The problem of controllability of the dynamical state of a network is central in network theory and has wide applications ranging from network medicine to financial markets. The driver nodes of the network are the nodes that can bring the network to the desired dynamical state if an external signal is applied to them. Using the framework of structural controllability, here, we show that the density of nodes with in degree and out degree equal to one and two determines the number of driver nodes in the network. Moreover, we show that random networks with minimum in degree and out degree greater than two, are always fully controllable by an infinitesimal fraction of driver nodes, regardless of the other properties of the degree distribution. Finally, based on these results, we propose an algorithm to improve the controllability of networks.

The torsional motion of a molecule composed of two substituted benzene rings, linked by a single bond, is coherently controlled by a pair of strong ($3\times 10^{13}\mathrm{W}{\mathrm{cm}}^{-2}$), nonresonant (800 nm) 200-fs-long laser pulses—both linearly polarized perpendicular to the single-bond axis. If the second pulse is sent at the time when the two benzene rings rotate toward (away from) each other the amplitude of the torsion is strongly enhanced (reduced). The torsional motion persists for more than 150 ps corresponding to approximately 120 torsional oscillations. Our calculations show that the key to control is the strong transient modification of the natural torsional potential by the laser-induced dynamic Stark effect.

We report the complex magnetic phase diagram and electronic structure of ${\mathrm{Cr}}_2({\mathrm{Te}}_{1-x}{\mathrm{W}}_x){\mathrm{O}}_6$ systems. While compounds with different $x$ values possess the same crystal structure, they display different magnetic structures below and above $x_c=0.7$, where both the transition temperature $T_N$ and sublattice magnetization ($M_s$) reach a minimum. Unlike many known cases where magnetic interactions are controlled either by injection of charge carriers or by structural distortion induced via chemical doping, in the present case it is achieved by tuning the orbital hybridization between $\mathrm{Cr}3d$ and $\mathrm{O}2p$ orbitals through $\mathrm{W}5d$ states. The result is supported by ab initio electronic structure calculations. Through this concept, we introduce a new approach to tune magnetic and electronic properties via chemical doping.

We propose a technique for engineering momentum-dependent dissipation in Bose-Einstein condensates with nonlocal interactions. The scheme relies on the use of momentum-dependent dark states in close analogy to velocity-selective coherent population trapping. During the short-time dissipative dynamics, the system is driven into a particular finite-momentum phonon mode, which in real space corresponds to an ordered structure with nonlocal density-density correlations. Dissipation-induced ordering can be observed and studied in present-day experiments using cold atoms with dipole-dipole or off-resonant Rydberg interactions. Because of its dissipative nature, the ordering does not require artificial breaking of translational symmetry by an optical lattice or harmonic trap. This opens up a perspective of direct cooling of quantum gases into strongly interacting phases.

The charge rearrangement in dissociating ${\mathrm{I}}_2^{n+}$ molecules is measured as a function of the internuclear distance $R$ using extreme ultraviolet pulses delivered by the free-electron laser in Hamburg. Within an extreme ultraviolet pump-probe scheme, the first pulse initiates dissociation by multiply ionizing ${\mathrm{I}}_2$, and the delayed probe pulse further ionizes one of the two fragments at a given time, thus triggering charge rearrangement at a well-defined $R$. The electron transfer between the fragments is monitored by analyzing the delay-dependent ion kinetic energies and charge states. The experimental results are in very good agreement with predictions of the classical over-the-barrier model demonstrating its validity in a thus far unexplored quasimolecular regime relevant for free-electron laser, plasma, and chemistry applications.

We study the multichannel Kondo impurity dynamics realized in a mesoscopic superconducting island connected to metallic leads. The effective “impurity spin” is nonlocally realized by Majorana bound states and strongly coupled to lead electrons by non-Fermi liquid correlations. We explore the spin dynamics and its observable ramifications near the low-temperature fixed point. The topological protection of the system raises the perspective to observe multichannel Kondo impurity dynamics in experimentally realistic environments.

We propose to engineer time-reversal-invariant topological insulators in two-dimensional crystals of transition-metal dichalcogenides (TMDCs). We note that, at low doping, semiconducting TMDCs under shear strain will develop spin-polarized Landau levels residing in different valleys. We argue that gaps between Landau levels in the range of 10–100 K are within experimental reach. In addition, we point out that a superlattice arising from a moiré pattern can lead to topologically nontrivial subbands. As a result, the edge transport becomes quantized, which can be probed in multiterminal devices made using strained 2D crystals and/or heterostructures. The strong $d$ character of valence and conduction bands may also allow for the investigation of the effects of electron correlations on the topological phases.

