Because of the recent development of thin film and artificial superstructure growth techniques, it is possible to control the dimensionality of the system, smoothly between two and three dimensions. In this Letter we unveil the dimensional crossover of emergent topological phenomena in correlated topological materials. In particular, by focusing on the thin film of pyrochlore iridate antiferromagnets grown along the [111] direction, we demonstrate that the thin film can have a giant anomalous Hall conductance, proportional to the thickness of the film, even though there is no Hall effect in 3D bulk material. Moreover, in the case of ultrathin films, a quantized anomalous Hall conductance can be observed, despite the fact that the system is an antiferromagnet. In addition, we uncover the emergence of a new topological phase, the nontrivial topological properties of which are hidden in the bulk insulator and manifest only in thin films. This shows that the thin film of correlated topological materials is a new platform to search for unexplored novel topological phenomena.

We propose a scheme to induce ${\mathbb{Z}}_3$ parafermion modes, exotic zero-energy bound states that possess non-Abelian statistics. We consider a minimal setup consisting of a bundle of four tunnel coupled nanowires hosting spinless electrons that interact strongly with each other. The hallmark of our setup is that it relies only on simple one-dimensional wires, a uniform magnetic field, and strong interactions, but does not require the presence of superconductivity or exotic quantum Hall phases.

While it is known that the $\mathrm{Si}\text{−}(7\times 7)$ is a conducting surface, measured conductivity values differ by 7 orders of magnitude. Here we report a combined STM and transport method capable of surface conductivity measurement of step-free or single-step containing surface regions and having minimal interaction with the sample, and by which we quantitatively determine the intrinsic conductivity of the $\mathrm{Si}\text{−}(7\times 7)$ surface. We found that a single step has a conductivity per unit length about 50 times smaller than the flat surface. Our first principles quantum transport calculations confirm and lend insight into the experimental observation.

The topological features of low-dimensional superconductors have created a lot of excitement recently because of their broad range of applications in quantum information and their potential to reveal novel phases of quantum matter. A potential problem for practical applications is the presence of phase slips that break phase coherence. Dissipation in nontopological superconductors suppresses phase slips and can restore long-range order. Here, we investigate the role of dissipation in a topological Josephson junction. We show that the combined effects of topology and dissipation keep phase and antiphase slips strongly correlated so that the device is superconducting even under conditions where a nontopological device would be resistive. The resistive transition occurs at a critical value of the dissipation that is 4 times smaller than that expected for a conventional Josephson junction. We propose that this difference could be employed as a robust experimental signature of topological superconductivity.

We show that a simple model of noninteracting quasiparticles accurately describes resonant inelastic x-ray scattering (RIXS) experiments in the hole-doped cuprate superconductors. Band structure alone yields signatures previously attributed to collective magnetic modes, such as the dispersing peaks and nontrivial polarization dependence found in several experiments. We conclude that RIXS data can be explained without positing the existence of magnetic excitations that persist with increasing doping. In so doing we develop a formalism for RIXS in itinerant electron systems that accounts for the positively charged core hole exactly and discover a mechanism by which the core hole produces polarization dependence mimicking that of a magnetic system.

In this Letter, a new approach to distinguish liquid water and ice based on dual spectrum neutron radiography is presented. The distinction is based on arising differences between the cross section of water and ice in the cold energy range. As a significant portion of the energy spectrum of the ICON beam line at Paul Scherrer Institut is in the thermal energy range, no differences can be observed with the entire beam. Introducing a polycrystalline neutron filter (beryllium) inside the beam, neutrons above its cutoff energy are filtered out and the cold energy region is emphasized. Finally, a contrast of about 1.6% is obtained with our imaging setup between liquid water and ice. Based on this measurement concept, the temporal evolution of the aggregate state of water can be investigated without any prior knowledge of its thickness. Using this technique, we could unambiguously prove the production of supercooled water inside fuel cells with a direct measurement method.

