We report a pronounced Hebel-Slichter coherence peak in the zero field nuclear quadrupolar resonance (NQR) spin-lattice relaxation rate of the topological crystalline superconductor ${\mathrm{LaNiGa}}_2$ in the superconducting state. Previously, a two-band internally antisymmetric nonunitary triplet pairing state was proposed for this system, with equal spin pairing and two distinct gaps associated with different spins. A detailed examination of the temperature dependence of the NQR data shows that the data best fit an internally antisymmetric triplet pairing model if the two gaps are equal and the model is unitary. Even a tiny nonunitarity with two unequal gaps causes the coherence peak to diminish rapidly and deviate from the data. On the other hand, the data are well fit by a two-band singlet Bardeen-Cooper-Schrieffer (BCS)-like pairing with two distinct gaps consistent with previous measurements. This raises doubts on the identification of nonunitary triplet pairing with time-reversal symmetry breaking in this material.

The superconducting transition temperatures ($T_{\mathrm{c}}$’s) of trilayer or quadruple-layer cuprates typically surpass those of single-layer or bilayer systems. However, the lack of direct electronic-structure and superconducting-gap measurements in optimal-$T_{\mathrm{c}}$ quadruple-layer cuprates has impeded a comprehensive understanding of the origin of the enhanced $T_{\mathrm{c}}$ in multilayer systems. In this Letter, using angle-resolved photoemission spectroscopy, we investigate the quadruple-layer cuprate $(\mathrm{Cu},\mathrm{C}){\mathrm{Ba}}_2{\mathrm{Ca}}_3{\mathrm{Cu}}_4{\mathrm{O}}_{11+\delta }$ (CuC-1234) with a high $T_{\mathrm{c}}$ of 110 K, and resolved distinct superconducting-gap behaviors between the inner ${\mathrm{CuO}}_2$ planes and outer ${\mathrm{CuO}}_2$ planes, in contrast to that reported for trilayer cuprates. Outer ${\mathrm{CuO}}_2$ planes develop their own superconducting gap and superconducting coherence peak at a temperature much lower than the $T_{\mathrm{c}}$ of the material, while the large pairing strength and phase coherence concurrently emerge at the underdoped inner ${\mathrm{CuO}}_2$ planes at $T_{\mathrm{c}}$. Our findings suggest that ${\mathrm{CuO}}_2$ planes free of apical oxygen can have significant contribution to superconductivity up to 110 K in multilayer cuprates, even at a doping level of 0.07 holes per Cu, a level that lies deep in the underdoped regime of single- and bilayer cuprates. These findings provide new insights into the origin of high $T_{\mathrm{c}}$ in multilayer cuprates.

Tunable Kondo lattice and heavy fermion physics have been recently reported in moiré materials, but most of the studies have focused on the electrical and magnetic properties. Quantitative thermoelectric measurements, which can reveal entropic information of the heavy fermions, have yet to be achieved. Here, we report a comprehensive thermoelectric study on the moiré heavy fermion phase realized in hole-doped angle-aligned ${\mathrm{MoTe}}_2/{\mathrm{WSe}}_2$ bilayers. By electrically gating the material to the Kondo lattice region of the phase diagram, we observe a sign change in the Seebeck coefficient near the Kondo coherence temperature, where the heavy fermion phase with an electronlike Fermi surface evolves into an itinerant Fermi liquid with a holelike Fermi surface. We compare the results with the semiclassical Mott relation and discuss the observed discrepancies. In addition to the thermal dissociation of Kondo singlets in the heavy Fermi liquid, a sign change accompanied by a strong peak in the Seebeck coefficient is also observed near a Zeeman breakdown of the Kondo singlets, signaling an entropy accumulation. Our results provide entropic information on both the formation and breakdown of heavy fermions in moiré semiconductors.

Robust flavor-polarized phases are a striking hallmark of many flat-band moiré materials. In this Letter, we trace the origin of this spontaneous polarization to a lesser-known quantum-geometric quantity: the quantum-geometric dipole. Analogous to how the quantum metric governs the spatial spread of wave packets, we show that the quantum-geometric dipole sets the characteristic size of particle-hole excitations, e.g., magnons in a ferromagnet, which in turn boosts their gap and stiffness. Indeed, the larger the particle-hole separation, the weaker the mutual attraction and the stronger the excitation energy. In topological bands, this energy enhancement admits a lower bound within the local-mode approximation, highlighting the crucial role of topology in flat-band ferromagnetism. We illustrate these effects in microscopic models, emphasizing their generality and relevance to moiré materials. Our results establish the quantum-geometric dipole as a predictive geometric indicator for ferromagnetism in flat bands, a crucial prerequisite for topological order.

