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We present a theoretical study of the optical angular momentum transfer from a circularly polarized plane wave to thin metal nanoparticles of different rotational symmetries. While absorption has been regarded as the predominant mechanism of torque generation on the nanoscale, we demonstrate numerically how the contribution from scattering can be enhanced by using multipolar plasmon resonance. The multipolar modes in non-circular particles can convert the angular momentum carried by the scattered field and thereby produce scattering-dominant optical torque, while a circularly symmetric particle cannot. Our results show that the optical torque induced by resonant scattering can contribute to 80% of the total optical torque in gold particles. This scattering-dominant torque generation is extremely mode-specific, and deserves to be distinguished from the absorption-dominant mechanism. Our findings might have applications in optical manipulation on the nanoscale as well as new designs in plasmonics and metamaterials.

What causes Cooper pairs to form in unconventional superconductors is often elusive because experimental signatures that connect to a specific pairing mechanism are rare. Here, we observe distinct dependences of the superconducting transition temperature Tc on carrier density n2D for electron gases formed at KTaO3 (111), (001) and (110) interfaces. For the (111) interface, a remarkable linear dependence of Tc on n2D is observed over a range of nearly one order of magnitude. Further, our study of the dependence of superconductivity on gate electric fields reveals the role of the interface in mediating superconductivity. We find that the extreme sensitivity of superconductivity to crystallographic orientation can be explained by pairing via inter-orbital interactions induced by an inversion-breaking transverse optical phonon and quantum confinement. This mechanism is also consistent with the dependence of Tc on n2D. Our study may shed light on the pairing mechanism in other superconducting quantum paraelectrics. A distinct dependence of the superconducting transition temperature on carrier density for electron gases formed at KTaO3 interfaces is reported. In addition, these interfaces are shown to play a role in mediating superconductivity in this system. The crystallographic orientation and carrier density dependent superconductivity at KTaO3 interfaces can be explained by Cooper pairing via inter-orbital interactions and quantum confinement. [ABSTRACT FROM AUTHOR]

Materials with Kagome layers are expected to give rise to rich physics arising from band structures with topological properties, spin liquid behavior, and the formation of Skyrmions. Until now, most work on Kagome materials has been performed on bulk samples due to difficulties in thin film synthesis. Here, by using molecular beam epitaxy, layered Kagome-structured FeSn films are synthesized on the (111) oriented LaAlO3 substrate. Both in situ and ex situ characterizations indicate that these films are highly crystalline and c-axis oriented, with atomically smooth surfaces. The films grow as disconnected islands, with lateral dimensions on the micron meter scale. By patterning Pt electrodes using a focused electron beam, the longitudinal and transverse resistance of single islands have been measured in magnetic fields. Our work opens a pathway for exploring mesoscale transport properties in thin films of Kagome materials and related devices. [ABSTRACT FROM AUTHOR]

Single electrons are one of the simplest quantum objects in nature. In free space or conventional materials, single electrons hardly interact with optical (ultraviolet‐visible‐infrared) photons, so their quantum states cannot be easily manipulated by optics. Here, a notable exception is theoretically demonstrated: a single electron in condensed helium‐4 can be self‐confined in a nanometric bubble of 1 to 2 nm radius and resonantly interact with mid‐infrared photons of 3 to 12 µm wavelength. A femtosecond laser can drive the electron into Rabi oscillations and prepare it onto arbitrary superposition states between the ground and excited states. After the laser pulse, the electron bubble can exhibit remarkable nonequilibrium quantum dynamics and evolve toward various final states with various lifetimes. These processes are accompanied with intense phonon radiation. [ABSTRACT FROM AUTHOR]

We introduce a compact finite-temperature density functional model to study electron self-trapping in both liquid and vapor 3He and 4He. This model can quantitatively reproduce the most essential thermodynamic properties of 3He and 4He along their liquid-vapor coexistence lines. The structures and energetics of self-trapped electron bubbles on the 1S ground state and 1P excited state are particularly investigated. Our results show that 1S and 1P bubbles exist in liquid at any temperature, whereas 1S bubbles exist in vapor only above 1.6 K in 3He and above 2.8 K in 4He, 1P bubbles exist in vapor only above 2.5 K in 3He and 4.0 K in 4He. An initially spherical 1P bubble is unstable against deformation towards a peanut shape. In liquid, a peanut-shaped 1P bubble is held from fission by surface tension until reaching the liquid-vapor critical point, whereas in vapor it always splits into two smaller bubbles. The existence of 1P bubbles in finite-temperature liquid helium and their fission instability in helium vapor reveal interesting physics in this system. [ABSTRACT FROM AUTHOR]

