We report the beam energy ($\sqrt{s_{NN}}=7.7–200\mathrm{GeV}$) and collision centrality dependence of the mean ($M$), standard deviation ($\sigma$), skewness ($S$), and kurtosis ($\kappa$) of the net-proton multiplicity distributions in $\mathrm{Au}+\mathrm{Au}$ collisions. The measurements are carried out by the STAR experiment at midrapidity ($|y|<0.5$) and within the transverse momentum range $0.4<p_T<0.8\mathrm{GeV}/c$ in the first phase of the Beam Energy Scan program at the Relativistic Heavy Ion Collider. These measurements are important for understanding the quantum chromodynamic phase diagram. The products of the moments, $S\sigma$ and $\kappa {\sigma }^2$, are sensitive to the correlation length of the hot and dense medium created in the collisions and are related to the ratios of baryon number susceptibilities of corresponding orders. The products of moments are found to have values significantly below the Skellam expectation and close to expectations based on independent proton and antiproton production. The measurements are compared to a transport model calculation to understand the effect of acceptance and baryon number conservation and also to a hadron resonance gas model.

We report on the realization of an ultracold mixture of lithium atoms in the ground state and ytterbium atoms in an excited metastable (${}^3{P}_2$) state. Such a mixture can support broad magnetic Feshbach resonances which may be utilized for the production of ultracold molecules with an electronic spin degree of freedom, as well as novel Efimov trimers. We investigate the interaction properties of the mixture in the presence of an external magnetic field and find an upper limit for the background interspecies two-body inelastic decay coefficient of $K_2^{\prime }<3\times {10}^{-12}{\mathrm{cm}}^3/\mathrm{s}$ for the ${}^3{P}_2$ $m_J=-1$ substate. We calculate the dynamic polarizabilities of the $\mathrm{Yb}({}^3{P}_2)$ magnetic substates for a range of wavelengths, and find good agreement with our measurements at 1064 nm. Our calculations also allow the identification of magic frequencies where Yb ground and metastable states are identically trapped and the determination of the interspecies van der Waals coefficients.

We demonstrate recording and retrieval of the digital document with a nearly unlimited lifetime. The recording process of multiplexed digital data was implemented by femtosecond laser nanostructuring of fused quartz. The storage allows unprecedented parameters including hundreds of terabytes per disc data capacity, thermal stability up to $1000°\mathrm{C}$, and virtually unlimited lifetime at room temperature. We anticipate that this demonstration will open a new era of eternal data archiving.

Qi-Wa refers to the up curl on the lengths of hand scrolls and hanging scrolls, which has troubled Chinese artisans and emperors for as long as the art of painting and calligraphy has existed. This warp is unwelcome not only for aesthetic reasons, but its potential damage to the fiber and ink. Although it is generally treated as a part of the cockling and curling due to moisture, consistency of paste, and defects from the mounting procedures, we demonstrate that the spontaneous extrinsic curvature incurred from the storage is in fact more essential to understanding and curing Qi-Wa. In contrast to the former factors whose effects are less predictable, the plastic deformation and strain distribution on a membrane are a well-defined mechanical problem. We study this phenomenon by experiments, theoretical models, and molecular dynamics simulation, and obtain consistent scaling relations for the Qi-Wa height. This knowledge enables us to propose modifications on the traditional mounting techniques that are tested on real mounted paper to be effective at mitigating Qi-Wa. By experimenting on polymer-based films, we demonstrate the possible relevance of our study to the modern development of flexible electronic paper.

The first experimental study is presented of a corrugated wall device that uses wakefields to remove a linear energy correlation in a relativistic electron beam (a “dechirper”). Time-resolved measurements of both longitudinal and transverse wakefields of the device are presented and compared with simulations. This study demonstrates the feasibility to employ a dechirper for precise control of the beam phase space in the next generation of free-electron-lasers.

We have developed a new formula for a relativistic ponderomotive force of transversely localized laser fields based on the noncanonical Lie perturbation method by finding proper coordinates and gauges in the variational principle. The formula involves new terms represented by second and third spatial derivatives of the field amplitude, so that the ponderomotive force depends not only on the local field gradient, but also on the curvature and its variation. The formula is then applicable to a regime in which the conventional formula is hardly applied such that nonlocal and/or global extent of the field profile becomes important. The result can provide a theoretical basis for describing nonlinear laser-plasma interaction including such nonlocal effects, which is examined via particle-in-cell simulation of laser propagation in a plasma with a super Gaussian transverse field profile.

The evolution of beam phase space in ionization injection into plasma wakefields is studied using theory and particle-in-cell simulations. The injection process involves both longitudinal and transverse phase mixing, leading initially to a rapid emittance growth followed by oscillation, decay, and a slow growth to saturation. An analytic theory for this evolution is presented and verified through particle-in-cell simulations. This theory includes the effects of injection distance (time), acceleration distance, wakefield structure, and nonlinear space charge forces, and it also shows how ultralow emittance beams can be produced using ionization injection methods.

