Classical electromagnetism forms the foundation of modern technology. In condensed matter systems, the Berry phase acquired by conduction electrons acts as an emergent electromagnetic field, facilitating phenomena analogous to classical electromagnetism, such as the Lorentz force and electromagnetic induction, and paving the way for next-generation spintronics. Magnetic skyrmions, spin vortices with non-trivial topology, serve as a key platform for such devices. For example, non-trivial transport responses are recognised as being induced by the emergent Lorentz force and the emergent electromagnetic induction. Despite remarkable progress in skyrmion physics, emergent reactance, in which the phase of an applied AC current is modified by emergent electromagnetism, has not been thoroughly investigated. Here, we report emergent reactance in a micro-fabricated device of the prototypical skyrmion-hosting material, MnSi. Our findings reveal that the internal deformation degrees of freedom in skyrmions are an important factor for efficient generation of the emergent reactance.

We determine the magnetic ground state of the kagome lattice magnet Nd3Ru4Al12 by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet ("hex-FM") with uniform moment length and ordering vector Q = 0, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, here called the "ortho-FM" state. Our analysis of the flipping ratio in polarized neutron scattering is consistent with the hex-FM state. The results provide a microscopic basis for understanding the large fluctuation-induced Hall and Nernst responses near TC approximate to 41 K, as previously reported for Nd3Ru4Al12.

All-optical control of antiferromagnetic order is essential for realizing next-generation energy-efficient spintronic and high-speed memory applications. However, the optical writing of antiferromagnetic domains remains a fundamental challenge, because conventional opto-magnetic recording techniques rely on net magnetization, which is absent in antiferromagnets. In certain multiferroic antiferromagnets, the magnetic toroidal moment provides an additional degree of freedom through its inherent magnetoelectric coupling, which manifests as directional asymmetry in light propagation. Here we demonstrate the all-optical writing of antiferromagnetic domains using the inverse optical magnetoelectric effect in ferrotoroidic LiNiPO4, driven solely by reversing the light propagation direction. This directional control arises from a strong coupling between the photon linear momentum and the magnetic toroidal moment, enabling non-volatile, deterministic and repeatable switching between time-reversed domains with arbitrary light polarization. Our findings establish an inverse optical magnetoelectric effect as a distinct mechanism for manipulating antiferromagnetic order, opening a new paradigm in opto-magnetism driven by photon momentum.

We report the first observation of a topological thermal Hall effect (tTHE) of electrons moving through a magnetic skyrmion lattice (SkL) of short period, where the skyrmion diameter is only a few nanometers. In the hexagonal intermetallic Gd2PdSi3, we observe a characteristic anomaly in the magnetic field dependence of the thermal Hall conductivity κ x y , which scales well with the anomaly in the electrical Hall conductivity σ x y and is closely related to the topological winding number of the SkL ground state. The relative magnitude of entropy and charge currents, defined as the Lorenz ratio ∼ κ x y / ( σ x y T ) , is consistent with a nondissipative, or intrinsic, mechanism for the topological Hall effect. We stress that the Berry phase in momentum space ( k -space) causes such a nondissipative Hall transport, independent of the carrier relaxation time.

The bilayer nickelate La3Ni2O7 has attracted intense interest following the discovery of high-temperature superconductivity under pressure, representing the first nickelate superconductor realized in bulk form. However, the crystal structure of the superconducting phase remains under active discussion, complicating efforts to establish its microscopic origin. Here we resolve these structural controversies by establishing a definitive pressure-temperature phase diagram, including the superconducting region of stoichiometric La3Ni2O7 single crystals under hydrostatic conditions using helium as the pressure-transmitting medium. At ambient pressure, La3Ni2O7 adopts a polar orthorhombic Am2m structure characterized by charge order between inequivalent Ni sites and NiO6 octahedral tilting. Upon compression, the system undergoes a direct transition from the charge-ordered Am2m phase to the tetragonal I4/mmm phase near 10 GPa, coinciding with the onset of bulk superconductivity. These results establish the intrinsic structural evolution of La3Ni2O7 and provide a structural framework for microscopic theories of nickelate superconductivity.

