We report simulation evidence that the structure of the first water layer next to the surface can strongly affect the contact angle of water droplets. Molecular dynamics simulations show that a small uniform strain ($\pm 3\%$) applied to the lattice constant of a multilayer hydrophilic surface can introduce a marked change in the wetting tendency. In particular, when the lattice constant of a hydrophilic surface matches the projected oxygen-oxygen distance of bulk water to the surface, a contact-angle minimum is resulted. In stark contrast, such a lattice strain has little effect on the wetting properties of hydrophobic surfaces. The structure of the first water layer next to the hydrophilic surface gradually loses characteristics of liquid water when moving away from the contact-angle minimum. Our results demonstrate a close correlation among the length of lattice constant, contact angle of the water droplet, and the structure and dynamics of vicinal water.

We introduce a novel class of low-dimensional topological tight-binding models that allow for bound states that are fractionally charged fermions and exhibit non-Abelian braiding statistics. The proposed model consists of a double (single) ladder of spinless (spinful) fermions in the presence of magnetic fields. We study the system analytically in the continuum limit as well as numerically in the tight-binding representation. We find a topological phase transition with a topological gap that closes and reopens as a function of system parameters and chemical potential. The topological phase is of the type BDI and carries two degenerate midgap bound states that are localized at opposite ends of the ladders. We show numerically that these bound states are robust against a wide class of perturbations.

In the exact Kohn-Sham density-functional theory, the total energy versus the number of electrons is a series of linear segments between integer points. However, commonly used approximate density functionals produce total energies that do not exhibit this piecewise-linear behavior. As a result, the ionization potential theorem, equating the highest occupied eigenvalue with the ionization potential, is grossly disobeyed. Here, we show that, contrary to conventional wisdom, most of the required piecewise linearity of an arbitrary approximate density functional can be restored by careful consideration of the ensemble generalization of density-functional theory. Furthermore, the resulting formulation introduces the desired derivative discontinuity to any approximate exchange-correlation functional, even one that is explicitly density dependent. This opens the door to calculations of the ionization potential and electron affinity, even without explicit electron removal or addition. All these advances are achieved while neither introducing empiricism nor changing the underlying functional form. The power of the approach is demonstrated on benchmark systems using the local density approximation as an illustrative example.

Here we present the theoretical foundation of the strong coupling phenomenon between quantum emitters and propagating surface plasmons observed in two-dimensional metal surfaces. For that purpose, we develop a quantum framework that accounts for the coherent coupling between emitters and surface plasmons and incorporates the presence of dissipation and dephasing. Our formalism is able to reveal the key physical mechanisms that explain the reported phenomenology and also determine the physical parameters that optimize the strong coupling. A discussion regarding the classical or quantum nature of this phenomenon is also presented.

We report a large exchange-bias effect after zero-field cooling the new tetragonal Heusler compound ${\mathrm{Mn}}_2\mathrm{PtGa}$ from the paramagnetic state. The first-principles calculation and the magnetic measurements reveal that ${\mathrm{Mn}}_2\mathrm{PtGa}$ orders ferrimagnetically with some ferromagnetic inclusions. We show that ferrimagnetic ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled exchange bias during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field-induced irreversible magnetic behavior and a spin-glass-like phase. The field-induced irreversibility originates from an unusual first-order ferrimagnetic to antiferromagnetic transition, whereas the spin-glass-like state forms due to the existence of antisite disorder intrinsic to the material.

By many-body quantum-chemical calculations, we investigate the role of two structural effects—local ligand distortions and the anisotropic Cd-ion coordination—on the magnetic state of ${\mathrm{Cd}}_2{\mathrm{Os}}_2{\mathrm{O}}_7$, a spin $S=3/2$ pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially dependent on these geometrical features. Without trigonal distortions, a large easy-plane magnetic anisotropy develops. Their presence, however, reverses the sign of the zero-field splitting and causes a large easy-axis anisotropy ($D\simeq -6.8\mathrm{meV}$), which in conjunction with the antiferromagnetic exchange interaction ($J\simeq 6.4\mathrm{meV}$) stabilizes an all-in–all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets.

