We report on laser cooling of a large fraction of positronium (Ps) in free flight by strongly saturating the $1^{3}S\text{−}{2}^{3}P$ transition with a broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is produced in a magnetic and electric field-free environment. We observe two different laser-induced effects. The first effect is an increase in the number of atoms in the ground state after the time Ps has spent in the long-lived $2^{3}P$ states. The second effect is one-dimensional Doppler cooling of Ps, reducing the cloud’s temperature from 380(20) to 170(20) K. We demonstrate a 58(9)% increase in the fraction of Ps atoms with $v_{1\text{D}}<3.7\times {10}^4\mathrm{m}{\mathrm{s}}^{-1}$.

We theoretically study propagating correlation fronts in noninteracting fermions on a one-dimensional lattice starting from an alternating state, where the fermions occupy every other site. We find that, in the long-time asymptotic regime, all the moments of dynamical fluctuations around the correlation fronts are described by the universal correlation functions of Gaussian orthogonal and symplectic random matrices at the soft edge. Our finding here sheds light on a hitherto unknown connection between random matrix theory and correlation propagation in quantum dynamics.

We characterize the equation of state (EoS) of the $\mathrm{SU}(N>2)$ Fermi-Hubbard Model (FHM) in a two-dimensional single-layer square optical lattice. We probe the density and the site occupation probabilities as functions of interaction strength and temperature for $N=3$, 4, and 6. Our measurements are used as a benchmark for state-of-the-art numerical methods including determinantal quantum Monte Carlo and numerical linked cluster expansion. By probing the density fluctuations, we compare temperatures determined in a model-independent way by fitting measurements to numerically calculated EoS results, making this a particularly interesting new step in the exploration and characterization of the $\mathrm{SU}(N)$ FHM.

The production rate of ${\mathrm{\Lambda }}_b^0$ baryons relative to $B^0$ mesons in $pp$ collisions at a center-of-mass energy $\sqrt{s}=13\mathrm{TeV}$ is measured by the LHCb experiment. The ratio of ${\mathrm{\Lambda }}_b^0$ to $B^0$ production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in $e^{+}{e}^{-}$ collisions, and increases by a factor of $\sim 2$ with increasing multiplicity. At relatively low transverse momentum, the ratio of ${\mathrm{\Lambda }}_b^0$ to $B^0$ cross sections is higher than what is measured in $e^{+}{e}^{-}$ collisions, but converges with the $e^{+}{e}^{-}$ ratio as the momentum increases. These results imply that the evolution of heavy $b$ quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed.

We study the dynamics of an oscillating, free-floating robot that generates radially expanding gravity-capillary waves at a fluid surface. In open water, the device does not self-propel; near a rigid boundary, it can be attracted or repelled. Visualization of the wave field dynamics reveals that when near a boundary, a complex interference of generated and reflected waves induces a wave amplitude fluctuation asymmetry. Attraction increases as wave frequency increases or robot-boundary separation decreases. Theory on confined gravity-capillary wave radiation dynamics developed by Hocking in the 1980s captures the observed parameter dependence due to these “Hocking fields.” The flexibility of the robophysical system allows detailed characterization and analysis of locally generated nonequilibrium fluctuation-induced forces [M. Kardar and R. Golestanian, Rev. Mod. Phys. 71, 1233 (1999)].

We have measured the flexophotovoltaic effect of single crystals of halide perovskites ${\mathrm{MAPbBr}}_3$ and ${\mathrm{MAPbI}}_3$, as well as the benchmark oxide perovskite ${\mathrm{SrTiO}}_3$. For halide perovskites, the flexophotovoltaic effect is found to be orders of magnitude larger than for ${\mathrm{SrTiO}}_3$, and indeed large enough to induce photovoltages bigger than the band gap. Moreover, we find that in ${\mathrm{MAPbI}}_3$ the flexophotovoltaic effect is additional to a native bulk photovoltaic response that is switchable and ferroelectric-like. The results suggest that strain gradient engineering can be a powerful tool to modify the photovoltaic output even in already well-established photovoltaic materials.

