Evolution of 4π-Periodic Supercurrent in the Presence of an In-Plane Magnetic Field.

In the presence of a 4π-periodic contribution to the current phase relation, for example in topological Josephson junctions, odd Shapiro steps are expected to be missing. While missing odd Shapiro steps have been observed in several material systems and interpreted in the context of topological superconductivity, they have also been observed in topologically trivial junctions. Here, we study the evolution of such trivial missing odd Shapiro steps in Al-InAs junctions in the presence of an in-plane magnetic field Bθ. We find that the odd steps reappear at a crossover Bθ value, exhibiting an in-plane field angle anisotropy that depends on spin-orbit coupling effects. We interpret this behavior by theoretically analyzing the Andreev bound state spectrum and the transitions induced by the nonadiabatic dynamics of the junction and attribute the observed anisotropy to mode-to-mode coupling. Our results highlight the complex phenomenology of missing Shapiro steps and the underlying current phase relations in planar Josephson junctions designed to realize Majorana states.

Local Control of Supercurrent Density in Epitaxial Planar Josephson Junctions.

The critical current response to an applied out-of-plane magnetic field in a Josephson junction provides insight into the uniformity of its current distribution. In Josephson junctions with semiconducting weak links, the carrier density, and therefore the overall current distribution, can be modified electrostatically via metallic gates. Here, we show local control of the current distribution in an epitaxial Al-InAs Josephson junction equipped with five minigates. We demonstrate that not only can the junction width be electrostatically defined but also the current profile can be locally adjusted to form superconducting quantum interference devices. Our studies show enhanced edge conduction in such long junctions, which can be eliminated by minigates to create a uniform current distribution.

Quantum Interferences in Ultraclean Carbon Nanotubes.

Electronic analogs of optical interferences are powerful tools to investigate quantum phenomena in condensed matter. In carbon nanotubes (CNTs), it is well established that an electronic Fabry-Perot interferometer can be realized. Other types of quantum interferences should also arise in CNTs, but have proven challenging to realize. In particular, CNTs have been identified as a system to realize the electronic analog of a Sagnac interferometer-the most sensitive optical interferometer. To realize this Sagnac effect, interference between nonidentical transmission channels in a single CNT must be observed. Here, we use suspended, ultraclean CNTs of known chiral index to study both Fabry-Perot and Sagnac electron interferences. We verify theoretical predictions for the behavior of Sagnac oscillations and the persistence of the Sagnac oscillations at high temperatures. As suggested by existing theoretical studies, our results show that these quantum interferences may be used for electronic structure characterization of carbon nanotubes and the study of many-body effects in these model one-dimensional systems.

Band-Gap-Dependent Electronic Compressibility of Carbon Nanotubes in the Wigner Crystal Regime.

Electronic compressibility, the second derivative of ground-state energy with respect to total electron number, is a measurable quantity that reveals the interaction strength of a system and can be used to characterize the orderly crystalline lattice of electrons known as the Wigner crystal. Here, we measure the electronic compressibility of individual suspended ultraclean carbon nanotubes in the low-density Wigner crystal regime. Using low-temperature quantum transport measurements, we determine the compressibility as a function of carrier number in nanotubes with varying band gaps. We observe two qualitatively different trends in compressibility versus carrier number, both of which can be explained using a theoretical model of a Wigner crystal that accounts for both the band gap and the confining potential experienced by charge carriers. We extract the interaction strength as a function of carrier number for individual nanotubes and show that the compressibility can be used to distinguish between strongly and weakly interacting regimes.

Manifestation of Kinetic Inductance in Terahertz Plasmon Resonances in Thin-Film Cd3As2.

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with their linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, Cd3As2 has shown ultrahigh mobility and large Fermi velocity and has been hypothesized to support plasmons at terahertz frequencies. In this work, we experimentally demonstrate synthesis of high-quality large-area Cd3As2 thin films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodic arrays of Cd3As2 stripes. These arrays exhibit sharp resonances at terahertz frequencies with associated quality factors ( Q) as high as ∼3.7 (at 0.82 THz). Such spectrally narrow resonances can be understood on the basis of a long momentum scattering time, which in our films can approach ∼1 ps at room temperature. Moreover, we demonstrate an ultrafast tunable response through excitation of photoinduced carriers in optical pump/terahertz probe experiments. Our results evidence that the intrinsic 3D nature of Cd3As2 might provide for a very robust platform for terahertz plasmonic applications. Moreover, the long momentum scattering time as well as large kinetic inductance in Cd3As2 also holds enormous potential for the redesign of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits.

Colorimetric sensing of oxalate based on its inhibitory effect on the reaction of Fe (III) with curcumin nanoparticles.

In this research, a new colorimetric method for the determination of oxalate using curcumin nanoparticles (CURNs) in the presence Fe (III) is introduced. The method is based on the inhibitory effect of oxalate ion on the reaction of (CURNs) with Fe (III) in acidic media. This reaction was monitored by measuring the increase in absorbance of CURNs-Fe3+ complex in the presence of oxalate ion at 427nm. The effect of different parameters such as the pH of the sample solution, concentration of Fe (III), concentration of CURNs and the reaction time was examined and optimized. Under optimum experimental conditions, the absorption intensity was linear with the concentration of oxalate in the range of 0.15 to 1.70µgmL-1. The limit of detection (LOD) was 0.077µgmL-1 and the relative standard deviations (RSD) for 8 replicate measurements of 0.40 and 1.05µgmL-1 of oxalate were 4.20% and 2.74%, respectively. The developed method was successfully employed to the determination of oxalate in water, food and urine samples with satisfactory results.

Hexaaminobenzene as a building block for a Family of 2D Coordination Polymers.

A family of 2D coordination polymers were successfully synthesized through "bottom-up" techniques using Ni2+, Cu2+, Co2+, and hexaaminobenzene. Liquid-liquid and air-liquid interfacial reactions were used to realize thick (∼1-2 µm) and thin (<10 nm) stacked layers of nanosheet, respectively. Atomic-force microscopy and scanning electron microscopy both revealed the smooth and flat nature of the nanosheets. Selected area diffraction was used to elucidate the hexagonal crystal structure of the framework. Electronic devices were fabricated on thin samples of the Ni analogue and they were found to be mildly conducting and also showed back gate dependent conductance.