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We report experimental studies of quantum-matter heterostructures based on a ferromagnet/normal metal multilayer proximitized by Nb superconducting electrodes to form a novel Josephson weak-link device that is highly sensitive to magnetic fields. The device is a single Josephson junction containing Al/Ni or Al/Py (Py: Ni80Fe20) multilayer structures, which manifests quasi-sinusoidal critical current oscillations resembling the response of a dc Superconducting Quantum Interference Device (SQUID). Our analysis shows that the field sensitivity of this novel device, as measured by the magnetic field needed to form one period of the oscillations, is about twice that reported for recent micro- or nano-SQUIDs. We present an analysis of the temperature dependence of the period of the oscillations and the Josephson critical current, as well as the background current. We believe that our devices are promising candidates for a new generation of magnetic field nanosensors.

Chalcogenide-based phase change memory (PCM) is a key enabling technology for optical data storage and electrical nonvolatile memory. Here, we report a new phase change chalcogenide consisting of a...

We analyze the magnetic mode structure of axially-magnetized, finite-length, nanoscopic cylinders in a regime where the exchange interaction dominates, along with simulations of the mode frequencies of the ferrimagnet yttrium iron garnet. For the bulk modes we find that the frequencies can be represented by an expression given by Herring and Kittel by using wavevector components obtained by fitting the mode patterns emerging from these simulations. In addition to the axial, radial, and azimuthal modes that are present in an infinite cylinder, we find localized "cap modes" that are "trapped" at the top and bottom cylinder faces by the inhomogeneous dipole field emerging from the ends. Semi-quantitative explanations are given for some of the modes in terms of a one-dimensional Schrodinger equation which is valid in the exchange dominant case. The assignment of the azimuthal mode number is carefully discussed and the frequency splitting of a few pairs of nearly degenerate modes is determined through the beat pattern emerging from them.

We demonstrate that micrometer-scale spin waves can be excited in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) using patterned, multi-element antennas. The magnitude of the dynamic magnetic field generated by such antennas decays exponentially along the thickness direction, and this leads to an enhanced coupling to modes having a surface-like character as opposed to a more sinusoidal bulk-like character. We have used this property to identify spin waves having a mixed bulk/surface character.

Chalcogenide-based phase change memory (PCM) is a key enabling technology for optical data storage and electrical nonvolatile memory. Here, we report a new phase change chalcogenide consisting of a 3D network of ionic (K···Se) and covalent bonds (Bi-Se), K

Magnetization reversals in magnetic recording media are largely carried out by brute force: a field is applied opposite to the existing magnetization direction of some bit that has sufficient magnitude to nucleate a seed that then grows into an oppositely magnetized bit. The fields used are generally quite large, $\sim 10$ kG, requiring elaborate magnetic circuitry to keep the fields localized so they do not spill over onto neighboring bits. This situation is to be contrasted with the resonant magnetization reversals performed in NMR spin echo experiments in which r.f. fields of a few Gauss coherently reverse the magnetization in the presence of static fields of a few kG, by applying a so-called Pi pulse; two such pulses restores the original alignment.

In this work, we realize a physical system---nanoengineered singly connected Josephson junction with a periodic superparamagnetic $\mathrm{Ni}/\mathrm{Al}$ multilayer---that manifests supercurrent-versus-magnetic field response typical of a dc superconducting quantum interference device (SQUID); however, unlike a SQUID, which involves a superconducting loop occupying significant space, our lumped device is more suitable for miniaturization. In addition, we show that it exhibits enhanced magnetic field sensitivity as compared with conventional superconductor-insulator-superconductor Josephson junctions. SQUID-like oscillatory response to external magnetic fields, analogous to the two-slit optical interference, is explained in terms of the dominance of Andreev bound states localized at the barrier edges in the comparatively thick and strongly anisotropic weak links. Our results may lead to significant advancement in development of nanoscale magnetic sensing techniques applicable to individual molecules or magnetic nanoparticles.

We report the experimental and theoretical characterization of the angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged on a honeycomb lattice. The magnetic field and microwave frequency dependence, measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes that is strongly affected by the microstate of the network. Based on symmetry arguments with respect to the external field, we show that certain parts of the ferromagnetic network contribute to the detected signal. A comparison of the experimental data with micromagnetic simulations reveals that different subsections of the lattice predominantly contribute to the high-frequency response of the array. This is confirmed by optical characterizations using microfocused Brillouin light scattering. Furthermore, we find indications that nucleation and annihilation of vortex-like magnetization configurations in the low-field range affect the dynamics, which is different from clusters of ferromagnetic nanoellipses. Our work opens up new perspectives for designing magnonic devices that combine geometric frustration in gyrotropic vortex crystals at low frequencies with magnonic crystals at high frequencies.

