Recently, charge density wave (CDW) order in the ${\mathrm{CuO}}_2$ planes of underdoped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+\delta }$ was detected using resonant soft x-ray scattering. An important question remains: is the chain layer responsible for this charge ordering? Here, we explore the energy and polarization dependence of the resonant scattering intensity in a detwinned sample of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.75}$ with ortho-III oxygen ordering in the chain layer. We show that the ortho-III CDW order in the chains is distinct from the CDW order in the planes. The ortho-III structure gives rise to a commensurate superlattice reflection at $Q=[0.330L]$ whose energy and polarization dependence agrees with expectations for oxygen ordering and a spatial modulation of the Cu valence in the chains. Incommensurate peaks at [0.30 0 $L$] and [0 0.30 $L$] from the CDW order in the planes are shown to be distinct in $Q$ as well as their temperature, energy, and polarization dependence, and are thus unrelated to the structure of the chain layer. Moreover, the energy dependence of the CDW order in the planes is shown to result from a spatial modulation of energies of the Cu $2p$ to $3d_{x^2-y^2}$ transition, similar to stripe-ordered 214 cuprates.

We present the results of a magnetoresistance study of the disorder-induced superconductor-insulator transition in an amorphous indium-oxide thin film patterned by a nanoscale periodic array of holes. We observed Little-Parks-like oscillations over our entire range of disorder spanning the transition. The period of oscillations was unchanged and corresponded to the superconducting flux quantum in the superconducting as well as in the insulating phases. Our results provide direct evidence for electron pairing in the insulator bordering with superconductivity.

${\mathrm{BiCu}}_2{\mathrm{PO}}_6$ is a frustrated two-leg spin-ladder compound with a spin gap that can be closed with a magnetic field of approximately 20 T. This quantum phase transition and its related phase diagram as a function of magnetic field and temperature ($H$, $T$) are investigated up to 60 T by means of specific heat, magnetocaloric effect, magnetization, and magnetostriction measurements. In contrast to other gapped quantum magnets, ${\mathrm{BiCu}}_2{\mathrm{PO}}_6$ undergoes a series of unexpected first- and second-order phase transitions when an external magnetic field is applied along the crystallographic $c$ axis. The application of a magnetic field along the $b$ axis induces two second-order phase transitions. We propose that the anisotropy and complex phase diagram result from the interplay between strong geometrical frustration and spin-orbit interaction necessary for the description of this fascinating magnetic system.

Based on the microscopic model including spin-orbit coupling, on-site Coulomb and Hund’s interactions, as well as crystal field effects, we investigate the magnetic and optical properties of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$. Taking into account all intermediate state multiplets generated by virtual hoppings of electrons, we calculate the isotropic, pseudodipolar, and Dzyaloshinsky-Moriya coupling constants, which describe the experiment quite well. The optical conductivity $\sigma (\omega )$ evaluated by the exact diagonalization method shows two peaks at $\sim 0.5$ and $\sim 1.0\mathrm{eV}$ in agreement with experiment. The two-peak structure of $\sigma (\omega )$ arises from the unusual Fano-type overlap between the electron-hole continuum of the $J_{\mathrm{eff}}=1/2$ band and the intrasite spin-orbit exciton observed recently in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$.

High-resolution ultrasonic velocity measurements have been used to determine the temperature—magnetic-field phase diagram of the monoclinic multiferroic CuO. A new transition at $T_{N3}=230\mathrm{K}$, corresponding to an intermediate state between the antiferromagnetic noncollinear spiral phase observed below $T_{N2}=229.3\mathrm{K}$ and the paramagnetic phase, is revealed. Anomalies associated with a first order transition to the commensurate collinear phase are also observed at $T_{N1}=213\mathrm{K}$. For fields with $\mathbf{B}\parallel \mathbf{b}$, a spin-flop transition is detected between 11 T–13 T at lower temperatures. Moreover, our analysis using a Landau-type free energy clearly reveals the necessity for an incommensurate collinear phase between the spiral and the paramagnetic phase. This model is also relevant to the phase diagrams of other monoclinic multiferroic systems.

Neutron scattering in strong magnetic fields is used to show the spin resonance in superconducting ${\mathrm{CeCoIn}}_5$ ($T_c=2.3\mathrm{K}$) is a doublet. The underdamped resonance ($\hslash \Gamma =0.069\pm 0.019\mathrm{meV}$) Zeeman splits into two modes at $E_{\pm }=\hslash {\Omega }_0\pm \alpha {\mu }_B{\mu }_{0}H$ with $\alpha =0.96\pm 0.05$. A linear extrapolation of the lower peak reaches zero energy at $11.2\pm 0.5\mathrm{T}$, near the critical field for the incommensurate “$Q$ phase.” Kenzelmann et al. [Science 321, 1652 (2008)] This, taken with the integrated weight and polarization of the low-energy mode ($E_{-}$), indicates that the $Q$ phase can be interpreted as a Bose condensate of spin excitons.