We present an ab initio many-body theory of optical activity in solids within the $GW$ approximation plus Bethe-Salpeter equation framework. Dielectric spatial dispersion is formulated in two complementary forms: exciton envelope modulation and sum-over-exciton-states expansion. Our application to $\alpha$-quartz reveals that the envelope-modulated formulation captures the low-frequency region, whereas the sum-over-exciton-states formulation is essential to reproduce the correct full frequency dependence. Comparisons with the independent-particle approximation and simple local-field corrections further highlight the decisive role of excitonic many-body effects in shaping the spectral dispersion of optical activity in solids.

Thermal photons, arising from thermally populated vacuum quantum fields, ubiquitously inhabit all physical systems within thermal environments. Interactions between vacuum fields and media have led to seminal quantum electrodynamics phenomena, and time-modulated optical media are known to convert zero-point fluctuations into real photon pairs. Although several schemes have been proposed for thermal control using time-modulated media, a clear and general law governing how such modulation affects thermally populated photons has remained elusive. Here, we uncover the general principle governing the action of time-modulated optical systems on thermal photons. By establishing a general pseudoconservation law for photon numbers, we demonstrate how thermal photons are rearranged in energy and direction, generating fluxes within the thermal bath. These fluxes exhibit diverse behaviors, including input-output disparities across frequencies and photon transport that is controllable via modulation phase. These findings provide fundamental insights into the dynamical processes related to thermal vacuum fields and offer a guiding principle for the design of thermal-photon manipulation schemes.

We present a symmetry-based formulation of nonlinear fluctuating hydrodynamics (NFH) for one-dimensional many-particle systems with generic homogeneous nearest-neighbor interactions. We derive the hydrodynamic equations solely from symmetry and conservation principles, ensuring full consistency with thermalization. Using the dynamic renormalization group, we identify a Kardar-Parisi-Zhang (KPZ)-type fixed point, characterized by the dynamical exponent $z=3/2$ for both the sound and heat modes. Extensive numerical simulations of the derived NFH equations confirm this exponent and further reveal that both modes are close to the universal KPZ scaling function—the Prähofer-Spohn function. These findings establish a unified, symmetry-based framework for understanding universal transport and fluctuation phenomena in one-dimensional nonequilibrium systems, independent of microscopic details.

Using computer simulations and experiments, we demonstrate a mechanism for simultaneous size-specific control over the trajectories of isotropic colloidal particles. Magnetic microparticles of different diameters suspended above a periodic magnetic film are driven by loops traced by the orientation of a uniform external magnetic field. The uniform time-dependent magnetic field couples to the inhomogeneous static magnetic field of the pattern, generating a complex energy landscape for the microparticles. The energy landscape varies with height above the pattern, acting on particles of different sizes in distinct ways, as their centers are located at different elevations. At a specific elevation, distinct modulation loops exist that transport the particles to a neighboring unit cell of the pattern. The transport is topologically protected because it is determined only by a set of winding numbers of the modulation loop, which act as topological invariants. The set of winding numbers depends on the elevation, and hence, on the particle size, allowing simultaneous and independent driving of different-sized particles along arbitrarily complex and distinct trajectories.

A novel machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27 500 tagged $B_s^0\to J/\psi \varphi (1020)$ decays from $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$, collected by the CMS experiment and corresponding to an integrated luminosity of $96.5{\mathrm{fb}}^{-1}$. A time- and flavor-dependent angular analysis of the ${\mu }^{+}{\mu }^{-}{K}^{+}{K}^{-}$ final state, consistent with a $\varphi (1020)\to K^{+}{K}^{-}$ decay, is used to measure parameters of the $B_s^0-{\overline{B}}_s^0$ system. The weak phase is measured to be ${\varphi }_{\mathrm{s}}=-73\pm 22(\mathrm{stat})\pm 10(\mathrm{syst})\mathrm{mrad}$, which, combined with the $\sqrt{s}=8\mathrm{TeV}$ CMS result, gives ${\varphi }_{\mathrm{s}}=-75\pm 23\mathrm{mrad}$. This value differs from zero by 3.2 standard deviations, providing the first evidence for mixing-induced $CP$ violation in $B_s^0\to J/\psi \varphi (1020)$ decays. All measured physics parameters are found to agree with standard model predictions where available.

