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We compare the dynamical behavior of magnetic skyrmions interacting with square and triangular defect arrays just above commensuration using both an atomistic model and a particle-based model. Under an applied drive, the initial motion is a kink traveling through the pinned skyrmion lattice. For the square defect array, both models agree well and show a regime in which the soliton motion is locked along 45$^\circ$. The atomistic model also produces locking of a soliton along 30$^\circ$, while the particle-based model does not. For the triangular defect array, the atomistic model exhibits soliton motion locked to 30$^\circ$ over a wide region of external driving force values. In contrast, the particle-based model gives soliton motion locked to 45$^\circ$ over only a small range of external driving force values. The difference arises because the nondeforming particle model facilitates meandering skyrmion orbits while the deformable atomistic model enables stronger skyrmion-skyrmion interactions that reduce the meandering. Our results indicate that soliton motion through pinned skyrmion lattices on a periodic substrate is a robust effect and could open the possibility of using solitons as information carriers. Our results also provide a better understanding of the regimes for which particle-based models of skyrmions are best suited., Comment: 7 pages, 5 figures

We demonstrate the non-reciprocity of electrically and thermally-generated incoherent magnon transport using the magnetization direction of a Py wire placed on top of an ultrathin YIG film. We show that the transport properties of thermally-generated magnons under a Py wire depends on the relative orientation between the temperature gradient and the Py-magnetization direction. The symmetries of this non-reciprocal magnon transport match with those predicted by the remote dipolar interaction between YIG and Py magnons, controlled by the chirality of the YIG magnon dipolar stray fields. We also show that the directional magnon generation by the spin Seebeck effect from the Py wire displays the symmetries expected from the chiral spin Seebeck effect.

Using atomistic simulations, we investigate the dynamical behavior of magnetic skyrmions in dimer and trimer molecular crystal arrangements, as well as bipartite lattices at 3/2 and 5/2 fillings, under ac driving over a square array of anisotropy defects. For low ac amplitudes, at all fillings we find reversible motion where the skyrmions return to their original positions at the end of each ac drive cycle and the diffusion is zero. We also identify two distinct irreversible regimes. The first is a translating regime in which the skyrmions form channels of flow in opposing directions and translate by one substrate lattice constant per ac drive cycle. The translating state appears in the dimer and trimer states, and produces pronounced peaks in the diffusivity in the direction perpendicular to the external drive. For larger ac amplitudes, we find chaotic irreversible motion in which the skyrmions can randomly exchange places with each other over time, producing long-time diffusive behavior both parallel and perpendicular to the ac driving direction., Comment: 16 pages, 5 figures

We investigate the electronic properties of nanoribbons made out of monolayer Lieb, transition, and kagome lattices using the tight-binding model with a generic Hamiltonian. It allows us to map the evolutionary stages of the interconvertibility process between Lieb and kagome nanoribbons by means of only one control parameter. Results for the energy spectra, the density of states, and spatial probability density distributions are discussed for nanoribbons with three types of edges: straight, bearded, and asymmetric. We explore for different nanoribbon terminations: (i) the semiconductor-metallic transition due to the interconvertibility of the Lieb and kagome lattices, (ii) the effect of both nanoribbon width and inclusion of the next-nearest-neighbor hopping term on the degeneracy of the quasi-flat states, (iii) the behavior of the energy gap versus the nanoribbon width, (iv) the existence and evolution of edge states, and (v) the nodal spatial distributions of the total probability densities of the non-dispersive states., Comment: 21 pages, 12 figures

Latching techniques are widely used to enhance readout of qubits. These methods require precise tuning of multiple tunnel rates, which can be challenging to achieve under realistic experimental conditions, such as when a qubit is coupled to a single reservoir. Here, we present a method for single-shot measurement of a quantum dot qubit with a single reservoir using a latched-readout scheme. Our approach involves pulsing a barrier gate to dynamically control qubit-to-reservoir tunnel rates, a method that is readily applicable to the latched readout of various spin-based qubits. We use this method to enable qubit state latching and to reduce the qubit reset time in measurements of coherent Larmor oscillations of a Si/SiGe quantum dot hybrid qubit., Comment: 6 pages, including supplemental materials

Pushing the sensitivity of nuclear magnetic resonance spectroscopy to the single spin level would have a major impact in chemistry and biology and is the goal of intense research efforts. Individual nuclear spins have been detected via their hyperfine coupling to an individual electronic paramagnetic system, itself measured by optical or electrical means. These methods are however only applicable when suitable optical transitions or electron-spin-to-charge conversion mechanisms exist, and a more universal method is currently lacking. Here, we report spectroscopic measurements of individual $^{183}\mathrm{W}$ nuclear spins in a CaWO$_4$ crystal via their hyperfine interaction with a neighboring $\mathrm{Er}^{3+}$ ion detected by microwave photon counting at millikelvin temperatures. We observe real-time quantum jumps of the nuclear spin state, a proof of their individual nature. We perform single-spin ELDOR-detected NMR spectroscopy by microwave driving the zero- and double-quantum transitions of the $^{183}$W--Er$^{3+}$ coupled system. By repeated driving of these transitions, we also achieve single-spin solid-effect dynamical nuclear polarization. Relying exclusively on microwave driving and microwave detection, the methods reported here apply in principle to any nuclear spin coupled to a paramagnetic impurity, and therefore open the way to single-nuclear-spin spectroscopy in a large class of samples.

