We report an experimental study of the emergence of nontrivial topological winding and long-range order across the paramagnetic-to-skyrmion lattice transition in the transition metal helimagnet MnSi. ...Combining measurements of the susceptibility with small-angle neutron scattering, neutron-resonance spin-echo spectroscopy, and all-electrical microwave spectroscopy, we find evidence of skyrmion textures in the paramagnetic state exceeding103Å, with lifetimes above several10−9s. Our experimental findings establish that the paramagnetic-to-skyrmion lattice transition in MnSi is well described by the Landau soft-mode mechanism of weak crystallization, originally proposed in the context of the liquid-to-crystal transition. As a key aspect of this theoretical model, the modulation vectors of periodic small-amplitude components of the magnetization form triangles that add to zero. In excellent agreement with our experimental findings, these triangles of the modulation vectors entail the presence of the nontrivial topological winding of skyrmions already in the paramagnetic state of MnSi when approaching the skyrmion lattice transition.
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Abstract
Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, ...was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd
3
to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature—the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.
We report a comprehensive small-angle neutron scattering (SANS) study of magnetic correlations in Mn1−xFexSi at zero magnetic field. To delineate changes of magnetocrystalline anisotropies (MCAs) ...from effects due to defects and disorder, we recorded complementary susceptibility and high-resolution specific heat data and investigated selected compositions of Mn1−xCoxSi. For all systems studied, the helimagnetic transition temperature and magnetic phase diagrams evolve monotonically with composition consistent with literature. The SANS intensity patterns of the spontaneous magnetic order recorded under zero-field cooling, which were systematically tracked over forty angular positions, display strong changes of the directions of the intensity maxima and smeared out intensity distributions as a function of composition. We show that cubic MCAs account for the complex evolution of the SANS patterns, where for increasing x the character of the MCAs shifts from terms that are fourth order to terms that are sixth order in spin-orbit coupling. The magnetic field dependence of the susceptibility and SANS establishes that the helix reorientation as a function of magnetic field for Fe- or Co-doped MnSi is dominated by pinning due to defects and disorder. The presence of well-defined thermodynamic anomalies of the specific heat at the phase boundaries of the skyrmion lattice phase in the doped samples and properties observed in Mn1−xCoxSi establishes that the pinning due to defects and disorder remains, however, weak and comparable to the field scale of the helix reorientation. The observation that MCAs, which are sixth order in spin-orbit coupling, play an important role for the spontaneous order in Mn1−xFexSi and Mn1−xCoxSi offers a fresh perspective for a wide range of topics in cubic chiral magnets such as the generic magnetic phase diagram, the morphology of topological spin textures, the paramagnetic-to-helical transition, and quantum phase transitions.
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The longitudinal neutron resonant spin echo spectrometer RESEDA Franz, C.; Soltwedel, O.; Fuchs, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2019, Volume:
939
Journal Article
Peer reviewed
The instrumental layout and technical realisation of the neutron resonant spin echo (NRSE) spectrometer RESEDA at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany, is presented. RESEDA is ...based on a longitudinal field configuration, boosting both dynamic range and maximum resolution of the spectrometer compared to the conventional transverse layout. The resonant neutron spin echo technique enables the realisation of two complementary implementations: A longitudinal NRSE (LNRSE) option comparable to the classical neutron spin echo (NSE) method for highest energy resolution and large momentum transfers as well as a Modulation of Intensity with Zero Effort (MIEZE) option for depolarising samples or sample environments such as high magnetic fields, and strong incoherent scattering samples. With their outstanding dynamic range, exceeding nominally seven orders of magnitude, both options cover new fields for ultra-high resolution neutron spectroscopy in hard and soft condensed matter systems. In this paper the concept of RESEDA as well as the technical realisation along with reference measurements are reported.
•Instrumental concept and technical realisation of the of the RESEDA spectrometer.•Two measurement options: NRSE and MIEZE.•MIEZE allows for ultra-high resolution measurements under depolarising conditions.•Both options allow extreme dynamic range over nominally seven orders of magnitude.•Reference measurements are compared to analytical calculations and MC-simulations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Longitudinal neutron resonance spin echo (LNRSE) spectroscopy offers very high energy resolution due to the self correction of the resonant spin flippers, and a wide dynamical range nominally ...exceeding six orders of magnitude in resolution down to sub-ps range. In this paper, the technical realisation how to achieve such low Fourier times at the spectrometer RESEDA at the MLZ Garching is described. The requirements of data collection and data analysis in the limit of very low Fourier times, notably those related to the breakdown of the spin echo approximation, are discussed. A method to infer the scattering function from the experimental data under large energy tansfers beyond the spin echo approximation is presented.
