The thermal conductivity of heavy-fermion superconductor ${\mathrm{CeCoIn}}_5$ was measured with a magnetic field rotating in the tetragonal $a-b$ plane, with the heat current in the antinodal direction, $J||[100]$. We observe a sharp resonance in thermal conductivity for the magnetic field at an angle $\mathrm{\Theta }\approx 12°$, measured from the heat current direction [100]. This resonance corresponds to the reported resonance at an angle ${\mathrm{\Theta }}^{\prime }\approx 33°$ from the direction of the heat current applied along the nodal direction, $J||[110]$. Both resonances, therefore, occur when the magnetic field is applied in the same crystallographic orientation in the two experiments, regardless of the direction of the heat current, proving conclusively that these resonances are due to the structure of the Fermi surface of ${\mathrm{CeCoIn}}_5$. We argue that the uncondensed Landau quasiparticles, emerging with field, are responsible for the observed resonance. We support our experimental results with density-functional-theory model calculations of the density of states in a rotating magnetic field. Our calculations, using a model Fermi surface of ${\mathrm{CeCoIn}}_5$, reveal several sharp peaks as a function of the field direction. Our study demonstrates that the thermal-conductivity measurement in rotating magnetic field can probe the normal parts of the Fermi surface deep inside the superconducting state.

The recently discovered Van der Waals antiferromagnets have suffered from the lack of a comprehensive method to study their magnetic properties. Here, we propose an ac intrinsic magnon spin Hall current driven by surface acoustic waves as a novel probe for such antiferromagnets. Our results pave the way towards mechanical detection and manipulation of the magnetic order in two-dimensional antiferromagnets. Furthermore, they will overcome the difficulties with weak magnetic responses inherent in the use of antiferromagnets and hence provide a building block for future antiferromagnetic spintronics.

Integer and fractional Chern insulators have been extensively explored in correlated flat band models. Recently, the prediction and experimental observation of fractional quantum anomalous Hall (FQAH) states with spontaneous time-reversal symmetry breaking have garnered attention. While the thermodynamics of integer quantum anomalous Hall (IQAH) states have been systematically studied, our theoretical knowledge on thermodynamic properties of FQAH states has been severely limited. Here, we delve into the general thermodynamic response and collective excitations of both IQAH and FQAH states within the paradigmatic flat Chern-band model with remote band considered. Our key findings include (i) in both $\nu =1$ IQAH and $\nu =1/3$ FQAH states, even without spin fluctuations, the charge-neutral collective excitations would lower the onset temperature of these topological states, to a value significantly smaller than the charge gap, due to band mixing and multiparticle scattering; (ii) by employing large-scale thermodynamic simulations in FQAH states in the presence of strong interband mixing between $C=\pm 1$ bands, we find that the lowest collective excitations manifest as the zero-momentum excitons in the IQAH state, whereas in the FQAH state, they take the form of magnetorotons with finite momentum; (iii) the unique charge oscillations in FQAH states are exhibited with distinct experimental signatures, which we propose to detect in future experiments.

Geometric fluctuations of the density mode in a fractional quantum Hall (FQH) state can give rise to a nematic FQH phase, a topological state with a spontaneously broken rotational symmetry. While experiments on FQH states in the second Landau level have reported signatures of putative FQH nematics in anisotropic transport, a realistic model for this state has been lacking. We show that the standard model of particles in the lowest Landau level interacting via the Coulomb potential realizes the FQH nematic transition, which is reached by a progressive reduction of the strength of the shortest-range Haldane pseudopotential. Using exact diagonalization and variational wave functions, we demonstrate that the FQH nematic transition occurs when the system’s neutral gap closes in the long-wavelength limit while the charge gap remains open. We confirm the symmetry-breaking nature of the transition by demonstrating the existence of a “circular moat” potential in the manifold of states with broken rotational symmetry, while its geometric character is revealed through the strong fluctuations of the nematic susceptibility and Hall viscosity.

