When intense lightwaves accelerate electrons through a solid, the emerging high-order harmonic (HH) radiation offers key insights into the material
. Sub-optical-cycle dynamics-such as dynamical ...Bloch oscillations
, quasiparticle collisions
, valley pseudospin switching
and heating of Dirac gases
-leave fingerprints in the HH spectra of conventional solids. Topologically non-trivial matter
with invariants that are robust against imperfections has been predicted to support unconventional HH generation
. Here we experimentally demonstrate HH generation in a three-dimensional topological insulator-bismuth telluride. The frequency of the terahertz driving field sharply discriminates between HH generation from the bulk and from the topological surface, where the unique combination of long scattering times owing to spin-momentum locking
and the quasi-relativistic dispersion enables unusually efficient HH generation. Intriguingly, all observed orders can be continuously shifted to arbitrary non-integer multiples of the driving frequency by varying the carrier-envelope phase of the driving field-in line with quantum theory. The anomalous Berry curvature warranted by the non-trivial topology enforces meandering ballistic trajectories of the Dirac fermions, causing a hallmark polarization pattern of the HH emission. Our study provides a platform to explore topology and relativistic quantum physics in strong-field control, and could lead to non-dissipative topological electronics at infrared frequencies.
Delocalized Bloch electrons and the low-energy correlations between them determine key optical1, electronic2 and entanglement3 functionalities of solids, all the way through to phase transitions4,5. ...To directly capture how many-body correlations affect the actual motion of Bloch electrons, subfemtosecond (1 fs = 10-15 s) temporal precision6-15 is desirable. Yet, probing with attosecond (1 as = 10-18 s) high-energy photons has not been energy-selective enough to resolve the relevant millielectronvolt-scale interactions of electrons1-5,16,17 near the Fermi energy. Here, we use multi-terahertz light fields to force electron-hole pairs in crystalline semiconductors onto closed trajectories, and clock the delay between separation and recollision with 300 as precision, corresponding to 0.7% ofthe driving field's oscillation period. We detect that strong Coulomb correlations emergent in atomically thin WSe2 shift the optimal timing ofrecollisions by up to 1.2 ± 0.3 fs compared to the bulk material. A quantitative analysis with quantum-dynamic many-body computations in a Wigner-function representation yields a direct and intuitive view on how the Coulomb interaction, non-classical aspects, the strength ofthe driving field and the valley polarization influence the dynamics. The resulting attosecond chronoscopy of delocalized electrons could revolutionize the understanding of unexpected phase transitions and emergent quantum-dynamic phenomena for future electronic, optoelectronic and quantum-information technologies.
Strong light fields have created opportunities to tailor novel functionalities of solids
. Floquet-Bloch states can form under periodic driving of electrons and enable exotic quantum phases
. On ...subcycle timescales, lightwaves can simultaneously drive intraband currents
and interband transitions
, which enable high-harmonic generation
and pave the way towards ultrafast electronics. Yet, the interplay of intraband and interband excitations and their relation to Floquet physics have been key open questions as dynamical aspects of Floquet states have remained elusive. Here we provide this link by visualizing the ultrafast build-up of Floquet-Bloch bands with time-resolved and angle-resolved photoemission spectroscopy. We drive surface states on a topological insulator
with mid-infrared fields-strong enough for high-harmonic generation-and directly monitor the transient band structure with subcycle time resolution. Starting with strong intraband currents, we observe how Floquet sidebands emerge within a single optical cycle; intraband acceleration simultaneously proceeds in multiple sidebands until high-energy electrons scatter into bulk states and dissipation destroys the Floquet bands. Quantum non-equilibrium calculations explain the simultaneous occurrence of Floquet states with intraband and interband dynamics. Our joint experiment and theory study provides a direct time-domain view of Floquet physics and explores the fundamental frontiers of ultrafast band-structure engineering.
Age differences are well established for many memory tasks assessing both short-term and long-term memory. However, how age differences in performance vary with increasing delay between study and ...test is less clear. Here, we report two experiments in which participants studied a continuous sequence of object-location pairings. Test events were intermixed such that participants were asked to recall the precise location of an object following a variable delay. Older adults exhibit a greater degree of error (distance between studied and recalled locations) relative to younger adults at short (0-2 intervening events) and longer delays (10-25 intervening events). Mixture modeling of the distribution of recall error suggests that older adults do not fail to recall information at a significantly higher rate than younger adults. Instead, what they do recall appears to be less precise. Follow-up analyses demonstrated that this age difference emerges following only one or two intervening events between study and test. These findings are consistent with the suggestion that aging does not greatly impair recall from the focus of attention but that age differences emerge once information is displaced from this highly accessible state. Further, we suggest that age differences in the precision of memory, but not the probability of successful recall, may be due to the use of more gist-like representations in this task.
We use multi-terahertz (THz) light fields to force electron-hole pairs in crystalline semiconductors onto closed trajectories and clock the delay between separation and recollision with a 300 as ...precision. This value corresponds to 0.7% of the driving field's oscillation period. The strong Coulomb correlations emergent in atomically thin WSe 2 are found to shift the optimal timing of recollisions by up to 1.2 ± 0.3 fs compared to the bulk material. A quantitative analysis with quantum-dynamic many-body computations yields a direct and intuitive view on how the Coulomb interaction, non-classical aspects, the strength of the driving field, and the valley polarization influence the dynamics, opening unprecedented views of quantum many-body correlations and phase transitions.
