ResearchPad - applied-physics https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Observation of generalized Kibble-Zurek mechanism across a first-order quantum phase transition in a spinor condensate]]> https://www.researchpad.co/article/elastic_article_15998 The Kibble-Zurek mechanism provides a unified theory to describe the universal scaling laws in the dynamics when a system is driven through a second-order quantum phase transition. However, for first-order quantum phase transitions, the Kibble-Zurek mechanism is usually not applicable. Here, we experimentally demonstrate and theoretically analyze a power-law scaling in the dynamics of a spin-1 condensate across a first-order quantum phase transition when a system is slowly driven from a polar phase to an antiferromagnetic phase. We show that this power-law scaling can be described by a generalized Kibble-Zurek mechanism. Furthermore, by experimentally measuring the spin population, we show the power-law scaling of the temporal onset of spin excitations with respect to the quench rate, which agrees well with our numerical simulation results. Our results open the door for further exploring the generalized Kibble-Zurek mechanism to understand the dynamics across first-order quantum phase transitions.

]]>
<![CDATA[Optically pumped spin polarization as a probe of many-body thermalization]]> https://www.researchpad.co/article/elastic_article_15446 Disorder and many body interactions are known to impact transport and thermalization in competing ways, with the dominance of one or the other giving rise to fundamentally different dynamical phases. Here we investigate the spin diffusion dynamics of 13C in diamond, which we dynamically polarize at room temperature via optical spin pumping of engineered color centers. We focus on low-abundance, strongly hyperfine-coupled nuclei, whose role in the polarization transport we expose through the integrated impact of variable radio-frequency excitation on the observable bulk 13C magnetic resonance signal. Unexpectedly, we find good thermal contact throughout the nuclear spin bath, virtually independent of the hyperfine coupling strength, which we attribute to effective carbon-carbon interactions mediated by the electronic spin ensemble. In particular, observations across the full range of hyperfine couplings indicate the nuclear spin diffusion constant takes values up to two orders of magnitude greater than that expected from homo-nuclear spin couplings.

]]>
<![CDATA[Switchable giant nonreciprocal frequency shift of propagating spin waves in synthetic antiferromagnets]]> https://www.researchpad.co/article/elastic_article_15404 The nonreciprocity of propagating spin waves, i.e., the difference in amplitude and/or frequency depending on the propagation direction, is essential for the realization of spin wave–based logic circuits. However, the nonreciprocal frequency shifts demonstrated so far are not large enough for applications because they originate from interfacial effects. In addition, switching of the spin wave nonreciprocity in the electrical way remains a challenging issue. Here, we show a switchable giant nonreciprocal frequency shift of propagating spin waves in interlayer exchange–coupled synthetic antiferromagnets. The observed frequency shift is attributed to large asymmetric spin wave dispersion caused by a mutual dipolar interaction between two magnetic layers. Furthermore, we find that the sign of the frequency shift depends on relative configuration of two magnetizations, based on which we demonstrate an electrical switching of the nonreciprocity. Our findings provide a route for switchable and highly nonreciprocal spin wave–based applications.

]]>
<![CDATA[Three-dimensional vectorial holography based on machine learning inverse design]]> https://www.researchpad.co/article/elastic_article_15375 The three-dimensional (3D) vectorial nature of electromagnetic waves of light has not only played a fundamental role in science but also driven disruptive applications in optical display, microscopy, and manipulation. However, conventional optical holography can address only the amplitude and phase information of an optical beam, leaving the 3D vectorial feature of light completely inaccessible. We demonstrate 3D vectorial holography where an arbitrary 3D vectorial field distribution on a wavefront can be precisely reconstructed using the machine learning inverse design based on multilayer perceptron artificial neural networks. This 3D vectorial holography allows the lensless reconstruction of a 3D vectorial holographic image with an ultrawide viewing angle of 94° and a high diffraction efficiency of 78%, necessary for floating displays. The results provide an artificial intelligence–enabled holographic paradigm for harnessing the vectorial nature of light, enabling new machine learning strategies for holographic 3D vectorial fields multiplexing in display and encryption.

]]>
<![CDATA[Super-resolution nanoscopy by coherent control on nanoparticle emission]]> https://www.researchpad.co/article/elastic_article_15372 Super-resolution nanoscopy based on wide-field microscopic imaging provided high efficiency but limited resolution. Here, we demonstrate a general strategy to push its resolution down to ~50 nm, which is close to the range of single molecular localization microscopy, without sacrificing the wide-field imaging advantage. It is done by actively and simultaneously modulating the characteristic emission of each individual emitter at high density. This method is based on the principle of excited state coherent control on single-particle two-photon fluorescence. In addition, the modulation efficiently suppresses the noise for imaging. The capability of the method is verified both in simulation and in experiments on ZnCdS quantum dot–labeled films and COS7 cells. The principle of coherent control is generally applicable to single-multiphoton imaging and various probes.

]]>
<![CDATA[Under oil open-channel microfluidics empowered by exclusive liquid repellency]]> https://www.researchpad.co/article/elastic_article_15366 Recently, the functionality of under oil open microfluidics was expanded from droplet-based operations to include lateral flow in under oil aqueous channels. However, the resolution of the under oil fluidic channels reported so far is still far from comparable with that of closed-channel microfluidics (millimeters versus micrometers). Here, enabled by exclusive liquid repellency and an under oil sweep technique, open microchannels can now be prepared under oil (rather than in air), which shrinks the channel dimensions up to three orders of magnitude compared to previously reported techniques. Spatial trapping of different cellular samples and advanced control of mass transport (i.e., enhanced upper limit of flow rate, steady flow with passive pumping, and reversible fluidic valves) were achieved with open-channel designs. We apply these functional advances to enable dynamic measurements of dispersion from a pathogenic fungal biofilm. The ensemble of added capabilities reshapes the potential application space for open microfluidics.

