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Time-reversal symmetry breaking and entropy production are universal features of nonequilibrium phenomena. Despite its importance in the physics of active and living systems, the entropy production of systems with many degrees of freedom has remained of little practical significance because the high dimensionality of their state space makes it difficult to measure. Here we introduce a local measure of entropy production and a numerical protocol to estimate it. We establish a connection between the entropy production and extractability of work in a given region of the system and show how this quantity depends crucially on the degrees of freedom being tracked. We validate our approach in theory, simulation, and experiments by considering systems of active Brownian particles undergoing motility-induced phase separation, as well as active Brownian particles and E.coli in a rectifying device in which the time-reversal asymmetry of the particle dynamics couples to spatial asymmetry to reveal its effects on a macroscopic scale.

In periodically sheared suspensions there is a dynamical phase transition, characterized by a critical strain amplitude ${\ensuremath{\gamma}}_{c}$, between an absorbing state where particle trajectories are reversible and an active state where trajectories are chaotic and diffusive. Repulsive nonhydrodynamic interactions between ``colliding'' particles' surfaces have been proposed as a source of this broken time reversal symmetry. A simple toy model called random organization qualitatively reproduces the dynamical features of this transition. Random organization and other absorbing state models exhibit hyperuniformity, a strong suppression of density fluctuations on long length scales quantified by a structure factor $S(q\ensuremath{\rightarrow}0)\ensuremath{\sim}{q}^{\ensuremath{\alpha}}$ with $\ensuremath{\alpha}g0$, at criticality. Here we show experimentally that the particles in periodically sheared suspensions organize into structures with anisotropic short-range order but isotropic, long-range hyperuniform order when oscillatory shear amplitudes approach ${\ensuremath{\gamma}}_{c}$.

While the equilibrium properties, states, and phase transitions of interacting systems are well described by statistical mechanics, the lack of suitable state parameters has hindered the understanding of nonequilibrium phenomena in diverse settings, from glasses to driven systems to biology. The length of a losslessly compressed data file is a direct measure of its information content: The more ordered the data file is, the lower its information content and the shorter the length of its encoding can be made. Here, we describe how data compression enables the quantification of order in nonequilibrium and equilibrium many-body systems, both discrete and continuous, even when the underlying form of order is unknown. We consider absorbing state models on and off lattice, as well as a system of active Brownian particles undergoing motility-induced phase separation. The technique reliably identifies nonequilibrium phase transitions, determines their character, quantitatively predicts certain critical exponents without prior knowledge of the order parameters, and reveals previously unknown ordering phenomena. This technique should provide a quantitative measure of organization in condensed matter and other systems exhibiting collective phase transitions in and out of equilibrium.

We derive a minimal continuum model to investigate the hydrodynamic mechanism behind the fingering instability recently discovered in a suspension of microrollers near a floor [Driscoll et al. Nature Physics, 2016]. Our model, consisting of two continuous lines of rotlets, exhibits a linear instability driven only by hydrodynamics interactions, and reproduces the lengthscale selection observed in large scale particle simulations and in experiments. By adjusting only one parameter, the distance between the two lines, our dispersion relation exhibits quantitative agreement with the simulations and qualitative agreement with experimental measurements. Our linear stability analysis indicate that this instability is caused by the combination of the advective and transverse flows generated by the microrollers near a no-slip surface. Our simple model offers an interesting formalism to characterize other hydrodynamic instabilities that have not been yet well understood, such as size scale selection in suspensions of particles sedimenting adjacent to a wall, or the recently observed formations of traveling phonons in systems of confined driven particles.

We study the phase behavior of a system of charged colloidal particles that are electrostatically bound to an almost flat interface between two fluids. We show that, despite the fact that our experimental system consists of only $10^{3}$ - $10^{4}$ particles, the phase behavior is consistent with the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson and Young (KTHNY). Using spatial and temporal correlations of the bond-orientational order parameter, we classify our samples into solid, isotropic fluid, and hexatic phases. We demonstrate that the topological defect structure we observe in each phase corresponds to the predictions of KTHNY theory. By measuring the dynamic Lindemann parameter, $\gamma_{L}(\tau)$, and the non-Gaussian parameter, $\alpha_{2}(\tau)$, of the displacements of the particles relative to their neighbors, we show that each of the phases displays distinctive dynamical behavior.

