Our study reveals the emergence of ferroelectricity induced by incommensurate spin orders in the magnetic sulfide $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{S}}_4$, which has a $\mathrm{Hg}{\mathrm{Bi}}_2{\mathrm{S}}_4$-type centrosymmetric monoclinic structure ($C2/m$). This compound reveals multiple magnetic transitions at $T_{\mathrm{N}1}=27\mathrm{K}, T_{\mathrm{N}2}=23\mathrm{K}$, and $T_{\mathrm{N}3}=21.5\mathrm{K}$, associated with three distinct incommensurate spin structures (ICM1, ICM2, and ICM3). ICM1 is described as an antiferromagnetic spin density wave with an incommensurate modulation vector ${\mathit{k}}_1=\left(0,\beta ,\frac{1}{2}\right)$ and magnetic superspace group $C\overline{1}.1{}^{\prime }\left(\alpha ,\beta ,\gamma \right)0s$. While ICM2 has a similar propagation vector as ICM1, pyrocurrent measurements suggest the polar nature of this phase. This is further confirmed by neutron diffraction, which indicates a cycloidal structure with a magnetic superspace group $Bm.1{}^{\prime }\left(0,\frac{1}{2},\gamma \right)0s$. The magnetic ground state (ICM3) is a polar helical spin structure with magnetic space group $B2.1{}^{\prime }\left(0,0,\gamma \right)ss$ which is incommensurately modulated with propagation vector ${\mathit{k}}_2=\left(0,0,\gamma \right)$ where $\gamma =0.3793\left(1\right)$ (at 1.5 K).

We report a comprehensive study investigating the magnetic ordering properties of the quasi-two-dimensional breathing kagome lattice compound $\mathrm{Pb}\left(\mathrm{OF}\right){\mathrm{Cu}}_3{\left({\mathrm{SeO}}_3\right)}_2\left({\mathrm{NO}}_3\right)$ using neutron diffraction and thermodynamic measurements. A long-range magnetic order emerges below the Néel temperature, $T_{\mathrm{N}}=18\mathrm{K}$, characterized by a propagating vector $\mathbf{k}=(0,0,1.5)$. Refinement analysis reveals that the copper moments display a noncoplanar arrangement, with the $c$ components parallelly aligned within the breathing kagome plane and antiparallelly aligned between the layers. In-plane moment components form a chiral “tail-chase” structure. The magnetic order is quickly suppressed under moderate external fields applied both within and perpendicular to the kagome plane. Potential magnetic interactions that may be associated with the noncoplanar chiral magnetic structure are discussed.

The Ginzburg-Landau approach postulates an energy density, together with an interpretation for the supercurrent, and invokes Ohm's law. We consider quasi-one-dimensional nonuniform superconducting loops, either smooth or piecewise uniform, that enclose a magnetic flux, above the critical temperature. We evaluate the averages of the current and of the power per unit length delivered by the electric field due to thermal fluctuations. We consider three averages: the canonical ensemble average, the canonical ensemble in the reciprocal space, and the time average using a time-dependent model. All the evaluations imply that heat is imparted to part of the loop and removed in the other part, despite the assumption that the loop is at uniform temperature.

The nonreciprocal properties of coupled nanocavities incorporating a gain medium were investigated. The proposed coupled nanocavities can be considered as a photonic non-Hermitian heterostructure. Our study shows that the nonlinearity arising from gain saturation plays a crucial role in dictating the transmittance characteristics. With increasing optical excitation intensity, the transmittance for the forward and backward incident directions exhibits a distinct evolution, ultimately leading to broken reciprocity. Furthermore, there exist both stable and metastable states of cavity modes, and these two states coalesce under a strong optical nonlinear effect. The coalescence of these two states can be attributed to the intricate interplay between the gain saturation nonlinearity and mode coupling, thus giving rise to different nonlinear optical characteristics. Our findings offer valuable insights into nonreciprocal phenomena such as optical bistability, and have potential applications for innovative devices with tunable optical properties.

