We describe an efficient numerical approach to calculate the longitudinal and transverse Kubo conductivities of large systems using Bastin’s formulation. We expand the Green’s functions in terms of Chebyshev polynomials and compute the conductivity tensor for any temperature and chemical potential in a single step. To illustrate the power and generality of the approach, we calculate the conductivity tensor for the quantum Hall effect in disordered graphene and analyze the effect of the disorder in a Chern insulator in Haldane’s model on a honeycomb lattice.

Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of Earth’s lower mantle. With increasing pressure, the Fe ions in the material begin to collapse from a magnetic to nonmagnetic spin state. We present a finite-temperature first-principles phase diagram of this spin crossover, finding a broad pressure range with coexisting magnetic and nonmagnetic ions due to favorable enthalpy of mixing of the two. Furthermore, we find the electrical conductivity of the mineral to reach semimetallic values inside Earth.

We investigated site-specific magnetic behaviors of multiferroic ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{1.5}{\mathrm{Zn}}_2({\mathrm{Fe}}_{1-x}{\mathrm{Al}}_x{)}_{12}{\mathrm{O}}_{22}$ using Fe $L_{2,3}$-edge x-ray magnetic circular dichroism. The Al dopants mostly replace the ${\mathrm{Fe}}^{3+}$ ions at octahedral ($O_h$) sites, which contribute unquenched angular momenta through off-centering displacements. This replacement greatly reduces the magnetic anisotropy energy to change the magnetic order from a helical to a heliconical type with enhanced magnetoelectric susceptibility (${\alpha }_{\mathrm{ME}}$). The tetrahedral ($T_d$) Fe sites exhibit magnetic hysteresis distinguishable from that of the $O_h$ sites, especially at low magnetic fields. These results provide essential clues for the heliconical order with a giant ${\alpha }_{\mathrm{ME}}$ and multibit memory effects in the Al-doped Y-type hexaferrite.

Composed of square particles, the tetratic phase is characterized by a fourfold symmetry with quasi-long-range orientational order but no translational order. We construct the elastic free energy for tetratics and find a closed form solution for $\pm 1/4$ disclinations in planar geometry. Applying the same covariant formalism to a sphere, we show analytically that within the one elastic constant approximation eight $+1/4$ disclinations favor positions defining the vertices of a cube. The interplay between defect–defect interactions and bending energy results in a flattening of the sphere towards superspheroids with the symmetry of a cube.

We show that an electro-osmotic flow near the slippery hydrophobic surface depends strongly on the mobility of surface charges, which are balanced by counterions of the electrostatic diffuse layer. For a hydrophobic surface with immobile charges, the fluid transport is considerably amplified by the existence of a hydrodynamic slippage. In contrast, near the hydrophobic surface with mobile adsorbed charges, it is also controlled by an additional electric force, which increases the shear stress at the slipping interface. To account for this, we formulate electrohydrodynamic boundary conditions at the slipping interface, which should be applied to quantify electro-osmotic flows instead of hydrodynamic boundary conditions. Our theoretical predictions are fully supported by dissipative particle dynamics simulations with explicit charges. These results lead to a new interpretation of zeta potential of hydrophobic surfaces.

We consider the system of $N$ one-dimensional free fermions confined by a harmonic well $V(x)=m{\omega }^2{x}^2/2$ at finite inverse temperature $\beta =1/T$. The average density of fermions ${\rho }_N(x,T)$ at position $x$ is derived. For $N\gg 1$ and $\beta \sim \mathcal{O}(1/N)$, ${\rho }_N(x,T)$ is given by a scaling function interpolating between a Gaussian at high temperature, for $\beta \ll 1/N$, and the Wigner semicircle law at low temperature, for $\beta \gg N^{-1}$. In the latter regime, we unveil a scaling limit, for $\beta \hslash \omega =b{N}^{-1/3}$, where the fluctuations close to the edge of the support, at $x\sim \pm \sqrt{2\hslash N/(m\omega )}$, are described by a limiting kernel $K_b^{ff}(s,s^{\prime })$ that depends continuously on $b$ and is a generalization of the Airy kernel, found in the Gaussian unitary ensemble of random matrices. Remarkably, exactly the same kernel $K_b^{ff}(s,s^{\prime })$ arises in the exact solution of the Kardar-Parisi-Zhang equation in $1+1$ dimensions at finite time $t$, with the correspondence $t=b^3$.