The Kibble-Zurek mechanism (KZM) captures the key physics of nonequilibrium dynamics in second order phase transitions, and accurately predicts the density of topological defects formed in such processes. However, the central prediction of KZM—i.e., the scaling of the density of defects with the quench rate—still needs further experimental confirmation, particularly for quantum transitions. Here, we perform a quantum simulation of the nonequilibrium dynamics of the Landau-Zener model based on a nine-stage optical interferometer with an overall visibility of $0.975\pm 0.008$. The results support the adiabatic-impulse approximation, which is the core of Kibble-Zurek theory. Moreover, the developed high-fidelity multistage optical interferometer can support more complex linear optical quantum simulations.

We address, theoretically, the puzzling similarity observed in the thermodynamic behavior of independent clouds of cold dipolar excitons in coupled semiconductor quantum wells. We argue that the condensation of self-trapped exciton gas starts at the same critical temperature in all traps due to the specific scaling rule. As a consequence of the reduced dimensionality of the system, the scaling parameters appear to be insensitive to disorder.

We analyze the low energy excitations of spin lattice systems in two dimensions at zero temperature within the framework of projected entangled pair state models. Perturbations in the bulk give rise to physical excitations located at the edge. We identify the corresponding degrees of freedom, give a procedure to derive the edge Hamiltonian, and illustrate that it can exhibit a rich phase diagram. For topological models, the edge Hamiltonian is constrained by the topological order in the bulk, which gives rise to one-dimensional edge models with unconventional properties; for instance, a topologically ordered bulk can protect a ferromagnetic Ising chain at the edge against spontaneous symmetry breaking.

Recent studies indicated that noncompensated cation-anion codoping of wide-band-gap oxide semiconductors such as anatase ${\mathrm{TiO}}_2$ significantly reduces the optical band gap and thus strongly enhances the absorption of visible light [W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)]. We used soft x-ray spectroscopy to fully determine the location and nature of the impurity levels responsible for the extraordinarily large ($\sim 1\mathrm{eV}$) band gap reduction of noncompensated codoped rutile ${\mathrm{TiO}}_2$. It is shown that $\mathrm{Cr}/\mathrm{N}$ codoping strongly enhances the substitutional N content, compared to single element doping. The band gap reduction is due to the formation of Cr $3d^3$ levels in the lower half of the gap while the conduction band minimum is comprised of localized Cr $3d$ and delocalized N $2p$ states. Band gap reduction and carrier delocalization are critical elements for efficient light-to-current conversion in oxide semiconductors. These findings thus raise the prospect of using codoped oxide semiconductors with specifically engineered electronic properties in a variety of photovoltaic and photocatalytic applications.

We employ a single-charge counting technique to measure the full counting statistics of Andreev events in which Cooper pairs are either produced from electrons that are reflected as holes at a superconductor–normal-metal interface or annihilated in the reverse process. The full counting statistics consists of quiet periods with no Andreev processes, interrupted by the tunneling of a single electron that triggers an avalanche of Andreev events giving rise to strongly super-Poissonian distributions.

We report the observation of an isolated charged impurity in graphene and present direct evidence of the close connection between the screening properties of a 2D electron system and the influence of the impurity on its electronic environment. Using scanning tunneling microscopy and Landau level spectroscopy, we demonstrate that in the presence of a magnetic field the strength of the impurity can be tuned by controlling the occupation of Landau-level states with a gate voltage. At low occupation the impurity is screened, becoming essentially invisible. Screening diminishes as states are filled until, for fully occupied Landau levels, the unscreened impurity significantly perturbs the spectrum in its vicinity. In this regime we report the first observation of Landau-level splitting into discrete states due to lifting the orbital degeneracy.

In this work, we find that Majorana fermions induce selective equal spin Andreev reflections (SESARs), in which incoming electrons with certain spin polarization in the lead are reflected as counterpropagating holes with the same spin. The spin polarization direction of the electrons of this Andreev reflected channel is selected by the Majorana fermions. Moreover, electrons with opposite spin polarization are always reflected as electrons with unchanged spin. As a result, the charge current in the lead is spin polarized. Therefore, a topological superconductor which supports Majorana fermions can be used as a novel device to create fully spin-polarized currents in paramagnetic leads. We point out that SESARs can also be used to detect Majorana fermions in topological superconductors.