It is well-known that in elemental metals, the onsite Coulomb energy of transition-metal (TM) $d$-electrons, $U_{dd}$, is significantly smaller than $U_{ff}$ of $f$-electron rare-earth (RE) metals. Consequently, $U_{dd}$ is often neglected in RE-TM intermetallic alloys. In spite of the low value of $U_{dd}$ compared to $U_{ff}$, we quantify and clarify the important role of $U_{dd}$ in partially filled $d$-bands of RE-TM alloys. We investigate the electronic structure of a typical RE-TM ferrimagnetic series ${\mathrm{Gd}}_6{\left({\mathrm{Mn}}_{1-x}{\mathrm{M}}_x\right)}_{23}$ (M = Fe, Co; $x=0.0,0.3$), which shows promising magnetocaloric properties. Resonant photoemission and constant initial state spectroscopy is used to identify the Mn $3d$, Fe $3d$, and Co $3d$ partial density of states (PDOS) in the valence band. The photon energy-dependent spectral evolution allows us to separate out the lower Hubbard band and the two-hole correlation satellites in the Mn, Fe, and Co $3d$ PDOS. Using the Cini-Sawatzky method, we determine an average $U_{dd}=2.1\pm 0.4\mathrm{eV}, 2.2\pm 0.4\mathrm{eV}$, and $2.9\pm 0.4\mathrm{eV}$ for the Mn $3d$, Fe $3d$, and Co $3d$ states, respectively. The relatively larger $U_{dd}$ for Co compared to Fe $3d$ states results in lower DOS for the coherent feature at the Fermi level ($E_F$) and higher DOS in the lower Hubbard band away from $E_F$ in ${\mathrm{Gd}}_6{\left({\mathrm{Mn}}_{0.7}{\mathrm{Co}}_{0.3}\right)}_{23}$ compared to ${\mathrm{Gd}}_6{\left({\mathrm{Mn}}_{0.7}{\mathrm{Fe}}_{0.3}\right)}_{23}$. To understand the role of Coulomb correlations on the electronic structure and magnetic properties, ab initio electronic structure calculations using density functional theory with onsite Coulomb correlations ($\mathrm{DFT}+U$) were carried out for the parent ${\mathrm{Gd}}_6{\mathrm{Mn}}_{23}$. The results show that the calculated Mn magnetic moments are consistent with experiments when $U_{\text{Mn}}^{\text{DFT}}=0.75\mathrm{eV}$, corresponding to $U_{dd}=1.65\mathrm{eV}$ and $J_{dd}=0.9\mathrm{eV}$. Further, using the calculated Gd and Mn PDOS and known photoionization cross-sections, the simulated ${\mathrm{Gd}}_6{\mathrm{Mn}}_{23}$ spectrum is fairly consistent with the experimental valence band spectrum. The results indicate the crucial role of d-d correlations in the presence of large f-f correlations for tuning the electronic structure and magnetic properties of RE-TM intermetallics.

The random phase approximation (RPA) as formulated as an orbital-dependent, fifth-rung functional within the density functional theory framework offers a promising approach for calculating the ground-state energies and the derived properties of real materials. Its widespread use to large-size, complex materials is, however, impeded by the significantly increased computational cost, compared to lower-rung functionals. The standard implementation exhibits an $O\left(N^4\right)$-scaling behavior with respect to system size $N$. In this work, we develop a low-scaling RPA algorithm for periodic systems, based on the numerical atomic orbital (NAO) basis-set framework and a localized variant of the resolution of identity (RI) approximation. The rate-determining step for RPA calculations, the evaluation of noninteracting response function matrix, is reduced from $O\left(N^4\right)$ to $O\left(N^2\right)$ by just exploiting the sparsity of the RI expansion coefficients, resultant from localized RI (LRI) scheme and the strict locality of NAOs. The computational cost of this step can be further reduced to linear scaling if the decay behavior of the Green's function in real space can be further taken into account. Benchmark calculations against existing $\mathbf{k}$-space-based implementation confirms the validity and high numerical precision of the present algorithm and implementation. The new RPA algorithm allows us to readily handle three-dimensional, close-packed solid-state materials with over 1000 atoms. The algorithm and numerical techniques developed in this work also have implications for developing low-scaling algorithms for other correlated methods to be applicable to large-scale extended materials.