An ensemble of electrons trapped above the surface of superfluid helium is a paradigm system for investigating, and controlling, the collective charge dynamics of low-dimensional electronic matter. Of particular interest is the ability to engineer the spatial and spectral structure of surface plasmon modes in this system for integration into hybrid quantum systems or circuit quantum electrodynamic device architectures. Here we present experiments on a hybrid electron-on-helium microchannel device designed to host microwave-frequency plasmon modes having a spatial structure dictated by the geometry of the microchannel confinement. The plasma oscillations are generated via local microwave frequency excitation of the electrons in the microchannel. When this excitation is resonant with a particular surface plasmon-mode it produces a non-equilibrium decrease in the electron conductance, which we detect via simultaneous transport measurements. We find that the spatial structure of the surface plasmons is in excellent agreement with our device design parameters and modeling, and their frequency can be tuned over a broad range (several GHz) by precisely varying the areal density of electrons in the channel. By measuring the plasma resonance spectrum lineshape, and its power dependence, we can quantify the level of spatial homogeneity associated with each plasmon mode. The results highlight the versatility of electrons on helium as a model system for investigating, and engineering, the collective mode structure of low-dimensional Coulomb liquid and solid states and demonstrate a viable path for integrating precisely engineered surface plasmons in electrons on helium with future hybrid circuit quantum electrodynamic systems., Comment: 10 pages, 5 figures, 1 Appendix

Magnetic nanoparticle-based hyperthermia has emerged as a promising therapeutic modality for treating malignant solid tumors that exhibit resistance to conventional cancer treatments, including chemotherapy and radiation. Despite the clinical approval of superparamagnetic iron oxide nanoparticles (SPIONs) for the adjunct treatment of recurrent glioblastoma, their therapeutic potential is undercut by chemical synthesis-inherent limitations such as low saturation magnetization, superparamagnetic characteristics, and a wide nanoparticle size distribution. Here, we introduce an micromagnetic modelling-based SAF-MDP design with in-plane magnetization, optimized through specific uniaxial anisotropy adjustments to avert the spin-flop phenomenon and eliminate hysteresis-free hard-axis magnetization loops, paired with a mechanofluidic modeling approach to assess the alignment of the SAF-MDP to the applied alternating magnetic field (AMF). Magnetic Force Microscopy characterization provides unprecedented insights into the particle switching behaviour on a single particle scale. This comprehensive strategy spanning micromagnetics and advanced magnetic characterization enables the design of particles with heating efficiencies to approach the theoretical maximum, dictated by the saturation magnetization of the utilized materials and limited solely by the biologically acceptable frequencies and amplitudes of the oscillating magnetic field. Our work not only addresses the limitations encountered by previous methodologies but also sets the stage for the development of advanced SAF-MDP designs and alignment techniques. This opens a new avenue to hyperthermia-based cancer therapy, delineated only by the boundaries of physical laws and biological safety standards., Comment: 9 pages, 5 figures, 3 pages Methods

Quantum sensing based on solid-state spin defects provides a uniquely versatile platform for imaging physical properties at the nanoscale under diverse environmental conditions. Operation of most sensors used to-date is based on projective measurement along a single axis combined with computational extrapolation. Here, we show that the individually addressable carbon-related spin defect in hexagonal boron nitride is a multi-axis spin system for vectorial nanoscale magnetometry. We demonstrate how its low symmetry and strongly spin-selective direct and reverse intersystem crossing dynamics provide sub-$\mu$T/$\sqrt{\text{Hz}}$ magnetic-field sensitivity for both on and off-axis bias magnetic field exceeding 50 mT. Alongside these features, the room-temperature operation and the nanometer-scale proximity enabled by the van der Waals host material further consolidate this system as an exciting quantum sensing platform.

We have fabricated a device which includes two lateral p-n junctions on an n-type GaAs/Al$_{0.33}$Ga$_{0.67}$As heterostructure. A section of the n-type material has been converted to p-type by removing dopants and applying a voltage to a gate placed in this region. Controlled electroluminescence from both of the p-n junctions has been demonstrated by varying the applied bias voltages. An emission peak with a width of ~8 nm is observed around 812 nm. The electroluminescence seen from both junctions is considered to originate from the GaAs quantum well layer in the device. The lithographic techniques that we have developed are compatible for further integration of gated quantum devices such as single-electron pumps to build on-demand single-photon sources.

The quantum conductance of flat (Euclidean) circuits subject to Rashba spin-orbit coupling shows a symmetric response to the inversion of the spin-orbit field in Aharonov-Casher interference patterns. Here, we show that this symmetry breaks down in curved (non-Euclidean) circuits defined on a spherical two-dimensional electron gas. We demonstrate that this is a consequence of parallel spin transport and holonomy on the surface of the sphere, and that a symmetric response can be recovered when considering the parallel transport condition as an offset. We discuss triangular circuits defined along geodesic arcs on the sphere as a case study, and generalize it to regular polygons and parallel curves of given latitude., Comment: 18 pages, 10 figures

Controlled long-range transport of micro- and nano-scale objects is a key requirement in lab-on-a-chip and microfluidic applications, enabling the efficient capture, concentration, manipulation, and detection of analytes. Traditional methods such as microfluidic pumps and optical trapping face challenges including high power consumption and limited range of action. This study introduces a plasmonic Brownian ratchet designed for the directed transport of dielectric nanometer-sized particles at low optical powers. Through numerical simulations, the ratchet geometry was optimized to enhance electric fields, optical forces, and trapping potentials. Experimentally, the plasmonic ratchet demonstrated the ability to rectify random thermal motion of 40 nm polysterene spheres over extended distances in a specific direction, achieving velocities up to 2.4 $\mu$m/s at excitation powers as low as 0.785 kW/cm^2. This plasmonic ratchet offers a robust and efficient solution for the targeted delivery and concentration of nanoscale analytes on chips, with significant implications for advancing applications in the life sciences., Comment: to be submitted to ACS Nano

The quasiparticles (QPs) or quasiholes (QHs) of fractional quantum Hall states have been predicted to obey fractional braid statistics, which refers to the Berry phase (in addition to the usual Aharonov-Bohm phase) associated with an exchange of two QPs or two QHs, or equivalently, to half of the phase associated with a QP / QH going around another. Certain phase slips in interference experiments in the fractional quantum Hall regime have been interpreted as arising from the statistics associated with a QP moving along the edge of the sample around another QP in the interior. A conceptual difficulty with this interpretation is that the edge, being compressible, does not support a QP or a QH with a sharply quantized fractional charge or fractional statistics. We analyze the experiment in terms of composite fermions (CFs) obeying integral braid statistics and suggest that the observed phase slips can be naturally understood as a measure of the relative braid statistics of a CF in the ground state at the edge and a fractionally charged QP / QH in the interior; in contrast to fractionally charged excitations, the CFs are known to remain sharply defined even in compressible regions such as the edge or the CF Fermi liquid state at half filled Landau level. We further propose that transport through a closed $\textit{tunneling}$ loop confined entirely in the bulk can, in principle, allow an unambiguous measurement of the relative braid statistics of a fractionally charged QP / QH braiding around another fractionally charged QP / QH. Optimal parameters for this experimental geometry are determined from quantitative calculations.