The best method to measure right (RV) and left (LV) ventricle volumes of patients with corrected tetralogy of Fallot is considered cardiac magnetic resonance (CMR). However, to date, no standard ...protocol to measure RV volumes by CMR exists. RV volumes can be measured from a stack of short-axis slices or a stack of axial slices through the patient's chest. Therefore, the aim of this study was to determine whether short-axis or axial slices are more reliable for routine measurement of RV and LV volumes in patients with corrected tetralogy of Fallot. We studied consecutive patients with corrected tetralogy of Fallot (n = 46) undergoing routine CMR. The end-diastolic and end-systolic RV and LV volumes were measured by 2 investigators unaware of the results of the other measurements using short-axis and axial slices, and the inter- and intraobserver variances were compared. The design of the study was based on the Standards for Reporting of Diagnostic Accuracy. Interobserver variance was significantly smaller using axial slices than using short-axis slices for the RV end-systolic volumes (127.9%2 vs 315.1%2 ; p = 0.003), LV end-diastolic volumes (11.4%2 vs 36.1%2 ; p <0.001), and LV end-systolic volumes (31.9%2 vs 176.1%2 ; p <0.001). Intraobserver variance was significantly smaller using axial slices than using short-axis slices for the RV end-diastolic volumes (26.7%2 vs 51.1%2 ; p = 0.032), LV end-diastolic volumes (11.0%2 vs 23.5%2 ; p = 0.012), and LV end-systolic volumes (34.3%2 vs 86.1%2 ; p = 0.003). In conclusion, axial slices are more reproducible than short-axis slices for measuring ventricular volumes of patients with corrected tetralogy of Fallot by CMR.
Abstract Objectives This study sought to investigate the impact of tricuspid regurgitation (TR) on right ventricular function after percutaneous pulmonary valve implantation (PPVI). Background PPVI ...provides a less invasive alternative to surgery in patients with right ventricular-to-pulmonary artery (RV-PA) conduit dysfunction. Recovery of the right ventricle has been described after PPVI for patients with pulmonary stenosis and for those with pulmonary regurgitation. Additional TR enforces RV dysfunction by supplemental volume overload. Limited data are available on the potential of the right ventricle to recover in such a specific hemodynamic situation. Methods In a matched cohort study, we compared patients who underwent PPVI with additional TR with those without TR. Results The degree of TR improved in 83% of the patients. In our patients (n = 36) exercise capacity and right ventricular volume index improved similarly 6 months after PPVI in patients with and without important TR. None of them had significant TR in the long-term follow-up of median 78 months. Conclusions PPVI improves not only RV-PA-conduit dysfunction, but also concomitant TR. In patients with a dysfunctional RV-PA conduit and TR, the decision whether to fix TR should be postponed after PPVI.
Abstract Objectives Patients younger than 8 years are usually examined by cardiovascular magnetic resonance (CMR) under general anesthesia (GA) or sedation without intubation. Therefore, we sought to ...study the feasibility of CMR in patients aged 3 to 8 years without GA or sedation. Patients Data sets of 71 consecutive patients aged 3 to 8 years were studied retrospectively. Design The total cohort was divided into 2 groups: a no-GA or sedation without intubation group (no-GA or sedation) and a GA or sedation without intubation group (GA or sedation). Measurements The patients' age, scan durations for each group, successfully answered clinical question, and number of sequences per study were compared between both groups. Main results Scan duration in the no-GA or sedation group (n = 44) was 35 ± 20 minutes, and that in the GA or sedation group (n = 27) was 60 ± 31 minutes ( P < .001). The percentage of successful reports was 95% (42/44) in the no-GA or sedation group and 89% (24 of 27) in the GA or sedation group ( P = .29). Conclusion CMR in patients aged 3 to 8 years is usually successfully feasible without GA or sedation.
Strong light fields have created spectacular opportunities to tailor novel functionalities of solids. Floquet-Bloch states can form under periodic driving of electrons and enable exotic quantum ...phases. On subcycle time scales, lightwaves can simultaneously drive intraband currents and interband transitions, which enable high-harmonic generation (HHG) and pave the way towards ultrafast electronics. Yet, the interplay of intra- and interband excitations as well as their relation with Floquet physics have been key open questions as dynamical aspects of Floquet states have remained elusive. Here we provide this pivotal link by pioneering the ultrafast buildup of Floquet-Bloch bands with time- and angle-resolved photoemission spectroscopy. We drive surface states on a topological insulator with mid-infrared fields - strong enough for HHG - and directly monitor the transient band structure with subcycle time resolution. Starting with strong intraband currents, we observe how Floquet sidebands emerge within a single optical cycle; intraband acceleration simultaneously proceeds in multiple sidebands until high-energy electrons scatter into bulk states and dissipation destroys the Floquet bands. Quantum nonequilibrium calculations explain the simultaneous occurrence of Floquet states with intra- and interband dynamics. Our joint experiment-theory study opens up a direct time-domain view of Floquet physics and explores the fundamental frontiers of ultrafast band-structure engineering.
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