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Arnold Fege, President of the Public Advocacy for Kids nonprofit, reflects on what it takes to create equity and reimagine schooling in rural communities after COVID-19. His article centers around five questions: unpacking the United States' political will to resolve internet inequality; examining organizational changes needed to wholly care for students; identifying effective strategies to retain educators; looking to the relationship between federal funding and success in rural education; and predicting the role of state education agencies in providing school resources.

The noncentrosymmetric transition metal monopnictides NbP, TaP, NbAs and TaAs are a family of Weyl semimetals in which pairs of protected linear crossings of spin-resolved bands occur. These so-called Weyl nodes are characterized by integer topological charges of opposite sign associated with singular points of Berry curvature in momentum space. In such a system anomalous magnetoelectric responses are predicted, which should only occur if the crossing points are close to the Fermi level and enclosed by Fermi surface pockets penetrated by an integer flux of Berry curvature, dubbed Weyl pockets. TaAs was shown to possess Weyl pockets whereas TaP and NbP have trivial pockets enclosing zero net flux of Berry curvature. Here, via measurements of the magnetic torque, resistivity and magnetisation, we present a comprehensive quantum oscillation study of NbAs, the last member of this family where the precise shape and nature of the Fermi surface pockets is still unknown. We detect six distinct frequency branches, two of which have not been observed before. A comparison to density functional theory calculations suggests that the two largest pockets are topologically trivial, whereas the low frequencies might stem from tiny Weyl pockets. The enclosed Weyl nodes are within a few meV of the Fermi energy.

The delafossite series of layered oxides include some of the highest conductivity metals ever discovered. Of these, PtCoO2, with a room temperature resistivity of 1.8 microOhmcm for in-plane transport, is the most conducting of all. The high conduction takes place in triangular lattice Pt layers, separated by layers of Co-O octahedra, and the electronic structure is determined by the interplay of the two types of layer. We present a detailed study of quantum oscillations in PtCoO2, at temperatures down to 35 mK and magnetic fields up to 30 T. As for PdCoO2 and PdRhO2, the Fermi surface consists of a single cylinder with mainly Pt character, and an effective mass close to the free electron value. Due to Fermi-surface warping, two close-lying high frequencies are observed. Additionally, a pronounced difference frequency appears. By analysing the detailed angular dependence of the quantum-oscillation frequencies, we establish the warping parameters of the Fermi surface. We compare these results to the predictions of first-principles electronic structure calculations including spin-orbit coupling on Pt and Co and on-site correlation U on Co, and hence demonstrate that electronic correlations in the Co-O layers play an important role in determining characteristic features of the electronic structure of PtCoO2.

Weyl semimetals such as the TaAs family (TaAs, TaP, NbAs, NbP) host quasiparticle excitations resembling the long sought after Weyl fermions at special band-crossing points in the band structure denoted as Weyl nodes. They are predicted to exhibit a negative longitudinal magnetoresistance (LMR) due to the chiral anomaly if the Fermi energy is sufficiently close to the Weyl points. However, current jetting effects, i.e. current inhomogeneities caused by a strong, field-induced conductivity anisotropy in semimetals, have a similar experimental signature and therefore have hindered a determination of the intrinsic LMR in the TaAs family so far. This work investigates the longitudinal magnetoresistance of all four members of this family along the crystallographic $a$ and $c$ direction. Our samples are of similar quality as those previously studied in the literature and have a similar chemical potential as indicated by matching quantum oscillation (QO) frequencies. Care was taken to ensure homogeneous currents in all measurements. As opposed to previous studies where this was not done, we find a positive LMR that saturates in fields above 4 T in TaP, NbP and NbAs for $B||c$. Using Fermi-surface geometries from band structure calculations that had been confirmed by experiment, we show that this is the behaviour expected from a classical purely orbital effect, independent on the distance of the Weyl node to the Fermi energy. The TaAs family of compounds is the first to show such a simple LMR without apparent influences of scattering anisotropy. In configurations where the orbital effect is small, i.e. for $B||a$ in NbAs and NbP, we find a non-monotonous LMR including regions of negative LMR. We discuss a weak antilocalisation scenario as an alternative interpretation than the chiral anomaly for these results, since it can fully account for the overall field dependence.