Voltage-tunable quantum traps confining individual spatially indirect and long-living excitons are realized by providing a coupled double quantum well with nanoscale gates. This enables us to study the transition from confined multiexcitons down to a single, electrostatically trapped indirect exciton. In the few exciton regime, we observe discrete emission lines identified as resulting from a single dipolar exciton, a biexciton, and a triexciton, respectively. Their energetic splitting is well described by Wigner-like molecular structures reflecting the interplay of dipolar interexcitonic repulsion and spatial quantization.

To unify general relativity and quantum theory is hard in part because they are formulated in two very different mathematical languages, differential geometry and functional analysis. A natural candidate for bridging this language gap, at least in the case of the Euclidean signature, is the discipline of spectral geometry. It aims at describing curved manifolds in terms of the spectra of their canonical differential operators. As an immediate benefit, this would offer a clean gauge-independent identification of the metric’s degrees of freedom in terms of invariants that should be ready to quantize. However, spectral geometry is itself hard and has been plagued by ambiguities. Here, we regularize and break up spectral geometry into small, finite-dimensional and therefore manageable steps. We constructively demonstrate that this strategy works at least in two dimensions. We can now calculate the shapes of two-dimensional objects from their vibrational spectra.

The large-$N$ limit of gauge theories has been playing a crucial role in theoretical physics over the decades. Despite its importance, little is known outside the planar limit where the ’t Hooft coupling$\lambda =g_{\mathrm{YM}}^{2}N$ is fixed. In this Letter we consider more general large-$N$ limit—$\lambda$ grows with $N$, e.g., $g_{\mathrm{YM}}^2$ is fixed. Such a limit is important particularly in recent attempts to find the nonpertubative formulation of M theory. Based on various supporting evidence, we propose this limit is essentially identical to the planar limit, in the sense the order of the large-$N$ limit and the strong coupling limit commute. For a wide class of large-$N$ gauge theories, these two limits are smoothly connected, and the analytic continuation from the planar limit is justified. As simple examples, we reproduce a few properties of the six-dimensional $\mathcal{N}=(2,0)$ theory on $S^1$ from the five-dimensional maximal super Yang-Mills theory, supporting the recent conjecture by Douglas and Lambert et al. that these two theories are identical.

We present a search for new particles in an extension to the standard model that includes a heavy Higgs boson ($H^0$), a lighter charged Higgs boson ($H^{\pm }$), and an even lighter Higgs boson $h^0$, with decays leading to a $W$-boson pair and a bottom-antibottom quark pair in the final state. We use events with exactly one lepton, missing transverse momentum, and at least four jets in data corresponding to an integrated luminosity of $8.7{\mathrm{fb}}^{-1}$ collected by the CDF II detector in proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$. We find the data to be consistent with standard model predictions and report the results in terms of a simplified Higgs-cascade-decay model, setting 95% confidence level upper limits on the product of cross section and branching fraction from 1.3 pb to 15 fb as a function of $H^0$ and $H^{\pm }$ masses for $m_h^0=126\mathrm{GeV}/c^2$.

The effect of the tensor force on $\beta$ decay is studied in the framework of the proton-neutron random phase approximation with the Skyrme force. The investigation is performed for even-even semimagic and magic nuclei, ${}^{34}\mathrm{Si}$, ${}^{68,78}\mathrm{Ni}$, and ${}^{132}\mathrm{Sn}$. The tensor correlation induces strong impact on the low-lying Gamow-Teller state. In particular, it improves the $\beta$-decay half-lives. $Q$ and $ft$ values are also investigated and compared with experimental data.

We present evidence for Rydberg-Rydberg interaction in a gas of rubidium atoms above room temperature. Rabi oscillations on the nanosecond time scale to different Rydberg states are investigated in a vapor cell experiment. Analyzing the atomic time evolution and comparing to a dephasing model, we find a scaling with the Rydberg quantum number $n$ that is consistent with van der Waals interaction. Our results show that the interaction strength can be larger than the kinetic energy scale (Doppler width), which is the requirement for realization of thermal quantum devices in the GHz regime.