Stuck in the middle with you: The spin-wave mode localized in the contact area among macrospins in an artificial spin ice (ASI) is interesting for magnonic devices and applications. Detection and characterization of this mode is difficult, though. This study uses carefully designed lattices of individual macrospins with the right aspect ratio of individual nanoelements, the right geometry of macrospins on an ASI vertex, and the right configuration for clear detection of the spin dynamics. The localized mode is found to exhibit a peculiar sensitivity to the applied field's direction, which could impact applications such as magnonic position transducers.

Hybrid organic–inorganic perovskites are emerging semiconductors for cheap and efficient photovoltaics and light-emitting devices. Different from conventional inorganic semiconductors, hybrid perovskites consist of coexisting organic and inorganic sub-lattices, which present disparate atomic masses and bond strengths. The nanoscopic interpenetration of these disparate components, which lack strong electronic and vibrational coupling, presents fundamental challenges to the understanding of charge and heat dissipation. Here we study phonon population and equilibration processes in methylammonium lead iodide (MAPbI3) by transiently probing the vibrational modes of the organic sub-lattice following above-bandgap optical excitation. We observe inter-sub-lattice thermal equilibration on timescales ranging from hundreds of picoseconds to a couple of nanoseconds. As supported by a two-temperature model based on first-principles calculations, the slow thermal equilibration is attributable to the sequential phonon populations of the inorganic and organic sub-lattices, respectively. The observed long-lasting thermal non-equilibrium offers insights into thermal transport and heat management of the emergent hybrid material class., Hybrid organic-inorganic perovskites are emerging materials for efficient photovoltaics; however understanding how charge/heat dissipates inside the material remains a challenge. Here, the authors use a spectroscopic approach to observe unusually slow thermal equilibration between the organic and inorganic components.

We have observed the propagation of spin waves across a thin yttrium iron garnet film on (1 1 1) gadolinium gallium garnet for magnetic fields inclined with respect to the film plane. Two principle planes were studied: that for H in the plane defined by the wave vector k and the plane normal, n , with limiting forms corresponding to the Backward Volume and Forward Volume modes, and that for H in the plane perpendicular to k , with limiting forms corresponding to the Damon-Eshbach and Forward Volume modes. By exciting the wave at one edge of the film and observing the field dependence of the phase of the received signal at the opposing edge we determined the frequency vs. wavevector relation, ω = ω ( k ), of various propagating modes in the film. Avoided crossings are observed in the Damon-Eshbach and Forward Volume regimes when the propagating mode intersects the higher, exchange split, volume modes, leading to an extinction of the propagating mode; analysis of the resulting behavior allows a determination of the exchange parameter. The experimental results are compared with theoretical simulations.

Using a many spin micromagnetic simulation tool that directly integrates the Landau-Lifshitz equation, we demonstrate that by applying an r.f. pulse, generally referred to as a Pi pulse, it is possible to near-perfectly reverse the direction of the magnetization in a ferromagnet, provided that the sample is sufficiently small and the angular dependence of the precession frequency is continuously matched using an appropriately “chirped” r.f. pulse of the proper length. Simulations are carried out for “prolate” uniaxially symmetric cylindrical samples in the presence of dipole and exchange interactions. Such reversals can be performed in the presence of a static external magnetic field or, importantly, at zero field under the sample’s own internal demagnetization field. However, the ability to perform near-perfect Pi or two-Pi rotations is lost for samples above certain dimensions for which additional internal degrees of freedom are excited, particularly at higher static fields. In such larger samples the magnetization may still be reversed by utilizing damping, provided it can be rotated past a critical angle.

