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Despite the importance of structure and properties in organic mixed conductors, there exist very few material systems where the effects of relative crystallinity, crystallite size, and doping conce...

In this paper we demonstrate a novel methodology to electrically test and characterize resistive random-access memory (RRAM) single bit devices for deep learning application. We extract critical device performance metrics for validating and optimizing fabrication processes which feed into yield learning. We adopt the algorithm-based bias condition search methodology and extract forming and switching voltage parameters without overdriving the devices. This test methodology can be used for Technology Development Learning Cycle in a research and development environment.

To realize thermoelectric textiles that can convert body heat to electricity, fibers with excellent mechanical and thermoelectric properties are needed. Although poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is among the most promising organic thermoelectric materials, reports that explore its use for thermoelectric fibers are all but absent. Herein, the mechanical and thermoelectric properties of wet‐spun PEDOT:PSS fibers are reported, and their use in energy‐harvesting textiles is discussed. Wet‐spinning into sulfuric acid results in water‐stable semicrystalline fibers with a Young's modulus of up to 1.9 GPa, an electrical conductivity of 830 S cm−1, and a thermoelectric power factor of 30 μV m−1 K−2. Stretching beyond the yield point as well as repeated tensile deformation and bending leave the electrical properties of these fibers almost unaffected. The mechanical robustness/durability and excellent underwater stability of semicrystalline PEDOT:PSS fibers, combined with a promising thermoelectric performance, opens up their use in practical energy‐harvesting textiles, as illustrated by an embroidered thermoelectric fabric module.

[Image: see text] Because of their attractive mechanical properties, conducting polymers are widely perceived as materials of choice for wearable electronics and electronic textiles. However, most state-of-the-art conducting polymers contain harmful dopants and are only processable from solution but not in bulk, restricting the design possibilities for applications that require conducting micro-to-millimeter scale structures, such as textile fibers or thermoelectric modules. In this work, we present a strategy based on melt processing that enables the fabrication of nonhazardous, all-polymer conducting bulk structures composed of poly(3,4-ethylenedioxythiophene) (PEDOT) polymerized within a Nafion template. Importantly, we employ classical polymer processing techniques including melt extrusion followed by fiber spinning or fused filament 3D printing, which cannot be implemented with the majority of doped polymers. To demonstrate the versatility of our approach, we fabricated melt-spun PEDOT:Nafion fibers, which are highly flexible, retain their conductivity of about 3 S cm(–1) upon stretching to 100% elongation, and can be used to construct organic electrochemical transistors (OECTs). Furthermore, we demonstrate the precise 3D printing of complex conducting structures from OECTs to centimeter-sized PEDOT:Nafion figurines and millimeter-thick 100-leg thermoelectric modules on textile substrates. Thus, our strategy opens up new possibilities for the design of conducting, all-polymer bulk structures and the development of wearable electronics and electronic textiles.

Despite the great potential of polymer microfibers in human-friendly wearable electronics, most previous polymeric electronics have been limited to thin-film-based devices due to practical difficulties in fabricating microfibrillar devices, as well as defining the active channel dimensions in a reproducible manner. Herein, we report on conducting polymer microfiber-based organic electrochemical transistors (OECTs) and their application in single-strand fiber-type wearable ion concentration sensors. We developed a simple wet-spinning process to form very conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) microfibers using aqueous sulfuric acid solutions and carefully examined their electrical/electrochemical properties. In conjunction with fabricating substrate-free PEDOT:PSS microfiber-based OECT devices, the proposed novel characterization method demonstrated that the current variation ratio can be a reliable method for evaluating the device performance for sensing ion concentrations, regardless of the actual channel dimensions. Finally, we developed single-strand fiber-type skin-mountable OECTs by introducing a source-gate hybrid electrode and demonstrated that the resultant microfiber sensors can perform real-time repetitive measurements of the ion concentration in human sweat. A wearable device that analyses sweat and could help athletes optimize their intake of fluids and electrolytes has been developed by researchers in South Korea. Wearable electronics provide a way to monitor the body around the clock, and even deliver simple healthcare solutions. Such devices need to be light, robust, and flexible enough to adapt to the wearer’s movement. Sanghyun Ju from Kyonggi University in Suwon, Myung-Han Yoon from Gwangju Institute of Science and Technology and their colleagues have made a wearable device that can measure the ion concentration in human sweat. Previous materials used in such devices required a substrate, which limited their mechanical flexibility. Instead, Ju, Yoon and the team created highly conductive microfibers, which they used to fabricate electrochemical transistors. The current through the transistor varied with ion concentration, enabling real-time measurements. In textile electronics, micro to millimeter-scaled misalignment is commonly occurred during the high-throughput and bulk-scaled textile manufacturing process, thus the exact performance control of the fiber-based active devices is very difficult in low-cost wearable electronics. In this research, we developed novel single-strand organic electrochemical transistors and proposed dimension-independent characterization method (i.e., the current variation ratio in variation of logarithmic concentration of electrolyte) for ion concentration sensing. Furthermore, we demonstrated the pseudo two-terminal transistor operation by incorporating electrochemical gate electrode onto the surface of the source electrode, leading to single-strand fiber device platform.

