Volume 15 Issue 3, March 2019

In praise of the March meeting of the American Physical Society.

In 2016 and 2017, the LISA Pathfinder mission successfully proved that the technologies for the space-based gravitational wave detector LISA are ready. LISA is now scheduled to launch in the early 2030s, to open a so far unexploited scientific field.

Quark–gluon plasma has been recreated in heavy-ion collisions, providing a glimpse of the very early Universe. The PHENIX Collaboration offers new insights into the possible creation of this state in smaller collision systems.

A large-scale imaging study has tracked thousands of bacteria living in three-dimensional biofilms. This technical tour de force reveals the importance of mechanical interactions between cells for building local and global structure.

Zirconium alloys are widely used as cladding material in nuclear reactors due to their neutron transparency. Now, it is shown that ⁸⁸Zr has a surprisingly high neutron capture cross-section exceeding that of other zirconium isotopes by six orders of magnitude.

Some gravitational phenomena are difficult or even impossible to observe in real spacetime. Laboratory analogues of black-hole horizons offer new perspectives on field theory effects that might help our understanding of gravitation.

A quark–gluon plasma is produced in proton–gold, deuteron–gold and helium–gold collisions. Observing elliptic and triangular flow in this nearly inviscid fluid from these different initial geometries provides a unique benchmark for hydrodynamic models.

A ‘which-way’ scattering process can generate entanglement between single photons and collective chiral vibrations in two-dimensional tungsten diselenide. The result opens up ways for engineering non-reciprocal interactions at the quantum level.

Two-dimensional electronic spectroscopy experiments and first-principles many-electron calculations demonstrate the quantum mixing of different exciton states in monolayer MoS₂. This reveals the many-body effects and dynamics of exciton formation in 2D materials.

Experiments show two different energy scales associated with the onset of superconductivity in an amorphous superconductor. This validates the theory of Cooper pairs that condense to a superfluid at lower temperature than they form.

Report of the likely observation of a Mott insulator in trilayer graphene with a moiré potential. The Mott state can be tuned between different filling fractions via gating, which will enable the careful study of this paradigmatic many-body state.

Quantum interference between electronic pathways is generally difficult to observe in solid-state systems. Such interference is, however, now characterized in the second-harmonic generation from transition metal dichalcogenides, even at room temperature.

Using alkali metal dimers attached to helium droplets, a new decay mechanism for intermolecular Coulombic decay is demonstrated. The process leads to previously unresolved double ionization for excitation energies exceeding double ionization energies.

Single-cell tracking of up to 10,000 bacteria reveals the structure and dynamics of 3D biofilms—providing evidence to suggest that both local ordering and global biofilm architecture emerge from mechanical interactions.

While topological states are often characterized by their global properties related to the topological invariants, the introduced real-space topological markers provide new insights to these states.

Detailed neutron scattering, magnetic susceptibility and muon spin relaxation studies indicate the absence of long-range magnetic order in the quantum magnet TbInO₃ down to 0.46 K— an observation consistent with quantum spin liquid behaviour.

Ferromagnetism is observed at ferroelastic domain walls in strontium titanate and its heterostructures with other oxides. Applying strain can reverse the magnetism. This suggests the possibility of device engineering using domain walls.

The origin of size-dependent shifts of surface plasmon resonances in metal nanoparticles has been controversial for decades. A combined experimental and theoretical study on silver samples and their environments now provides a quantitative picture.

A major challenge for achieving useful thermonuclear fusion regimes is heating plasma to reactive temperature conditions. It is demonstrated experimentally how energetic ions, generated via neutral beam injection, can be exploited for this process.

Accurately capturing both microscopic and mesoscopic properties of fluid–gas interfaces is a long-standing challenge. Now, a microscopic theory of correlation functions that can be scaled up to explain mesoscopic surface tension phenomena is put forward.

A study of how single C. elegans cells establish the polarity required for cell division reveals a general principle for pattern formation in living systems controlled by biochemical cues.

In 2016, Peter Trueb computed 22.4 trillion digits of π. Ahead of π Day on 14 March, he reflects on the nature of π and its role in mathematics, science and philosophy.