We investigated phase defects in a quasi-one-dimensional commensurate charge-density wave (CDW) system, an In atomic wire array on Si(111), using low temperature scanning tunneling microscopy. The unique fourfold degeneracy of the CDW state leads to various phase defects, among which intrinsic solitons are clearly distinguished. The solitons exhibit a characteristic variation of the CDW amplitude with a coherence length of about 4 nm, as expected from the electronic structure, and a localized electronic state within the CDW gap. While most of the observed solitons are trapped by extrinsic defects, moving solitons are also identified and their novel interaction with extrinsic defects is disclosed.

We report a ${}^{75}\mathrm{As}$ single crystal NMR investigation of LaFeAsO, the parent phase of a pnictide high $T_c$ superconductor. We demonstrate that spin dynamics develop a strong twofold anisotropy within each orthorhombic domain below the tetragonal-orthorhombic structural phase transition at $T_{\mathrm{TO}}\approx 156\mathrm{K}$. This intermediate state with a dynamical breaking of the rotational symmetry freezes progressively into a spin density wave below $T_{\mathrm{SDW}}\approx 142\mathrm{K}$. Our findings are consistent with the presence of a spin nematic state below $T_{\mathrm{TO}}$ with an incipient magnetic order.

We report on the study of unusual spin glass properties in the geometrically frustrated pyrochlore ${\mathrm{Tb}}_2{\mathrm{Mo}}_2{\mathrm{O}}_7$, $T_g\simeq 24\mathrm{K}$. The analysis of the nonlinear part of dc and complex susceptibilities, near the glass transition regime, suggests the existence of a statistical distribution of relaxation times in short-range ordered ferromagnetic clusters. In addition, the magnetic spins are not sufficiently frozen below the glass transition temperature, which is apparently responsible for the nonequilibrium scaling behavior of the static critical exponents of nonlinear susceptibilities. Our report is expected to shed new light in understanding the freezing properties of frustrated pyrochlores with short-range ferromagnetic interactions.

Our first-principles results show that geometric frustration can be induced in thin films of multiferroic ${\mathrm{BiFeO}}_3$. We find that competing magnetic interactions occur in the so-called supertetragonal phase of this material, which can be grown on strongly compressive substrates. We show that the frustration level can be tuned by appropriately choosing the substrate; in fact, the phase diagram of the films presents a critical line at which the three-dimensional spin order gets annihilated. We argue that these effects are not exclusive to ${\mathrm{BiFeO}}_3$ and predict that they also occur in ${\mathrm{BiCoO}}_3$.

Magnetic properties of Au nanoparticles deposited on an archaeal $S$ layer are reported. X-ray magnetic circular dichroism and superconducting quantum interference device magnetometries demonstrate that the particles are strongly paramagnetic, without any indication of magnetic blocking down to 16 mK. The average magnetic moment per particle is $M_{\mathrm{part}}=2.36(7)$ ${\mu }_B$. This contribution originates at the particle’s Au $5d$ band, in which an increased number of holes with respect to the bulk value is observed. The magnetic moment per Au atom is 25 times larger than any measured in other Au nanoparticles or any other configurations up to date.

We explore the effect of charge carrier doping on ferroelectricity using density functional calculations and phenomenological modeling. By considering a prototypical ferroelectric material, ${\mathrm{BaTiO}}_3$, we demonstrate that ferroelectric displacements are sustained up to the critical concentration of 0.11 electron per unit cell volume. This result is consistent with experimental observations and reveals that the ferroelectric phase and conductivity can coexist. Our investigations show that the ferroelectric instability requires only a short-range portion of the Coulomb force with an interaction range of the order of the lattice constant. These results provide a new insight into the origin of ferroelectricity in displacive ferroelectrics and open opportunities for using doped ferroelectrics in novel electronic devices.

We perform a spectroscopic study of the collective spin-wave dynamics occurring in a pair of magnetic nanodisks coupled by the magnetodipolar interaction. We take advantage of the stray field gradient produced by the magnetic tip of a ferromagnetic resonance force microscope to continuously tune and detune the relative resonance frequencies between two adjacent nano-objects. This reveals the anticrossing and hybridization of the spin-wave modes in the pair. At the exact tuning, the measured frequency splitting between the binding and antibinding modes corresponds to the strength of the dynamical dipolar coupling $\Omega$. This accurate ferromagnetic resonance force microscope determination of $\Omega$ is measured versus the separation between the nanodisks. It agrees quantitatively with calculations of the expected dynamical magnetodipolar interaction in our sample.

