We report on the use of pairs of 10-cycle extreme ultraviolet wave packets with attosecond-controlled spacing emitted by individual relativistic electrons within an electron bunch passing through a tandem undulator. Based on the temporal coherent control technique with circular polarization, we succeeded in controlling the excited state alignment in the photoexcitation of helium atoms, which we verified through the observation of oscillation in fluorescence yield depending on the attosecond-controlled delay time. Our work demonstrates the potential of undulator radiation for the generation of longitudinally coherent wave packets suitable for attosecond coherent control, an application which has hitherto been hidden in the incoherent nature of the radiation pulse emitted by a bunch of electrons.

Mode locking is predicted in a nanolaser cavity forming an effective photonic harmonic potential. The cavity is substantially more compact than a Fabry-Perot resonator with a comparable pulsing period, which is here controlled by the potential. In the limit of instantaneous gain and absorption saturation, mode locking corresponds to a stable dissipative soliton, which is very well approximated by the coherent state of a quantum mechanical harmonic oscillator. This property is robust against noninstantaneous material response and nonzero phase-intensity coupling.

We show that semiconductor Fano lasers strongly suppress dynamic instabilities induced by external optical feedback. A comparison with conventional Fabry-Perot lasers shows orders of magnitude improvement in feedback stability and in many cases even total suppression of coherence collapse, which is of major importance for applications in integrated photonics. The laser dynamics are analyzed using a generalization of the Lang-Kobayashi model for semiconductor lasers with external feedback, and an analytical expression for the critical feedback level is derived.

Transition metal phosphorous trichalcogenides, $M\mathrm{P}{X}_3$ ($M$ and $X$ being transition metal and chalcogen elements, respectively), have been the focus of substantial interest recently because they are unusual candidates undergoing Mott transition in the two-dimensional limit. Here we investigate material properties of the compounds with $M=\mathrm{Mn}$ and Ni employing ab initio density functional and dynamical mean-field calculations, especially their electronic behavior under external pressure in the paramagnetic phase. Mott metal-insulator transitions (MIT) are found to be a common feature for both compounds, but their lattice structures show drastically different behaviors depending on the relevant orbital degrees of freedom, i.e., $t_{2g}$ or $e_g$. Under pressure, ${\mathrm{MnPS}}_3$ can undergo an isosymmetric structural transition within monoclinic space group by forming Mn-Mn dimers due to the strong direct overlap between the neighboring $t_{2g}$ orbitals, accompanied by a significant volume collapse and a spin-state transition. In contrast, ${\mathrm{NiPS}}_3$ and ${\mathrm{NiPSe}}_3$, with their active $e_g$ orbital degrees of freedom, do not show a structural change at the MIT pressure or deep in the metallic phase within the monoclinic symmetry. Hence ${\mathrm{NiPS}}_3$ and ${\mathrm{NiPSe}}_3$ become rare examples of materials hosting electronic bandwidth-controlled Mott MITs, thus showing promise for ultrafast resistivity switching behavior.

Using a first-principles approach, we design the heteroanionic oxynitride MoON to exhibit a first-order isosymmetric thermally activated Peierls-type metal-insulator transition (MIT). We identify a ground state insulating phase ($\alpha$-MoON) with monoclinic $Pc$ symmetry and a metastable high temperature metallic phase ($\beta$-MoON) of equivalent symmetry. We find that ordered fac-$\mathrm{Mo}{\mathrm{O}}_3{\mathrm{N}}_3$ octahedra with edge and corner connectivity stabilize the twisted Mo-Mo dimers present in the $\alpha$ phase, which activate the MIT through electron localization within the $4d$ $a_{1g}$ manifold. By analyzing the temperature dependence of the soft zone-boundary instability driving the MIT, we estimate an ordering temperature $T_{\mathrm{MIT}}\sim 900\mathrm{K}$. Our work shows that electronic transitions can be designed by exploiting multiple anions, and heteroanionic materials could offer new insights into the microscopic electron-lattice interactions governing unresolved transitions in homoanionic oxides.

