Volume 20 Issue 4, April 2024

Mathematical proofs of black hole physics are becoming too complex even for specialists.

AI needs to develop more solid assumptions, falsifiable hypotheses, and rigorous experimentation.

The time has come to consider appropriate guardrails to ensure quantum technology benefits humanity and the planet. With quantum development still in flux, the science community shares a responsibility in defining principles and practices.

Some quantum acoustic resonators possess a large number of phonon modes at different frequencies. Direct interactions between modes similar to those available for photonic devices have now been demonstrated. This enables manipulation of multimode states.

Experiments with unprecedented energy and momentum resolution reveal the nature of the pairing symmetry in KFe₂As₂ and pave the way for a unified theoretical description of unconventional superconductivity in iron-based materials.

Some exotic metals exhibit competing electronic states that can be influenced by small perturbations. Now, a study of a kagome superconductor shows that this competition is exquisitely sensitive to weak strain fields, providing insight into its anomalous electronic properties.

Phonons do not carry spin or charge, but they can couple to an external magnetic field and cause a sizable transverse thermal gradient. Experiments suggest that phonon handedness is a widespread effect in magnetic insulators with impurities.

Multiple mechanisms can create electrons with reduced kinetic energy in solids. Combining these mechanisms now appears as a promising route to enhancing quantum effects in flat band materials.

Some cerium and uranium compounds exhibit unusual transport properties due to localized electron states. Recent experiments demonstrate that quantum interference on frustrated lattices provides an alternative route to this behaviour.

Ageing is a non-linear, irreversible process that defines many properties of glassy materials. Now, it is shown that the so-called material-time formalism can describe ageing in terms of equilibrium-like properties.

When cracks creep forward in our three-dimensional world, they do so because of accompanying cracks racing perpendicular to the main direction of motion with almost sonic speed. Clever experiments have now directly demonstrated this phenomenon.

Quantum computers promise to efficiently predict the structure and behaviour of molecules. This Perspective explores how this could overcome existing challenges in computational drug discovery.

The transition from a metastable state to the ground state in classical many-body systems is mediated by bubble nucleation. This transition has now been experimentally observed in a quantum setting using coupled atomic superfluids.

Quantum gates require controlled interactions between different degrees of freedom. A tunable coupling has now been demonstrated between the phonon modes of a mechanical resonator designed for storing and manipulating quantum information.

High-precision photoemission measurements determine that the superconducting pairing symmetry in KFe₂As₂ is the same as in other types of iron-based superconductors, despite having different features in the band structure.

The electronic transport properties of charge-ordered kagome metals are controversial. Now careful measurements on unperturbed samples show that previously measured anisotropy in the transport occurs only when external perturbations are present.

The thermal Hall effect of phonons does not yet have a definitive explanation. Now a careful study of doped Sr₂IrO₄ suggests that the mechanism involves the scattering of phonons by impurities embedded in an antiferromagnetic environment.

Heterostructures of transition metal dichalcogenides are known to simulate the triangular-lattice Hubbard model. Now, by combining a monolayer and bilayer of different materials, this idea is extended to multi-orbital Hubbard models.

The mechanism of charge density wave formation has been hard to explain due to accompanying structural distortions. Now low-dimensional HfTe₂ is revealed to host a purely electronic exitonic charge density wave driven by reduced screening effects.

Observations of strong electron correlation effects have been mostly confined to compounds containing f orbital electrons. Now, the study of the 3d pyrochlore metal CuV₂S₄ reveals that similar effects can be induced by flat-band engineering.

Electrons in f orbitals can create localized states that interact strongly and drive strange metal and critical behaviour via the Kondo mechanism. Now a mechanism of geometric frustration enables similar phenomena with d electrons.

Control over magnetic skyrmions at room temperature has important applications in technology. Now the observation of skyrmions with high topological charge widens the potential for them to be used in unconventional computing techniques.

Most quantum simulations of spin models with trapped ions have been restricted to one dimension. Now, tunable simulations of Ising models with single-site detection have been demonstrated in two-dimensional ion crystals.

Time crystals spontaneously produce periodic oscillations that are robust to perturbations. A time crystal phase with a long coherence time has now been produced using the electron and nuclear spins of a semiconductor sample.

Physical ageing in glassy materials can be described in a linear way through the concept of material time. Multispeckle dynamic light scattering is now shown to provide experimental access to the material time, in terms of which fluctuations become statistically reversible.

When applying sufficient strain, the flow of dense granular matter becomes critical. It is now shown that this state corresponds to random loose packing for spheres with different friction coefficients and that these packings can be mapped onto the frictionless hard-sphere system.

Dense suspensions are granular materials suspended in a liquid at high packing fractions, exhibiting high viscosity. The latter is now shown to be related to the formation of a network of rigid clusters at large shear stress.

Understanding the three-dimensional nature of fracture formation and dynamics is challenging. Experiments now show that a fracture front, after originating at a particular locus in a material, propagates jump-wise and expands transversely at high speed.

Cytoplasmic flows in the fruit fly oocyte can reorganize cellular components. These structured vortical flows arise through self-organizing dynamics of microtubules, molecular motors and cytoplasm.

Bart Verberck uses the musical cent as a pretext to touch on some of the intricacies of musical tuning systems.