Solution-processable metal halide perovskites (MHPs) offer great promise for efficient light-harvesting and -emitting devices because of their long carrier lifetime and superior carrier transport properties. Similar to traditional oxide perovskites, MHPs exhibit strong dynamic disorders that may further impact their electronic properties. Here we investigate the coherent acoustic phonons of inorganic and organic–inorganic (hybrid) MHP single crystals (CsPbCl3, MAPbCl3, CsPbBr3, MAPbBr3, FAPbBr3, MAPbI3, and FAPbI3) using pump–probe reflection spectroscopy. We show significant phonon softening in the cubic phase of all compositions close to the cubic-to-tetragonal phase transition temperature. Such phonon softening in conjunction with strong acoustic damping is attributed to pretransitional polar fluctuations. Comparison of MHPs with different compositions show that the degree of pretransitional fluctuations is correlated with the size rather than the dipole moment of the A-site cations, and further with t...

Ferroelectricity in organic materials remains a subject of great interest, given its potential impact as lightweight information storage media. Here we report supramolecular charge-transfer cocrystals formed by electron acceptor and donor molecules that exhibit ferroelectric behavior along two distinct crystallographic axes. The solid-state superstructure of the cocrystals reveals that a 2:1 ratio of acceptor to donor molecules assemble into nearly orthogonal mixed stacks in which the molecules are positioned for charge-transfer in face-to-face and edge-to-face orientations, held together by an extended hydrogen-bonding network. Polarization hysteresis was observed along the face-to-face and edge-to-face axes at room temperature. The noncentrosymmetric nature of the cocrystals, required to observe ferroelectric behavior, is demonstrated using second harmonic generation measurements. This finding suggests the possibility of designing supramolecular arrays in which organic molecules support multidimensional information storage.

We report the results of a study of the current gain in high Josephson critical current density ( j ${}_{\rm c}$ ) superconducting-ferromagnetic transistors with the SISFIFS structure [where S, I, and F denote a superconductor (Nb), an insulator (AlO ${}_{x}$ ), and a ferromagnetic material (permalloy, Py), respectively]. The Nb/AlO ${}_{x}$ /Nb trilayer, which serves as the acceptor (SIS) junction, is estimated to have Josephson critical current density j ${}_{\rm c}$ of 19 kA/cm2. The Al/Py/Al/AlO ${}_{x}$ /Py/Al/Nb multilayer is deposited in a separate vacuum run after in situ ion milling of about 8 nm of the top Nb layer. The devices are patterned using optical lithography and tested at 4.2 K. We have observed a small-signal current gain in the range of 5–9. We demonstrate that proper device engineering allows one to efficiently control the maximum Josephson current in the SISF acceptor junction using the quasiparticle injection.

We synthesized the barium/strontium solid solution sequence Ba6−xSrx[Ag(4−y)Sn(y/4)](SnS4)4 for nonlinear optical (NLO) applications in the infrared (IR) via a flux synthesis route. All title compounds are isotypic, crystallizing in the cubic space group I 4 3d and are composed of a three-dimensional (3D) anionic framework of alternating corner-sharing SnS4 and AgS4 tetrahedra charge balanced by Ba and Sr. The shrinkage of Ba/Sr–S bond lengths causes the tetrahedra in the anionic framework to become more distorted, which results in a tunable band gap from 1.58 to 1.38 eV with increasing x values. The performance of the barium limit (x=0) is also superior to that of Sr (x=6), but surprisingly second harmonic generation (SHG) of the solid solution remains strong and is insensitive to the value of x over the range 0–3.8. Results show that the non-type-I phase-matched SHG produced by these cubic chalcogenides display intensities higher than the benchmark AgGaSe2 from 600 to 1000 nm.

We report experimental and theoretical results on the current gain in superconductor-ferromagnetic transistors (SFTs) with the SISFIFS structure [where S, I, and F denote a superconductor (Nb), an insulator ( ${\rm{AlO}}_{x}$ ), and a ferromagnetic material (Ni), respectively]. The Josephson critical current density $j_{{\rm{ca}}}$ of the acceptor (SISF) junction in the devices is above 9 kA/cm2, which is higher than that in our previous devices. The critical current gain is defined as $ \vert \delta I_{{\rm{ca}}}\vert / \vert \delta I_{i}\vert $ , where a change $\vert \delta I_{i}\vert $ in the injector (SFIFS junction) current produces a change $\vert \delta I_{{\rm{ca}}}\vert $ in the acceptor maximum Josephson current. We observed a small-signal gain as high as 7.8 and a large-signal current gain of about 2.2. In addition, we found that the Josephson current of the acceptor junction is sensitive to the state of the ferromagnetic layers. A theoretical model is proposed to describe the nonequilibrium processes in the SFT devices, which agrees with the experimental observations. The calculation shows that, in the present device configuration, the dominant contribution to the gap suppression in the middle Nb electrode is due to the quasiparticle injection; spin injection plays a secondary role. We demonstrate that proper device engineering allows one to efficiently control the maximum Josephson current in the SISF acceptor junction using the quasiparticle injection. We conclude that SFT devices can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

