We investigate the linear chain configurations of four-$\alpha$ clusters in ${}^{16}\mathrm{O}$ using a Skyrme cranked Hartree-Fock method and discuss the relationship between the stability of such states and angular momentum. We show the existence of a region of angular momentum ($13–18\hslash$) where the linear chain configuration is stabilized. For the first time we demonstrate that stable exotic states with a large moment of inertia (${\hslash }^2/2\Theta \sim 0.06–0.08\mathrm{MeV}$) can exist.

Stars are transparent to the passage of primordial black holes (PBHs) and serve as seismic detectors for such objects. The gravitational field of a PBH squeezes a star and causes it to ring acoustically. We calculate the seismic signature of a PBH passing through the Sun. The background for this signal is the observed spectrum of solar oscillations excited by supersonic turbulence. We predict that PBHs more massive than ${10}^{21}\mathrm{g}$ (comparable in mass to an asteroid) are detectable by existing solar observatories. The oscillations excited by PBHs peak at large scales and high frequencies, making them potentially detectable in other stars. The discovery of PBHs would have profound implications for cosmology and high-energy physics.

Drops placed on very hot solids levitate on a cushion of their own vapor, as discovered by Leidenfrost. This confers to these drops a remarkable mobility, which makes problematic their control and manipulation. Here we show how crenelated surfaces can be used to increase the friction of Leidenfrost drops by a factor on the order of 100, making them decelerate and be trapped on centimetric distances instead of the usual metric ones. We measure and characterize the friction force as a function of the design of the crenelations.

By selecting two dressed rotational states of ultracold polar molecules in an optical lattice, we obtain a highly tunable generalization of the $t\mathrm{\text{−}}J$ model, which we refer to as the $t\mathrm{\text{−}}J\mathrm{\text{−}}V\mathrm{\text{−}}W$ model. In addition to $XXZ$ spin exchange, the model features density-density interactions and density-spin interactions; all interactions are dipolar. We show that full control of all interaction parameters in both magnitude and sign can be achieved independently of each other and of the tunneling. As a first step towards demonstrating the potential of the system, we apply the density matrix renormalization group method to obtain the 1D phase diagram of the simplest experimentally realizable case. Specifically, we show that the tunability and the long-range nature of the interactions in the $t\mathrm{\text{−}}J\mathrm{\text{−}}V\mathrm{\text{−}}W$ model enable enhanced superfluidity. Finally, we show that Bloch oscillations in a tilted lattice can be used to probe the phase diagram experimentally.

Noble metals adopt close-packed structures at ambient pressure and rarely undergo structural transformation at high pressures. Platinum (Pt) is normally considered to be unreactive and is therefore not expected to form hydrides under pressure. We predict that platinum hydride (PtH) has a lower enthalpy than its constituents solid Pt and molecular hydrogen at pressures above 21.5 GPa. PtH transforms to a hexagonal close-packed or face-centered cubic (fcc) structure between 70 and 80 GPa. Linear response calculations indicate that PtH is a superconductor at these pressures with a critical temperature of about 10–25 K. These findings help to shed light on recent observations of pressure-induced metallization and superconductivity in hydrogen-rich materials. We show that the formation of fcc noble metal hydrides under pressure is common and examine the possibility of superconductivity in these materials.

We provide a model for the remarkable stability of surface nanobubbles to bulk dissolution. The key to the solution is that the gas in a nanobubble is of Knudsen type. This leads to the generation of a bulk liquid flow which effectively forces the diffusive gas to remain local. Our model predicts the presence of a vertical water jet immediately above a nanobubble, with an estimated speed of $\sim 3.3\mathrm{m}/\mathrm{s}$, in good agreement with our experimental atomic force microscopy measurement of $\sim 2.7\mathrm{m}/\mathrm{s}$. In addition, our model also predicts an upper bound for the size of nanobubbles, which is consistent with the available experimental data.

The fundamental collective degree of freedom of fractional quantum Hall states is identified as a unimodular two-dimensional spatial metric that characterizes the local shape of the correlations of the incompressible fluid. Its quantum fluctuations are controlled by a topologically quantized “guiding-center spin.” Charge fluctuations are proportional to its Gaussian curvature.

We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves, plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation.

$\mathrm{SmFe}{\mathrm{O}}_3$, a family of centrosymmetric rare-earth orthoferrites, is known to be nonferroelectric. However, we have found that $\mathrm{SmFe}{\mathrm{O}}_3$ is surprisingly ferroelectric at room temperature with a small polarization along the $b$ axis of $Pbnm$. First-principles calculations indicate that the canted antiferromagnetic ordering with two nonequivalent spin pairs is responsible for this extraordinary polarization and that the reverse Dzyaloshinskii-Moriya interaction dominates over the exchange-striction mechanism in the manifestation of the improper ferroelectricity. $\mathrm{SmFe}{\mathrm{O}}_3$ further exhibits an interesting phenomenon of spontaneous magnetization reversal at cryogenic temperatures. This reversal is attributed to the activation of the Sm-spin moment which is antiparallel to the Fe-spin moment below $\sim 5\mathrm{K}$.

