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1.
Phys Rev Lett ; 129(18): 187203, 2022 Oct 28.
Artículo en Inglés | MEDLINE | ID: mdl-36374676

RESUMEN

We report the control of Rashba spin-orbit interaction by tuning asymmetric hybridization between Ti orbitals at the LaAlO_{3}/SrTiO_{3} interface. This asymmetric orbital hybridization is modulated by introducing a LaFeO_{3} layer between LaAlO_{3} and SrTiO_{3}, which alters the Ti-O lattice polarization and traps interfacial charge carriers, resulting in a large Rashba spin-orbit effect at the interface in the absence of an external bias. This observation is verified through high-resolution electron microscopy, magnetotransport and first-principles calculations. Our results open hitherto unexplored avenues of controlling Rashba interaction to design next-generation spin orbitronics.

2.
Adv Mater ; : e2206128, 2022 Oct 31.
Artículo en Inglés | MEDLINE | ID: mdl-36314389

RESUMEN

Breakthrough in the in-memory computing technologies hinges on the development of appropriate material platforms that can overcome their existing limitations such as larger than optimal footprint and multiple serial computational steps, with potential accumulation of errors. We show that by using a molecular switching element with multiple non-monotonic and deterministic transitions, the device count and the number of computational steps can be substantially reduced. With molecular materials, however, the realization of a reliable and robust platform has been an unattained goal for decades. Here, we fabricated crossbar arrays with up to 64 molecular memristors and experimentally demonstrated 8-bit serial and 4-bit parallel adders that operated for thousands of measurement cycles with an estimated error probability of 10-16 . For performance benchmarking, a 32-bit parallel adder was designed and simulated with 260 million inputs including contributions from the peripheral circuitry showing a 47× higher energy efficiency, 93× faster operation, and 9% of the footprint, leading to 4390 times improved energy-delay product compared to a special purpose CMOS based multicore adder. This article is protected by copyright. All rights reserved.

3.
Zootaxa ; 5104(4): 531-544, 2022 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-35391022

RESUMEN

The adult female, first-instar nymph, male pupa and adult male of a new species of the genus Cyphococcus Laing (Hemiptera: Coccomorpha: Coccidae) from India, C. williamsi Joshi Rajgopal sp. n., are described and illustrated. This is the first record of the genus Cyphococcus and the subfamily Cyphococcinae from the Oriental region. Information on distribution, biology, host plants, associated coccinellid predators and hymenopteran parasitoids is given.


Asunto(s)
Hemípteros , Animales , Femenino , India , Masculino , Ninfa , Plantas , Pupa
4.
Nature ; 597(7874): 51-56, 2021 09.
Artículo en Inglés | MEDLINE | ID: mdl-34471273

RESUMEN

Profuse dendritic-synaptic interconnections among neurons in the neocortex embed intricate logic structures enabling sophisticated decision-making that vastly outperforms any artificial electronic analogues1-3. The physical complexity is far beyond existing circuit fabrication technologies: moreover, the network in a brain is dynamically reconfigurable, which provides flexibility and adaptability to changing environments4-6. In contrast, state-of-the-art semiconductor logic circuits are based on threshold switches that are hard-wired to perform predefined logic functions. To advance the performance of logic circuits, we are re-imagining fundamental electronic circuit elements by expressing complex logic in nanometre-scale material properties. Here we use voltage-driven conditional logic interconnectivity among five distinct molecular redox states of a metal-organic complex to embed a 'thicket' of decision trees (composed of multiple if-then-else conditional statements) having 71 nodes within a single memristor. The resultant current-voltage characteristic of this molecular memristor (a 'memory resistor', a globally passive resistive-switch circuit element that axiomatically complements the set of capacitor, inductor and resistor) exhibits eight recurrent and history-dependent non-volatile switching transitions between two conductance levels in a single sweep cycle. The identity of each molecular redox state was determined with in situ Raman spectroscopy and confirmed by quantum chemical calculations, revealing the electron transport mechanism. Using simple circuits of only these elements, we experimentally demonstrate dynamically reconfigurable, commutative and non-commutative stateful logic in multivariable decision trees that execute in a single time step and can, for example, be applied as local intelligence in edge computing7-9.