Nematic superconductivity with spontaneously broken rotation symmetry has recently been reported in doped topological insulators, $M_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$ ($M=\mathrm{Cu}$, Sr, Nb). Here we show that the electromagnetic (EM) response of these compounds provides a spectroscopy for bosonic excitations that reflect the pairing channel and the broken symmetries of the ground state. Using quasiclassical Keldysh theory, we find two characteristic bosonic modes in nematic superconductors: the nematicity mode and the chiral Higgs mode. The former corresponds to the vibrations of the nematic order parameter associated with broken crystal symmetry, while the latter represents the excitation of chiral Cooper pairs. The chiral Higgs mode softens at a critical doping, signaling a dynamical instability of the nematic state towards a new chiral ground state with broken time reversal and mirror symmetry. Evolution of the bosonic spectrum is directly captured by EM power absorption spectra. We also discuss contributions to the bosonic spectrum from subdominant pairing channels to the EM response.

Kitaev magnets are materials with bond-dependent Ising interactions between localized spins on a honeycomb lattice. Such interactions could lead to a quantum spin-liquid (QSL) ground state at zero temperature. Recent theoretical studies suggest two potential signatures of a QSL at finite temperatures, namely, a scaling behavior of thermodynamic quantities in the presence of quenched disorder, and a two-step release of the magnetic entropy. Here, we present both signatures in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$ which is synthesized from $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ by replacing the interlayer Li atoms with Ag atoms. In addition, the dc susceptibility data confirm the absence of a long-range order, and the ac susceptibility data rule out a spin-glass transition. These observations suggest a closer proximity to the QSL in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$ compared to its parent compound $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ that orders at 15 K. We discuss an enhanced spin-orbit coupling due to a mixing between silver $d$ and oxygen $p$ orbitals as a potential underlying mechanism.

We discuss quasi-one-dimensional magnetic Mott insulators from the pyroxene family where spin and orbital degrees of freedom remain tightly bound. We analyze their excitation spectrum and outline the conditions under which the orbital degrees of freedom become liberated so that the corresponding excitations become dispersive and the spectral weight shifts to energies much smaller than the exchange integral.

A large noncollinear magnetoresistance (NCMR) is observed for $\mathrm{Rh}/\mathrm{Co}$ atomic bilayers on Ir(111) using scanning tunneling microscopy and spectroscopy. The effect is 20% at the Fermi energy and large in a broad energy range. The NCMR can be used to electrically detect nanometer-scale domain walls and skyrmions directly in the tunnel current without the need for a differential measurement. The NCMR results from changes in the density of states of noncollinear spin textures with respect to the ferromagnetic state. Density functional theory calculations reveal that they originate from spin mixing between majority $d_{xz}$ and minority $p_z$ states.

We address the question of how interacting active systems in a nonequilibrium steady state respond to an external perturbation. We establish an extended fluctuation-dissipation theorem for active Brownian particles (ABP), which highlights the role played by the local violation of detailed balance due to activity. By making use of a Markovian approximation we derive closed Green-Kubo expressions for the diffusivity and mobility of ABP and quantify the deviations from the Stokes-Einstein relation. We compute the linear response function to an external force using unperturbed simulations of ABP and compare the results with the analytical predictions of the transport coefficients. Our results show the importance of the interplay between activity and interactions in the departure from equilibrium linear response.

The swimming of a rigid phoretic particle in an isotropic fluid is studied numerically as a function of the dimensionless solute emission rate (or Péclet number Pe). The particle sets into motion at a critical Pe. Whereas the particle trajectory is straight at a small enough Pe, it is found that it loses its stability at a critical Pe in favor of a meandering motion. When Pe is increased further, the particle meanders at a short scale but its trajectory wraps into a circle at a larger scale. Increasing even further, Pe causes the swimmer to escape momentarily the circular trajectory in favor of chaotic motion, which lasts for a certain time, before regaining a circular trajectory, and so on. The chaotic bursts become more and more frequent as Pe increases, until the trajectory becomes fully chaotic, via the intermittency scenario. The statistics of the trajectory is found to be of the run-and-tumble-like nature at a short enough time and of diffusive nature at a long time without any source of noise.

We employ a matrix-based solver for the linear rheology of fluid-immersed disordered spring networks to reveal four distinct dynamic response regimes. One regime—completely absent in the known vacuum response—exhibits coupled fluid flow and network deformation, with both components responding nonaffinely. This regime contains an additional plateau (peak) in the frequency-dependent storage (loss) modulus—features that vanish without full hydrodynamic interactions. The mechanical response of immersed networks such as biopolymers and hydrogels is thus richer than previously established and offers additional modalities for design and control through fluid interactions.

