Stuart Parkin

Max Planck Institute of Microstructure Physics | MPI · NISE: nanosystems from Ions, Spins and Electrons

Interstitial topological objects, such as skyrmions, within a natural 1-D helix are predicted to be free from ambiguous 'skyrmion Hall effect'. The helical ambience precipitate an additional potential that counteract the Magnus force arising from the gyrotropic motion of skyrmion. Here, we present the observation of ± 1 2 topological charge objects...

Appearance of quantum oscillations (QO) in both thermodynamic and transport properties of metals at low temperatures is the most striking experimental consequence of the existence of a Fermi surface (FS). The frequency of these oscillations and the temperature dependence of their amplitude provides essential information about the FS topology and fe...

We study the superconducting Josephson junction diode operating via the magnetic field of skyrmions. Inspired by the near-field optical microscopy, we propose to partially screen the magnetic field and analyze part-by-part the magnetic texture of the skyrmion. The detected asymmetric supercurrent is influenced by the skyrmionic magnetic field and m...

We study femtosecond spin currents through MgO tunneling barriers in CoFeB(2 nm)|MgO(d)|Pt(2 nm) stacks by terahertz emission spectroscopy. To obtain transport information independent of extrinsic experimental factors, we determine the complex-valued spin conductance G_d of the MgO layer (thickness d= 0-6 {\AA}) over a wide frequency range (0.5-8 T...

The quantum skyrmionic phase is modeled in a two-dimensional helical spin lattice. This topological skyrmionic phase retains its nature in a large parameter space before moving to a ferromagnetic phase. Next-nearest-neighbor interaction improves the stability and it also causes a shift of the topological phase in the parameter space. Nonanalytic be...

Tools for controlling electrically the motion of magnetic skyrmions are important elements towards their use in spintronic devices. Here, we propose and demonstrate the transport of skyrmions via GHz and THz electric pulses. The method relies on using polarization textured pulses such that the skyrmion experiences (via its inherent magnetoelectrici...

Quantum skyrmionic phase is modelled in a 2D helical spin lattice. This topological skyrmionic phase retains its nature in a large parameter space before moving to a ferromagnetic phase. Next nearest-neighbour interaction improves the stability and it also causes a shift of the topological phase in the parameter space. Nonanalytic behaviour of the...

Tools for controlling electrically the motion of magnetic skyrmions are important elements towards their use in spintronic devices. Here, we propose and demonstrate the transport of skyrmions via gigahertz and terahertz electric pulses. The method relies on using polarization-textured pulses such that the skyrmion experiences (via its inherent magn...

Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we ha...

We consider helical rotation of skyrmions confined in the potentials formed by nanodisks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Because of the distortion of the lattice, impurities, or pinning effect, confined skyrmions experien...

Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we ha...

We consider helical rotation of skyrmions confined in the potentials formed by nano-disks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Due to the distortion of the lattice, impurities, or pinning effect, confined skyrmions experience...

A nontrivial balance between Coulomb repulsion and kinematic effects determines the electronic structure of correlated electron materials. The use of electromagnetic fields strong enough to rival these native microscopic interactions allows us to study the electronic response as well as the time scales and energies involved in using quantum effects...

Topological Weyl semimetals (TWSs) are exotic crystals possessing emergent relativistic Weyl fermions connected by unique surface Fermi arcs (SFAs) in their electronic structures. To realize the TWS state, certain symmetries (such as the inversion or time reversal symmetry) must be broken, leading to a topological phase transition (TPT). Despite th...

Interfacing magnetism with superconducting condensates is rapidly emerging as a viable route for the development of innovative quantum technologies. In this context, the development of rational design strategies to controllably tune the interaction between magnetic moments is crucial. Here we address this problem demonstrating the possibility of tu...

High energy resolution spectroscopic studies of quantum magnets have proven to be extremely valuable in directly accessing magnetodynamics quantities, such as energy barriers, magnetic interactions, lifetime of excited states and fluctuations at the most fundamental level. Here, we explore the existence of a new flavor of low-energy spin-excitation...

Topologically trivial insulators come in two kinds: atomic, where the Wannier charge centers (WCCs) are localized on the atoms, and obstructed atomic, where the WCCs are located away from the atoms. The latter, which can exhibit interesting surface states and possibly have much larger band gaps than the topological insulators, have so far not been...

The discovery of new catalysts that are efficient, sustainable, and low-cost is a major research endeavor for many industrial chemical processes. This requires an understanding and determination of the catalytic origins for the given catalysts, which still remains a challenge. Here we describe a novel method to identify new catalysts based on searc...

