Ultrafast valley relaxation dynamics in monolayer MoS2 probed by nonequilibrium optical techniques

We study the exciton valley relaxation dynamics in single-layer MoS2 by a combination of two nonequilibrium optical techniques: time-resolved Faraday rotation and time-resolved circular dichroism. The depolarization dynamics, measured at 77 K, exhibits a peculiar biexponential decay, characterized by two distinct time scales of 200 fs and 5 ps. The fast relaxation of the valley polarization is in good agreement with a model including the intervalley electron-hole Coulomb exchange as the dominating mechanism. The valley relaxation dynamics is further investigated as a function of temperature and photoinduced exciton density. We measure a strong exciton density dependence of the transient Faraday rotation signal. This indicates the key role of exciton-exciton interactions in MoS2 valley relaxation dynamics

Scrivere in guerra. I notai negli eserciti dell\u2019Italia comunale (secoli XII-XIV)

Within the tradition of Diplomatic studies, since the most ancient contributions concerned with the history of documentation produced by central northern Italy cities, it is possible to point out that very little attention has been paid to the presence of the notaries and to the role of their deeds during military expeditions. The work here proposed aims, first of all, at conducting research into the roles played by the notaries within military organization, marking how they constantly worked together with capitani, costringitori and consiglieri of cities\u2019 armies and saw about the regular registration of the shirkers, of the weapons, of foodstuffs sold to the troops. The second part of this paper will investigate in detail how the registrations were done: we\u2019ll try to put in evidence the connexions between the forms and the functions of a kind of documentation surely \u2018non-typical\u2019, but that seems to represent a further, interesting point of view for observing a side until almost unknown of the so called \u201cdocumentary revolution\u201d and the topos of notarial omnipresence in Middle Ages Italy

Ultrafast valley relaxation dynamics in monolayer MoS2 probed by nonequilibrium optical techniques

We study the exciton valley relaxation dynamics in single-layer MoS2 by a combination of two nonequilibrium optical techniques: time-resolved Faraday rotation and time-resolved circular dichroism. The depolarization dynamics, measured at 77 K, exhibits a peculiar biexponential decay, characterized by two distinct time scales of 200 fs and 5 ps. The fast relaxation of the valley polarization is in good agreement with a model including the intervalley electron-hole Coulomb exchange as the dominating mechanism. The valley relaxation dynamics is further investigated as a function of temperature and photoinduced exciton density. We measure a strong exciton density dependence of the transient Faraday rotation signal. This indicates the key role of exciton-exciton interactions in MoS2 valley relaxation dynamics

Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites

Hybrid organic–inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (≲50 cm−1) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials

Disentangling intra and intervalley dynamics in monolayer MoS <inf>2</inf> by ultrafast optical techniques

Disentangling intra and intervalley dynamics in monolayer MoS 2 by ultrafast optical technique