The theoretical formulation that enables calculation of quasiparticle properties of two-dimensional (2D) semiconductors physisorbed at another 2D crystal is presented. The formulation is applied to calculate the induced correlation self-energy $\mathrm{\Delta }{\mathrm{\Sigma }}^{\text{C,S}}\left(\omega \right)$ and spectral line shapes of the valence and conduction bands in ${\mathrm{MoS}}_2$, ${\mathrm{WS}}_2$, and hBN caused by nearby pristine or doped graphenes. It is shown that graphene negligibly shifts the valence and conduction bands in ${\mathrm{MoS}}_2$ and ${\mathrm{WS}}_2$ causing the maximum band gap reduction of $-\mathrm{\Delta }{E}_{\text{g}}\sim 150\text{meV}$. The influence of graphene on hBN band structure is stronger, causing the band gap reduction of $-\mathrm{\Delta }{E}_{\text{g}}\sim 700\text{meV}$. The larger number of graphene layers or doped graphene negligibly affect the valence and conduction bands shifts, which are also approximately rigidly shifted along the entire Brillouin zone. The spatially dependent induced self-energy of point charge $\mathrm{\Delta }{\mathrm{\Sigma }}^{\text{S@2D}}\left(z_0\right)$ (image potential) is much weaker in ${\mathrm{MoS}}_2$ or ${\mathrm{WS}}_2$ than in hBN indicating that transition-metal dichalcogenides electronic screening efficiently cancel substrate polarization effects and thus protect the band structure from substrate influences. When graphene is brought next to the hBN it induces satellites in the hBN conduction and valence bands. Graphene's interband $\pi \to {\pi }^{*}$ transitions induce weak $\pi$ satellites, while Dirac plasmon, present in the doped graphene, induces more intensive D plasmaron, which might be observed in photoemission measurements.

In this study, we investigate the conductivity of a two-dimensional (2D) system in HgTe quantum well comprising two types of carriers with linear and quadratic spectra, respectively. The interactions between the two-dimensional Dirac holes and the heavy holes lead to the breakdown of Galilean invariance, resulting in interaction-limited resistivity. Our exploration of the transport properties spans from low temperatures, where both subsystems are fully degenerate, to higher temperatures, where the Dirac holes remain degenerate while the heavy holes follow Boltzmann statistics, creating a partially degenerate regime. Through a developed theory, we successfully predict the behavior of resistivity as $\rho \sim T^2$ and $\rho \sim T^3$ for the fully degenerate and partially degenerate regimes, respectively, which is in reasonable agreement with experimental observations. Notably, at elevated temperatures, the interaction-limited resistivity surpasses the resistivity caused by impurity scattering by a factor of 5–6. These findings imply that the investigated system serves as a versatile experimental platform for exploring various interaction-limited transport regimes in two component plasma.

We investigate an optical switching mechanism for applications in active integrated photonic circuits. The mechanism utilizes a large nonlinearity of indium-tin-oxide (ITO) in the epsilon-near-zero regime. The effect of optically induced switching is investigated in hybrid plasmonic waveguides (HPWGs) with an ITO layer that are often used as a platform for various active photonic components, including optical modulators. To study the effect, nonlinear Maxwell equations are solved numerically in time and frequency domains. The all-optical mechanism of switching in HPWGs is quantitatively compared with an electrical gating that is often used to manipulate hybrid modes. It is shown that the optical pumping could potentially cause more efficient switching. The influence of light intensity on HPWG properties and interplay between hybrid modes are investigated numerically in different regimes. Transmittance and phase variation are calculated as a function of light intensity for Si and ${\mathrm{Si}}_3{\mathrm{N}}_4$ waveguides. It is shown that the transmittance and its intensity dependence are strongly affected by the ITO thickness. A significant for applications steplike variation of phase and transmittance with intensity is detected. The possibility to control the excitation conditions for surface plasmon polaritons in HPWGs using the active layer of ITO in the nonlinear regime is demonstrated and discussed.

