Ceramics, often exhibiting important functional properties like piezoelectricity, superconductivity, and magnetism, are usually mechanically brittle at room temperature and even more brittle at low temperature due to their ionic or covalent bonding nature. The brittleness in their working temperature range (mostly from room down to cryogenic temperatures) has been a limiting factor for the usefulness of these ceramics. In this Letter, we report a surprising “low-temperature toughening” phenomenon in a La-doped ${\mathrm{CaTiO}}_3$ perovskite ceramic, where a $2.5\times$ increase of fracture toughness $K_{\mathrm{IC}}$ from 1.9 to $4.8\mathrm{MPa}{\mathrm{m}}^{1/2}$ occurs when cooling from above room temperature (323 K) down to a cryogenic temperature of 123 K, the lowest temperature our experiment can reach. In situ microscopic observations in combination with macroscopic characterizations show that this desired but counterintuitive phenomenon stems from a reentrant strain-glass transition, during which nanosized orthorhombic ferroelastic domains gradually emerge from the existing tetragonal ferroelastic matrix. The temperature stability of this unique microstructure and its stress-induced transition into the macroscopic orthorhombic phase provide a low-temperature toughening mechanism over a wide temperature range and explain the observed phenomenon. Our finding may open a way to design tough ceramics with a wide temperature range and shed light on the nature of reentrant transitions in other ferroic systems.

Higher-order topological phases have raised widespread interest in recent years with the occurrence of the topological boundary states of dimension two or more less than that of the system bulk. The higher-order topological states have been verified in gapped phases, in a wide variety of systems, such as photonic and acoustic systems, and recently also observed in gapless semimetal phase, such as Weyl and Dirac phases, in systems alike. The higher-order topology is signaled by the hinge states emerging in the common band gaps of the bulk states and the surface states. In this Letter, we report our first prediction and observation of a new type of hinge states, the bound hinge states in the continuum (BHICs) bulk band, in a higher-order Weyl semimetal implemented in phononic crystal. In contrast to the hinge state in gap, which is characterized by the bulk polarization, the BHIC is identified by the nontrivial surface polarization. The finding of the topological BHICs broadens our insight to the topological states, and may stimulate similar researches in other systems such as electronic, photonic, and cold atoms systems. Our Letter may pave the way toward high-$Q$ acoustic devices in application.

Dislocation glide, deformation twinning, and phase transition are critical mechanisms resulting in irreversible plastic deformations of materials. Because of the lack of dislocation movement, superhard ceramics generally exhibit brittle failure at room temperature. Here, by employing molecular dynamics simulations using a machine-learning force field, we reveal several plastic deformation mechanisms in superhard boron carbide as a small amount of aluminum (Al) is doped. Under shear deformation, dislocation nucleation and glide occur in Al-doped boron carbide (${\mathrm{B}}_{12}$-CAlC) due to the breakage of weakened chain bonds rather than the disintegration of icosahedral clusters. The dislocation activities then cause twin boundaries to migrate, thereby mitigating amorphization and enhancing ductility. Furthermore, the mobile dislocation with the Burgers vector of $\mathit{b}=⟨1\overline{1}0⟩\{111\}$ is observed in the tensile nanopillar, which is well consistent with the experiment. This Letter demonstrates that mobile dislocation could be activated in superstrong covalent materials through a simple doping strategy.

As the complexity of quantum systems such as quantum bit arrays increases, efforts to automate expensive tuning are increasingly worthwhile. We investigate machine learning based tuning of gate arrays using the covariance matrix adaptation evolution strategy algorithm for the case study of Majorana wires with strong disorder. We find that the algorithm is able to efficiently improve the topological signatures, learn intrinsic disorder profiles, and completely eliminate disorder effects. For example, with only 20 gates, it is possible to fully recover Majorana zero modes destroyed by disorder by optimizing gate voltages.