Organic-inorganic hybrid perovskites such as methylammonium lead iodide (CH3NH3PbI3) are game-changing semiconductors for solar cells and light-emitting devices owing to their defect tolerance and exceptionally long carrier lifetimes and diffusion lengths. Determining whether the dynamically disordered organic cations with large dipole moment benefit the optoelectronic properties of CH3NH3PbI3 has been an outstanding challenge. Herein, via transient absorption measurements employing an infrared pump pulse tuned to a methylammonium vibration, we observe slow, nanosecond-long thermal dissipation from the selectively excited organic mode to the inorganic sublattice. The resulting transient electronic signatures, during the period of thermal-nonequilibrium when the induced thermal motions are mostly concentrated on the organic sublattice, reveal that the induced atomic motions of the organic cations do not alter the absorption or the photoluminescence response of CH3NH3PbI3, beyond thermal effects. Our results suggest that the attractive optoelectronic properties of CH3NH3PbI3 mainly derive from the inorganic lead-halide framework., It has been challenging to probe whether dynamically disordered organic cations affect optical properties of CH3NH3PbI3. Here, Guo et al. employ infrared-pump electronic-probe spectroscopy and show that pump-induced atomic motions of the organic cations do not substantially alter optoelectronic properties.

Using a set of wave-vector-specific multielement antennas, we have characterized the dispersion of spin waves in an yttrium iron garnet film at submicron lengths and resolved the dispersion relations of multiple backward volume modes, particularly in the region of their minima. The techniques developed now facilitate the characterization of spin waves at length scales limited only by available lithography and at a spectral resolution that generally exceeds that of Brillouin scattering. The data obtained are in excellent agreement with theoretical predictions based on a model Hamiltonian.

We experimentally and theoretically characterize the angular-dependent microwave response of three-macrospin-vertex structures that can serve as a node in various spin ice lattices. The macrospins consist of patterned permalloy thin films with an elliptical cross section together with an in-plane aspect ratio allowing an Ising-like behavior together with bulk modes as low-frequency excitations in the field range of interest. Various branches of the frequency-magnetic field curves display atypical behaviors and discontinuities, together with softening due to macrospin reversals. The overall behavior observed accurately corresponds to a superposition of the spectra of the individual macrospins. The measured ferromagnetic resonance spectra are in good agreement with theoretical modeling. In particular, they reveal a close correlation between the field direction (relative to the individual macrospins), and the corresponding frequency-magnetic field curve, i.e., between the geometry and the magnetic response.

Active control of light is important for photonic integrated circuits, optical switches, and telecommunications. Coupling light with acoustic vibrations in nanoscale optical resonators offers optical modulation capabilities with high bandwidth and small footprint. Instead of using noble metals, here we introduce indium-tin-oxide nanorod arrays (ITO-NRAs) as the operating media and demonstrate optical modulation covering the visible spectral range (from 360 to 700 nm) with ∼20 GHz bandwidth through the excitation of coherent acoustic vibrations in ITO-NRAs. This broadband modulation results from the collective optical diffraction by the dielectric ITO-NRAs, and a high differential transmission modulation up to 10% is achieved through efficient near-infrared, on-plasmon-resonance pumping. By combining the frequency signatures of the vibrational modes with finite-element simulations, we further determine the anisotropic elastic constants for single-crystalline ITO, which are not known for the bulk phase. This technique to determine elastic constants using coherent acoustic vibrations of uniform nanostructures can be generalized to the study of other inorganic materials.

