We demonstrated that a nitric oxide (NO) molecule on Cu(110) acts as an “ON-OFF-ON toggle switch” that can be turned on and off by repulsive force and electron injection, respectively. On the surface, NO molecules exist in three configurations: flat along the [001] direction (ON), upright (OFF), and flat along $[00\overline{1}]$ (ON). An NO-functionalized tip, which was characterized by scanning tunneling microscopy and inelastic electron tunneling spectroscopy, can convert an upright NO adsorbate into a flat-lying NO. Atomic force microscopy and a simulation of the interactions between the NO molecules reveal that a repulsive force not aligned with the N—O bond provides the torque that detrudes the NO toggle; i.e., the upright NO adsorbate is tilted away from the tip. Therefore, the NO adsorbate behaves as a nonvolatile sensor for the detection of locally applied repulsive torque.

The control of the exciton intervalley coherence renders transition metal dichalcogenides monolayers promising candidates for quantum information science. So far, generating intervalley coherence has the need for an external coherent field. Here, we theoretically demonstrate spontaneous generation (i.e., without any external field) of exciton intervalley coherence. We achieve this by manipulating the vacuum field in the vicinity of the monolayer with a designed polarization-dependent metasurface, inducing an anisotropic decay rate for in-plane excitonic dipoles. Harnessing quantum coherence and interference effects in two-dimensional materials may provide the route for novel quantum valleytronic devices.

Electronic stopping power in the $\mathrm{keV}/\AA$ range is accurately calculated from first principles for high atomic-number projectiles and the effect of core states is carefully assessed. The energy loss to electrons in self-irradiated nickel is studied using real-time time-dependent density functional theory. Different core states are explicitly included in the simulations to understand their involvement in the dissipation mechanism. The core electrons of the projectile are found to open additional dissipation channels as the projectile velocity increases. Almost all of the energy loss is accounted for, even for high projectile velocities, when core electrons as deep as $2s^{2}2p^6$ are explicitly treated. In addition to their expected excitation at high velocities, a flapping dynamical response of the projectile core electrons is observed at intermediate velocities. The empirical reference data are well reproduced in the projectile velocity range of 1.0–12.0 a.u. (1.5–210 MeV).

We investigate a topological switch between second-order topological insulators (SOTIs) and topological crystalline insulators (TCIs). Both the SOTI and the TCI are protected by the mirror and inversion symmetries, for which we define the bulk topological numbers of the same type. When an in-plane magnetic field is introduced parallel to one of the helical edges, the system becomes a TCI. The conductance along the edge is 1 in the unit of the conductance quantum $e^2/h$. When it becomes orthogonal to a diagonal line, two topological corner states emerge on its vertices, and the system becomes a SOTI. This may be used as a basis of a topological circuit-changing switch. Alternatively, the device may be used as a sensor to measure local magnetization on a sample surface with a resolution of 10 nm.

The interplay between strongly correlated liquid and crystal phases for two-dimensional electrons exposed to a high transverse magnetic field is of fundamental interest. Through the nonperturbative fixed-phase diffusion Monte Carlo method, we determine the phase diagram of the Wigner crystal in the $\nu -\kappa$ plane, where $\nu$ is the filling factor and $\kappa$ is the strength of Landau-level (LL) mixing. The phase boundary is seen to exhibit a striking $\nu$ dependence, with the states away from the magic filling factors $\nu =n/(2pn+1)$ being much more susceptible to crystallization due to Landau-level mixing than those at $\nu =n/(2pn+1)$. Our results explain the qualitative difference between the experimental behaviors observed in $n$- and $p$-doped gallium arsenide quantum wells and, in particular, the existence of an insulating state for $\nu <1/3$ and also for $1/3<\nu <2/5$ in low-density $p$-doped systems. We predict that, in the vicinity of $\nu =1/5$ and $\nu =2/9$, increasing LL mixing causes a transition not into an ordinary electron Wigner crystal, but rather into a strongly correlated crystal of composite fermions carrying two vortices.

