According to Noether’s theorem, symmetries in a physical system are intertwined with conserved quantities. These symmetries often determine the system topology, which is made ever more complex with increased dimensionality. Quasicrystals have neither translational nor global rotational symmetry, yet they intrinsically inhabit a higher-dimensional space in which symmetry resurfaces. Here, we discovered topological charge vectors in four dimensions (4D) that govern the real-space topology of 2D quasicrystals and reveal their inherent conservation laws. We demonstrate control over the topology in pentagonal plasmonic quasilattices, mapped by both phase-resolved and time-domain near-field microscopy, showing that their temporal evolution continuously tunes the 2D projections of their distinct 4D topologies. Our work provides a route to experimentally probe the thermodynamic properties of quasicrystals and topological physics in 4D and above.

Hyperbolic metasurfaces (HMSs) are artificially-engineered interfaces, exhibiting high anisotropy manifested as hyperbolic dispersion. Their ability to support extremely large momenta with negative diffraction and refraction places them as promising platforms for on-chip super-resolution and enhanced light-matter interaction. While the hyperbolic nature of these structures is experimentally demonstrated, only a limited number of studies have concentrated on their super-resolution capabilities, which are never obtained at visible-frequency for fully harnessing their immense resolution potential. Here, a near-field investigation of visible-frequency HMSs is presented, exploiting their super-resolution capabilities to their maximum potential. The impulse response of waves propagating across HMSs is measured and demonstrates deep sub-wavelength anomalous focusing and on-chip reflectionless negative refraction at the interface of parabolic and hyperbolic media, independent of incident angle. The approach lays the foundation for sub-wavelength imaging in 2D space for the advancement of imaging and wave compression devices, leveraging the capabilities of HMSs.

AbstractNanoparticles obtained by solid-state dewetting are known to exhibit an extraordinarily high mechanical strength under uniaxial compression. While most of such particles are single-crystalline, some may contain a coherent twin boundary (CTB) parallel to the substrate. The role of the CTB in the mechanical properties of such particles remained unknown. This work combines nano-mechanical testing, advanced characterization methods, and atomistic computer simulations to investigate the CTB effect of the mechanical behavior of Ni-Co nanoparticles produced by solid-state dewetting on a sapphire substrate. The results indicate that the CTB does not make any significant impact on the particle strength, toughness, solute softening, or strain hardening. These properties remain virtually the same as those of single-crystalline particles of the same alloy. The mechanisms of dislocation nucleation and the dislocation-CTB interactions are investigated in detail. The work lends additional confidence to the previous results for the mechanical behavior of nanoparticles produced by solid-state dewetting, some of which could have contained twin boundaries.

Organic mixed ionic–electronic conductors (OMIECs), which can be used to build organic electrochemical transistors (OECTs), are of potential use in flexible, large-area and bioelectronic systems. Although hole-transporting p-type OMIECs are susceptible to oxidation, and oxygen leads to OECT instability, it is unclear whether oxygen also behaves as an uncontrolled p-dopant. We show that oxygen dissolved in a solvent can act as a p-dopant in OMIECs and OECTs by filling traps to enable effective electrochemical doping. To address the fact that the presence of oxygen simultaneously jeopardizes OECT stability, we develop a two-step strategy in which we first degas the solvent, and then dope the OMIEC in a controlled manner using a chemical dopant. Our approach improves the stability of both p-type and n-type OECTs, while increasing the on–off ratio, tuning the threshold voltage and enhancing the transconductance, charge carrier mobility, and the µC* product—that is, the product of mobility and the volumetric capacitance.

The morphological dynamics of water sheet jets generated by microfluidic convergent nozzles represent a critical area of research with significant implications for advancing controlled spray formation. This study employs anodically bonded Silicon wafer chips with etched converging nozzle geometries to investigate the effects of geometric parameters under varying flow conditions. High-speed shadowgraph imaging is utilized to assess the influence of nozzle thickness, outlet width, converging angle, and flow rate on the size and stability of water sheet jets. Experimental results demonstrate that sheet size is primarily governed by flow rate, while stability is strongly affected by nozzle design.  Scaling correlations are developed to quantitatively describe water sheet dimensions and transitions between jet breakup, stable sheets, and unstable sheet spray breakup. These findings advance the understanding of water sheet jet dynamics and provide a robust framework for designing microfluidic systems optimized for planar and controlled spray formation.

