Despite strenuous research efforts for more than one century, identifying the magnitude and sign of the apparent line tension for a liquid-solid-gas system remains an elusive goal. Herein we accurately determine the apparent line tension from the size-dependent contact angle of sessile nanodrops on surfaces with different wetting properties via atomic force microscopy measurements and molecular dynamics simulations. We show that the apparent line tension has a magnitude of ${10}^{-11}–{10}^{-10}\mathrm{J}/\mathrm{m}$, in good agreement with theoretical predictions. Furthermore, while it is positive and favors shorter contact lines for droplets on very lyophilic surfaces, the apparent line tension changes its sign and favors longer contact lines on surfaces with an apparent contact angle higher than a critical value. By analyzing the density and the potential energy of liquid molecules within the sessile droplet, we demonstrate that the sign of the apparent line tension is a thermodynamic property of the liquid-solid-gas system rather than the local effect of intermolecular interactions in the three-phase confluence region.

A small nonaxisymmetric (3D) magnetic field can induce nonambipolar transport of the particle species confined in a tokamak and thus a significant change of plasma rotation. This process can be in a favor of instability control in the region where the tokamak plasma is sufficiently collisional and resistive, as observed in the applications of $n=1$ resonant magnetic perturbations to the KSTAR tokamak. The plasma rotation can be globally accelerated due to radially drifting electrons and constrained to the electron root, if the radial transport is enhanced by an amplified 3D response. This mechanism is verified by a kinetically self-consistent magnetohydrodynamic modeling for both response and transport, which offers the quantitative explanations on the internal $n=1$ structure detected by electron-cyclotron-emission imaging and the cocurrent plasma spinning observed in the experiments.

We evaluate the density matrix of an arbitrary quantum mechanical system in terms of the quantities pertinent to the solution of the time-dependent density functional theory (TDDFT) problem. Our theory utilizes the adiabatic connection perturbation method of Görling and Levy, from which the expansion of the many-body density matrix in powers of the coupling constant $\lambda$ naturally arises. We then find the reduced density matrix ${\rho }_{\lambda }(\mathbf{r},{\mathbf{r}}^{\prime },t)$, which, by construction, has the $\lambda$ independent diagonal elements ${\rho }_{\lambda }(\mathbf{r},\mathbf{r},t)=n(\mathbf{r},t)$, $n(\mathbf{r},t)$ being the particle density. The off-diagonal elements of ${\rho }_{\lambda }(\mathbf{r},{\mathbf{r}}^{\prime },t)$ contribute importantly to the processes unaccessible via the density, directly or by the use of the known TDDFT functionals. Of those, we consider the momentum-resolved photoemission, doing this to the first order in $\lambda$, i.e., on the level of the exact exchange theory. In illustrative calculations of photoemission from the quasi-2D electron gas and isolated atoms, we find quantitatively strong and conceptually far-reaching differences with the independent-particle Fermi’s golden rule formula.

We report measurements of the diffusion rate of isolated ion-implanted ${}^8{\mathrm{Li}}^{+}$ within $\sim 120\mathrm{nm}$ of the surface of oriented single-crystal rutile ${\mathrm{TiO}}_2$ using a radiotracer technique. The $\alpha$ particles from the ${}^8\mathrm{Li}$ decay provide a sensitive monitor of the distance from the surface and how the depth profile of ${}^8\mathrm{Li}$ evolves with time. The main findings are that the implanted ${\mathrm{Li}}^{+}$ diffuses and traps at the (001) surface. The $T$ dependence of the diffusivity is described by a bi-Arrhenius expression with activation energies of 0.3341(21) eV above 200 K, whereas at lower temperatures it has a much smaller barrier of 0.0313(15) eV. We consider possible origins for the surface trapping, as well the nature of the low-$T$ barrier.

Significant effort has been devoted to the study of “non-Fermi-liquid” (NFL) metals: gapless conducting systems that lack a quasiparticle description. One class of NFL metals involves a finite density of fermions interacting with soft order parameter fluctuations near a quantum critical point. The problem has been extensively studied in a large-$N$ limit ($N$ corresponding to the number of fermion flavors) where universal behavior can be obtained by solving a set of coupled saddle-point equations. However, a remarkable study by Lee revealed the breakdown of such approximations in two spatial dimensions. We show that an alternate approach, in which the fermions belong to the fundamental representation of a global $\mathrm{SU}(N)$ flavor symmetry, while the order parameter fields transform under the adjoint representation (a “matrix large-$N$” theory), yields a tractable large $N$ limit. At low energies, the system consists of an overdamped boson with dynamical exponent $z=3$ coupled to a non-Fermi-liquid with self-energy $\mathrm{\Sigma }(\omega )\sim {\omega }^{2/3}$, consistent with previous studies.