Orbital currents have recently emerged as a promising tool to achieve electrical control of the magnetization in thin-film ferromagnets. Efficient orbital-to-spin conversion is required in order to torque the magnetization. Here, we show that the injection of an orbital current in a ferrimagnetic ${\mathrm{Gd}}_{\mathrm{y}}{\mathrm{Co}}_{100-\mathrm{y}}$ alloy generates strong orbital torques whose sign and magnitude can be tuned by changing the Gd content and temperature. The effective spin-orbital Hall angle reaches up to $-0.25$ in a ${\mathrm{Gd}}_{\mathrm{y}}{\mathrm{Co}}_{100-\mathrm{y}}/{\mathrm{CuO}}_{\mathrm{x}}$ bilayer compared to $+0.03$ in $\mathrm{Co}/{\mathrm{CuO}}_{\mathrm{x}}$ and $+0.13$ in ${\mathrm{Gd}}_{\mathrm{y}}{\mathrm{Co}}_{100-\mathrm{y}}/\mathrm{Pt}$. This behavior is attributed to the local orbital-to-spin conversion taking place at the Gd sites, which is about 5 times stronger and of the opposite sign relative to Co. Furthermore, we observe a manyfold increase in the net orbital torque at low temperature, which we attribute to the improved conversion efficiency following the magnetic ordering of the Gd and Co sublattices.

The combination of optical tweezer arrays with strong interactions—via dipole exchange of molecules and Van der Waals interactions of Rydberg atoms—has opened the door for the exploration of a wide variety of quantum spin models. A next significant step will be the combination of such settings with mobile dopants. This will enable one to simulate the physics believed to underlie many strongly correlated quantum materials. Here, we propose an experimental scheme to realize bosonic $t–J$ models via encoding the local Hilbert space in a set of three internal atomic or molecular states. By engineering antiferromagnetic (AFM) couplings between spins, competition between charge motion and magnetic order similar to that in high-$T_c$ cuprates can be realized. Since the ground states of the 2D bosonic AFM $t–J$ model we propose to realize have not been studied extensively before, we start by analyzing the case of two dopants—the simplest instance in which their bosonic statistics plays a role—and compare our results to the fermionic case. We perform large-scale density matrix renormalization group calculations on six-legged cylinders, and find a strong tendency for bosonic holes to form stripes. This demonstrates that bosonic, AFM $t–J$ models may contain similar physics as the collective phases in strongly correlated electrons.

Integrable systems offer rare examples of solvable many-body problems in the quantum world. Because of the fine-tuned structure, their realization in nature and experiment is never completely accurate, and therefore effects of integrability are observed only transiently. One way to overcome this limitation is to weakly couple nearly integrable systems to baths and driving: this will stabilize integrable effects up to arbitrary time and encode them in the stationary state approximated by a generalized Gibbs ensemble. However, the description of such driven dissipative nearly integrable models is challenging and no exact analytical methods have been proposed so far. Here, we develop an iterative scheme in which integrability breaking perturbations (baths) determine the conserved quantities that play the leading role in a highly efficient truncated generalized Gibbs ensemble description. Our scheme paves the way for easier calculations in thermodynamically large systems and can be used to construct unknown conserved quantities.

In this Letter, we demonstrate how to use the generalized $\delta N$ formalism, which enables us to compute the evolution of all the large-scale fluctuations, including gravitational waves, solely by solving the evolution of the background homogeneous Universe. Using the Noether charge density, we derive an analytic formula which describes the mapping between the fluctuations at the horizon crossing and the sourced gravitational waves at the end of inflation. This formula can apply also to an inflation model with an anisotropic background. Using this formula, we discuss the condition for the nonvanishing linear polarization and the qualitative difference between single- and multigauge field models.

Using $(10.087\pm 0.044)\times {10}^9$ $J/\psi$ events collected with the BESIII detector at the BEPCII storage ring, the processes $\mathrm{\Lambda }p\to \mathrm{\Lambda }p$ and $\overline{\mathrm{\Lambda }}p\to \overline{\mathrm{\Lambda }}p$ are studied, where the $\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}$ baryons are produced in the process $J/\psi \to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in $-0.9\le \cos {\theta }_{\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}}\le 0.9$ are measured to be $\sigma (\mathrm{\Lambda }p\to \mathrm{\Lambda }p)=(12.2\pm {1.6}_{\mathrm{stat}}\pm {1.1}_{\mathrm{syst}})$ and $\sigma (\overline{\mathrm{\Lambda }}p\to \overline{\mathrm{\Lambda }}p)=(17.5\pm {2.1}_{\mathrm{stat}}\pm {1.6}_{\mathrm{syst}})\mathrm{mb}$ at the $\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}$ momentum of $1.074\mathrm{GeV}/c$ within a range of $\pm 0.017\mathrm{GeV}/c$, where the ${\theta }_{\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}}$ are the scattering angles of the $\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}$ in the $\mathrm{\Lambda }p/\overline{\mathrm{\Lambda }}p$ rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for $\mathrm{\Lambda }p\to \mathrm{\Lambda }p$, and a strong forward peak for $\overline{\mathrm{\Lambda }}p\to \overline{\mathrm{\Lambda }}p$. We present an approach to extract the total elastic cross sections by extrapolation. The study of $\overline{\mathrm{\Lambda }}p\to \overline{\mathrm{\Lambda }}p$ represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.