Hydrophobic poly(methyl methacrylate) (PMMA) colloidal particles, when dispersed in oil with a relatively high dielectric constant, can become highly charged. In the presence of an interface with a conducting aqueous phase, image-charge effects lead to strong binding of colloidal particles to the interface, even though the particles are wetted very little by the aqueous phase. We study both the behavior of individual colloidal particles as they approach the interface and the interactions between particles that are already interfacially bound. We demonstrate that using particles which are minimally wetted by the aqueous phase allows us to isolate and study those interactions which are due solely to charging of the particle surface in oil. Finally, we show that these interactions can be understood by a simple image-charge model in which the particle charge q is the sole fitting parameter.

We present simultaneous measurements of angular-dependent magnetoresistance and thermopower along all three crystal axes in ${(\mathrm{TMTSF})}_{2}{\mathrm{PF}}_{6}$ for pressures to 7.4 kbar and magnetic fields to 35 T. ${(\mathrm{TMTSF})}_{2}{\mathrm{PF}}_{6}$ under pressure shows the coexistence of spin density wave and metal-superconducting orders. We suggest that this coexistence results neither in microscopic coexistence nor in a new soliton wall phase, contrary to previous suggestions, but in phase separation into domains of the high-pressure metal and the low-pressure spin density wave phases. Simultaneous measurement of transport along all crystal axes allows us to unambiguously describe the domain structure, whereas the superconducting transition temperature and four independent Fermi surface-sensitive magnetoresistance signatures allow us to unambiguously characterize the coexisting metallic domains.

The resistive upper critical field along the b axis ${(H}_{c2}\ensuremath{\parallel}b)$ in ${(\mathrm{TMTSF})}_{2}{\mathrm{PF}}_{6}$ is investigated in detail in fields to 17.5 T and temperatures to ${T/T}_{c}\ensuremath{\sim}\frac{1}{60},$ at various pressures near the border between spin-density wave and metallic states. Remarkably, in an optimum pressure setting reported here, it is found that the onset of superconductivity persists up to 9 T $(g{4H}_{p}),$ which strongly suggests triplet Cooper pairing. Strong upward curvature with nearly diverging behavior of the critical field seems to suggest a field-dependent dimensional crossover, although the ${H}_{c2}$ enhancement is considerably more than that predicted by recent theories.

We have performed magnetoresistance measurements along the least conducting $c$ direction in ${(\mathrm{TMTSF})}_{2}{\mathrm{ClO}}_{4}$ under 6 kbar pressure while the magnetic field was rotated in the $\mathrm{bc}$ plane. Here 6 kbar is sufficient to suppress the $(0,1/2,0)$ ordering transition observed at ambient pressure. Comparison with similar experiments on anion-ordered ${(\mathrm{TMTSF})}_{2}{\mathrm{ClO}}_{4}$ and with ${(\mathrm{TMTSF})}_{2}{\mathrm{PF}}_{6}$ allow the following conclusions: The periodicity is ill defined in the $b$ but not the $c$ direction in the presence of anion disorder, the disorder has a small to negligible effect on the scattering rate along $c,$ and the anion ordering is not responsible for previously observed differences in angular-dependent magnetoresistance in these sister salts.

Using particle image velocimetry we have measured the sedimentation dynamics of non-Brownian colloidal spheres over a wide range of low concentrations ( $\ensuremath{\varphi}\ensuremath{\le}0.05$) and sample cell sizes $W$. Fluctuations in the settling velocity show universal large-scale finite-range correlations, in the form of swirls, which depend simply on volume fraction and particle radius and follow $〈\ensuremath{\delta}{V}_{z}(0)\ensuremath{\delta}{V}_{z}(z){〉}^{1/2}\ensuremath{\simeq}{2.0V}_{\mathrm{sed}}{\ensuremath{\varphi}}^{1/3}\mathrm{exp}(\ensuremath{-}z/2\ensuremath{\xi})$, where $\ensuremath{\xi}\ensuremath{\simeq}20a{\ensuremath{\varphi}}^{\ensuremath{-}1/3}$. In turn, the predicted divergence of the velocity variance with increasing cell size $W$ is cut off in a universal way as $W$ exceeds the swirl size and is well represented by $〈\ensuremath{\delta}{V}_{z}^{2}(0){〉}^{1/2}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.0V}_{\mathrm{sed}}{\ensuremath{\varphi}}^{1/3}[1\ensuremath{-}\mathrm{exp}(\ensuremath{-}W/60a{\ensuremath{\varphi}}^{\ensuremath{-}1/3})]$.

