Material shock release generally happens in the targets of high-energy-density (HED) and inertial confinement fusion (ICF) experiments but has been challenging to study experimentally, theoretically, or computationally. Here, we report extensive studies of polystyrene (CH) shock release by employing large-scale nonequilibrium molecular dynamics and laser-drive experiments at various shock strengths. Our experimental design prevents radiation preheating of the sample and employs a witness foil to investigate the release of shocked CH across a vacuum gap. We observe earlier acceleration of the foil by the release of CH under stronger shocks as well as reflectivity changes in the interferometry data before the foil moves, which is strong evidence of hydrogen streaming ahead of carbon at the release front, consistent with findings from our simulations. Furthermore, our calculations show that lighter species or hydrogen isotopes can carry more mass by one to two orders of magnitude to farther distances during the release and that only less than 0.1 times thermal expansion as predicted by hydrodynamics is needed to explain the high velocities and large scale lengths of low-density plasmas observed in radiation-preheated CH release experiments. These results highlight the significant role of species separation in the shock release of compounds. This process shall be considered, and its potential effects shall be clarified, in the design, interpretation, and analysis of future HED and ICF experiments.

We study classical $J_1-J_2$ models with distinct spin degrees of freedom on a honeycomb lattice. For the XY and Heisenberg spins, the system develops a spiral spin liquid (SSL) that is a thermal cooperative paramagnetic regime with spins fluctuating around the spiral contours in the momentum space, and at low temperatures supports a vector spin-chirality order despite the absence of long-range magnetic order. In a strong contrast, for the Ising moments, the low-temperature spin correlation forms a reciprocal kagome structure in the momentum space that resembles the SSL behaviors and persists for a range of exchange couplings. The unexpected emergence and persistence of the reciprocal kagome structure are attributed to the stiffness of the Ising moments and the frustration. At higher temperatures when the thermal fluctuations are strong and the spin correlation is not fully melted, the reciprocal structures evolve from kagome structure towards the ones demanded by the soft-spin limit. This contrasts strongly with the behaviors of the spiral contours in the SSL regime for the continuous spins. We suggest various experimentally relevant systems including van der Waals magnets such as the transition-metal phosphorus trichalcogenides ${\mathrm{TMPX}}_3, {\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$, the rare-earth chalcohalides (such as HoOF, ErOF, and DyOF), and other isostructural systems to realize the SSL-like behaviors and/or the reciprocal kagome structure.

Fermi-edge singularity and Anderson's orthogonality catastrophe are paradigmatic examples of non-equilibrium many-body physics in conductors, appearing after a quench is created by the sudden change of a localized potential. We investigate if the signal carried by the quench can be used to transmit a long ranged interaction, reminiscent of the RKKY interaction, but with the inclusion of the full many-body propagation over space and time. We calculate the response of a conductor to two quenches induced by localized states at different times and locations. We show that building up and maintaining coherence between the localized states is possible only with finely tuned interaction between the localized states and the conductor. This puts bounds to the use of time controlled RKKY type interactions and may limit the speed at which some quantum gates could operate.

A close connection between antiferromagnetism and superconductivity is at the core of high-temperature superconductivity. Here, we put forward the projected BCS theory for the unification of antiferromagnetism and strongly correlated superconductivity. Specifically, it is shown that, with the $d$-wave pairing symmetry, the projected BCS theory can provide excellent trial states at general doping for the exact ground states of the $t\text{−}J$ model in the square lattice, generating a unified theory of high-temperature superconductivity as a continuous function of hole concentration. A key to the success of the projected BCS theory is an accurate treatment of the strong correlation between Cooper pairs, which not only causes the breakdown of superconductivity itself at half filling but also defines the precise nature of strongly correlated superconductivity at moderate doping. Also, via the proper incorporation of particle number fluctuations, the projected BCS theory allows direct computation of the superconducting order parameter, shedding important light on the pseudogap phenomenon.

