Low-density amorphous ice (LDA) is one of the most common solid materials in the Universe and a key material for understanding the many famous anomalies of liquid water. Yet, despite its significance and its discovery nearly 90 years ago, the structure of LDA is debated. It is unclear if LDA is a glassy state representing a liquid or a heavily disordered crystal; indeed, two forms (LDA-I and LDA-II) have been discussed as amorphous and partially crystalline in the literature, respectively. Here, with two widely used water models, we show that the experimental structure factor of LDA is best reproduced computationally by a partially crystalline structure. Models for both LDA-I and LDA-II are highly similar, with differences only due to subtle differences in crystallinity and/or experimental error. Further support for this structural model of LDA comes from experiments: if LDA is partially crystalline, then its route to formation should result in different nanocrystallite cubicities, and thus give rise to different cubicities upon recrystallization. This memory effect of LDA's creation route is observed and it is incompatible with a fully amorphous material. The results present a unified computational and experimental view that LDA is not fully amorphous but instead a partially crystalline material. This impacts LDA's many roles in nature and potentially our understanding of liquid water. Furthermore, the “reidentification” of such an intensely studied material highlights that great care will be needed when classifying the nature of glassy materials going forward.

In this work, we revisit the phase diagram of the $t\text{−}{t}^{\prime }\text{−}\delta$ Fermi-Hubbard model on the square lattice to gain a more comprehensive understanding of this correlated model at half filling. This model has recently become a prominent topic of research because it hosts altermagnetic phases. Using mean-field analysis, we identify four metallic phases and two insulating phases with nontrivial magnetic orders at an intermediate value of $\delta =0.5$, presenting a rich ground-state phase diagram in the $U\text{−}{t}^{\prime }$ plane. We also highlight the distinct features of the Fermi surface topology for each metallic phase. To go beyond the mean-field theory, we employ the density-matrix renormalization group method to simulate the ground state numerically. The phase boundaries are determined from the discontinuities and peaks in the entanglement entropy and magnetizations. In addition to the phases identified in the mean-field theory, we find a valence-bond solid state in a narrow intermediate-$t^{\prime }$ region. Our work offers a firm step forward in understanding the complex behaviors of correlated electrons in the $t\text{−}{t}^{\prime }\text{−}\delta$ Hubbard model over a large parameter space.

We present a bosonized effective field theory for a two-dimensional Fermi surface in a weak magnetic field using the coadjoint-orbit approach, which was recently developed as a nonlinear bosonization method in phase space for Fermi liquids and non-Fermi liquids. We show that by parametrizing the phase space with the guiding center and the mechanical momentum, and by using techniques in noncommutative field theory, the physics of Landau levels and Landau level degeneracy ($N_{\mathrm{\Phi }}$) naturally arises. For a parabolic dispersion, the resulting theory describes $N_{\mathrm{\Phi }}$ flavors of free chiral bosons propagating in momentum space. In addition, the action contains a linear term in the bosonic field, which upon mode expansion becomes a topological $\theta$ term. By properly quantizing this theory, we reproduce the well-known thermal and magnetic responses of a Fermi surface, including linear-in-$T$ specific heat, Landau diamagnetism, and the de Haas–van Alphen effect. In particular, the de Haas–van Alphen effect is shown to be a direct consequence of the topological $\theta$ term. Our theory paves the way toward understanding correlated gapless fermionic systems in a magnetic field using the powerful approach of bosonization.

It is demonstrated that the Aharonov-Casher (AC) phase is a geometric phase that, in general, depends on the details of the closed path taken by a particle with a magnetic moment that is subject to an electric field. Consequently, it is not a topological phase. The proof of this statement is obtained by developing a counterexample that elucidates the dependence of the AC phase on the details of the path. Furthermore, we demonstrate that, in the particular example considered here, paths having an Abelian AC phase factor also have an AC phase that is path independent, whereas paths having a non-Abelian AC phase factor may have an AC phase that is path dependent (i.e., not topological).

Under a high frequency drive, Josephson junctions demonstrate Shapiro steps of quantized voltage. These are dynamically stabilized states in which the phase across the junction locks to the external drive. We explore the stochastic switching between two symmetric steps at $\frac{\hslash \omega }{2e}$ and $-\frac{\hslash \omega }{2e}$. Surprisingly, the switching rate exhibits a pronounced nonmonotonicity as a function of temperature, violating the general expectation that transitions should become faster with temperature. We explain this behavior by realizing that the system retains memory of the dynamic state from which it is switching, thereby breaking the conventional simplifying assumptions about separations of timescales.

