The interaction between water and the ${\mathrm{TiO}}_2$ anatase (101) surface with a subsurface $V_{\mathrm{O}}$ is studied using first-principles calculations. Upon water adsorption, the relative stability of the subsurface and surface $V_{\mathrm{O}}$ reverses. The surface $V_{\mathrm{O}}$ becomes energetically more stable than its subsurface counterpart, which induces $V_{\mathrm{O}}$ to migrate from the subsurface to the surface with a very low energy barrier. Then the adsorbed water molecule can easily dissociate through a barrierless pathway facilitated by surface $V_{\mathrm{O}}$. This reaction pathway has a similar energy barrier with another pathway under which water dissociates with the presence of subsurface $V_{\mathrm{O}}$ followed by $V_{\mathrm{O}}$ migration from the subsurface layer to the surface layer, indicating that subsurface $V_{\mathrm{O}}$ can facilitate water dissociation directly, or, via surface $V_{\mathrm{O}}$ indirectly. This novel interplay between the adsorbate and substrate defects may provide a new way to explain the origin of the activity of anatase (101) in photocatalysis in aqueous surroundings.

Single crystals of the heavy-fermion antiferromagnet ${\mathrm{CePt}}_2{\mathrm{In}}_7$ with a Néel temperature ($T_N$) of 5.2 K at ambient pressure have been investigated by zero-field ${}^{115}\mathrm{In}$-nuclear magnetic and quadrupole resonance measurements as a function of applied pressure. Within the antiferromagnetic state, the character of Ce’s $4f$ electron appears to change from localized to itinerantlike at $P^{*}\sim 2.4\mathrm{GPa}$, approximately the pressure where superconductivity first emerges. With increased pressure, the superconducting transition $T_c$ reaches a maximum just at or slightly before antiferromagnetic order disappears, and not at the pressure $P_c\sim 3.4\mathrm{GPa}$, where the steeply decreasing Néel boundary extrapolates to zero temperature. For $P>P_c$, the spin relaxation rate drops sharply by more than 2 orders of magnitude at $T_c$, suggestive of a first-order transition.

An intersection between one-dimensional chiral channels functions as a topological current splitter. We find that the splitting of a chiral zero-line mode obeys very simple yet highly counterintuitive partition laws that relate current paths to the geometry of the intersection. Our results have far reaching implications for electron beam splitter and interferometer device proposals based on chiral transport, and for understanding transport in systems in which multiple topological domains lead to a statistical network of chiral channels.

The optical properties of graphene are strongly affected by electron-electron ($e\text{−}e$) and electron-hole ($e\text{−}h$) interactions. Here we tune these many-body interactions through varying the density of free charge carriers. Measurements from the infrared to the ultraviolet reveal significant changes in the optical conductivity of graphene for both electron and hole doping. The shift, broadening, and modification in shape of the saddle-point exciton resonance reflect strong screening of the many-body interactions by the carriers, as well as changes in quasiparticle lifetimes. Ab initio calculations by the $GW$ Bethe-Salpeter equation method, which take into account the modification of both the repulsive $e\text{−}e$ and the attractive $e\text{−}h$ interactions, provide excellent agreement with experiment. Understanding the optical properties and high-energy carrier dynamics of graphene over a wide range of doping is crucial for both fundamental graphene physics and for emerging applications of graphene in photonics.

Surfactant distribution heterogeneities at a fluid-fluid interface trigger the Marangoni effect, i.e., a bulk flow due to a surface tension gradient. The influence of surfactant solubility in the bulk on these flows remains incompletely characterized. Here we study Marangoni flows sustained by injection of hydrosoluble surfactants at the air-water interface. We show that these flows have a finite size that increases with a decrease of the critical micelle concentration of the surfactants. We document the universality of the surface velocity field of these finite flows and predict scaling laws based on hydrodynamics and surfactant physical chemistry that capture the flow features.

We use numerical simulations to investigate the effect that different models of energy dissipation have on the rheology of soft-core frictionless disks, below jamming in two dimensions. We find that it is not necessarily the mass of the particles that determines whether a system has Bagnoldian or Newtonian rheology, but rather the presence or absence of large connected clusters of particles. We demonstrate the key role that tangential dissipation plays in the formation of such clusters and in several models find a transition from Bagnoldian to Newtonian rheology as the packing fraction $\varphi$ is varied. For each model, we show that appropriately scaled rheology curves approach a well defined limit as the mass of the particles decreases and collisions become strongly inelastic.

We note that the standard inverse system volume scaling for finite-size corrections at a first-order phase transition (i.e., $1/L^3$ for an $L\times L\times L$ lattice in 3D) is transmuted to $1/L^2$ scaling if there is an exponential low-temperature phase degeneracy. The gonihedric Ising model which has a four-spin interaction, plaquette Hamiltonian provides an exemplar of just such a system. We use multicanonical simulations of this model to generate high-precision data which provide strong confirmation of the nonstandard finite-size scaling law. The dual to the gonihedric model, which is an anisotropically coupled Ashkin-Teller model, has a similar degeneracy and also displays the nonstandard scaling.

We propose an effective scheme for the generation of intense coherent extreme-ultraviolet light beams carrying orbital angular momentum (OAM). The light is produced by a high-gain harmonic-generation free-electron laser (FEL), seeded using a laser pulse with a transverse staircaselike phase pattern. During amplification, diffraction and mode selection drive the radiation profile towards a dominant OAM mode at saturation. With a seed laser at 260 nm, gigawatt power levels are obtained at wavelengths approaching those of soft x rays. Compared to other proposed schemes to generate OAM with FELs, our approach is robust, easier to implement, and can be integrated into already existing FEL facilities without extensive modifications of the machine layout.