We develop a boundary field theory approach to electron spin resonance in open $S=1/2$ Heisenberg antiferromagnetic chains with an effective staggered field. In terms of the sine Gordon effective field theory with boundaries, we point out the existence of boundary bound states of elementary excitations, and modification of the selection rules at the boundary. We argue that several “unknown modes” found in electron spin resonance experiments on ${\mathrm{KCuGaF}}_6$ [I. Umegaki, H. Tanaka, T. Ono, H. Uekusa, and H. Nojiri, Phys. Rev. B 79, 184401 (2009)] and Cu-PM [S. A. Zvyagin, A. K. Kolezhuk, J. Krzystek, and R. Feyerherm, Phys. Rev. Lett. 93, 027201 (2004)] can be understood as boundary resonances introduced by these effects.

$X$-band microwave spectroscopy is applied to study the cyclotron resonance in ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ exposed to ambient conditions. With its help, intraband transitions between Landau levels of relativistic fermions are observed. The Fermi velocity equals to $3260\mathrm{m}/\mathrm{s}$, which is much lower than has been reported in the literature for samples cleaved in vacuum. Simultaneous observation of bulk Shubnikov–de Haas oscillations by contactless microwave spectroscopy allows determination of the Fermi-level position. Occupation of topological surface states depends not only on bulk Fermi level but also on the surface band bending.

Extreme electron accumulation with sheet density greater than ${10}^{13}{\mathrm{cm}}^{-2}$ is almost universally present at the surface of indium nitride (InN). Here, x-ray photoemission spectroscopy and secondary ion mass spectrometry are used to show that the surface Fermi level decreases as the Mg concentration increases, with the sheet electron density falling to below ${10}^8{\mathrm{cm}}^{-2}$. Surface space-charge calculations indicate that the lowering of the surface Fermi level increases the density of unoccupied donor-type surface states and that these are largely compensated by Mg acceptors in the near-surface hole depletion region rather than by accumulated electrons. This is a significant step towards the realization of InN-based optoelectronic devices.

How does pore liquid reconfigure within shear bands in wet granular media? Conventional wisdom predicts that liquid is drawn into dilating granular media. We, however, find a depletion of liquid in shear bands despite increased porosity due to dilatancy. This apparent paradox is resolved by a microscale model for liquid transport at low liquid contents induced by rupture and reconfiguration of individual liquid bridges. Measured liquid content profiles show macroscopic depletion bands similar to results of numerical simulations. We derive a modified diffusion description for rupture-induced liquid migration.

We present that modulation of fluorescence emission by linearly polarized excitation light can allow us to resolve spatially two fluorescent molecules within a diffraction limit and to determine simultaneously their precise dipole directions. Using polarization-dependent photoswitching, we imaged the 2D geometry of the DNA Holliday junction in a 10-nm length scale by measuring both the distance and the in-plane dipole angle between Cy3 emitters stacked onto the ends of two adjacent branches of the Holliday junction. The proposed polarization-modulated imaging technique provides a simple and nonstochastic imaging process to visualize the nanostructure, including directional information, of biomolecules beyond the diffraction limit.

We consider population dynamics on a network of patches, having the same local dynamics, with different population scales (carrying capacities). It is reasonable to assume that if the patches are coupled by very fast migration the whole system will look like an individual patch with a large effective carrying capacity. This is called a “well-mixed” system. We show that, in general, it is not true that the total population has the same dynamics as each local patch when the migration is fast. Different global dynamics can emerge, and usually must be figured out for each individual case. We give a general condition which must be satisfied for the total population to have the same dynamics as the constituent patches.