Magnon transistors that can effectively regulate magnon transport by an electric field are desired for magnonics, which aims to provide a Joule-heating free alternative to the conventional electronics owing to the electric neutrality of magnons (the key carriers of spin-angular momenta in the magnonics). However, also due to their electric neutrality, magnons have no access to directly interact with an electric field and it is thus difficult to manipulate magnon transport by voltages straightforwardly. Here, we demonstrated a gate voltage ($V_{\mathrm{g}}$) applied on a nonmagnetic metal and magnetic insulator (MI) interface that bent the energy band of the MI and then modulated the probability for conduction electrons in the nonmagnetic metal to tunnel into the MI, which can consequently enhance or weaken the spin-magnon conversion efficiency at the interface. A voltage-controlled magnon transistor based on the magnon-mediated electric current drag (MECD) effect in a $\mathrm{Pt}\text{−}{\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}\text{−}\mathrm{Pt}$ sandwich was then experimentally realized with $V_{\mathrm{g}}$ modulating the magnitude of the MECD signal. The obtained efficiency (the change ratio between the MECD voltage at $\pm V_{\mathrm{g}}$) reached $10\%/(\mathrm{MV}/\mathrm{cm})$ at 300 K. This prototype of magnon transistor offers an effective scheme to control magnon transport by a gate voltage.

We study experimentally and theoretically the hybridization among intralayer and interlayer moiré excitons in a ${\mathrm{MoSe}}_2/{\mathrm{WS}}_2$ heterostructure with antiparallel alignment. Using a dual-gate device and cryogenic white light reflectance and narrow-band laser modulation spectroscopy, we subject the moiré excitons in the ${\mathrm{MoSe}}_2/{\mathrm{WS}}_2$ heterostack to a perpendicular electric field, monitor the field-induced dispersion and hybridization of intralayer and interlayer moiré exciton states, and induce a crossover from type I to type II band alignment. Moreover, we employ perpendicular magnetic fields to map out the dependence of the corresponding exciton Landé $g$ factors on the electric field. Finally, we develop an effective theoretical model combining resonant and nonresonant contributions to moiré potentials to explain the observed phenomenology, and highlight the relevance of interlayer coupling for structures with close energetic band alignment as in ${\mathrm{MoSe}}_2/{\mathrm{WS}}_2$.

Five previously unknown isotopes (${}^{182,183}\mathrm{Tm}$, ${}^{186,187}\mathrm{Yb}$, ${}^{190}\mathrm{Lu}$) were produced, separated, and identified for the first time at the Facility for Rare Isotope Beams (FRIB) using the Advanced Rare Isotope Separator (ARIS). The new isotopes were formed through the interaction of a ${}^{198}\mathrm{Pt}$ beam with a carbon target at an energy of $186\mathrm{MeV}/u$ and with a primary beam power of 1.5 kW. Event-by-event particle identification of $A$, $Z$, and $q$ for the reaction products was performed by combining measurements of the energy loss, time of flight, magnetic rigidity $B\rho$, and total kinetic energy. The ARIS separator has a novel two-stage design with high resolving power to strongly suppress contaminant beams. This successful new isotope search was performed less than one year after FRIB operations began and demonstrates the discovery potential of the facility which will ultimately provide 400 kW of primary beam power.

Using the fusion-evaporation reaction ${}^{106}\mathrm{Cd}({}^{58}\mathrm{Ni},4n){}^{160}\mathrm{Os}$ and the gas-filled recoil separator SHANS, two new isotopes ${}_{76}{}^{160}\mathrm{Os}$ and ${}_{74}{}^{156}\mathrm{W}$ have been identified. The $\alpha$ decay of ${}^{160}\mathrm{Os}$, measured with an $\alpha$-particle energy of 7080(26) keV and a half-life of ${201}_{-37}^{+58}\mathrm{\mu }\mathrm{s}$, is assigned to originate from the ground state. The daughter nucleus ${}^{156}\mathrm{W}$ is a ${\beta }^{+}$ emitter with a half-life of ${291}_{-61}^{+86}\mathrm{ms}$. The newly measured $\alpha$-decay data allow us to derive $\alpha$-decay reduced widths (${\delta }^2$) for the $N=84$ isotones up to osmium ($Z=76$), which are found to decrease with increasing atomic number above $Z=68$. The reduction of ${\delta }^2$ is interpreted as evidence for the strengthening of the $N=82$ shell closure toward the proton drip line, supported by the increase of the neutron-shell gaps predicted in theoretical models.