The temperature dependence of the upper critical magnetic field ${H}_{c2}(T)$ in the quasi-one-dimensional molecular superconductor (TMTSF${)}_{2}$P${\mathrm{F}}_{6}$ was determined via resistivity, for the intrachain (a), interchain (b), and interplane $({\mathbf{c}}^{*})$ directions. For H along a and b, ${H}_{c2}(T)$ exhibits pronounced positive curvature, with no sign of saturation to 0.1 K. A novel anisotropy inversion is observed, wherein ${H}_{c2}^{b}$ grows larger than ${H}_{c2}^{a}$ and exceeds the paramagnetic limit by more than 200%. The anomalous shape of ${H}_{c2}(T)$ is consistent with recent predictions of unconventional behavior in anisotropic superconductors, including the possibility of triplet pairing and reentrant superconductivity in very high field.

We study $I$-$V$ characteristics of periodic square Nb wire networks as a function of temperature in a transverse magnetic field, with a focus on three fillings 2/5, 1/2, and 0.618 that represent very different levels of incommensurability. For all three fillings, a scaling behavior of $I$-$V$ characteristics is found, suggesting a finite temperature continuous superconducting phase transition. The low-temperature $I$-$V$ characteristics are found to have an exponential form, indicative of the domain-wall excitations., 5 pages, also available at http://www.neci.nj.nec.com/homepages/tang.html

We have investigated the temperature, pressure, and field dependence of the spin density wave (SDW) transition in the organic superconductor (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$ and derived parameters for this transition. The SDW can be characterized by the degree to which the two Fermi surfaces couple or ``nest'' as measured by the imperfect nesting bandwidth ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}}$. Perfect nesting (maximum ${\mathit{T}}_{\mathrm{SDW}}$) occurs for ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}}$=0, and increasing pressure increases ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}}$ and suppresses ${\mathit{T}}_{\mathrm{SDW}}$ to 0 K at a critical value ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}\mathrm{*}}$. The increase of ${\mathit{T}}_{\mathrm{SDW}}$ with field has been shown to be orbitally driven, and the field dependence is nearly quadratic for fields in the c direction. We have made quantitative observations of the field dependence of ${\mathit{T}}_{\mathrm{SDW}}$ at ambient pressure to 29 T and under hydrostatic pressure to 8 T. From our measurements at ambient pressure we are able to extract ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}}$ and ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}\mathrm{*}}$ using mean field theory and observe ${\mathit{T}}_{\mathrm{SDW}}$=12.1\ifmmode\pm\else\textpm\fi{}0.1 K, ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}}$=4.5\ifmmode\pm\else\textpm\fi{}0.3 K, and ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}\mathrm{*}}$=11.3\ifmmode\pm\else\textpm\fi{}0.2 K. Under a hydrostatic pressure of 5.2\ifmmode\pm\else\textpm\fi{}0.2 kbar, ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}}$ increases to 11.0\ifmmode\pm\else\textpm\fi{}0.3 K with ${\mathit{T}}_{\mathrm{SDW}}$ decreasing to 3.3\ifmmode\pm\else\textpm\fi{}0.1 K. The high pressure results are consistent with the value of ${\mathit{t}}_{\mathit{b}}^{\ensuremath{'}\mathrm{*}}$ from the ambient pressure measurements. We also observe no dependence of ${\mathit{T}}_{\mathrm{SDW}}$ with field in the a or b directions, in contrast to previous results. \textcopyright{} 1996 The American Physical Society.