The phase of the transmission amplitude through a mesoscopic system contains information about the system’s quantum mechanical state and excitations thereof. In the absence of an external magnetic field, abrupt phase lapses occur between transmission resonances of quantum dots and can be related to the signs of tunneling matrix elements. They are smeared at finite temperatures. By contrast, we show here that in the presence of a strong magnetic field, phase lapses represent a genuine interaction effect and may occur also on resonance. We identify a relevant physical regime where these phase lapses are robust against finite temperature broadening.

Quantum melting of a ferroelectric moment in the frustrated hydrogen-bonded system with the “ice rule” is studied theoretically by using quantum Monte Carlo simulation. The large number of nearly degenerate configurations are described as the gauge degrees of freedom; i.e., the model is mapped to a lattice gauge theory, which shows the confinement-deconfinment transition (CDT). The dipole-dipole interaction $J_2$, on the other hand, explicitly breaks the gauge symmetry leading to the ferroelectric transition at finite temperature $T$. It is found that the crossover from the FT to CDT manifests itself in the reduced correlation length of the polarization ${\xi }_{\mathrm{FT}}\sim \mathrm{\Delta }(K-K_c{)}^{-\nu }$, with $\mathrm{\Delta }\propto \sqrt{J_2}$ while $K_c$ and $\nu$ remains finite in the limit $J_2\to 0$. In contrast, the Curie-Weiss-like law for the susceptibility $\chi$ and the spontaneous polarization behaves smoothly and the length scale ${\xi }_{\mathrm{CDT}}$, related to the molecular symmetry and volume for CDT, does not reduce in this limit.

We study the problem of irreversibility when the dynamical evolution of a many-body system is described by a stochastic quantum circuit. Such evolution is more general than a Hamiltonian one, and since energy levels are not well defined, the well-established connection between the statistical fluctuations of the energy spectrum and irreversibility cannot be made. We show that the entanglement spectrum provides a more general connection. Irreversibility is marked by a failure of a disentangling algorithm and is preceded by the appearance of Wigner-Dyson statistical fluctuations in the entanglement spectrum. This analysis can be done at the wave-function level and offers an alternative route to study quantum chaos and quantum integrability.

The observed value of the Higgs boson mass indicates that the Higgs potential becomes small and flat at the scale around ${10}^{17}\mathrm{GeV}$. Having this fact in mind, we reconsider the Higgs inflation scenario proposed by Bezrukov and Shaposhnikov. It turns out that the nonminimal coupling $\xi$ of the Higgs squared to the Ricci scalar can be smaller than 10. For example, $\xi =7$ corresponds to the tensor-to-scalar ratio $r\simeq 0.2$, which is consistent with the recent observation by BICEP2.

We study the response of a highly excited time-dependent quantum many-body state to a sudden local perturbation, a sort of orthogonality catastrophe problem in a transient nonequilibrium environment. To this extent we consider, as a key quantity, the overlap between time-dependent wave functions, which we write in terms of a novel two-time correlator generalizing the standard Loschmidt echo. We discuss its physical meaning, general properties, and its connection with experimentally measurable quantities probed through nonequilibrium Ramsey interferometry schemes. Then we present explicit calculations for a one-dimensional interacting Fermi system brought out of equilibrium by a sudden change of the interaction, and perturbed by the switching on of a local static potential. We show that different scattering processes give rise to remarkably different behaviors at long times, quite opposite from the equilibrium situation. In particular, while the forward scattering contribution retains its power-law structure even in the presence of a large nonequilibrium perturbation, with an exponent that is strongly affected by the transient nature of the bath, the backscattering term is a source of nonlinearity which generates an exponential decay in time of the Loschmidt Echo, reminiscent of an effective thermal behavior.

Multiferroic hexagonal $R{\mathrm{MnO}}_3$ ($R=\text{rare}\text{earths}$) crystals exhibit dense networks of vortex lines at which six domain walls merge. While the domain walls can be readily moved with an applied electric field, the vortex cores so far have been impossible to control. Our experiments demonstrate that shear strain induces a Magnus-type force pulling vortices and antivortices in opposite directions and unfolding them into a topological stripe domain state. We discuss the analogy between this effect and the current-driven dynamics of vortices in superconductors and superfluids.