We investigated the magnetic anisotropy energy of monatomic surface-step atoms in antiferromagnetic/ferromagnetic (AF/FM) epitaxial $\mathrm{Mn}/\mathrm{Co}$ bilayers grown on vicinal Cu(001) surfaces. The step-induced anisotropy of the $\mathrm{Co}/\mathrm{Cu}(001)$ films was quenched upon submonolayer Mn deposition, but a reentrant uniaxial surface anisotropy was observed for Mn thickness ($t_{\mathrm{Mn}}$) between 1 and 2 monolayers, which disappears for Mn thickness above 2 monolayers. In the $\mathrm{Mn}/\mathrm{Co}/\mathrm{Cu}(001)$ system, Mn films undergo a $t_{\mathrm{Mn}}$-dependent transition from FM to AF in the 1–2 Mn monolayer thickness range, which entails the coexistence of FM and AF Mn phases in the film. The observation of a sizeable uniaxial anisotropy exclusively in the Mn-thickness range of coexistence of the FM and AF phases points out the crucial role of the boundaries between FM and AF regions within the Mn film. A symmetry-breaking mechanism of a magnetic type, rather than a purely geometric one, is therefore proposed as the origin of the reentrant anisotropy.

We discuss the form of the damping of magnetic excitations in a metal near a ferromagnetic instability. The paramagnon theory predicts that the damping term should have the form $\gamma (q,\mathrm{\Omega })\propto \mathrm{\Omega }/\mathrm{\Gamma }(q)$, with $\mathrm{\Gamma }(q)\propto q$ (the Landau damping). However, the experiments on uranium metallic compounds $\mathrm{UGe}{}_2$ and UCoGe showed that $\mathrm{\Gamma }(q)$ is essentially independent of $q$. A nonzero $\gamma (q=0,\mathrm{\Omega })$ is impossible in systems with one type of carrier (either localized or itinerant) because it would violate the spin conservation. It has been conjectured recently that a near-constant $\mathrm{\Gamma }(q)$ in $\mathrm{UGe}{}_2$ and UCoGe may be due to the presence of both localized and itinerant electrons in these materials, with ferromagnetism involving predominantly localized spins. We present the microscopic analysis of the damping of near-critical localized excitations due to interaction with itinerant carriers. We show explicitly how the presence of two types of electrons breaks the cancellation between the contributions to $\mathrm{\Gamma }(0)$ from the self-energy and vertex correction insertions into the spin polarization bubble. We compare our theory with the available experimental data.

In a multiferroic orthoferrite ${\mathrm{Dy}}_{0.7}{\mathrm{Tb}}_{0.3}{\mathrm{FeO}}_3$, which shows electric-field-($E$-)driven magnetization ($M$) reversal due to a tight clamping between polarization ($P$) and $M$, a gigantic effect of magnetic-field ($H$) biasing on $P\text{−}E$ hysteresis loops is observed in the case of rapid $E$ sweeping. The magnitude of the bias $E$ field can be controlled by varying the magnitude of $H$, and its sign can be reversed by changing the sign of $H$ or the relative clamping direction between $P$ and $M$. The origin of this unconventional biasing effect is ascribed to the difference in the Zeeman energy between the $+P$ and $-P$ states coupled with the $M$ states with opposite sign.

The kinetic energy of a freely cooling granular gas decreases as a power law $t^{-\theta }$ at large times $t$. Two theoretical conjectures exist for the exponent $\theta$. One based on ballistic aggregation of compact spherical aggregates predicts $\theta =2d/(d+2)$ in $d$ dimensions. The other based on Burgers equation describing anisotropic, extended clusters predicts $\theta =d/2$ when $2\le d\le 4$. We do extensive simulations in three dimensions to find that while $\theta$ is as predicted by ballistic aggregation, the cluster statistics and velocity distribution differ from it. Thus, the freely cooling granular gas fits to neither the ballistic aggregation or a Burgers equation description.

We reveal universal dynamical scaling behavior across adiabatic quantum phase transitions in networks ranging from traditional spatial systems (Ising model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our findings, which lie beyond traditional critical exponent analysis and adiabatic perturbation approximations, are applicable even where excitations have not yet stabilized and, hence, provide a time-resolved understanding of quantum phase transitions encompassing a wide range of adiabatic regimes. We show explicitly that even though two systems may traditionally belong to the same universality class, they can have very different adiabatic evolutions. This implies that more stringent conditions need to be imposed than at present, both for quantum simulations where one system is used to simulate the other and for adiabatic quantum computing schemes.

We consider a quantum Otto cycle for a time-dependent harmonic oscillator coupled to a squeezed thermal reservoir. We show that the efficiency at maximum power increases with the degree of squeezing, surpassing the standard Carnot limit and approaching unity exponentially for large squeezing parameters. We further propose an experimental scheme to implement such a model system by using a single trapped ion in a linear Paul trap with special geometry. Our analytical investigations are supported by Monte Carlo simulations that demonstrate the feasibility of our proposal. For realistic trap parameters, an increase of the efficiency at maximum power of up to a factor of 4 is reached, largely exceeding the Carnot bound.