Using angle-resolved photoelectron spectroscopy, we compare the electronic band structure of an ultrathin (1.8 nm) {\delta}-layer of boron-doped diamond with a bulk-like boron doped diamond film (3 {\mu}m). Surprisingly, the measurements indicate that except for a small change in the effective mass, there is no significant difference between the electronic structure of these samples, irrespective of their physical dimensionality. While this suggests that, at the current time, it is not possible to fabricate boron-doped diamond structures with quantum properties, it also means that nanoscale doped diamond structures can be fabricated which retain the classical electronic properties of bulk-doped diamond, without a need to consider the influence of quantum confinement., Comment: 7 pages, 4 figures. please contact the corresponding author to access the supplementary material

Unusual behavior of quantum materials commonly arises from their effective low-dimensional physics, which reflects the underlying anisotropy in the spin and charge degrees of freedom. Torque magnetometry is a highly sensitive technique to directly quantify the anisotropy in quantum materials, such as the layered high-T$_c$ superconductors, anisotropic quantum spin-liquids, and the surface states of topological insulators. Here we introduce the magnetotropic coefficient $k=\partial^2 F/\partial \theta^2$, the second derivative of the free energy F with respect to the angle $\theta$ between the sample and the applied magnetic field, and report a simple and effective method to experimentally detect it. A sub-$\mu$g crystallite is placed at the tip of a commercially available atomic force microscopy cantilever, and we show that $k$ can be quantitatively inferred from a shift in the resonant frequency under magnetic field. While related to the magnetic torque $\tau=\partial F/\partial \theta$, $k$ takes the role of torque susceptibility, and thus provides distinct insights into anisotropic materials akin to the difference between magnetization and magnetic susceptibility. The thermodynamic coefficient $k$ is discontinuous at second-order phase transitions and subject to Ehrenfest relations with the specific heat and magnetic susceptibility. We apply this simple yet quantitative method on the exemplary cases of the Weyl-semimetal NbP and the spin-liquid candidate RuCl$_3$, yet it is broadly applicable in quantum materials research., Comment: 7 pages including 6 figures and methods section

Recently, the existence of massless chiral (Weyl) fermions has been postulated in a class of semi-metals with a non-trivial energy dispersion.These materials are now commonly dubbed Weyl semi-metals (WSM).One predicted property of Weyl fermions is the chiral or Adler-Bell-Jackiw anomaly, a chirality imbalance in the presence of parallel magnetic and electric fields. In WSM, it is expected to induce a negative longitudinal magnetoresistance (NMR), the chiral magnetic effect.Here, we present experimental evidence that the observation of the chiral magnetic effect can be hindered by an effect called "current jetting". This effect also leads to a strong apparent NMR, but it is characterized by a highly non-uniform current distribution inside the sample. It appears in materials possessing a large field-induced anisotropy of the resistivity tensor, such as almost compensated high-mobility semimetals due to the orbital effect.In case of a non-homogeneous current injection, the potential distribution is strongly distorted in the sample.As a consequence, an experimentally measured potential difference is not proportional to the intrinsic resistance.Our results on the MR of the WSM candidate materials NbP, NbAs, TaAs, TaP exhibit distinct signatures of an inhomogeneous current distribution, such as a field-induced "zero resistance' and a strong dependence of the `measured resistance" on the position, shape, and type of the voltage and current contacts on the sample. A misalignment between the current and the magnetic-field directions can even induce a "negative resistance". Finite-element simulations of the potential distribution inside the sample, using typical resistance anisotropies, are in good agreement with the experimental findings. Our study demonstrates that great care must be taken before interpreting measurements of a NMR as evidence for the chiral anomaly in putative Weyl semimetals., Comment: 13 pages, 6 figures

Are the nation's 90,000-plus school board members critical players in enhancing student learning? Are they part of the problem? Are they harmless bystanders? Among the takeaways are the following: (1) Board members, by and large, possess accurate information about their districts when it comes to finance, teacher pay, collective bargaining, and class size. Whether they were knowledgeable from the outset or surround themselves with savvy staff and administrators, many are making decisions from an informed point of view. (2) Such knowledge is not uniformly distributed. Surprisingly, members who were never educators themselves are more accurately informed than their peers who once were (or still are) educators. Likewise, political moderates appear to have more accurate knowledge than their liberal or conservative counterparts. (3) A district's success in "beating the odds" academically is related to board members' focus on the improvement of academics. Unfortunately, not all board members have this focus; some prefer a broader approach, such as developing the "whole child." (4) Board members elected during on-cycle, at-large elections are more likely to serve in districts that "beat the odds" than those chosen by voters off-cycle or by ward. In some localities, how board members are elected may deter the best and brightest from taking on these key roles. What does this mean for education governance? School board members and their attitudes do matter--so it's important to take seriously who gets elected and how. Even as we strive to bring about structural reforms and governance innovations in the education system, we should also be working to get better results from the structures in place in most communities today. Those interested in the details of the methodology of this report are encouraged to consult the Appendix. [The foreword and summary for this report were written by Dara Zeehandelaar and Amber M. Northern.]

