Rotational wave packets of the weakly bound ${\mathrm{C}}_2{\mathrm{H}}_2\text{−}\mathrm{He}$ complex have been created using impulsive alignment. The coherent rotational dynamics were monitored for 600 ps enabling extraction of a frequency spectrum showing multiple rotational energy levels up to $J=4$. spectrum has been combined with ab initio calculations to show that the complex has a highly delocalized structure and is bound only by ca. $7{\mathrm{cm}}^{-1}$. The experiments demonstrate how highly featured rotational spectra can be obtained from an extremely cold environment where only the lowest rotational energy states are initially populated.

Magnetic feedback control of the resistive-wall mode has enabled the DIII-D tokamak to access stable operation at safety factor $q_{95}=1.9$ in divertor plasmas for 150 instability growth times. Magnetohydrodynamic stability sets a hard, disruptive limit on the minimum edge safety factor achievable in a tokamak, or on the maximum plasma current at a given toroidal magnetic field. In tokamaks with a divertor, the limit occurs at $q_{95}=2$, as confirmed in DIII-D. Since the energy confinement time scales linearly with current, this also bounds the performance of a fusion reactor. DIII-D has overcome this limit, opening a whole new high-current regime not accessible before. This result brings significant possible benefits in terms of fusion performance, but it also extends resistive-wall mode physics and its control to conditions never explored before. In present experiments, the $q_{95}<2$ operation is eventually halted by voltage limits reached in the feedback power supplies, not by intrinsic physics issues. Improvements to power supplies and to control algorithms have the potential to further extend this regime.

Based on ab initio density functional calculations, we propose $\gamma \text{−}\mathrm{P}$ and $\delta \text{−}\mathrm{P}$ as two additional stable structural phases of layered phosphorus besides the layered $\alpha \text{−}\mathrm{P}$ (black) and $\beta \text{−}\mathrm{P}$ (blue) phosphorus allotropes. Monolayers of some of these allotropes have a wide band gap, whereas others, including $\gamma \text{−}\mathrm{P}$, show a metal-insulator transition caused by in-layer strain or changing the number of layers. An unforeseen benefit is the possibility to connect different structural phases at no energy cost. This becomes particularly valuable in assembling heterostructures with well-defined metallic and semiconducting regions in one contiguous layer.

We analyze the dephasing effect on the backscattering behavior of the helical surface states in 3D topological insulators. We show that the combination of dephasing and impurity scattering can cause backscattering in the helical states. Especially for the charge impurity case, the backscattering cross section becomes extremely large around the Dirac point. This large backscattering behavior can lead to the anomalous “gaplike” features found in recent experiments [T. Sato et al., Nat. Phys. 7, 840 (2011)].

Using polarized neutron reflectometry, we observe an induced magnetization of $75\pm 25\mathrm{kA}/\mathrm{m}$ at 10 K in a ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ $(\mathrm{LSMO})/{\mathrm{BiFeO}}_3$ superlattice extending from the interface through several atomic layers of the ${\mathrm{BiFeO}}_3$ (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of band gap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.