Due to the trade-off between their electrical/electrochemical performance and underwater stability, realizing polymer-based, high-performance direct cellular interfaces for electrical stimulation and recording has been very challenging. Herein, we developed transparent and conductive direct cellular interfaces based on a water-stable, high-performance poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) film via solvent-assisted crystallization. The crystallized PEDOT:PSS on a polyethylene terephthalate (PET) substrate exhibited excellent electrical/electrochemical/optical characteristics, long-term underwater stability without film dissolution/delamination, and good viability for primarily cultured cardiomyocytes and neurons over several weeks. Furthermore, the highly crystallized, nanofibrillar PEDOT:PSS networks enabled dramatically enlarged surface areas and electrochemical activities, which were successfully employed to modulate cardiomyocyte beating via direct electrical stimulation. Finally, the high-performance PEDOT:PSS layer was seamlessly incorporated into transparent microelectrode arrays for efficient, real-time recording of cardiomyocyte action potentials with a high signal fidelity. All these results demonstrate the strong potential of crystallized PEDOT:PSS as a crucial component for a variety of versatile bioelectronic interfaces. Cardiomyocyte cells can be cultured and made to pulse on demand using transparent polymers with good stability. Conductive thin films formed from poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have low impedances, making them ideal for bioelectronic interfaces. But they suffer from severe fragility in aqueous environments. Myung-Han Yoon from Korea’s Gwangju Institute of Science and Technology and colleagues have made PEDOT:PSS films that show no degradation up to three weeks underwater. They achieved this by immersing the films in concentrated sulfuric acid to initiate solvent-assisted crystallization. The crystalline films had improved electrical/electrochemical properties and biocompatibility over approaches such as polymer cross-linking, and supported photolithographic patterning into microelectrode arrays. Using cardiac cells as a model, the researchers demonstrated the feasibility of modulating beating frequencies with direct electrical stimulation under 1V while simultaneously capturing real-time action potentials and calcium signals. The high performance polymer-based conductive cellular interface was developed by a solvent-assisted crystallization of PEDOT:PSS. The crystallized PEDOT:PSS(c-PEDOT:PSS) exhibited mechanical and electrical robustness over 21days as well as excellent electrical conductivity and electrochemical activities. Thanks to such advantageous properties for the cellular interfaces, the beating rates of cardiomyocytes cultured on c-PEDOT:PSS were successfully modulated through pulsed direct stimulation under 1 V. In addition, c-PEDOT:PSS incorporated Multielectrode arrays (MEAs) recorded real-time action potentials originated from cardiomyocytes with high signal fidelity. we expect c-PEDOT:PSS with high-performance and high-stability to be a promising candidate for long-term bioelectronic interface development.

