The complex interplay between superconductivity, nematicity, and magnetism in iron-based superconductors remains a significant challenge in understanding its high-temperature superconductivity. Despite that numerous experiments aim at revealing the underlying mechanisms for superconductivity and nematicity by varying multiple tuning parameters, the inherent entanglement of these parameters complicates the isolation of the fundamental factors that drive the transitions. Here, by introducing a novel hydrothermal treatment to FeSe, we are able to effectively reduce interstitial Fe without altering the crystal structure and magnetic properties. This treatment results in a notable increase in carrier density and mobility, simultaneously enhancing both superconducting and nematic transition temperatures. Combining our experimental results with previous investigations, we reveal distinct pocket-influenced mechanisms: superconducting order is primarily influenced by electron pockets, while nematic order is driven by hole pockets. The results demonstrate the independent mechanisms of superconductivity and nematicity in FeSe, offering new perspectives on high-temperature superconductivity.

A successful microscopic theory of activated relaxation in metastable supercooled liquids is extended to the equilibrated deep glass regime. Surprisingly, the predicted power-law scaling connections of the dynamic barrier with diverse scalar order parameters (medium-range order correlation length, dimensionless compressibility, shear modulus) remain unchanged up to astronomically long timescales, despite a fundamental crossover of equilibrium thermodynamics and structure near the laboratory kinetic vitrification point. Quantitative tests against experiments on aged to equilibrium glass-forming liquids up to nearly 20 decades in time scale reveal good agreement. This conflicts with the idea of a crossover from super-Arrhenius to literal Arrhenius relaxation around the laboratory glass transition temperature, and supports the robustness of the theoretical idea that ultraslow dynamics is causally related to medium-range structural order. New avenues of experimental and theoretical research in the deep glass regime are suggested.

Two-terminal conductance quantization in the context of quantum Hall (QH) physics is intimately related to the current carried by a discrete number of chiral edge modes. Upon pinching off a QH bar, one may engineer setups where some modes are fully transmitted (while the others are fully reflected), giving rise to the orthodox theory of quantized conductance plateaus. Here, we note that the observation of quantized plateaus does not uniquely indicate the underlying mechanism. Our Letter demonstrates explicitly that (i) such plateaus may be the manifestations of entirely different mechanisms; (ii) conductance measurements alone will not suffice to distinguish one from the other. We further show that measurements of shot noise (auto- and cross-correlation) at the plateau may discriminate among different mechanisms. While our observations apply to a broad class of QH states, we demonstrate their applicability employing a prototypical example: the bulk state of filling factor $\nu =2/3$. We present distinctly different scenarios that lead to a conductance plateau $G_{2\text{-terminal}}=e^2/3h$ (observed previously) and likewise qualitatively different mechanisms leading to $e^2/2h$ (recently observed). We also predict the possibility of a new conductance plateau at $5e^2/9h$, following a nonorthodox scenario.

Conjugational defects, also known as solitons, play an important role in the electronic, magnetic, and optical properties of materials. Understanding solitons can uncover intriguing physics and provide insights for designing quantum materials with tailored band structures and electronic properties. Here, we propose a framework to create and control solitons via topological phase transitions in a class of graphene nanoribbons (GNRs) called square-root GNRs, using a transverse electric field. To demonstrate the experimental feasibility, we design and synthesize a representative GNR with a bottom-up approach, with first-principles calculations revealing topological soliton states at the domain wall induced by the electric field. The framework introduced in this Letter can potentially enable direct manipulation of solitons and provide a platform to study them systematically.

