Articles in 2020

Control of nonlinear optical processes at the nanoscale is vital for the generation of on-chip short-wavelength sources, yet strong re-absorption of this radiation limits its efficiency in solids. Here, high harmonics are generated in an array of 1D silicon ridge waveguides, mitigating bulk re-absorption.

Generation of high-energy positron beams is more complex than for electrons, requiring positrons to be pre-generated and compensation of defocusing effects. Here, a system allowing positron creation, injection and acceleration in a single setup is considered theoretically.

The unique optical and optoelectronic properties of transition metal dichalcogenides are dominated by excitonic effects, whose structure is not fully characterised. Here, exciton and trion transitions in a monolayer MoS₂ phototransistor are investigated by low temperature photocurrent spectroscopy.

Piezoelectric materials are used for a broad range of industrial and research applications. The authors use synchrotron X-ray scattering and digital imaging correlation to investigate the microscopic mechanisms behind electromechanical strains in a lead-free piezoceramic material, which suggests an unconventional domain switching mechanism and ability to enhance the temperature range of operation by suitable doping strategies.

Quantifying the coupling underlying synchronization in forced turbulent oscillator flows through phase-amplitude reduction analysis is typically computationally demanding. Here, the authors propose a data-driven approach coupling Stuart-Landau oscillator models with unknown forcing dynamics and apply it to the study of the wake behind a D-shaped body subject to periodic blowing.

Antiferromagnetic systems are becoming an appealing alternative for spintronic-based devices due to the more rapid magnetisation dynamics when compared to their ferromagnetic counterparts. Here, using spin dynamic simulations, the authors demonstrate that the motion of domain walls can achieve supermagnonic speeds in an antiferromagnetic system by means of generation of additional domain wall pairs.

The Coulomb drag effect describes long-range electronic interactions between the charge carriers of two conducting channels separated by an insulating layer. Here, the authors report a graphene/MoS₂ heterostructure which operates using the Coulomb drag effect with energy barrier and exhibits high carrier mobility and on/off current ratio at room temperature

Refracting light waves can split at two different angles, a phenomenon called birefringence, whereas for reflected waves the incident and reflected angle are usually the same. Here, using time-resolved magneto-optical microscopy the authors report the bi-reflection of magnetic spin waves when hybridising with elastic waves.

Spin-orbit torque driven oscillators, such as spin Hall oscillators, form a class of devices that are intensively studied due to potential practical applications in spintronics. Here, the authors modify the conventional ferromagnetic/nonmagnetic stack to include an additional ferromagnetic layer and leverage the giant magnetoresistance effect to enhance the direct conversion of an in-plane driving current into the microwave output signal.

There is an ever-increasing requirement for coolant systems and current apparatus typically exhibits low efficiency as well as relying on environmentally detrimental refrigerants. Here, the authors report a design involving a caloric material and the condensation and evaporation of a heat transfer fluid, which achieves a marked increase in performance in comparison to other types of system.

Optical clocks have many applications, from improved GNSS measurements to fundamental tests of general relativity, but their frequency stability is limited by quantum noise and the Dick effect. The authors present and demonstrate a method to estimate the phase of an optical clock laser beyond the laser coherence time that can be used to improve the stability of these devices for applications in metrology and the search for new physics.

Interrogating emergent nonequilibrium phenomena in light-driven quantum materials requires probing microscopic spin, charge and orbital excitations at ultrafast timescales. In this Perspective, time-resolved resonant inelastic X-ray scattering is discussed as a nascent method to investigate photoinduced states of matter.

Controlling the positioning of spheroids in 3D during bioprinting is one of the main challenges hindering the scaffold-free fabrication of biologically-relevant tissues and organs. Here, the authors combine cutting edge aspiration-assisted freeform bioprinting of spheroids with self-healing yield-stress gels, obtaining precise positioning and self-assembly into 3D complex configurations.

Optical methods are extensively used for tissue imaging in the biomedical sector but they are limited for deep tissue analysis due to massive losses by strong light scattering, which can be mitigated with the use of ultrasound. The authors present proof-of-concept experiments showing transient ultrasound waves transversal to the direction of propagation of laser light that can be used to waveguide in the bulk of the scattering medium to a depth of 90 mean free paths.

Extensive theoretical and experimental efforts have been devoted to the effect of quantum criticality in our understanding of the physics of high-temperature superconductors and strongly correlated electron materials, yet it remains a puzzle in condensed matter physics. The authors report observations of a quantum criticality by investigating the non-Fermi liquid thermodynamics and transport behaviour in a non-superconducting iron pnictide.

Sources of spin-polarized electrons have important applications in various branches of physics. This paper predicts that a 2D lattice of point magnets can act as a spin filter, and so may be employed to deliver spin-polarized currents.

In practice, free-space optical communication systems are subjected to atmospheric turbulence in addition to attenuation and noise. Here, the authors develop a combined approach based on generative machine learning and convolutional neural networks, able to correct distortion effects due to turbulence and attenuation.

Non-thermal populations of electrons and holes in metals relax via a complex cascade process consisting of multiple scattering mechanisms that are energy-dependent. This work presents a systematic analysis of relaxation dynamics in different metals based on simple expressions for their time-dependent distributions.

The formation of a massive black hole (BH) by coalescence of two BHs is a fascinating cosmological event that leaves a gravitational signal that, if detected, can probe extreme gravity and the BH horizon. The authors report non-trivial features of gravitational wave signals from non-equal mass binaries that could be observed by gravitational wave detectors in the coming years, and describe their connection to the evolving shape of the new-born BH.