Hard-x-ray spectroscopy relies on a suite of modern techniques for studies of vibrational, electronic, and magnetic excitations in condensed matter. At present, the energy resolution of these techniques can be improved only by decreasing the spectral window of the involved optics—monochromators and analyzers—thereby sacrificing the intensity. Here, we demonstrate hard-x-ray spectroscopy with greatly improved energy resolution without narrowing the spectral window by adapting principles of spectrographic imaging to the hard-x-ray regime. Similar to Newton’s classical prism, the hard-x-ray spectrograph disperses different “colors”—i.e., energies—of x-ray photons in space. Then, selecting each energy component with a slit ensures high energy resolution, whereas measuring x-ray spectra with all components of a broad spectral window keeps the intensity. We employ the principles of spectrographic imaging for phonon spectroscopy. Here the new approach revealed anomalous soft atomic dynamics in $\alpha$-iron, a phenomenon which was not previously reported in the literature. We argue that hard-x-ray spectrographic imaging also could be a path to discovering new physics in studies of electronic and magnetic excitations.

Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing-down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photoinduced transition of a model charge-density-wave (CDW) compound ${\mathrm{LaTe}}_3$. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing-down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.

Quantum phase transitions are intriguing and fundamental cooperative phenomena in physics. Analyzing a superconducting nanowire with spin-dependent non-Hermitian hopping, we discover a topological quantum phase transition driven by infinitesimal cascade instability. The anomalous phase transition is complementary to the universal non-Bloch wave behavior of non-Hermitian systems. We show that an infinite small magnetic field drastically suppresses the non-Hermitian skin effect, inducing a topological phase with Majorana boundary states. Furthermore, by identifying the bulk topological invariant, we establish the non-Hermitian bulk-boundary correspondence that does not have a Hermitian counterpart. We also discuss an experimental realization of the system by using the spin-current injection to a quantum wire.

The nematic liquid crystal (LC) director field can contain defects that are both singular and nonsingular, but nonsingular defects with an integer winding number of the director are typically metastable because of their high energy. We demonstrate topology-mediated generation and stabilization of nonsingular wall loops in a sandwich-type LC cell by combining a patterned substrate with a planar substrate. We implement a design which imposes a topological constraint on a singular disclination loop such that it irreversibly annihilates upon application of a field, and it results in the generation of a stable nonsingular wall loop when the field is removed. Theoretical modeling agrees with experimental observations, providing insight into the wall generation mechanism and its stability. The concept to stabilize high-energy structures through orientation-patterning-defined topological constraints extends our ability to control orientationally ordered matter.

We report a straightforward, model-free approach for measuring pair potentials from particle-coordinate data, based on enforcing consistency between the pair distribution function measured separately by the distance-histogram and test-particle insertion routes. We demonstrate the method’s accuracy and versatility in simulations of simple fluids, before applying it to an experimental system composed of superparamagnetic colloidal particles. The method will enable experimental investigations into many-body interactions and allow for effective coarse graining of interactions from simulations.

We formulate a discretization of $\sigma$ models suitable for simulation by quantum computers. Space is substituted with a lattice, as usually done in lattice field theory, while the target space (a sphere) is replaced by the “fuzzy sphere”, a construction well known from noncommutative geometry. Contrary to more naive discretizations of the sphere, in this construction the exact O(3) symmetry is maintained, which suggests that the discretized model is in the same universality class as the continuum model. That would allow for continuum results to be obtained for very rough discretizations of the target space as long as the space discretization is made fine enough. The cost of performing time evolution, measured as the number of controlled-not operations necessary, is $12LT/\mathrm{\Delta }t$, where $L$ is the number of spatial sites, $T$ the maximum time extent, and $\mathrm{\Delta }t$ the time spacing.

