Tracking local magnetic dynamics via high-energy charge excitations in a relativistic Mott insulator

We use time- and energy-resolved optical spectroscopy to investigate the coupling of electron-hole excitations to the magnetic environment in the relativistic Mott insulator Na$_2$IrO$_3$. We show that, on the picosecond timescale, the photoinjected electron-hole pairs delocalize on the hexagons of the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations and the exchange of energy with the short-range-ordered zig-zag magnetic background. The possibility of mapping the magnetic dynamics, which is characterized by typical frequencies in the THz range, onto high-energy (1-2 eV) charge excitations provides a new platform to investigate, and possibly control, the dynamics of magnetic interactions in correlated materials with strong spin-orbit coupling, even in the presence of complex magnetic phases.Comment: 5 pages, 4 figures, supplementary informatio

Long-term physical impairments in survivors of COVID-19-associated ARDS compared with classic ARDS: A two-center study

Purpose: This work aimed to compare physical impairment in survivors of classic ARDS compared with COVID-19-associated ARDS (CARDS) survivors. Material and methods: This is a prospective observational cohort study on 248 patients with CARDS and compared them with a historical cohort of 48 patients with classic ARDS. Physical performance was evaluated at 6 and 12 months after ICU discharge, using the Medical Research Council Scale (MRCss), 6-min walk test (6MWT), handgrip dynamometry (HGD), and fatigue severity score (FSS). We also assessed activities of daily living (ADLs) using the Barthel index. Results: At 6 months, patients with classic ARDS had lower HGD (estimated difference [ED]: 11.71 kg, p < 0.001; ED 31.9% of predicted value, p < 0.001), 6MWT distance (ED: 89.11 m, p < 0.001; ED 12.96% of predicted value, p = 0.032), and more frequent significant fatigue (OR 0.35, p = 0.046). At 12 months, patients with classic ARDS had lower HGD (ED: 9.08 kg, p = 0.0014; ED 25.9% of predicted value, p < 0.001) and no difference in terms of 6MWT and fatigue. At 12 months, patients with classic ARDS improved their MRCss (ED 2.50, p = 0.006) and HGD (ED: 4.13 kg, p = 0.002; ED 9.45% of predicted value, p = 0.005), while those with CARDS did not. Most patients in both groups regained independence in ADLs at 6 months. COVID-19 diagnosis was a significant independent predictor of better HGD (p < 0.0001) and 6MWT performance (p = 0.001), and lower prevalence of fatigue (p = 0.018). Conclusions: Both classic ARDS and CARDS survivors experienced long-term impairments in physical functioning, confirming that post-intensive care syndrome remains a major legacy of critical illness. Surprisingly, however, persisting disability was more common in survivors of classic ARDS than in CARDS survivors. In fact, muscle strength measured with HGD was reduced in survivors of classic ARDS compared to CARDS patients at both 6 and 12 months. The 6MWT was reduced and fatigue was more common in classic ARDS compared to CARDS at 6 months but differences were no longer significant at 12 months. Most patients in both groups regained independent function in ADLs at 6 months

Ultrafast orbital manipulation and Mott physics in multi-band correlated materials

Multiorbital correlated materials are often on the verge of multiple electronic phases (metallic, insulating, superconducting, charge and orbitally ordered), which can be explored and controlled by small changes of the external parameters. The use of ultrashort light pulses as a mean to transiently modify the band population is leading to fundamentally new results. In this paper we will review recent advances in the field and we will discuss the possibility of manipulating the orbital polarization in correlated multi-band solid state systems. This technique can provide new understanding of the ground state properties of many interesting classes of quantum materials and offers a new tool to induce transient emergent properties with no counterpart at equilibrium. We will address: the discovery of high-energy Mottness in superconducting copper oxides and its impact on our understanding of the cuprate phase diagram; the instability of the Mott insulating phase in photoexcited vanadium oxides; the manipulation of orbital-selective correlations in iron-based superconductors; the pumping of local electronic excitons and the consequent transient effective quasiparticle cooling in alkali-doped fullerides. Finally, we will discuss a novel route to manipulate the orbital polarization in a a k-resolved fashion

Electrophysiological neuromuscular alterations and severe fatigue predict long-term muscle weakness in survivors of COVID-19 acute respiratory distress syndrome