It has recently been suggested that the highly anisotropic organic conductor ${(\mathrm{TMTSF})}_{2}$P${\mathrm{F}}_{6}$ is marginally a three-dimensional Fermi liquid which can be destabilized by a small field in the intermediate conducting b direction, ${H}_{b}$. This field would cause the interplane transport to become incoherent. We examine the 3D Fermi surface and find it coherent for ${H}_{b}=0$ and incoherent or nonexistent for small ${H}_{b}$. At similar ${H}_{b}$ the magnetoresistances become power laws in the field applied perpendicular to the conducting planes (${\ensuremath{\rho}}_{a}\ensuremath{\propto}{H}_{\ensuremath{\perp}}^{\frac{1}{2}}$ and ${\ensuremath{\rho}}_{c}\ensuremath{\propto}{H}_{\ensuremath{\perp}}^{\frac{3}{2}}$). These are 2D, non-Fermi-liquid properties.

We use ac susceptibility to study the vortex pinning force anisotropy and the magnetic lock-in effect in the organic superconductor (TMTSF${)}_{2}$${\mathrm{ClO}}_{4}$, which is believed to have an in-plane anisotropy of ${\ensuremath{\gamma}}_{\mathit{b}\mathit{a}}$\ensuremath{\sim}10 and a maximum out-of-plane anisotropy ${\ensuremath{\gamma}}_{\mathit{c}\mathit{a}}$\ensuremath{\sim}100. Our measurements show only weak effects of the in-plane anisotropy. The pinning force for Josephson vortices (parallel to the conducting planes) is nearly independent of their orientation, except for a small but narrow peak (full width at half maximum \ensuremath{\simeq}6\ifmmode^\circ\else\textdegree\fi{}) when the vortices are parallel to the TMTSF stacks (a axis). The pinning force initially decreases as the vortices unlock from the layers, contrary to the behavior previously observed in the organic superconductor (BEDT-TTF${)}_{2}$Cu(SCN${)}_{2}$. The lock-in threshold field is only weakly dependent on the initial angle of the Josephson vortices in the ab plane.

In this Letter we establish the phase diagram of $(\mathrm{TMTSF}{)}_{2}$ ${\mathrm{ClO}}_{4}$ to 30 T and above 0.5 K by transport and magnetization measurements. The high field region is bounded above by a second order transition from metallic to field induced spin density wave state at 5.5 K. Completely contained inside this boundary is a first order line terminating in a critical point. Neither phase boundary shows the large oscillations predicted in recent models. Our results suggest that there are separate transitions on each of the two Fermi surfaces, with only weak coupling between the order parameters.

The standard model for the field-induced spin-density-wave (FISDW) transitions in the Bechgaard salts (TMTSF${)}_{2}$X, where TMTSF is tetramethyltetraselenafulvalene, explains a cascade of phase trasitions with each phase associated with the quantum Hall effect. The ${\mathrm{ClO}}_{4}$ salt is sufficiently different that it has inspired a series of theoretical modifications from the standard model. To test these models we have performed simultaneous ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{x}}$, ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$, specific-heat, magnetocaloric effect, and magnetization measurements in the field range from 0--9 T. We find that all of the transport transitions, specifically the Hall resistance jumps, are associated with thermodynamic transitions. We observe the emergence of a new FISDW state characterized by a distinct Hall plateau. It arises from what was originally believed to be a tetracritical point in the phase diagram. We find no evidence for an arborescent phase diagram, but rather the signature of a single pairwise splitting of the phase boundaries. The higher-field transitions are decidedly first order, hysteretic, and ``lossy.'' Anion disorder decreases the number of observed phases and shifts the transition fields.

Shear can impart a high degree of orientational order to supported block copolymer thin films containing one or more layers of cylindrical microdomains, leading to a striped pattern with a period of tens of nanometers extending over macroscopic (centimeter-squared) areas. Though the as-deposited films have a polygrain structure, after shearing at sufficiently high stresses the only defects which remain are isolated dislocations, and the orientational order can be quite high (nematic or twofold orientational order parameter g0.99, as measured by tapping-mode atomic force microscopy). The effect of isolated dislocations on orientational order is adequately captured by an isotropic elastic continuum model of the structure surrounding the dislocation, producing a linear decrease of order parameter with dislocation density. Even at zero dislocation density, however, the order parameter does not quite reach unity, due to small-amplitude undulations of the cylinders about their axes which persist in the transverse direction over several cylinder periods.