All-optical control of plasmons can enable optical switches with high speeds, small footprints and high on/off ratios. Here we demonstrate ultrafast plasmon modulation in the near-infrared (NIR) to mid-infrared (MIR) range by intraband pumping of indium tin oxide nanorod arrays (ITO-NRAs). We observe redshifts of localized surface plasmon resonances arising from a change of the plasma frequency of ITO, which is governed by the conduction band non-parabolicity. We generalize the plasma frequency for non-parabolic bands, quantitatively model the fluence-dependent plasma frequency shifts, and show that different from noble metals, the lower electron density in ITO enables a remarkable change of electron distributions, yielding a significant plasma frequency modulation and concomitant large transient bleaches and induced absorptions, which can be tuned spectrally by tailoring the ITO-NRA geometry. The low electron heat capacity explains the sub-picosecond kinetics that is much faster than noble metals. Our work demonstrates a new scheme to control infrared plasmons for optical switching, telecommunications and sensing. Ultrafast plasmon modulation has been realized in the near- to mid-infrared range by intraband pumping of indium tin oxide nanorod arrays.

We report broadband ferromagnetic resonance measurements of the in-plane magnetic field response of three- and four-fold symmetric vertices formed by non-contacting permalloy nano-ellipses together with extended lattices constructed from them. Complementing the experimental data with simulations, we are able to show that, as far as the most intense FMR responses are concerned, the spectra of vertices and lattices can largely be interpreted in terms of a superposition of the underlying hysteretic responses of the individual ellipses, as elemental building blocks of the system. This property suggest that it is possible to understand the orientation of the individual magnetic dipole moments in a dipole network in terms of dynamic measurements alone, thereby offering a powerful tool to analyze the alignment statistics in frustrated systems that are exposed to various magnetic histories.

Using parametric excitation, we have studied the minimum frequency associated with the backward volume (BV) spin wave branch in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) for the magnetic field lying in plane and parallel to the wave vector as well as for out-of-plane field angles. We find that there is a drastic change in the efficiency of parametric excitation between two different pumping frequency regimes.

Using a multielement antenna, we have performed measurements of the angular dependence of propagating magnetostatic spin waves in a thin yttrium iron garnet film, both in-plane and out-of-plane, and compared the measurements with existing theoretical models. For most magnetic field directions, theory and experiments agree reasonably well. However, there is a range of magnetic field directions where differences between theory and experiment become large.

Two-dimensional Ruddlesden–Popper organic–inorganic hybrid layered perovskites (2D RPs) are solution-grown semiconductors with prospective applications in next-generation optoelectronics. The heat-carrying, low-energy acoustic phonons, which are important for heat management of 2D RP-based devices, have remained unexplored. Here we report on the generation and propagation of coherent longitudinal acoustic phonons along the cross-plane direction of 2D RPs, following separate characterizations of below-bandgap refractive indices. Through experiments on single crystals of systematically varied perovskite layer thickness, we demonstrate significant reduction in both group velocity and propagation length of acoustic phonons in 2D RPs as compared to the three-dimensional methylammonium lead iodide counterpart. As borne out by a minimal coarse-grained model, these vibrational properties arise from a large acoustic impedance mismatch between the alternating layers of perovskite sheets and bulky organic cations. Our results inform on thermal transport in highly impedance-mismatched crystal sub-lattices and provide insights towards design of materials that exhibit highly anisotropic thermal dissipation properties., Two-dimensional, organic-inorganic hybrid perovskites have sustained research interest due to attractive optoelectronic and excitonic properties. Here, Guo et al. systematically investigate coherent acoustic phonon transport versus layer thickness in these materials with strong acoustic impedance mismatch

Excitations of free electrons and optical phonons are known to permit access to the negative real part of relative permittivities (ϵ^{'}

We report experimental results on characteristics of SFIFS junctions and multiterminal SFIFSIS and SISFIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (Ni), respectively). The SFIFS (SFIS) junctions serve as injectors in the SFIFSIS (SISFIS) devices, which have transistorlike properties; for this reason, we call them superconducting-ferromagnetic transistors. We have found the F (Ni) thickness at which the SFIFS current-voltage characteristic becomes linear. For three-terminal SFIFSIS devices, we focused on studying the influence of the injection current through the SFIFS junction on the maximum Josephson current of the SIS acceptor. For four-terminal SISFIS devices, we studied dependence of the transport current through the middle Nb electrode on injection current level through the SFIS junction. In both cases, we found that the output superconducting current (either Josephson or transport) can be efficiently modulated by the quasiparticle injection from SFIFS or SFIS input junction. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI3, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the isolation of 6 new hybrid semiconductors. Using CsGeI3 (1) as the prototype compound, we have prepared methylammonium, CH3NH3GeI3 (2), formamidinium, HC(NH2)2GeI3 (3), acetamidinium, CH3C(NH2)2GeI3 (4), guanidinium, C(NH2)3GeI3 (5), trimethylammonium, (CH3)3NHGeI3 (6), and isopropylammonium, (CH3)2C(H)NH3GeI3 (7) analogues. The crystal structures of the compounds are classified based on their dimensionality with 1–4 forming 3D perovskite frameworks and 5–7 1D infinite chains. Compounds 1–7, with the exception of compounds 5 (centrosymmetric) and 7 (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 eV (1), 1.9 eV (2), 2.2 eV (3), and 2.5 eV (4), while the 1D compounds have indirect band gaps of 2.7 eV (5), 2.5 eV (6), and 2.8 eV (7). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to ∼3 GW/cm(2)). The second-order nonlinear susceptibility, χS(2), was determined to be 125.3 ± 10.5 pm/V (1), (161.0 ± 14.5) pm/V (2), 143.0 ± 13.5 pm/V (3), and 57.2 ± 5.5 pm/V (4). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation.