We demonstrate how Exceptional Points (EPs) naturally occur in the Luttinger Liquid (LL) theory describing the low-energy excitations of a microscopic lattice model with sublattice dependent electron-electron interaction. Upon bosonization, this sublattice dependence directly translates to a non-standard sine-Gordon-type term responsible for the non-Hermitian matrix structure of the single-particle Green Function (GF). As the structure in the lifetime of excitations does not commute with the underlying free Bloch Hamiltonian, non-Hermitian topological properties of the single-particle GF emerge -- despite our Hermitian model Hamiltonian. Both finite temperature and a non-trivial Luttinger parameter $K\neq 1$ are required for the formation of EPs, and their topological stability in one spatial dimension is guaranteed by the chiral symmetry of our model. In the presence of the aforementioned sine-Gordon-term, we resort to leading order Perturbation Theory (PT) to compute the single-particle GF. All qualitative findings derived within LL theory are corroborated by comparison to both numerical simulations within the conserving second Born approximation, and, for weak interactions and high temperatures, by fermionic plain PT. In certain parameter regimes, quantitative agreement can be reached by a suitable parameter choice in the effective bosonized model., Comment: 7+9 pages, 5+1 figures

We report device level damping measurements using spin-torque driven ferromagnetic resonance on perpendicular magnetic random-access memory (MRAM) cells. It is shown that thermal agitation enhances the apparent damping for cells smaller than about 55 nm. The effect is fundamental and does not reflect a true damping increase. In addition to the thermal effect, it is still found that device level damping is higher than film level damping and increases with decreasing cell size. This is attributed to edge damage caused by device patterning., Comment: 19 pages, 10 figures

Quantum materials with stacking van der Waals (vdW) layers that can host non-trivial band structure topology and magnetism have shown many interesting properties. Here using high-throughput density functional theory calculations, we design and predict tetragonal vdW-layered quantum materials in the MPd$_5$I$_2$ structure (M=Ga, In and 3d transition metals). Our study shows that besides the known AlPd$_5$I$_2$, the -MPd$_5$- structural motif of three-layer slabs separated by two I layers can host a variety of metal elements giving arise to topological interesting features and highly tunable magnetic properties in both bulk and single layer 2D structures. Among them, TiPd$_5$I$_2$ and InPd$_5$I$_2$ host a pair of Dirac points and a likely strong topological insulator state for the band manifolds just above and below the top valence band, respectively, with their single layers possibly hosting quantum spin Hall states. CrPd$_5$I$_2$ is a ferromagnet with a large out-of-plane magneto-anisotropy energy, desirable for rare-earth-free permanent magnets., Comment: 25 pages, 6 figures

Using atomistic simulations, we show that new types of skyrmion states called skyrmion molecular crystals and skyrmion superlattices can be realized on triangular substrates when there are two or three skyrmions per substrate minimum. We find that as a function of the magnetic field and substrate periodicity, a remarkably wide variety of ordered phases appear similar to those found in colloidal or Wigner molecular crystals, including ferromagnetic and herringbone states. The ability of the skyrmions to annihilate, deform, and change size gives rise to a variety of superlattice states in which a mixture of different skyrmion sizes and shapes produces bipartate or more complex lattice structures. Our results are relevant for skyrmions on structured triangular substrates, in magnetic arrays, or skyrmions in moire materials., Comment: 6 pages, 4 figures

The manipulation of low-energy matter properties such as superconductivity, ferromagnetism and ferroelectricity via cavity quantum electrodynamics engineering has been suggested as a way to enhance these many-body collective phenomena. In this work, we investigate the effective interactions between low-energy matter excitations induced by the off-resonant coupling with cavity electromagnetic modes. We extend previous work by going beyond the dipole approximation accounting for the full polarization and magnetization densities of matter. We further include the often neglected diamagnetic interaction and, for the cavity, we consider general linear absorbing media with possibly non-local and non-reciprocal response. We demonstrate that, even in this general scenario, the effective cavity-induced interactions between the matter degrees of freedom are of electrostatic and magnetostatic nature. This confirms the necessity of a multimode description for cavity engineering of matter systems where the low-energy assumption holds. Our findings provide a theoretical framework for studying the influence of general optical environments on extended low-energy matter excitations.

The exploration of topological quantum materials and topological phase transitions is at the forefront of modern condensed matter physics. Quasi-one-dimensional (quasi-1D) bismuth iodide Bi4I4 exhibits versatile topological phases of matter including weak topological insulator (WTI) and higher-order topological insulator (HOTI) phases with high tunability in response to external parameters. In this work, performing laser-based angle-resolved photoemission spectroscopy with submicron spatial resolution (micro-ARPES), we comprehensively investigate the fine electronic structure and topological phase transition of Bi4I4. Our examination of the low-temperature {\alpha}-phase reveals the presence of an energy gap on the (100) surface, providing spectroscopic evidence for the HOTI phase. Conversely, the high-temperature {\beta}-Bi4I4 harbors a gapless Dirac fermion on the (100) surface alongside gapped states on the (001) surface, thereby establishing a WTI phase. By tracking the temperature evolution of the (100) surface states, we unveil a thermal hysteresis of the surface gap in line with the {\alpha}-{\beta} structural phase transition. Our findings elucidate the topological properties of Bi4I4 and directly evidence a temperature-induced topological phase transition from WTI to HOTI, which paves the way to potential applications based on the room-temperature topological phase transition in the quasi-1D topological quantum material.