Lightweight nano/microscale wearable devices that are directly attached to or worn on the human body require enhanced flexibility so that they can facilitate body movement and overall improved wearability. In the present study, a flexible poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) fiber-based sensor is proposed, which can accurately measure the amount of salt (i.e., sodium chloride) ions in sweat released from the human body or in specific solutions. This can be performed using one single strand of hair-like conducting polymer fiber. The fabrication process involves the introduction of an aqueous PEDOT:PSS solution into a sulfuric acid coagulation bath. This is a repeatable and inexpensive process for producing monolithic fibers, with a simple geometry and tunable electrical characteristics, easily woven into clothing fabrics or wristbands. The conductivity of the PEDOT:PSS fiber increases in pure water, whereas it decreases in sweat. In particular, the conductivity of a PEDOT:PSS fiber changes linearly according to the concentration of sodium chloride in liquid. The results of our study suggest the possibility of PEDOT:PSS fiber-based wearable sensors serving as the foundation of future research and development in skin-attachable next-generation healthcare devices, which can reproducibly determine the physiological condition of a human subject by measuring the sodium chloride concentration in sweat.

Specialized hardware for deep learning using analog memory devices has the potential to outperform conventional GPUs by a large margin. At the core of such hardware are arrays of non-volatile-memory (NVM) devices that can perform the simple matrix operations needed for deep learning in parallel and in constant time. Several implementations can be found in the literature that use different materials as memory elements, including phase-change-memory (PCM), resistive-random-access-memory (RRAM), electrochemical-random-access-memory (ECRAM), and ferroelectric devices. While the current focus is to demonstrate functionality, there is an increasing concern about the reliability margins of this emerging technology. In this paper we will briefly describe operation and device requirements, and then focus on possible reliability exposure in terms of variability, stability and drift, retention and durability.

Colloidal particles with a repulsive interparticle potential spontaneously form crystalline lattices, which are used as a motif for photonic materials. It is difficult to predict the crystal arrangement in spherical volume as lattices are incompatible with a spherical surface. Here, the optimum arrangement of charged colloids is experimentally investigated by encapsulating them in double-emulsion drops. Under conditions of strong interparticle repulsion, the colloidal crystal rapidly grows from the surface toward the center of the microcapsule, forming an onion-like arrangement. By contrast, for weak repulsion, crystallites slowly grow and fuse through rearrangement to form a single-crystal phase. Single-crystal structure is energetically favorable even for strong repulsion. Nevertheless, a high energy barrier to colloidal rearrangement kinetically arrests the onion-like structure formed by heterogeneous nucleation. Unlike the isotropic onion-shaped product, the anisotropic single-crystal-containing microcapsules selectively display-at certain orientations but not others-one of the distinct colors from the various crystal planes.

Topological insulators (TIs) host spin-momentum locked surface states that are inherently susceptible to magnetic proximity modulations, making them promising for nano-electronic, spintronic, and quantum computing applications. While much effort has been devoted to studying (quantum) anomalous Hall effects in magnetic magnetically doped TIs, the inherent magnetoresistance (MR) properties in magnetic proximity-coupled surface states remain largely unexplored. Here, we directly exfoliate Bi2Se3 TI flakes onto a magnetic insulator, yttrium iron garnet, and measure the MR at various temperatures. We experimentally observe an anisotropic magnetoresistance that is consistent with a magnetized surface state. Our results indicate that the TI has magnetic anisotropy out of the sample plane, which opens an energy gap between the surface states. By applying a magnetic field along any in-plane orientation, the magnetization of the TI rotates toward the plane and the gap closes. Consequently, we observe a large (∼6.5%) MR signal that is attributed to an interplay between coherent rotation of magnetization within a topological insulator and abrupt switching of magnetization in the underlying magnetic insulator.