A new series of metal chalcogenides with the formula Ba6Ag2.67+4δSn4.33−δS16–xSex (x = 0 for 1, x = 6.47 for 2, and x = 16 for 3) were synthesized. Compounds 1–3 are isotypic with a three-dimension...

The rich physics associated with magnetism often centers around directional effects. Here we demonstrate how spin-transfer torques in general result in unidirectional ferromagnetic resonance dynamics upon field reversal. The unidirectionality is a direct consequence of both field-like and damping-like dynamic torques simultaneously driving the motion. This directional effect arises from the field-like torque being odd and the damping-like torque being even under field reversal. The directional effect is observed when the magnetization has both an in-plane and out-of-plane component, since then the linear combination of the torques rotates with a different handedness around the magnetization as the magnetization is tipped out-of-plane. The effect is experimentally investigated via spin-torque ferromagnetic resonance measurements with the field applied at arbitrary directions away from the interface normal. The measured asymmetry of the voltage spectra are well explained within a phenomenological torque model.

In complex networks of ferromagnetic macrospins, like artificial spin ices or artificial quasi-crystals, much interest has focused on the dynamics of Dirac strings, i.e. the apparently irregular path followed by macrospin reversals, producing a magnetic charge drift across the network.

Previous studies of artificial spin ice have been largely restricted to periodic dot lattices. Ferromagnetic switching of segments in an applied magnetic field is stochastic in periodic spin ice systems, which makes emergent phenomena, such as the formation of vortex loops, hard to control or predict. We fabricated finite, aperiodic Penrose P2 tilings as antidot lattices with fivefold rotational symmetry in permalloy thin films. Measurements of the field dependence of the static magnetization reveal reproducible knee anomalies whose number and form are temperature dependent, which suggests they mark cooperative rearrangements of the tiling magnetic texture. Our micromagnetic simulations of the P2 tiling are in good agreement with experimental magnetization data and exhibit non-stochastic magnetic switching of segments in applied field, and vortex loops that are stable over an extended field interval during magnetic reversal.

We report experimental results on the dc and ac characterization of multiterminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator $(\hbox{AlO}_{x})$ , and a ferromagnetic material (Ni), respectively), which display transistor-like properties. We investigated two types of such superconducting–ferromagnetic transistors (SFTs): ordinary devices with a single acceptor (SIS) junction, and devices with a double acceptor. The devices with the single SIS acceptor were investigated and demonstrated a modulation of the maximum Josephson current as a function of the SFIFS current injection level. For devices of the second type, by applying an ac signal (in the kilohertz range) with a constant dc bias current to the injector (SFIFS) junction, we observed a voltage gain of about 25 on the double acceptor with the operating point chosen in the subgap region of the acceptor current-voltage characteristic. We also observed an excellent input–output isolation in our SFIFSIS devices. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

We report on properties of Nb(/Ti)–carbon–(Ti/)Nb junctions fabricated on graphite flakes using e-beam lithography. The devices were characterized at temperatures above 1.8 K where a Josephson current was not observed, but the differential conductivity revealed features below the critical temperature of Nb, and overall metallic conductivity, in spite of a high-junctions resistance. Since the conductivity of graphite along the planes is essentially two-dimensional (2D), we use a theoretical model developed for metal/graphene junctions for interpretation of the results. The model involves two very different graphene “access” lengths. The shorter length characterizes ordinary tunneling between the three-dimensional Nb(/Ti) electrode and 2D graphene, while the second, much longer length, is associated with the Andreev reflections (AR) inside the junction and involves also “reflectionless” AR processes. The relevant transmission factors are small in the first case and much larger in the second, which explains ...