The first searches for $B^0\to K^{+}{\pi }^{-}{\tau }^{+}{\tau }^{-}$ and $B_s^0\to K^{+}{K}^{-}{\tau }^{+}{\tau }^{-}$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. The tau leptons are reconstructed using the ${\tau }^{+}\to {\mu }^{+}{\overline{\nu }}_{\tau }{\nu }_{\mu }$ decay and the results are presented in bins of $K^{+}{\pi }^{-}$ or $K^{+}{K}^{-}$ mass. No signal is observed and upper limits are set on the branching fractions. The searches result in the first upper limits for $B^0\to K^{+}{\pi }^{-}{\tau }^{+}{\tau }^{-}$ decays outside the $K^{*}(892{)}^0$ region in $K^{+}{\pi }^{-}$ mass and the first limits for $B_s^0\to K^{+}{K}^{-}{\tau }^{+}{\tau }^{-}$ decays. The searches are recast into limits on the decays $B^0\to K^{*}(892{)}^0{\tau }^{+}{\tau }^{-}$ and $B_s^0\to \varphi (1020){\tau }^{+}{\tau }^{-}$, yielding $2.8\times {10}^{-4}$ ($2.5\times {10}^{-4}$) and $4.7\times {10}^{-4}$ ($4.1\times {10}^{-4}$) at the 95% (90%) confidence level, respectively. For the decay $B^0\to K^{*}(892{)}^0{\tau }^{+}{\tau }^{-}$, this result improves on the current best upper limit by an order of magnitude.

The flavor space of particles produced in collider environments contains informative quantum correlations. We present a systematic approach for constructing the complete flavor density matrix for a meson and antimeson system ($M\overline{M}$) in the Bloch vector space at a given time $t$, which can be at or after production. We point out that the $B_s^0$ and $K^0$ systems are superior to the $B_d^0$ and $D^0$ systems for quantum tomography because of their flavor oscillation and decay properties. Performing quantum tomography for the $M\overline{M}$ system can facilitate the study of production mechanisms, decoherence phenomena, quantum information variables, and potential new sources of $CP$ violation.

While electron and muon dipole moments are well-established precision probes of physics beyond the standard model, it is notoriously challenging to test realistic new physics (NP) scenarios for the $\tau$ lepton. Constructing suitable asymmetries in $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ has emerged as a promising such avenue, providing access to the electric and magnetic dipole moment once a polarized electron beam is available, e.g., with the proposed polarization upgrade of the SuperKEKB $e^{+}{e}^{-}$ collider. However, this interpretation relies on an effective-field-theory (EFT) argument that only applies if the NP scale is large compared to the center-of-mass energy. In this Letter, we address the consequences of the asymmetry measurements in the case of light NP, using light spin-0 and spin-1 bosons as test cases, to show how results can again be interpreted as constraints on dipole moments, albeit in a model-dependent manner, and how the decoupling to the EFT limit proceeds in these cases. In particular, we observe that the imaginary parts generated by light new particles can yield nonvanishing asymmetries even without electron polarization, which can again be interpreted as constraints on the $\tau$ anomalous magnetic moment. This proposed measurement, thus, presents a novel opportunity for NP searches that can be realized already with present data at Belle II.

$\beta$-decay rates of extreme neutron-rich nuclei remain largely unknown experimentally, while they are critical inputs for $r$-process nucleosynthesis. We present first ab initio calculations of total $\beta$-decay half-lives, with a focus on $N=50$ nuclei. Starting from nuclear forces and currents based on chiral effective field theory, we use the in-medium similarity renormalization group to consistently derive valence-space Hamiltonians and weak operators, from which we calculate the nuclear states involved and the Gamow-Teller transition strengths, without phenomenological adjustments. In addition, we explore effects of first-forbidden contributions. Our results show that the inclusion of two-body currents increases the total half-lives, which then show good agreement with the existing experimental data, thereby validating the predictive capability of our approach.