The shot noise in tunneling experiments reflects the Poissonian nature of the tunneling process. The shot-noise power is proportional to both the magnitude of the current and the effective charge of the carrier. Shot-noise spectroscopy thus enables us, in principle, to determine the effective charge $q$ of the charge carriers of that tunnel. This can be used to detect electron pairing in superconductors: In the normal state, the noise corresponds to single electron tunneling ($q=1e$), while in the paired state, the noise corresponds to $q=2e$. Here, we use a newly developed amplifier to reveal that in typical mesoscopic superconducting junctions, the shot noise does not reflect the signatures of pairing and instead stays at a level corresponding to $q=1e$. We show that transparency can control the shot noise, and this $q=1e$ is due to the large number of tunneling channels with each having very low transparency. Our results indicate that in typical mesoscopic superconducting junctions, one should expect $q=1e$ noise and lead to design guidelines for junctions that allow the detection of electron pairing.

The entanglement entropy is a unique probe to reveal universal features of strongly interacting many-body systems. In two or more dimensions these features are subtle, and detecting them numerically requires extreme precision, a notoriously difficult task. This is especially challenging in models of interacting fermions, where many such universal features have yet to be observed. In this Letter we tackle this challenge by introducing a new method to compute the Rényi entanglement entropy in auxiliary-field quantum Monte Carlo simulations, where we treat the entangling region itself as a stochastic variable. We demonstrate the efficiency of this method by extracting, for the first time, universal subleading logarithmic terms in a two-dimensional model of interacting fermions, focusing on the half-filled honeycomb Hubbard model at $T=0$. We detect the universal corner contribution due to gapless fermions throughout the Dirac semi-metal phase and at the Gross-Neveu-Yukawa critical point, where the latter shows a pronounced enhancement depending on the type of entangling cut. Finally, we observe the universal Goldstone mode contribution in the antiferromagnetic Mott insulating phase.

Recent generalizations of the Hopfield model of associative memories are able to store a number $P$ of random patterns that grows exponentially with the number $N$ of neurons, $P=\exp (\alpha N)$. Besides the huge storage capacity, another interesting feature of these networks is their connection to the attention mechanism which is part of the Transformer architecture widely applied in deep learning. In this work, we study a generic family of pattern ensembles using a statistical mechanics analysis which gives exact asymptotic thresholds for the retrieval of a typical pattern, ${\alpha }_1$, and lower bounds for the maximum of the load $\alpha$ for which all patterns can be retrieved, ${\alpha }_c$, as well as sizes of attraction basins. We discuss in detail the cases of Gaussian and spherical patterns, and show that they display rich and qualitatively different phase diagrams.

Interferometry is a vital tool for studying fundamental features in the quantum Hall effect. For instance, Aharonov-Bohm interference in a quantum Hall interferometer can probe the wave-particle duality of electrons and quasiparticles. Here, we report an unusual Aharonov-Bohm interference of the outermost edge mode in a quantum Hall Fabry-Pérot interferometer, whose Coulomb interactions were suppressed with a grounded drain in the interior bulk of the interferometer. In a descending bulk filling factor from ${\mathit{\nu }}_{\mathbf{b}}=3$ to ${\mathit{\nu }}_{\mathbf{b}}\approx (5/3)$, the magnetic field periodicity, which corresponded to a single “flux quantum,” agreed accurately with the enclosed area of the interferometer. However, in the filling range, ${\mathit{\nu }}_{\mathbf{b}}\approx (5/3)$ to ${\mathit{\nu }}_{\mathbf{b}}=1$, the field periodicity increased markedly, a priori suggesting a drastic shrinkage of the Aharonov-Bohm area. Moreover, the modulation gate voltage periodicity decreased abruptly at this range. We attribute these unexpected observations to edge reconstruction, leading to area changing with the field and a modified modulation gate-edge capacitance. These reproducible results support future interference experiments with a quantum Hall Fabry-Pérot interferometer.

Transport measurement, which applies an electric field and studies the migration of charged particles, i.e., the current, is the most widely used technique in condensed matter studies. It is generally assumed that the quantum phase remains unchanged when it hosts a sufficiently small probing current, which is, surprisingly, rarely examined experimentally. In this Letter, we study the ultra-high-mobility two-dimensional electron system using a propagating surface acoustic wave, whose traveling speed is affected by the electrons’ compressibility. The acoustic power used in our Letter is several orders of magnitude lower than previous reports, and its induced perturbation to the system is smaller than the transport current. Therefore we are able to observe the quantum phases become more incompressible when hosting a perturbative current.