We consider diffusion of an inertial Brownian particle moving in a symmetric spatially periodic potential and driven by an unbiased time periodic force of a moderate frequency. The study is focused on the dependence of its diffusion coefficient $D$ on the damping $\gamma$ ranging from the weak to strong one. We reveal the mechanisms of counterintutive effects in which diffusion can increase despite the grow of friction and exhibits both minima and maxima. Their origin is explained by analysis of the deterministic dynamics perturbed by thermal fluctuations. In the weak damping regime the maximum of diffusion is induced by a non-monotonic change of population of the running orbits when the friction increases. In the strong dissipation regime the effect is caused by bifurcation of periodic orbits oscillating symmetrically around the potential maximum and their displacement towards the potential minimum when the damping coefficient increases. It induces the change of the effective barrier of the periodic potential and its vanishing at the maximum of $D$.

An exciton is a Coulomb-driven bound state, which normally consists of an electron and a hole. Under the influence of charge fractionalization, an exotic construction of excitons arises from pairing between fractional particle and hole charge. Despite numerous theoretical considerations, experimental realization of fractional excitons remains largely unexplored. In this work, we report hallmark transport signatures of excitonic pairing that coexist with fractional quantum Hall effect states. By investigating the composition of interlayer excitons and their role in the construction of the underlying wavefunction, we describe two types of never-before-seen fractional quantum Hall effect orders. One can be viewed as the fractional analogue of the exciton condensate at total filling of one. The other involves a different type of exciton, which obeys fermionic and anyonic quantum statistics., Comment: 9 pages for main text with 4 figures. In total of 23 pages and 14 figures

Widefield quantum diamond microscopy is a powerful technique for imaging magnetic fields with high sensitivity and spatial resolution. However, current methods to approach the ultimate spatial resolution ($<500\,$nm) are impractical for routine use as they require time-consuming fabrication or transfer techniques to precisely interface the diamond sensor with the sample to be imaged. To address this challenge, we have designed a co-axial sensor holder that enables simple, repeatable sensor-sample interfacing while being compatible with high numerical aperture (NA) optics. With our new design we demonstrate low standoffs $<500\,$nm with a millimetre sized sensor. We also explore the relationship between spatial resolution and NA spanning from 0.13 to 1.3. The spatial resolution shows good agreement with the optical diffraction limit at low NA but deviates at high NA, which is shown to be due to optical aberrations. Future improvements to our design are discussed, which should enable magnetic imaging with $<500\,$nm resolution in an accessible, easy-to-use instrument.

A key virtue of spin qubits is their sub-micron footprint, enabling a single silicon chip to host the millions of qubits required to execute useful quantum algorithms with error correction. With each physical qubit needing multiple control lines however, a fundamental barrier to scale is the extreme density of connections that bridge quantum devices to their external control and readout hardware. A promising solution is to co-locate the control system proximal to the qubit platform at milli-kelvin temperatures, wired-up via miniaturized interconnects. Even so, heat and crosstalk from closely integrated control have potential to degrade qubit performance, particularly for two-qubit entangling gates based on exchange coupling that are sensitive to electrical noise. Here, we benchmark silicon MOS-style electron spin qubits controlled via heterogeneously-integrated cryo-CMOS circuits with a low enough power density to enable scale-up. Demonstrating that cryo-CMOS can efficiently enable universal logic operations for spin qubits, we go on to show that mill-kelvin control has little impact on the performance of single- and two-qubit gates. Given the complexity of our milli-kelvin CMOS platform, with some 100-thousand transistors, these results open the prospect of scalable control based on the tight packaging of spin qubits with a chiplet style control architecture.

Recent experiments reported the realization of a heavy Fermi liquid in AB-stacked MoTe$_2$/WSe$_2$ heterobilayers. In this paper we show that the AB-stacked heterobilayer configuration is particularly suited to realize topological Kondo semimetal and topological Kondo insulator ground states at a doping of two holes per moir\'e unit cell. The small lattice mismatch between the MoTe$_2$ and WSe$_2$ monolayers and the different bandwidths of their highest lying moir\'e valence bands means that, in the experimentally relevant range of hole dopings, the MoTe$_2$ layer is effectively a Mott insulator with only low-lying magnetic excitations Kondo-coupled to more itinerant electrons in the WSe$_2$. The crucial consequence of the AB-stacking configuration is that the interlayer tunnelling connects orbitals of opposite parity in the two layers, leading to a chiral Kondo coupling. We show that the chiral Kondo coupling favors a topological Kondo semimetal at filling $\nu=1+1$, with a non-quantized spin Hall conductance arising from edge modes, whose spectrum and overlap with bulk states we determine. We further show that a spatially random strain field that locally breaks the rotation symmetry can convert the Kondo semimetal to a narrow gap topological Kondo insulator featuring a quantized spin Hall conductance., Comment: 12 pages, 11 figures

To apply the powerful many-body techniques of tensor networks to massless Dirac fermions one wants to discretize the $p\cdot\sigma$ Hamiltonian and construct a matrix-product-operator (MPO) representation. We compare two alternative discretization schemes, one with a sine dispersion, the other with a tangent dispersion, applied to a one-dimensional Luttinger liquid with Hubbard interaction. Both types of lattice fermions allow for an exact MPO representation of low bond dimension, so they are efficiently computable, but only the tangent dispersion gives a power law decay of the propagator in agreement with the continuum limit: The sine dispersion is gapped by the interactions, evidenced by an exponentially decaying propagator. Our construction of a tensor network with an unpaired Dirac cone works around the fermion-doubling obstruction by exploiting the fact that the \textit{nonlocal} Hamiltonian of tangent fermions permits a \textit{local} generalized eigenproblem., Comment: 8 pages, 5 figures