Taking the measure of a magnet The recent discovery of magnetism in two-dimensional (2D) materials has inspired efforts to understand its nature. Whereas the magnetism of monolayers of chromium iodide (CrI 3 ) can be understood in terms of out-of-plane magnetic anisotropy, the related material chromium chloride (CrCl 3 ) has spins that lie in the p...

The proximity-coupling of a chiral non-collinear antiferromagnet (AFM)1–5 with a singlet superconductor allows spin-unpolarized singlet Cooper pairs to be converted into spin-polarized triplet pairs6–8, thereby enabling non-dissipative, long-range spin correlations9–14. The mechanism of this conversion derives from fictitious magnetic fields that a...

Nonequilibrium studies of two-dimensional (2D) superconductors (SCs) with Ising spin–orbit coupling are prerequisite for their successful application to equilibrium spin-triplet Cooper pairs and, potentially, Majorana Fermions. By taking advantage of the recent discoveries of 2D SCs and their compatibility with any other materials, we fabricate her...

Data-intensive computing operations, such as training neural networks, are essential for applications in artificial intelligence but are energy intensive. One solution is to develop specialized hardware onto which neural networks can be directly mapped, and arrays of memristive devices can, for example, be trained to enable parallel multiply–accumu...

The controllability of carrier density and major carrier type of transition metal dichalcogenides(TMDCs) is critical for electronic and optoelectronic device applications. To utilize doping in TMDC devices, it is important to understand the role of dopants in charge transport properties of TMDCs. Here, the effects of molecular doping on the charge...

The current induced motion of domain walls forms the basis of several advanced spintronic technologies. The most efficient domain wall motion is found in synthetic antiferromagnetic (SAF) structures that are composed of an upper and a lower ferromagnetic layer coupled antiferromagnetically via a thin ruthenium layer. The antiferromagnetic coupling...

Spin transmission at ferromagnet/heavy metal interfaces is of vital importance for many spintronic devices. Usually the spin current transmission is limited by the spin mixing conductance and loss mechanisms such as spin memory loss. In order to understand these effects, we study the interface transmission when an insulating interlayer is inserted...

The spin torque ferromagnetic resonance (STFMR) is one of the popular methods for measurement of the spin Hall angle, θ SH. However, in order to accurately determine θ SH from STFMR measurements, the acquired data must be carefully analyzed. The resonance linewidth should be determined to an accuracy of a fraction of an Oe, while the dynamical inte...

Magnetic nano‐objects, namely antiskyrmions and Bloch skyrmions, have been found to coexist in single‐crystalline lamellae formed from bulk crystals of inverse tetragonal Heusler compounds with D2d symmetry. Here evidence is shown for magnetic nano‐objects in epitaxial thin films of Mn2RhSn formed by magnetron sputtering. These nano‐objects exhibit...

Heterostructures formed from interfaces between materials with complementary properties often display unconventional physics. Of especial interest are heterostructures formed with ferroelectric materials. These are mostly formed by combining thin layers in vertical stacks. Here the first in situ molecular beam epitaxial growth and scanning tunnelin...

Interfacing magnetism with superconducting condensates is rapidly emerging as a viable route for the development of innovative quantum technologies. In this context, the development of rational design strategies to controllably tune the interaction between magnetic moments is crucial. In the metallic regime, the indirect interaction mediated by con...

Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Her...

Dirac semimetals (DSMs) are classified into different phases based on the types of the Dirac fermions. Tuning the transition among different types of the Dirac fermions in one system remains challenging. Recently, KMgBi was predicted to be located at a critical state that various types of Dirac fermions can be induced owing to the existence of a fl...

Topological band theory has achieved great success in the high-throughput search for topological band structures both in paramagnetic and magnetic crystal materials. However, a significant proportion of materials are topologically trivial insulators at the Fermi level. In this paper, we show that, remarkably, for a subset of the topologically trivi...

Topological electronic flatten bands near or at the Fermi level are a promising avenue towards unconventional superconductivity and correlated insulating states. In this work, we present a catalogue of all the three-dimensional stoichiometric materials with flat bands around the Fermi level that exist in nature. We consider 55,206 materials from th...

Topological Weyl semimetals (TWSs) are exotic crystals possessing emergent relativistic Weyl fermions connected by unique surface Fermi-arcs (SFAs) in their electronic structures. To realize the TWS state, certain symmetry (such as the inversion or time reversal symmetry) must be broken, leading to a topological phase transition (TPT). Despite the...

The current induced manipulation of chiral spin textures is of great interest for both fundamental research and technological applications1–3. Of particular interest are magnetic non-volatile memories formed from synthetic antiferromagnetic racetracks in which chiral composite domain walls (DWs), that act as data bits, can be efficiently moved by c...

