The dynamics of magnetic flux quanta (Abrikosov vortices) determine the resistive response of superconductors. In pinning-free planar thin films, the penetration and motion of vortices are controlled by edge defects, leading to such arrangements as vortex chains, vortex jets, and phase-slip regimes. Here, relying upon the time-dependent Ginzburg-Landau equation, we predict that these vortex patterns should appear in superconductor open nanotubes even without edge defects, due to the inhomogeneity of the normal magnetic induction component $B_\mathrm{n}$, caused by the 3D tube geometry. The crossing of the half-tubes by dc-driven vortices induces GHz-frequency voltage $U$ oscillations with spectra $U_\mathrm{f}(B)$ evolving between $nf_1$ and $\frac{n}{m}f_1$ [$f_1$: vortex nucleation frequency; $n,m\geq 2$] and blurred in certain ranges of currents and fields. An $nf_1$-spectrum corresponds to a single vortex-chain regime typical for low $B$ and for tubes of small radii. At higher fields, an $\frac{n}{m}f_1$-spectrum points to the presence of $m$ vortex chains in the vortex jets which, in contrast to planar thin films, are not diverging because of constraint to the tube areas where $B_\mathrm{n}$ is close to maximum. A blurry spectrum implies complex arrangements of vortices because of multifurcations of their trajectories. Finally, due to a stronger confinement of single vortex chains in tubes of small radii, we reveal peaks in $dU/dB$ and jumps in the frequency of microwave generation, which occur when the number of fluxons moving in the half-tubes increases by one. In all, our findings are essential for novel 3D superconductor devices which can operate in few- and multi-fluxon regimes.

The resistance of a heavy metal can be modulated by an adjacent magnetic material through the combined effects of the spin Hall effect, inverse spin Hall effect, and dissipation of the spin accumulation at the interface. This phenomenon is known as the spin Hall magnetoresistance. The dissipation of the spin accumulation can occur via various mechanisms, with spin-transfer torque being the most extensively studied. In this work, we report the observation of spin Hall magnetoresistance at the interface between platinum and an insulating altermagnetic candidate, Ba$_2$CoGe$_2$O$_7$. Our findings reveal that this heterostructure exhibits a relatively large spin Hall magnetoresistance signal, which is anisotropic with respect to the crystal orientation of the current channel. We explore and rule out several potential explanations for this anisotropy and propose that our results may be understood in the context of the anisotropies of the spin current channels across the Pt/altermagnetic Ba$_2$CoGe$_2$O$_7$ interface.

We report a rich anisotropic magnetic phase diagram of Na$_3$Co$_2$SbO$_6$, a previously proposed cobaltate Kitaev candidate, based on field- and temperature-dependent magnetization, specific heat, and magnetocaloric effect studies. At low temperatures, our experiments uncover a low-lying $j_{\textrm{eff}} = \frac{1}{2}$ state with an antiferromagnetic ground state and pronounced in-plane versus out-of-plane anisotropy. The experimentally identified magnetic phases are theoretically characterized through classical Monte Carlo simulations within an extended Kitaev-Heisenberg model with additional ring exchange interactions. The resulting phase diagram reveals a variety of exotic field-induced magnetic phases, including double-$\textbf{q}$, $\frac{1}{3}$-AFM, zigzag, and vortex phases.

Microstructural features play an important role for the quality of permanent magnets. The coercivity is greatly influenced by crystallographic defects, which is well known for MnAl-C, for example. In this work we show a direct link of microstructural features to the local coercivity of MnAl-C grains by machine learning. A large number of micromagnetic simulations is performed directly from Electron Backscatter Diffraction (EBSD) data using an automated meshing, modeling and simulation procedure. Decision trees are trained with the simulation results and predict local switching fields from new microscopic data within seconds.

