Nanoscale Rings Research Articles

Dynamic and static dipole polarizability of an Aharonov–Bohm ring

The properties of nanoscale rings are sensitive to Aharonov–Bohm fluxes threading the ring. In particular, neighboring angular momentum eigenstates become degenerate in cases of half-integer flux. Such degeneracies have a profound effect on the dipole polarizability leading to a divergent response. We analyze circular finite-width nanorings and derive a simple and compact expression for the polarizability valid for arbitrary ring geometry, frequency and magnetic flux. The dipole response is significantly reduced by finite-width effects, yet divergencies at half-integer flux are predicted irrespective of width. Finally, a non-divergent (but large) response is restored through a non-perturbative treatment of both magnetic and electric fields.

Evolution of ring structures and method for inhibition in polishing of fused silica

Fused silica is widely used in many fields due to its unique properties, which are linked strongly to its nanoscale ring structures. Although an ultra-smooth surface could be achieved by polishing, it still introduces complex changes in the nanoscale ring structures, leading to a degradation of properties. Thus, understanding the polishing-induced evolution of ring structures is of great importance. In this paper, experiments and molecular dynamics simulations were performed to analyze the evolution mechanism, distribution and influencing factors of ring structures during polishing. Finally, an evolution-free surface was obtained. The results demonstrated that the evolution towards small rings occurred at the expense of large rings during polishing. The evolution was driven by the generation and breakage of siloxane bonds due to the coupling action of the load and hydroxylation. A rise of load on a single particle facilitated the evolution and increased the critical evolution depth by generating overcoordinated (OC) atoms. In contrast, the hydroxylation broke rings directly and reduced the load-induced generation of OC atoms, causing the inhibition of the evolution without altering the critical evolution depth. The results provide valuable insights into the evolution of rings and guide the precision machining of fused silica.

A sex-specific switch in a single glial cell patterns the apical extracellular matrix

Apical extracellular matrix (aECM) constitutes the interface between every tissue and the outside world. It is patterned into diverse tissue-specific structures through unknown mechanisms. Here, we show that a male-specific genetic switch in a single C.elegans glial cell patterns the overlying aECM from a solid sheet to an ∼200nm pore, thus allowing a male sensory neuron to access the environment. Using cell-specific genetic sex reversal, we find that this switch reflects an inherent sex difference in the glial cell that is independent of the sex identity of the surrounding neurons. Through candidate and unbiased genetic screens, we find that this glial sex difference is controlled by factors shared with neurons (mab-3, lep-2, and lep-5) as well as previously unidentified regulators whose effects may be glia specific (nfya-1, bed-3, and jmjd-3.1). The switch results in male-specific glial expression of a secreted Hedgehog-related protein, GRL-18, that we discover localizes to transient nanoscale rings at sites where aECM pores will form. Using electron microscopy, we find that blocking male-specific gene expression in glia prevents pore formation, whereas forcing male-specific glial gene expression induces an ectopic pore. Thus, a switch in gene expression in a single cell is necessary and sufficient to pattern aECM into a specific structure. Our results highlight that aECM is not a simple homogeneous meshwork, but instead is composed of discrete local features that reflect the identity of the underlying cells.

Unconventional Giant "Magnetoresistance" in Bosonic Semiconducting Diamond Nanorings.

The emergence of superconductivity in doped insulators such as cuprates and pnictides coincides with their doping-driven insulator-metal transitions. Above the critical doping threshold, a metallic state sets in at high temperatures, while superconductivity sets in at low temperatures. An unanswered question is whether the formation of Cooper pairsin a well-established metal will inevitably transform the host material into a superconductor, as manifested by a resistance drop. Here, this question is addressed by investigating the electrical transport in nanoscale rings (full loops) and half loops manufactured from heavily boron-doped diamond. It is shown that in contrast to the diamond half-loops (DHLs) exhibiting a metal-superconductor transition, the diamond nanorings (DNRs) demonstrate a sharp resistance increase up to 430% and a giant negative "magnetoresistance" below the superconducting transition temperature of the starting material. The finding of the unconventional giant negative "magnetoresistance", as distinct from existing categories of magnetoresistance, that is, the conventional giant magnetoresistancein magnetic multilayers, the colossal magnetoresistancein perovskites, and the geometric magnetoresistance in semiconductor-metal hybrids, reveals the transformation of the DNRs from metals to bosonic semiconductors upon the formation of Cooper pairs. DNRs like these could be used to manipulate Cooper pairs in superconducting quantum devices.

