First Anniversary

The Hubble constant can be estimated from measurements of both the early and late Universe, but the two estimates disagree. In 2019 a number of independent measurements using different methods made this discrepancy harder to ignore.

In 2019, new optical phenomena have been revealed in stacks of atomically thin semiconducting transition metal dichalcogenides. These effects can be understood in terms of well-known, but also new, exotic, types of exciton.

Artificial spin ices are metamaterials displaying fascinating phenomena arising from the collective behaviour of nanoscale magnets. We review recent developments in terms of emergent magnetic monopoles, phase transitions, dynamics and geometries, and discuss future directions for research and potential applications.

Pseudo-electromagnetic fields emerge in inhomogeneous materials. This Review discusses the properties of such fields in the context of 3D topological semimetals, the origin and consequences of pseudo-fields in real materials and their field theory description.

The geometric phase is a deep and influential concept in modern physics and related sciences. This Review briefly discusses its origin, mathematical formulation and various forms, some of which are topological; then elaborates on contemporary optical and condensed-matter applications.

Cosmological computer simulations of galaxy formation emerged as the primary tool to study structure formation in the Universe. This Technical Review describes the main techniques and ingredients of such simulations and their application to develop and constrain galaxy formation theories.

Angle-resolved photoemission spectroscopy (ARPES) is a tool for directly probing the electronic structure of solids and has had a crucial role in studying topological materials. In this Technical Review, we discuss the latest developments of various ARPES techniques and their applications to topological materials

The Large Synoptic Survey Telescope (LSST), an upcoming astronomical survey, will deeply observe the entire southern sky in a broad range of colours. We present the LSST science opportunities and technical challenges in the field of galaxy formation and evolution.

Random lasing, which exploits disorder to enhance stimulated emission, challenges the conventional descriptions of lasing. This Expert Recommendation describes experimental methods required to properly assess and demonstrate random lasing action.

Quantum sensors based on atom interferometry are moving from fundamental research towards commercial applications in metrology, geophysics, space, civil engineering, oil and minerals exploration, and navigation, but a number of challenges need to be overcome.