We present a systematic study on the excited electron-bubble states in superfluid 4He using a time-dependent density functional approach. For the evolution of the 1P bubble state, two different functionals accompanied with two different time-development schemes are used, namely an accurate finite-range functional for helium with an adiabatic approximation for electron versus an efficient zero-range functional for helium with a real-time evolution for electron. We make a detailed comparison between the quantitative results obtained from the two methods, which allow us to employ with confidence the optimal method for suitable problems. Based on this knowledge, we use the finite-range functional to calculate the time-resolved absorption spectrum of the 1P bubble, which in principle can be experimentally determined, and we use the zero-range functional to real-time evolve the 2P bubble for several hundreds of picoseconds, which is theoretically interesting due to the break down of adiabaticity for this state. Our results discard the physical realization of relaxed, metastable configurations above the 1P state. [ABSTRACT FROM AUTHOR]

Lead magnesium niobate-lead titanate (PMN-xPT) single crystal plates were prepared close to the morphotropic phase boundary with PT compositions 27%-31%. The piezoelectric and dielectric properties of these plates at liquid-helium temperature (4.2 K) were obtained by fitting measured impedance curves. In particular, the piezoelectric strain constant e33 is found to be in the range of 5.1-5.7 C m-2 at 4.2 K, which indicates an extraordinarily large piezoelectric effect compared with other materials even at such a low temperature. This result shows that PMN-xPT single crystals are promising candidates for ultrasonic transducers at low temperatures. [ABSTRACT FROM AUTHOR]

Motivated by the advanced photon source upgrade, a new hard X-ray microscope called "Velociprobe" has been recently designed and built for fast ptychographic imaging with high spatial resolution. We are addressing the challenges of high-resolution and fast scanning with novel hardware designs, advanced motion controls, and new data acquisition strategies, including the use of high-bandwidth interferometric measurements. The use of granite, air-bearing-supported stages provides the necessary long travel ranges for coarse motion to accommodate real samples and variable energy operation while remaining highly stable during fine scanning. Scanning the low-mass zone plate enables high-speed and high-precision motion of the probe over the sample. With an advanced control algorithm implemented in a closed-loop feedback system, the setup achieves a position resolution (3σ) of 2 nm. The instrument performance is evaluated by 2D fly-scan ptychography with our developed data acquisition strategies. A spatial resolution of 8.8 nm has been demonstrated on a Au test sample with a detector continuous frame rate of 200 Hz. Using a higher flux X-ray source provided by double-multilayer monochromator, we achieve 10 nm resolution for an integrated circuit sample in an ultrafast scan with a detector's full continuous frame rate of 3000 Hz (0.33 ms per exposure), resulting in an outstanding imaging rate of 9 × 104 resolution elements per second. [ABSTRACT FROM AUTHOR]

Within the framework of the single electron spintronic model, we systematically studied the barrier-height and bias-voltage-controlled spin-filter effect and tunneling magnetoresistance (TMR) in ferromagnetic metal/ferromagnetic insulator/ferromagnetic metal (FM/FI/FM) tunnel junctions. We find that it is the extended quantum-coherence factor of Slonczewski, κL↑2-kL↑kL↓, that physically controls the sign of the zero-bias TMR. This factor is a linear function of the mean barrier height. The zero-bias TMR is positive when the mean barrier is high, and negative when the mean barrier gets low, which agrees well with the experimental results observed in GdOx-barrier junctions. As a cooperative result of the mean barrier and spin-filter effect, a positively or negatively large TMR can be maintained in a rather wide range near the zero bias if the mean barrier of the FI spacer is much higher or much lower. This property is believed to be of practical use in designing spintronic devices. Besides, the TMR can oscillate positively, or negatively, or alternately with the applied voltage within the high bias region, which is different from conventional FM/I/FM tunnel junctions. [ABSTRACT FROM AUTHOR]