Superconducting high kinetic inductance elements constitute a valuable resource for quantum circuit design and millimeter-wave detection. Granular aluminum (grAl) in the superconducting regime is a particularly interesting material since it has already shown a kinetic inductance in the range of $\mathrm{nH}/\square$ and its deposition is compatible with conventional $\mathrm{Al}/\mathrm{AlOx}/\mathrm{Al}$ Josephson junction fabrication. We characterize microwave resonators fabricated from grAl with a room temperature resistivity of $4\times {10}^3\mu \mathrm{\Omega }\mathrm{cm}$, which is a factor of 3 below the superconductor to insulator transition, showing a kinetic inductance fraction close to unity. The measured internal quality factors are on the order of $Q_i={10}^5$ in the single photon regime, and we demonstrate that nonequilibrium quasiparticles (QPs) constitute the dominant loss mechanism. We extract QP relaxation times in the range of 1 s and we observe QP bursts every $\sim 20\mathrm{s}$. The current level of coherence of grAl resonators makes them attractive for integration in quantum devices, while it also evidences the need to reduce the density of nonequilibrium QPs.

We report an extraordinary pressure dependence of the magnetic interactions in the metal-organic system $[{\mathrm{CuF}}_2({\mathrm{H}}_2\mathrm{O}{)}_2{]}_2\text{pyrazine}$. At zero pressure, this material realizes a quasi-two-dimensional spin-$1/2$ square-lattice Heisenberg antiferromagnet. By high-pressure, high-field susceptibility measurements we show that the dominant exchange parameter is reduced continuously by a factor of 2 on compression. Above 18 kbar, a phase transition occurs, inducing an orbital re-ordering that switches the dimensionality, transforming the quasi-two-dimensional lattice into weakly coupled chains. We explain the microscopic mechanisms for both phenomena by combining detailed x-ray and neutron diffraction studies with quantitative modeling using spin-polarized density functional theory.

Herewith, first-principles calculations based on density functional theory are used to describe the ideal magnetization reversal through polarization switching in ${\mathrm{BaCuF}}_4$ which, according to our results, could be accomplished close to room temperature. We also show that this ideal coupling is driven by a single soft mode that combines both polarization, and octahedral rotation. The later being directly coupled to the weak ferromagnetism of ${\mathrm{BaCuF}}_4$. This, added to its strong Jahn-Teller distortion and its orbital ordering, makes this material a very appealing prototype for crystals in the $AB{X}_4$ family for multifunctional applications. The described mechanism behaves ideally as it couples the ferroelectric and the magnetic properties naturally and it has not been reported previously.

Drawing an analogy to the paradigm of quasielastic neutron scattering, we present a general approach for quantitatively investigating the spatiotemporal dependence of structural anisotropy relaxation in deformed polymers by using small-angle neutron scattering. Experiments and nonequilibrium molecular dynamics simulations on polymer melts over a wide range of molecular weights reveal that their conformational relaxation at relatively high momentum transfer $Q$ and short time can be described by a simple scaling law, with the relaxation rate proportional to $Q$. This peculiar scaling behavior, which cannot be derived from the classical Rouse and tube models, is indicative of a surprisingly weak direct influence of entanglement on the microscopic mechanism of single-chain anisotropy relaxation.

The emergence and maintenance of polymers with complex sequences pose a major question in the study of the origin of life. To answer this, we study a model polymerization reaction, where polymers are synthesized by stepwise ligation from two types of monomers, catalyzed by a long polymer as a template. Direct stochastic simulation and dynamical systems analysis reveal that the most dominant polymer sequence in a population successively changes, depending on the flow rate of monomers to the system, with more complex sequences selected at a lower flow rate. We discuss the relevance of this kinetic sequence selection through nonequilibrium flow to the origin of complex polymers.

Bacteria can adjust the structure of colonies and biofilms to enhance their survival rate under external stress. Here, we explore the link between bacterial interaction forces and colony structure. We show that the activity of extracellular pilus motors enhances local ordering and accelerates fusion dynamics of bacterial colonies. The radial distribution function of mature colonies shows local fluidlike order. The degree and dynamics of ordering are dependent on motor activity. At a larger scale, the fusion dynamics of two colonies shows liquidlike behavior whereby motor activity strongly affects surface tension and viscosity.

A recent study of red blood cells (RBCs) in shear flow [Lanotte et al., Proc. Natl. Acad. Sci. U.S.A. 113, 13289 (2016)] has demonstrated that RBCs first tumble, then roll, transit to a rolling and tumbling stomatocyte, and finally attain polylobed shapes with increasing shear rate, when the viscosity contrast between cytosol and blood plasma is large enough. Using two different simulation techniques, we construct a state diagram of RBC shapes and dynamics in shear flow as a function of shear rate and viscosity contrast, which is also supported by microfluidic experiments. Furthermore, we illustrate the importance of RBC shear elasticity for its dynamics in flow and show that two different kinds of membrane buckling trigger the transition between subsequent RBC states.