Graphene is a privileged 2D platform for hosting confined light-matter excitations known as surface plasmon-polaritons (SPPs), as it possesses low intrinsic losses with a high degree of optical confinement. However, the inherently isotropic optical properties of graphene limit its ability to guide and focus SPPs, making it less suitable than anisotropic elliptical and hyperbolic materials as a platform for polaritonic lensing and canalization. Here, we present the graphene/CrSBr heterostructure as an engineered 2D interface that hosts highly anisotropic SPP propagation over a wide range of frequencies in the mid-infrared and terahertz. Using a combination of scanning tunneling microscopy (STM), scattering-type scanning near-field optical microscopy (s-SNOM), and first-principles calculations, we demonstrate mutual doping in excess of 10$^{13}$ cm$^{-2}$ holes/electrons between the interfacial layers of graphene/CrSBr heterostructures. SPPs in graphene activated by charge transfer interact with charge-induced anisotropic intra- and interband transitions in the interfacial doped CrSBr, leading to preferential SPP propagation along the quasi-1D chains that compose each CrSBr layer. This multifaceted proximity effect both creates SPPs and endows them with anisotropic transport and propagation lengths that differ by an order-of-magnitude between the two in-plane crystallographic axes of CrSBr.

In this work, we investigate the massive Kane-Mele model for graphene in the presence of disclination and an external magnetic field, where graphene behaviors as a topological insulator. In the low-energy limit, the effective field equation for graphene is described by a Dirac equation with three different degrees of freedom. We succeed to decouple the set of eight components of the Dirac equation by using the spin projector \hat{C} in the disclinated geometry. As consequence, we obtain the Landau levels in this framework, in which we note the emergence of zero modes as edge states due to the inversion symmetry breaking. We also note that for different sites in sublattices \mathcal{A/B}, one can have different values of gap width., Comment: 12 pages and 8 figures

Several domains of society will be disrupted once millions of high-quality qubits can be brought together to perform fault-tolerant quantum computing (FTQC). All quantum computing hardware available today is many orders of magnitude removed from the requirements for FTQC. The intimidating challenges associated with integrating such complex systems have already been addressed by the semiconductor industry -hence many qubit makers have retrofitted their technology to be CMOS-compatible. This compatibility, however, can have varying degrees ranging from the mere ability to fabricate qubits using a silicon wafer as a substrate, all the way to the co-integration of qubits with high-yield, low-power advanced electronics to control these qubits. Extrapolating the evolution of quantum processors to future systems, semiconductor spin qubits have unique advantages in this respect, making them one of the most serious contenders for large-scale FTQC. In this review, we focus on the overlap between state-of-the-art semiconductor spin qubit systems and CMOS industry Very Large-Scale Integration (VLSI) principles. We identify the main differences in spin qubit operation, material, and system requirements compared to well-established CMOS industry practices. As key players in the field are looking to collaborate with CMOS industry partners, this review serves to accelerate R&D towards the industrial scale production of FTQC processors., Comment: 36 pages, 5 figures

The surface magnetization of Fe$_3$GeTe$_2$ was examined by low-energy electron microscopy (LEEM) using an off-normal incidence electron beam. We found that the 180$^o$ domain walls are of Bloch type. Temperature-dependent LEEM measurements yield a surface magnetization with a surface critical exponent $\beta$1 = 0.79 +/- 0.02. This result is consistent with surface magnetism in the 3D semi-infinite Heisenberg ($\beta$1 = 0.84 +/- 0.01) or Ising ($\beta$1 = 0.78 +/- 0.02) models, which is distinctly different from the bulk exponent ($\beta$ = 0.34 +/- 0.07). The measurements reveal the power of LEEM with a tilted beam to determine magnetic domain structure in quantum materials. Single crystal diffraction measurements reveal inversion symmetry-breaking weak peaks and yield space group P-6m2. This Fe site defect-derived loss of inversion symmetry enables the formation of skyrmions in this Fe$_3$GeTe$_2$ crystal.

Magnon based spintronic devices require the modulation of magnon spin transport for their operations. We provide a proof-of-principle of two unconventional non-local magnon transport devices in which we modulate the diffusive magnon transport of incoherent magnons in the van der Waals antiferromagnet Chromium thiophosphate, CrPS4. The non-local signals generated electrically by spin injection via the spin Hall effect (SHE) and thermally via the spin Seebeck effect (SSE) are altered by a modulator electrode. The current through the modulator increases or decreases the magnon chemical potential via the SHE and changes the magnon temperature through Joule heating. We achieve up to 25%/mA and 16%/mA modulation efficiencies for the electrically and thermally generated magnon spin transport, respectively, for CrPS4 in the collinear state at in plane fields >7T at a temperature of 25K.

We investigate the injection, transport and detection of magnon spins in the van der Waals antiferromagnet chromium thiophosphate (CrPS4). We electrically and thermally inject magnon spins by platinum contacts and examine the non-local resistance as a function of in-plane magnetic field up to 12 Tesla. We observe a large non-local resistance from both the electrically and thermally excited magnon modes above the spin-flip field where CrPS4 is in the collinear state. At 25 K for an in-plane field of ranging 5 - 12 T, we extract the magnon relaxation length ranging $200-800$ nm and a typical magnon conductivity of 1e4 Sm-1, which is one order of magnitude smaller than in yttrium iron garnet (YIG) films at room temperature. Moreover, we find that the magnon conductivity is almost zero for CrPS4 in the non-collinear state. Our results open up the way to understanding the role of the antiferromagnetic magnon modes on spin injection into antiferromagnets and implementation of two-dimensional magnets for scalable magnonic circuits., Comment: 7 pages, 5 figures

