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Overlaying two atomic layers with a slight lattice mismatch or at a small rotation angle creates a moiré superlattice, which has properties that are markedly modified from (and at times entirely absent in) the ‘parent’ materials. Such moiré materials have progressed the study and engineering of strongly correlated phenomena and topological systems in reduced dimensions. The fundamental understanding of the electronic phases, such as superconductivity, requires a precise control of the challenging fabrication process, involving the rotational alignment of two atomically thin layers with an angular precision below 0.1 degrees. Here we review the essential properties of moiré materials and discuss their fabrication and physics from a reproducibility perspective. The essential properties of moiré materials and the progress and latest developments in the field are reviewed, and their fabrication and physics are discussed from a reproducibility perspective.

In a flat band superconductor, the charge carriers’ group velocity v F is extremely slow. Superconductivity therein is particularly intriguing, being related to the long-standing mysteries of high-temperature superconductors 1 and heavy-fermion systems 2 . Yet the emergence of superconductivity in flat bands would appear paradoxical, as a small v F in the conventional Bardeen–Cooper–Schrieffer theory implies vanishing coherence length, superfluid stiffness and critical current. Here, using twisted bilayer graphene 3 – 7 , we explore the profound effect of vanishingly small velocity in a superconducting Dirac flat band system 8 – 13 . Using Schwinger-limited non-linear transport studies 14 , 15 , we demonstrate an extremely slow normal state drift velocity v n  ≈ 1,000 m s –1 for filling fraction ν between −1/2 and −3/4 of the moiré superlattice. In the superconducting state, the same velocity limit constitutes a new limiting mechanism for the critical current, analogous to a relativistic superfluid 16 . Importantly, our measurement of superfluid stiffness, which controls the superconductor’s electrodynamic response, shows that it is not dominated by the kinetic energy but instead by the interaction-driven superconducting gap, consistent with recent theories on a quantum geometric contribution 8 – 12 . We find evidence for small Cooper pairs, characteristic of the Bardeen–Cooper–Schrieffer to Bose–Einstein condensation crossover 17 – 19 , with an unprecedented ratio of the superconducting transition temperature to the Fermi temperature exceeding unity and discuss how this arises for ultra-strong coupling superconductivity in ultra-flat Dirac bands. The authors investigate the effect of small velocity in a superconducting Dirac flat band system, finding evidence for small pairs and that superfluid stiffness is not dominated by kinetic energy.

The development of strategies for addressing arrays of nanoscale devices is central to the implementation of integrated nanosystems such as biological sensor arrays and nanocomputers. We report a general approach for addressing based on molecular-level modification of crossed semiconductor nanowire field-effect transistor (cNW-FET) arrays, where selective chemical modification of cross points in the arrays enables NW inputs to turn specific FET array elements on and off. The chemically modified cNW-FET arrays function as decoder circuits, exhibit gain, and allow multiplexing and demultiplexing of information. These results provide a step toward the realization of addressable integrated nanosystems in which signals are restored at the nanoscale.

Because of their ultrafast intrinsic dynamics and robustness against stray fields, antiferromagnetic insulators1–3 are promising candidates for spintronic components. Therefore, long-distance, low-dissipation spin transport and electrical manipulation of antiferromagnetic order are key research goals in antiferromagnetic spintronics. Here, we report experimental evidence of robust spin transport through an antiferromagnetic insulator, in our case the gate-controlled state that appears in charge-neutral graphene in a magnetic field4–6. Utilizing quantum Hall edge states as spin-dependent injectors and detectors, we observe large, non-local electrical signals across charge-neutral channels that are up to 5 μm long. The dependence of the signal on magnetic field, temperature and filling factor is consistent with spin superfluidity1,2,4,7–10 as the spin-transport mechanism. This work demonstrates the utility of graphene in the quantum Hall regime as a powerful model system for fundamental studies in antiferromagnetic spintronics.

A single hydrogen molecule can be used to drive the tip motion of a scanning tunneling microscope. In physical systems, mechanical energy usually flows from the large to the small in the form of dissipation into the random thermal motion of the molecules and atoms in the system. In biology, many natural systems have evolved to reverse this trend, enabling the flow of energy from the small to the large, with examples including photosynthesis ( 1 ) or motor protein motion ( 2 ). The desire to recreate this ability in artificial systems motivates a search for strategies and concepts that enable energy harvesting from very small subsystems. On page 779 of this issue, Lotze et al. ( 3 ) now show how the motion of a macroscopic cantilever beam can be excited using the driven motion of only a single molecule. In this case, a single hydrogen molecule is trapped between a copper surface and a scanning tunneling microscopy tip mounted on a flexible springlike cantilever. The authors find that when a particular bias voltage between the tip and copper is applied, the electric current causes the hydrogen to switch stochastically between two different positional states and the cantilever begins to oscillate spontaneously.

In the version of this Letter originally published, the number in the middle yellow box of Fig. 2d was incorrectly given as +2; it should have been 0. This has now been corrected.

At the charge neutrality point, bilayer graphene (BLG) is strongly susceptible to electronic interactions and is expected to undergo a phase transition to a state with spontaneously broken symmetries. By systematically investigating a large number of single-and double-gated BLG devices, we observe a bimodal distribution of minimum conductivities at the charge neutrality point. Although σ ₘᵢₙ is often approximately 2–3 e ²/ h (where e is the electron charge and h is Planck’s constant), it is several orders of magnitude smaller in BLG devices that have both high mobility and low extrinsic doping. The insulating state in the latter samples appears below a transition temperature T c of approximately 5 K and has a T = 0 energy gap of approximately 3 meV. Transitions between these different states can be tuned by adjusting disorder or carrier density.

The Mott insulating state is a manifestation of strong electron interactions in nominally metallic systems. Using transport spectroscopy, we showed that an energy gap exists in nominally metallic carbon nanotubes and occurs in addition to the band gap in small-band-gap nanotubes, indicating that carbon nanotubes are never metallic. This gap has a magnitude of ~10 to 100 milli-electron volts and a nanotube radius (r) dependence of ~1/r, which is in good agreement with predictions for a nanotube Mott insulating state. We also observed neutral excitations within the gap, as predicted for this state. Our results underscore nanotubes' exceptional capabilities for use in studying correlated electron phenomena in one dimension.

We explore Andreev states at the interface of graphene and a superconductor for a uniform pseudo-magnetic field. Near the zeroth-pseudo Landau level, we find a topological transition as a function of applied Zeeman field, at which a gapless helical mode appears. This 1D mode is protected from backscattering as long as intervalley- and spin-flip scattering are suppressed. We discuss a possible experimental platform to detect this gapless mode based on strained suspended membranes on a superconductor, in which dynamical strain causes charge pumping