We propose ferroelectric layer sliding as a new approach to realize and manipulate topological quantum states in two-dimensional (2D) bilayer magnetic van der Waals materials. We show that stacking monolayer ferromagnetic topological states into layer-spin-locked bilayer antiferromagnetic structures, and introducing sliding ferroelectricity leads to asynchronous topological evolution of different layers (spins) owing to the existence of polarization potentials, thereby giving rise to rich layer-resolved topological phases. As a specific example, by means of a lattice model, we show that a bilayer magnetic 2D second order topological insulator (SOTI) reveals an unrecognized spin-hybrid-order topological insulator after undergoing ferroelectric sliding. Interestingly, in such a phase, the spin-up (top layer) and spin-down (bottom layer) channels exhibit first-order and second-order topological properties, respectively. Moreover, other topological phases such as the SOTI, quantum spin Hall insulator, quantum anomalous Hall insulator, and trivial insulator, can also emerge through changes in the parameters of the system; and the relevant topological indices are also discussed. In terms of materials, based on first principles calculations, we predict the material ${\mathrm{ScI}}_2$ can serve as an ideal platform to realize our proposal. Further, we predict that the anomalous Nernst effect of these several topological phases exhibits distinct differences, and therefore can be used as a signal for experimental probing.

Discrete-step walks describe the dynamics of particles in a lattice subject to hopping or splitting events at discrete times. Despite being of primordial interest to the physics of quantum walks, the topological properties arising from their discrete-step nature have been hardly explored. Here we report the observation of topological phases unique to discrete-step walks. We use light pulses in a double-fiber ring setup whose dynamics maps into a two-dimensional lattice subject to discrete splitting events. We show that the number of edge states is not simply described by the bulk invariants of the lattice (i.e., the Chern number and the Floquet winding number) as would be the case in static lattices and in lattices subject to smooth modulations. The number of edge states is also determined by a topological invariant associated to the discrete-step unitary operators acting at the edges of the lattice. This situation goes beyond the usual bulk-edge correspondence and allows manipulating the number of edge states without the need to go through a gap closing transition. Our Letter opens new perspectives for the engineering of topological modes for particles subject to quantum walks.

Phase-shaped electron energy-loss spectroscopy (PSEELS) measures the scattering probability of structured free electron beams by a target. Over the last decade, it was shown that this scheme can be employed to emulate polarized optical spectroscopies with electrons, and therefore to transpose macroscopic optical concepts—such as dichroism—down to the deep subwavelength scale. In this Letter, we theoretically demonstrate that PSEELS can, in fact, go way further than mimicking optics and enables to map a plethora of so far inaccessible nano-optical quantities such as the electric quadrupolar momentum.

We perform the first search for ultralight dark matter using a magnetically levitated particle. A submillimeter permanent magnet is levitated in a superconducting trap with a measured force sensitivity of $0.2\mathrm{fN}/\sqrt{\mathrm{Hz}}$. We find no evidence of a signal and derive limits on dark matter coupled to the difference between baryon and lepton number, $B-L$, in the mass range $(1.10360-1.10485)\times {10}^{-13}\mathrm{eV}/c^2$. Our most stringent limit on the coupling strength is $g_{B-L}\lesssim 2.98\times {10}^{-21}$. We propose the POLONAISE (Probing Oscillations using Levitated Objects for Novel Accelerometry In Searches of Exotic physics) experiment, which features short-, medium-, and long-term upgrades that will give us leading sensitivity in a wide mass range, demonstrating the promise of this novel quantum sensing technology in the hunt for dark matter.

We propose a novel method to experimentally access the gravitational form factors of the charged pion ${\pi }^{+}$ through the Sullivan process in electron-proton scattering. We demonstrate that the cross sections of $J/\psi$ photoproduction and $\varphi$ electroproduction near the respective thresholds are dominated by the gluon gravitational form factor of the pion to next-to-leading order in perturbative QCD. We predict cross sections for the Electron-Ion Collider and the Jefferson Lab experiments.

We present the first complete next-to-next-to-next-to-leading-order calculation of the matching coefficients that link unpolarized flavor nonsinglet parton distribution functions with lattice QCD computable correlation functions. By using this high-order result, we notice a reduction in theoretical uncertainties compared to relying solely on previously known lower-order matching coefficients. Furthermore, based on this result we have extracted the three-loop unpolarized flavor nonsinglet splitting function, which is in agreement with the state-of-the-art result. Because of the simplicity of our method, it has the potential to advance the calculation of splitting functions to the desired four-loop order.

