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Magneto-oscillations have revealed many interesting phenomena in graphene and quantum Hall systems, but they are typically measured at low currents and in equilibrium. Here, the authors report several non-equilibrium quantum effects observed in magneto-oscillations in graphene at high currents.

For small twist angles, electrons can resonantly tunnel between graphene layers in a van der Waals heterostructure. It is now shown that the tunnelling not only preserves energy and momentum, but also the chirality of electronic states.

A polariton is a hybrid excitation resulting from strong light–matter coupling. The magneto-transport measurements have now revealed the crucial role played by its electronic component.

The fractional quantum Hall effect occurs when electrons move in Landau levels. In this study, using a theoretical flat-band lattice model, the fractional quantum Hall effect is observed in the presence of repulsive interactions when the band is one third full and in the absence of Landau levels.

Landau-Zener transitions near an avoided level crossing are a broadly relevant concept in quantum systems. Here the authors use a superconducting flux qubit to shed new light on the role of the environment in Landau-Zener tunneling by observing a crossover between weak and strong coupling.

Strain-engineered pseudomagnetic fields realized in two-dimensional photonic crystals induce flat-band Landau levels at discrete energies as well as chiral edge states. The high density of states and high degeneracy of the flat bands has implications for both on-chip and radiating light fields.

Two-dimensional electron systems at half-filled Landau levels can form unusual electronic states such as paired fractional quantum Hall and nematic phases. Here the authors observe the transition between these two phases at filling factors 5/2 and 7/2 and demonstrate the important influence of interactions.

Optical transitions between Landau levels (LL) in solids are described by selection rules associated with the LL index. Here, the authors perform photocurrent spectroscopy measurements on high-quality bilayer graphene to investigate the interband LL transitions, and observe valley-dependent optical transitions obeying unusual selection rules.

Tunability of the electronic properties of magnetic topological insulators is highly desired for future device applications. Here, the authors study the effect of substitutional impurities on the topological properties of Sb-doped MnBi₂Te₄ devices and uncover tunable layer-dependent electronic states.

Using torque magnetometry, the thermodynamic signatures of bosonic Landau level transitions are observed in a layered superconductor, owing to the formation of Cooper pairs with finite momentum.

The transport behavior of the carriers residing in the lowest Landau level is hard to observe in most topological materials. Here, Liu et al. report a surprising angular dependence of the interlayer magnetoresistivity and Hall conductivity arising from the lowest Landau level under high magnetic field in type II Weyl semimetal YbMnBi₂.

Single molecules on metal surfaces are paradigmatic systems for the study of many-body phenomena. Here, the authors show that several spectroscopic experiments on iron phthalocyanine on Au(111) surface can be described in a unified way in terms of a strongly interacting topologically non-trivial (non-Landau) Fermi liquid.

Monitoring the photocurrent generated as a laser scans across a graphene field-effect device subjected to low temperature and high magnetic fields enables the spatial distribution of Landau levels across a graphene sheet to be mapped. This in turn allows the relative contribution of bulk and edge states to the macroscopic electrical characteristics of these devices to be determined.

Experimental signatures of a Berry phase for composite fermions in the fractional quantum Hall effect provide support for the predictions that these composite fermions are Dirac particles.

Graphene and topological-insulator surfaces are well known for their two-dimensional conic electronic dispersion relation. Now three-dimensional hyperconic dispersion is shown for electrons in a HgCdTe crystal—once again bridging solid-state physics and quantum electrodynamics.

Most of the notable properties of graphene are a result of the cone-like nature of the points in its electronic structure where its conduction and valance bands meet. Similar structures arise in 2D HgTe quantum wells, but without the spin- and valley-degeneracy of graphene; their properties are also likely to be easier to control.

Here, the authors show that Brown-Zak fermions in graphene-on-boron-nitride superlattices exhibit mobilities above 10⁶ cm²/V s and micrometer scale ballistic transport.

This study demonstrates 3D printing of hierarchically ordered, porous transition metal oxides and nitrides directed by block copolymer self-assembly, with record surface areas and nanoconfinement-induced critical fields in the nitride superconductors

The fractional quantum Hall state at the filling factor 5/2 has been intensively studied due to its predicted non-Abelian statistics. Petrescu et al. measure the composite fermion effective mass of this state and find that it is several times larger than that in the half-filled lowest Landau level.

Reducing the switching energy of ferroelectric films remains an important goal. Here, the authors elucidate the fundamental role of lattice dynamics in ferroelectric switching on both freestanding BiFeO₃ membranes and films clamped to a substrate.

Understanding collective behaviour is an important aspect of managing the pandemic response. Here the authors show in a large global study that participants that reported identifying more strongly with their nation reported greater engagement in public health behaviours and support for public health policies in the context of the pandemic.

Increasing the size of mesoscopic devices based on van der Waals heterostructures triggers additional quantum effects. Here, the authors observe distinct magnetoresistance oscillations in graphene/h-BN Hall bars only in devices wider than 10 μm due to resonant scattering of charge carriers by transverse acoustic phonons in graphene.