Andreev bound states with opposite phase-inversion asymmetries are observed in local tunneling spectra at the two ends of a superconductor-semiconductor-superconductor planar Josephson junction in the presence of a perpendicular magnetic field, while the nonlocal spectra remain phase symmetric. Spectral signatures agree with a theoretical model, yielding a physical picture in which phase textures in superconducting leads localize and control the position of Andreev bound states in the junction, demonstrating a simple means of controlling the position and size of Andreev states within a planar junction.

We provide strong evidence of the spin-nematic state in a paradigmatic ferro-antiferromagnetic $J_1\text{−}{J}_2$ model using analytical and density-matrix renormalization group methods. In zero field, the attraction of spin-flip pairs leads to a first-order transition and no nematic state, while pair repulsion at larger $J_2$ stabilizes the nematic phase in a narrow region near the pair-condensation field. A devil’s staircase of multipair condensates is conjectured for weak pair attraction. A suppression of the spin-flip gap by many-body effects leads to an order-of-magnitude contraction of the nematic phase compared to naïve expectations. The proposed phase diagram should be broadly valid.

Reconstructing network dynamics from data is crucial for predicting the changes in the dynamics of complex systems such as neuron networks; however, previous research has shown that the reconstruction is possible under strong constraints such as the need for lengthy data or small system size. Here, we present a recovery scheme blending theoretical model reduction and sparse recovery to identify the governing equations and the interactions of weakly coupled chaotic maps on complex networks, easing unrealistic constraints for real-world applications. Learning dynamics and connectivity lead to detecting critical transitions for parameter changes. We apply our technique to realistic neuronal systems with and without noise on a real mouse neocortex and artificial networks.

Salty water is the most abundant electrolyte aqueous mixture on Earth, however, very little is known about the NaCl–saturated solution interfacial free energy (${\gamma }_s$). Here, we provide the first direct estimation of ${\gamma }_s$ for several NaCl crystallographic planes by means of the mold integration technique, a highly efficient computational method to evaluate interfacial free energies with anisotropic crystal resolution. Making use of the $\mathrm{JC}\text{−}\mathrm{SPC}/\mathrm{E}$ model, one of the most benchmarked force fields for NaCl water solutions, we measure ${\gamma }_s$ of four different crystal planes, (100), (110), (111), and $(11\overline{2})$ with the saturated solution at normal conditions. We find high anisotropy between the different crystal orientations with values ranging from 100 to $150\mathrm{mJ}{\mathrm{m}}^{-2}$, and the average value of the distinct planes being ${\overline{\gamma }}_s=137(20)\mathrm{mJ}{\mathrm{m}}^{-2}$. This value for the coexistence interfacial free energy is in reasonable agreement with previous extrapolations from nucleation studies. Our Letter represents a milestone in the computational calculation of interfacial free energies between ionic crystals and aqueous solutions.

A novel analysis is performed, incorporating time-of-flight (TOF) information to study the interactions of dark matter (DM) with standard model particles. After supernova (SN) explosions, DM with mass $m_{\chi }\lesssim \mathcal{O}(\mathrm{MeV})$ in the halo can be boosted by SN neutrinos ($\mathrm{SN}\nu$) to relativistic speed. The $\mathrm{SN}\nu$ boosted DM (BDM) arrives on Earth with TOF which depends only on $m_{\chi }$ and is independent of the cross section. These BDMs can interact with detector targets in low-background experiments and manifest as afterglow events after the arrival of $\mathrm{SN}\nu$. The characteristic TOF spectra of the BDM events can lead to large background suppression and unique determination of $m_{\chi }$. New cross section constraints on $\sqrt{{\sigma }_{\chi e}{\sigma }_{\chi \nu }}$ are derived from SN1987a in the Large Magellanic Cloud with data from the Kamiokande and Super-Kamiokande experiments. Potential sensitivities for the next galactic SN with Hyper-Kamiokande are projected. This analysis extends the existing bounds on $\sqrt{{\sigma }_{\chi e}{\sigma }_{\chi \nu }}$ over a broad range of $r_{\chi }={\sigma }_{\chi \nu }/{\sigma }_{\chi e}$. In particular, the improvement is by 1–3 orders of magnitude for $m_{\chi }<\mathcal{O}(100\mathrm{keV})$ for ${\sigma }_{\chi e}\sim {\sigma }_{\chi \nu }$. Prospects of exploiting TOF information in other astrophysical systems to probe exotic physics with other DM candidates are discussed.