A randomly walking quantum particle evolving by Schrödinger’s equation searches on $d$-dimensional cubic lattices in $O(\sqrt{N})$ time when $d\ge 5$, and with progressively slower runtime as $d$ decreases. This suggests that graph connectivity (including vertex, edge, algebraic, and normalized algebraic connectivities) is an indicator of fast quantum search, a belief supported by fast quantum search on complete graphs, strongly regular graphs, and hypercubes, all of which are highly connected. In this Letter, we show this intuition to be false by giving two examples of graphs for which the opposite holds true: one with low connectivity but fast search, and one with high connectivity but slow search. The second example is a novel two-stage quantum walk algorithm in which the walking rate must be adjusted to yield high search probability.

We show that the stochastic field theory for directed percolation in the presence of an additional conservation law [the conserved directed-percolation (C-DP) class] can be mapped exactly to the continuum theory for the depinning of an elastic interface in short-range correlated quenched disorder. Along one line of the parameters commonly studied, this mapping leads to the simplest overdamped dynamics. Away from this line, an additional memory term arises in the interface dynamics; we argue that this does not change the universality class. Since C-DP is believed to describe the Manna class of self-organized criticality, this shows that Manna stochastic sandpiles and disordered elastic interfaces (i.e., the quenched Edwards-Wilkinson model) share the same universal large-scale behavior.

While the standard model of particle physics does not include free particles with fractional charge, experimental searches have not ruled out their existence. We report results from the Cryogenic Dark Matter Search (CDMS II) experiment that give the first direct-detection limits for cosmogenically produced relativistic particles with electric charge lower than $e/6$. A search for tracks in the six stacked detectors of each of two of the CDMS II towers finds no candidates, thereby excluding new parameter space for particles with electric charges between $e/6$ and $e/200$.

The Higgs boson is thought to provide the interaction that imparts mass to the fundamental fermions, but while measurements at the Large Hadron Collider (LHC) are consistent with this hypothesis, current analysis techniques lack the statistical power to cross the traditional $5\sigma$ significance barrier without more data. Deep learning techniques have the potential to increase the statistical power of this analysis by automatically learning complex, high-level data representations. In this work, deep neural networks are used to detect the decay of the Higgs boson to a pair of tau leptons. A Bayesian optimization algorithm is used to tune the network architecture and training algorithm hyperparameters, resulting in a deep network of eight nonlinear processing layers that improves upon the performance of shallow classifiers even without the use of features specifically engineered by physicists for this application. The improvement in discovery significance is equivalent to an increase in the accumulated data set of 25%.

We propose a Bell-measurement scheme by employing a logical qubit in Greenberger-Horne-Zeilinger entanglement with an arbitrary number of photons. Remarkably, the success probability of the Bell measurement as well as teleportation of the Greenberger-Horne-Zeilinger entanglement can be made arbitrarily high using only linear optics elements and photon on-off measurements as the number of photons increases. Our scheme outperforms previous proposals using single-photon qubits when comparing the success probabilities in terms of the average photon usages. It has another important advantage for experimental feasibility in that it does not require photon-number-resolving measurements. Our proposal provides an alternative candidate for all-optical quantum information processing.

The key to generating stable optical pulses is mastery of nonlinear light dynamics in laser resonators. Modern techniques to control the buildup of laser pulses are based on nonlinear science and include classical solitons, dissipative solitons, parabolic pulses (similaritons) and various modifications and blending of these methods. Fiber lasers offer remarkable opportunities to apply one-dimensional nonlinear science models for the design and optimization of very practical laser systems. Here, we propose a new concept of a laser based on the adiabatic amplification of a soliton pulse in the cavity—the adiabatic soliton laser. The adiabatic change of the soliton parameters during evolution in the resonator relaxes the restriction on the pulse energy inherent in traditional soliton lasers. Theoretical analysis is confirmed by extensive numerical modeling.