The quest for a global quantum internet is based on the realization of a scalable network which requires quantum hardware with exceptional performance. Among them are quantum light sources providing deterministic, high brightness, high-fidelity entangled photons and quantum memories with coherence times in the millisecond range and above. To operate the network on a global scale, the quantum light source should emit at telecommunication wavelengths with minimum propagation losses. A cornerstone for the operation of such a quantum network is the demonstration of quantum teleportation. Here we realize full-photonic quantum teleportation employing one of the most promising platforms, i.e. semiconductor quantum dots, which can fulfill all the aforementioned requirements. Two remote quantum dots are used, one as a source of entangled photon pairs and the other as a single-photon source. The frequency mismatch between the triggered sources is erased using two polarization-preserving quantum frequency converters, enabling a Bell state measurement at telecommunication wavelengths. A post-selected teleportation fidelity of up to 0.721(33) is achieved, significantly above the classical limit, demonstrating successful quantum teleportation between light generated by distinct sources. These results mark a major advance for the semiconductor platform as a source of quantum light fulfilling a key requirement for a scalable quantum network. This becomes particularly relevant after the seminal breakthrough of addressing a nuclear spin in semiconductor quantum dots demonstrating long coherence times, thus fulfilling another crucial step towards a scalable quantum network.

A magnet is a collection of magnetic moments. How those interact is determined by what lies in between. In transition-metal and rare-earth magnetic compounds, the configuration of the ligands around each magnetic center and the connectivity of the ligand cages are therefore pivotal -- for example, the mutual interaction of magnetic species connected through one single ligand is qualitatively different from the case of two bridging anions. Two bridging ligands are encountered in Kitaev magnets. The latter represent one of the revelations of the 21st century in magnetism research: they feature highly anisotropic intersite couplings with seemingly counterintuitive directional dependence for adjacent pairs of magnetic sites and unique quantum spin-liquid ground states that can be described analytically. Current scenarios for the occurrence of pair-dependent magnetic interactions as proposed by Kitaev rely on $indirect$ exchange mechanisms based on intersite electron hopping. Analyzing the wavefunctions of Kitaev magnetic bonds at both single- and multi-configuration levels, we find however that $direct$, Coulomb exchange may be at least as important, in 5$d$ and 4$d$ $t_{2g}^5$, 3$d$ $t_{2g}^5e_g^2$, and even rare-earth 4$f^1$ Kitaev-Heisenberg magnets. Our study provides concept clarification in Kitaev magnetism research and the essential reference points for reliable computational investigation of how novel magnetic ground states can be engineered in Kitaev, Kitaev-Heisenberg, and Heisenberg edge-sharing systems.

The discovery of chiral helical magnetism (CHM) in Cr$_{1/3}$NbS$_2$ and the stabilization of a chiral soliton lattice (CSL) has attracted considerable interest in view of their potential technological applications. However, there is an ongoing debate regarding whether the sister compound, Mn$_{1/3}$NbS$_2$, which shares the same crystal structure, exhibits similar nontrivial properties which rely on the stabilization of the lack of inversion symmetry at the magnetic ion. In this study, we conduct a comprehensive investigation of the magnetically ordered states of both compounds, using $^{53}$Cr, $^{55}$Mn and $^{93}$Nb nuclear magnetic resonance. Our results, supported by density functional calculations, detect in a high-quality single crystal of Cr$_{1/3}$NbS$_2$ all the signatures of the monoaxial CHM in a magnetic field, identifying it as a textbook NMR case. The detailed understanding of this prototypic behavior provides a reference for Mn$_{1/3}$NbS$_2$. Despite the much larger density of specific defects in this second single crystal, we confirm the presence of a CHM phase in the Mn compound, characterized by a very large critical field for the forced ferromagnetic phase ($\approx 5$ T for H$\parallel\hat c$).

A magnet is a collection of magnetic moments. How those interact is determined by what lies in between. In transition-metal and rare-earth magnetic compounds, the configuration of the ligands around each magnetic center and the connectivity of the ligand cages are therefore pivotal -- for example, the mutual interaction of magnetic species connected through one single ligand is qualitatively different from the case of two bridging anions. Two bridging ligands are encountered in Kitaev magnets. The latter represent one of the revelations of the 21st century in magnetism research: they feature highly anisotropic intersite couplings with seemingly counterintuitive directional dependence for adjacent pairs of magnetic sites and unique quantum spin-liquid ground states that can be described analytically. Current scenarios for the occurrence of pair-dependent magnetic interactions as proposed by Kitaev rely on $indirect$ exchange mechanisms based on intersite electron hopping. Analyzing the wavefunctions of Kitaev magnetic bonds at both single- and multi-configuration levels, we find however that $direct$, Coulomb exchange may be at least as important, in 5$d$ and 4$d$ $t_{2g}^5$, 3$d$ $t_{2g}^5e_g^2$, and even rare-earth 4$f^1$ Kitaev-Heisenberg magnets. Our study provides concept clarification in Kitaev magnetism research and the essential reference points for reliable computational investigation of how novel magnetic ground states can be engineered in Kitaev, Kitaev-Heisenberg, and Heisenberg edge-sharing systems.