Binding of ligands to DNA can be studied by measuring the change of the persistence length of the complex formed, in single-molecule assays. We propose a methodology for persistence length data analysis based on a quenched disorder statistical model and describing the binding isotherm by a Hill-type equation. We obtain an expression for the effective persistence length as a function of the total ligand concentration, which we apply to our data of the DNA-cationic $\beta$-cyclodextrin and to the DNA-HU protein data available in the literature, determining the values of the local persistence lengths, the dissociation constant, and the degree of cooperativity for each set of data. In both cases the persistence length behaves nonmonotonically as a function of ligand concentration and based on the results obtained we discuss some physical aspects of the interplay between DNA elasticity and cooperative binding of ligands.

Studies of stochastic biological dynamics typically compare observed fluctuations to theoretically predicted variances, sometimes after separating the intrinsic randomness of the system from the enslaving influence of changing environments. But variances have been shown to discriminate surprisingly poorly between alternative mechanisms, while for other system properties no approaches exist that rigorously disentangle environmental influences from intrinsic effects. Here, we apply the theory of generalized random walks in random environments to derive exact rules for decomposing time series and higher statistics, rather than just variances. We show for which properties and for which classes of systems intrinsic fluctuations can be analyzed without accounting for extrinsic stochasticity and vice versa. We derive two independent experimental methods to measure the separate noise contributions and show how to use the additional information in temporal correlations to detect multiplicative effects in dynamical systems.

Bacteriophages infect cells by attaching to the outer membrane and injecting their DNA into the cell. The phage DNA is then transcribed by the cell’s transcription machinery. A number of physical mechanisms by which DNA can be translocated from the phage capsid into the cell have been identified. A fast ejection driven by the elastic and electrostatic potential energy of the compacted DNA within the viral capsid appears to be used by most phages, at least to initiate infection. In recent in vitro experiments, the speed of DNA translocation from a $\lambda$ phage capsid has been measured as a function of ejected length over the entire duration of the event. Here, a mechanical model is proposed that is able to explain the observed dependence of exit velocity on ejected length, and that is also consistent with the accepted picture of the geometric arrangement of DNA within the viral capsid.

The numerical study of 3D vesicles with a reduced volume equal to that of human red blood cells leads to the discovery of three types of dynamics: (i) squaring motion, in which the angle between the direction of the longest distance and the flow velocity undergoes discontinuous jumps over time, (ii) spontaneous parity breaking of the shape leading to cross-streamline migration, and (iii) $\mathsf{S}$ tumbling where the vesicle tumbles, exhibiting a pronounced $\mathsf{S}$-like shape with a waisted morphology in the center. We report on the phase diagram within a wide range of relevant parameters. Our estimates reveal that healthy and pathological red blood cells are also prone to these types of motion, which may affect blood microcirculation and impact oxygen transport.

When a DNA molecule is stretched, the zero-force correlation length for its bending fluctuations—the persistence length $A$—bifurcates into two different correlation lengths—the shorter “longitudinal” correlation length ${\xi }_{\parallel }(f)$ and the longer “transverse” correlation length ${\xi }_{\perp }(f)$. In the high-force limit, ${\xi }_{\parallel }(f)={\xi }_{\perp }(f)/2=\sqrt{k_{B}TA/f}/2$. When DNA-bending proteins bind to the DNA molecule, there is an effective interaction between the protein-generated bends mediated by DNA elasticity and bending fluctuations. Surprisingly, the range of this interaction is not the longest correlation length associated with transverse fluctuations of the tangent vector along the polymer, but instead is the second longest longitudinal correlation length ${\xi }_{\parallel }(f,\mu )$. The effect arises from the protein-bend contribution to the Hamiltonian having an axial rotational symmetry which eliminates its coupling to the transverse fluctuations.

By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of near field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as in the kinetics of growth. In microgravity purely diffusive aggregation is observed. By using the continuously variable particle interaction potential we can for the first time experimentally relate the strength of attraction between the particles and the structure of the aggregates.

We report herein the first evidence that an F-actin solution shows shear banding, which is characterized by the spontaneous separation of homogeneous shear flow into two macroscopic domains of different definite shear rates. The constant shear stress observed in the F-actin solution is explained by the banded flow with volume fractions that obey the lever rule. Nonhomogenous reversible flows were observed in the F-actin solution with respect to upward and downward changes in the shear rate. This is the first time shear banding has been observed in a simple biomacromolecule. The biological implications and dynamic aspects of shear flow velocity characteristic patterns are discussed.