Understanding the role of electron correlations in strong spin-orbit transition-metal oxides is key to the realisation of numerous exotic phases including spin-orbit assisted Mott insulators, correlated topological solids, and prospective new high-temperature superconductors. To date, most attention has been focussed on the $5d$ iridium-based oxides. Here, we instead consider the Pt-based delafossite oxide PtCoO$_2$. Our transport measurements, performed on single-crystal samples etched to well-defined geometries using focussed ion-beam techniques, yield a room-temperature resistivity of only 2.1~$\mu\Omega$cm, establishing PtCoO$_2$ as the most conductive oxide known. From angle-resolved photoemission and density-functional theory, we show that the underlying Fermi surface is a single cylinder of nearly hexagonal cross-section, with very weak dispersion along k$_z$. Despite being predominantly composed of $d$-orbital character, the conduction band is remarkably steep, with an average effective mass of only 1.14$m_e$. Moreover, the sharp spectral features observed in photoemission remain well-defined with little additional broadening for over 500~meV below E$_F$, pointing to suppressed electron-electron scattering. Together, our findings establish PtCoO$_2$ as a model nearly-free electron system in a $5d$ delafossite transition-metal oxide., Comment: Accepted in Science Advances. arXiv admin note: text overlap with arXiv:1411.6162

Graphite is a model system for the study of three-dimensional electrons and holes in the magnetic quantum limit, in which the charges are confined to the lowest Landau levels. We report magneto-transport measurements in pulsed magnetic fields up to 60 T, which resolve the collapse of two density wave states in two, electron and hole, Landau levels at 52.3 and 54.2 T respectively. We report evidence for a commensurate density wave at 47.1 T in the electron Landau level. The theoretical modelling of these results predicts that the ultra-quantum limit is entered above 73.5 T. This state is an insulator, and we discuss its correspondence to the "metallic" state reported earlier. We propose that this (interaction-induced) insulating phase supports surface states that carry no charge or spin within the planes, but does however support charge transport out of plane.

The concept of "teacher quality" has undergone a profound transformation in the last decade. Through the late 1990s, most policymakers assumed that educator effectiveness was immeasurable and that our only hopes to increase it were tied to classroom experience and academic credentials. Yet since 2001, through a series of notable research findings, changing political pressures, and landmark policy changes, we have come to view teacher quality as independent of licensure and individually measurable. We now approach evaluating the quality of our teachers by measuring their ongoing performance in the classroom. The key markers in the transformation: (1) Declining trust in teacher education: Data from the Higher Education Act of 1998 showed that teacher education programs graduated students of widely variable ability; (2) Ineffective credential requirements: Despite federal requirements for high-quality teachers, by 2006, students in high-poverty schools were still more likely to have lower-quality teachers than their peers in other schools; (3) Bipartisan agreement: By 2009, major federal politicians in both political parties, including Democratic politicians heavily supported by unions, agreed that low teacher quality was a barrier to high-quality education; and (4) New era of measurement: No Child Left Behind created a treasure trove of individual student data that, though imperfect in many ways, led to new opportunities for research to link teachers and students. No consensus has emerged about how to improve teacher quality, but policymakers continue to experiment with teacher preparation programs, recruitment incentives, tenure provisions, and differential pay. (Contains 71 notes.)

This paper analyzes charter school state laws in terms of two general dimensions: (1) the flexibility, freedom, and support extended in the law; and (2) the degree of public accountability required of charter schools. The paper proposes a much more complex set of analyses of those laws than have been accomplished to date. After analyzing the empirical properties of the subscales, it briefly compares them to the widely used Center for Education Reform scale. It estimates which state characteristics appear to best predict flexibility and accountability. The paper examines the relationship between variance in laws, other independent variables and the number of charter schools established in a state. It finds that flexibility in laws along multiple dimensions is also highly correlated with high levels of required public accountability. It finds, however, a number of interesting relationships between the number of charters existing in states and the nature of their laws, as well as other demographic and political factors. Appended is sample item coding. (Contains 24 references, 18 notes, 7 tables, and 3 figures.) (Author/BT)