Cellular micromotors are attractive for locally delivering high concentrations of drug and targeting hard-to-reach disease sites such as cervical cancer and early ovarian cancer lesions by non-invasive means. Spermatozoa are highly efficient micromotors perfectly adapted to traveling up the female reproductive system. Indeed, bovine sperm-based micromotors have recently been reported as a potential candidate for the drug delivery toward gynecological cancers of clinical unmet need. However, due to major differences in the molecular make-up of bovine and human sperm, a key translational bottleneck for bringing this technology closer to the clinic is to transfer this concept to human sperm. Here, we successfully load human sperm with a chemotherapeutic drug and perform treatment of relevant 3D cervical cancer and patient-representative 3D ovarian cancer cell cultures, resulting in strong anti-cancer effects. Additionally, we show the subcellular localization of the chemotherapeutic drug within human sperm heads and assess drug effects on sperm motility and viability over time. Finally, we demonstrate guidance and release of human drug-loaded sperm onto cancer cell cultures by using streamlined microcap designs capable of simultaneously carrying multiple human sperm towards controlled drug dosing by transporting known numbers of sperm loaded with defined amounts of chemotherapeutic drug.

Medical imaging plays an important role in diagnosis and treatment of multiple diseases. It is a field under continuous development which seeks for improved sensitivity and spatiotemporal resolution to allow the dynamic monitoring of diverse biological processes that occur at the micro- and nanoscale. Emerging technologies for targeted diagnosis and therapy such as nanotherapeutics, micro-implants, catheters and small medical tools also need to be precisely located and monitored while performing their function inside the human body. In this work, we show for the first time the real-time tracking of moving single micro-objects below centimeter thick tissue-mimicking phantoms, using multispectral optoacoustic tomography (MSOT). This technique combines the advantages of ultrasound imaging regarding depth and resolution with the molecular specificity of optical methods, thereby facilitating the discrimination between the spectral signatures of the micro-objects from those of intrinsic tissue molecules. The resulting MSOT signal is further improved in terms of contrast and specificity by coating the micro-objects surface with gold nanorods, possessing a unique absorption spectrum, which will allow their discrimination from surrounding biological tissues when translated to in vivo settings.

Understanding ductility or brittleness of monolithic bulk metallic glasses (BMGs) requires detailed knowledge of the amorphous structure. The medium range order (MRO) of ductile Pd$_{40}$Ni$_{40}$P$_{20}$ and brittle Zr$_{52.5}$Cu$_{17.9}$Ni$_{14.6}$Al$_{10}$Ti$_5$ (Vit105) was characterized prior to and after notched 3-point bending tests using variable-resolution fuctuation electron microscopy. Here we show the presence of a second larger MRO correlation length in the ductile material which is not present in the brittle material. A comparison with literature suggests that the larger correlation length accounts for larger shear transformation zones (STZs) which increase the heterogeneity. This enables an easier shear band formation and thus explains the difference in deformability.

Martensitic materials show a complex, hierarchical microstructure containing structural domains separated by various types of twin boundaries. Several concepts exist to describe this microstructure on each length scale, however, there is no comprehensive approach bridging the whole range from the nano- up to the macroscopic scale. Here, we describe for a Ni-Mn-based Heusler alloy how this hierarchical microstructure is built from scratch with just one key parameter: the tetragonal distortion of the basic building block at the atomic level. Based on this initial block, we introduce five successive levels of nested building blocks. At each level, a larger building block is formed by twinning the preceding one to minimise the relevant energy contributions locally. This naturally explains the occurrence of different types of twin boundaries. We compare this scale-bridging approach of nested building blocks with experiments in real and reciprocal space. Our approach of nested building blocks is versatile as it can be applied to the broad class of functional materials exhibiting diffusionless transformations.