The two-body scattering amplitude and energy spectrum of confined ultracold atoms are of fundamental importance for both theoretical and experimental studies of ultracold-atom physics. For many systems, one can efficiently calculate these quantities via the zero-range Huang-Yang pseudopotential (HYP), in which the interatomic interaction is characterized by the scattering length $a$. Furthermore, when the scattering length is dependent on the kinetic energy ${\varepsilon }_{\mathrm{r}}$ of two-atom relative motion, i.e., $a=a\left({\varepsilon }_{\mathrm{r}}\right)$, the results are applicable for a broad energy region. However, when the free Hamiltonian of atomic internal state (e.g., the Zeeman Hamiltonian) does not commute with the interatomic interaction, or the center-of-mass (c.m.) motion is coupled to the relative motion, the generalization of this technique is still lacking. In this work we solve this problem and construct a reasonable energy-dependent multichannel HYP, which is characterized by a “scattering length operator” ${\widehat{a}}_{\mathrm{eff}}$, for the above complicated cases. Here, ${\widehat{a}}_{\mathrm{eff}}$ is an operator for atomic internal states and c.m. motion, and depends on both the total two-atom energy and the external field as well as the trapping parameter. The effects from the internal-state or c.m.-relative motion coupling can be self-consistently taken into account by ${\widehat{a}}_{\mathrm{eff}}$. We further show a method based on the quantum defect theory, with which ${\widehat{a}}_{\mathrm{eff}}$ can be analytically derived for systems with van der Waals interatomic interaction. To demonstrate our method, we calculate the spectrum of two ultracold fermionic alkaline-earth-like atoms [in electronic ${}^{1}S_0$ $\left(\right|g\rangle )$ and ${}^{3}P_0$ $\left(\right|e\rangle )$ states, respectively] confined in an optical lattice. By comparing our results with the recent experimental measurements for two ${}^{173}\mathrm{Yb}$ atoms and two ${}^{171}\mathrm{Yb}$ atoms, we calibrate the scattering lengths $a_{\pm }$ with respect to antisymmetric and symmetric nuclear-spin states to be $a_{+}=2012\left(19\right)a_0$ and $a_{-}=193\left(4\right)a_0$ for ${}^{173}\mathrm{Yb}$, and $a_{+}=232\left(3\right)a_0$ and $a_{-}=372\left(1\right)a_0$ for ${}^{171}\mathrm{Yb}$.

We present a systematic inelastic neutron scattering and neutron diffraction study on the magnetic structure of the quasi-one-dimensional spin-$\frac{1}{2}$ magnet ${\mathrm{SrCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$, where the interchain coupling in the Néel-type antiferromagnetic ground state breaks the static spin lattice into two independent domains. At zero magnetic field, we have observed two new spin excitations with small spectral weights inside the gapped region defined by the spinon bound states. In an external magnetic field along the chain axis, the Néel order gets partially destabilized at ${\mu }_0{H}^{★}=2.0\mathrm{T}$ and completely suppressed at ${\mu }_0{H}_{\mathrm{p}}=3.9\mathrm{T}$, above which a quantum disordered Tomonaga–Luttinger liquid (TLL) prevails. The low-energy spin excitations between ${\mu }_0{H}^{★}$ and ${\mu }_0{H}_{\mathrm{p}}$ are not homogeneous, containing the dispersionless (or weakly dispersive) spinon bound states excited in the Néel phase and the highly dispersive psinon-antipsinon mode characteristic of a TLL. We propose that the two new modes at zero field are spinon excitations inside the domain walls. Since they have a smaller gap than those excited in the Néel domains, the underlying spin chains enter the TLL state via a local quantum phase transition at ${\mu }_0{H}^{★}$, making the Néel/TLL coexistence a stable configuration until the excitation gap in the Néel domains closes at ${\mu }_0{H}_{\mathrm{p}}$.

We study the transport properties of generic out-of-equilibrium quantum systems connected to fermionic reservoirs. We develop a perturbation scheme in the inverse system size, named $1/N$ expansion, to study a large class of out of equilibrium diffusive/ohmic systems. The bare theory is described by a Gaussian action corresponding to a set of independent two level systems at equilibrium. This allows a simple and compact derivation of the diffusive current as a first-order pertubative term. In addition, we obtain exact solutions for a large class of quantum stochastic Hamiltonians (QSHs) with time and space dependent noise, using a self-consistent Born diagrammatic method in the Keldysh representation. We show that these QSHs exhibit diffusive regimes, which are encoded in the Keldysh component of the single particle Green's function. The exact solution for these QSHs models confirms the validity of our system size expansion ansatz, and its efficiency in capturing the transport properties. We consider in particular three fermionic models: (i) a model with local dephasing, (ii) the quantum simple symmetric exclusion process model, and (iii) a model with long-range stochastic hopping. For (i) and (ii) we compute the full temperature and dephasing dependence of the conductance of the system, both for two- and four-points measurements. Our solution gives access to the regime of finite temperature of the reservoirs, which could not be obtained by previous approaches. For (iii), we unveil a ballistic-to-diffusive transition governed by the range and the nature (quantum or classical) of the hopping. As a byproduct, our approach equally describes the mean behavior of quantum systems under continuous measurement.