In this Letter we identify the general rules that determine the synchronization properties of interconnected networks. We study analytically, numerically, and experimentally how the degree of the nodes through which two networks are connected influences the ability of the whole system to synchronize. We show that connecting the high-degree (low-degree) nodes of each network turns out to be the most (least) effective strategy to achieve synchronization. We find the functional relation between synchronizability and size for a given network of networks, and report the existence of the optimal connector link weights for the different interconnection strategies. Finally, we perform an electronic experiment with two coupled star networks and conclude that the analytical results are indeed valid in the presence of noise and parameter mismatches.

We deform conformal field theories with classical gravity duals by marginally relevant random disorder. We show that the disorder generates a flow to IR fixed points with a finite amount of disorder. The randomly disordered fixed points are characterized by a dynamical critical exponent $z>1$ that we obtain both analytically (via resummed perturbation theory) and numerically (via a full simulation of the disorder). The IR dynamical critical exponent increases with the magnitude of disorder, probably tending to $z\to \infty$ in the limit of infinite disorder.

We study ’t Hooft anomalies for a global discrete internal symmetry $G$. We construct examples of bosonic field theories in three dimensions with a nonvanishing ’t Hooft anomaly for a discrete global symmetry. We also construct field theories in three dimensions with a global discrete internal symmetry $G_1\times G_2$ such that gauging $G_1$ necessarily breaks $G_2$ and vice versa. This is analogous to the Adler-Bell-Jackiw axial anomaly in four dimensions and parity anomaly in three dimensions.

Measurements of four-lepton ($4\ell$, $\ell =e,\mu$) production cross sections at the $Z$ resonance in $pp$ collisions at the LHC with the ATLAS detector are presented. For dilepton and four-lepton invariant mass regions $m_{{\ell }^{+}{\ell }^{-}}>5\mathrm{GeV}$ and $80<m_{4\ell }<100\mathrm{GeV}$, the measured cross sections are $76\pm 18\text{(stat)}\pm 4\text{(syst)}\pm 1.4\text{(lumi)}\mathrm{fb}$ and $107\pm 9\text{(stat)}\pm 4\text{(syst)}\pm 3.0\text{(lumi)}\mathrm{fb}$ at $\sqrt{s}=7$ and 8 TeV, respectively. By subtracting the nonresonant $4\ell$ production contributions and normalizing with $Z\to {\mu }^{+}{\mu }^{-}$ events, the branching fraction for the $Z$ boson decay to $4\ell$ is determined to be $(3.20\pm 0.25\text{(stat)}\pm 0.13\text{(syst)})\times 10^{-6}$, consistent with the standard model prediction.

We show that a fluid dynamical scenario, already well tested against identified particle $p_t$ spectra, describes quantitatively the observed mass splitting of the elliptical flow coefficients $v_2$ for pions and protons. This provides a strong argument in favor of the existence of a fluid dynamical expansion in $p\text{−}\mathrm{Pb}$ collisions at 5.02 TeV.

Resonances in the photoabsorption spectrum of the generating medium can modify the spectrum of high-order harmonics. In particular, window-type Fano resonances can reduce photoabsorption within a narrow spectral region and, consequently, lead to an enhanced emission of high-order harmonics in absorption-limited generation conditions. For high harmonic generation in argon it is shown that the $3s3p^{6}n{p}^1{P}_1$ window resonances ($n=4$, 5, 6) give rise to enhanced photon yield. In particular, the $3s3p^{6}4p^1{P}_1$ resonance at $26.6\mathrm{eV}$ allows a relative enhancement up to a factor of 30 in a 100 meV bandwidth compared to the characteristic photon emission of the neighboring harmonic order. This enhanced, spectrally isolated, and coherent photon emission line has a relative energy bandwidth of only $\mathrm{\Delta }E/E=3\times {10}^{-3}$. Therefore, it might be very useful for applications such as precision spectroscopy or coherent diffractive imaging. The presented mechanism can be employed for tailoring and controlling the high harmonic emission of manifold target materials.