Optically induced antiferromagnetic order in dielectric metasurfaces with complex supercells

Metasurfaces are 2D planar lattices of nanoparticles that allow the manipulation of incident light properties. Because of that attribute, metasurfaces are promising candidates to replace bulky optical components. Traditionally, metasurfaces are made from a periodic arrangement of identical unit cells. However, more degrees of freedom are accessible if an increasing number of structured unit cells are combined. The present study explores a type of dielectric metasurface with complex supercells composed of Mie-resonant dielectric nanocylinders and nanoscale rings. We numerically and experimentally demonstrate the signature of an optical response that relies on the structures sustaining staggered optically induced magnetic dipole moments. The optical response is associated with an optical antiferromagnetism. The optical antiferromagnetism exploits the presence of pronounced coupling between dissimilar Mie-resonant dielectric nanoparticles. The coupling is manipulated by engineering the geometry and distance between the nanoparticles, which ultimately enhances their effective magnetic response. Our results suggest possible applications in resonant nanophotonics by broadening the modulation capabilities of metasurfaces.

Mapping the direction of electron ionization to phase delay between VUV and IR laser pulses

We theoretically demonstrate a one-to-one mapping between the direction of electron ionization and the phase delay between a linearly polarized VUV and a circular IR laser pulse. To achieve this, we use an ultrashort VUV pulse that defines the moment in time and space when an above threshold electron is released in the IR pulse. The electron can then be accelerated to high velocities escaping in a direction completely determined by the phase delay between the two pulses. The dipole matrix element to transition from an initial bound state of the N$_2$ molecule, considered in this work, to the continuum is obtained using quantum mechanical techniques that involve computing accurate continuum molecular states. Following release of the electron in the IR pulse, we evolve classical trajectories, neglecting the Coulomb potential and accounting for quantum interference, to compute the distribution of the direction and magnitude of the final electron momentum. The concept we theoretically develop can be implemented to produce nanoscale ring currents that generate large magnetic fields.

Ferroelectric superdomain controlled graphene plasmon for tunable mid-infrared photodetector with dual-band spectral selectivity

Dual-band infrared photodetectors (DBIPs) can discriminate desired signals from complex scenes and thus are highly expected for threat-warning, remote sensing, and astronomy applications. Conventional DBIPs with high performances are, however, typically based on semiconductor thin films, but remain the challenges of expensive growth and cooling requirements. Here, we report a room-temperature graphene plasmonic photodetector with tunable dual-band infrared spectral selectivity driven by ferroelectric superdomain. The periodic ferroelectric polarization array with nanoscale ring shapes provides an ultrahigh electrostatic field for spatially doping of monolayer graphene to desired patterns, and is further used to excite and confine intrinsic graphene plasmons. Our devices exhibit tunable resonance photoresponse in both two bands of 3.7–16.3 μm and 15.1–52.1 μm. The numerical calculations show that our devices own ultrahigh responsivities of 667–1080 A W−1 at room temperature in the range of 5–50 μm. Our devices make possible the applications of the infrared imaging system and both stationary and motion states of objects detection. These investigations provide a novel approach for advanced infrared system construction by employing a simple, low-cost, uncooled multispectral detectors array.

A tunable nonlinear plasmonic multiplexer/demultiplexer device based on nanoscale ring resonators

A tunable nonlinear plasmonic multiplexer/demultiplexer device based on nanoscale ring resonators

Isotropic all-electric spin analyzer based on a quantum ring with spin–orbit couplings

Isotropic spin analysis is a key step in spintronics and could be useful in quantum information, which usually requires light as an essential component. It has not yet been realized in a solid-state device. Here, we propose an isotropic all electrical spin analyzer designed from a quantum ring with spin–orbit couplings by analytically and numerically modeling how the charge transmission rate depends on the polarization of the incident spin. The spin transport features are also demonstrated to be robust against ring structure defects, disorder, and a bias between the two leads at finite temperature in the nanoscale ring. Similar to the light polarizer/analyzer, this interesting two-dimensional electron system can be designed as a spin filter, spin polarizer, and a general spin analyzer with high resolution by simply tuning the spin–orbit couplings, which paves the way for realizing the tunable and integrable spintronics devices.