Sodium clusters formed in the regular nanospace of sodalite (aluminosilicate zeolite) are known to show antiferromagnetic order without any magnetic elements. The clusters are arrayed in a body centered cubic structure. We have performed a neutron diffraction study and succeeded in detecting the magnetic Bragg peaks of the $s$-electron spins for the first time. The observation of both 001 and 111 magnetic reflections confirms the antiferromagnetic order with the antiparallel coupling between the nearest neighbor clusters. The magnetic form factor was examined by analyzing the intensity ratios of the magnetic and nuclear Bragg peaks. The result is in good agreement with the shape of the $s$-electron wave function derived from theoretical studies of the sodium nanoclusters in the cages.

A key property that drives research in ferroelectric perovskite oxides is their strong piezoelectric response in which an electric field is induced by an applied strain, and vice versa for the converse piezoelectric effect. We have achieved an experimental enhancement of the piezoelectric response and dielectric tunability in artificially layered epitaxial ${\mathrm{PbTiO}}_3/{\mathrm{CaTiO}}_3$ superlattices through an engineered rotation of the polarization direction. As the relative layer thicknesses within the superlattice were changed from sample to sample we found evidence for polarization rotation in multiple x-ray diffraction measurements. Associated changes in functional properties were seen in electrical measurements and piezoforce microscopy. The results demonstrate a new approach to inducing polarization rotation under ambient conditions in an artificially layered thin film.

We present simulations that reveal a surprisingly large effect of hydrodynamic coupling on the speed of thermal ratchet motors. The model that we use considers particles performing thermal ratchet motion in a hydrodynamic solvent. Using particle-based, mesoscopic simulations that maintain local momentum conservation, we analyze quantitatively how the coupling to the surrounding fluid affects ratchet motion. We find that coupling can increase the mean velocity of the moving particles by almost 2 orders of magnitude, precisely because ratchet motion has both a diffusive and a deterministic component. The resulting coupling also leads to the formation of aggregates at longer times. The correlated motion that we describe increases the efficiency of motor-delivered cargo transport and we speculate that the mechanism that we have uncovered may play a key role in speeding up molecular motor-driven intracellular transport.

Superresolution microscopy enables imaging in the optical far field with $\sim 20\mathrm{nm}$-scale resolution. However, classical concepts of resolution using point-spread and modulation-transfer functions fail to describe the physical limits of superresolution techniques based on stochastic localization of single emitters. Prior treatments of stochastic localization microscopy have defined how accurately a single emitter’s position can be determined, but these bounds are restricted to sparse emitters, do not describe conventional microscopy, and fail to provide unified concepts of resolution for all optical methods. Here we introduce a measure of resolution, the information transfer function (ITF), that gives physical limits for conventional and stochastic localization techniques. The ITF bounds the accuracy of image determination as a function of spatial frequency and for conventional microscopy is proportional to the square of the modulation-transfer function. We use the ITF to describe how emitter density and photon counts affect imaging performance across the continuum from conventional to superresolution microscopy, without assuming emitters are sparse. This unified physical description of resolution facilitates experimental choices and designs of image reconstruction algorithms.

We present Brownian dynamics simulations of the facilitated diffusion of a protein, modeled as a sphere with a binding site on its surface, along DNA, modeled as a semiflexible polymer. We consider both the effect of DNA organization in three dimensions and of sequence heterogeneity. We find that in a network of DNA loops, which are thought to be present in bacterial DNA, the search process is very sensitive to the spatial location of the target within such loops. Therefore, specific genes might be repressed or promoted by changing the local topology of the genome. On the other hand, sequence heterogeneity creates traps which normally slow down facilitated diffusion. When suitably positioned, though, these traps can, surprisingly, render the search process much more efficient.

We illustrate a new phenomenon in the dynamics of molecular ensembles subjected to moderately intense, far-off-resonance laser fields, namely, field-driven formation of perfectly ordered, defect-free assembly. Interestingly, both the arrangement of the constituting molecules within the individual assembly and the long-range order of the assembly with respect to one another are subject to control through choice of the field polarization. Relying on strong induced dipole-induced dipole interactions that are established in dense molecular media, the effect is expected to be general.