5.
Sci Rep ; 11(1): 7760, 2021 04 08.
Artículo en Inglés | MEDLINE | ID: mdl-33833345

RESUMEN

Fall Armyworm (FAW), Spodoptera frugiperda, is a polyphagous pest capable of feeding over 80 plant species and was indigenous to the Western Hemisphere. Within a span of 4 years, FAW has established itself throughout most of the regions in Africa and Asia causing significant losses in maize production. Owing to its revamped distribution range, it would be prudent to analyze the ensuing genetic changes and study the emerging phylogeographic patterns across the world. In this regard, we would like to provide a current snapshot of genetic diversity of FAW in India 2 years after the initial introduction and compare it with the worldwide diversity in order to trace the origins and evolutionary trajectories of FAW in India. We have investigated around 190 FAW samples from different regions in India for strain identity and polymorphism analysis on the basis of partial mitochondrial cytochrome oxidase I (COI) gene sequences. Apart from the ancestral rice and corn strain haplotype, our study demonstrates the presence of 14 more haplotypes unique to India at a haplotype diversity of 0.356. We were also able to record inter-strain hybrid haplotypes of rice and corn strains in India. Regional heterogeneity within Indian populations seems to be quite low representative of extensive migration of FAW within India. Distribution analysis of pairwise differences and rejection of neutrality tests suggest that the FAW population in India might be undergoing expansion. Our data is consistent with the findings suggesting a recent and common origin for invasive FAW populations in Asia and Africa, and does not indicate multiple introductions to India. This study reports the highest genetic diversity for Indian FAW populations to date and will be useful to track the subsequent evolution of FAW in India. The findings would have important ramifications for FAW behavior and composition throughout the world.


Asunto(s)
Variación Genética , Spodoptera/crecimiento & desarrollo , Animales , Haplotipos , India , Spodoptera/genética
6.
Nat Commun ; 12(1): 1668, 2021 Mar 12.
Artículo en Inglés | MEDLINE | ID: mdl-33712582

RESUMEN

Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe2O3 (haematite) - now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe2O3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe2O3.

7.
Nature ; 590(7844): 74-79, 2021 02.
Artículo en Inglés | MEDLINE | ID: mdl-33536652

RESUMEN

In the quest for post-CMOS (complementary metal-oxide-semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic 'whirls' such as skyrmions1-8 and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices1,9-11. However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures3,6,8,9,12, and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques9,10,12, have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus9,13-19, but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe2O3-an Earth-abundant oxide insulator-capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble-Zurek mechanism20,21, we stabilize exotic merons and antimerons (half-skyrmions)8 and their pairs (bimerons)16,22, which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature1,9-11,23.

8.
Front Physiol ; 11: 594845, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-33329043

RESUMEN

The shoot and fruit borer, Leucinodes orbonalis (Lepidoptera: Crambidae) is the major cause of low productivity in eggplant and insecticides being the mainstay of management of L. orbonalis. However, field control failures are widespread due to the evolution of insecticide resistance. Taking advantage of the whole genome sequence information, the present study investigated the level of insecticide resistance and the expression pattern of individual carboxylesterase (CE) and glutathione S-transferases (GSTs) genes in various field collected populations of L. orbonalis. Dose-mortality bioassays revealed a very high level of resistance development against fenvalerate (48.2-160-fold), phosalone (94-534.6-fold), emamectin benzoate (7.2-55-fold), thiodicarb (9.64-22.7-fold), flubendiamide (187.4-303.0-fold), and chlorantraniliprole (1.6-8.6-fold) in field populations as compared to laboratory-reared susceptible iso-female colony (Lo-S). Over-production of detoxification enzymes viz., CE and GST were evident upon enzyme assays. Mining of the draft genome of L. orbonalis yielded large number of genes potentially belonging to the CE and GST gene families with known history of insecticide resistance in other insects. Subsequent RT-qPCR studies on relative contribution of individual genes revealed over-expression of numerous GSTs and few CEs in field populations, indicating their possible involvement of metabolic enzymes in insecticide resistance. The genomic information will facilitate the development of novel resistance management strategies against this pest.