Despite the importance of carrier mobility, recent research efforts have been mainly focused on the improvement of volumetric capacitance in order to maximize the figure-of-merit, μC* (product of carrier mobility and volumetric capacitance), for high-performance organic electrochemical transistors. Herein, high-performance microfiber-based organic electrochemical transistors with unprecedentedly large μC* using highly ordered crystalline poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) microfibers with very high carrier mobilities are reported. The strain engineering via uniaxial tension is employed in combination with solvent-mediated crystallization in the course of drying coagulated fibers, resulting in the permanent preferential alignment of crystalline PEDOT:PSS domains along the fiber direction, which is verified by atomic force microscopy and transmission wide-angle X-ray scattering. The resultant strain-engineered microfibers exhibit very high carrier mobility (12.9 cm2 V-1 s-1 ) without the trade-off in volumetric capacitance (122 F cm-3 ) and hole density (5.8 × 1020 cm-3 ). Such advantageous electrical and electrochemical characteristics offer the benchmark parameter of μC* over ≈1500 F cm-1 V-1 s-1 , which is the highest metric ever reported in the literature and can be beneficial for realizing a new class of substrate-free fibrillar and/or textile bioelectronics in the configuration of electrochemical transistors and/or electrochemical ion pumps.

This study describes a fabrication method of microsized AgNW patterns based on poly dimethylsiloxane (PDMS) substrate using a poly(p-xylylene) (parylene) stencil technique. Various patterns of AgNW conductive sheets were created on the wafer scale area in the forms of straight and serpentine lines, texts, and symbols, which dimensions ranged from a few tens of micrometers to hundreds of micrometers. We demonstrated the electrical performance of straight line and serpentine line patterned AgNW electrodes when subjected to mechanical strains. The gauge factor and stretchability ranged from 0.5 to 55.2 at 2% uniaxial strain and from 4.7 to 55.7%, respectively, depending on the shapes and structures of the AgNW electrodes. Using the developed AgNW patterning technique, we fabricated strain sensors to detect small body signals epidermally such as hand motion, eye blink and heart rate. Also, tactile sensors were fabricated and exhibited the sensitivity of 3.91 MPa(-1) in the pressure range lower than 50 kPa, and 0.28 MPa(-1) in the pressure range greater than 50 kPa up to 1.3 MPa. From these results, we concluded that the proposed technique enables the fabrication of reliable AgNW patterns on wafer-scale PDMS substrate and the potential applications for various flexible electronic devices.

In this work, we report an extensive experimental investigation of the important statistical properties of resistive random access memory (RRAM) switching conductance. We demonstrate the Gumbel statistics, a maximum extreme-value distribution for switching-filament conductance, as opposed to the minimum extreme-value distribution such as Weibull model. We apply a Poisson random statistical distribution for the spatial generation of percolation filaments to link the RRAM conductance measurements with device areas. As a result, we can derive two important relations: area scaling properties of percentiles and scale-factors. We show the validity of this maximum extreme-value distribution model by rigorously examining the vertical percentile-scaling characteristics of experimental data. The independently extracted shape-factor from the area-dependence of scale-factors captures the merged conductance distributions in good agreement with the experimental conductance data. It is revealed that larger variability associated with RRAM conductance measurements is directly linked to the maximum-valued statistical characteristics of this model. We also demonstrate that RRAM conductance, rather than resistance, is a fundamental statistical variable.

Owing to the mixed electron/hole and ion transport in the aqueous environment, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based organic electrochemical transistor has been regarded as one of the most promising device platforms for bioelectronics. Nonetheless, there exist very few in-depth studies on how intrinsic channel material properties affect their performance and long-term stability in aqueous environments. Herein, we investigated the correlation among film microstructural crystallinity/composition, device performance, and aqueous stability in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films. The highly organized anisotropic ordering in crystallized conducting polymer films led to remarkable device characteristics such as large transconductance (similar to 20 mS), extraordinary volumetric capacitance (113 F.cm(-3)), and unprecedentedly high [mu C*] value (similar to 490 F.cm(-1) V-1 s(-1)). Simultaneously, minimized poly(styrenesulfonate) residues in the crystallized film substantially afforded marginal film swelling and robust operational stability even after amp;gt;20-day water immersion, amp;gt;2000-time repeated on-off switching, or high-temperature/pressure sterilization. We expect that the present study will contribute to the development of long-term stable implantable bioelectronics for neural recording/stimulation. Funding Agencies|National Research Foundation of Korea (NRF) - Ministry of Science and ICT [NRF-2017R1A2B4003873, NRF-2018M3A7B4070988, NRF-2018M3D1A1051602]

