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Surface Fermi arcs (SFAs) are characteristic features of a topological Weyl semimetal but there is no easy way to manipulate them so far. Here, the authors report manipulation of the shape, size and connections of SFAs in a Weyl semimetal NbAs, leading to an unusual topological Lifshitz transition.

The origin of superconductivity enhancement in FeSe monolayer grown on SrTiO₃ compared to bulk FeSe is still a debated issue. Here, Shi et al. report a further 15 K jump of T_c accompanying a second Lifshitz transition triggered by electron doping in FeSe/SrTiO₃monolayer films.

Each valley of the mini-Brillouin zone ("mini valley") of twisted bilayer graphene (TBG) contains two Dirac cones that hybridize to form flat bands. Theory predicts that these two Dirac cones have the same chirality, leading to topological obstruction. Here, the authors confirm this prediction experimentally.

When doubly-degenerate band crossings known as Kramers nodal lines intersect the Fermi level, they form exotic three-dimensional Fermi surfaces composed of massless Dirac fermions. Here, the authors present evidence that the 3R polytypes of TaS₂ and NbS₂ are Kramers nodal line metals with open octdong and spindle-torus Fermi surfaces, respectively.

It remains to be seen if high-T_c superconductors rely on similar Fermi-surface instabilities as their BCS counterparts. Miao et al. study the high-T_c compound LiFe_1−xCo_xAs with high-resolution ARPES and find a robust gap with Co doping that suggests the order parameter is not tied to such instabilities.

Hund’s exchange interaction energy in two-dimensional materials is challenging to extract from experiments. Now, this is achieved in rhombohedral graphene, which allows an estimate of the interactions that drive the variety of correlated states in this material.

The understanding of the reemergence of pressure induced superconductivity in alkali-metal intercalated FeSe is hampered by sample complexities. Here, Sun et al. report the electronic properties of (Li_1–xFe _x )OHFe_1–ySe single crystal not only in the reemerged superconducting state but also in the normal state.

Rashba-type splitting is an effective way to manipulate the spin degrees of freedom in a solid without external magnetic field. Here, the authors demonstrate a strong Rashba-type splitting at the interface of LaTiO₃ and SrTiO₃ which is promising for the development of oxide-based spintronics.

Experimental study of the Kondo insulator SmB₆ provides an alternative route to realize a Fermi surface in the absence of a conventional Fermi liquid.

A. G. Eaton et al. directly probe the Fermi surface of the candidate triplet superconductor UTe2 by measuring magnetic quantum oscillations in ultra-pure crystals. By comparison with model calculations, the data are found to be consistent with a Fermi surface that consists of two cylindrical sections of electron and hole-type respectively.

An insulator does not conduct electricity, and so cannot in general be used to transmit an electrical signal. But an insulator's electrons possess spin in addition to charge, and so can transmit a signal in the form of a spin wave. Here a hybrid metal–insulator–metal structure is reported, in which an electrical signal in one metal layer is directly converted to a spin wave in the insulating layer; this wave is then transmitted to the second metal layer, where the signal can be directly recovered as an electrical voltage.

Local electronic compressibility measurements of magic-angle twisted bilayer graphene show that the insulating and superconducting phases of this system are both derived from a high-energy symmetry-broken state.

Neural interactions taking place in the brain seemingly occur at criticality, but little is known about how this state is achieved. Moretti and Muñoz identify the signatures of so-called Griffiths phases stemming from the hierarchical topology of brain networks, which could point to an explanation.

Current methods to remove oil microdroplets from wastewater are ineffective at the variable pH conditions commonly found in wastewater. This study presents a surface-engineered sponge that synergistically combines surface chemistry, charge and roughness, providing a solution to this problem.

Observation of charge order in the overdoped (Bi,Pb)₂Sr₂CuO_6+δ superconductor using resonant X-ray scattering and angular-resolved photoemission spectroscopy, over a wide temperature range.

Angle-resolved photoemission spectroscopy of CaNi₂ shows a band with vanishing dispersion across the full 3D Brillouin zone that is identified with the pyrochlore flat band as well as two additional flat bands that arise from multi-orbital interference of Ni d-electrons.

Electron correlation normally makes electrons less mobile, but it is still not clear when correlation becomes very strong in Dirac semimetals. Here, Fujioka et al. report a very high electron mobility exceeding 60,000 cm²V⁻¹s⁻¹ in correlated Dirac semimetal of perovskite CaIrO3, due to the enhanced electron correlation nearby the Mott transition.

A magneto-transport study of twisted bilayer graphene near the magic angle further reveals its rich physics.

Finite momentum superconducting pairing refers to a class of unconventional superconducting states where Cooper pairs acquire a non-zero momentum. Here the authors report a new superconducting state in bulk 4Hb-TaS₂, where magnetic fields induce finite momentum pairing via magnetoelectric coupling.

