong peak close longitudinal optical (LO) phonon energy....

Transition metal dichalcogenide (TMDC) monolayers are newly discovered semiconductors for a wide range of applications in electronics and optoelectronics. Most studies have focused on binary that share common properties: direct optical bandgap, spin-orbit (SO) splittings hundreds meV, light-matter interaction dominated by robust excitons coupled spin-valley states electrons. Studies alloy-based more recent, yet they may not only extend the possibilities TMDC through specific engineering but...

In semiconductor physics, many essential optoelectronic material parameters can be experimentally revealed via optical spectroscopy in sufficiently large magnetic fields. For monolayer transition-metal dichalcogenide semiconductors, this field scale is substantial-tens of teslas or more-due to heavy carrier masses and huge exciton binding energies. Here we report absorption [Formula: see text], text] very high fields 91 T. We follow the diamagnetic shifts valley Zeeman splittings not only...

The intricate interplay between optically dark and bright excitons governs the light-matter interaction in transition metal dichalcogenide monolayers. We have performed a detailed investigation of ``spin-forbidden'' ${\mathrm{WSe}}_{2}$ monolayers by optical spectroscopy an out-of-plane magnetic field ${\mathrm{B}}_{\mathrm{z}}$. In agreement with theoretical predictions deduced from group theory analysis, magnetophotoluminescence experiments reveal zero-field splitting...

The photoluminescence (PL) spectrum of transition-metal dichalcogenides (TMDs) shows a multitude emission peaks below the bright exciton line, and not all them have been explained yet. Here, we study traces phonon-assisted recombinations indirect excitons. To this end, develop microscopic theory describing simultaneous exciton, phonon, photon interaction including consistent many-particle dephasing. We explain drastically different PL in tungsten- molybdenum-based materials as result...

We have studied the electron spin relaxation in semiconductor InAs/GaAs quantum dots by time-resolved optical spectroscopy. The average polarization of electrons an ensemble p-doped decays down to 1/3 its initial value with a characteristic time T(Delta) approximately 500 ps, which is attributed hyperfine interaction randomly oriented nuclear spins. show that this efficient mechanism can be suppressed external magnetic field as small 100 mT.

The direct gap interband transitions in transition metal dichalcogenide monolayers are governed by chiral optical selection rules. Determined laser helicity, either the K+ or K− valley momentum space induced. Linearly polarized excitation prepares a coherent superposition of states. Here, we demonstrate control exciton coherence monolayer WSe2 tuning applied magnetic field perpendicular to plane. We show rotation this states angles as large 30° fields up 9 T. This on ps time scale could be...

We investigate valley exciton dynamics in MoSe2 monolayers polarization- and time-resolved photoluminescence (PL) spectroscopy at 4 K. Following circularly polarized laser excitation, we record a low circular polarization degree of the PL typically ≤5%. This is about 10 times lower than induced under comparable conditions MoS2 WSe2 monolayers. The evolution as function excitation energy power monitored experiments. Fast emission are recorded for both neutral ≤3 ps charged (trion) 12 ps.

We perform photoluminescence experiments at 4 K on two different transition metal diselenide monolayers, namely MoSe2 and WSe2 in magnetic fields Bz up to 9 T applied perpendicular the sample plane.In monolayers valley polarization of neutral charged exciton (trion) can be tuned by field, independent excitation laser polarization.In investigated monolayer evolution trion depends both field helicity, while only latter.Remarkably we observe a reversal sign between MoSe2.For systems clear...

Abstract Excitons, Coulomb bound electron–hole pairs, are composite bosons and their interactions in traditional semiconductors lead to condensation light amplification. The much stronger interaction transition metal dichalcogenides such as WSe 2 monolayers combined with the presence of valley degree freedom is expected provide new opportunities for controlling excitonic effects. But so far bosonic character exciton scattering processes remains largely unexplored these two-dimensional...

Using time-resolved Kerr rotation, we measure the spin/valley dynamics of resident electrons and holes in single charge-tunable monolayers archetypal transition-metal dichalcogenide (TMD) semiconductor WSe2. In n-type regime, observe long (70 ns) polarization relaxation that is sensitive to in-plane magnetic fields $B_y$, indicating spin relaxation. marked contrast, extraordinarily (2 microsecond) revealed p-type unaffected by directly confirming long-standing expectations strong spin-valley...