Evidence from the BICEP2 experiment for a significant gravitational-wave background has focused attention on inflaton potentials $V(\varphi )\propto {\varphi }^{\alpha }$ with $\alpha =2$ (“chaotic” or “$m^2{\varphi }^2$” inflation) or with smaller values of $\alpha$, as may arise in axion-monodromy models. Here we show that reheating considerations may provide additional constraints to these models. The reheating phase preceding the radiation era is modeled by an effective equation-of-state parameter $w_{\text{re}}$. The canonical reheating scenario is then described by $w_{\text{re}}=0$. The simplest $\alpha =2$ models are consistent with $w_{\text{re}}=0$ for values of $n_s$ well within the current $1\sigma$ range. Models with $\alpha =1$ or $\alpha =2/3$ require a more exotic reheating phase, with $-1/3<w_{\text{re}}<0$, unless $n_s$ falls above the current $1\sigma$ range. Likewise, models with $\alpha =4$ require a physically implausible $w_{\text{re}}>1/3$, unless $n_s$ is close to the lower limit of the $2\sigma$ range. For $m^2{\varphi }^2$ inflation and canonical reheating as a benchmark, we derive a relation ${\log }_{10}(T_{\text{re}}/{10}^6\mathrm{GeV})\simeq 2000(n_s-0.96)$ between the reheat temperature $T_{\text{re}}$ and the scalar spectral index $n_s$. Thus, if $n_s$ is close to its central value, then $T_{\text{re}}\lesssim {10}^6\mathrm{GeV}$, just above the electroweak scale. If the reheat temperature is higher, as many theorists may prefer, then the scalar spectral index should be closer to $n_s\simeq 0.965$ (at the pivot scale $k=0.05{\text{Mpc}}^{-1}$), near the upper limit of the $1\sigma$ error range. Improved precision in the measurement of $n_s$ should allow $m^2{\varphi }^2$, axion monodromy, and ${\varphi }^4$ models to be distinguished, even without precise measurement of $r$, and to test the $m^2{\varphi }^2$ expectation of $n_s\simeq 0.965$.

We measure the inclusive forward–backward asymmetry of the charged-lepton pseudorapidities from top-quark pairs produced in proton–antiproton collisions and decaying to final states that contain two charged leptons (electrons or muons). The data are collected with the Collider Detector at Fermilab and correspond to an integrated luminosity of $9.1{\mathrm{fb}}^{-1}$. We measure the leptonic forward–backward asymmetry, $A_{\mathrm{FB}}^{\ell }$, to be $0.072\pm 0.060$ and the leptonic pair forward–backward asymmetry, $A_{\mathrm{FB}}^{\ell \ell }$, to be $0.076\pm 0.082$. The measured values can be compared with the standard model predictions of $A_{\mathrm{FB}}^{\ell }=0.038\pm 0.003$ and $A_{\mathrm{FB}}^{\ell \ell }=0.048\pm 0.004$, respectively. Additionally, we combine the $A_{\mathrm{FB}}^{\ell }$ result with a previous determination from a final state with a single lepton and hadronic jets and obtain $A_{\mathrm{FB}}^{\ell }=0.090_{-0.026}^{+0.028}$.

We revisit the Saffman-Taylor experiment focusing on the forced-imbibition regime where the displacing fluid wets the confining walls. We demonstrate a new class of invasion patterns that do not display the canonical fingering shapes. We evidence that these unanticipated patterns stem from the entrainment of thin liquid films from the moving meniscus. We then theoretically explain how the interplay between the fluid flow at the contact line and the interface deformations results in the destabilization of liquid interfaces. In addition, this minimal model conveys a unified framework which consistently accounts for all the liquid-entrainment scenarios that have been hitherto reported.

Radiation-reaction effects in the interaction of an electron bunch with a superstrong focused ultrashort laser pulse are investigated in the quantum radiation-dominated regime. The angle-resolved Compton scattering spectra are calculated in laser pulses of variable duration using a semiclassical description for the radiation-dominated dynamics and a full quantum treatment for the emitted radiation. In dependence of the laser-pulse duration we find signatures of quantum radiation reaction in the radiation spectra, which are characteristic for the focused laser beam and visible in the qualitative behavior of both the angular spread and the spectral bandwidth of the radiation spectra. The signatures are robust with respect to the variation of the electron and laser-beam parameters in a large range. Qualitatively, they differ fully from those in the classical radiation-reaction regime and are measurable with presently available laser technology.

The magnetic reconnection process is studied in relativistic pair plasmas when the thermal and inertial properties of the magnetohydrodynamical fluid are included. We find that in both Sweet-Parker and Petschek relativistic scenarios there is an increase of the reconnection rate owing to the thermal-inertial effects, both satisfying causality. To characterize the new effects we define a thermal-inertial number which is independent of the relativistic Lundquist number, implying that reconnection can be achieved even for vanishing resistivity as a result of only thermal-inertial effects. The current model has fundamental importance for relativistic collisionless reconnection, as it constitutes the simplest way to get reconnection rates faster than those accessible with the sole resistivity.