Vanadium dioxide (VO2) is a phase change material that can reversibly change between high and low resistivity states through electronic and structural phase transitions. Thus far, VO2 memory devices have essentially been volatile at room temperature, and nonvolatile memory has required non‐ambient surroundings (e.g., elevated temperatures, electrol...

The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the Dirac semimetal ZrTe 5 . It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a sta...

Two-dimensional (2D) superconductors (SCs) with Ising spin-orbit coupling are regarded as a central ingredient for the topological protection of spin-triplet Cooper pairs and, thereby, Majorana fermions. Here, we fabricate non-local magnon devices to examine how such 2D Ising superconductivity affects the conversion efficiency of magnon spin to qua...

The recently introduced theories of Topological Quantum Chemistry and Symmetry-Based Indicators (SIs) have facilitated the discovery of novel topological phases of matter and large-scale searches for materials with experimentally accessible topological properties at the Fermi energy ($E_F$). In this work, we have completed the first catalog of stab...

Weyl semimetals, a class of 3D topological materials, exhibit a unique electronic structure featuring linear band crossings and disjoint surface states (Fermi‐arcs). While first demonstrations of topologically driven phenomena have been realized in bulk crystals, efficient routes to control the electronic structure have remained largely unexplored....

We study the interplay of superconductivity, ferromagnetism, and the Kondo effect in a single system, using vertical geometry and planar magnetic tunnel junction devices, in which a thin CoFe layer is inserted in the middle of the MgO layer, forming a quantum dot like system. It is shown that the Kondo resonance peak at the zero bias coexists with...

Artificially engineered topological superconductivity has emerged as a viable route to create Majorana modes. In this context, proximity-induced superconductivity in materials with a sizable spin–orbit coupling has been intensively investigated in recent years. Although there is convincing evidence that superconductivity may indeed be induced, it h...

As spins move through a chiral electric field, the resulting spin current can acquire chirality through a spin–orbit interaction. Such spin currents are highly useful in creating spin–orbit torques that can be used to manipulate chiral topological magnetic excitations, for example, chiral magnetic domain walls or skyrmions. When the chiral domain w...

2H-MoS2 is a well-studied and promising non-noble metal electrocatalyst for heterogeneous reactions, such as the hydrogen evolution reaction (HER). The performance is largely limited by the chemically inert basal plane, which is unfavorable for surface adsorption and reactions. Herein, we report a facile method to boost the HER activities of 2H-MoS...

The superconducting analog to the semiconducting diode, the Josephson diode, has long been sought, with multiple avenues to realization proposed by theorists. Exhibiting magnetic-field free, single directional superconductivity with Josephson coupling of the supercurrent across a tunnel barrier, it would serve as the building-block for next-generat...

The spin-orbit coupling (SOC) lifts the band degeneracy that plays a vital role in the search for different topological states, such as topological insulators (TIs) and topological semimetals (TSMs). In TSMs, the SOC can partially gap a degenerate nodal line, leading to the formation of Dirac/Weyl semimetals (DSMs/WSMs). However, such SOC-induced g...

The state-of-the-art knowledge of ferroelectric and ferroelastic group-IV monochalcogenide monolayers is surveyed. These semiconductors feature remarkable structural and mechanical properties, such as a switchable in-plane spontaneous polarization, soft elastic constants, structural degeneracies, and thermally driven two-dimensional structural tran...

Topological physics and strong electron–electron correlations in quantum materials are typically studied independently. However, there have been rapid recent developments in quantum materials in which topological phase transitions emerge when the single-particle band structure is modified by strong interactions. Here we demonstrate that the room-te...

Local spins coupled to superconductors give rise to several emerging phenomena directly linked to the competition between Cooper pair formation and magnetic exchange. These effects are generally scrutinized using a spectroscopic approach which relies on detecting the in-gap bound modes arising from Cooper pair breaking, the so-called Yu-Shiba-Rusin...

Local spins coupled to superconductors give rise to several emerging phenomena directly linked to the competition between Cooper pair formation and magnetic exchange. These effects are generally scrutinized using a spectroscopic approach which relies on detecting the in-gap bound modes arising from Cooper pair breaking, the so-called Yu-Shiba-Rusin...

The current induced motion of domain walls forms the basis of several advanced spintronic technologies. The most efficient domain wall motion is found in synthetic antiferromagnetic (SAF) structures that are composed of an upper and a lower ferromagnetic layer coupled antiferromagnetically via a thin ruthenium layer. The antiferromagnetic coupling...

Magnetic racetrack devices are promising candidates for next-generation memories. These spintronic shift-register devices are formed from perpendicularly magnetized ferromagnet/heavy metal thin-film systems. Data are encoded in domain wall magnetic bits that have a chiral Néel structure that is stabilized by an interfacial Dzyaloshinskii-Moriya int...

A Correction to this paper has been published: https://doi.org/10.1038/s41567-021-01169-4.