We propose the angular distribution of lepton pairs produced in ultrarelativistic heavy-ion collisions as a probe of thermalization of the quark-gluon plasma. We focus on dileptons with invariant masses large enough that they are produced through quark–antiquark annihilation in the early stages of the collision. The angular distribution of the lepton in the rest frame of the pair then reflects the angular distribution of quark momenta. At early times, the transverse pressure of the quark-gluon plasma is larger than its longitudinal pressure as a result of the fast longitudinal expansion, which results in an oblate lepton distribution. By contrast, direct (Drell-Yan) production by quarks and antiquarks from incoming nuclei, whose momenta are essentially longitudinal, results in a prolate distribution. As the invariant mass increases, Drell-Yan gradually becomes the dominant source of dilepton production, and the lepton distribution evolves from oblate to prolate. The invariant mass at which the transition occurs is highly sensitive to the equilibration time of the quark-gluon plasma or, equivalently, the shear viscosity over entropy ratio $\eta /s$ in the early stages of the collision.

The recently observed abnormal bifurcation of the double binding energy differences $\delta V_{pn}$ between the odd-odd and even-even nuclei along the $N=Z$ line from Ni to Rb has challenged the nuclear theories. To solve this problem, a shell-model-like approach based on the relativistic density functional theory is established, by treating simultaneously the neutron-neutron, proton-neutron, and proton-proton pairing correlations both microscopically and self-consistently. Without any ad hoc parameters, the calculated results well reproduce the observations, and the mechanism for this abnormal bifurcation is found to be due to the enhanced proton-neutron pairing correlations in the odd-odd $N=Z$ nuclei, compared with the even-even ones. The present results provide an excellent interpretation for the abnormal $\delta V_{pn}$ bifurcation, and provide a clear signal for the existence of the proton-neutron pairing correlations for nuclei close to the $N=Z$ line.

We experimentally study the influence of the binding energy on nondipole effects in $K$-shell single-photon ionization of atoms at high photon energies. We find that for each ionization event, as expected by momentum conservation, the photon momentum is transferred almost fully to the recoiling ion. The momentum distribution of the electrons becomes asymmetrically deformed along the photon propagation direction with a mean value of $8/(5c)(E_{\gamma }-I_P)$ confirming an almost 100 year old prediction by Sommerfeld and Schur [Ann. Phys. (N.Y.) 396, 409 (1930)]. The emission direction of the photoions results from competition between the forward-directed photon momentum and the backward-directed recoil imparted by the photoelectron. Which of the two counteracting effects prevails depends on the binding energy of the emitted electron. As an example, we show that at 20 keV photon energy, ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ar}}^{+}$ photoions are pushed backward towards the radiation source, while ${\mathrm{Kr}}^{+}$ photoions are emitted forward along the light propagation direction.

We report a new precision measurement of the dc Stark shift of the $6s{{}^{2}S}_{1/2}\to 7s{{}^{2}S}_{1/2}$ transition in atomic cesium-133. Our result is $0.72246(29)\mathrm{Hz}(\mathrm{V}/\mathrm{cm}{)}^{-2}$. This result differs from a previous measurement of the Stark shift by $\sim 0.5\%$, or $4.7\sigma$. We use this value to recalculate the magnitude of the reduced dipole matrix elements $⟨7s||r||7p_j⟩$, as well as the vector transition polarizability for the $6s\to 7s$ transition, $\tilde{\beta }=27.043(36)a_0^3$. This determination helps resolve a critical discrepancy between two techniques for determining the vector polarizability.