Nanoscience offers a unique opportunity to design modern materials from the bottom up via low-cost, solution processed assembly of nanoscale building blocks. These systems promise electronic band structure engineering using not only the nanoscale structural modulation, but also the mesoscale spatial patterning, although experimental realization of the latter has been challenging. Here, we design and fabricate a new type of artificial solid by stacking graphene on a self-assembled, nearly periodic array of nanospheres, and experimentally observe superlattice miniband effects. We find conductance dips at commensurate fillings of charge carriers per superlattice unit cell, which are key features of minibands that are induced by the quasi-periodic deformation of the graphene lattice. These dips become stronger when the lattice strain is larger. Using a tight-binding model, we simulate the effect of lattice deformation as a parameter affecting the inter-atomic hopping integral, and confirm the superlattice transport behavior. This 2D material-nanoparticle heterostructure enables facile band structure engineering via self-assembly, promising for large-area electronics and optoelectronics applications. A hybrid heterostructure of self-assembled nanoparticles on graphene displays conductance dips due to superlattice miniband effects. A team led by Yingjie Zhang and Nadya Mason at the University of Illinois designed and fabricated a large-area artificial solid combining self-assembled dielectric nanospheres and graphene grown by chemical vapor deposition. Taking advantage of the structural versatility of SiO2 nanoparticle assembly and the high mobility of graphene, the resulting heterostructure displays miniband effects in the electronic transport characteristics as a result of superlattice formation. Due to the size variability and imperfect ordering of the nanospheres, a broadening was observed in the miniband density of states. This effect can find an application in optoelectronic devices, such as optical modulators and sensor, requiring broadband modulation of their optical spectrum.

Recent demonstrations on manipulating antiferromagnetic (AF) order have triggered a growing interest in antiferromagnetic metal (AFM), and potential high-density spintronic applications demand further improvements in the anisotropic magnetoresistance (AMR). The antiferromagnetic semimetals (AFS) are newly discovered materials that possess massless Dirac fermions that are protected by the crystalline symmetries. In this material, a reorientation of the AF order may break the underlying symmetries and induce a finite energy gap. As such, the possible phase transition from the semimetallic to insulating phase gives us a choice for a wide range of resistance ensuring a large AMR. To further understand the robustness of the phase transition, we study thermal fluctuations of the AF order in AFS at a finite temperature. For macroscopic samples, we find that the thermal fluctuations effectively decrease the magnitude of the AF order by renormalizing the effective Hamiltonian. Our finding suggests that the insulating phase exhibits a gap narrowing at elevated temperatures, which leads to a substantial decrease in AMR. We also examine spatially correlated thermal fluctuations for microscopic samples by solving the microscopic Landau-Lifshitz-Gilbert equation finding a qualitative difference of the gap narrowing in the insulating phase. For both cases, the semimetallic phase shows a minimal change in its transmission spectrum illustrating the robustness of the symmetry protected states in AFS. Our finding may serve as a guideline for estimating and maximizing AMR of the AFS samples at elevated temperatures., 19 pages, 7 figures

An antiferromagnetic semimetal has been recently identified as a new member of topological semimetals that may host three-dimensional symmetry-protected Dirac fermions. A reorientation of the N\'{e}el vector may break the underlying symmetry and open a gap in the quasi-particle spectrum, inducing the (semi)metal-insulator transition. Here, we predict that such transition may be controlled by manipulating the chemical potential location of the material. We perform both analytical and numerical analysis on the thermodynamic potential of the model Hamiltonian and find that the gapped spectrum is preferred when the chemical potential is located at the Dirac point. As the chemical potential deviates from the Dirac point, the system shows a possible transition from the gapped to the gapless phase and switches the corresponding N\'{e}el vector configuration. We perform density functional theory calculations to verify our analysis using a realistic material and discuss a two terminal transport measurement as a possible route to identify the voltage induced switching of the N\'{e}el vector., Comment: 16 pages, 9 figures, the density functional theory calculation analysis (Section IV.D) has been modified

A new vertical tunnel FET design based on black phosphorus is presented in this paper adopting asymmetric layer numbers for top and bottom layer with undoped drain. The results show that the SS and I on /I off can be maintained below 10 mV/dec and beyond 105, respectively, when channel length is down to 3 nm.