We demonstrate VO 2 optical memory integrated onto a silicon waveguide. Optical information is stored in the bistable states of VO 2 and read out as the change in the optical transmission of the waveguide.

Recently a zoology of non-collinear chiral spin textures has been discovered, most of which, such as skyrmions and antiskyrmions, have integer topological charges that provides them with enhanced stability. Here we report the experimental real-space observation of the formation and stability of fractional antiskyrmions and fractional elliptical sky...

Spin-momentum locking in topological insulators and materials with Rashba-type interactions is an extremely attractive feature for novel spintronic devices and is therefore under intense investigation. Significant efforts are underway to identify new material systems with spin-momentum locking, but also to create heterostructures with new spintroni...

Traditional electronic devices are well-known to improve in speed and energy-efficiency as their dimensions are reduced to the nanoscale. However, this scaling behavior remains unclear for nonlinear dynamical circuit elements, such as Mott neuron-like spiking oscillators, which are of interest for bio-inspired computing. Here we show that shrinking...

Materials with transition metals in triangular lattices are of great interest for their potential combination of exotic magnetism and electronic topology. Kagome nets, also known as trihexagonal, are of particular importance since the discovery of geometrically frustrated magnetism and massive Dirac fermions in crystals like Herbertsmithite and $\m...

Chiral spin textures are of considerable interest for applications in spintronics. It has recently been shown that magnetic materials with D 2d symmetry can sustain several distinct spin textures. Here, we show, using Lorentz transmission electron microscopy, that single and double chains of antiskyrmions can be generated at room temperature in nan...

Although recent experiments and theories have shown a variety of exotic transport properties of nonequilibrium quasiparticles (QPs) in superconductor (SC)-based devices with either Zeeman or exchange spin-splitting, how a QP interplays with magnon spin currents remains elusive. Here, using nonlocal magnon spin-transport devices where a singlet SC (...

The physical mechanism of the plasmonic skyrmion lattice formation in a magnetic layer deposited on a metallic substrate is studied theoretically. The optical lattice is the essence of the standing interference pattern of the surface plasmon polaritons created through coherent or incoherent laser sources. The nodal points of the interference patter...

Here, we report an exhaustive study of the frequency-dependent ac-magnetic susceptibility of the $D_{2d}$ symmetric Heusler system Mn-Pt(Pd)-Sn that hosts antiskyrmions over a wide temperature range. Magnetic relaxation studies using Cole-Cole formalism reveal a Debye-type relaxation with a nearly negligible distribution in relaxation times. In con...

Artificially engineered topological superconductivity has emerged as a viable route to create Majorana modes, exotic quasiparticles which have raised great expectations for storing and manipulating information in topological quantum computational schemes. The essential ingredients for their realization are spin non-degenerate metallic states proxim...

Time-reversal-symmetry-breaking Weyl semimetals (WSMs) have attracted great attention recently because of the interplay between intrinsic magnetism and topologically nontrivial electrons. Here, we present anomalous Hall and planar Hall effect studies on Co3Sn2S2 nanoflakes, a magnetic WSM hosting stacked Kagome lattice. The reduced thickness modifi...

Here, we report an exhaustive study of the frequency-dependent ac magnetic susceptibility of the D 2d-symmetric Heusler system Mn-Pt(Pd)-Sn that hosts antiskyrmions over a wide temperature range. Magnetic relaxation studies using Cole-Cole formalism reveal a Debye-type relaxation with a nearly negligible distribution in relaxation times. In contras...

Vanadium dioxide (VO2) is a phase change material that can reversibly change between high and low resistivity states through electronic and structural phase transitions. Thus far, VO2 memory devices have essentially been volatile at room temperature, and nonvolatile memory has required non-ambient surroundings (e.g., elevated temperatures, electrol...

The development of high‐density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat‐assisted magnetic recording was developed,...

X-ray absorption spectroscopy (XAS) and the directly linked X-ray reflectivity near absorption edges yield a wealth of specific information on the electronic structure around the resonantly addressed element. Observing the dynamic response of complex materials to optical excitations in pump–probe experiments requires high sensitivity to small chang...

Magnetic skyrmions and antiskyrmions are observed in material classes with different crystal symmetries, where the Dzyaloshinskii-Moriya interaction stabilizes either skyrmions or antiskyrmions. Here, we report the observation of two distinct peaks in the topological Hall effect in a thin film of Mn2RhSn. Utilizing a phenomenological approach and e...

The properties and characteristics of thin-film materials strongly depend on their textures and orientations. However, the attainable film morphologies are severely limited by substrates and growth thermodynamics. Metastable films that otherwise cannot be grown by conventional growth methods may overcome these limitations, thus allowing a dramatic...