9.
Phys Rev Lett ; 125(8): 086803, 2020 Aug 21.
Artículo en Inglés | MEDLINE | ID: mdl-32909796

RESUMEN

Electrons commonly couple through Fröhlich interactions with longitudinal optical phonons to form polarons. However, trions possess a finite angular momentum and should therefore couple instead to rotational optical phonons. This creates a polaronic trion whose binding energy is determined by the crystallographic orientation of the lattice. Here, we demonstrate theoretically within the Fröhlich approach and experimentally by photoluminescence emission that the bare trion binding energy (20 meV) is significantly enhanced by the phonons at the interface between the two-dimensional semiconductor MoS_{2} and the bulk transition metal oxide SrTiO_{3}. The low-temperature binding energy changes from 60 meV in [001]-oriented substrates to 90 meV for [111] orientation, as a result of the counterintuitive interplay between the rotational axis of the MoS_{2} trion and that of the SrTiO_{3} phonon mode.

10.
Nature ; 581(7807): 171-177, 2020 05.
Artículo en Inglés | MEDLINE | ID: mdl-32405019

RESUMEN

Two-dimensional (2D) materials1-5 offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants6,7; however, post-growth intercalation has usually been limited to alkali metals8-10. Here we show that the self-intercalation of native atoms11,12 into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites7,13. By performing growth under high metal chemical potential14,15 we can access a range of tantalum-intercalated TaS(Se)y, including 25% Ta-intercalated Ta9S16, 33.3% Ta-intercalated Ta7S12, 50% Ta-intercalated Ta10S16, 66.7% Ta-intercalated Ta8Se12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta9Se12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V11S16, In11Se16 and FexTey can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties.

11.
Nat Nanotechnol ; 15(5): 380-389, 2020 05.
Artículo en Inglés | MEDLINE | ID: mdl-32203436

RESUMEN

Electronic symmetry breaking by charge disproportionation results in multifaceted changes in the electronic, magnetic and optical properties of a material, triggering ferroelectricity, metal/insulator transition and colossal magnetoresistance. Yet, charge disproportionation lacks technological relevance because it occurs only under specific physical conditions of high or low temperature or high pressure. Here we demonstrate a voltage-triggered charge disproportionation in thin molecular films of a metal-organic complex occurring in ambient conditions. This provides a technologically relevant molecular route for simultaneous realization of a ternary memristor and a binary memcapacitor, scalable down to a device area of 60 nm2. Supported by mathematical modelling, our results establish that multiple memristive states can be functionally non-volatile, yet discrete-a combination perceived as theoretically prohibited. Our device could be used as a binary or ternary memristor, a binary memcapacitor or both concomitantly, and unlike the existing 'continuous state' memristors, its discrete states are optimal for high-density, ultra-low-energy digital computing.

12.
Chem Sci ; 11(34): 9226-9236, 2020 Aug 20.
Artículo en Inglés | MEDLINE | ID: mdl-34123171

RESUMEN

We demonstrate a strategy inspired by natural siderophores for the dissolution of platinum nanoparticles that could enable their size-selective synthesis, toxicological assessment, and the recycling of this precious metal. From the fabrication of electronics to biomedical diagnosis and therapy, PtNPs find increasing use. Mitigating concerns over potential human toxicity and the need to recover precious metal from industrial debris motivates the study of bio-friendly reagents to replace traditional harsh etchants. Herein, we report a family of redox-active siderophore-viz. π-acceptor azo aromatic ligands (L) that spontaneously ionize and chelate Pt atoms selectively from nanoparticles of size ≤6 nm. The reaction produces a monometallic diradical complex, PtII(L˙-)2, isolated as a pure crystalline compound. Density functional theory provides fundamental insights on the size dependent PtNP chemical reactivity. The reported findings reveal a generalized platform for designing π-acceptor ligands to adjust the size threshold for dissolution of Pt or other noble metals NPs. Our approach may, for example, be used for the generation of Pt-based therapeutics or for reclamation of Pt nano debris formed in catalytic converters or electronic fabrication industries.