Microwave-driven persistent currents in a nanoscale quantum ring

Time-dependent electron current through a nanoscale phase-coherent quantum ring with leads, coupled to reservoirs biased by a sinusoidal voltage, is studied. We argue that Floquet states in such samples, driven also by external time-periodic magnetic field, can be coherently manipulated. Some examples show that on-demand structures in the frequency domain, tunable by the joint action of the voltage bias and a microwave pumping, can be generated this way.

Ferroelectric Superdomain Controlled Graphene Plasmon for Tunable Mid-Infrared Photodetector with Dual-Band Spectral Selectivity

Dual-band infrared photodetectors (DBIPs) can discriminate desired signals from complex scenes and thus are highly expected for threat-warning, remote sensing, and astronomy applications. Conventional DBIPs with high-performances are, however, typically based on semiconductor thin films, but remain the challenges of complex spatial align, expensive growth and cooling requirement. Here, we report a tunable graphene plasmonic photodetector with dual-band infrared spectral selectivity driven by ferroelectric superdomain. The periodic ferroelectric polarization array with nanoscale ring shapes provides ultrahigh electrostatic field for spatially doping of monolayer graphene to desired patterns, and is further used to excite and confine intrinsic graphene plasmons. Our devices exhibit tunable resonance photoresponse in both two bands of 3.7-16.3 um and 15.1-52.1 um. The numerical calculations show that our devices own ultrahigh responsivities of 667-1080 A W-1 at room temperature in range of 5-50 um. Our devices make possible the applications of infrared imaging system and both stationary and motion state of objects detection. These investigations provide a novel approach for advanced infrared system construction by employing simple, low-cost, uncooling multispectral detectors array.

Numerical analysis of tunable nonlinear plasmonic router based on nanoscale ring resonators

In the advanced plasmonics integrated circuits (PICs) there has been outstanding, continuing interest in developing routers to harness light-matter interactions in nanoscale dimensions with wanted optical properties. In this regard, herein, we introduce an all-optical router based on nanometer ring resonator which surface plasmon resonance (SPR) and nonlinear materials are used simultaneously to enhance high performance range. By changing the radius of the ring resonator and the intensity of the light we achieved control of the parameters and the routing. The results of routing and shifting the central frequency with light intensity and radius of the ring resonator are studied. The performance of the router indicates that a ring is required for each ports, which changes the control parameters to change its central frequency, as well as we can be said the use of switches and filters as other design features. These routers have advantages such as nano scale size, low light intensity, fast response time, integratable and etc., which are highly used in all-optical circuits, image processing and today's modern technology. In our simulation, we consider transmission or reflection of light in each ports based on the finite difference time domain (FDTD).

Optical Activity from the Exciton Aharonov–Bohm Effect: A Floquet Engineering Approach

Floquet engineering is a convenient strategy to induce nonequilibrium phenomena in molecular and solid-state systems, or to dramatically alter the physicochemical properties of matter, bypassing costly and time-consuming synthetic modifications. In this article, we investigate theoretically some interesting consequences of the fact that an originally achiral molecular system can exhibit nonzero circular dichroism (CD) when it is driven with elliptically polarized light. More specifically, we consider an isotropic ensemble of small cyclic molecular aggregates in solution whose local low-frequency vibrational modes are driven by an elliptically polarized continuous-wave infrared pump. We attribute the origin of a nonzero CD signal to time-reversal symmetry breaking due to an excitonic Aharonov-Bohm (AB) phase arising from a time-varying laser electric field, together with coherent interchromophoric exciton hopping. The obtained Floquet engineered excitonic AB phases are far more tunable than analogous magnetically-induced electronic AB phases in nanoscale rings, highlighting a virtually unexplored potential that Floquet engineered AB phases have in the coherent control of molecular processes and simultaneously introducing new analogues of magneto-optical effects in molecular systems which bypass the use of strong magnetic fields.

Towards an Observable Test of Noncommutative Quantum Mechanics

The conceptual incompatibility of spacetime in gravity and quantum physics implies the existence of noncommutative spacetime and geometry on the Planck scale. We present the formulation of a noncommutative quantum mechanics based on the Seiberg–Witten map, and we study the Aharonov–Bohm effect induced by the noncommutative phase space. We investigate the existence of the persistent current in a nanoscale ring with an external magnetic field along the ring axis, and we introduce two observables to probe the signal coming from the noncommutative phase space. Based on this formulation, we give a value-independent criterion to demonstrate the existence of the noncommutative phase space.

