Dissociative electron attachment (DEA) plays a key role in radiation damage of biomolecules under high-energy radiation conditions. The initial step in DEA is often rationalized in terms of resonant electron capture into one of the metastable valence states of a molecule followed by its fragmentation. Our combined theoretical and experimental investigations indicate that the manifold of states responsible for electron capture in the DEA process can be dominated by core-excited (shake-up) dipole-supported resonances. Specifically, we present the results of experimental and computational studies of the gas-phase DEA to three prototypical peptide molecules, formamide, $N$-methylformamide (NMF), and $N$,$N$-dimethyl-formamide (DMF). In contrast to the case of electron capture by positively charged peptides in which amide bond rupture is rare compared to $\mathrm{N}─{\mathrm{C}}_{\alpha }$ bond cleavage, fragmentation of the amide bond was observed in each of these three molecules. The ion yield curves for ions resulting from this amide bond cleavage, such as ${\mathrm{NH}}_2^{-}$ for formamide, ${\mathrm{NHCH}}_3^{-}$ for NMF, and $\mathrm{N}({\mathrm{CH}}_3{)}_2^{-}$ for DMF, showed a double-peak structure in the region between 5 and 8 eV. The peaks are assigned to Feshbach resonances including core-excited dipole-supported resonances populated upon electron attachment based on high-level electronic structure calculations. Moreover, the lower energy peak is attributed to formation of the core-excited resonance that correlates with the triplet state of the neutral molecule. The latter process highlights the role of optically spin-forbidden transitions promoted by electron impact in the DEA process.

Negative friction coefficients, where friction is reduced upon increasing normal load, are predicted for superlubric graphite–hexagonal boron nitride heterojunctions. The origin of this counterintuitive behavior lies in the load-induced suppression of the moiré superstructure out-of-plane distortions leading to a less dissipative interfacial dynamics. Thermally induced enhancement of the out-of-plane fluctuations leads to an unusual increase of friction with temperature. The highlighted frictional mechanism is of a general nature and is expected to appear in many layered material heterojunctions.

FeSe is argued as a superconductor in the Bardeen-Cooper-Schrieffer Bose-Einstein condensation crossover regime where the superconducting gap size and the superconducting transition temperature $T_c$ are comparable to the Fermi energy. In this regime, vortex bound states should be well quantized and the preformed pairs above $T_c$ may yield a pseudogap in the quasiparticle-excitation spectrum. We performed spectroscopic-imaging scanning tunneling microscopy to search for these features. We found Friedel-like oscillations near the vortex, which manifest the quantized levels, whereas the pseudogap was not detected. These apparently conflicting observations may be related to the multiband nature of FeSe.

Molecular exchange processes are important equilibration and transport mechanisms in both synthetic and biological self-assembled systems such as micelles, vesicles, and membranes. Still, these processes are not entirely understood, in particular the effect of crystallinity and the interplay between cooperative melting processes and chain exchange. Here we focus on a set of simple polymer micelles formed by binary mixtures of poly(ethylene oxide)-mono-$n$-alkyl-ethers (${\mathrm{C}}_n\text{−}\mathrm{PEO}5$) which allows the melting point to be tuned over a wide range. We show that the melting transition is cooperative in the confined 4–5 nm micellar core, whereas the exchange process is widely decoupled and unimeric in nature. As confirmed by differential scanning calorimetry, the total activation energy for ejecting a molecule out of the micellar core below the melting point is the sum of the enthalpy of fusion and the corresponding activation energy in the melt state. This suggests that a “local, single-chain melting process” preludes the molecular diffusion out of the micelle during chain exchange.

A two-dimensional (2D) harmonically trapped interacting Fermi gas is anticipated to exhibit a quantum anomaly and possesses a breathing mode at frequencies different from a classical scale-invariant value ${\omega }_B=2{\omega }_{\perp }$, where ${\omega }_{\perp }$ is the trapping frequency. The predicted maximum quantum anomaly ($\sim 10\%$) has not been confirmed in experiments. Here, we theoretically investigate the zero-temperature density equation of state and the breathing mode frequency of an interacting Fermi superfluid at the dimensional crossover from three to two dimensions. We find that the simple model of a 2D Fermi gas with a single $s$-wave scattering length is not adequate to describe the experiments in the 2D limit, as commonly believed. A more complete description of quasi-2D leads to a much weaker quantum anomaly, consistent with the experimental observations. We clarify that the reduced quantum anomaly is due to the significant confinement-induced effective range of interactions.

We present a technique for reducing the computational requirements by several orders of magnitude in the evaluation of semidefinite relaxations for bounding the set of quantum correlations arising from finite-dimensional Hilbert spaces. The technique, which we make publicly available through a user-friendly software package, relies on the exploitation of symmetries present in the optimization problem to reduce the number of variables and the block sizes in semidefinite relaxations. It is widely applicable in problems encountered in quantum information theory and enables computations that were previously too demanding. We demonstrate its advantages and general applicability in several physical problems. In particular, we use it to robustly certify the nonprojectiveness of high-dimensional measurements in a black-box scenario based on self-tests of $d$-dimensional symmetric informationally complete positive-operator-valued measurements.