In this Letter, we study the collinear limit of the energy-energy correlator in single-inclusive jet production in proton-proton and proton-nucleus collisions. We introduce a nonperturbative model that allows us to describe the energy-energy correlator in the entire angular region of the current experiments. Our results for proton-proton collisions show excellent agreement with CMS and ALICE data over a wide range of jet transverse momenta. For proton-nucleus collisions, we include modifications from the nuclear medium, and our predictions align well with the trends observed in recent ALICE measurements.

We show that a nonchiral atom can act as an antenna to induce a photoelectron circular dichroism in a nearby chiral molecule in a three-step process: The donor atom (antenna) is initially resonantly excited by circularly polarized radiation. It then transfers its excess energy to the acceptor molecule by means of resonant interatomic Coulombic decay. The latter finally absorbs the energy and emits an electron that exhibits the aforementioned circular dichroism in its angular distribution. We study the process on the basis of the retarded dipole–dipole interaction and report an asymptotic analytic expression for the distance-dependent chiral asymmetry of the photoelectron as induced by resonant interatomic Coulombic decay for random line-of-sight and acceptor orientations. In the nonretarded limit, the predicted chiral asymmetry is reversed as compared to that of a direct photoelectron circular dichroism of the molecule.

Dipolar Bose-Einstein condensates (dBECs) exhibit a plethora of physics phenomena, from supersolidity to the rotonlike minimum in the elementary excitation spectrum. In this work we first demonstrate the existence of axis-symmetric solitary waves in (quasi-)two-dimensional dBECs: these localized excitations are characterized by quantized vortex dipoles that continuously transit to vortex-free density depletions. We then show how the presence of the roton minimum fundamentally alters the fate of such solutions when approaching Landau’s critical speed: when propagating along the polarization direction where the roton minimum occurs, the solitary wave transits into roton excitations rather than into phonons as for standard contact-interaction BECs. This finding suggests that Feynman’s hypothesis, conjectured for 3D superfluid liquid helium regarding the creation of rotons as fading vortex excitations, is valid in the context of 2D dBECs.

Anderson localization, i.e., destructive quantum interference of multiple-scattering paths, halts transport entirely. Contrarily, time-dependent random forces expedite transport via Fermi acceleration, proposed as a mechanism for high-energy cosmic rays. Their competition creates interesting dynamics, but experimental observations are scarce. Here, we experimentally study the expansion of an ultracold Fermi gas inside time-dependent disorder and observe distinct regimes from sub- to superdiffusion. Unexpectedly, quantum interference counteracts acceleration in strong disorder before a transition to a diffusive state occurs in the driven system. Our system enables the investigation of Fermi acceleration in the quantum-transport regime.

Density-functional theory is well known to rely on approximations to the unknown exchange-correlation ($xc$) energy functional, which can be constructed from the satisfaction of a number of known properties. One of those properties is the asymptotic behavior of exchange and correlation in localized or extended many-electron systems. However, the actual asymptotics of the $xc$ energy and potential in the vacuum region of a metal surface have remained elusive over the years. Here, we report what we consider to be a final word for the asymptotics of the $xc$ energy per particle ${ϵ}_{xc}[n](z)$ and the $xc$ Kohn-Sham potential $v_{xc}[n](z)$ in the vacuum side of both an extended semi-infinite metal and a localized metal slab, which are always universal (i.e., electron-density independent), negative, and inversely proportional to the distance from the surface. We find that, contrary to previous conclusions by other authors, while for extended systems the asymptotics are dominated by a type of correlation, for metal slabs they are dominated by exchange, as in the case of systems that are finite in all directions, like atoms, molecules, and metal clusters.