13.
Rev Sci Instrum ; 90(4): 043901, 2019 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-31043012

RESUMEN

We present a new measurement method which can be used to image the gap nodal structure of superconductors whose pairing symmetry is under debate. This technique utilizes a high quality factor microwave resonance involving the sample of interest. While supporting a circularly symmetric standing wave current pattern, the sample is perturbed by a scanned laser beam, creating a photoresponse that was previously shown to reveal the superconducting gap anisotropy. Simulation and the measurement of the photoresponse of an unpatterned Nb film show less than 8% anisotropy, as expected for a superconductor with a nearly isotropic energy gap along with expected systematic uncertainty. On the other hand, measurement of a YBa2Cu3O7-δ thin film shows a clear 4-fold symmetric image with ∼12.5% anisotropy, indicating the well-known 4-fold symmetric dx2-y2 gap nodal structure in the ab-plane. The deduced gap nodal structure can be further cross-checked by low temperature surface impedance data, which are simultaneously measured. The important advantage of the presented method over the previous spiral resonator method is that it does not require a complicated lithographic patterning process which limits one from testing various kinds of materials due to photoresponse arising from patterning defects. This advantage of the presented technique, and the ability to measure unpatterned samples such as planar thin films and single crystals, enables one to survey the pairing symmetry of a wide variety of unconventional superconductors.

14.
J Phys Condens Matter ; 31(3): 033001, 2019 01 23.
Artículo en Inglés | MEDLINE | ID: mdl-30523972

RESUMEN

Growth and survival of biological cells (eukaryotes and prokaryotes) on artificial environments often depend on their interactions with the specific surface. Various organic materials can be coated on substrates to assist cells' adhesion and other subsequent cellular processes. However, these coatings are expensive, degrade over short time period, and may even interfere with the cells' signaling processes. Therefore, the use of inorganic surfaces in order to control cellular interactions is of scientific importance from fundamental and application perspectives. Among inorganic materials, oxide thin films have received considerable attention. Thin films of oxides have the advantage of tailoring the surfaces for cellular interactions while using a negligible amount of the oxide material. Here, we review the lesser known application of inorganic oxide coatings as biocompatible and implantable platforms for different purposes, such as biofilm inhibition, cell culture and implant enhancements.


Asunto(s)
Materiales Biocompatibles Revestidos/química , Óxidos/química , Óxidos/farmacología , Animales , Materiales Biocompatibles Revestidos/farmacología , Humanos
15.
Rev Sci Instrum ; 89(11): 113113, 2018 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-30501296

RESUMEN

A new beamline and a six-circle UHV diffractometer have been constructed at the Singapore Synchrotron Light Source with a broad energy coverage from 3.5 to 1500 eV. The beamline is optimized for ultraviolet-vacuum-ultraviolet optical reflectivity and resonant soft X-ray scattering with medium energy resolution over a broad energy range, achieved by using a self-focusing monochromator consisting of a plane mirror and three variable line spacing gratings. The unique character of the diffractometer comprises 4-circles in the vertical plane and 2-circles in the horizontal plane. Thirteen motions are available inside the UHV chamber with a base pressure of 1 × 10-9 mbar. Two sample holders working independently over a temperature range of 37 K-400 K are controlled by a closed-cycle cryostat, while the bottom holder inside a high field compact pulsed magnet is available for measurements requiring a magnetic field.

16.
Phys Rev Lett ; 121(14): 146802, 2018 Oct 05.
Artículo en Inglés | MEDLINE | ID: mdl-30339445

RESUMEN

Electrolyte gating is a powerful means for tuning the carrier density and exploring the resultant modulation of novel properties on solid surfaces. However, the mechanism, especially its effect on the oxygen migration and electrostatic charging at the oxide heterostructures, is still unclear. Here we explore the electrolyte gating on oxygen-deficient interfaces between SrTiO_{3} (STO) crystals and LaAlO_{3} (LAO) overlayer through the measurements of electrical transport, x-ray absorption spectroscopy, and photoluminescence spectra. We found that oxygen vacancies (O_{vac}) were filled selectively and irreversibly after gating due to oxygen electromigration at the amorphous LAO/STO interface, resulting in a reconstruction of its interfacial band structure. Because of the filling of O_{vac}, the amorphous interface also showed an enhanced electron mobility and quantum oscillation of the conductance. Further, the filling effect could be controlled by the degree of the crystallinity of the LAO overlayer by varying the growth temperatures. Our results reveal the different effects induced by electrolyte gating, providing further clues to understand the mechanism of electrolyte gating on buried interfaces and also opening a new avenue for constructing high-mobility oxide interfaces.