We study the superconducting properties of the thin film BCS superconductor proximity coupled to a magnetically doped time-reversal invariant topological insulator (TI). Using mean-field theory, we show that Fulde-Ferrell (FF) pairing can be induced in the conventional superconductor through the inverse proximity effect (IPE). This occurs when the IPE of the TI to the superconductor is large enough that the normal bands of the superconductor possess a proximity induced spin-orbit coupling and magnetization. We find that the energetics of the different pairings are dependent on the coupling strength between the TI and the BCS superconductor and the thickness of the superconductor film. As the thickness of the superconductor film is increased, we find a crossover from the FF pairing to the BCS pairing phase. This is a consequence of the increased number of the superconducting bands, which favor the BCS pairing, implying that the FF phase can only be observed in the thin film limit. In addition, we also propose transport experiments that show distinct signatures of the FF phase.

Three-dimensional (3D) deformation of two-dimensional materials offers a route toward band structure engineering. In the case of graphene, a spatially nonuniform deformation and strain are known to generate an effective magnetic field, i.e., a pseudomagnetic field, although experimental realization of this effect in electronic devices has been challenging. Here, we engineer the 3D deformation profile of graphene to create a strain superlattice and study the resultant magnetotransport behavior both experimentally and via quantum transport simulations. We observe a weakening of superlattice features as we increase the magnetic field, which we find to be consistent with competing interactions between the external magnetic field and the strain-induced pseudomagnetic field. Our results demonstrate that strain superlattices are promising platforms to modulate the band structure and engineer the electronic transport behavior in graphene.Three-dimensional (3D) deformation of two-dimensional materials offers a route toward band structure engineering. In the case of graphene, a spatially nonuniform deformation and strain are known to generate an effective magnetic field, i.e., a pseudomagnetic field, although experimental realization of this effect in electronic devices has been challenging. Here, we engineer the 3D deformation profile of graphene to create a strain superlattice and study the resultant magnetotransport behavior both experimentally and via quantum transport simulations. We observe a weakening of superlattice features as we increase the magnetic field, which we find to be consistent with competing interactions between the external magnetic field and the strain-induced pseudomagnetic field. Our results demonstrate that strain superlattices are promising platforms to modulate the band structure and engineer the electronic transport behavior in graphene.

As a promising candidate system to realize topological superconductivity, the system of a 3D topological insulator (TI) grown on top of the $s$-wave superconductor has been extensively studied. To access the topological superconductivity experimentally, the 3D TI sample must be thin enough to allow for Cooper pair tunneling to the exposed surface of TI. The use of magnetically ordered dopants to break time-reversal symmetry may allow the surface of a TI to host Majorana fermion, which are believed to be a signature of topological superconductivity. In this work, we study a magnetically-doped thin film TI-superconductor hybrid system. Considering the proximity induced order parameter in thin film of TI, we analyze the gap closing points of the Hamiltonian and draw the phase diagram as a function of relevant parameters: the hybridization gap, Zeeman energy, and chemical potential of the TI system. Our findings provide a useful guide in choosing relevant parameters to facilitate the observation of topological superconductivity in thin film TI-superconductor hybrid systems. In addition, we further perform numerical analysis on a TI proximity coupled to an $s$-wave superconductor and find that, due to the spin-momentum locked nature of the surface states in TI, the induced $s$-wave order parameter of the surface states persists even at large magnitude of the Zeeman energy.