We present a technique for recovering the spectrum of a non-Markovian bosonic bath and/or non-Markovian noises coupled to a harmonic oscillator. The treatment is valid under the conditions that the environment is large and hot compared to the oscillator, and that its temporal autocorrelation functions are symmetric with respect to time translation and reflection—criteria which we consider fairly minimal. We model a demonstration of the technique as deployed in the experimental scenario of a nanosphere levitated in a Paul trap, and show that it would effectively probe the spectrum of an electric field noise source from $10^2$ to $10^6\mathrm{Hz}$ with a resolution inversely proportional to the measurement time. This technique may be deployed in quantum sensing, metrology, computing, and in experimental probes of foundational questions.

We present the first determination of the Hubble constant $H_0$ from strong lensing time delay data and type Ia supernova luminosity distances that is independent of the cosmological model. We also determine the spatial curvature model independently. We assume that light propagation over long distances is described by the Friedmann-Lemaître-Robertson-Walker (FLRW) metric and geometrical optics holds, but make no assumption about the contents of the Universe or the theory of gravity on cosmological scales. We find $H_0={75.7}_{-4.4}^{+4.5}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ and ${\mathrm{\Omega }}_{K0}=0.12_{-0.25}^{+0.27}$. This is a 6% determination of $H_0$. A weak prior from the cosmic microwave background on the distance to the last scattering surface improves this to $H_0={76.8}_{-3.8}^{+4.2}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ and ${\mathrm{\Omega }}_{K0}=0.18_{-0.18}^{+0.25}$. Assuming a zero spatial curvature, we get $H_0={74.2}_{-2.9}^{+3.0}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, a precision of 4%. The measurements also provide a consistency test of the FLRW metric: we find no evidence against it.

We use data from the T-SAGE instrument on board the MICROSCOPE space mission to search for Lorentz violation in matter-gravity couplings as described by the Lorentz violating standard model extension (SME) coefficients $({\overline{a}}_{\mathrm{eff}}{)}_{\mu }^w$, where ($\mu =T$, $X$, $Y$, $Z$) and ($w=e$, $p$, $n$) for the electron, proton, and neutron. One of the phenomenological consequences of a nonzero value of those coefficients is that test bodies of different composition fall differently in an external gravitational field. This is similar to “standard” tests of the universality of free fall, but with a specific signature that depends on the orbital velocity and rotation of Earth. We analyze data from five measurement sessions of MICROSCOPE spread over a year finding no evidence for such a signature, but setting constraints on linear combinations of the SME coefficients that improve on best previous results by 1 to 2 orders of magnitude. Additionally, our independent linear combinations are different from previous ones, which increases the diversity of available constraints, paving the way towards a full decorrelation of the individual coefficients.

By analyzing a $2.93{\mathrm{fb}}^{-1}$ data sample of $e^{+}{e}^{-}$ collisions, recorded at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we report the first observation of the semileptonic $D^{+}$ transition into the axial-vector meson $D^{+}\to {\overline{K}}_1(1270{)}^0{e}^{+}{\nu }_e$ with a statistical significance greater than $10\sigma$. Its decay branching fraction is determined to be $\mathcal{B}[D^{+}\to {\overline{K}}_1(1270{)}^0{e}^{+}{\nu }_e]=(2.30\pm {0.26}_{-0.21}^{+0.18}\pm 0.25)\times {10}^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of ${\overline{K}}_1(1270{)}^0\to K^{-}{\pi }^{+}{\pi }^0$.

We investigate a Bose-Einstein condensate strongly coupled to an optical cavity via a repulsive optical lattice. We detect a stable self-ordered phase in this regime, and show that the atoms order through an antisymmetric coupling to the $P$ band of the lattice, limiting the extent of the phase and changing the geometry of the emergent density modulation. Furthermore, we find a nonequilibrium phase with repeated intense bursts of the intracavity photon number, indicating nontrivial driven-dissipative dynamics.

The material release on the side opposite to the laser drive of a CH shell was probed at conditions relevant to inertial confinement fusion. The release was found to expand further with a longer scale length than that predicted by radiation-hydrodynamic simulations. The simulations show that a relaxation of the back side of the shell consistent with measurements explains the experimentally observed reduction in inertial confinement fusion implosion performance—specifically, reduced areal density at peak compression.