This paper presents a tunable active bandpass filter with bandwidth-adjustable notches close to the passband for wideband blocker suppression with high attenuation. The proposed filter is composed of a 3-pole N-path bandstop filter in cascade with an N-path bandpass filter, where the center frequency of the bandpass filter is offset from the bandstop filters. With proper tuning of the coupling capacitors in the bandstop filter, three adjacent notches can be created which provides a larger suppression bandwidth. An implementation of the filter in 65-nm CMOS exhibits a passband tunable between 0.1-1.1 GHz, with a 3-dB bandwidth of 12.4-14.2 MHz, a gain of 9.5-10.3 dB, a noise figure of 4.3-5.8 dB, and a total power consumption of 40-64.3 mW. The blocker 1-dB compression point is 6.5 dBm and the out-of-band IIP3 is 18.4 dBm. The reported filter provides a promising solution to multi-standard, multi-frequency software-defined radio applications.

The search for topological phases of matter is evolving towards strongly interacting systems, including magnets and superconductors, where exotic effects emerge from the quantum-level interplay between geometry, correlation and topology. Over the past decade or so, scanning tunnelling microscopy has become a powerful tool to probe and discover emergent topological matter, because of its unprecedented spatial resolution, high-precision electronic detection and magnetic tunability. Scanning tunnelling microscopy can be used to probe various topological phenomena, as well as complement results from other techniques. We discuss some of these proof-of-principle methodologies applied to probe topology, with particular attention to studies performed under a tunable vector magnetic field, which is a relatively new direction of recent focus. We then project the future possibilities for atomic-resolution tunnelling methods in providing new insights into topological matter.

This paper presents a tunable active bandpass filter (BPF) with adjustable transmission zeros (TZs) close to the passband for software-defined radio (SDR) applications. The RF front-end frequency selectivity is enhanced by the creation of TZs that also improve the out-of-band (OOB) input-referred third-order intercept point (IIP3). The filter is based on two-path signal cancellation and consists of a tunable BPF in parallel with two tunable bandstop filters. This combination ensures the correct amplitude and phase relationships across a wide tuning range to create adjustable TZs without sacrificing the gain of the passband. This paper presents in detail the design considerations and guidelines, as well as analysis of the filter performance in the presence of nonidealities such as parasitics and imperfect clock signal shape. The proposed filter is implemented with high-Q N-path filter blocks in a 65-nm CMOS process. The passband of the filter is tunable from 0.1 to 1.4 GHz with a 3-dB bandwidth of 9.8-10.2 MHz, a gain of 21.5-24 dB, a noise figure of 3-4.2 dB, and a total power consumption of 50-73 mW. TZs are created on both sides of the passband with a minimal offset of 25 MHz and are tunable across a 20-MHz range with up to a 60-dB rejection. The measured blocker 1-dB compression point is 8 dBm and the OOB IIP3 is 23 dBm. The reported filter provides a promising on-chip filtering solution for multistandard multifrequency SDR applications with improved interference mitigation capabilities.

This paper presents a tunable active bandpass filter with adjustable notch close to the passband for blocker rejection. The proposed filter is based on two-path signal cancellation and consists of a top-C coupled tunable bandpass filter in parallel with an inductor. The proposed filter is implemented with high-Q N-path filter/resonator blocks in 65-nm CMOS process. The passband of the filter is tunable from 0.4 GHz to 2.2 GHz with a 3-dB bandwidth of 14.4-15.6 MHz, an insertion loss of 3.6-5.8 dB, a noise figure of 3.8-6 dB, and a total power consumption of 12.4-42 mW. Transmission zero is created close to the passband with a minimal offset of 40 MHz and are tunable across a 25 MHz range with up to 54 dB rejection. The blocker 1-dB compression point is 8.5 dBm and the out-of-band IIP3 is 23.5 dBm. The proposed filter provides a promising solution to multi-standard, multi-frequency software-defined radio applications.

We investigate the dynamics and site-selectivity in the dissociation of transient anions formed upon attachment of low energy electrons to acetic acid by anion fragment momentum imaging experiments. The resonances at 6.7 and 7.7 eV are confirmed to dissociate exclusively by the O-H bond, while a third resonance at 9.1 eV dissociates primarily by both C-H break and O-H break. A fourth resonance near 10 eV is found to dissociate by O-H break. For each resonance, the measured kinetic energy release indicates two-body dissociation produces a neutral radical in the ground electronic state, for all four resonances. The measured angular distributions are consistent with all four resonances having A' symmetry.