]]>
<![CDATA[Steering valley-polarized emission of monolayer MoS<sub>2</sub> sandwiched in plasmonic antennas]]> https://www.researchpad.co/article/elastic_article_15042 Monolayer transition metal dichalcogenides have intrinsic spin-valley degrees of freedom, making it appealing to exploit valleytronic and optoelectronic applications at the nanoscale. Here, we demonstrate that a chiral plasmonic antenna consisting of two stacked gold nanorods can modulate strongly valley-polarized photoluminescence (PL) of monolayer MoS2 in a broad spectral range at room temperature. The valley-polarized PL of the MoS2 using the antenna can reach up to ~47%, with approximately three orders of PL magnitude enhancement within the plasmonic nanogap. Besides, the K and K′ valleys under opposite circularly polarized light excitation exhibit different emission intensities and directivities in the far field, which can be attributed to the modulation of the valley-dependent excitons by the chiral antenna in both the excitation and emission processes. The distinct features of the ultracompact hybrid suggest potential applications for valleytronic and photonic devices, chiral quantum optics, and high-sensitivity detection.

]]>
<![CDATA[Zero-energy bound states in the high-temperature superconductors at the two-dimensional limit]]> https://www.researchpad.co/article/Nebc4e9f6-2947-4436-b93e-4a4e0edc4d2c

Zero-energy bound states representing Majorana zero modes are detected in monolayer high-temperature superconducting films.

]]>
<![CDATA[Cooperative deformation in high-entropy alloys at ultralow temperatures]]> https://www.researchpad.co/article/N23bc1f92-b9f0-4969-aa1c-65aba37b8b94

In situ neutron diffraction revealed a unique deformation pathway in high-entropy alloys with unusually large ductility at 15 K.

]]>
<![CDATA[Demonstration of a third-order hierarchy of topological states in a three-dimensional acoustic metamaterial]]> https://www.researchpad.co/article/N8f52331a-e382-4013-84a6-83b350bf2670

A 3D acoustic higher-order topological metamaterial supports a hierarchy of topological boundary states.

]]>
<![CDATA[Mitigating cavitation erosion using biomimetic gas-entrapping microtextured surfaces (GEMS)]]> https://www.researchpad.co/article/N0b49f81c-52d6-4f4b-9dcf-c8b798a2a87b

Insect-inspired surfaces repel bubble jets.

]]>
<![CDATA[Atomic-scale insights into the interfacial instability of superlubricity in hydrogenated amorphous carbon films]]> https://www.researchpad.co/article/N1976f537-9496-44a9-9b62-19d0d5b6cd01

Atomic-scale characterization reveals the origins of oxygen- and moisture-induced structural instability of superlubricity.

]]>
<![CDATA[Reversible spin storage in metal oxide—fullerene heterojunctions]]> https://www.researchpad.co/article/N01ca8386-b9be-4319-a253-c5c8e54bc5d6

Hybrid interfaces form a spin capacitor for the generation and storage of spin angular momentum via optical or electronic stimuli.

]]>
<![CDATA[Light-induced assembly of living bacteria with honeycomb substrate]]> https://www.researchpad.co/article/N6f87ebcc-83b4-45e6-b712-b2dc0d8bc422

Honeycomb substrate enables high-density light-induced assembly for enhancing energy conversion of electricity-producing bacteria.

]]>
<![CDATA[Cargo capture and transport by colloidal swarms]]> https://www.researchpad.co/article/Ned482d70-9977-486a-bd2c-07ecaee75705

Multiagent stochastic control enables self-propelled colloidal swarms to perform cooperative tasks as micromachines.

]]>
<![CDATA[When and how self-cleaning of superhydrophobic surfaces works]]> https://www.researchpad.co/article/Nd484bbd2-d060-4961-8554-7499890eaeaf

We monitor the self-cleaning process on a single-particle level and quantify the involved forces.

]]>
<![CDATA[Imperceptible magnetic sensor matrix system integrated with organic driver and amplifier circuits]]> https://www.researchpad.co/article/Na19cbd22-de16-4eeb-8e83-88be64cc4b25

Imperceptible magnetic sensor matrix system realizes real-time mapping of 2D magnetic field distribution.

]]>
<![CDATA[Inverting singlet and triplet excited states using strong light-matter coupling]]> https://www.researchpad.co/article/Ne9ae9391-0501-4778-888e-e3b57f93022b

Molecules sandwiched in an optical cavity can form hybrid light-matter states at energies below the dark spin triplet state.

]]>
<![CDATA[Strictures of a microchannel impose fierce competition to select for highly motile sperm]]> https://www.researchpad.co/article/5c8014c8d5eed0c484a9e31f

Motility-based competition dynamics at microfluidic strictures suggests a sperm-selection mechanism in the reproductive tract.

]]>
<![CDATA[Multimaterial 3D laser microprinting using an integrated microfluidic system]]> https://www.researchpad.co/article/5c7ead9bd5eed0c4848a117a

An instrument brings 3D laser printing to a new level, exemplified by 3D fluorescent microstructures composed of five materials.

]]>