Volume 20 Issue 1, January 2024

The Kondo effect — the screening of an impurity spin by conduction electrons — is a fundamental many-body effect. However, recent experiments combined with simulations have caused a long-standing model system for the single-atom Kondo effect to fail.

Semiconducting dipolar excitons — bound states of electrons and holes — in artificial moiré lattices constitute a promising condensed matter system to explore the phase diagram of strongly interacting bosonic particles.

The ability to extract information from diffuse background signals in ultrafast electron diffraction experiments now enables a direct view of the formation of topological defects during a light-induced phase transition.

Trojan beams, which are optical counterparts of Trojan asteroids that maintain stable orbits alongside planets, have been successfully showcased in experiments, opening up possibilities for transporting light in unconventional settings.

A nonlinear optical approach has now enabled picosecond control of a complex band structure, driving a non-Hermitian topological phase transition across an exceptional-point singularity.

A decade ago, the anti-laser made waves as a new type of perfect absorber that functions as a one-way trap door for light. Experiments have now demonstrated the control of light without absorbing it.

Electrons trapped above the surface of solid neon can be used to create qubits using spatial states with different charge distributions. These charge qubits combine direct electric field control with long coherence times.

Networks of dynamic actin filaments and myosin motors, confined in cell-like droplets, drive diverse spatiotemporal patterning of contractile flows, waves, and spirals. This multiscale active sculpting is tuned by the system dynamics and size.

Physical networks, composed of nodes and links that occupy a spatial volume, are hard to study with conventional techniques. A meta-graph approach that elucidates the impact of physicality on network structure has now been introduced.

Subwavelength photonic gratings can host long-lived, negative-effective-mass photonic modes that couple strongly to electron transitions in constituent active materials. The resulting bosonic hybrid light–matter modes, or exciton-polaritons, can be optically configured to accumulate into various macroscopic artificial complexes and lattices of coherent quantum fluids.

Landau’s theory of Fermi liquids predicts that impurities embedded in a Fermi sea of atoms form quasiparticles called polarons that interact with one another via the surrounding medium. Such mediated polaron–polaron interactions have been directly observed and are shown to depend on the quantum statistics of the impurities.

Neutron spectroscopy, entanglement analysis, and simulations provide evidence that KYbSe₂ closely approximates a 2D quantum spin liquid. Although KYbSe₂ displays magnetic ordering at low temperatures, its magnetic dynamics are dominated by fractionalized excitations that exhibit anomalously large quantum entanglement, indicating that on finite timescales KYbSe₂ exhibits quantum spin liquid physics.

Despite the theoretical prediction of spinaron quasiparticles in artificial nanostructures, experimental evidence has not yet been seen. Now it has been observed in a hybrid system comprising Co atoms on a Cu(111) surface.

Interactions between excitons and correlated electrons can lead to the formation of interesting states. Now, evidence suggests that these interactions can give rise to a Mott insulator of excitons.

Metallic kagome compounds are known to host several different electronic phases. Now, evidence for a form of nematic order that breaks time-reversal symmetry and is odd under a parity transformation is found in CsV₃Sb₅.

Time-resolved measurements show that coupling between electrons and phonons in lead halide perovskites can mediate attractive interactions between excitons, although the interaction strength depends on the specific material.

Topological defects play a crucial role in the behaviour of strongly correlated materials out of equilibrium. Now, ultrafast electron diffraction measurements on 1T-TiSe₂ shed light on the defect formation process at sub-picosecond timescales.

Bound states in the continuum are topological states with useful symmetry protection properties. An experiment now shows how to use them to form macroscopically coherent complexes of polariton condensates.

Polarons are quasi-particles formed by impurities together with induced excitations in a surrounding medium. Now, mediated interactions between polarons have been detected using atomic impurities embedded in a Fermi gas of ultracold atoms.

A detailed analysis of inelastic neutron scattering data, including the evaluation of entanglement witnesses used in quantum information theory, supports the proposal that the triangular-lattice antiferromagnet KYbSe₂ is close to a spin-liquid phase.

Interactions between a localized magnetic moment and electrons in a metal can produce an emergent resonance that affects the metal’s properties. A realization of this Kondo effect in MoS₂ provides an opportunity to study it in microscopic detail.

A computational method capable of capturing the effects of electronic interactions and scattering can help interpret the vibrational reflectance measurements in superconducting and bad metals.

Twisted structures are shown to confine and guide light without total internal reflection, using an effect analogous to the stable Lagrange points in celestial mechanics.

The phase transition from a topologically trivial state to non-Hermitian conducting edge modes can be controlled by optical nonlinearities, achieving picosecond switching speeds.

Non-Hermitian physics enables dynamic control of optical behaviour in real time, such as reflectionless scattering modes, which have now been demonstrated in a chaotic photonic microcavity.

Individual electrons trapped on the surface of solid neon can operate as charge qubits with very long coherence times.

The behaviour of actomyosin networks with turnover emerges from the interplay between advection and percolation. The contraction pattern is shown to be size-dependent with continuous contraction in small droplets and periodic waves in larger systems.

Heating and cooling are shown to happen along distinct thermodynamic pathways, which makes the former faster than the latter. This finding calls for a rethink of the fundamentals of thermalization processes at the microscale and of devices like Brownian heat engines.

Physical networks are systems composed of physical entities, which conventional graph-based approaches fail to capture. Theoretical work now introduces a meta-graph technique to uncover the impact of physicality on the structure of networks.

Network geometry is an emerging framework used to describe several topological and organizational features of complex networks. Now this approach has been extended to directed networks, which contain both symmetric and asymmetric interactions.

Cell division is governed by the positioning of a cytoskeletal structure called the spindle. Two methods, one based on laser ablation and the other on fluid flow assessments, are now shown to be useful tools for studying spindle positioning.

Quantum technologies change our notion of measurement. Chenyu Wang elaborates on how quantum squeezing enhances the precision of gravitational-wave interferometers.