Lattice deformations in graphene couple to the low-energy electronic degrees of freedom as pseudo scalar and gauge fields. Using molecular dynamics simulations, we show that the optical component of the displacement field, i.e., the relative motion of different sublattices, contributes at equal order as the acoustic component and effectively screens the pseudo gauge fields. In particular, we consider twisted bilayer graphene and corrugated monolayer graphene. In both cases, optical lattice displacement significantly reduce the overall magnitude of the pseudo magnetic fields. For corrugated graphene, we further show that the corresponding electronic bands are significantly modified by the screened pseudo magnetic field. Previous studies based on continuum elasticity, which ignores this effect, have therefore systematically overestimated the strength of the strain-induced pseudo magnetic field. Our results have important consequences for the interpretation of experiments and design of straintronic applications., Comment: 7 + 14 pages, 4 + 11 figures

In this paper, we investigate the influence of Majorana bound states on the Fano-Rashba effect in a two-channel Fano-Anderson model. Employing Green's function formalism and the equation of motion method, we compute the transmission through the quantum dot and the density of states. Our analysis reveals that the Majorana bound states, localized at the ends of the topological superconductor nanowire, penetrate into the quantum dot, thereby altering the interference pattern in the electronic transmission profile through it, resulting from their interaction with the bound states in the continuum. Furthermore, we explore the robustness of the bound state in the continuum concerning its connection to Majorana bound states and the energy induced by the magnetic field. We posit that our findings contribute to a deeper comprehension of the Fano-Rashba effect in a two-channel quantum dot coupled to a topological superconducting nanowire., Comment: 8 pages, 6 figures

Dark-field X-ray Microscopy (DFXM) is a novel diffraction-based imaging technique that non-destructively maps the local deformation from crystalline defects in bulk materials. While studies have demonstrated that DFXM can spatially map 3D defect geometries, it is still challenging to interpret DFXM images of the high dislocation density systems relevant to macroscopic crystal plasticity. This work develops a scalable forward model to calculate virtual DFXM images for complex discrete dislocation (DD) structures obtained from atomistic simulations. Our new DD-DFXM model integrates a non-singular formulation for calculating the local strain from the DD structures and an efficient geometrical optics algorithm for computing the DFXM image from the strain. We apply the model to complex DD structures obtained from a large-scale molecular dynamics (MD) simulation of compressive loading on a single-crystal silicon. Simulated DFXM images exhibit prominent feature contrast for dislocations between the multiple slip systems, demonstrating the DFXM's potential to resolve features from dislocation multiplication. The integrated DD-DFXM model provides a toolbox for DFXM experimental design and image interpretation in the context of bulk crystal plasticity for the breadth of measurements across shock plasticity and the broader materials science community.

Random networks offer fertile ground for achieving complexity and criticality, both crucial for an unconventional computing paradigm inspired by biological brains' features. In this work, we focus on characterizing and modeling different electrical transport regimes of self-assemblies of silver nanowires (AgNWs). As percolation plays an essential role in such a scenario, we explore a broad range of areal density coverage. Close-to-percolation realizations (usually used to demonstrate neuromorphic computing capabilities) have large pristine resistance and require an electrical activation. Up to now, highly conductive over-percolated systems (commonly used in electrode fabrication technology) have not been thoroughly considered for hardware-based neuromorphic applications, though biological systems exhibit such an extremely high degree of interconnections. Here, we show that high current densities in over-percolated low-resistance AgNW networks induce a fuse-type process, allowing a switching operation. Such electro-fusing discriminates between weak and robust NW-to-NW links and enhances the role of filamentary junctions. Their reversible resistive switching enable different conductive paths exhibiting linear I-V features. We experimentally study both percolation regimes and propose a model comprising two types of junctions that can describe, through numerical simulations, the overall behavior and observed phenomenology. These findings unveil a potential interplay of functionalities of neuromorphic systems and transparent electrodes.

We consider longitudinal electronic transport in a graphene monolayer with an external in-plane magnetic field and with extrinsic spin-orbit Rashba interaction. Our main interest is in the in-plane magnetoresistance, observed experimentally. We show, that scattering on Rashba spin-orbit fluctuations leads to a negative magnetoresistance, in agreement with experimental observations. To calculate transport properties we assume an effective model valid for low energy states around the Dirac points, and use the Green function method to derive the electron scattering rate and longitudinal conductivity., Comment: 10 pages, 7 figures

In rare earth nickelates (RENiO$_3$), electron-lattice coupling drives a concurrent metal-to-insulator and bond disproportionation phase transition whose microscopic origin has long been the subject of active debate. Of several proposed mechanisms, here we test the hypothesis that pairs of self-doped ligand holes spatially condense to provide local spin moments that are antiferromagnetically coupled to Ni spins. These singlet-like states provide a basis for long-range bond and spiral spin order. Using magnetic resonant X-ray scattering on NdNiO$_3$ thin films, we observe the chiral nature of the spin-disproportionated state, with spin spirals propagating along the crystallographic (101)$_\mathrm{ortho}$ direction. These spin spirals are found to preferentially couple to X-ray helicity, establishing the presence of a hitherto-unobserved macroscopic chirality. The presence of this chiral magnetic configuration suggests a potential multiferroic coupling between the noncollinear magnetic arrangement and improper ferroelectric behavior as observed in prior studies on NdNiO$_3$ (101)$_\mathrm{ortho}$ films and RENiO$_3$ single crystals. Experimentally constrained theoretical double-cluster calculations confirm the presence of an energetically stable spin-disproportionated state with Zhang-Rice singlet-like combinations of Ni and ligand moments., Comment: 6 pages, 4 figures