Non-Hermitian Hamiltonians with complex eigenenergies are useful tools for describing the dynamics of open quantum systems. In particular, parity and time ($\mathcal{P}\mathcal{T}$) symmetric Hamiltonians have generated interest due to the emergence of exceptional-point degeneracies, where both eigenenergies and eigenvectors coalesce as the energy spectrum transitions from real to complex valued. Because of the abrupt spectral response near exceptional points, such systems have been proposed as candidates for precision quantum sensing. In this Letter, we emulate a passive $\mathcal{P}\mathcal{T}$ dimer using a two-mode, non-Hermitian system of superconducting qubits comprising one high-coherence qubit coupled to an intentionally lossy qubit via a tunable coupler. The loss is introduced by strongly coupling the qubit to a continuum of photonic modes in an open waveguide environment. Using both pulsed and continuous-wave measurements, we characterize the system dynamics near the exceptional point. We observe a behavior broadly consistent with an ideal passive $\mathcal{P}\mathcal{T}$ dimer with some corrections due to the tunable coupler element. We extract the complex eigenenergies associated with the two modes and calculate the sensitivity as a function of the coupling strength. Confirming theoretical predictions, we observe no sensitivity enhancement near the quantum exceptional point. This Letter elucidates the limitations of exceptional-point systems as candidates for quantum-enhanced sensing. We establish waveguide quantum electrodynamics as a versatile platform for exploring non-Hermitian quantum dynamics in superconducting circuits.

Intense light fields with spatiotemporally structured wave fronts open new avenues for exploring nonlinear light-matter interactions in ultrafast spectroscopy and photonic technologies. Here, we report the observation of geometric phase induced spin-orbit interaction (SOI) in high harmonic generation from crystalline solids. The geometric phase imprinted on the high-order harmonics originates from spin flips driven by crystal anisotropy. By employing a specially designed metasurface, the conversion from spin to orbital angular momentum can be achieved, sculpting the wave front of harmonics into arbitrary vortex structures. Furthermore, the SOI enables the realization of vectorial shaping, giant photonic spin Hall effects, and metalenses for high-harmonic light.

Quasimonochromatic (QM) coherent extreme ultraviolet (EUV) pulses have emerged as crucial tools for spectroscopic and imaging applications. Such pulses could be obtained by selectively enhancing a specific harmonic order in high-harmonic generation (HHG). However, it is still challenging to directly generate circularly polarized QM-EUV via HHG, which is essential in ultrafast circular dichroism spectroscopies and circular-dichroism-integrated imaging techniques. Here, we experimentally demonstrate the generation of circularly polarized QM-EUV radiation by driving nonaligned ${\mathrm{CO}}_2$ molecules with bichromatic counter-rotating circularly polarized fields. An unreported selective enhancement of a single harmonic order, distinct from the previously observed phenomena in HHG from gases, is observed. The enhanced harmonic is over 50 times stronger than the adjacent harmonics and at least 25 times stronger than the other high harmonics. More importantly, its efficiency is higher than the counterpart with the monochromatic linearly polarized driving laser. This enhancement originates from the resonance due to the overlap between the excited state and photon-dressed autoionizing state. The polarization of the singly enhanced harmonic is experimentally characterized with an EUV polarizer, indicating an ellipticity up to 0.92.

How much current does a sliding electron crystal carry? The answer to this simple question has important implications for the dynamics of the crystal, such as the frequency of its cyclotron motion, and its phonon spectrum. In this work we introduce a precise definition of a sliding crystal and compute the corresponding current ${\mathit{j}}_c$ for topological electron crystals in the presence of magnetic field. Our result is fully nonperturbative, does not rely on Galilean invariance, and applies equally to Wigner crystals and (anomalous) Hall crystals. In terms of the electron density $\rho$ and magnetic flux density $\varphi$, we find that ${\mathit{j}}_c=e(\rho -C\varphi )\mathit{v}$. Surprisingly, the current receives a contribution from the many-body Chern number $C$ of the crystal. When $\rho =C\varphi$, sliding crystals therefore carry zero current. The crystalline current fixes the Lorentz force felt by the sliding crystal and the dispersion of low-energy phonons of such crystals. This gives us a simple counting rule for the number of gapless phonons: if a sliding crystal carries nonzero current in a magnetic field, there is a single gapless mode, while otherwise there are two gapless modes. The constraint can also be understood from anomaly matching of emanant discrete translation symmetries—an idea that is also applicable to the dispersion of skyrmion crystals. Our results lead to novel experimental implications and invite further conceptual developments for electron crystals.