We develop a new method to constrain primordial non-Gaussianities of the local kind using unclustered tracers of the large scale structure. We show that, in the limit of low noise, zero bias tracers yield large improvement over standard methods, mostly due to vanishing sampling variance. We propose a simple technique to construct such a tracer, using environmental information obtained from the original sample and validate our method with $N$-body simulations. Our results indicate that ${\sigma }_{f_{\mathrm{NL}}^{\text{loc}}}\simeq 1$ can be reached using only information on a single tracer of sufficiently high number density.

$\mathcal{N}=4$ supergravity is understood to contain a $\mathrm{U}(1)$ anomaly which manifests itself via the nonvanishing of loop-level scattering amplitudes that violate a tree-level charge conservation rule. In this Letter we provide detailed evidence that at one loop such anomalous amplitudes can be set to zero by the addition of a finite local counterterm. We show that the same counterterm also cancels evanescent contributions that play an important role in the analysis of ultraviolet divergences in dimensionally regularized gravity. These cancellations call for a reanalysis of the four-loop ultraviolet divergences previously found in this theory without the addition of such counterterms.

We address the $\mathrm{\Lambda }$ hypernuclear “overbinding problem” in light hypernuclei which stands for a 1–3 MeV excessive $\mathrm{\Lambda }$ separation energy calculated in ${}_{\mathrm{\Lambda }}{}^5\mathrm{He}$. This problem arises in most few-body calculations that reproduce ground-state $\mathrm{\Lambda }$ separation energies in the lighter $\mathrm{\Lambda }$ hypernuclei within various hyperon-nucleon interaction models. Recent pionless effective field theory ($\cancel{\pi }\mathrm{EFT}$) nuclear few-body calculations are extended in this work to $\mathrm{\Lambda }$ hypernuclei. At leading order, the $\mathrm{\Lambda }N$ low-energy constants are associated with $\mathrm{\Lambda }N$ scattering lengths, and the $\mathrm{\Lambda }NN$ low-energy constants are fitted to $\mathrm{\Lambda }$ separation energies ($B_{\mathrm{\Lambda }}^{\exp }$) for $A\le 4$. The resulting $\cancel{\pi }\mathrm{EFT}$ interaction reproduces in few-body stochastic variational method calculations the reported value $B_{\mathrm{\Lambda }}^{\exp }({}_{\mathrm{\Lambda }}{}^5\mathrm{He})=3.12\pm 0.02\mathrm{MeV}$ within a fraction of MeV over a broad range of $\cancel{\pi }\mathrm{EFT}$ cutoff parameters. Possible consequences and extensions to heavier hypernuclei and to neutron-star matter are discussed.

The role of the nuclear degrees of freedom in nonlinear two-photon single ionization of ${\mathrm{H}}_2$ molecules interacting with short and intense vacuum ultraviolet pulses is investigated, both experimentally and theoretically, by selecting single resonant vibronic intermediate neutral states. This high selectivity relies on the narrow bandwidth and tunability of the pulses generated at the FERMI free-electron laser. A sustained enhancement of dissociative ionization, which even exceeds nondissociative ionization, is observed and controlled as one selects progressively higher vibronic states. With the help of ab initio calculations for increasing pulse durations, the photoelectron and ion energy spectra obtained with velocity map imaging allow us to identify new photoionization pathways. With pulses of the order of 100 fs, the experiment probes a timescale that lies between that of ultrafast dynamical processes and that of steady state excitations.

A recent ultrafast pump-probe technique has allowed measurement of time delays during photoemission in a variety of systems ranging from atoms and molecules to solids with unprecedented temporal resolution. However, identifying the underlying physics is still a challenge especially in complicated multichannel above-threshold ionization (ATI) experiments. Here we demonstrate that the time delays of different ionization pathways in ATI can be clearly resolved and extracted with a semiclassical statistical method. The remarkable phase shift of near threshold photoelectrons can be attributed to a temporary retrapping of a photoelectron by the atomic potential in a quasibound state after emerging in the continuum state. This continuum-bound-continuum scattering manifests as a new resonant effect in strong-field photoemission. Our results unify the seemingly opposing quantum Eisenbud-Wigner-Smith time delay and classical Coulomb-induced time delay by highlighting the same physical picture, which holds promise for an intuitive interpretation of time-resolved fundamental electronic processes in strong-field experiments and epistemological reexamination of the quantum-classical correspondence.