We explore the effects of stress on silicon donor bound exciton ($\mathrm{D^0X}$) transitions in bulk silicon and in microfabricated silicon devices. We first study $\mathrm{D^0X}$ transitions in an isotopically purified silicon-28 bulk doped sample under controlled uniaxial stress, confirming the validity of existing models in the low strain ($\lesssim 10^{-5}$) regime. We then demonstrate the localised photoconductive detection of a few thousand donors illuminated by a 1078 nm resonant laser with $4~\mathrm{\mu m}$ spot focused on a microfabricated device consisting of an implanted phosphorus layer between a pair of metallic contacts. We observe local variations in the strained exciton peak splitting from $10~\mathrm{\mu eV}$ to $200~\mathrm{\mu eV}$, and obtain scanning microscopy stress maps in good agreement with finite-element-model thermal stress simulations. Our results suggest a potential use of donor bound excitons for in-situ stress sensing, and demonstrate pathways for the miniaturisation of $\mathrm{D^0X}$ photoconductive detection., Comment: 8 pages, 4 figures

Quantum transport studies of spin-dependent phenomena in solids commonly employ the Kubo or Keldysh formulas for the steady-state density matrix in the linear-response regime. Its trace with operators of interest -- such as, spin density, spin current density or spin torque -- gives expectation values of experimentally accessible observables. For such local quantities, these formulas require summing over the manifolds of {\em both} Fermi-surface and Fermi-sea quantum states. However, debates have been raging in the literature about vastly different physics the two formulations can apparently produce, even when applied to the same system. Here, we revisit this problem using a testbed of infinite-size graphene with proximity-induced spin-orbit and magnetic exchange effects. By splitting this system into semi-infinite leads and central active region, in the spirit of Landauer two-terminal setup for quantum transport, we prove the {\em numerically exact equivalence} of the Kubo and Keldysh approaches via the computation of spin Hall current density and spin-orbit torque in both clean and disordered limits. The key to reconciling the two approaches are the numerical frameworks we develop for: ({\em i}) evaluation of Kubo(-Bastin) formula for a system attached to semi-infinite leads, which ensure continuous energy spectrum and evade the need for phenomenological broadening in prior calculations; and ({\em ii}) proper evaluation of Fermi-sea term in the Keldysh approach, which {\em must} include the voltage drop across the central active region even if it is disorder free., Comment: 9 pages, 3 figures, 111 references

Potential patches are responsible for a force between closely-spaced objects that forms a parasitic contribution to sensitive force measurements. Existing analytical models cannot account for the patch force in the 3D geometries of real experiments. Here, we present a finite-element method model to evaluate the impact of patches in arbitrary geometries. First, we test our model against the plate-plate and sphere-plate geometries, for which the exact solutions are known. Then, we apply it to the analytically unwieldy case of plate-concave plate that is relevant for Casimir force measurements. This work provides a reliable estimation of the parasitic contribution from random potential patches., Comment: 4 pages, 3 figures

A charge current flowing through a three-dimensional topological insulator (3D-TI) can inject a spin current into a ferromagnet placed on the surface of the 3D-TI. Here, we report leveraging this mechanism to implement a nano-antenna that radiates an electromagnetic wave (1-10 GHz) into the surrounding medium efficiently despite being orders of magnitude smaller than the radiated free space wavelength. An alternating charge current of 1-10 GHz frequency is injected into a thin film of the 3D-TI Bi2Se3, resulting in the injection of an alternating spin current (of the same frequency) into a periodic array of cobalt nanomagnets deposited on the surface of the 3D-TI. This causes the magnetizations of the nanomagnets to oscillate in time and radiate electromagnetic waves in space, thereby implementing a nano-antenna. Because it is so much smaller than the free space wavelength, the nano-antenna is effectively a "point source" and yet it radiates anisotropically because of internal anisotropy. One can change the anisotropic radiation pattern by changing the direction of the injected alternating charge current, which implements beam steering. This would normally not have been possible in a conventional extreme sub-wavelength antenna.

Exchange bias is applied ubiquitously throughout the spintronics industry for its ability to provide a reference direction robust to external magnetic field disturbances. For some applications, reorienting the exchange-biased reference axis may add to or enhance functionality of devices. Conventional methods for achieving this reorientation require assisting magnetic fields with long setting times and are thus limited in terms of speed and versatility. In this study, we show that by integrating functionalized materials (Co/Gd multilayers) into an existing thin film stack (Pt/Co/IrMn), perpendicular exchange bias can be reoriented $180^\circ$ by exciting it with a single femtosecond laser pulse, without an external field and on an ultrafast timescale. We found this effect to be repeatable arbitrarily many times, with only the first laser pulse incurring a loss of the initial exchange bias magnitude, yet preserving the unidirectionality required for referencing. By combining an experimental mapping of three key parameters (stack, laser and magnetic field properties) with microscopic models we were able to unravel the processes and features of the exchange bias reversal by considering the relevance of Curie, N\'eel and blocking temperatures. The outcomes of this study provide guiding principles towards designing fully optically reprogrammable magnetic sensing devices., Comment: 15 pages, 11 figures. To be submitted

We present strain tuning of excitonic emission in monolayer MoSe$_2$ by using a high-temperature physical vapor deposition (PVD). The use of two amorphous substrates, Si$_{3}$N$_{4}$ and SiO$_{2}$, provides two setpoints to induce distinct amounts of \textit{biaxial} tensile strain determined by a thermal expansion mismatch between the monolayer and the substrate. The tuning rate of the $A$-exciton transition energy is found to be 103 meV/\% by photoluminescence (PL), which represents the highest value realized by biaxial strain in transition metal dichalcogenides. The biaxial nature of the tensile strain is confirmed by polarization-resolved second harmonic generation, which reveals unperturbed in-plane three-fold symmetry of the monolayer. Furthermore, a softening of $A_\mathrm{1g}$ out-of-plane lattice vibration is identified in the Raman spectroscopy, which is known to be insignificant for uniaxial strain. Concomitantly, PL mapping of our PVD monolayers demonstrates (i) larger strain occurs in the interior of the mono-domain islands compared to the edges and (ii) the absence of island-size dependence in the magnitude of induced strain. Our results demonstrate an effective path towards strain engineering of excitons by using growth substrates, which holds great promise as a building block for future optoelectronic applications.