Spike train regularity of the noisy neural auditory system model under the influence of two sinusoidal signals with different frequencies is investigated. For the increasing ratio $m/n$ of the input signal frequencies ($m$, $n$ are natural numbers) the linear growth of the regularity is found at the fixed difference ($m-n$). It is shown that the spike train regularity in the model is high for harmonious chords of input tones and low for dissonant ones.

We extend the Mermin-Wagner theorem to a system of lattice spins which are spin coupled to itinerant and interacting charge carriers. We use the Bogoliubov inequality to rigorously prove that neither (anti-) ferromagnetic nor helical long-range order is possible in one and two dimensions at any finite temperature. Our proof applies to a wide class of models including any form of electron-electron and single-electron interactions that are independent of spin. In the presence of Rashba or Dresselhaus spin-orbit interactions (SOI) magnetic order is not excluded and intimately connected to equilibrium spin currents. However, in the special case when Rashba and Dresselhaus SOIs are tuned to be equal, magnetic order is excluded again. This opens up a new possibility to control magnetism electrically.

We investigate nuclear magnetic resonance (NMR) in near zero field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction ($J$ coupling). This is in stark contrast to the high-field case, where heteronuclear $J$ couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectra. Experimental results are in good agreement with first-order perturbation theory and with full numerical simulation when perturbation theory breaks down. We present simple rules for understanding the splitting patterns in near-zero-field NMR, which can be applied to molecules with nontrivial spectra.

The dependency of wave velocity in reaction-diffusion (RD) systems on the local front curvature determines not only the stability of wave propagation, but also the fundamental properties of other spatial configurations such as vortices. This Letter gives the first derivation of a covariant eikonal-curvature relation applicable to general RD systems with spatially varying anisotropic diffusion properties, such as cardiac tissue. The theoretical prediction that waves which seem planar can nevertheless possess a nonvanishing geometrical curvature induced by local anisotropy is confirmed by numerical simulations, which reveal deviations up to 20% from the nominal plane wave speed.

The Rabi model is a paradigm for interacting quantum systems. It couples a bosonic mode to the smallest possible quantum model, a two-level system. I present the analytical solution which allows us to consider the question of integrability for quantum systems that do not possess a classical limit. A criterion for quantum integrability is proposed which shows that the Rabi model is integrable due to the presence of a discrete symmetry. Moreover, I introduce a generalization with no symmetries; the generalized Rabi model is the first example of a nonintegrable but exactly solvable system.

A search for three-jet hadronic resonance production in $pp$ collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of $35{\mathrm{pb}}^{-1}$. Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed using a signature-based approach. The number of expected standard model background events is found to be in good agreement with the observed events. Limits on the cross section times branching ratio are set in a model of gluino pair production with an $R$-parity-violating decay to three quarks, and the data rule out such particles within the mass range of 200 to $280\mathrm{GeV}/c^2$.

We study the interplay of photons interacting with an artificial atom in the presence of a controlled dephasing. Such artificial atoms consisting of several independent scatterers can exhibit remarkable properties superior to single atoms with a prominent example being a superatom based on Rydberg blockade. We demonstrate that the induced dephasing allows for the controlled absorption of a single photon from an arbitrary incoming probe field. This unique tool in photon-matter interaction opens a way for building novel quantum devices, and several potential applications such as a single photon transistor, high fidelity $n$-photon counters, or the creation of nonclassical states of light by photon subtraction are presented.

Size effects in heat conduction, which occur when phonon mean free paths (MFPs) are comparable to characteristic lengths, are being extensively explored in many nanoscale systems for energy applications. Knowledge of MFPs is essential to understanding size effects, yet MFPs are largely unknown for most materials. Here, we introduce the first experimental technique which can measure MFP distributions over a wide range of length scales and materials. Using this technique, we measure the MFP distribution of silicon for the first time and obtain good agreement with first-principles calculations.

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.

We show that a crystal of mesoscopic ${\mathrm{Fe}}_8$ single-molecule magnets is an experimental realization of the quantum Ising model in a transverse field, with dipolar interactions. Quantum annealing has enabled us to explore the quantum and classical phase transitions between the paramagnetic and ferromagnetic phases, at thermodynamical equilibrium. The phase diagram and critical exponents that we obtain agree with expectations for the mean-field universality class.

Recent experiments have observed bulk superconductivity in doped topological insulators. Here we ask whether vortex Majorana zero modes, previously predicted to occur when $s$-wave superconductivity is induced on the surface of topological insulators, survive in these doped systems with metallic normal states. Assuming inversion symmetry, we find that they do but only below a critical doping. The critical doping is tied to a topological phase transition of the vortex line, at which it supports gapless excitations along its length. The critical point depends only on the vortex orientation and a suitably defined SU(2) Berry phase of the normal state Fermi surface. By calculating this phase for available band structures we determine that superconducting $p$-doped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, among others, supports vortex end Majorana modes. Surprisingly, superconductors derived from topologically trivial band structures can support Majorana modes too.