Using time- and angle-resolved photoemission spectroscopy, we examine the unoccupied electronic structure and electron dynamics of the type-I Weyl semimetal PtBi$_2$. Using the ability to change the probe photon energy over a wide range, we identify the predicted Weyl points in the unoccupied three-dimensional band structure and we discuss the effect of $k_\perp$ broadening in the normally unoccupied states. We characterise the electron dynamics close to the Weyl point and in other parts of three-dimensional Brillouin zone using $k$-means, an unsupervised machine learning technique. This reveals distinct differences -- in particular, dynamics that are faster in the parts of the Brillouin zone that host most of the bulk Fermi surface than in parts close to the Weyl points.

The electron dynamics in the unoccupied states of the Weyl semimetal PtBi$_2$ is studied by time- and angle-resolved photoemission spectroscopy (TR-ARPES). The measurement's result is the photoemission intensity $I$ as a function of at least four parameters: the emission angle and kinetic energy of the photoelectrons, the time delay between pump and probe laser pulses, and the probe laser photon energy that needs to be varied to access the full three-dimensional Brillouin zone of the material. The TR-ARPES results are reported in an accompanying paper. Here we focus on the technique of using $k$-means, an unsupervised machine learning technique, in order to discover trends in the four-dimensional data sets. We study how to compare the electron dynamics across the entire data set and how to reveal subtle variations between different data sets collected in the vicinity of the bulk Weyl points.

Quantum rings have emerged as a playground for quantum mechanics and topological physics, with promising technological applications. Experimentally realizable quantum rings, albeit at the scale of a few nanometers, are 3D nanostructures. Surprisingly, no theories exist for the topology of the Fermi sea of quantum rings, and a microscopic theory of superconductivity in nanorings is also missing. In this paper, we remedy this situation by developing a mathematical model for the topology of the Fermi sea and Fermi surface, which features non-trivial hole pockets of electronic states forbidden by quantum confinement, as a function of the geometric parameters of the nanoring. The exactly solvable mathematical model features two topological transitions in the Fermi surface upon shrinking the nanoring size either, first, vertically (along its axis of revolution) and, then, in the plane orthogonal to it, or the other way round. These two topological transitions are reflected in a kink and in a characteristic discontinuity, respectively, in the electronic density of states (DOS) of the quantum ring, which is also computed. Also, closed-form expressions for the Fermi energy as a function of the geometric parameters of the ring are provided. These, along with the DOS, are then used to derive BCS equations for the superconducting critical temperature of nanorings as a function of the geometric parameters of the ring. The $T_c$ varies non-monotonically with the dominant confinement size and exhibits a prominent maximum, whereas it is a monotonically increasing function of the other, non-dominant, length scale. For the special case of a perfect square toroid (where the two length-scales coincide), the $T_c$ increases monotonically with increasing the confinement size, and in this case, there is just one topological transition.

Layered semimetallic van der Waals materials TiSe2 has attracted a lot of attention because of interplay of a charge density wave (CDW) state and superconductivity. Its sister compound TiS2, being isovalent to TiSe2 and having the same crystal structure, shows a semiconducting behavior. The natural rises what happens at the transition point in TiSe2-xSx, which is expected for x close to 1. Here we report the growth and characterization of TiSeS single crystals and the study of the electronic structure using density functional theory (DFT) and angle-resolved photoemission (ARPES). We show that TiSeS single crystals have the same morphology as TiSe2. Transport measurements reveal a metallic state, no evidence of CDW was found. DFT calculations suggest that the electronic band structure in TiSeS is similar to that of TiSe2, but the electron and hole pockets in TiSeS are much smaller. The ARPES results are in good agreement with the calculations.