Topological magnetic semimetals with kagomé lattices have attracted significant attention due to their nontrivial electronic band structures and pronounced electromagnetic responses. The search for kagomé-lattice topological semimetals exhibiting magnetic ordering above room temperature is essential for advancing their potential in device applications. In this work, we report direct observations of topological magnetic textures and anomalous Hall effects driven by topological nodal lines in MnRhP, a room-temperature ferromagnet with a distorted kagomé lattice. Using single-crystal magnetization measurements and powder neutron diffraction, we reveal a weak uniaxial magnetic anisotropy. Lorentz transmission electron microscopy observations confirm the presence of stable magnetic skyrmions above room temperature. Moreover, both the ordinary and anomalous Hall effects are significantly enhanced upon cooling, with a large anomalous Hall conductivity (AHC) observed at low temperatures. First-principles calculations indicate significant contributions to electronic states near the Fermi level from both in-plane and out-of-plane d orbitals of Mn and Rh, resulting in the low magnetic anisotropy energy. The calculated Berry curvature reproduces the experimentally observed large AHC, providing direct evidence for an intrinsic mechanism linked to the topological nodal lines. These findings establish MnRhP as a promising kagomé-lattice magnet for investigating topological magnetic textures and anomalous transport phenomena at room temperature.

The emergent properties of materials are governed by the symmetries of their underlying atomic, spin and charge order. Therefore, intrinsic material properties usually constrain the exploration of symmetry-breaking effects. Focused ion beam (FIB) fabrication now enables the structuring of bulk crystals into ultraprecise transport devices, allowing the study of geometrical symmetry breaking on mesoscopic length scales. Here we extend FIB nanostructuring into three-dimensional, curvilinear geometries. Using single crystals of the high-mobility, centrosymmetric magnetic Weyl semimetal Co3Sn2S2, we sculpt helices with lengths of 3–14 μm, diameters of 1–4 μm and pitches ranging from 500 nm to 2 μm. Lock-in measurements on the helical devices at temperatures between 10 K and 190 K show that the combination of imposed inversion symmetry-breaking geometry and ferromagnetism yields non-reciprocal electron transport—or diode effect—at zero applied magnetic field, exceeding classical self-field expectations by orders of magnitude at low temperatures. We attribute this behaviour to the quasi-ballistic motion of carriers as the mean free path approaches the length scale of the chiral device geometry. Finally, we show that current pulses can switch the magnetization of the device. These results highlight the potential of FIB nanosculpting to engineer symmetry and functionality beyond conventional device geometries. Focused ion beam-based nanofabrication enables the production of 3D helical devices from single-crystalline Co3Sn2S2. The resulting chiral geometry-driven symmetry breaking produces a diode-like electrical response in transport measurements.

Novel antiferromagnets with broken time reversal symmetry (TRS) have launched a new direction in spintronics research, combining the advantageous dynamical properties of conventional antiferromagnets with the controllability typically associated with ferromagnets. However, antiferromagnetic domains are notoriously challenging to image in real-space. X-ray magnetic circular dichroism (XMCD) offers a route to overcome this difficulty: XMCD contrast may be finite in TRS-breaking antiferromagnets with an appropriate magnetic space group. Here, we exploit this to image the octupole domains in a focused ion beam-fabricated device of the non-collinear antiferromagnet Mn$_3$Sn. Using scanning transmission x-ray microscopy, we spatially resolve the weak pre-edge XMCD contrast (of 0.2%) that is sensitive to $T_z$, achieving a contrast resolution better than 0.02%. We observe hysteretic switching of the octupole order through both the XMCD contrast and the corresponding anomalous Hall effect within the same device. These results confirm the bulk nature of this contrast, and establish XMCD-based microscopy as a powerful real space imaging method for TRS-breaking antiferromagnets, including altermagnets, enabling future studies of their dynamics, switching, and symmetry-tunable phenomena.