Stimulated Raman scattering (SRS) in its strongly nonlinear, kinetic regime is controlled by a technique of deterministic, strong temporal modulation and spatial scrambling of laser speckle patterns, called spike trains of uneven duration and delay (STUD) pulses [B. Afeyan and S. Hüller (unpublished)]. Kinetic simulations show that the proper use of STUD pulses decreases SRS reflectivity by more than an order of magnitude over random-phase-plate or induced-spatial-incoherence beams of the same average intensity and comparable bandwidth.

We propose a simple scheme for tomography of band-insulating states in one- and two-dimensional optical lattices with two sublattice states. In particular, the scheme maps out the Berry curvature in the entire Brillouin zone and extracts topological invariants such as the Chern number. The measurement relies on observing—via time-of-flight imaging—the time evolution of the momentum distribution following a sudden quench in the band structure. We consider two examples of experimental relevance: the Harper model with $\pi$ flux and the Haldane model on a honeycomb lattice. Moreover, we illustrate the performance of the scheme in the presence of a parabolic trap, noise, and finite measurement resolution.

We consider weakly interacting bosons in a 1D quasiperiodic potential (Aubry-Azbel-Harper model) in the regime where all single-particle states are localized. We show that the interparticle interaction may lead to the many-body delocalization and we obtain the finite-temperature phase diagram. Counterintuitively, in a wide range of parameters the delocalization requires stronger coupling as the temperature increases. This means that the system of bosons can undergo a transition from a fluid to insulator (glass) state under heating.

In situ dielectric spectroscopy has been used to characterize vapor-deposited glasses of methyl-$m$-toluate (MMT), an organic glass former with low fragility ($m=60$). Deposition near $0.84T_g$ produces glasses of very high kinetic stability; these materials are comparable in stability to the most stable glasses produced from more fragile glass formers. Highly stable glasses of MMT, when annealed above $T_g$, transform into the supercooled liquid by a heterogeneous mechanism. A constant velocity propagating front is initiated at the free surface and controls the transformation of thin films. The transition to a bulk-dominated transformation process occurs at $5\mu \mathrm{m}$, the largest length scale reported for any glass. Contrary to recent conclusions, we find that physical vapor deposition can form highly stable organic glasses across the entire range of liquid fragilities.

We investigate the effect of finite size on phase boundaries of hydride formation in ultrathin metallic films, using $\mathrm{Fe}/\mathrm{V}$(001) superlattices as a model system. The critical temperature is determined to scale linearly with the inverse thickness of the V layers. The decrease of the ordering temperature with decreasing layer thickness arises from the missing H neighbors at the interfaces, analogous to observed finite-size effects in magnetic layers and nanosized ice crystals.

The interplay of massive electrons with spin-orbit coupling in bulk graphene results in a spin-valley dependent gap. Thus, a barrier with such properties can act as a filter, transmitting only opposite spins from opposite valleys. In this Letter we show that a strain induced pseudomagnetic field in such a barrier will enforce opposite cyclotron trajectories for the filtered valleys, leading to their spatial separation. Since spin is coupled to the valley in the filtered states, this also leads to spin separation, demonstrating a spin-valley filtering effect. The filtering behavior is found to be controllable by electrical gating as well as by strain.

We develop a theory for optical Faraday rotation noise in two-dimensional Dirac materials. In contrast to spin noise in conventional semiconductors, we find that the Faraday rotation fluctuations are influenced not only by spins but also the valley degrees of freedom attributed to intervalley scattering processes. We illustrate our theory with two-dimensional transition-metal dichalcogenides and discuss signatures of spin and valley noise in the Faraday noise power spectrum. We propose optical Faraday noise spectroscopy as a technique for probing both spin and valley relaxation dynamics in two-dimensional Dirac materials.