We prove that soft theorems uniquely fix tree-level scattering amplitudes in a wide range of massless theories, including Yang-Mills, gravity, the nonlinear sigma model, Dirac-Born-Infeld, dilaton effective theories, extended theories like the $\mathrm{NLSM}\oplus {\varphi }^3$ (nonlinear sigma model ${\varphi }^3$), as well as some higher derivative corrections to these theories. We conjecture the same is true even when imposing more general soft behavior, simply by assuming the existence of soft operators, or by imposing gauge invariance or the Adler zero only up to a finite order in soft expansions. Besides reproducing known amplitudes, this analysis reveals a new higher order correction to the NLSM and two interesting facts: the subleading theorem for the dilaton, and the subsubleading theorem for DBI follow automatically from the more leading theorems. These results provide motivation that asymptotic symmetries contain enough information to fully fix a holographic $S$ matrix.

We present several results concerning the free energy of odd-dimensional conformal field theories (CFTs) on squashed spheres. First, we propose a formula which computes this quantity for holographic CFTs dual to higher-curvature gravities with second-order linearized equations of motion. As opposed to standard on-shell action methods for Taub geometries, our formula only involves a simple evaluation of the corresponding bulk Lagrangian on an auxiliary pure anti–de Sitter (AdS) space. The expression is closely related to the function determining the possible AdS vacua of the bulk theory in question, which we argue to act as a generating functional from which correlation functions of the boundary stress tensor can be easily characterized. Finally, based on holographic results and free-field numerical calculations, we conjecture that the subleading term in the squashing-parameter free-energy expansion is universally controlled by the stress-tensor three-point function charge $t_4$ for general ($2+1$)-dimensional CFTs.

Inspired by recent experimental subatomic measurements using analytical aberration-corrected scanning transmission electron microscopes, we study electron probe propagation in crystalline ${\mathrm{SrTiO}}_3$ at the subatomic length scale. Here, we report the existence of subatomic channeling and the formation of a helicon-type beam at this scale. The results of beam propagation simulations, which are performed at various crystal temperatures, STEM probe convergence angles (10–50 mrad), and beam energies (80–300 keV), showed that reducing the ambient temperature can enhance the subatomic channeling and STEM probe parameters can be used to control the features of helicon-type beams.

We analyze the “higher rank” gauge theories that capture some of the phenomenology of the fracton order. It is shown that these theories lose gauge invariance when an arbitrarily weak and smooth curvature is introduced. We propose a resolution to this problem by introducing a theory invariant under area-preserving diffeomorphisms, which reduce to the higher rank gauge transformations upon linearization around a flat background. The proposed theory is geometric in nature and is interpreted as a theory of chiral topological elasticity. This theory exhibits some of the fracton phenomenology. We explore the conservation laws, topological excitations, linear response, various kinematical constraints, and canonical structure of the theory. Finally, we emphasize that the very structure of Riemann-Cartan geometry, which we use to formulate the theory, encodes some of the fracton phenomenology, suggesting that the fracton order itself is geometric in nature.

A $d$-dimensional second-order topological insulator (SOTI) can host topologically protected ($d-2$)-dimensional gapless boundary modes. Here, we show that a 2D non-Hermitian SOTI can host zero-energy modes at its corners. In contrast to the Hermitian case, these zero-energy modes can be localized only at one corner. A 3D non-Hermitian SOTI is shown to support second-order boundary modes, which are localized not along hinges but anomalously at a corner. The usual bulk-corner (hinge) correspondence in the second-order 2D (3D) non-Hermitian system breaks down. The winding number (Chern number) based on complex wave vectors is used to characterize the second-order topological phases in 2D (3D). A possible experimental situation with ultracold atoms is also discussed. Our work lays the cornerstone for exploring higher-order topological phenomena in non-Hermitian systems.

$\mathrm{Yb}({\mathrm{Rh}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{Si}}_2$ is a model system to address two challenging problems in the field of strongly correlated electron systems. The first is the intriguing competition between ferromagnetic (FM) and antiferromagnetic (AFM) order when approaching a magnetic quantum critical point (QCP). The second is the occurrence of magnetic order along a very hard crystalline electric field (CEF) direction, i.e., along the one with the smallest available magnetic moment. Here, we present a detailed study of the evolution of the magnetic order in this system from a FM state with moments along the very hard $c$ direction at $x=0.27$ towards the yet unknown magnetic state at $x=0$. We first observe a transition towards an AFM canted state with decreasing $x$ and then to a pure AFM state. This confirms that the QCP in ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$ is AFM, but the phase diagram is very similar to those observed in some inherently FM systems like ${\mathrm{NbFe}}_2$ and CeRuPO, which suggests that the basic underlying instability might be FM. Despite the huge CEF anisotropy the ordered moment retains a component along the $c$ axis also in the AFM state. The huge CEF anisotropy in $\mathrm{Yb}({\mathrm{Rh}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{Si}}_2$ excludes that this hard-axis ordering originates from a competing exchange anisotropy as often proposed for other heavy-fermion systems. Instead, it points to an order-by-disorder based mechanism.

