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Recent advances in quantum technologies are highly influencing the current technological scenario. Hybrid devices combining superconductors and topological insulators represent an excellent opportunity to study the topological superconducting phase, which offers interesting features that might have significant implications in the development of quantum sensing and quantum computing. Furthermore, focused ion beam techniques, whose versatility enables to create sophisticated devices with high degree of customization, can enhance the creation of complex devices. Here, we develop a novel approach for creating single-crystal devices that is applied to the fabrication of superconducting devices based on topological insulator Bi 2 Se 3 in a geometry characteristic of a superconducting quantum interference device. Characterization of these devices reveals that superconductivity is induced in our crystal and the supercurrent is modulated by applying an external magnetic field. These results open the way to tailoring the response of hybrid devices that combine superconductors and topological insulators by focused ion beam techniques.

The creation and annihilation of magnetic skyrmions are mediated by three-dimensional topological defects known as Bloch points. Investigation of such dynamical processes is important both for understanding the emergence of exotic topological spin textures, and for future engineering of skyrmions in technological applications. However, while the annihilation of skyrmions has been extensively investigated in two dimensions, in three dimensions the phase transitions are considerably more complex. We report field-dependent experimental measurements of metastable skyrmion lifetimes in an archetypal chiral magnet, revealing two distinct regimes. Comparison to supporting three-dimensional geodesic nudged elastic band simulations indicates that these correspond to skyrmion annihilation into either the helical and conical states, each exhibiting a different transition mechanism. The results highlight that the lowest energy magnetic configuration of the system plays a crucial role when considering the emergence and stability of topological spin structures via defect-mediated dynamics. Skyrmions are topologically non-trivial, vortex-like magnetic structures the dynamics of which have been mostly studied in 2D systems, but they are also able to exist as 3D tube-like structures. Here, the authors report a combination of experimental and computational results investigating the annihilation dynamics of 3D skyrmion structures in order to better understand how to stabilise topological structures in other bulk magnetic systems.

Unconventional superconductivity, where electron pairing does not involve electron-phonon interactions, is often attributed to magnetic correlations in a material. Well known examples include high- T c cuprates and uranium-based heavy fermion superconductors. Less explored are unconventional superconductors with strong spin-orbit coupling, where interactions between spin-polarised electrons and external magnetic field can result in multiple superconducting phases and field-induced transitions between them, a rare phenomenon in the superconducting state. Here we report a magnetic-field driven phase transition in β-PdBi 2 , a layered non-magnetic superconductor. Our tunnelling spectroscopy on thin PdBi 2 monocrystals incorporated in planar superconductor-insulator-normal metal junctions reveals a marked discontinuity in the superconducting properties with increasing in-plane field, which is consistent with a transition from conventional (s-wave) to nodal pairing. Our theoretical analysis suggests that this phase transition may arise from spin polarisation and spin-momentum locking caused by locally broken inversion symmetry, with p-wave pairing becoming energetically favourable in high fields. Our findings also reconcile earlier predictions of unconventional multigap superconductivity in β-PdBi 2 with previous experiments where only a single s-wave gap could be detected. β-PdBi2 superconducting properties have been known about since the 1950s, with various works since then indicating the possibility of multiple superconducting gaps and unconventional superconductivity. However, so far only a single gap s-wave superconductivity was detected. Here, using tunnelling spectroscopy under an applied magnetic field, Powell et al observe a transition from s-wave to nodal pairing.

The intertwined nature of magnetic and electric degrees of freedom in magnetoelectric (ME) materials is well described by ME-coupling theory. When an external electric field is applied to a ME material, the ME coupling induces unique and intriguing magnetic responses. Such responses underpin the utilisation of ME materials across diverse applications, ranging from electromagnetic sensing to low-energy digital memory technologies. Here, we use small angle neutron scattering and discover a novel magnetic response within an archetypal chiral ME material, Cu 2 OSeO 3 . We find that the propagation direction of an incommensurate magnetic spiral is deterministically actuated and deflected along controllable trajectories. Furthermore, we predict the emergence of distinct non-linear regimes of spiral-deflection behaviour with external electric and magnetic fields, unlocking innovative devices that leverage controlled and customisable variations in macroscopic polarisation and magnetisation. In a magnetoelectric material, an applied electric field can drive changes in the magnetic order. This feature has profound technology prospects and here, Moody et al demonstrate deterministic control of the direction of magnetic spiral order via an applied electric field in Cu 2 OSeO 3 .