Inspired by recent advancement of ferroelectric-gated memories and transistors, we propose a design of ferroelectric-gated nanoplasmonic devices based on graphene sheets clamped in ferroelectric crystals. We show that the two-dimensional plasmons in graphene can strongly couple with the phonon-polaritons in ferroelectrics, leading to characteristic modal wavelength of the order of 100-200 nm at low temperature and low-THz frequencies albeit with an appreciable dissipation. By patterning the ferroelectrics into different domains, one can produce compact on-chip plasmonic waveguides, which exhibit negligible crosstalk even at 20 nm separation distance. Harnessing the memory effect of ferroelectrics, low-power operation can be achieved on these plasmonic waveguides. [ABSTRACT FROM AUTHOR]

Single electrons trapped on solid-neon surfaces have recently emerged as a promising platform for charge qubits. Experimental results have revealed their exceptionally long coherence times, yet the actual quantum states of these trapped electrons, presumably on imperfectly flat neon surfaces, remain elusive. In this Letter, we examine the electron's interactions with neon surface topography, such as bumps and valleys. By evaluating the surface charges induced by the electron, we demonstrate its strong perpendicular binding to the neon surface. The Schrödinger equation for the electron's lateral motion on the curved 2D surface is then solved for extensive topographical variations. Our results reveal that surface bumps can naturally bind an electron, forming unique quantum ring states that align with experimental observations. We also show that the electron's excitation energy can be tuned using a modest magnetic field to facilitate qubit operation. This study offers a leap in our understanding of electron-on-solid-neon qubit properties and provides strategic insights on minimizing charge noise and scaling the system to propel forward quantum computing architectures.

Cavity magnonics is an emerging research area focusing on the coupling between magnons and photons. Despite its great potential for coherent information processing, it has been long restricted by the narrow interaction bandwidth. In this Letter, we theoretically propose and experimentally demonstrate a novel approach to achieve broadband photon-magnon coupling by adopting slow waves on engineered microwave waveguides. To the best of our knowledge, this is the first time that slow wave is combined with hybrid magnonics. Its unique properties promise great potentials for both fundamental research and practical applications, for instance, by deepening our understanding of the light-matter interaction in the slow wave regime and providing high-efficiency spin wave transducers. The device concept can be extended to other systems such as optomagnonics and magnomechanics, opening up new directions for hybrid magnonics.

Electromagnonics-the hybridization of spin excitations and electromagnetic waves-has been recognized as a promising candidate for coherent information processing in recent years. Among its various implementations, the lack of available approaches for real-time manipulation on the system dynamics has become a common and urgent limitation. In this work, by introducing a fast and uniform modulation technique, we successfully demonstrate a series of benchmark coherent gate operations in hybrid magnonics, including semiclassical analogies of Landau-Zener transitions, Rabi oscillations, Ramsey interference, and controlled mode swap operations. Our approach lays the groundwork for dynamical manipulation of coherent signals in hybrid magnonics and can be generalized to a broad range of applications.

The distinctive electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. Here we report on the discovery of superconductivity in electron gases formed at interfaces between (111)-oriented KTaO 3 and insulating overlayers of either EuO or LaAlO 3 The superconducting transition temperature, as high as 2.2 kelvin, is about one order of magnitude higher than that of the LaAlO 3 /SrTiO 3 system. Notably, similar electron gases at KTaO 3 (001) interfaces remain normal down to 25 millikelvin. The critical field and current-voltage measurements indicate that the superconductivity is two-dimensional. In EuO/KTaO 3 (111) samples, a spontaneous in-plane transport anisotropy is observed before the onset of superconductivity, suggesting the emergence of a distinct "stripe"-like phase, which is also revealed near the critical field., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Hybrid magnonics has recently attracted intensive attention as a promising platform for coherent information processing. In spite of its rapid development, on-demand control over the interaction of magnons with other information carriers, in particular, microwave photons in electromagnonic systems, has been long missing, significantly limiting the potential broad applications of hybrid magnonics. Here, we show that, by introducing Floquet engineering into cavity electromagnonics, coherent control on the magnon-microwave photon coupling can be realized. Leveraging the periodic temporal modulation from a Floquet drive, our first-of-its-kind Floquet cavity electromagnonic system enables the manipulation of the interaction between hybridized cavity electromagnonic modes. Moreover, we have achieved a new coupling regime in such systems: the Floquet ultrastrong coupling, where the Floquet splitting is comparable with or even larger than the level spacing of the two interacting modes, beyond the conventional rotating-wave picture. Our findings open up new directions for magnon-based coherent signal processing.

