Future information technology demands ever-faster, low-loss quantum control. Intense light fields have facilitated milestones along this way, including the induction of novel states of matter
, ...ballistic acceleration of electrons
and coherent flipping of the valley pseudospin
. These dynamics leave unique 'fingerprints', such as characteristic bandgaps or high-order harmonic radiation. The fastest and least dissipative way of switching the technologically most important quantum attribute-the spin-between two states separated by a potential barrier is to trigger an all-coherent precession. Experimental and theoretical studies with picosecond electric and magnetic fields have suggested this possibility
, yet observing the actual spin dynamics has remained out of reach. Here we show that terahertz electromagnetic pulses allow coherent steering of spins over a potential barrier, and we report the corresponding temporal and spectral fingerprints. This goal is achieved by coupling spins in antiferromagnetic TmFeO
(thulium orthoferrite) with the locally enhanced terahertz electric field of custom-tailored antennas. Within their duration of one picosecond, the intense terahertz pulses abruptly change the magnetic anisotropy and trigger a large-amplitude ballistic spin motion. A characteristic phase flip, an asymmetric splitting of the collective spin resonance and a long-lived offset of the Faraday signal are hallmarks of coherent spin switching into adjacent potential minima, in agreement with numerical simulations. The switchable states can be selected by an external magnetic bias. The low dissipation and the antenna's subwavelength spatial definition could facilitate scalable spin devices operating at terahertz rates.
Harnessing the carrier wave of light as an alternating-current bias may enable electronics at optical clock rates
. Lightwave-driven currents have been assumed to be essential for high-harmonic ...generation in solids
, charge transport in nanostructures
, attosecond-streaking experiments
and atomic-resolution ultrafast microscopy
. However, in conventional semiconductors and dielectrics, the finite effective mass and ultrafast scattering of electrons limit their ballistic excursion and velocity. The Dirac-like, quasi-relativistic band structure of topological insulators
may allow these constraints to be lifted and may thus open a new era of lightwave electronics. To understand the associated, complex motion of electrons, comprehensive experimental access to carrier-wave-driven currents is crucial. Here we report angle-resolved photoemission spectroscopy with subcycle time resolution that enables us to observe directly how the carrier wave of a terahertz light pulse accelerates Dirac fermions in the band structure of the topological surface state of Bi
Te
. While terahertz streaking of photoemitted electrons traces the electromagnetic field at the surface, the acceleration of Dirac states leads to a strong redistribution of electrons in momentum space. The inertia-free surface currents are protected by spin-momentum locking and reach peak densities as large as two amps per centimetre, with ballistic mean free paths of several hundreds of nanometres, opening up a realistic parameter space for all-coherent lightwave-driven electronic devices. Furthermore, our subcycle-resolution analysis of the band structure may greatly improve our understanding of electron dynamics and strong-field interaction in solids.
Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light. Intense terahertz pulses can couple to spins on the ...intrinsic energy scale of magnetic excitations. Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field. Using the prototypical antiferromagnet thulium orthoferrite (TmFeO sub(3)), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe super(3+) spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials.
Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct ...spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism-information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching.
In solids, the high density of charged particles makes many-body interactions a pervasive principle governing optics and electronics112. However, Walter Kohn found in 1961 that the cyclotron ...resonance of Landau-quantized electrons is independent of the seemingly inescapable Coulomb interaction between electrons2. Although this surprising theorem has been exploited in sophisticated quantum phenomena1315, such as ultrastrong lightmatter coupling16, superradiance17 and coherent control18, the complete absence of nonlinearities excludes many intriguing possibilities, such as quantum-logic protocols19. Here, we use intense terahertz pulses to drive the cyclotron response of a two-dimensional electron gas beyond the protective limits of Kohns theorem. Anharmonic Landau ladder climbing and distinct terahertz four- and six-wave mixing signatures occur, which our theory links to dynamic Coulomb eects between electrons and the positively charged ion background. This new context for Kohns theorem unveils previously inaccessible internal degrees of freedom of Landau electrons, opening up new realms of ultrafast quantum control for electrons.
