Quantum materials

This Review surveys the electronic properties of quantum materials through the prism of the electron wavefunction, and examines how its entanglement and topology give rise to a rich variety of quantum states and phases.

The exploration of the properties and applications of quantum materials relies on advances in synthesis techniques. The approaches pursued to realize thin films and other materials revealing emergent quantum behaviour are reviewed here.

The key to exploiting quantum materials for applications is the control of their properties. This Review discusses strategies to externally modify their properties on demand.

Topology and collective phenomena give quantum materials emergent functions that provide a platform for developing next-generation quantum technologies, as surveyed in this Review.

Specialized imaging methods are now available to measure the quantum properties of materials with high sensitivity and resolution. These techniques are key to the design, synthesis and understanding of materials with exotic functionalities.

The emergent phenomena that characterize quantum materials have received prominent exposure thanks to experimental techniques based on photoemission. In turn, the challenges and opportunities presented by quantum materials have driven improvements in the photoemission technology itself.

Emergent phenomena are common in condensed matter. Their study now extends beyond strongly correlated electron systems, giving rise to the broader concept of quantum materials.

This Perspective discusses recent progress in the field of topological states in condensed matter; initiated by the quantum Hall effect, it now includes systems like topological insulators, topological superconductors, and Weyl/Dirac semimetals.

Condensed-matter physics brings us quasiparticles that behave like massless fermions.

From magnetism, ferroelectricity and superconductivity to electrical and thermal properties, oxides show a broad range of phenomena of fundamental as well as practical relevance. Reviewed here are the emergent phenomena arising at the interface between oxide materials, which have attracted considerable interest based on advances in thin-film deposition techniques.

The term 'high-temperature superconductor' used to refer only to copper-based compounds — now, iron-based pnictides have entered the frame. The comparison of these two types of superconductor is revealing, and suggestive of what might be needed to achieve even higher transition temperatures.

Collective quantum phenomena such as magnetism, superfluidity and superconductivity have been pre-eminent themes of condensed-matter physics in the past century. Neutron scattering has provided unique insights into the microscopic origin of these phenomena.

Monolayer films of iron selenide deposited on strontium titanate display signatures of superconductivity at temperatures as high as 109 K. These recent developments may herald a flurry of exciting findings concerning superconductivity at interfaces.

Physicists have discovered a new topological phase of matter, the Weyl semimetal, whose surface features a non-closed Fermi surface whereas the low-energy quasiparticles in the bulk emerge as Weyl fermions. A brief review of these developments and perspectives on the next steps forward are presented.

Topological semimetals and metals have emerged as a new frontier in the field of quantum materials. Novel macroscopic quantum phenomena they exhibit are not only of fundamental interest, but may hold some potential for technological applications.

The 2016 Nobel Prize in Physics has been awarded to David Thouless, Duncan Haldane and Michael Kosterlitz “for theoretical discoveries of topological phase transitions and topological phases of matter”.

Topological semimetals give access to new quantum phenomena — for example, massless fermions have not been observed as elementary particles, yet they can be realized in the form of quasiparticles in these materials — and could allow the development of robust quantum devices.

Quasiparticles are an extremely useful concept that provides a more intuitive understanding of complex phenomena in many-body physics. As such, they appear in various contexts, linking ideas across different fields and supplying a common language.

The interplay between spin–orbit coupling and two-dimensionality has led to the emergence of new phases of matter, such as spin-polarized surface states in topological insulators, interfacial chiral spin interactions, and magnetic skyrmions in thin films, with great potential for spin-based devices.

A review of the phases of copper oxides (especially the ‘strange metal’), discussing their high-temperature superconductivity and their various forms of quantum matter, and the implications for fundamental theory.

Fabrication techniques developed for graphene research allow the disassembly of many layered crystals (so-called van der Waals materials) into individual atomic planes and their reassembly into designer heterostructures, which reveal new properties and phenomena.

Klaus von Klitzing tells the story of the quantum Hall effect's impact on metrology.

This Review covers the recent developments in the observation and modelling of magnetic skyrmions, including their topological properties, current-induced dynamics and potential in future information storage devices.

Magnetic skyrmions are topologically protected spin whirls that hold promise for applications because they can be controllably moved, created and annihilated. In this Review, the underlying physics of the stabilization of skyrmions at room temperature and their prospective use for spintronic applications are discussed.