For the successful implementation of organic electrochemical transistors in neuromorphic computing, bioelectronics, and real-time sensing applications it is essential to understand the factors that influence device switching times. This work describes a physical-electrochemical model of the transient response to a step of the gate voltage. The model incorporates 1) ion diffusion inside the channel that governs the electronic conductivity, 2) horizontal electron transport, and 3) the external elements (capacitance, ionic resistance) of the ion dynamics in the electrolyte. This work finds a general expression of two different time constants that determine the vertical insertion process in terms of the transport/polarization parameters, in addition to the electronic transit time. The work highlights the central role of the chemical capacitance in determining the modulation of the lateral conductivity. The different types of response of the drain current are classified, and the significance for synaptic operation in neuromorphic circuits is discussed. The model is confirmed by detailed simulations that enable to visualize the different ions distributions and dynamics.

The study of the net magneto-capacitance, C(B), in thin films of the conducting polymer Poly(3 4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is presented. In the films there are charged electrically-conducting PEDOT-rich regions surrounded by PSS insulating charged material. The high-conductivity grade PEDOT:PSS thin films are studied at low temperature, where the hopping conduction is dominant. It is experimentally observed that there is a finite net magneto-capacitance, C(B), in the temperature range T = 1.7–3 K. Thus, the observed C(B) is a direct evidence for an intra-site Coulomb interaction, U ≈ 2 meV, among the mobile charge carriers in the PEDOT-rich regions. The lifting of spin degeneracy motivates PEDOT for use in spintronic applications.

The modulation of channel conductance in field-effect transistors (FETs) via metal-oxide-semiconductor (MOS) structures has revolutionized information processing and storage. However, the limitations of silicon-based FETs in electrical switching have driven the search for new materials capable of overcoming these constraints. Electrostatic gating of competing electronic phases in a Mott material near its metal to insulator transition (MIT) offers prospects of substantial modulation of the free carriers and electrical resistivity through small changes in band filling. While electrostatic control of the MIT has been previously reported, the advancement of Mott materials towards novel Mott transistors requires the realization of their charge gain prospects in a solid-state device. In this study, we present gate-control of electron correlation using a solid-state device utilizing the oxide Mott system $La_{1-x}Sr_xVO_3$ as a correlated FET channel. We report on a gate resistance response that cannot be explained in a purely electrostatic framework, suggesting at least $\times100$ charge gain originating from the correlated behavior. These preliminary results pave the way towards the development of highly efficient, low-power electronic devices that could surpass the performance bottlenecks of conventional FETs by leveraging the electronic phase transitions of correlated electron systems.

Four-terminal indirectly heated phase-change switches (IPCSs) have emerged as excellent candidates for radio-frequency integrated circuit (RFIC) applications due to their state-of-the-art cutoff frequency, nonvolatility, CMOS compatibility, and exceptional linearity. However, IPCS performance is limited by relatively low-power handling capabilities in the OFF-state, limited by the Ovonic threshold switching (OTS) phenomenon. In this article, we propose the use of a quad configuration consisting of two series-connected IPCS in parallel with another two series-connected IPCS. This series connection increases the effective threshold voltage, thereby enhancing power handling compared to a single device. We experimentally demonstrate the implementation of this quad configuration in asymmetric and symmetric single-pole double-throw (SPDT) switches. Fabricated using an in-house process, these designs achieve an insertion loss (IL) below 0.8 dB and isolation higher than 17 dB within the dc-15 GHz frequency band. Furthermore, we explore techniques, such as reducing the probing pads and series-shunt configuration, to boost isolation beyond 30 dB. Thanks to the quad configuration, the threshold voltage increases from 5 to 13.5 V, predicatively enabling power handling above 35 dBm.

Shaping and controlling electromagnetic fields at the nanoscale is vital for advancing efficient and compact devices used in optical communications, sensing and metrology, as well as for the exploration of fundamental properties of light-matter interaction and optical nonlinearity. Real-time feedback for active control over light can provide a significant advantage in these endeavors, compensating for ever-changing experimental conditions and inherent or accumulated device flaws. Scanning nearfield microscopy, being slow in essence, cannot provide such a real-time feedback that was thus far possible only by scattering-based microscopy. Here, we present active control over nanophotonic near-fields with direct feedback facilitated by real-time near-field imaging. We use far-field wavefront shaping to control nanophotonic patterns in surface waves, demonstrating translation and splitting of near-field focal spots at nanometer-scale precision, active toggling of different near-field angular momenta and correction of patterns damaged by structural defects using feedback enabled by the real-time operation. The ability to simultaneously shape and observe nanophotonic fields can significantly impact various applications such as nanoscale optical manipulation, optical addressing of integrated quantum emitters and near-field adaptive optics.