The "Poor Man's Majorana" [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection has been theoretically predicted to rely on the minimal Kitaev chain. Afterward, a pair of superconducting and spinless quantum dots turned the proposal practicable and differential conductance pinpointed consistent fingerprints with such a scenario [Nature 614, 445 (2023) and Nature 630, 329 (2024)]. In this work, we propose a model wherein the "Poor Man's Majorana" presents protection when one of the dots is exchange coupled to a quantum spin. If this quantum dot is perturbed by tuning the exchange coupling, the well-known spill over-like behavior of this Majorana surprisingly remains unchanged, and solely half of the fine structure is unexpectedly viewed. As a matter of fact, the "Poor Man's Majorana" zero mode consists in squeezing of the other half at zero frequency, which imposes its pinning there and prevents the mixing of the mode with the explicit fine structure. We claim that if the supposed unavoidable split of the zero mode by the fine structure is unexpectedly absent, then the "Poor Man's Majorana" can be considered robust against the quantum spin. In this way, it becomes protected and the lack of topological protection paradigm of the "Poor Man's Majorana" has been revisited, pushing this seemingly well-established issue into a new direction.

A central goal in spintronics and magnonics is the use of spin waves rather than electrons for efficient information processing. The key to integrate such spintronic circuits with electronic circuits is the ability to inject, control and detect coherent spin waves with charge currents. Here, we propose a tunable setup consisting of a synthetic antiferromagnet in an inhomogeneous magnetic field in which one of the magnetic layers is thin and biased by spin-orbit torque. We show that for appriopriate conditions single-mode coherent spin waves are emitted in this set-up. The set-up implements coupling of continuum spin waves with a finite region of negative energy spin waves, such that specific frequencies become self-amplified and thus start lasing. We show there exist a large region in parameter space for which the coherent spin wave laser is stabilized by non-linearities and spin-orbit torques. Our findings may lead to new ways of injecting coherent spin waves with direct currents.

Sodium niobate, a lead-free ferroic material, hosts delicately-balanced, competing order parameters, including ferroelectric states that can be stabilized by epitaxial strain. Here, we show that the resulting macroscopic ferroelectricity exhibits an unconventional microscopic structure using multislice electron ptychography. This technique overcomes multiple scattering artifacts limiting conventional electron microscopy, enabling both lateral spatial resolution beyond the diffraction limit and recovery of three-dimensional structural information. These imaging capabilities allow us to separate the ferroelectric interior of the sample from the relaxed surface structure and identify the soft phonon mode and related structural distortions with picometer precision. Unlike conventional ferroelectric perovskites, we find that the polar distortion in this material involves minimal distortions of the cation sublattices and is instead dominated by anion displacements. We establish limits on film thickness for interfacial octahedral rotation engineering and directly visualize an incommensurate octahedral rotation pattern, arising from the flat dispersion of the associated phonon mode., Comment: 63 pages, 5 figures, 17 supplementary figures

The magnetic properties of hole quantum dots in Ge are sensitive to their shape due to the interplay between strong spin-orbit coupling and confinement. We show that the split-off band, surrounding SiGe layers, and hole-hole interactions have a strong influence on calculations of the effective $g$ factor of a lithographic quantum dot in a Ge/SiGe heterostructure. Comparing predictions from a model including these effects to raw magnetospectroscopy data, we apply maximum-likelihood estimation to infer the shape of a quantum dot with up to four holes. We expect that methods like this will be useful in assessing qubit-to-qubit variability critical to further scaling quantum computing technologies based on spins in semiconductors., Comment: 9 pages, 6 figures

Coulomb drag is a powerful tool to study interactions in coupled low-dimensional systems. Historically, Coulomb drag has been attributed to a frictional force arising from momentum transfer whose direction is dictated by the current flow. However recent findings in one-dimensional systems have also identified a rectified contribution that is independent of the current flow direction. In this work, we present Coulomb drag measurements between vertically coupled GaAs/AlGaAs quantum wires separated vertically by a hard barrier only 15 nm wide where both momentum transfer and rectified Coulomb drag signals are observed simultaneously, and whose relative magnitude are temperature and gate tunable. Our study opens up the possibility of studying the physical mechanisms behind the onset of both momentum transfer and charge rectification drag simultaneously in a single device, ultimately leading to a better understanding of Luttinger liquids in multi-channel wires and paving the way for the creation of energy harvesting devices., Comment: 9 pages, 5 figures

Circuit-based quantum devices rely on keeping electrons at millikelvin temperatures. Improved coherence and sensitivity as well as discovering new physical phenomena motivate pursuing ever lower electron temperatures, accessible using on-chip cooling techniques. Here we show that a two-dimensional electron gas (2DEG), manipulated using gate voltages, works as an on-chip heat sink only limited by a fundamental phonon heat-leak. A single-shot 2DEG cooler can reduce the electron temperature by a factor of two with a hold time up to a second. Integrating an array of such coolers to obtain continuous cooldown in will allow reaching down to microkelvin device temperatures., Comment: 7 pages, 3 figures, 1 table

We study the appearance of a chiral edge mode on the two-dimensional (2D) surface of a 3D topological insulator (TI). The edge mode appears along the 1D boundary with a magnetic insulator (MI), dependent on the angle $\theta$ which the magnetization $M$ makes with the normal to surface and on the chemical potential mismatch $\delta\mu$ across the TI--MI interface (assuming $1>\delta\mu/M\equiv\sin\phi)$. The propagation along the interface is chiral, with velocity $v\cos(\theta-\phi)$ smaller than the Dirac fermion velocity $v$. In momentum space the edge mode is an arc state, extending over the finite momentum interval that connects the Dirac point of the gapless Dirac fermions with the magnetic band gap. An electric field parallel to the boundary pumps charge between TI and MI via this arc state., Comment: 5 pages, 5 figures