In interface instabilities, deformations first grow exponentially, then enter a nonlinear regime affecting amplitude and symmetry. Most extant studies have focused on amplitude alone. Here, we study a 2D Rayleigh-Taylor instability for an initial sinusoidal deformation, analyzing its amplitude and asymmetry over time. For the latter, we define a metric based on the zero crossings of the interface. We develop a weakly nonlinear model and compare it to experimental data. It shows that our asymmetry metric complements the amplitude for an improved description of the instabilities’ nonlinear phases.

A puzzle of oceanic dynamics is the contrast between the observed geostrophic balance, involving gravity, pressure gradient, and Coriolis forces, and the necessary turbulent transport: in the former case, energy flows to large scales, leading to spectral condensation, whereas in the latter, it is transferred to small scales, where dissipation prevails. The known bidirectional constant-flux energy cascade maintaining both geostrophic balance and mixing tends towards flux equilibration as turbulence strengthens, contradicting models and recent observations which find a dominant large-scale flux. Analyzing a large ensemble of high-resolution direct numerical simulations of the Boussinesq equations in the presence of rotation and no salinity, we show that the ratio of the dual energy flux to large and to small scales agrees with observations, and we predict that it scales with the inverse of the Froude and Rossby numbers when stratification is (realistically) stronger than rotation. Furthermore, we show that the kinetic and potential energies separately undergo a bidirectional transfer to larger and smaller scales. Altogether, this allows for small-scale mixing which drives the global oceanic circulation and will thus potentially lead to more accurate modeling of climate dynamics.

Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide ($a\text{−}{\mathrm{SiO}}_2$) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as $E^{\prime }$ centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have significant implications for our understanding of processes in silica glass and nanoscaled silica, e.g., in porous low-permittivity insulators, and strained variants of $a\text{−}{\mathrm{SiO}}_2$.

The electron-phonon interaction is well known to create major resistance to electron transport in metals and semiconductors, whereas fewer studies are directed to its effect on phonon transport, especially in semiconductors. We calculate the phonon lifetimes due to scattering with electrons (or holes), combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon interaction, all from first principles, and evaluate the effect of the electron-phonon interaction on the lattice thermal conductivity of silicon. Unexpectedly, we find a significant reduction of the lattice thermal conductivity at room temperature as the carrier concentration goes above ${10}^{19}{\mathrm{cm}}^{-3}$ (the reduction reaches up to 45% in $p$-type silicon at around ${10}^{21}{\mathrm{cm}}^{-3}$), a range of great technological relevance to thermoelectric materials.

We studied the ultrafast transient response of photoexcitations in two hybrid organic-inorganic perovskite films used for high efficiency photovoltaic cells, namely, ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$ and ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_{1.1}{\mathrm{Br}}_{1.9}$ using polarized broadband pump-probe spectroscopy in the spectral range of 0.3–2.7 eV with 300 fs time resolution. For ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$ with above-gap excitation we found both photogenerated carriers and excitons, but only carriers are photogenerated with below-gap excitation. In contrast, mainly excitons are photogenerated in ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_{1.1}{\mathrm{Br}}_{1.9}$. Surprisingly, we also discovered in ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$, but not in ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_{1.1}{\mathrm{Br}}_{1.9}$, transient photoinduced polarization memory for both excitons and photocarriers, which is also reflected in the steady state photoluminescence. From the polarization memory dynamics we obtained the excitons diffusion constant in ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$, $D\approx 0.01{\mathrm{cm}}^2{\mathrm{s}}^{-1}$.

A general scheme to realize a perceptron for hardware neural networks is presented, where multiple interconnections are achieved by a superposition of Schrödinger waves. Spatially patterned potentials process information by coupling different points of reciprocal space. The necessary potential shape is obtained from the Hebbian learning rule, either through exact calculation or construction from a superposition of known optical inputs. This allows implementation in a wide range of compact optical systems, including (1) any nonlinear optical system, (2) optical systems patterned by optical lithography, and (3) exciton-polariton systems with phonon or nuclear spin interactions.