An intrinsic antiferromagnetic topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ arises when intercalating a Mn-Te bilayer chain in a topological insulator, ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. We present observations on the inter- and intralayer phonon modes of the generalized $\mathrm{Mn}{\mathrm{Bi}}_{2n}{\mathrm{Te}}_{3n+1}\left(n=1,2,3,4\right)$ family using cryogenic low-frequency Raman spectroscopy with various polarization configurations. Two peaks at 66 and $112\mathrm{c}{\mathrm{m}}^{\text{–}1}$ show abnormal perturbation in Raman linewidths below magnetic transition temperature due to spin-phonon coupling. In ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$, ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ layers induce Davydov splitting of the $A_{1g}$ mode around $137\mathrm{c}{\mathrm{m}}^{\text{–}1}$ at 5 K. The out-of-plane interlayer force constant estimated using the linear chain model was $(3.98\pm 0.14)\times {10}^{19}\mathrm{N}/{\mathrm{m}}^3$, three times weaker than that of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. Adding more ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ layers, such as ${\mathrm{MnBi}}_6{\mathrm{Te}}_{10}$ and ${\mathrm{MnBi}}_8{\mathrm{Te}}_{13}$, makes ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ properties more dominant than magnetic properties. Our work experimentally and theoretically discovers the dynamics of phonon modes of $\mathrm{Mn}{\mathrm{Bi}}_{2n}{\mathrm{Te}}_{3n+1}$ family, facilitating utilization of magnetic topological heterostructures.

Dipolar magnon-magnon coupling has long been predicted in nanopatterned artificial spin systems. However, observation of such phenomena and related collective spin-wave signatures have until recently proved elusive or been limited to low-power edge modes which are difficult to measure experimentally. Here we describe the requisite conditions for dipolar mode-hybridization, how it may be controlled, why it was not observed earlier, and how strong coupling may occur between nanomagnet bulk modes. We experimentally investigate four nanopatterned artificial spin system geometries: chevron arrays, square, staircase, and brickwork artificial spin ices. We observe significant dynamic dipolar-coupling in all systems with relative coupling strengths and avoided-crossing gaps supported by micromagnetic-simulation results. We demonstrate reconfigurable mode-hybridization regimes in each system via microstate control, and in doing so elucidate the underlying dynamics governing dynamic dipolar-coupling with implications across reconfigurable magnonics. We demonstrate that confinement of the bulk modes via edge effects plays a critical role in dipolar hybridized modes, and treating each nanoisland as a coherently precessing macro-spin or a standing spin-wave is insufficient to capture experimentally observed coupling phenomena. Finally, we present a parameter-space search detailing how coupling strength may be tuned via nanofabrication dimensions and material properties.

Density functional theory is the standard theory for computing the electronic structure of materials, which is based on a functional that maps the electron density to the energy. However, a rigorous form of the functional is not known and has been heuristically constructed by interpolating asymptotic constraints known for extreme situations, such as isolated atoms and uniform electron gas. Recent studies have demonstrated that the functional can be effectively approximated using machine learning (ML) approaches. However, most ML models do not satisfy asymptotic constraints. In this paper, by applying a ML model architecture, we demonstrate a neural network-based exchange-correlation functional satisfying physical asymptotic constraints. Calculations reveal that the trained functional is applicable to various materials with an accuracy higher than that of existing functionals, even for materials whose electronic properties are not included in training dataset. Our proposed method thus improves the accuracy and generalization performance of the ML-based functional by combining the advantages of ML and analytical modeling.