Two closely spaced two-dimensional systems can remain strongly coupled by electron–electron interactions even though they cannot physically exchange particles. Coulomb drag is a manifestation of this interaction—in which an electric current passed through one layer causes frictional charge flow in the other—now experimentally observed in bilayer graphene

Recent work has reported a realization of a time crystal in the form of the Bose-Einstein condensate of magnons in superfluid ³He. Here, the authors study the dynamics of a pair of such quantum time crystals and show that it closely resembles the evolution of a two-level system, modified by nonlinear feedback.

Using a system to adjust the strength of cavity vacuum fields penetrating a Hall bar, a study describes the effect of the vacuum field of a cavity on electronic correlations in quantum Hall systems.

Applications of rare-earth nickelates are hampered by lack of global understanding of the interplay among various degrees of freedom. Here, Mercy et al. propose that the metal-insulator transition of nickelates arises from the softening of an oxygen breathing distortion, providing a united picture of electronic, structural and magnetic properties.

The technological application of ultrafast terahertz magnons in itinerant ferromagnetic nanostructures is currently limited by magnon relaxation due to Landau damping. Here, Qin et al. demonstrate suppressed Landau damping and enhanced magnon lifetimes in ultrathin films of Fe–Pd alloy.

The electronic structure of the helimagnet CrAs is unusual due to its nonsymmorphic crystal symmetry. Here, the authors observe quasilinear magnetoresistance close to a pressure-driven superconducting transition, which may arise from the interaction of the band structure and magnetic fluctuations.

In Weyl semimetals, unusual electronic transport phenomena are predicted to occur, such as an axial anomaly which violates the conservation of chiral fermions. Here, the authors evidence such behaviour via the occurrence of negative magnetoresistance in layered high-purity non-magnetic metals.

Huang et al. study fractional quantum Hall (fQH) states in high-quality GaAs/AlGaAs samples. They report evidence for a fQH state at filling factor ν = 9/11, which they associate with the formation of six-flux composite fermions.

Confining electrons to two dimensions can drastically alter the way they interact with each other. Here, the authors show that electrons in quantum wells can form into two distinct solid-like phases when placed in a large magnetic field.

The motion of particles in a quantum condensate state are described by a single macroscopic wave function, leading to a host of unusual properties. Here, the authors generate such a condensation of magnetically induced excitons, known as cyclotron magnetoexcitons, in a high-mobility quantum well.

The interplay between charge density wave states in emerging kagome superconductors is a topic of ongoing debate. Here, the authors unveil the out-of-equilibrium competition between two coexisting charge density waves in CsV₃Sb₅ by harnessing time-resolved X-ray diffraction.

The electronic properties of bismuth under an applied magnetic field have latterly become a topic of interest. An angle-resolved magnetostriction approach is now used to provide thermodynamic evidence for unusual symmetry-breaking effects.

Conventionally, the states of a two-dimensional quantum ring in a high magnetic field have a well-defined spatial structure. But Coulomb repulsion between individual orbits causes oscillations in the size of this structure each time a magnetic flux-quantum enters or leaves the system. This effect has now been measured experimentally in semiconducting quantum rings.

Monolayer graphene can be magnetized by coupling to an antiferromagnetic thin film of chromium selenide, resulting in an exchange splitting energy as high as 134 meV at 2 K.

A spatially resolved optical polarimetry technique is used to identify a three-state Potts-nematic order parameter in a triangular lattice antiferromagnetic material.

The Haldane model is a paradigmatic example of topological behaviour but has not previously been implemented in condensed-matter experiments. Now a moiré bilayer is shown to realize this model with the accompanying quantized transport response.

Scanning tunnelling microscopy shows that 1D channels between quantum Hall states with different valley polarization are metallic or insulating depending on constraints imposed on electron–electron interaction by valley flavour.

The topological character of electrons in semimetals subtly influences their bulk properties, leading typically to weak experimental signatures. Here, Moll et al. report a distinctive anomaly in the magnetic torque upon entering quantum limit state in the Weyl semimetal NbAs, which only appears due to the presence of Weyl fermions.

Moiré superlattices arising in bilayer graphene coupled to hexagonal boron nitride provide a periodic potential modulation on a length scale ideally suited to studying the fractal features of the Hofstadter energy spectrum in large magnetic fields.

A powerful new spectroscopic technique (high-resolution time-domain capacitance spectroscopy) for detailed exploration of the energy structure of two-dimensional electron systems (2DES) gives a quantitative and precise view of electron–electron interactions in a 2DES, and reveals several phenomena at energies that cannot be reached with other techniques.

Understanding transformations of non-equilibrium materials is a key open scientific question. Here the pathway by which different polar supertextures undergo dynamical correlations and collectively transform into a metastable supercrystal state is revealed experimentally and theoretically over seven orders of magnitude timescale.