A Weyl semimetal has Weyl nodes that always come in pairs with opposite chiralities. Notably, different ways of connection between nodes are possible and would lead to distinct topologies. Here we identify their differences in many respects from two proposed models with different vorticities. One prominent feature is the behaviour of zeroth Landau levels (LLs) under magnetic field. We demonstrate that the magnetic tunneling does not always expel LLs from zero energy because the number of zero-energy modes is protected by the vorticity of the Weyl nodes, instead of the chirality. Other respects in disorder effects for weak (anti-)localization, surface Fermi arcs, and Weyl-node annihilation, are interesting consequences that await more investigation in the future.

Quantum materials hosting Weyl fermions have opened a new era of research in condensed matter physics. First proposed in 1929 in the context of particle physics, Weyl fermions have yet to be observed as elementary particles. In 2015, Weyl fermions were detected as collective electronic excitations in the strong spin–orbit coupled material tantalum arsenide, TaAs. This discovery was followed by a flurry of experimental and theoretical explorations of Weyl phenomena in materials. Weyl materials naturally lend themselves to the exploration of the topological index associated with Weyl fermions and their divergent Berry curvature field, as well as the topological bulk–boundary correspondence, giving rise to protected conducting surface states. Here, we review the broader class of Weyl topological phenomena in materials, starting with the observation of emergent Weyl fermions in the bulk and Fermi arc states on the surface of the TaAs family of crystals by photoemission spectroscopy. We then discuss several exotic optical and magnetic responses observed in these materials, as well as progress in developing related chiral materials. We discuss the conceptual development of high-fold chiral fermions, which generalize Weyl fermions, and we review the observation of high-fold chiral fermion phases by taking the rhodium silicide, RhSi, family of crystals as a prime example. Lastly, we discuss recent advances in Weyl line phases in magnetic topological materials. With this Review, we aim to provide an introduction to the basic concepts underlying Weyl physics in condensed matter, and to representative materials and their electronic structures and topology as revealed by spectroscopic studies. We hope this work serves as a guide for future theoretical and experimental explorations of chiral fermions and related topological quantum systems with potentially enhanced functionalities.

In this paper, an adaptive N-path filter design technique is presented. The filter designed by this method can be reconfigured to different shapes, e.g., Butterworth or Chebyshev with variable bandwidth (BW), based on the user requirements. In addition, an analytical synthesis procedure is introduced to realize high-order bandpass filters (BPFs) based on N-path architecture with a prescribed set of specifications. A proof-of-concept BPF is fabricated and measured in a 65-nm CMOS process. The filter can be reconfigured to realize different filter shapes by changing coupling capacitors. The BW of the proposed filter is also tunable. The passband of the filter is tunable from 0.2 to 1.2 GHz with a gain of 14.5-18 dB, a noise figure of 3.7-5.5 dB, and a total power consumption of 37.5-52.7 mW. The channel BW can be varied from 20 to 40 MHz and the filter out-of-band third-order intercept point (Δ f=50 MHz) is 25 dBm.

In this paper, we have experimentally investigated the theoretical predictions of VO-Zni to be a native donor in ZnO. Intrinsically zinc-rich n-type ZnO thin films having ND ∼ 6.23 × 1018 cm-3 grown by molecular beam epitaxy on Si (0 0 1) substrate were annealed in oxygen environment at 500-800 °C, keeping a step of 100 °C for 1 h, each. Room temperature Hall measurements demonstrated that free donor (VO-Zni) concentration decreased exponentially and Arrhenius plot yielded activation energy to be 1.2 ± 0.01 eV. This value is in agreement with theoretically reported activation energy of VO-Zni donor complex in ZnO. We argue; this observation can be explained by two-step process: (i) incoming oxygen fills VO of VO-Zni complex leaving behind Zni; (ii) Zni releases its energy and moves to a lower energy state with respect to the conduction band minima and/or occupies an inactive location. Consequently, Zni-VO complex loses its donor role in the lattice. Our experimental data supported theoretical predictions of VO-Zni to be a native donor. Results from photoluminescence spectroscopy carried out on Zn-rich ZnO additionally justify the existence of VO-Zni complex. © 2013 IOP Publishing Ltd.