Ultrafast transition between exciton phases in van der Waals heterostructures

\ua9 2019, The Author(s), under exclusive licence to Springer Nature Limited. Heterostructures of atomically thin van der Waals bonded monolayers have opened a unique platform to engineer Coulomb correlations, shaping excitonic1–3, Mott insulating4 or superconducting phases5,6. In transition metal dichalcogenide heterostructures7, electrons and holes residing in different monolayers can bind into spatially indirect excitons1,3,8–11 with a strong potential for optoelectronics11,12, valleytronics1,3,13, Bose condensation14, superfluidity14,15 and moir\ue9-induced nanodot lattices16. Yet these ideas require a microscopic understanding of the formation, dissociation and thermalization dynamics of correlations including ultrafast phase transitions. Here we introduce a direct ultrafast access to Coulomb correlations between monolayers, where phase-locked mid-infrared pulses allow us to measure the binding energy of interlayer excitons in WSe2/WS2 hetero-bilayers by revealing a novel 1s–2p resonance, explained by a fully quantum mechanical model. Furthermore, we trace, with subcycle time resolution, the transformation of an exciton gas photogenerated in the WSe2 layer directly into interlayer excitons. Depending on the stacking angle, intra- and interlayer species coexist on picosecond scales and the 1s–2p resonance becomes renormalized. Our work provides a direct measurement of the binding energy of interlayer excitons and opens the possibility to trace and control correlations in novel artificial materials

Head roll dependent variability of subjective visual vertical and ocular counterroll

We compared the variability of the subjective visual vertical (SVV) and static ocular counterroll (OCR), and hypothesized a correlation between the measurements because of their shared macular input. SVV and OCR were measured simultaneously in various whole-body roll positions [upright, 45 degrees right-ear down (RED), and 75 degrees RED] in six subjects. Gains of OCR were -0.18 (45 degrees RED) and -0.12 (75 degrees RED), whereas gains of compensation for body roll in the SVV task were -1.11 (45 degrees RED) and -0.96 (75 degrees RED). Normalized SVV and OCR variabilities were not significantly different (P > 0.05), i.e., both increased with increasing roll. Moreover, a significant correlation (R (2) = 0.80, slope = 0.29) between SVV and OCR variabilities was found. Whereas the gain of OCR is different from the gain of SVV, trial-to-trial variability of OCR follows the same roll-dependent modulation observed in SVV variability. We propose that the similarities in variability reflect a common otolith input, which, however, is subject to distinct central processing for determining the gain of SVV and OCR