In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of $KK$ hollow atoms (atoms without $n=1$ electrons) from thin Al foils was observed at pulse intensities of $3\times {10}^{20}\mathrm{W}/{\mathrm{cm}}^2$. The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the $KK$ hollow atom production. We estimate that this x-ray field has an intensity of $>5\times {10}^{18}\mathrm{W}/{\mathrm{cm}}^2$ and is in the 3 keV range.

We investigate the properties of the metallic state obtained by photodoping carriers into a Mott insulator. In a strongly interacting system, these carriers have a long lifetime, so that they can dissipate their kinetic energy to a phonon bath. In the relaxed state, the scattering rate saturates at a nonzero temperature-independent value, and the momentum-resolved spectral function features broad bands which differ from the well-defined quasiparticle bands of a chemically doped system. Our results indicate that a photodoped Mott insulator behaves as a bad metal, in which strong scattering between doublons and holes inhibits Fermi-liquid behavior down to low temperature.

A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in $p$-type silicon ($p$-Si). Ferromagnetic resonance and effective $s\mathrm{\text{−}}d$ coupling in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ results in spin accumulation at the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/p$-Si interface, inducing spin injection and the generation of spin current in the $p$-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the $p$-Si. This approach demonstrates the generation and transport of pure spin current in $p$-Si at room temperature.

An electromechanical resonator harboring an atomlike spectrum of discrete mechanical vibrations, namely, phonon modes, has been developed. A purely mechanical three-mode system becomes available in the electromechanical atom in which the energy difference of the two higher modes is resonant with a long-lived lower mode. Our measurements reveal that even an incoherent input into the higher mode results in coherent emission in the lower mode that exhibits all the hallmarks of phonon lasing in a process that is reminiscent of Brillouin lasing.

Using the density matrix renormalization group, we determine the phase diagram of the spin-$1/2$ Heisenberg antiferromagnet on a honeycomb lattice with a nearest-neighbor interaction $J_1$ and a frustrating, next-nearest-neighbor exchange $J_2$. As frustration increases, the ground state exhibits Néel, plaquette, and dimer orders, with critical points at $J_2/J_1=0.22$ and 0.35. We observe that both the spin gap and the corresponding order parameters vanish continuously at both the critical points, indicating the presence of deconfined quantum criticality.

Using the density matrix renormalization group, we investigate the $S=1/2$ Heisenberg model on the honeycomb lattice with first ($J_1$) and second ($J_2$) neighbor interactions. We are able to study long open cylinders with widths up to 12 lattice spacings. For $J_2/J_1$ near 0.3, we find an apparently paramagnetic phase, bordered by an antiferromagnetic phase for $J_2\lesssim 0.26$ and by a valence bond crystal for $J_2\gtrsim 0.36$. The longest correlation length that we find in this intermediate phase is for plaquette valence bond order. This correlation length grows strongly with cylinder circumference, indicating either quantum criticality or weak plaquette valence bond order.

A first principles approach for spin- and angle-resolved resonant photoemission is developed within multiple scattering theory and applied to a Cr(110) surface at the $2p\mathrm{\text{−}}3d$ resonance. The resonant photocurrent from this nonferromagnetic system is found to be strongly spin polarized by circularly polarized light, in agreement with experiments on antiferromagnetic and magnetically disordered systems. By comparing the antiferromagnetic and Pauli-paramagnetic phases of Cr, we explicitly show that the spin polarization of the photocurrent is independent of the existence of local magnetic moments, solving a long-standing debate on the origin of such polarization. New spin polarization effects are predicted for the paramagnetic phase even with unpolarized light, opening new directions for full mapping of spin interactions in macroscopically nonmagnetic or nanostructured systems.

We present a theory for the description of energy relaxation in a nonequilibrium condensate of bosonic particles. The approach is based on coupling to a thermal bath of other particles (e.g., phonons in a crystal, or noncondensed atoms in a cold atom system), which are treated with a Monte Carlo type approach. Together with a full account of particle-particle interactions, dynamic driving, and particle loss, this offers a complete description of recent experiments in which Bose-Einstein condensates are seen to relax their energy as they propagate in real space and time. As an example, we apply the theory to the solid-state system of microcavity exciton polaritons, in which nonequilibrium effects are particularly prominent.