We present a systematic study of light scattering from indium-tin-oxide (ITO) nanorods in the near-infrared with a special focus on the resonant coupling of plasmonic transverse mode and photonic modes in 2-D periodic arrays. Using theoretical analysis combined with simulations, a set of experiments has been designed to study such interactions. Near-field mapping from the simulations shows a strong interaction of localized surface plasmon resonances (LSPR) with a photonic resonance; together they explain the scattering phenomenon observed in our experiments carried out in the far field. We observed the shift of LSPR as the plasma frequency was varied, resulting in a modification of the spectral shape. Utilizing the high aspect ratios of the ITO nanorods, the LSPR strength can be turned on and off by the polarization of the incident light.

We propose an arbitrary pattern lithography process using interference of Bose-Einstein condensates (BECs). A symmetric three-pulse Raman atom interferometer (AI) is used to implement the system. The pattern information, in the form of a phase-only mask, is optically encoded into the BEC order parameter in one of the AI arms. The lithographic pattern is represented by a two-dimensional intensity variation, and is transformed into a two-dimensional phase variation in the BEC order parameter via the use of ac-Stark shift induced by a pulsed laser field. The BEC probability distribution of the interference result at the end of the AI is proportional to the required pattern. In order to produce features smaller than the diffraction limit for the used optical elements, we employ a three-dimensional atomic lens system to scale down the resulting pattern. The operating conditions for this lens structure are investigated in order to identify practical constraints. Simulations of the overall system using the parameters of $^{87}\mathrm{Rb}$ BEC were performed to illustrate its functionality. The proposed process, while perhaps not suitable for general purpose usage, may enable the creation of special purpose patterns on a very small scale, with features as small as a few nanometers.

We report the experimental and theoretical characterization of the angular dependent magnetic field and microwave frequency response of isolated mesoscopic permalloy nanoellipses for geometries in which the static magnetic field is either parallel or perpendicular to the microwave magnetic field. We show how these spectra form a basis for interpreting the ferromagnetic resonance spectra of lattices based on such structures, including those containing frustrated regions, such as artificial spin ice structures.We report the experimental and theoretical characterization of the angular dependent magnetic field and microwave frequency response of isolated mesoscopic permalloy nanoellipses for geometries in which the static magnetic field is either parallel or perpendicular to the microwave magnetic field. We show how these spectra form a basis for interpreting the ferromagnetic resonance spectra of lattices based on such structures, including those containing frustrated regions, such as artificial spin ice structures.

We report experiments which characterize spin wave propagation in a thin (111) yttrium iron garnet film for arbitrary angles between the in-plane magnetic field and the mode wavevectors. By measuring the magnetic field evolution of the phase of the wave traveling across the film, we deduce the frequency dependence of the wavevector, the dispersion relation, from which the mode velocity follows. Additionally, we observe multiple nodes in the regime of the propagating Damon-Eshbach mode; these arise from avoided crossings associated with the higher, exchange split, standing wave modes along the film normal, the positions of which correlate with the direct absorption measurements of their positions. This information allows a determination of the exchange parameter. Using this technique, we examine the nonreciprocity in spin wave propagation that results from an adjacent metal layer.We report experiments which characterize spin wave propagation in a thin (111) yttrium iron garnet film for arbitrary angles between the in-plane magnetic field and the mode wavevectors. By measuring the magnetic field evolution of the phase of the wave traveling across the film, we deduce the frequency dependence of the wavevector, the dispersion relation, from which the mode velocity follows. Additionally, we observe multiple nodes in the regime of the propagating Damon-Eshbach mode; these arise from avoided crossings associated with the higher, exchange split, standing wave modes along the film normal, the positions of which correlate with the direct absorption measurements of their positions. This information allows a determination of the exchange parameter. Using this technique, we examine the nonreciprocity in spin wave propagation that results from an adjacent metal layer.