Among its interesting properties, SrTiO₃ can show both superconductivity and ferroelectric quantum criticality at low temperatures. Tomioka et al. use La and oxygen-isotope doping to tune electron-doped SrTiO₃ to the critical region and observe enhanced superconductivity, suggesting a link between them.

Conversion of an external angular momentum, for example, from mechanical rotation or light into ferromagnetic moment has a long history. Here, Sasaki et al. demonstrate the conversion of phonon angular momentum, in ferromagnetic moment, potentially allowing for new types of control for spintronics.

Transition metal oxides with 5d ions present novel emergent behaviour based on the enhanced coupling of material properties compared to those with 3d ions. Here, the authors demonstrate a large spin-phonon coupling in NaOsO₃which results from a large Os–O electronic orbital overlap.

Remarkably stable excitations known as skyrmions have recently garnered significant attention in condensed-matter systems. It is now shown that skyrmions in thin films of MnSi and Cu₂OSeO₃ can be made to rotate as a result of thermal fluctuations.

The spin–orbit interaction can be used to optically generate and control terahertz electric photocurrents in metallic ferromagnetic heterostructures.

Antiferromagnetic magnons have two distinct chiralities, left handed and right handed. Here, Shiota and coauthors demonstrate both the manipulation and electrical readout of this handedness in a synthetic antiferromagnet.

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.

The electronic properties of graphene depends on how many layers are involved. Monolayer graphene is a zero-gapped semi-metal. Bilayer graphene is a small-gapped semiconductor. Magnetotransport measurements indicate trilayer graphene can be both, depending on its stacking.

Magnetic skyrmions are topologically stable swirls in a spin structure. Here, the authors demonstrate new ways of controlling them by showing that the absorption of an electromagnetic wave by a skyrmion depends on the direction of incidence and that the resonance modes respond to a magnetic field.

Light can provide ultrafast ways of spin manipulation in magnetic materials, but existing methods are limited by long thermal recovery or low temperature. Here, the authors demonstrate ultrafast spin precession via optical charge-transfer processes in exchange-coupled Fe/CoO at room temperature.

In BaFe₂As₂, the lattice couples strongly to the magnetic and electronic degrees of freedom, providing a way to control them. Here, by means of time-resolved X-ray scattering, the authors measure rapid lattice oscillations, which can induce changes in the material’s electronic and magnetic properties.

Despite being a charge insulator, YbB₁₂ behaves like a thermal metal. Low-temperature heat-transport measurements of this compound showed its gapless, itinerant and charge-neutral excitations.

The geometry dependence of the Casimir force could enable applications in nanomechanical systems if the effects can be enhanced. Here, the authors demonstrate that the Casimir force between two interpenetrating nanoscale gratings can exceed the proximity force approximation by a factor of 500.

A topological insulator has surface metallic states that are topologically protected by time-reversal symmetry. Tin telluride is now shown to be a ‘topological crystalline insulator’, in which the surface metallic state is instead protected by the mirror symmetry of the crystal.

Sr_1−yMn_1−zSb₂ (y, z < 0.1) is reported to be a magnetic topological semimetal exhibiting nearly massless relativistic fermions.

Short-lived precursors typically occur before molecules chemisorb on surfaces. Liu et al. predict that for benzene derivatives on metal surfaces, the precursors can be long-lived and the transition to chemisorption states can be reversible, which may be useful in molecular switch applications.

Artificial spin ices are composed of a honeycomb lattice of nanoscale magnets. Depending on the orientation of the magnets in the lattice, the spin ice can host high or low effective magnetic charge at each vertex. Here, Guo et al use neutron spin echo spectroscopy to show that these magnetic charges exhibit sub-ns relaxation times, analogous to bulk spin-ices.

Charge-neutral excitations have been proposed to explain metal-like thermal transport in Kondo insulators. Here, the authors demonstrate the coupling between charge-neutral excitations and spin degrees of freedom in a Kondo insulator YbIr₃Si₇, which puts restrictions on current theories.

The authors demonstrate high-order terahertz nonlinear magnonics using two-dimensional coherent spectroscopy, revealing the emergence of seventh-order spin-wave mixing and sixth harmonic magnon generation within an antiferromagnetic orthoferrite.

Magnetic skyrmions are particle-like spin textures with non-trivial topology which are stabilized by local magnetic interactions. Here, the authors demonstrate theoretically a class of skyrmions which are stabilized dynamically in the absence of interactions in a nanocontact spin-torque oscillator.

Graphene on boron nitride gives rise to a moiré superlattice displaying the Hofstadter butterfly: a fractal dependence of energy bands on external magnetic fields. Now, by means of capacitance spectroscopy, further aspects of this system are revealed—most notably, suppression of quantum Hall antiferromagnetism at particular commensurate magnetic fluxes.

In two-dimensional electron systems, strong Coulomb interactions lead to the formation of new phases. Here the authors observe a transition between two of these correlated phases, a composite fermion liquid and Wigner solid, in a zinc oxide heterostructure.