Eigenstate multifractality is of significant interest with potential applications in various fields of quantum physics. Most of the previous studies concentrated on fine-tuned quantum models to realize multifractality, which is generally believed to be a critical phenomenon and fragile to random perturbations. In this work, we propose a set of generic principles based on the power-law decay of the eigenstates that allow us to distinguish a fractal phase from a genuine multifractal phase. We demonstrate the above principles in a 1D tight-binding model with inhomogeneous nearest-neighbor hopping that can be mapped to the standard quantum harmonic oscillator via energy-coordinate duality. We analytically calculate the fractal dimensions and the spectrum of fractal dimensions, which are in agreement with numerical simulations.

Diffusion is a ubiquitous phenomenon. It is a widespread belief that, if the area under a current autocorrelation function converges in time, the corresponding spatiotemporal density dynamics should be diffusive. This may be viewed as a result of the combination of linear response theory with the Einstein relation. However, attempts to derive this statement from first principles are notoriously challenging. We first present a counterexample by constructing a correlation function of some density wave, such that the area under the corresponding current autocorrelation function converges, but the dynamics do not obey a diffusion equation. Then we introduce a method based on the recursion method and the Mori memory formalism that may help to identify diffusion. For a decisive answer, one would have to know infinitely many so-called Lanczos coefficients, which is unattainable in most cases. However, in the examples examined in this paper, we find that the practically computable number of Lanczos coefficients suffices for a strong guess.

Motivated by the ongoing interest in understanding the actual magnetic ground state of the promising axion insulator candidate ${\mathrm{EuIn}}_2{\mathrm{As}}_2$, we present here a spin symmetry analysis and ab initio calculations, aiming to identify specific exchange-dominated physics that could offer insights into the current debate. We investigate two noncollinear coplanar magnetic orders reported in this compound: the helical and broken-helical phases. Our symmetry analysis shows that magnetic-exchange alone results in the formation of an out-of-plane odd-parity wave order in momentum space with a single unpolarized nodal plane in both phases. Additionally, we identify an in-plane $g$-wave order that emerges exclusively in the broken-helical phase, providing a distinguishing feature for this phase. Furthermore, we report a nonrelativistic Edelstein effect with a distinct out-of-plane polarized spin density that dominates over spin-orbit coupling effects. Our ab initio calculations reveal a significant contrast in the magnitude of this effect between both phases, which could serve as a means to identify the magnetic transition and distinguish them from other magnetic ground states proposed for this compound.

Altermagnets, magnetic materials with zero magnetization and spin-split band structure, have gained tremendous attention recently for their rich physics and potential applications. Here, we report on a microscopic tight-binding model that unveils a unique coupling between orbitals and spins in $d$-wave altermagnets, which gives rise to momentum-dependent and spin-selective optical absorption. This coupling promotes the controlled optical excitation of up or down spins depending on the polarization direction of linearly polarized light. Such an effect originates from the coupling of orbitals to the sublattice degree of freedom through the crystal field, which is then coupled to spins through the antiferromagnetic interaction. Our crystal field analysis, which is general to any type of altermagnet, helps understand the onset of altermagnetism from a microscopic point of view, and we use our results to propose clear magneto-optical signatures of our predictions. Our findings shine light on the interplay between orbitals and spins in altermagnets, thus paving the way towards novel orbitronic and optospintronic devices.

Recent studies have shown some unusual nonlinear dispersion behaviors that are disconnected from the linear regime. However, existing analytical techniques, such as perturbation methods, fail to correctly capture these behaviors. Here I propose an equivalent eigenvalue approach that converts the nonlinear wave equation to an equivalent linear eigenvalue problem, which directly gives the nonlinear dispersion relation and modal vectors. The theoretical approach is employed to one-dimensional (1D) phononic chains and 2D hexagonal lattices with alternating softening and hardening nonlinearities, revealing amplitude-induced bandgap opening and closing phenomena. The theoretical results are validated via full-scale simulations with initial excitations and periodic boundary conditions, in which steady-state nonlinear plane wave responses are numerically obtained. Moreover, these nonlinear phenomena are leveraged to achieve tunable frequency splitting and focusing effects. Thus this work opens paradigms for understanding nonlinear wave physics and for achieving tunable wave control capabilities.

This paper experimentally investigates topologically protected edge modes in a water wave channel through a direct geometric mapping to the one-dimensional Su-Schrieffer-Heeger (SSH) model. By designing a periodic channel with alternating widths, we replicate the key features of the SSH model, leading to the emergence of robust zero-energy sloshing edge modes localized at the boundaries. Experimental data show excellent agreement with theoretical predictions, supported by two-dimensional numerical simulations. In the nonlinear regime, two distinct bifurcations are observed, indicating the appearance of secondary resonances. This study highlights the relevance of the SSH model for water-wave systems and provides an accessible method to explore topological edge states in classical wave systems.