We present heat-transport measurements conducted with a vacuum-operated scanning thermal microscope to study the thermal conductance of monolayers of nine different alkane thiols self-assembled on Au(111) surfaces as a function of their length (2 to 18 methylene units). The molecular thermal conductance is probed in a confined area with a diameter below 10 nm in the contact between a silicon tip and the self-assembled monolayer. This yields a $\mathrm{p}{\mathrm{WK}}^{-1}$ sensitivity per molecule at a tip temperature of $200–300°\mathrm{C}$ versus the gold at room temperature. We found a conductance variance of up to a factor of 3 as a function of alkane chain length, with maximum conductance for a chain length of four carbon atoms.

Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton beam of the cooler synchrotron COSY, we determine the excitation function for the $pp\to pp{\eta }^{\prime }$ reaction close to threshold. Combining these data with previous results, we extract the scattering length for the ${\eta }^{\prime }$-proton potential in free space to be $\mathrm{Re}(a_{p{\eta }^{\prime }})=0\pm 0.43\mathrm{fm}$ and $\mathrm{Im}(a_{p{\eta }^{\prime }})={0.37}_{-0.16}^{+0.40}\mathrm{fm}$.

Dynamical localization prevents driven atomic systems from fast fragmentation by hampering the excitation process. We present numerical simulations within a collinear model of microwave-driven helium Rydberg atoms and prove that dynamical localization survives the impact of electron-electron interaction, even for doubly excited states in the presence of fast autoionization. We conclude that the effect of electron-electron repulsion on localization can be described by an appropriate rescaling of the atomic level density and of the external field with the strength of the interaction.

We propose a scheme to couple short single photon pulses to superconducting qubits. An optical photon is first absorbed into an inhomogeneously broadened rare-earth doped crystal using controlled reversible inhomogeneous broadening. The optical excitation is then mapped into a spin state using a series of $\pi$ pulses and subsequently transferred to a superconducting qubit via a microwave cavity. To overcome the intrinsic and engineered inhomogeneous broadening of the optical and spin transitions in rare-earth doped crystals, we make use of a special transfer protocol using staggered $\pi$ pulses. We predict total transfer efficiencies on the order of 90%.

Using molecular dynamics simulations and a model AlN-GaN interface, we demonstrate that the interfacial thermal resistance $R_{\mathrm{K}}$ (Kapitza resistance) between a substrate and thin film depends on the thickness of the film and the film surface roughness when the phonon mean free path is larger than film thickness. In particular, when the film (external) surface is atomistically smooth, phonons transmitted from the substrate can travel ballistically in the thin film, be scattered specularly at the surface, and return to the substrate without energy transfer. If the external surface scatters phonons diffusely, which is characteristic of rough surfaces, $R_{\mathrm{K}}$ is independent of film thickness and is the same as $R_{\mathrm{K}}$ that characterizes smooth surfaces in the limit of large film thickness. At interfaces where phonon transmission coefficients are low, the thickness dependence is greatly diminished regardless of the nature of surface scattering. The film thickness dependence of $R_{\mathrm{K}}$ is analogous to the well-known fact of lateral thermal conductivity thickness dependence in thin films. The difference is that phonon-boundary scattering lowers the in-plane thermal transport in thin films, but it facilitates thermal transport from the substrate to the thin film.

We report the observation of a dense triangular network of one-dimensional (1D) metallic modes in a continuous and uniform monolayer of ${\mathrm{MoSe}}_2$ grown by molecular-beam epitaxy. High-resolution transmission electron microscopy and scanning tunneling microscopy and spectroscopy studies show that these 1D modes are midgap states at inversion domain boundaries. Scanning tunneling microscopy and spectroscopy measurements further reveal intensity undulations of the metallic modes, presumably arising from the superlattice potentials due to the moiré pattern and the quantum confinement effect. A dense network of the metallic modes with a high density of states is of great potential for heterocatalysis applications. The interconnection of such midgap 1D conducting channels may also imply new transport behaviors distinct from the 2D bulk.

Simulations of five different coarse-grained models of symmetric diblock copolymers are compared to demonstrate a universal (i.e., model-independent) dependence of the free energy and order-disorder transition (ODT) on the invariant degree of polymerization $\overline{N}$. The actual values of $\chi N$ at the ODT approach predictions of the Fredrickson-Helfand (FH) theory for $\overline{N}\gtrsim {10}^4$ but significantly exceed FH predictions at lower values characteristic of most experiments. The FH theory fails for modest $\overline{N}$ because the competing phases become strongly segregated near the ODT, violating an underlying assumption of weak segregation.