Topological antiferromagnetic (AFM) spintronics is an emerging field of research, which exploits the Néel vector to control the topological electronic states and the associated spin-dependent transport properties. A recently discovered Néel spin-orbit torque has been proposed to electrically manipulate Dirac band crossings in antiferromagnets; however, a reliable AFM material to realize these properties in practice is missing. In this Letter, we predict that room-temperature AFM metal ${\mathrm{MnPd}}_2$ allows the electrical control of the Dirac nodal line by the Néel spin-orbit torque. Based on first-principles density functional theory calculations, we show that reorientation of the Néel vector leads to switching between the symmetry-protected degenerate state and the gapped state associated with the dispersive Dirac nodal line at the Fermi energy. The calculated spin Hall conductivity strongly depends on the Néel vector orientation and can be used to experimentally detect the predicted effect using a proposed spin-orbit torque device. Our results indicate that AFM Dirac nodal line metal ${\mathrm{MnPd}}_2$ represents a promising material for topological AFM spintronics.

The eigenstate thermalization hypothesis (ETH) is one of the cornerstones of contemporary quantum statistical mechanics. The extent to which ETH holds for nonlocal operators is an open question that we partially address in this Letter. We report on the construction of highly nonlocal operators, behemoths, that are building blocks for various kinds of local and nonlocal operators. The behemoths have a singular distribution and width $w\sim {\mathcal{D}}^{-1}$ ($\mathcal{D}$ being the Hilbert space dimension). From there, one may construct local operators with the ordinary Gaussian distribution and $w\sim {\mathcal{D}}^{-1/2}$ in agreement with ETH. Extrapolation to even larger widths predicts sub-ETH behavior of typical nonlocal operators with $w\sim {\mathcal{D}}^{-\delta }$, $0<\delta <1/2$. This operator construction is based on a deep analogy with random matrix theory and shows striking agreement with numerical simulations of nonintegrable many-body systems.

We set constraints and future sensitivity projections on millicharged particles (MCPs) based on electron scattering data in numerous neutrino experiments, starting with MiniBooNE and the Liquid Scintillator Neutrino Detector (LSND). Both experiments are found to provide new (and leading) constraints in certain MCP mass windows: 5–35 MeV for LSND and 100–180 MeV for MiniBooNE. Furthermore, we provide projections for the ongoing Fermilab SBN program, the Deep Underground Neutrino Experiment (DUNE), and the proposed Search for Hidden Particles (SHIP) experiment. In the SBN program, SBND and MicroBooNE have the capacity to provide the leading bounds in the 100–300 MeV mass regime. DUNE and SHIP are capable of probing parameter space for MCP masses in the range of $5\mathrm{MeV}–5\mathrm{GeV}$ that is significantly beyond the reach of existing bounds, including those from collider searches and, in the case of DUNE, the SLAC mQ experiment.

Time delays for atomic photoemission obtained in streaking or reconstruction of attosecond bursts by interference of two-photon transitions experiments originate from a combination of the quantum mechanical Wigner time and the Coulomb-laser coupling. While the former was investigated intensively theoretically as well as experimentally, the latter attracted less interest in experiments and has mostly been subject to calculations. Here, we present a measurement of the Coulomb-laser coupling-induced time shifts in photoionization of neon at 59.4 eV using a terahertz (THz) streaking field ($\lambda =152\mu \mathrm{m}$). Employing a reaction microscope at the THz beamline of the free-electron laser in Hamburg (FLASH), we have measured relative time shifts of up to 70 fs between the emission of $2p$ photoelectrons ($\sim 38\mathrm{eV}$) and low-energetic ($<1\mathrm{eV}$) photoelectrons. A comparison with theoretical predictions on Coulomb-laser coupling reveals reasonably good agreement.

We study the sedimentation of highly viscous droplets confined inside Hele-Shaw cells with textured walls of controlled topography. In contrast with common observations on superhydrophobic surfaces, roughness tends here to significantly increase viscous friction, thus substantially decreasing the droplets mobility. However, reducing confinement induces a jump in the velocity as droplets can slide on a lubricating layer of the surrounding fluid thicker than the roughness features. We demonstrate that increasing the viscosity of the surrounding liquid may counterintuitively enhance the mobility of a droplet sliding along a rough wall. Similarly, a sharp change of the droplet mobility is observed as the amplitude of the roughness is modified. These results illustrate the nontrivial friction processes at the scale of the roughness, and the coupling between viscous dissipation in the drop, in the front meniscus, and in the lubricating film. They could enable one to specifically control the speed of droplets or capsules in microchannels, based on their rheological properties.