Ferroelectric halide perovskites provide a fertile platform for optoelectronic functions based on the bulk photovoltaic effect, where broken inversion symmetry couples with quantum geometry of wave functions. The most prominent manifestation is the shift current, second-order nonlinear photocurrent arising from change in the Berry connection during optical transitions. Here we report a gigantic shift current response in epitaxial thin films of a lead-free ferroelectric halide perovskite CsGeI3. High-quality films grown by molecular beam epitaxy exhibit clear hallmarks of shift current, including spectral sign reversals, light-polarization dependence, and reversible electric-field modulation associated with switchable ferroelectric polarization. Remarkably, the normalized shift current magnitude surpasses those ever reported for other compounds by more than an order of magnitude, establishing a benchmark for bulk photovoltaic performance. These results identify ferroelectric halide perovskites as a powerful platform for exploring quantum-geometry-driven photoresponses and open a pathway toward next-generation photovoltaic and nonlinear optoelectronic technologies beyond the conventional junction-based architectures.

Quantum geometry of Bloch electron in crystalline solids produces various exotic quantum phenomena. The shift current photovoltaic effect driven by the photo creation of quasiparticle is one such emerging example that enables the conversion from terahertz photon into dc charge current with absence of dissipative photocarrier. Despite wide-ranging potential applications, however, the fundamental nature of terahertz photovoltaic response has remained elusive. Here, we show the large photocurrent generation driven by terahertz phonons (<10 milli-electron volts) in ferroelectric semiconductor SbSI with the electronic bandgap of 2.3 electron volts. Zero-bias terahertz photocurrent is found to be resonantly enhanced by optical phonons. Its generation efficiency is larger than that for the direct interband transition and is comparable to the electronic shift current in Weyl semimetal TaAs. The theoretical scaling law of terahertz shift current and first-principles calculation reasonably explain these observations. The present work establishes the universality and high efficiency of phonon-driven shift current, opening the pathway to terahertz technology based on quantum geometry.

Electrical control of spins and their collective textures, such as topologically protected skyrmions, is highly desirable for unlocking their potential in future electronic technologies. Here, we design and fabricate thin films of FeGe and Co8.5Zn8.5Mn3, each containing a small central hole comparable in size to individual skyrmions, to investigate how nonuniform electron flow influences skyrmions and drives nonreciprocal skyrmion dynamics. Using in situ real-space imaging, we observe that current crowding around the hole triggers skyrmion nucleation and produces direction-dependent skyrmion motion, in agreement with theoretical models and numerical simulations. Notably, the current-driven nonequilibrium skyrmion reveals a striking manifestation of topological spin textures, offering new opportunities for information processing that leverages skyrmion nonreciprocity, such as in reservoir computing.

We investigate effects of uniaxial stress to magnetic orders and electrical resistivity of the centrosymmetric magnetic skyrmion compound Gd_2PdSi_3, which has a hexagonal crystal structure composed of triangular lattice layers of magnetic Gd^3+ ions. This compound is known to exhibit the triple-q magnetic skyrmion lattice phase with a giant topological Hall effect in the first field induced phase [T. Kurumaji et al. Science 365, 914-918 (2019)]. In contrast to the established picture of the field-induced phase, the ground state of this system still remains to be studied. Although previous studies reported the existence of the incommensurate magnetic modulations described by a magnetic modulation wave vector q=(q,0,0) where q∼ 0.14 and its equivalents, it is still unclear whether the magnetic structure is a single-q structure or a multiple-q structure. In the present study, we performed magnetization, resistivity and neutron diffraction measurements with a compressive uniaxial stress applied perpendicular to the c axis. The observed data revealed that the system did not exhibit anisotropic magnetic and electric properties expected from a single-q magnetic order, suggesting that the magnetic ground state of this system is a multi-q magnetic order.

Microwaves provide coherent access to low-energy excitations and serve as effective probes of high-frequency spin dynamics in quantum and magnetic systems. For topological spin textures, microwave excitation is expected to generate rich collective responses, yet direct real-space observation of ultrafast dynamics remains limited. Here we use time-resolved Lorentz transmission electron microscopy to visualize microwave-driven dynamics in a hybrid antiskyrmion structure composed of a central antiskyrmion and surface skyrmions. We resolve the picosecond evolution of antiskyrmion area and second-harmonic signals, evidencing nonlinear responses of spin textures under microwave excitations. We track the core motions of the antiskyrmion and surface skyrmions, which follow distinct trajectories while sharing the same rotational sense. Micromagnetic simulations reproduce the key observations and associate the dynamic modes with the spatial modulation of the core profile along the thickness. These achievements establish ultrafast electron microscopy as a powerful real-space approach for probing high-frequency microwave-driven dynamics of topological magnetic solitons.