Gravitational atoms produced from the superradiant extraction of rotational energy of spinning black holes can reach energy densities significantly higher than that of dark matter, turning black holes into powerful potential detectors for ultralight bosons. These structures are formed by coherently oscillating bosons, which induce oscillating metric perturbations deflecting photon geodesics passing through their interior. The deviation of nearby geodesics can be further amplified near critical bound photon orbits. We discuss the prospect of detecting this deflection using photon ring autocorrelations with the Event Horizon Telescope and its next-generation upgrade, which can probe a large unexplored region of the cloud mass parameter space when compared with previous constraints.

We report on measurements of sequential $\mathrm{\Upsilon }$ suppression in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ with the STAR detector at the Relativistic Heavy Ion Collider (RHIC) through both the dielectron and dimuon decay channels. In the 0%–60% centrality class, the nuclear modification factors ($R_{AA}$), which quantify the level of yield suppression in heavy-ion collisions compared to $p+p$ collisions, for $\mathrm{\Upsilon }(1S)$ and $\mathrm{\Upsilon }(2S)$ are $0.40\pm 0.03(\mathrm{stat})\pm 0.03(\mathrm{sys})\pm 0.09(\mathrm{norm})$ and $0.26\pm 0.08(\mathrm{stat})\pm 0.02(\mathrm{sys})\pm 0.06(\mathrm{norm})$, respectively, while the upper limit of the $\mathrm{\Upsilon }(3S)$ $R_{AA}$ is 0.17 at a 95% confidence level. This provides experimental evidence that the $\mathrm{\Upsilon }(3S)$ is significantly more suppressed than the $\mathrm{\Upsilon }(1S)$ at RHIC. The level of suppression for $\mathrm{\Upsilon }(1S)$ is comparable to that observed at the much higher collision energy at the Large Hadron Collider. These results point to the creation of a medium at RHIC whose temperature is sufficiently high to strongly suppress excited $\mathrm{\Upsilon }$ states.

We report the ionization reduction of atoms in two-color femtosecond laser fields in this joint theoretical-experimental study. For the multiphoton ionization of atoms using a 400 nm laser pulse, the ionization probability is reduced if another relatively weak 800 nm laser pulse is overlapped. Such ionization reduction consistently occurs regardless of the relative phase between the two pulses. The time-dependent Schrödinger equation simulation results indicate that with the assisted 800 nm photons the electron can be launched to Rydberg states with large angular quantum numbers, which stand off the nuclei and thus are hard to be freed in the multiphoton regime. This mechanism works for hydrogen, helium, and probably some other atoms if two-color laser fields are properly tuned.

In recent times the possibility of nonreciprocity in heat transfer between two bodies has been extensively studied. In particular the role of strong magnetic fields has been investigated. A much simpler approach with considerable flexibility would be to consider heat transfer in synthetic electric and magnetic fields that are easily applied. We demonstrate the breakdown of detailed balance for the heat transfer function $\mathcal{T}(\omega )$, i.e., the spectrum of heat transfer between two objects due to the presence of synthetic electric and magnetic fields. The spectral measurements carry much more physical information and are the reason for the quantum theory of radiation. We demonstrate explicitly the synthetic field induced nonreciprocity in the heat transfer transmission function between two graphene flakes and for the Casimir coupling between two objects. Unlike many other cases of heat transfer, the latter case has interesting features of the strong coupling. Further the presence of synthetic fields affects the mean occupation numbers of two membranes and we propose this system for the experimental verification of the breakdown of detailed balance.