17.
Nano Lett ; 18(11): 6898-6905, 2018 11 14.
Artículo en Inglés | MEDLINE | ID: mdl-30260651

RESUMEN

Hexagonal boron nitride (h-BN) was recently reported to display single photon emission from ultraviolet to near-infrared range due to the existence of defects. Single photon emission has potential applications in quantum information processing and optoelectronics. These findings trigger increasing research interests in h-BN defects, such as revealing the nature of the defects. Here, we report another intriguing defect property in h-BN, namely photoluminescence (PL) upconversion (anti-Stokes process). The energy gain by the PL upconversion is about 162 meV. The anomalous PL upconversion is attributed to optical phonon absorption in the one-photon excitation process, based on excitation power, excitation wavelength, and temperature-dependence investigations. Possible constitutions of the defects are discussed from the results of scanning transmission electron microscopy (STEM) studies and theoretical calculations. These findings show that defects in h-BN exhibit strong defect-phonon coupling. The results from STEM and theoretical calculations are beneficial for understanding the constitution of the h-BN defects.

18.
Nat Commun ; 9(1): 3319, 2018 08 20.
Artículo en Inglés | MEDLINE | ID: mdl-30127419

RESUMEN

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO3 ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unit-cell-thick BiFeO3 films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO3 films. Based on first-principles calculations and Kelvin probe force microscopy measurements, we explain the mechanism of polarization stabilization by the ionic displacements in oxide electrode and the surface charges. Our results indicate that critical thickness for ferroelectricity in the BiFeO3 film is virtually absent, making it a promising candidate for high-density nonvolatile memories.

19.
Adv Mater ; 30(22): e1707428, 2018 May.
Artículo en Inglés | MEDLINE | ID: mdl-29667241

RESUMEN

The interactions between delocalized and localized charges play important roles in correlated electron systems. Here, using a combination of transport measurements, spectroscopic ellipsometry (SE), and X-ray absorption spectroscopy (XAS) supported by theoretical calculations, we reveal the important role of interfacial localized charges and their screening effects in determining the mobility of (La0.3 Sr0.7 )(Al0.65 Ta0.35 )O3 /SrTiO3 (LSAT/SrTiO3 ) interfaces. When the LSAT layer thickness reaches the critical value of 5 uc, the insulating interface abruptly becomes conducting, accompanied by the appearance of a new midgap state. This midgap state emerges at ≈1 eV below the Ti t2g band and shows a strong character of Ti 3dxy - O 2p hybridization. Increasing the LSAT layer from 5 to 18 uc, the number of localized charges increases, resulting in an enhanced screening effect and higher mobile electron mobility. This observation contradicts the traditional semiconductor interface where the localized charges always suppress the carrier mobility. These results demonstrate a new strategy to probe localized charges and mobile electrons in correlated electronic systems and highlight the important role of screening effects from localized charges in improving the mobile electron mobility at complex oxide interfaces.

20.
ACS Appl Mater Interfaces ; 10(11): 9774-9781, 2018 Mar 21.
Artículo en Inglés | MEDLINE | ID: mdl-29517231

RESUMEN

Along with an unexpected conducting interface between nonmagnetic insulating perovskites LaAlO3 and SrTiO3 (LaAlO3/SrTiO3), striking interfacial magnetisms have been observed in LaAlO3/SrTiO3 heterostructures. Interestingly, the strength of the interfacial magnetic moment is found to be dependent on oxygen partial pressures during the growth process. This raises an important, fundamental question on the origin of these remarkable interfacial magnetic orderings. Here, we report a direct evidence of room-temperature stable magnetism in a LaAlO3/SrTiO3 heterostructure prepared at high oxygen partial pressure by using element-specific soft X-ray magnetic circular dichroism at both Ti L3,2 and O K edges. By combining X-ray absorption spectroscopy at both Ti L3,2 and O K edges and first-principles calculations, we qualitatively ascribe that this strong magnetic ordering with dominant interfacial Ti3+ character is due to the coexistence of LaAlO3 surface oxygen vacancies and interfacial (TiAl-AlTi) antisite defects. On the basis of this new understanding, we revisit the origin of the weak magnetism in LaAlO3/SrTiO3 heterostructures prepared at low oxygen partial pressures. Our calculations show that LaAlO3 surface oxygen vacancies are responsible for the weak magnetism at the interface. Our result provides direct evidence on the presence of room-temperature stable magnetism and a novel perspective to understand magnetic and electronic reconstructions at such strategic oxide interfaces.

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