Chiral magnets host topologically protected spin textures whose nonequilibrium dynamics are crucial in phase transitions and domain evolution, yet ultrafast defect-mediated processes remain poorly understood. Here, we investigate photothermally induced helical-to-paramagnetic phase transition in Co_9Zn_9Mn_2 using pump-probe Lorentz transmission electron microscopy (LTEM). Following the suppression of the magnetic stripe contrast induced by femtosecond pulsed laser, we observe a directional recovery process of magnetic order driven by the anisotropic thermal diffusion, toward the thick region that effectively acts as a heat sink. Remarkably, around a magnetic edge dislocation, the magnetic contrast recovery exhibits a pronounced delay accompanied by a transient blurring of LTEM contrast. These findings suggest that the recovery dynamics around the magnetic edge dislocation proceed through multiple relaxation paths that are selected stochastically. Our results indicate a possible enhancement of stochasticity around topological defects during the recovery dynamics of magnetic phase transitions.

Magnetic frustration in kagom & eacute; lattice materials has attracted considerable attention as a source of novel magnetic properties and magnetotransport phenomena. Here we report experimental evidence for collinear ferrimagnetic ordering and multiple field-induced magnetic transitions in Tb3Ru4Al12 with a breathing kagom & eacute; lattice, revealed by field-dependent resonant x-ray scattering measurements performed at 8 K. The Hall response shows significant deviation from the conventional behavior above the ordering temperature, which can be plausibly interpreted in terms of thermally induced scalar spin chirality. Theoretical calculations reveal the emergence of net scalar spin chirality, whose magnitude depends on Ising-type magnetic anisotropy, in good agreement with experimental results on breathing kagom & eacute; magnets with different magnitude of the easy-axis anisotropy. This study highlights that nontrivial magnetotransport phenomena in breathing kagom & eacute; magnets may arise from thermally fluctuating spin moments with finite scalar spin chirality, even when the ground state is a collinear ferrimagnet.

The discovery of high-critical-temperature (high-Tc) superconductivity near 80 K in bilayer nickelates under high pressure has sparked extensive studies. Whereas superconductivity exceeding 40 K was subsequently discovered at ambient pressure in compressively strained films, the relationship between ambient- and high-pressure regimes remains an open question. Here we present a systematic investigation of superconductivity in compressively strained La2LnNi2O7 films (where Ln is a lanthanide) at ambient and high pressures. The normal-state resistivity at ambient pressure, revealed by suppressing the superconductivity with magnetic fields of 59 T, tends towards T2 behaviour. Under high pressure in a cubic anvil cell, Tc was enhanced from 41-42 K at ambient pressure to 67-73 K at 16 GPa. On the other hand, lattice compression induced by Ln substitution, which may mimic the effects of pressure, lowers Tc. In both cases, Tc correlates with the evolution of normal-state transport between T2 and T-linear behaviour, offering insight into the interplay between lattice structure and superconductivity in bilayer nickelates.

Emergent topological spin textures, such as nanometric skyrmions and antiskyrmions, not only exhibit a wealth of novel physical phenomena but also represent promising candidates for next-generation spintronic devices due to their topological stability and low-current-driven dynamics. Investigating their responses to electric currents is essential for uncovering unique electromagnetic properties and advancing their integration into electronic technologies. While considerable progress has been made through extensive research over the past decade, key challenges still persist. In this study, we demonstrate the novel, current-driven oppositely rotating dynamics of skyrmion and antiskyrmion assemblies in terms of Lorentz transmission electron microscopy. Their senses of rotation are strongly dictated by their inherent topological charges and remain largely unaffected by current direction, showing consistent behavior observed across various sample geometries. Further experimental analyses have revealed a reduction in angular velocity as (anti)skyrmions move away from the sample edge. The theoretical analyses, combined with micromagnetic simulations, highlight the critical roles of boundary-induced confining potentials and gyrotropic forces in steering the rotational dynamics of (anti)skyrmions. These findings offer new insights into current-driven (anti)skyrmion dynamics and open promising avenues for advancing topological concepts in confined spintronic systems.