The early-science observations made by the James Webb Space Telescope (JWST) have revealed an excess of ultramassive galaxy candidates that appear to challenge the standard cosmological model ($\mathrm{\Lambda }\mathrm{CDM}$). Here, we argue that any modifications to $\mathrm{\Lambda }\mathrm{CDM}$ that can produce such ultramassive galaxies in the early Universe would also affect the UV galaxy luminosity function (UV LF) inferred from the Hubble Space Telescope (HST). The UV LF covers the same redshifts ($z\approx 7–10$) and host-halo masses ($M_{\mathrm{h}}\approx {10}^{10}–{10}^{12}{M}_{\odot }$) as the JWST candidates, but tracks star-formation rate rather than stellar mass. We consider beyond-$\mathrm{\Lambda }\mathrm{CDM}$ power-spectrum enhancements and show that any departure large enough to reproduce the abundance of ultramassive JWST candidates is in conflict with the HST data. Our analysis, therefore, severely disfavors a cosmological explanation for the JWST abundance problem. Looking ahead, we determine the maximum allowable stellar-mass function and provide projections for the high-$z$ UV LF given our constraints on cosmology from current HST data.

The perturbed ion temperature and toroidal flow were measured in rotating neoclassical tearing modes (NTM) in a tokamak for the first time. These toroidally and radially resolved profiles were obtained by impurity ion spectroscopy in a 2,1 NTM in DIII-D. In agreement with drift-kinetic simulations, the electron temperature profile is flat, while the ion temperature gradient is restored across the magnetic island $O$ point in the presence of fast ions; the perturbed flow has minima in the $O$ points and maxima at the $X$ points. These measurements provide the first confirmation of the theoretically expected ion temperature and flow response to a magnetic island needed to predict the NTM onset threshold scaling for ITER and other future tokamaks.

Recent investigations on the dipolar-octupolar compounds ${\mathrm{Ce}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ and ${\mathrm{Ce}}_2{\mathrm{Sn}}_2{\mathrm{O}}_7$ suggest that they may stabilize so-called $\pi$-flux octupolar quantum spin ice ($\pi$-O-QSI), a novel three-dimensional quantum spin liquid hosting emergent photons. Confirmation of such an exotic phase would require the prediction of a distinctive signature and its subsequent experimental observation. So far, however, theoretical predictions for any such sharp smoking-gun signatures are lacking. In this Letter, we thoroughly investigate O-QSI using an extension of gauge mean-field theory. This framework produces a phase diagram consistent with previous work and an energy-integrated neutron scattering signal with intensity-modulated rod motifs, as reported in experiments and numerical studies. We predict that the dynamical spin structure factor of $\pi$-O-QSI is characterized by a broad continuum with three distinctive peaks as a consequence of the two mostly flat spinon bands. These three peaks should be measurable by high-resolution inelastic neutron scattering. Such spectroscopic signatures would be clear evidence for the realization of $\pi$-flux quantum spin ice.

The stacking degree of freedom is a crucial factor in tuning material properties and has been extensively investigated in layered materials. The kagome superconductor ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ was recently discovered to exhibit a three-dimensional CDW phase below $T_{\mathrm{CDW}}\sim 94\mathrm{K}$. Despite the thorough investigation of in-plane modulation, the out-of-plane modulation has remained ambiguous. Here, our polarization- and temperature-dependent Raman measurements reveal the breaking of $C_6$ rotational symmetry and the presence of three distinct domains oriented at approximately 120° to each other. The observations demonstrate that the CDW phase can be naturally explained as a 2c staggered order phase with adjacent layers exhibiting a relative $\pi$ phase shift. Further, we discover a first-order structural phase transition at approximately 65 K and suggest that it is a stacking order-disorder phase transition due to stacking fault, supported by the thermal hysteresis behavior of a Cs-related phonon mode. Our findings highlight the significance of the stacking degree of freedom in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ and offer structural insights to comprehend the entanglement between superconductivity and CDW.

Higher-order topological insulators and semimetals, which generalize the conventional bulk-boundary correspondence, have attracted extensive research interest. Among them, higher-order Weyl semimetals feature twofold linear crossing points in three-dimensional momentum space, 2D Fermi-arc surface states, and 1D hinge states. Higher-order nodal-point semimetals possessing Weyl points or Dirac points have been implemented. However, higher-order nodal-line or nodal-surface semimetals remain to be further explored in experiments in spite of many previous theoretical efforts. In this work, we realize a second-order nodal-line semimetal in 3D phononic crystals. The bulk nodal lines, 2D drumhead surface states guaranteed by Zak phases, and 1D flat hinge states attributed to $k_z$-dependent quadrupole moments are observed in simulations and experiments. Our findings of nondispersive surface and hinge states may promote applications in acoustic sensing and energy harvesting.