In planar superconductor thin films, the places of nucleation and arrangements of moving vortices are determined by structural defects. However, various applications of superconductors require reconfigurable steering of fluxons, which is hard to realize with geometrically predefined vortex pinning landscapes. Here, on the basis of the time-dependent Ginzburg-Landau equation, we present an approach for steering of vortex chains and vortex jets in superconductor nanotubes containing a slit. The idea is based on tilting of the magnetic field $\mathbf{B}$ at an angle $\alpha$ in the plane perpendicular to the axis of a nanotube carrying an azimuthal transport current. Namely, while at $\alpha=0^\circ$ vortices move paraxially in opposite directions within each half-tube, an increase of $\alpha$ displaces the areas with the close-to-maximum normal component $|B_\mathrm{n}|$ to the close(opposite)-to-slit regions, giving rise to descending (ascending) branches in the induced-voltage frequency spectrum $f_\mathrm{U}(\alpha)$. At lower $B$, upon reaching the critical angle $\alpha_\mathrm{c}$, close-to-slit vortex chains disappear, yielding $f_\mathrm{U}$ of the $nf_1$-type ($n\geq1$: an integer; $f_1$: vortex nucleation frequency). At higher $B$, $f_\mathrm{U}$ is largely blurry because of multifurcations of vortex trajectories, leading to the coexistence of a vortex jet with two vortex chains at $\alpha=90^\circ$. In addition to prospects for tuning of GHz-frequency spectra and steering of vortices as information bits, our findings lay foundations for on-demand tuning of vortex arrangements in 3D superconductor membranes in tilted magnetic fields.

High-harmonic generation (HHG) offers an all-optical approach to discern structural symmetries through its selection rules and probe topological phases with its spectral signatures. Here we develop a universal theoretical framework -- the Jones matrix formalism -- establishing the fundamental relationship between pulse-crystal shared symmetries and HHG selection rules. Applying this to the Weyl semimetal (WSM) material TaAs, shows that the anomalous harmonics excited by linearly and circularly polarized pulses are governed respectively by the shared twofold and fourfold rotational symmetries of laser pulses and lattice, rather than the topology of Weyl nodes. The common observables of HHG, including intensity, circular dichroism, ellipticity dependence, and carrier-envelope phase dependence, are not found to carry a signature of the Weyl cones. This insight into TaAs can be extended to other WSMs, indicating that HHG is not a particularly effective tool for investigating the topological features of WSMs. However, the Jones matrix formalism lays the groundwork for both HHG probing crystal symmetry and controlling harmonic polarization states.

Icing has become a hot topic both in academia and in the industry given its implications in strategic sectors such as transport, robotics, wind turbines, photovoltaics, and electricity supply. Recently proposed de-icing solutions involving the propagation of acoustic waves (AWs) at suitable substrates may open the path for a sustainable alternative to standard de-icing or anti-icing protocols. Herein we experimentally unravel some of the basic interactions that contribute to the de-icing and/or hinder the icing (ice accretion) on AW-activated substrates. The response toward icing of a model substrate system consisting of a piezoelectric LiNbO3 plate AW activated by radio-frequency (rf) signaling to planar electrodes has been characterized both at a laboratory scale and in an icing wind tunnel under forced convection conditions. Main features related to de-icing mechanisms, a decrease of ice adhesion, or the avoidance of ice accretion have been disclosed by this holistic investigation. Furthermore, additional experiments have shown that the piezoelectric substrate surfaces modified with a fluorinated ZnO thin film or a ZnO/CFx bilayer present anti-icing functionality and a synergistic response when activated with AWs. A careful analysis of the dependence of resonance frequency of the piezoelectric substrates on experimental variables such as temperature, ice formation, or wind velocity shows that this parameter can be used as an internal control procedure for real-time monitoring of icing processes onto AW-activated devices

The notion of an electronic flat band refers to a collectively degenerate set of quantum mechanical eigenstates in periodic solids. The vanishing kinetic energy of flat bands relative to the electron-electron interaction is expected to result in a variety of many-body quantum phases of matter. Despite intense theoretical interest, systematic design and experimental realization of such flat band-driven correlated states in natural crystals have remained a challenge. Here we report the realization of a partially filled flat band in a new single crystalline kagome metal Ni$_3$In. This flat band is found to arise from the Ni $3d$-orbital wave functions localized at triangular motifs within the kagome lattice plane, where an underlying destructive interference among hopping paths flattens the dispersion. We observe unusual metallic and thermodynamic responses suggestive of the presence of local fluctuating magnetic moments originating from the flat band states, which together with non-Fermi liquid behavior indicate proximity to quantum criticality. These results demonstrate a lattice and orbital engineering approach to designing flat band-based many-body phenomena that may be applied to integrate correlation with topology and as a novel means to construct quantum criticality.