The GaV 4 S 8− y Se y ( y = 0 to 8) family of materials have been synthesized in both polycrystalline and single crystal form, and their structural and magnetic properties thoroughly investigated. Each of these materials crystallizes in the F 4 ˉ 3 m space group at ambient temperature. However, in contrast to the end members GaV 4 S 8 and GaV 4 Se 8 , that undergo a structural transition to the R 3 m space group at 42 and 41 K respectively, the solid solutions ( y = 1 to 7) retain cubic symmetry down to 1.5 K. In zero applied field the end members of the family order ferromagnetically at 13 K (GaV 4 S 8 ) and 18 K (GaV 4 Se 8 ), while the intermediate compounds exhibit a spin-glass-like ground state. We demonstrate that the magnetic structure of GaV 4 S 8 shows localization of spins on the V cations, indicating that a charge ordering mechanism drives the structural phase transition. We conclude that the observation of both structural and ferromagnetic transitions in the end members of the series in zero field is a prerequisite for the stabilization of a skyrmion phase, and discuss how the absence of these transitions in the y = 1 to 7 materials can be explained by their structural properties.

The charge ordered structure of ions and vacancies characterizing rare-earth pyrochlore oxides serves as a model for the study of geometrically frustrated magnetism. The organization of magnetic ions into networks of corner-sharing tetrahedra gives rise to highly correlated magnetic phases with strong fluctuations, including spin liquids and spin ices. It is an open question how these ground states governed by local rules are affected by disorder. Here we demonstrate in the pyrochlore Tb 2 Hf 2 O 7 , that the vicinity of the disordering transition towards a defective fluorite structure translates into a tunable density of anion Frenkel disorder while cations remain ordered. Quenched random crystal fields and disordered exchange interactions can therefore be introduced into otherwise perfect pyrochlore lattices of magnetic ions. We show that disorder can play a crucial role in preventing long-range magnetic order at low temperatures, and instead induces a strongly fluctuating Coulomb spin liquid with defect-induced frozen magnetic degrees of freedom. Experimental studies of frustrated spin systems such as pyrochlore magnetic oxides test our understanding of quantum many-body physics. Here the authors show experimentally that Tb 2 Hf 2 O 7 may be a model material for investigating how structural disorder can stabilize a quantum spin liquid phase.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The friction of surfaces in relative motion and separated by a few nanometres is thought to be dominated by electronic effects. It is now found that the friction sensed by an AFM tip oscillating above a NbSe 2 surface takes the form of giant dissipation peaks, and that the peaks are related to a hysteresis cycle where the oscillating tip locally pumps 2π slips in the phase of a charge-density wave. Understanding nanoscale friction and dissipation is central to nanotechnology 1 , 2 , 3 , 4 . The recent detection of the electronic-friction drop caused by the onset of superconductivity in Nb (ref.  5 ) by means of an ultrasensitive non-contact pendulum atomic force microscope (AFM) raised hopes that a wider variety of mechanical-dissipation mechanisms become accessible. Here, we report a multiplet of AFM dissipation peaks arising a few nanometres above the surface of NbSe 2 —a layered compound exhibiting an incommensurate charge-density wave (CDW). Each peak appears at a well-defined tip–surface interaction force of the order of a nanonewton, and persists up to 70 K, where the short-range order of CDWs is known to disappear. Comparison of the measurements with a theoretical model suggests that the peaks are associated with local, tip-induced 2π phase slips of the CDW, and that dissipation maxima arise from hysteretic behaviour of the CDW phase as the tip oscillates at specific distances where sharp local slips occur.

Mn3Al2Ge3O12 is a member of the garnet family of compounds, A3B2(CO4)3, whose magnetic properties are affected by a high degree of geometrical frustration. The magnetic frustration is at the origin of the intriguing magnetic properties that these materials exhibit, such as a long range hidden order derived from multipoles formed from 10-spin loops in the gadolinium gallium garnet, Gd3Ga5O12. Mn3Al2Ge3O12 garnet is isostructural to the thoroughly investigated Gd garnets, Gd3Ga5O12 and Gd3Al5O12. Moreover, in Mn3Al2Ge3O12, the Heisenberg-like Mn2+ magnetic ions (L= 0) are also arranged in corner sharing triangles that form a hyperkagomé structure. The identical crystallographic structures and similar Heisenberg-like behaviour of the magnetic ions make manganese aluminium germanium garnet the closest compound to the gadolinium garnets in its magnetic properties. Here, we report, for the first time, the growth of a large, high quality single crystal of the Mn3Al2Ge3O12 garnet by the floating zone method. X-ray diffraction techniques were used to characterise and confirm the high crystalline quality of the Mn3Al2Ge3O12 crystal boule. Temperature-dependent magnetic susceptibility measurements reveal an antiferromagnetic ordering of the Mn2+ ions below TN= 6.5 K. The high quality of the single crystal obtained makes it ideal for detailed investigations of the magnetic properties of the system, especially using neutron scattering techniques.