A classical impurity spin coupled to the spinful Su-Schrieffer-Heeger (SSH) chain is known to exhibit complex switching dynamics with incomplete spin relaxation. Here, we study the corrections that result from a full quantum treatment of the impurity spin. We find that in the topologically trivial case, the quantum spin behaves similarly to the classical one due to the absence of the Kondo effect for the trivial insulator. In the topological case, the quantum spin is significantly less likely to relax: It can be stuck at a prerelaxation plateau with a sizable deviation from the expected relaxed value, and there is a large parameter regime where it does not relax at all but features an anomalously large Larmor frequency. Furthermore, we find an additional quantum effect where the prerelaxation plateau can be hyperpolarized, i.e., the spin is stuck at a polarization value larger than the ground-state expectation value. This is possible due to the (incomplete) Kondo screening of the quantum spin, which is absent in the classical case. Our results are obtained via the ground-state density-matrix renormalization group algorithm (DMRG) and the time-dependent variational principle (TDVP), where the charge-SU(2) symmetry of the problem was exploited. Furthermore, we introduce and benchmark a method to predict the dynamics from the given numerical data based on the sparse identification of nonlinear dynamics (SINDy). This allows us to prolong the simulation timescale by a factor of 2.5, up to a maximal time of ${10}^3$ inverse hoppings.

We report a phase diagram of the antiferromagnetic spin-1 chain with nearest-neighbor Heisenberg and three-site interactions in the presence of single-ion anisotropy. We show that the Gaussian and Ising transitions that separate the topological Haldane phase from the two anisotropic phases eventually fuse into a higher symmetry point characterized by the Wess-Zumino-Witten (WZW) $\mathrm{SU}{\left(2\right)}_2$ critical theory providing a lattice realization of the conformal embedding. On the other side of the WZW multicritical point, the Ising critical line reappears together with the eight-vertex transition. This transition is a one-dimensional realization of a deconfined quantum criticality separating the dimerized and Ising antiferromagnetic phases – two ordered phases with incompatible order parameters.

Conventional antiferromagnets (AFMs) preserve time-reversal symmetry (TRS). Recently, altermagnets (AMs) which break TRS and show momentum-dependent spin splitting have been proposed. The occurrence of AMs depends on a special geometry around the magnetic ion. Here, we show that AMs can be induced in a general lattice by leveraging the coupling between the charge and spin degrees of freedom. We study numerically the quantum phases in bimetallic systems by modeling them using an interpenetrated bipartite square lattice. Our mean-field theory calculations of this model's band structures reveal that charge order and antiferromagnetic spin order in different sublattices lead to altermagnetism. The origin of AM phase is further shown analytically to stem from a unitary transformation of the Hamiltonian matrix between the up spin at $(k_x,k_y)$ and down spin at $(k_x,-k_y)$ when the $A$ sublattice is charge ordered. The proposed model is then validated by comparing the band structures of pristine ${\mathrm{LaMnO}}_3$ and doped ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3 (x=0.5)$ (LSMO) using density functional theory. This suggests a tunable approach to achieving altermagnetism in bimetallic systems, broadening the range of such materials.

${\mathrm{CuGaCr}}_4{\mathrm{S}}_8$, which contains a chromium breathing pyrochlore network, exhibits diverse magnetic phases, including an incommensurate helical state below 31 K and a $\frac{1}{2}$-magnetization plateau above 40 T, owing to the interplay between magnetic frustration and spin-lattice coupling. Here, we perform a single-shot powder x-ray diffraction experiment on ${\mathrm{CuGaCr}}_4{\mathrm{S}}_8$ in a pulsed high magnetic field of 55 T, revealing an orthorhombic-to-cubic (or pseudocubic) structural transition upon entering the $\frac{1}{2}$-magnetization plateau phase at low temperatures. This observation suggests the emergence of a commensurate ferrimagnetic order, where a 3-up–1-down spin configuration is realized in each small tetrahedron, and the all up or all down in each large tetrahedron. We propose two types of 16-sublattice magnetic structures, which are degenerate within exchange interactions between the first-, second-, and third-nearest neighbors.