Measurements of thermal transport through contacts between individual multiwall carbon nanotubes show that, contrary to common expectation, the normalized contact thermal conductance per unit area depends linearly on the tube diameter. The result is corroborated with and extended to multilayer graphene nanoribbons through molecular dynamics simulations. Semiquantitative analyses show that these intriguing observations are consistent with an explanation based on an unexpectedly large phonon mean free path in the $c$-axis direction of graphite, phonon reflection at free surfaces, and phonon focusing in highly anisotropic graphitic materials.

We investigate the structural and magnetic properties of two molecule-based magnets synthesized from the same starting components. Their different structural motifs promote contrasting exchange pathways and consequently lead to markedly different magnetic ground states. Through examination of their structural and magnetic properties we show that $[\mathrm{Cu}(\mathrm{pyz})({\mathrm{H}}_2\mathrm{O})(\mathrm{gly}{)}_2]({\mathrm{ClO}}_4{)}_2$ may be considered a quasi-one-dimensional quantum Heisenberg antiferromagnet whereas the related compound $[\mathrm{Cu}(\mathrm{pyz})(\mathrm{gly})]({\mathrm{ClO}}_4)$, which is formed from dimers of antiferromagnetically interacting ${\mathrm{Cu}}^{2+}$ spins, remains disordered down to at least 0.03 K in zero field but shows a field-temperature phase diagram reminiscent of that seen in materials showing a Bose-Einstein condensation of magnons.

We present the thermodynamic modeling and experimental evidence of the occurrence of lithium storage at abrupt junctions, which describes the transition from an electrostatic capacitor to a chemical capacitor. In both $\mathrm{Ru}:{\mathrm{Li}}_2\mathrm{O}$ and Ni:LiF systems, the functionalities and extracted parameters are in good agreement with the thermodynamic model, based on the dependence of the storage capacity on open-circuit voltage. Moreover, it is set out that a complete understanding of a conventional storage mechanism requires unifying both the space charge and bulk storage for a nanocrystalline electroactive electrode.

We consider an effective field theory for a gauge singlet Dirac dark matter particle interacting with the standard model fields via effective operators suppressed by the scale $\mathrm{\Lambda }\gtrsim 1\mathrm{TeV}$. We perform a systematic analysis of the leading loop contributions to spin-independent Dirac dark matter–nucleon scattering using renormalization group evolution between $\mathrm{\Lambda }$ and the low-energy scale probed by direct detection experiments. We find that electroweak interactions induce operator mixings such that operators that are naively velocity suppressed and spin dependent can actually contribute to spin-independent scattering. This allows us to put novel constraints on Wilson coefficients that were so far poorly bounded by direct detection. Constraints from current searches are already significantly stronger than LHC bounds, and will improve in the near future. Interestingly, the loop contribution we find is isospin violating even if the underlying theory is isospin conserving.

Polymer chains form lamellar structures during crystallization which display a memory of thermal history. Using molecular dynamics simulations and primitive path analysis, we show a direct dependence of both density and crystalline stem length on the local entanglement length. The slow relaxation of the entanglement state after a change of external conditions can directly explain the role of thermal history for polymer crystallization, in particular memory effects. The analysis of the local entanglement state can be used to predict the occurrence of nucleation events. Our results present a fresh insight of the nonequilibrium properties of polymer crystals which might be identified as “frozen topology” of polymer melts.

We investigate properties of a topological Mott insulator in one dimension by examining the bulk topological invariant and the entanglement spectrum of a correlated electron model. We clarify how gapless edge states in a noninteracting topological band insulator evolve into spinon edge states in a topological Mott insulator. Furthermore, we propose a topological Mott transition, which is a new type of topological phase transition which has never been observed in free fermion systems. This unconventional transition occurs in spin liquid phases in the Mott insulator and is accompanied by zeros of the single-electron Green’s function and a gap closing in the spin excitation spectrum.

Polymer dispersed liquid crystals are a useful model system for studying the relationship between surface topology and defect structures. They are comprised of a polymer matrix with suspended spherical nematic drops and are topologically constrained to host defects of an elementary hedgehog charge per droplet, such as bulk or surface point defects or closed disclination loops. We control the genus of the closed surfaces confining such micrometer-sized nematic drops with tangential boundary conditions for molecular alignment imposed by the polymer matrix, allowing us to avoid defects or, on the contrary, to generate them in a controlled way. We show, both experimentally and through numerical modeling, that topological constraints in nematic microdrops can be satisfied by hosting topologically stable half-integer bulk defect lines anchored to opposite sides of handlebody surfaces. This enriches the interplay of topologies of closed surfaces and fields with nonpolar symmetry, yielding new unexpected configurations that cannot be realized in vector fields, having potential implications for topologically similar defects in cosmology and other fields.

We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.

Faster and more accurate state measurement is required for progress in superconducting qubit experiments with greater numbers of qubits and advanced techniques such as feedback. We have designed a multiplexed measurement system with a bandpass filter that allows fast measurement without increasing environmental damping of the qubits. We use this to demonstrate simultaneous measurement of four qubits on a single superconducting integrated circuit, the fastest of which can be measured to 99.8% accuracy in 140 ns. This accuracy and speed is suitable for advanced multiqubit experiments including surface-code error correction.

We show that momentum operators of a topological soliton may not commute among themselves when the soliton is associated with the second cohomology $H^2$ of the target space. The commutation relation is proportional to the winding number, taking a constant value within each topological sector. The noncommutativity makes it impossible to specify the momentum of a topological soliton, and induces a Magnus force.