Intrinsic Josephson junctions in high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8+δ  (BSCCO) are known for their capability to emit high-power terahertz photons with widely tunable frequencies. Hotspots, as inhomogeneous temperature distributions across the junctions, are believed to play a critical role in synchronizing the gauge-invariant phase difference among the junctions, so as to achieve coherent strong emission. In this paper, we demonstrate an on-chip in situ sensing technique that can characterize hotspot distributions on BSCCO. This is achieved by fabricating a series of micro-nanosized "sensor" junctions on top of an "emitter" junction and measuring the critical current on the sensors versus the bias current applied to the emitter. This fully electronic on-chip design can enable efficient close-loop control of hotspots in BSCCO junctions and significantly enhance the functionality of superconducting terahertz emitters.

When rotating classical fluid drops merge together, angular momentum can be advected from one to another due to the viscous shear flow at the drop interface. It remains elusive what the corresponding mechanism is in inviscid quantum fluids such as Bose-Einstein condensates (BECs). Here we report our theoretical study of an initially static BEC merging with a rotating BEC in three-dimensional space along the rotational axis. We show that a solitonlike sheet, resembling a corkscrew, spontaneously emerges at the interface. Rapid angular-momentum transfer at a constant rate universally proportional to the initial angular-momentum density is observed. Strikingly, this transfer does not necessarily involve fluid advection or drifting of the quantized vortices. We reveal that the corkscrew structure can exert a torque that directly creates angular momentum in the static BEC and annihilates angular momentum in the rotating BEC. Uncovering this intriguing angular-momentum transport mechanism may benefit our understanding of various coherent matter-wave systems, spanning from atomtronics on chips to dark matter BECs at cosmic scales.

Exceptional points (EPs) are singularities of energy levels in generalized eigenvalue systems. In this Letter, we demonstrate the surface of EPs on a magnon polariton platform composed of coupled magnons and microwave photons. Our experiments show that EPs form a three-dimensional exceptional surface (ES) when the system is tuned in a four-dimensional synthetic space. We demonstrate that there exists an exceptional saddle point (ESP) in the ES which originates from the unique couplings between magnons and microwave photons. Such an ESP exhibits unique anisotropic behaviors in both the real and imaginary parts of the eigenfrequencies. To the best of our knowledge, this is the first experimental observation of ES, opening up new opportunities for high-dimensional control of non-Hermitian systems.

With a honeycomb single-atomic-layer structure similar to those of graphene and hexagonal boron nitride (hBN), the graphitic phase of ZnO (gZnO) have been predicted to offer many advantages for engineering, including high-temperature stability in ambient conditions and great potential in heterostructure applications. However, there is little experimental data about this hexagonal phase due to the difficulty of synthesizing large-area gZnO for characterization and applications. In this work, we demonstrate a solution-based approach to realize gZnO nanoflakes with thicknesses down to a monolayer and sizes up to 20 μm. X-ray photoelectron spectroscopy, X-ray absorption near-edge spectroscopy, photoluminescence, atomic force microscopy, and electron microscopy characterizations are conducted on synthesized gZnO samples. Measurements show significant changes to the electronic band structure compared to its bulk phase, including an increase of the band gap to 4.8 eV. The gZnO nanosheets also exhibit excellent stability at temperatures as high as 800 °C in ambient environment. This wide band gap layered material provides us with a platform for harsh environment electronic devices, deep ultraviolet optical applications, and a practical alternative for hBN. Our synthesis method may also be applied to achieve other types of 2D oxides.

We propose a two-dimensional plasmonic platform-periodically patterned monolayer graphene-which hosts topological one-way edge states operable up to infrared frequencies. We classify the band topology of this plasmonic system under time-reversal-symmetry breaking induced by a static magnetic field. At finite doping, the system supports topologically nontrivial band gaps with mid-gap frequencies up to tens of terahertz. By the bulk-edge correspondence, these band gaps host topologically protected one-way edge plasmons, which are immune to backscattering from structural defects and subject only to intrinsic material and radiation loss. Our findings reveal a promising approach to engineer topologically robust chiral plasmonic devices and demonstrate a realistic example of high-frequency topological edge states.