Nonlinear resonances of plasma waves in field-effect transitors enable a well-known photodetection mechanism, first introduced by Dyakonov and Shur in the 1990s, especially suited to the Terahertz (THz) frequency range. Theoretical analyses of the mechanism always assume that the gate of the transistor, which is coupled to the antenna receiving the THz signal, is as long as the channel itself, at odds with typical experimental devices based on III-V compounds or graphene, where short gates are usually employed, e.g., due to fabrication constraints. In this work we overcome this limitation and provide a complete theory of Dyakonov-Shur photodetection in the presence of short gates. We develop our theory in such a general fashion that allows us to also treat the case in which multiple gates are present. We find that a suboptimal positioning of the gates can substantially decrease the detection efficiency of the device and provide a compact analytical formula to quickly estimate the optimal gate position.

Noise is often regarded as a limitation of quantum computers. In this work, we show that in the dynamical mean-field theory (DMFT) approach to strongly correlated systems, it can actually be harnessed to our advantage. Indeed, DMFT maps a lattice model onto an impurity model, namely, a finite system coupled to a dissipative bath. While standard approaches require a large number of high-quality qubits in a unitary context, we propose a circuit that harvests amplitude damping to reproduce the dynamics of this model with a blend of noisy and noiseless qubits. We find compelling advantages with this approach: a substantial reduction in the number of qubits, the ability to reach longer time dynamics, and no need for ground-state search and preparation. This method would naturally fit in a partial quantum error correction framework.

In equilibrium, confined films of superfluid ${}^3\mathrm{He}$-A have the chiral axis $\widehat{\mathbf{\ell }}$ locked normal to the surface of the film. There are two degenerate ground states, $\widehat{\mathbf{\ell }}\left|\right|\pm \widehat{\mathbf{z}}$. However, for a temperature quench, i.e., cool down through the phase transition at a finite rate, causally disconnected regions of order parameter fluctuations develop and evolve into an inhomogeneous ordered phase that hosts both domain walls between time-reversed chiral phases as well as vortices with winding numbers $p\in \mathbb{Z}$. We present simulations based on a time-dependent generalization of Ginzburg-Landau theory for strong-coupling ${}^3\mathrm{He}$ that reveal both types of topological defects to be present following the temperature quench. Results for the dynamics of vortices interacting with antivortices as well as domain walls are presented. The vortex number density as a function of quench rate agrees well with the scaling predicted by Kibble and Zurek. We also present results for the number distribution and compare with other theoretical models for full-counting statistics of the topological defect density. Finally, we present results for an asymmetry in the post-freeze-out populations of inequivalent vortex core structures that are characteristic of a chiral superfluid.

We study clean, edge-contacted graphene/superconductor interfaces in both the quantum Hall (QH) and zero field regimes. We find that Andreev reflection is substantially stronger than at an interface with a semiconductor two-dimensional electron gas: The large velocity at graphene's conical Dirac points makes the requirement of current continuity to a metal much less restrictive. In both our tight-binding and continuum models, we find a wide range of parameters for which Andreev reflection is strong. For a transparent interface, we demonstrate the following for graphene in the lowest Landau level QH state: (i) Excellent electron-hole hybridization occurs: the electron and hole components in graphene are simply related by an exchange of sublattice. The spatial profile for the electron component is predominantly Gaussian on one sublattice and peaked at the interface, and so very different from the QH edge state of a terminated lattice. (ii) The degree of hybridization is independent of the graphene filling: no fine-tuning is needed. (iii) The spectrum is valley degenerate: The dispersion of each chiral Andreev edge mode (CAEM) self-aligns to be antisymmetric about the center of each valley, independent of filling. Achieving a transparent interface requires the absence of any barrier as well as a superconductor that is suitably matched to graphene; we argue that the latter condition is not very stringent. We further consider the effect of reduced transparency and Zeeman splitting on both the wavefunctions of the CAEM and their dispersion.

Fractional charges in the fractional quantum Hall effect were first observed via dc shot noise measurements of anyons tunneling at a quantum point contact (QPC). However, in scenarios with simultaneous tunneling of different types of charges at the QPC, the connection between dc shot noise and tunneling charge is less transparent. Photoassisted shot noise (PASN), induced by periodic ac voltage, offers a promising alternative. Here, we investigate PASN in the hierarchical states of the fractional quantum Hall effect, where different types of charges are expected to tunnel concurrently at QPCs. In the particular case of the fractional quantum Hall state $\nu =2/3$, our analysis demonstrates that PASN can be employed as a robust tool to detect different tunneling charges, even when the tunneling amplitude of one type is significantly smaller compared to the other. We show that the features predicted by our calculations are still visible for typical values of temperature and frequency achieved in state-of-the-art experiments. Our general formalism can be used to compute PASN for general Abelian quantum Hall systems with multiple edge modes and charge types.