Coherence is a fundamental resource in quantum information processing, which can be certified by a coherence witness. Due to the imperfection of measurement devices, a conventional coherence witness may lead to fallacious results. We show that the conventional witness could mistake an incoherent state as a state with coherence due to the inaccurate settings of measurement bases. In order to make the witness result reliable, we propose a measurement-device-independent coherence witness scheme without any assumptions on the measurement settings. We introduce the decoy-state method to significantly increase the capability of recognizing states with coherence. Furthermore, we experimentally demonstrate the scheme in a time-bin encoding optical system.

We present a method to detect lower bounds to the classical capacity of quantum communication channels by means of few local measurements (i.e., without complete process tomography), reconstruction of sets of conditional probabilities, and classical optimization. The method does not require any a priori information about the channel. We illustrate its performance for significant forms of noisy channels.

Dark matter comprises the bulk of the matter in the Universe, but its particle nature and cosmological origin remain mysterious. Knowledge of the dark matter density distribution in the Milky Way Galaxy is crucial both to our understanding of the standard cosmological model and for grounding direct and indirect searches for the particles comprising dark matter. Current measurements of Galactic dark matter content rely on model assumptions to infer the forces acting upon stars from the distribution of observed velocities. Here, we propose to apply the precision radial velocity method, optimized in recent years for exoplanet astronomy, to measure the change in the velocity of stars over time, thereby providing a direct probe of the local gravitational potential in the Galaxy. Using numerical simulations, we develop a realistic strategy to observe the differential accelerations of stars in our Galactic neighborhood with next-generation telescopes, at the level of ${10}^{-8}\mathrm{cm}/{\mathrm{s}}^2$. Our simulations show that detecting accelerations at this level with an ensemble of ${10}^3$ stars requires the effect of stellar noise on radial velocity measurements to be reduced to $<10\mathrm{cm}/\mathrm{s}$. The measured stellar accelerations may then be used to extract the local dark matter density and morphological parameters of the density profile.

A recent proposal suggests that experimental discrepancies on the lifetime of neutrons can be resolved if neutrons decay to dark matter. At the same time it has been demonstrated that such a decay mode would soften the nuclear equation of the state resulting in neutron stars with a maximum mass much below currently observed ones. In this Letter, we demonstrate that appropriate dark matter-baryon interactions can accommodate neutron stars with mass above two solar masses. We compare this stabilization mechanism to one based on dark matter self-interactions, finding that it is less sensitive to the details of the nuclear equation of state. We present a simple microscopic model realization of this mechanism.

We present a detailed experimental and theoretical study on the relativistic nondipole effects in strong-field atomic ionization by near-infrared linearly polarized few-cycle laser pulses in the intensity range of $10^{14}–10^{15}\mathrm{W}/{\mathrm{cm}}^2$. We record high-resolution photoelectron momentum distributions of argon using a reaction microscope and compare our measurements with a truly ab initio fully relativistic 3D model based on the time-dependent Dirac equation. We observe counterintuitive peak shifts of the transverse electron momentum distribution in the direction opposite to that of laser propagation as a function of laser intensity and demonstrate an excellent agreement between the experimental results and theoretical predictions.

We show that for a quantum system coupled to both vibrational and electromagnetic environments, enforcing additivity of their combined influences results in nonequilibrium dynamics that does not respect the Franck-Condon principle. We overcome this shortcoming by employing a collective coordinate representation of the vibrational environment, which permits the derivation of a nonadditive master equation. When applied to a two-level emitter our treatment predicts decreasing photon emission rates with increasing vibrational coupling, consistent with Franck-Condon physics. In contrast, the additive approximation predicts the emission rate to be completely insensitive to vibrations. We find that nonadditivity also plays a key role in the stationary nonequilibrium model behavior, enabling two-level population inversion under incoherent electromagnetic excitation.

Spontaneous pattern formation plays an important role in a wide variety of natural phenomena and materials systems. A key ingredient for the occurrence of modulated phases is the presence of competing interactions, generally of different physical origins. We demonstrate that in dipolar films, a prototypical system for pattern formation, patterns can be induced by dielectric effects alone. A rich phase diagram arises, where striped and circular morphologies emerge with geometric properties that can be controlled through variation of particle shape and substrate permittivity or permeability. These effects are particularly enhanced by metamaterial substrates.