Single crystals of cuprous oxide (Cu2O) with minimal defects were grown using the optical floating zone technique. Copper vacancies were removed through the promotion of CuO precipitation within the bulk Cu2O crystal following the reaction CuCuCu2O + VCuCu2O + OOCu2O → CuCuCuO + OOCuO. This reaction was promoted through the use of high purity samples and by growing crystals under an oxidizing atmosphere. Although an increase in the oxygen concentration of the atmosphere will initially increase the oxygen to copper ratio, the excess oxygen in the final Cu2O crystal is ultimately decreased through the formation of CuO as the crystal cools. Copper vacancies were reduced further, and the CuO phase was eventually removed from the Cu2O crystal when thin slices of the crystal were annealed.

We have used ferromagnetic resonance (FMR) at fixed frequency 9.7 GHz to investigate permalloy thin films patterned with antidots to form a five-fold quasicrystal pattern. For DC applied fields H below 3.5 kOe, we observed robust FMR spectra exhibiting two-fold rotational symmetry instead of the five-fold symmetry expected for quasicrystals. Dynamic micromagnetic simulations of the FMR spectra performed at H = 1 kOe and 12 kOe exhibit two-fold and ten-fold rotational symmetry, respectively. The ten-fold symmetry observed in simulations is consistent with a saturated state of isolated write fields. We infer the two-fold rotational symmetry observed for H = 1 kOe is due to an unsaturated state of five-fold write fields closely spaced on a square lattice.

A series of new metal chalcogenides Ba4CuGa5Q12 (Q = S, S0.75Se0.25, Se) were synthesized using KBr flux at 750 °C. The three compounds are isostructural and adopt the noncentrosymmetric space group P421c. Crystal data are as follows: Ba4CuGa5S12, 1, a = 13.040(1) A, c = 6.304(1) A, and Z = 2; Ba4CuGa5S9.00(1)Se2.92(1), 2, a = 13.1585(2) A, c = 6.3520(2) A, and Z = 2; Ba4CuGa5Se12, 3, a = 13.598(1) A, c = 6.527(1) A, and Z = 2. The three-dimensional framework in 1 is constructed by infinite columns ∞1[CuGa4S10]7– that surround the discrete GaS4 tetrahedra situated on a 4 axis. The discrete GaS4 tetrahedra on the stacking (112) planes and canted oriented edge-sharing CuS4 tetrahedra within the columns may account for the occurrence of strong second-harmonic generation (SHG) responses. Compounds 1–3 are transparent in the mid-infrared range and have the absorption edges at 2.82, 2.05, and 1.45 eV, respectively. The new nonlinear optical (NLO) materials are type-I nonphase matching at 693 nm and display st...

We have performed broadband (10 MHz-14 GHz) ferromagnetic resonance measurements on permalloy thin films patterned with square lattices of diamond-shaped antidots of variable size and separation. We observe remarkably reproducible mode structures in the low-frequency, hysteretic regime in which various domain wall patterns and unsaturated magnetization textures exist and are strongly affected by the geometry of the antidot lattice. The magnetic field, frequency and angular dependences of the observed modes (some not previously reported) are in good agreement with recently developed micromagnetic simulations. The mode reproducibility is attributed to a reproducible evolution of domain wall textures governed by their pinning to antidot edges. We conclude variations of antidot size, shape and spacing can be used to control magnetic reversal, domain wall pinning and spin wave mode structure.

Bulk spin Hall effects are well know to provide spin orbit torques, which can be used to drive magnetization dynamics [1]. But one of the reoccurring questions is to what extend spin orbit torques may also originate at the interface between materials with strong spin orbit coupling and the ferromagnets. Using spin torque driven ferromagnetic resonance we show for two systems, where interfacial torques dominate, that they can be large enough to be practically useful. First, we show spin transfer torque driven magnetization dynamics based on Rashba-Edelstein effects at the Bi/Ag interface [2]. Second, we will show that combining permalloy with monolayer MoS2 gives rise to sizable spin-orbit torques. Given the monolayer nature of MoS2 it is clear that bilk spin Hall effects are negligible and therefore the spin transfer torques are completely interfacial in nature. Interestingly the spin orbit torques with MoS2 show a distinct dependence on the orientation of the magnetization in the permalloy, and become strongly enhanced, when the magnetization is pointing perpendicular to the interfacial plane. This work was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division. [1] A. Hoffmann, IEEE Trans. Mag. 49, 5172 (2013). [2] W. Zhang et al., J. Appl. Phys. 117, 17C727 (2015). [3] M. B. Jungfleisch et al., arXiv:1508.01410.