Unconventional superconductivity has been predicted to arise in the topologically non-trivial Fermi surface of doped inversion symmetric Weyl semimetals (WSM). In particular, Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and nodal BCS states are theoretically predicted to be possible superconductor pairing states in inversion symmetric doped WSM. In an effort to resolve preferred pairing state, we theoretically study two separate four terminal quantum transport methods that each exhibit a unique electrical signature in the presence of FFLO and nodal BCS states in doped WSMs. We first introduce a Josephson junction that consists of a doped WSM and an s-wave superconductor in which we show that the application of a transverse uniform current in s-wave superconductor effectively cancels the momentum carried by FFLO states in doped WSM. From our numerical analysis, we find a peak in Josephson current amplitude at finite uniform current in s-wave superconductor that serves as an indicator of FFLO states in doped WSMs. Furthermore, we show using a four terminal measurement configuration that the nodal points may be shifted by an application of transverse uniform current in doped WSM. We analyze the topological phase transitions induced by nodal pair annihilation in non-equilibrium by constructing the phase diagram and we find a characteristic decrease in the density of states that serves as a signature of the quantum critical point in the topological phase transition, thereby identifying nodal BCS states in doped WSM., 8 pages, 4 figures (5 pages, 2 figures for supplementary material)

Correction to:NPG Asia Materials (2018) 10.1038/s41427-018-0014-9 published online on 16 April 2018

Colloidal glasses, bird feathers, and beetle scales can all show structural colors arising from short-ranged spatial correlations between scattering centers. Unlike the structural colors arising from Bragg diffraction in ordered materials like opals, the colors of these photonic glasses are independent of orientation, owing to their disordered, isotropic microstructures. However, there are few examples of photonic glasses with angle-independent red colors in nature, and colloidal glasses with particle sizes chosen to yield structural colors in the red show weak color saturation. Using scattering theory, we show that the absence of angle-independent red color can be explained by the tendency of individual particles to backscatter light more strongly in the blue. We discuss how the backscattering resonances of individual particles arise from cavity-like modes, and how they interact with the structural resonances to prevent red. Finally, we use the model to develop design rules for colloidal glasses with red, angle-independent structural colors., 8 pages, 9 figures

We present a new type of hydrogel photonic crystal with a stop band that can be rapidly modulated across the entire visible spectrum. We make these materials by using a high-molecular-weight polymer to induce a depletion attraction between polystyrene-poly(N-isopropylacrylamide-co-bisacrylamide-co-acrylic acid) core-shell particles. The resulting crystals display a stop band at visible wavelengths that can be tuned with temperature at a rate of 60 nm/s, nearly three orders of magnitude faster than previous photonic-crystal hydrogels. Above a critical concentration of depleting agent, the crystals do not melt even at 40 degrees Celsius. As a result, the stop band can be modulated continuously from red (650 nm) to blue (450 nm), with nearly constant reflectivity throughout the visible spectrum. The unusual thermal stability is due to the polymer used as the depleting agent, which is too large to enter the hydrogel mesh and therefore induces a large osmotic pressure that holds the particles together. The fast response rate is due to the collective diffusion coefficient of our hydrogel shells, which is more than three orders of magnitude larger than that of conventional bulk hydrogels. Finally, the constant reflectivity from red (650 nm) to blue (450 nm) is due to the core-shell design of the particles, whose scattering is dominated by the polystyrene cores and not the hydrogel. These findings provide new insights into the design of responsive photonic crystals for display applications and tunable lasers.

We use self-consistent quantum transport theory to investigate the influence of electron-electron interactions on interlayer transport in semiconductor electron bilayers in the absence of an external magnetic field. We conclude that, even though spontaneous pseudospin order does not occur at zero field, interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer torques do alter tunneling I-V characteristics, and can lead to time-dependent response to a dc bias voltage., 9 pages, 7 figures

We study the effects of disorder on the interlayer transport properties of disordered semiconductor bilayers outside of the quantum Hall regime by performing self-consistent quantum transport calculations. We find that the addition of material disorder to the system affects interlayer interactions leading to significant deviations in the interlayer transfer characteristics. In particular, we find that disorder decreases and broadens the tunneling peak, effectively reducing the interacting system to the non-interacting system, when the mean-free path for the electrons becomes shorter than the system length. Our results suggest that the experimental observation of exchange-enhanced interlayer transport in semiconductor bilayers requires materials with mean-free paths larger than the spatial extent of the system., Comment: 4 pages, 3 figures