Effect of long-range Coulomb interactions on electron transport in a nanoscale one-dimensional ring

The effect of long-range Coulomb interactions on electron transport in a one-dimensional ring is investigated by a numerical method with the time-dependent Hartree–Fock equation. Our results show that long-range Coulomb interactions induce a multi-electron wave packet state. Moreover, the number of electrons in the multi-electron wave packet varies depending on the strength of the long-range Coulomb interactions.

Strong Aharonov-Bohm quantum interference in simply connected LaAlO3/SrTiO3 structures

We report Aharonov-Bohm (AB)-type quantum interference in simply-connected devices created at the LaAlO$_3$/SrTiO$_3$ interface using conductive-atomic force microscope (c-AFM) lithography. The oscillations are multi-periodic functions of magnetic field strength, and they exhibit a substantial magnetic hysteresis with frequencies that depends on the magnetic sweep direction. The oscillation amplitude for the lowest two frequencies approaches $e^2/h$, consistent with the theoretical maximum for the AB effect, and harmonics up to third order are observable. Broadband quasiperiodic behavior is reported in a fraction of simply-connected electron waveguide devices that exhibit magnetic asymmetries. Curiously, nanoscale ring devices that are multiply-connected lack signatures of AB quantum interference. The interference phenomena are associated with an inhomogeneous magnetic landscape within the LaAlO$_3$/SrTiO$_3$ nanostructures.

Effects of geometry on spin-orbit Kramers states in semiconducting nanorings

The holonomic manipulation of spin-orbital degenerate states, encoded in the Kramers doublet of narrow semiconducting channels with spin-orbit interaction, is shown to be intimately intertwined with the geometrical shape of the nanostructures. The presence of doubly degenerate states is not sufficient to guarantee a non-trivial mixing by only changing the Rashba spin-orbit coupling. We demonstrate that in nanoscale quantum rings the combination of arbitrary inhomogeneous curvature and adiabatic variation of the spin-orbit amplitude, e.g., through electric-field gating, can be generally employed to get non-trivial combinations of the degenerate states. Shape symmetries of the nanostructure act to constrain the adiabatic quantum evolution. While for circular rings the geometric phase is not generated along a non-cyclic path in the parameters space, remarkably, for generic mirror-symmetric shape deformed rings the spin-orbit driving can lead to a series of dynamical quantum phase transitions. We explicitly show this occurrence and propose a route to detect such topological transitions by measuring a variation of the electron conductance into the semiconducting channel.

Exploration of Nano-Saturns: A Spectacular Sphere-Ring Supramolecular System.

Saturn-like systems consisting of nanoscale rings and spheres are fascinating motifs in supramolecular chemistry. Several ring molecules are known to include spherical molecules at the center of the cavity via noncovalent attractive interactions. In this Minireview, we generalize the molecular design, the structural features, and the supramolecular chemistry of such "nano-Saturns", which consist of monocyclic rings and fullerene spheres (mainly C60 ), on the basis of previous experimental and theoretical studies. Ring molecules are classified into three types (loop, belt, and disk) according to their shapes and possible interactions. Whereas typical belt-shaped rings tend to form tight complexes due to the wide contact area via π-π interactions, flat disk-shaped rings generally form weak complexes due to the narrow contact area mainly via CH-π interactions. In spite of the small association energies, disk-shaped rings are attractive because such rings can mimic the planet Saturn precisely as exemplified by an anthracene cyclic hexamer-C60 complex.

Phonon–polaritons in nanoscale waveguides

We investigate the phenomena of Brillouin induced opacity in nanoscale linear waveguides and Brillouin induced transparency in nanoscale ring waveguides. The concept of phonon–polariton is required in order to get a deep understanding of such phenomena. Phonon–polaritons are coherent superposition of photons and phonons obtained in the strong coupling regime induced through stimulated Brillouin scattering in the presence of a pump field. The formation of phonon–polaritons can be observed via linear optical spectra that are calculated here using the input–output formalism. For a linear waveguide, the signature of phonon–polaritons appears as two peaks in the transmission spectrum with an opacity gap, and for a ring waveguide as two dips in the transmission spectrum with a transparency gap.

Rapid macroscale shape morphing of 3D-printed polyrotaxane monoliths amplified from pH-controlled nanoscale ring motions

Controlling ring motions in a polyrotaxane-based 3D-printed monolith by pH variation results in a rapid and reversible macroscale shape morphing.