Attempts to create quantum degenerate gases without evaporative cooling have been pursued since the early days of laser cooling, with the consensus that polarization gradient cooling (PGC, also known as “optical molasses”) alone cannot reach condensation. In the present work, we report that simple PGC can generate a small Bose-Einstein condensate (BEC) inside a corrugated micrometer-sized optical dipole trap. The experimental parameters enabling BEC creation were found by machine learning, which increased the atom number by a factor of 5 and decreased the temperature by a factor of 2.5, corresponding to almost 2 orders of magnitude gain in phase space density. When the trapping light is slightly misaligned through a microscopic objective lens, a BEC of $\sim 250$ ${}^{87}\mathrm{Rb}$ atoms is formed inside a local dimple within 40 ms of PGC after MOT loading.

The differential heating of electrons and ions by turbulence in weakly collisional magnetized plasmas and the scales at which such energy dissipation is most effective are still debated. Using a large data sample measured in Earth’s magnetosheath by the magnetospheric multiscale mission and the coarse-grained energy equations derived from the Vlasov-Maxwell system, we find evidence of a balance over two decades in scales between the energy cascade and dissipation rates. The decline of the cascade rate at kinetic scales (in contrast with a constant one in the inertial range), is balanced by an increasing ion and electron heating rates, estimated via the pressure strain. Ion scales are found to contribute most effectively to ion heating, while electron heating originates from both ion and electron scales. These results can potentially impact the current understanding of particle heating in turbulent magnetized plasmas as well as their theoretical and numerical modeling.

Recent experiments have confirmed the presence of interlayer excitons in the ground state of transition metal dichalcogenide bilayers. The interlayer excitons are expected to show remarkable transport properties when they undergo Bose condensation. In this Letter, we demonstrate that quantum geometry of Bloch wave functions plays an important role in the phase stiffness of the interlayer exciton condensate. Notably, we identify a geometric contribution that amplifies the stiffness, leading to the formation of a robust condensate with an increased Berezinskii-Kosterlitz-Thouless temperature. Our results have direct implications for the ongoing experimental efforts on interlayer excitons in materials that have nontrivial quantum geometry. We provide estimates for the geometric contribution in transition metal dichalcogenide bilayers through a realistic continuum model with gated Coulomb interaction, and find that the substantially increased stiffness may allow an interlayer exciton condensate to be realized at amenable experimental conditions.

Braiding is a geometric concept that manifests itself in a variety of scientific contexts from biology to physics, and has been employed to classify bulk band topology in topological materials. Topological edge states can also form braiding structures, as demonstrated recently in a type of topological insulators known as Möbius insulators, whose topological edge states form two braided bands exhibiting a Möbius twist. While the formation of Möbius twist is inspiring, it belongs to the simple Abelian braid group ${\mathbb{B}}_2$. The most fascinating features about topological braids rely on the non-Abelianness in the higher-order braid group ${\mathbb{B}}_N$ ($N\ge 3$), which necessitates multiple edge bands, but so far it has not been discussed. Here, based on the gauge enriched symmetry, we develop a scheme to realize non-Abelian braiding of multiple topological edge bands. We propose tight-binding models of topological insulators that are able to generate topological edge states forming non-Abelian braiding structures. Experimental demonstrations are conducted in two acoustic crystals, which carry three and four braided acoustic edge bands, respectively. The observed braiding structure can correspond to the topological winding in the complex eigenvalue space of projective translation operator, akin to the previously established point-gap winding topology in the bulk of the Hatano-Nelson model. Our Letter also constitutes the realization of non-Abelian braiding topology on an actual crystal platform, but not based on the “virtual” synthetic dimensions.

Short-range repulsion governs the dynamics of matter from atoms to animals. Using theory, simulations, and experiments, we find that an ensemble of repulsive particles spreads compactly with a sharp boundary, in contrast to the diffusive spreading of Brownian particles. Starting from the pair interactions, at high densities, the many-body dynamics follow nonlinear diffusion with a self-similar expansion, growing as $t^{1/4}$; At longer times, thermal motion dominates with the classic $t^{1/2}$ expansion. A logarithmic growth controlled by nearest-neighbor interactions connects the two self-similar regimes.