Helimagnetic materials offer a versatile platform for spin-based device concepts owing to their long-range, tunable spiral order. Here, we demonstrate controlled manipulation of the helimagnetic propagation vector q by geometrical confinement, using FeGe as a model Dzyaloshinskii–Moriya interaction (DMI)-driven chiral magnet. Micromagnetic simulations based on the nonlinear sigma model reveal that open boundaries give rise to a chiral surface twist acting as an effective surface anisotropy, which dictates the preferred helix orientation in the absence of magnetostatic shape effects. This geometry-induced anisotropy is quantitatively captured by an analytical model derived from the DMI boundary condition. Magnetic force microscopy measurements on focused-ion-beam structured FeGe confirm the predicted orientation behavior and establish geometry-controlled helimagnetic order as a robust, tunable mechanism for steering DMI-stabilized spin-spiral states. The concept provides a general route toward device-level control of chiral magnetic order in non-centrosymmetric systems. Micromagnetic simulations and magnetic force microscopy reveal how the lateral shape of a confined chiral magnet controls the orientation of its helical spin order. The propagation vector of the spin helix aligns according to sample geometry through a boundary-induced chiral surface twist that acts as an effective anisotropy.

Pressure-induced superconductivity in bilayer nickelates provides a platform for investigating intertwined roles of charge/spin orders and electric transport in unconventional superconductivity. However, important quantitative information on the transport, such as the absolute value of the resistivity, the anisotropy, and the scattering rate of carriers, remains insufficient due to the lack of accurate measurements using large single crystals. Here we establish a high-precision pressure-temperature phase diagram of high-quality La3Ni2O7 single crystals, by measuring the in-plane and out-of-plane resistivities. We resolve two distinct anomalies associated with density-wave formation with contrasting pressure dependences. The pressure-induced structural transition enhances not only the resistivity values for both directions, but also its anisotropy at low temperatures, demonstrating a pronounced effect of density-wave order on the charge dynamics. Superconductivity with zero-resistance emerges near the boundary where the density-wave phases are fully suppressed, and above Tc, the resistivity exhibits a temperature-linear dependence over a wide temperature range while the scattering rate falls within a regime of the Planckian limit. Our results show that pressure dramatically changes the anisotropic charge transport via modifying density-wave orders, and eventually produces a pronounced strange-metal state with strong scatterings, from which superconductivity develops. This establishes robust density-wave correlations and Planckian dissipation as remarkable features of La3Ni2O7.

The discovery of high critical-temperature T_c superconductivity in La_3Ni_2O_7 under high pressure has led to a rapid expansion of the T_c range through lanthanide Ln substitution, and to ambient-pressure superconductivity in strained thin films, yet the exploration of new bilayer nickelates remains strongly constrained by thermodynamic stability. Beyond the difficulty of synthesis of bulk single-crystals, here we report on the pressure-induced high-T_c superconductivity in epitaxially-stabilized Pr_3Ni_2O_7 thin films. While the Pr_3Ni_2O_7 films exhibit insulating behaviour at ambient pressure regardless of ozone-annealing treatment, they show T-linear metallic transport and superconductivity reaching an onset T_c of 66 K and zero-resistance at nearly 40 K at 22 GPa. Furthermore, Nd_3Ni_2O_7, with the smaller rare-earth ion Nd, can also be stabilized, however, superconductivity is not observed in the measured pressure range. Epitaxial stabilization enables us to examine the dependence of T_c and the critical pressure P_c for superconductivity on the Ln ion in Ln_3Ni_2O_7 (Ln = La, Pr, Nd). These results suggest that a higher P_c is required for smaller Ln ions, consistent with trends observed in bulk studies of Ln substitution. This study demonstrates that epitaxial stabilization is a powerful technique to further expand the family of superconducting bilayer nickelates.