We describe a new class of nonequilibrium quantum many-body phenomena in the form of networks of caustics that dominate the many-body wave function in the semiclassical regime following a sudden quench. It includes the light cone-like propagation of correlations as a particular case. Caustics are singularities formed by the birth and death of waves and form a hierarchy of universal patterns whose natural mathematical description is via catastrophe theory. Examples in classical waves range from rainbows and gravitational lensing in optics to tidal bores and rogue waves in hydrodynamics. Quantum many-body caustics are discretized by second quantization (“quantum catastrophes”) and live in Fock space, which can potentially have many dimensions. We illustrate these ideas using the Bose Hubbard dimer and trimer models, which are simple enough that the caustic structure can be elucidated from first principles and yet run the full range from integrable to nonintegrable dynamics. The dimer gives rise to discretized versions of fold and cusp catastrophes whereas the trimer allows for higher catastrophes including the codimension-3 hyperbolic and elliptic umbilics, which are organized by, and projections of, an 8-dimensional corank-2 catastrophe known as $X_9$. These results describe a hitherto unrecognized form of universality in quantum dynamics organized by singularities that manifest as strong fluctuations in mode population probabilities.

Ultrafast magnetization dynamics are governed by energy flow between electronic, magnetic, and lattice degrees of freedom. A quantitative understanding of these dynamics must be based on a model that agrees with experimental results for all three subsystems. However, ultrafast dynamics of the lattice remain largely unexplored experimentally. Here we combine femtosecond electron diffraction experiments of the lattice dynamics with energy-conserving atomistic spin dynamics (ASD) simulations and ab initio calculations to study the intrinsic energy flow in the $3d$ ferromagnets cobalt (Co) and iron (Fe). The simulations yield a good description of experimental data, in particular an excellent description of our experimental results for the lattice dynamics. We find that the lattice dynamics are influenced significantly by the magnetization dynamics due to the energy cost of demagnetization. Our results highlight the role of the spin system as the dominant heat sink in the first hundreds of femtoseconds. Together with previous findings for nickel [Zahn et al., Phys. Rev. Research 3, 023032 (2021)], our work demonstrates that energy-conserving ASD simulations provide a general and consistent description of the laser-induced dynamics in all three elemental $3d$ ferromagnets.

Dynamic and steady-state aspects of wave propagation are deeply connected in lossless open systems in which the scattering matrix is unitary. There is then an equivalence among the energy excited within the medium through all channels, the Wigner time delay, which is the sum of dwell times in all channels coupled to the medium, and the density of states. But these equivalences fall away in the presence of material loss or gain. In this paper, we use microwave measurements, numerical simulations, and theoretical analysis to discover the changing relationships among fundamental wave properties with loss and gain, and their dependence upon dimensionality and spectral overlap. We begin with the demonstrations that the transmission time in random 1D media is equal to the density of states even in the presence of ultrastrong absorption and that its ensemble average is independent of the strengths of scattering and absorption. In contrast, the Wigner time becomes imaginary in the presence of loss, with real and imaginary parts that fall with absorption. In multichannel media, the transmission time remains equal to the density of states and is independent of the scattering strength in unitary systems but falls with absorption to a degree that increases with the strengths of absorption and scattering, and the number of channels coupled to the medium. We show that the relationships between key propagation variables in non-Hermitian systems can be understood in terms of the singularities of the phase of the determinant of the transmission matrix. The poles of the transmission matrix are the same as those of the scattering matrix, but the transmission zeros are fundamentally different. Whereas the zeros of the scattering matrix are the complex conjugates of the poles, the transmission zeros are topological: in unitary systems they occur only singly on the real axis or as conjugate pairs. We follow the evolution and statistics of zeros in the complex plane as random samples are deformed. The sensitivity of the spacing of zeros in the complex plane with deformation of the sample has a square-root singularity at a zero point at which two single zeros and a complex pair interconvert. The transmission time is a sum of Lorentzian functions associated with poles and zeros. The sum over poles is the density of states with an average that is independent of scattering and dissipation. But the sum over zeros changes with loss, gain, scattering strength and the number of channels in ways that make it possible to control ultranarrow spectral features in transmission and transmission time. We show that the field, including the contribution of the still coherent incident wave, is a sum over modal partial fractions with amplitudes that are independent of loss and gain. The energy excited may be expressed in terms of the resonances of the medium and is equal to the dwell time even in the presence of loss or gain.

Using first-principles calculations and group-theory-based models, we study the stabilization of ferrielectricity (FiE) in ${\mathrm{CuInP}}_2{\mathrm{Se}}_6$. We find that the FiE ground state is stabilized by a large anharmonic coupling between the polar mode and a fully symmetric Raman-active mode. Our results open possibilities for controlling the single-step switching barrier for polarization by tuning the Raman-active mode. We discuss the implications of our findings in the context of designing next-generation optoelectronic devices that can overcome the voltage-time dilemma.