Strong local passivity is a property of multipartite quantum systems from which it is impossible to extract energy locally. Surprisingly, if the strong local passive state displays entanglement, it could be possible to locally activate energy density by adding classical communication between different partitions of the system, through so-called “quantum energy teleportation” protocols. Here, we report both the first experimental observation of local activation of energy density on an entangled state and the first realization of a quantum energy teleportation protocol using nuclear magnetic resonance on a bipartite quantum system.

We identify examples of single field inflationary trajectories beyond the slow-roll regime that improve the fit to Planck 2018 data compared to a baseline $\mathrm{\Lambda }$ cold dark matter model with power law form of primordial spectrum and at the same time alleviate existing tensions between different datasets in the estimate of cosmological parameters such as $H_0$ and $S_8$. A damped oscillation in the first Hubble flow function—or equivalently a feature in the potential—and the corresponding localized oscillations in the primordial power spectrum partially mimic the improvement in the fit of Planck data due to $A_L$ or ${\mathrm{\Omega }}_K$. Compared to the baseline model, this model can lead simultaneously to a larger value of $H_0$ and a smaller value of $S_8$, a trend that can be enhanced when the most recent SH0ES measurement for $H_0$ is combined with Planck and BICEP-Keck 2018 data. Large scale structure data and more precise cosmic microwave background polarization measurements will further provide critical tests of this intermediate fast-roll phase.

We present the first search for the pair production of dark particles $X$ via $K_L^0\to XX$ with $X$ decaying into two photons using the data collected by the KOTO experiment. No signal was observed in the mass range of $40–110\mathrm{MeV}/c^2$ and $210–240\mathrm{MeV}/c^2$. This sets upper limits on the branching fractions as $\mathcal{B}(K_L^0\to XX)<(1–4)\times {10}^{-7}$ and $\mathcal{B}(K_L^0\to XX)<(1–2)\times {10}^{-6}$ at the 90% confidence level for the two mass regions, respectively.

Long-term quantum coherence constitutes one of the main challenges when engineering quantum devices. However, easily accessible means to quantify complex decoherence mechanisms are not readily available, nor are sufficiently stable systems. We harness novel phase-space methods—expressed through non-Gaussian convolutions of highly singular Glauber-Sudarshan quasiprobabilities—to dynamically monitor quantum coherence in polariton condensates with significantly enhanced coherence times. Via intensity- and time-resolved reconstructions of such phase-space functions from homodyne detection data, we probe the systems’ resourcefulness for quantum information processing up to the nanosecond regime. Our experimental findings are confirmed through numerical simulations, for which we develop an approach that renders established algorithms compatible with our methodology. In contrast to commonly applied phase-space functions, our distributions can be directly sampled from measured data, including uncertainties, and yield a simple operational measure of quantum coherence via the distribution’s variance in phase. Therefore, we present a broadly applicable framework and a platform to explore time-dependent quantum phenomena and resources.

We study two-phase displacement via the steady compression of an air reservoir connected to an oil-filled capillary tube. Our experiments and modeling reveal complex displacement dynamics depending on compression rate and reservoir volume that, for large reservoirs, depend on a single dimensionless compressibility number. We identify two distinct displacement regimes, separated by a critical value of the compressibility number. While the subcritical regime exhibits quasisteady displacement after an initial transient, the supercritical regime exhibits burstlike expulsion.

The linear growth and nonlinear energy transfer of the electron drift instability (EDI) are experimentally measured in the plume of a low-temperature, Hall effect discharge. A frequency-based bispectral analysis technique applied to fast ion density fluctuation measurements shows a growth rate function that is qualitatively similar to predictions from the linear instability dispersion relation, but an order of magnitude smaller. Calculation of the nonlinear transfer function indicates multiple three-wave interactions between high-frequency resonances of the instability in addition to an inverse energy cascade toward lower-frequency modes. These results are discussed in the context of recent theoretical, numerical, and experimental efforts on the EDI in Hall effect discharges and how the EDI may impact anomalous cross field transport.