One big achievement in modern condensed matter physics is the recognition of the importance of various band geometric quantities in physical effects. As prominent examples, Berry curvature and Berry curvature dipole are connected to the linear and the second-order Hall effects, respectively. Here, we show that the Berry connection polarizability (BCP) tensor, as another intrinsic band geometric quantity, plays a key role in the third-order Hall effect. Based on the extended semiclassical formalism, we develop a theory for the third-order charge transport and derive explicit formulas for the third-order conductivity. Our theory is applied to the two-dimensional (2D) Dirac model to investigate the essential features of BCP and the third-order Hall response. We further demonstrate the combination of our theory with the first-principles calculations to study a concrete material system, the monolayer FeSe. Our work establishes a foundation for the study of third-order transport effects, and reveals the third-order Hall effect as a tool for characterizing a large class of materials and for probing the BCP in band structure.

Unconventional Weyl points (WPs), carrying topological charge 2 or higher, possess interesting properties different from ordinary charge-1 WPs, including multiple Fermi arcs that stretch over a large portion of the Brillouin zone. Thus far, such WPs have been observed in chiral materials and acoustic metamaterials, but there has been no clean demonstration in photonics in which the unconventional photonic WPs are separated from trivial bands. We experimentally realize an ideal symmetry-protected photonic charge-2 WP in a three-dimensional topological chiral microwave metamaterial. We use field mapping to directly observe the projected bulk dispersion, as well as the two long surface arcs that form a noncontractible loop wrapping around the surface Brillouin zone. The surface states span a record-wide frequency window of around 22.7% relative bandwidth. We demonstrate that the surface states exhibit a novel topological self-collimation property and are robust against disorder. This work provides an ideal photonic platform for exploring fundamental physics and applications of unconventional WPs.

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Computer vision has achieved impressive progress in recent years. Meanwhile, mobile phones have become the primary computing platforms for millions of people. In addition to mobile phones, many autonomous systems rely on visual data for making decisions and some of these systems have limited energy (such as unmanned aerial vehicles also called drones and mobile robots). These systems rely on batteries and energy efficiency is critical. This article serves two main purposes: (1) Examine the state-of-the-art for low-power solutions to detect objects in images. Since 2015, the IEEE Annual International Low-Power Image Recognition Challenge (LPIRC) has been held to identify the most energy-efficient computer vision solutions. This article summarizes 2018 winners' solutions. (2) Suggest directions for research as well as opportunities for low-power computer vision.

Topological orders and associated topological protected excitations satisfying non-Abelian statistics have been widely explored in various platforms. The Z3 parafermions are regarded as the most natural generation of the Majorana fermions to realize these topological orders. Here we investigate the topological phase and emergent Z2 spin phases in an extended parafermion chain. This model exhibits rich variety of phases, including not only topological ferromagnetic phase, which supports non-Abelian anyon excitation, but also spin-fluid, dimer and chiral phases from the emergent Z2 spin model. We generalize the measurement tools in Z2 spin models to fully characterize these phases in the extended parafermion model and map out the corresponding phase diagram. Surprisingly, we find that all the phase boundaries finally merge to a single supercritical point. In regarding of the rather generality of emergent phenomena in parafermion models, this approach opens a wide range of intriguing applications in investigating the exotic phases in other parafermion models.Topological orders have been one of the major concerns in modern physics due to their potential realization of non-Abelian anyons for topological quantum computation [1,2]. Along this line, the Majorana zero modes have been realized in experiments in semiconductor/topological insulator and superconductor hybrid structures [3][4][5][6][7][8]. This approach may be directly generalized to Z k parafermion[9-13] (with k = 2 for Majorana fermions) with k-fold ground state degeneracy, following the pioneering work by Fendley [14][15][16]. In these phases, the Z 3 parafermion model is most intriguing due to its potential construction of Fibonacci anyons [17][18][19][20][21][22] for universal quantum computation. Recently, these parafermions are proposed to be constructed in semiconductor and fractional quantum Hall state hybrid structures [17,20,21,23,24].In this work, we explore the emergent phenomena in the parafermion models. We consider an extended parafermion Z 3 model, which is mapped to a Z 3 clock model with next nearest neighboring (NNN) interaction. In the presence of strong Zeeman field, the clock model can be projected to a conventional Z 2 spin model, giving rise to emergent spin-fluid (SF), dimer and chiral phases. This model exhibits rich variety of phases, which are characterized using various tools directly generalized from Z 2 spin models. We map out the whole phase diagram and find that the topological ferromagnetic parafermion (FP) phase is greatly enhanced in the presence of ferromagnetic interaction between NNN sites. Strikingly, all the phase boundaries finally merge to a single supercritical (SC) point. This approach lays foundation for understanding exotic phases in other parafermion models.Model and Hamiltonian. We consider the following extended Z 3 parafermion chains,wherewith ω = e i2π/3 and α j are parafermions satisfying α 3 j = 1, α † j = α 2 j and α i α j = α j α i ω sgn(i−j) , J and h correspond to the pairings -0.5 0.5 Dimer SF Topolog...