Terahertz near fields of gold metamaterials resonant at a frequency of 0.88 THz allow us to enter an extreme limit of nonperturbative ultrafast terahertz electronics: Fields reaching a ponderomotive ...energy in the keV range are exploited to drive nondestructive, quasistatic interband tunneling and impact ionization in undoped bulk GaAs, injecting electron-hole plasmas with densities in excess of 10^{19} cm^{-3}. This process causes bright luminescence at energies up to 0.5 eV above the band gap and induces a complete switch-off of the metamaterial resonance accompanied by self-amplitude-modulation of transmitted few-cycle terahertz transients. Our results pave the way towards highly nonlinear terahertz optics and optoelectronic nanocircuitry with subpicosecond switching times.
The quality of surgical teamwork contributes to performance of the operating theatre team, service quality and patient safety in surgery. Observational tools are a feasible and reliable way to ...capture and evaluate teamwork in the operating theatre (OT). We introduce the German version of the Observational Teamwork Assessment for Surgery (OTAS-D) and present the first observational results from German OTs.
Quality of surgical teamwork was assessed with observational teamwork assessment for surgery (OTAS-D). It evaluates five dimensions of OT teamwork: communication, coordination, cooperation/backup behaviour, leadership, and team monitoring/situation awareness. Each dimension is evaluated for each profession (surgical, nursing, and anaesthesia team) as well for each phase of the procedure (pre-, intra-, and post-operative). We observed n = 63 procedures, mainly in abdominal/general and orthopaedic surgery. Additionally, all OT team members scored their individual evaluation of the intra-operative teamwork (standardised 1-item questions).
The OTAS-D evaluations showed meaningful results and differences for the OT professions as well as across the different phases of the procedures. Overall, a medium to good level of the OT teamwork was observed. There were no differences in regard to type of surgery (minimally invasive vs. open) or surgical specialties. With an increased coordination of the surgical team we observed a significantly increased cooperation of the nursing team (r = 0.36, p = 0.004). Concerning the OT staffs self-reports, the surgical and nursing teams reported higher scores for quality of surgical teamwork during the procedure than their anaesthesia team members. No significant relationships between observed quality of OT teamwork and self-reports were found.
The German version of OTAS-D is a psychometrically robust method to capture the quality of teamwork in operating theatres. It enables the analyses of teamwork between the surgical, nursing and anaesthesia professions in acute surgical care. Limitations of the first application results are considered. Finally, potential applications for surgical teaching, research and quality management are discussed.
The treatment of patients in the trauma room places extraordinary demands on the multidisciplinary and multiprofessional team with regard to expert qualifications and teamwork. The present study ...triangulates data extracted from observation, interviews and questionnaires. In general, team climate and teamwork are good, yet some problems could be identified. Not all team members-especially younger physicians and nurses-feel free to express their doubts and uncertainties. Furthermore, the treatment plan is not always clear for all team members. Absent or unclear leadership is seen as a main problem when a treatment proceeds negatively. The establishment of a team leader is therefore recommended.
Phase-locked few-cycle pulses in the ultrabroadband terahertz (THz) spectral window 1-4 have become a powerful tool to access low-energy elementary dynamics in solids, on time scales shorter than a ...single oscillation cycle of light 5-14 . Here, we tackle the role of excitons and their dynamics in modern dichalcogenide monolayers and exciton-polariton condensates 7-9 . Furthermore, intense THz pulses are used as atomically strong bias fields to explore high-harmonic generation by dynamical Bloch oscillations in bulk solids 11-13 . Finally, we develop a novel microscope that introduces sub-cycle resolution on the few-nm length scale 14 . The experiments reviewed here challenge modern quantum theories and spark hope for electronics and magnetic storage at optical clock rates.
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