Understanding the relationship between stripe order and other phenomena, including antiferromagnetism and superconductivity, is one of the central issues in cuprate superconductors. The discovery that similar phase diagram exhibits in both hole-doped and electron-doped cuprates brings a chance to explore the subtle role that stripe order plays in the mechanism of superconductivity. To investigate this question, we study the behavior of the superconducting pairing interaction within an inhomogeneous Hubbard model by the quantum Monte Carlo method. Our study shows that stripe order may play a different role in the electron-doped and hole-doped cases. For hole doping, the effective pairing interaction of dominant $d_{x^2-y^2}$ pairing symmetry can be enhanced by stripe potential $V_0$ at moderate hole-doping concentration, but suppressed by $V_0$ at low hole-doping regions. However, for electron doping, the effective pairing interaction of $d_{x^2-y^2}$ pairing symmetry is always suppressed by $V_0$. Surprisingly, when the dominant $d_{x^2-y^2}$ pairing disappears, there exists a robust $d_{xy}$ pairing channel induced by $V_0$. Besides, with the occurrence of $d_{xy}$ pairing, the $(\pi ,\pi )$ magnetic correlation is suppressed. In general, our unbiased numerical simulations provide an understanding of the superconducting mechanism in cuprate superconductors and offer possible evidence that the charge density waves have an important effect on superconductivity.

Motivated by recent angle-resolved photoemission spectroscopy (ARPES) experiments on doped one-dimensional (1D) cuprates, we investigate spectral properties of a 1D extended Hubbard model with both on-site repulsion $U$ and nearest-neighbor interaction $V$, by employing bosonization analysis and the high-precision time-dependent variational principle (TDVP) calculations with large scale up to 300 sites. From state-of-the-art TDVP calculations, we find that the spectral weights of the holon-folding and $3k_F$ branches evolve oppositely as a function of $V$, and a moderate attractive $V$ may best fit the experimental results, hinting at the possible existence of sizable electron-phonon coupling in cuprates. From bosonization analysis, we show that this peculiar dichotomy of holon-folding and $3k_F$ branches can be explained by a universal relation between the spectral intensity at arbitrary harmonic branches and the Luttinger parameters. We argue that the relation we establish can be used for detecting different interactions in various 1D systems.

The presence of gauge symmetry in 1+1 dimensions is known to be redundant, since it does not imply the existence of dynamical gauge bosons. As a consequence, in the continuum, the Abelian-Higgs model (i.e., the theory of bosonic matter interacting with photons) just possesses a single phase, as the higher-dimensional Higgs and Coulomb phases are connected via nonperturbative effects. However, recent research published in Phys. Rev. Lett. 128, 090601 (2022) has revealed an unexpected phase transition when the system is discretized on the lattice. This transition is described by a conformal field theory with a central charge of $c=3/2$. In this paper, we aim to characterize the two components of this $c=3/2$ theory—namely the free Majorana fermionic and bosonic parts—through equilibrium and out-of-equilibrium spectral analyses.

Dielectric composites are believed to tightly obey the effective-medium theory (EMT) when their dimensions are much smaller compared to the wavelength inside them. It is naturally expected that when the refractive indices of a part of the constituent materials approach zero, the validity of the EMT is further strengthened. Here, we demonstrate that the EMT breaks down in deep-subwavelength dielectric composites containing homogeneous epsilon-near-zero (ENZ) constituents, which is contrary to the above intuitive picture, as validated by both the Bloch-wave analysis and numerical simulations. This breakdown of EMT originates in the presence of strong evanescent waves emerging on the interfaces between the constituent materials, which stem from the extreme mismatch of energy-flux distributions between them. The energy flux within such composites is highly nonuniform: significantly enhanced in the ENZ constituents and largely depressed in other normal constituents. When such composites are illuminated by planar waves with uniform energy-flux distributions, evanescent waves for redistributing flux into the ENZ constituents are generated on the internal interfaces of the composites, and lead to properties beyond the prediction of traditional EMT. Our work unveils the mechanism of EMT breakdown in dielectric composites with constituents of near-zero permittivity.

Two-dimensional (2D) moiré superlattices have been extensively investigated, whereas the one-dimensional (1D) moiré superlattices have remained largely unexplored, due to the difficulty in achieving 1D moiré superlattices experimentally. Recent theoretical studies have predicted that certain collapsed chiral carbon nanotubes (CNTs) behave as 1D moiré superlattices with novel strongly correlated physics, owing to the emergence of 1D flat bands. However, the realization of 1D flat bands is limited to CNTs with a narrow range of chirality, which hinders the experimental investigation. Here, using molecular dynamics simulations and tight-binding calculations, we reveal that the application of external pressure can induce 1D moiré flat bands in a wide range of collapsed CNTs of both metallic and semiconducting types. We further provide a comprehensive analysis of the emergence of the 1D flat bands, and derive critical pressures for CNTs of various chiralities. Our study presents a versatile approach for creating 1D flat bands, and therefore could greatly facilitate the experimental exploration of 1D strongly correlated physics in collapsed CNT moiré superlattices.