While the influence of dipolar interactions on the spin-wave dispersion in ferromagnets with localized magnetic moments has been studied in detail, similar studies in itinerant electron systems are ...rather scarce due to experimental difficulties. Using the newly developed neutron Larmor precession technique MIEZE in a longitudinal field configuration, we succeeded to map out the spin-wave dispersion in Fe at small momentum q and energy transfers E. The results demonstrate an excellent agreement of the magnon dispersion with the Holstein-Primakoff theory, which takes the dipolar interactions into account. At larger q, the data is in agreement with previous investigations by Collins et al., Phys. Rev. 179, 417 (1969). The q dependence of the linewidth of the magnons is proportional to q2.5 in agreement with dynamical scaling theory. The critical exponent for the stiffness, μ=0.35±0.01, agrees with field theory. The spin dynamics in Fe is now explored by neutron scattering over an energy range 15μeV<Esw<120meV, i.e., over about four orders of magnitude in energy.
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As systems for quantum computing keep growing in size and number of qubits, challenges in scaling the control capabilities are becoming increasingly relevant. Efficient schemes to simultaneously ...mediate coherent interactions between multiple quantum systems and to reduce decoherence errors can minimize the control overhead in next-generation quantum processors. Here, we present a superconducting qubit architecture based on tunable parametric interactions to perform two-qubit gates, reset, leakage recovery and to read out the qubits. In this architecture, parametrically driven multi-element couplers selectively couple qubits to resonators and neighbouring qubits, according to the frequency of the drive. We consider a system with two qubits and one readout resonator interacting via a single coupling circuit and experimentally demonstrate a controlled-Z gate with a fidelity of \(98.30\pm 0.23 \%\), a reset operation that unconditionally prepares the qubit ground state with a fidelity of \(99.80\pm 0.02 \%\) and a leakage recovery operation with a \(98.5\pm 0.3 \%\) success probability. Furthermore, we implement a parametric readout with a single-shot assignment fidelity of \(88.0\pm 0.4 \%\). These operations are all realized using a single tunable coupler, demonstrating the experimental feasibility of the proposed architecture and its potential for reducing the system complexity in scalable quantum processors.
Studying the prototypical ferromagnetic superconductor UGe2 we reveal the potential of the modulated intensity by zero effort (MIEZE) technique—a novel neutron spectroscopy method with ultrahigh ...energy resolution of at least 1 μ eV —for the study of quantum matter. We reveal purely longitudinal spin fluctuations in UGe2 with a dual nature arising from 5f electrons that are hybridized with the conduction electrons. Local spin fluctuations are perfectly described by the Ising universality class in three dimensions, whereas itinerant spin fluctuations occur over length scales comparable to the superconducting coherence length, demonstrate that MIEZE is able to spectroscopically disentangle the complex low-energy behavior characteristic of quantum materials.
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We report an experimental study of the emergence of non-trivial topological winding and long-range order across the paramagnetic to skyrmion lattice transition in the transition metal helimagnet ...MnSi. Combining measurements of the susceptibility with small angle neutron scattering, neutron resonance spin echo spectroscopy and all-electrical microwave spectroscopy, we find evidence of skyrmion textures in the paramagnetic state exceeding \(10^3\)\AA with lifetimes above several 10\(^{-9}\)s. Our experimental findings establish that the paramagnetic to skyrmion lattice transition in MnSi is well-described by the Landau soft-mode mechanism of weak crystallization, originally proposed in the context of the liquid to crystal transition. As a key aspect of this theoretical model, the modulation-vectors of periodic small amplitude components of the magnetization form triangles that add to zero. In excellent agreement with our experimental findings, these triangles of the modulation-vectors entail the presence of the non-trivial topological winding of skyrmions already in the paramagnetic state of MnSi when approaching the skyrmion lattice transition.
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