The isostatic state plays a central role in organizing the response of many amorphous materials. We construct a diverging length scale in nearly isostatic spring networks that is defined both above and below isostaticity and at finite frequencies and relate the length scale to viscoelastic response. Numerical measurements verify that proximity to isostaticity controls the viscosity, shear modulus, and creep of random networks.

We describe collective oscillatory behavior in the kinetics of irreversible coagulation with a constant input of monomers and removal of large clusters. For a broad class of collision rates, this system reaches a nonequilibrium stationary state at large times and the cluster size distribution tends to a universal form characterized by a constant flux of mass through the space of cluster sizes. Universality, in this context, means that the stationary state becomes independent of the cutoff as the cutoff grows. This universality is lost, however, if the aggregation rate between large and small clusters increases sufficiently steeply as a function of cluster sizes. We identify a transition to a regime in which the stationary state vanishes as the cutoff grows. This nonuniversal stationary state becomes unstable as the cutoff is increased. It undergoes a Hopf bifurcation after which the stationary state is replaced by persistent and periodic collective oscillations. These oscillations, which bear some similarities to relaxation oscillations in excitable media, carry pulses of mass through the space of cluster sizes such that the average mass flux through any cluster size remains constant. Universality is partially restored in the sense that the scaling of the period and amplitude of oscillation is inherited from the dynamical scaling exponents of the universal regime.

Analytic expressions that describe Casimir interactions over the entire range of separations have been limited to planar surfaces. Here we derive analytic expressions for the classical or high-temperature limit of Casimir interactions between two spheres (interior and exterior configurations), including the sphere-plane geometry as a special case, using bispherical coordinates. We consider both Dirichlet boundary conditions and metallic boundary conditions described by the Drude model. At short distances, closed-form expansions are derived from the exact result, displaying an intricate structure of deviations from the commonly employed proximity force approximation.

The neutron-rich lead isotopes, up to ${}^{216}\mathrm{Pb}$, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond ${}^{208}\mathrm{Pb}$.

We here demonstrate that the superfluid ${}^3\mathrm{He}\mathrm{\text{−}}B$ under a magnetic field in a particular direction stays topological due to a discrete symmetry, that is, in a symmetry protected topological order. Because of the symmetry protected topological order, helical surface Majorana fermions in the $B$ phase remain gapless and their Ising spin character persists. We unveil that the competition between the Zeeman magnetic field and dipole interaction involves an anomalous quantum phase transition in which a topological phase transition takes place together with spontaneous symmetry breaking. Based on the quasiclassical theory, we illustrate that the phase transition is accompanied by anisotropic quantum criticality of spin susceptibilities on the surface, which is detectable in NMR experiments.

Thin Pb films epitaxially grown on $7\times 7$ reconstructed Si(111) represent an ideal model system for studying the electron-phonon interaction at the metal-insulator interface. For this system, using a combination of scanning tunneling microscopy and inelastic electron tunneling spectroscopy, we performed direct real-space imaging of the electron-phonon coupling parameter. We found that $\lambda$ increases when the electron scattering at the $\mathrm{Pb}/\mathrm{Si}(111)$ interface is diffuse and decreases when the electron scattering is specular. We show that the effect is driven by transverse redistribution of the electron density inside a quantum well.

We study transport through a Coulomb blockaded topologically nontrivial superconducting wire (with Majorana end states) contacted by metallic leads. An exact formula for the current through this interacting Majorana single-charge transistor is derived in terms of wire spectral functions. A comprehensive picture follows from three different approaches. We find Coulomb oscillations with universal halving of the finite-temperature peak conductance under strong blockade conditions, where the valley conductance mainly comes from elastic cotunneling. The nonlinear conductance exhibits finite-voltage sidebands due to anomalous tunneling involving Cooper pair splitting.

A complete and exact solution of the ground-state problem for the Ising model on the Shastry-Sutherland lattice in an applied magnetic field is found. The magnetization plateau at one third of the saturation value is shown to be the only possible fractional plateau in this model. However, stripe magnetic structures with $1/2$ and $1/n$ ($n>3$) magnetization, observed in the rare-earth-metal tetraborides $R{\mathrm{B}}_4$, occur at the boundaries of the three-dimensional regions of the ground-state phase diagram. These structures give rise to new magnetization plateaus if interactions of longer range are taken into account. For instance, an additional third-neighbor interaction is shown to produce a $1/2$ plateau. The results obtained significantly refine the understanding of the magnetization process in $R{\mathrm{B}}_4$ compounds, especially in ${\mathrm{TmB}}_4$ and ${\mathrm{ErB}}_4$, which are strong Ising magnets.