Since the discovery of the fascinating properties in magic-angle graphene, the exploration of moiré systems in other two-dimensional materials has garnered significant attention and given rise to a field known as “moiré physics.” Within this realm, the magnetic van der Waals heterostructure and the magnetic proximity effect in moiré superlattices have also become subjects of great interest. However, the spin-polarized transport property in these moiré structures is still a problem to be explored. Here, we investigate the spin-polarized transport properties in a moiré superlattice formed by a two-dimensional ferromagnet ${\mathrm{CrI}}_3$ stacked on a monolayer BAs, where the spin degeneracy is lifted because of the magnetic proximity effect associated with the moiré superlattices. We find that the conductance exhibits spin-resolved miniband transport properties at a small twist angle because of the periodic moiré superlattices. When the incident energy is in the spin-resolved minigaps, the available states are spin polarized, thus providing a spin-polarized current from the superlattice. Moreover, only a finite number of moiré period is required to obtain a net spin polarization of 100%. In addition, the interlayer distance of the heterojunction is also moiré modifiable, so a perpendicular electric field can be applied to modulate the direction of the spin polarization. Our finding points to an opportunity to realize spin functionalities in magnetic moiré superlattices.

Under the coaction of off-resonant circularly polarized light and antiferromagnetic exchange field, epitaxial graphene undergoes various topological phases. Considering the self-rotation of the wave packet and the Berry curvature driving topological effect, we investigate the spin- and valley-dependent anomalous Nernst effect in epitaxial graphene and propose two alternative methods to differentiate various topological phases. Firstly, the charge Nernst current appears only when the light field exists, while for achieving the spin Nernst current, two external fields must be applied simultaneously. Due to the existence of a substrate potential, a thermally induced pure valley current can be demonstrated, and its magnitude and sign can be controlled by changing the antiferromagnetic exchange field. Single-spin and single-valley Nernst currents can be collected in the quantum valley Hall–quantum anomalous Hall insulator phase. Secondly, the abundant topological phases in epitaxial graphene can be distinguished by detecting the sign change of the charge, spin, and valley Nernst conductivities by tuning the Fermi level. Thirdly, the temperature dependence provides another efficient method to distinguish various topological phases. After deriving an analytical expression from the semiclassical Mott relation, it is shown that by adjusting the sample temperature, the variation trend of the spin-valley Nernst currents can be detected. These findings are experimentally verifiable in the future and can be promising for spin and valley caloritronic applications.

For the study of topological phases in photonics, while quantum-Hall-type first-order chiral edge states are routinely realized in magneto-optical photonic crystals, higher-order topological states are mostly explored in all-dielectric photonic crystals. In this work, we study both first- and second-order topological photonic states in magneto-optical photonic crystals. In specific, we revisit a simple magneto-optical photonic crystal in a square lattice with one gyromagnetic cylinder in each unit cell. However, rather than investigating the conventional unit cell where the cylinder is at the center of the square unit cell as previous works have done, we consider a configuration where the cylinders are located at the four corners of the square unit cell and show that this configuration hosts rich topological phases, such as dual-band Chern, dipole, and quadrupole topological phases. Our detailed characterizations of these topological states are based on the Wannier bands and their polarizations via the Wilson loop and nested Wilson loop methods. We study in detail both the edge and corner states of the different topological phases and show that they exhibit a special feature of “spectrum robustness.” For example, though the edge and corner states of the dipole phases living in a band gap could be pushed into the bulk bands by tuning the boundary conditions, they can pass through the bulk bands and reappear within a different band gap. For dual-band quadrupole phases, we can find a regime where both band gaps host a set of corner states simultaneously and, intriguingly, the filling anomaly of one set of corner states can leave their signatures in the filling anomaly of the other set of corner states though they are separated by an extensive number of bulk states. The rich topological physics revealed in a simple magneto-optical photonic crystal not only provides new insights on higher-order topological phases in time-reversal symmetry-broken photonic systems, the results may also find promising applications by harnessing the potentials of both edge and corner states.