IntroductionLong-term weakness is common in survivors of COVID-19-associated acute respiratory distress syndrome (CARDS). We longitudinally assessed the predictors of muscle weakness in patients evaluated 6 and 12 months after intensive care unit discharge with in-person visits.MethodsMuscle strength was measured by isometric maximal voluntary contraction (MVC) of the tibialis anterior muscle. Candidate predictors of muscle weakness were follow-up time, sex, age, mechanical ventilation duration, use of steroids in the intensive care unit, the compound muscle action potential of the tibialis anterior muscle (CMAP-TA-S100), a 6-min walk test, severe fatigue, depression and anxiety, post-traumatic stress disorder, cognitive assessment, and body mass index. We also compared the clinical tools currently available for the evaluation of muscle strength (handgrip strength and Medical Research Council sum score) and electrical neuromuscular function (simplified peroneal nerve test [PENT]) with more objective and robust measures of force (MVC) and electrophysiological evaluation of the neuromuscular function of the tibialis anterior muscle (CMAP-TA-S100) for their essential role in ankle control.ResultsMVC improved at 12 months compared with 6 months. CMAP-TA-S100 (P = 0.016) and the presence of severe fatigue (P = 0.036) were independent predictors of MVC. MVC was strongly associated with handgrip strength, whereas CMAP-TA-S100 was strongly associated with PENT.DiscussionElectrical neuromuscular abnormalities and severe fatigue are independently associated with reduced MVC and can be used to predict the risk of long-term muscle weakness in CARDS survivors

Polarization-resolved broadband time-resolved optical spectroscopy for complex materials: application to the case of MoTe2 polytypes

Time-resolved optical spectroscopy (TR-OS) has emerged as a fundamental spectroscopic tool for probing complex materials, to both investigate ground-state-related properties and trigger phase transitions among different states with peculiar electronic and lattice structures. We describe a versatile approach to perform polarization-resolved TR-OS measurements, by combining broadband detection with the capability to simultaneously probe two orthogonal polarization states. This method allows us to probe, with femtoseconds resolution, the frequency-resolved reflectivity or transmittivity variations along two mutually orthogonal directions, matching the principal axis of the crystal structure of the material under scrutiny. We report on the results obtained by acquiring the polarization-dependent transient reflectivity of two polytypes of the MoTe2 compound, with 2H and 1T' crystal structures. We reveal marked anisotropies in the time-resolved reflectivity signal of IT'-MoTe2, which are connected to the crystal structure of the compound. Polarization- and time- resolved spectroscopic measurements can thus provide information about the nature and dynamics of both the electronic and crystal lattice subsystems, advancing the comprehension of their inter-dependence, in particular in the case of photoinduced phase transitions; in addition, they provide a broadband measurement of transient polarization rotations. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Crystallization and second harmonic generation in potassium-sodium niobiosilicate glasses

Transparent glasses having molar composition (23−x)K2O·xNa2O·27Nb2O5·50SiO2 (x=0, 5, 10, 15 and 23) have been synthesized by the melt-quenching technique and their devitrification behaviour has been investigated by DTA and XRD. Depending on the composition, the glasses showed a glass transition temperature in the range 660–680 °C and devitrified in several steps. XRD measurements showed that the replacement of K2O by Na2O strongly affects the crystallization behaviour. Particularly, in the glasses with only potassium or low sodium content the first devitrification step is related to the crystallization of an unidentified phase, while in the glass containing only sodium, NaNbO3 crystallizes. For an intermediate sodium content (x=10 and 15) a potassium sodium niobate crystalline phase, belonging to the tungsten-bronze family, is formed by bulk nucleation. This system looks promising to produce active nanostructured glasses as the tungsten-bronze type crystals have ferroelectric, electro-optical and non-linear optical properties. Preliminary measurements evidenced SHG activity in the crystallized glasses containing this phase

External screening and lifetime of exciton population in single-layer ReSe2_2 probed by time- and angle-resolved photoemission spectroscopy

The semiconductor ReSe$_2$ is characterized by a strongly anisotropic optical absorption and is therefore promising as an optically active component in two-dimensional heterostructures. However, the underlying femtosecond dynamics of photoinduced excitations in such materials has not been sufficiently explored. Here, we apply an infrared optical excitation to single-layer ReSe$_2$ grown on a bilayer graphene substrate and monitor the temporal evolution of the excited state signal using time- and angle-resolved photoemission spectroscopy. We measure an optical gap of $(1.53 \pm 0.02)$ eV, consistent with resonant excitation of the lowest exciton state. The exciton distribution is tunable via the linear polarization of the pump pulse and exhibits a biexponential decay with time constants given by $\tau_1 = (110 \pm 10)$ fs and $\tau_2 = (650 \pm 70)$ fs, facilitated by recombination via an in-gap state that is pinned at the Fermi level. By extracting the momentum-resolved exciton distribution we estimate its real-space radial extent to be greater than 17.1 \AA, implying significant exciton delocalization due to screening from the bilayer graphene substrate