Willis materials provide degrees of freedom to control mechanical waves unavailable in conventional materials, but our understanding of wave-matter interaction in these exotic media has been limited by their unconventional constitutive equations. This work derives an equivalence between the acoustic Willis wave equation inside a general inhomogeneous and anisotropic Willis medium and the well-known wave equation in conventional acoustic materials with embedded continuous distributions of monopole and dipole sources. It thus enables accurate and efficient computation of sound scattering from arbitrarily shaped general acoustic Willis materials in one, two, and three dimensions. The result is validated by showing in numerical simulations that realizable bulk Willis metamaterials, obtained by periodically replicating a labyrinthine cell, scatter sound identically to its equivalent material with embedded continuous source distributions. Furthermore, the equivalence provides insights into the physics of Willis materials. For example, it shows that multiple pairs of Willis coupling vectors produce exactly the same sound scattering regardless of excitation. It also directly shows whether the effective material parameters extracted from single Willis cell simulations maintain validity in bulk metamaterials based on that cell. This equivalence model will advance the design of Willis metamaterials and provide the tool to better understand the physics of Willis media.

Fe-Co alloys with induced tetragonal strain are promising materials for rare-earth-free permanent magnets. However, as ultrathin-film studies have shown, tetragonal Fe-Co structures tend to a rapid relaxation toward a cubic structure as the thickness of the deposited film increases. One of the main methods of inducing the stable strain in the bulk material is interstitial doping with small atoms, like B, C, or N. In this work, we present a full configuration-space analysis in the density functional theory approach for ${\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)}_{16}\mathrm{C}$ supercells with a single C impurity in one of the octahedral interstitial positions and for the full range of Co concentrations $x$. We discuss all assumptions and considerations leading to calculated lattice parameters, mixing enthalpies, magnetic moments, and averaged magnetocrystalline anisotropy energies (MAE). We present a comprehensive qualitative analysis of the structural and magnetic properties' dependence on short- and long-range ordering parameters. We analyzed all unique Fe/Co atom occupancies at all stoichiometric concentrations possible in $2\times 2\times 2$ supercell based on two-atom tetragonal representation. We rely on the thermodynamic averaging method and large sample count to obtain accurate MAE values. We place the utilized method in the context of several chemical disorder approximation methods, including effective medium methods (virtual crystal approximation and coherent potential approximation) and special quasirandom structures method applied to Fe-Co-based alloys. We observe a structural phase transition from the body-centered-tetragonal structure above 70% Co concentration and confirm the structural stability of Fe-Co-C alloys in the tetragonal range. We show the presence of a broad MAE maximum around about 50% Co concentration and notably high MAE values for Co content $x$ as low as 25%. In addition, we show the presence of a positive correlation between MAE and mixing enthalpy.

Structural phase transitions accompanied by incommensurate and commensurate charge density wave (CDW) modulations of unconventional nature have been reported in $\mathrm{Ba}{\mathrm{Ni}}_2{\mathrm{As}}_2$, a nonmagnetic cousin of the parent compound of Fe-based superconductors, ${\mathrm{BaFe}}_2{\mathrm{As}}_2$. The strong dependence of the structural and CDW transitions of $\mathrm{Ba}{\mathrm{Ni}}_2{\mathrm{As}}_2$ on isoelectronic substitutions alongside original dynamical lattice effects suggests strong tunability of the electronic phase of the system through structural effects. Here, we present a comprehensive synchrotron x-ray diffraction and first-principles calculation study of the evolution of the crystal structure and lattice instabilities of $\mathrm{Ba}{\mathrm{Ni}}_2{\mathrm{As}}_2$ as a function of temperature and hydrostatic pressure (up to 12 GPa). We report a cascade of pressure-induced structural phase transitions and electronic instabilities up to $\approx 10$ GPa, above which all CDW superstructures disappear. We reveal that the stable high-pressure phase consists of planar Ni zigzag chains, from which the surrounding As atoms have been pushed away. This yields a strong reduction of the interlayer As-As distance (along the original $c$ axis), akin to what is observed in the collapsed tetragonal structure of other pnictides, albeit here with a monoclinic structure. The discovery of polymorphs in the pressure-temperature phase diagram of $\mathrm{Ba}{\mathrm{Ni}}_2{\mathrm{As}}_2$ emphasizes the importance of the relative Ni-Ni and Ni-As bond lengths in controlling the electronic ground state of this compound and increases our understanding of viable electronic phases under extreme conditions.