We present evidence for and study the properties of coreless Josephson vortices (parallel to the superconducting layers) in the organic superconductor (BEDT-TTF${)}_{2}$Cu(NCS${)}_{2}$, using ac susceptibility measurements in the mixed state. We observe (1) extremely weak-pinning restoring forces for flux motion parallel to the layers, due to the absence of the vortex normal core; (2) single vortex (noncollective) pinning, due to weak interactions between Josephson vortices; (3) the ``lock-in'' of the vortices parallel to the layers when the dc field is applied at an arbitrary angle; and (4) highly nonlinear response to the ac field h in the lock-in state, above a threshold of h\ensuremath{\sim}0.5 G. The behavior of tilted flux lines is dominated by the much stronger pinning and collective interactions of two-dimensional Abrikosov ``pancake'' vortices, and linear response is largely restored when the flux lines unlock from the layers. We measure the Josephson penetration depth to be ${\ensuremath{\lambda}}_{\mathrm{\ensuremath{\perp}}}$(T=5 K)\ensuremath{\sim}200 \ensuremath{\mu}m, yielding a penetration depth anisotropy of \ensuremath{\gamma}=${\ensuremath{\lambda}}_{\mathrm{\ensuremath{\perp}}}$/${\ensuremath{\lambda}}_{\mathrm{\ensuremath{\parallel}}}$\ensuremath{\sim}160-350.

Using a vibrating-reed technique, we studied the flux penetration in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ single crystals in the strong pinning regime well below the irreversibility line. The resonant frequency and damping of the vibrating superconductor are dramatically enhanced by the nonuniform and hysteretical penetration of the flux lines at low temperature. Using a critical-state model, we determine the critical current density ${\mathit{J}}_{\mathit{c}}$ to be about 3.5\ifmmode\times\else\texttimes\fi{}${10}^{6}$ A/${\mathrm{cm}}^{2}$ at 4.2 K. We also found that ${\mathit{J}}_{\mathit{c}}$ obeys an exponential temperature dependence and the flux creep at low temperature can be characterized by a low activation energy barrier on the order of 20 K.

We have discovered a new type of angular dependent magnetotransport which permits the measurement of the Fermi surface parameters of quasi-one-dimensional metals. Resistance measurements of (TMTSF${)}_{2}$${\mathrm{ClO}}_{4}$ in the c (least conducting) direction show pronounced resonances when the field is rotated in the a-c plane near the a axis. At these resonances each electron trajectory across the warped Fermi surface sheets has an average velocity along c approaching zero. The resonance angles are determined by the bandwidths and allow us, for example, to extract ${\mathit{t}}_{\mathit{b}}$. For (TMTSF${)}_{2}$${\mathrm{ClO}}_{4}$ in the anion ordered state, we measure ${\mathit{t}}_{\mathit{b}}$=0.012\ifmmode\pm\else\textpm\fi{}0.001 eV.

Conventional diffusion $⟨\ensuremath{\Delta}{R}^{2}(t)⟩=2Dt$ gives way to subdiffusion $⟨\ensuremath{\Delta}{R}^{2}(t)⟩\ensuremath{\sim}{t}^{\ensuremath{\mu}}$, $0l\ensuremath{\mu}l1$ when the waiting time distribution $\ensuremath{\varphi}(\ensuremath{\tau})$ is nonintegrable. We have studied a model system, colloidal particles functionalized with DNA ``sticky ends'' diffusing on a complementary coated surface. We observe a crossover from subdiffusive to conventional behavior for $⟨\ensuremath{\Delta}{R}^{2}(t)⟩$ and $\ensuremath{\varphi}(\ensuremath{\tau})$ as temperature is increased near the particle-surface melting temperature consistent with a simple Gaussian distribution of sticky ends. Our results suggest that any system with randomness in its binding energy should exhibit subdiffusive behavior as it unbinds. This will strongly affect the kinetics of self-assembly.

Muon-spin-rotation and relaxation (\ensuremath{\mu}SR) studies of the organic compounds (TMTSF${)}_{2}$-X (X=${\mathrm{PF}}_{6}$, ${\mathrm{NO}}_{3}$, and ${\mathrm{ClO}}_{4}$) at ambient pressure are reported. We observe spin-density-wave (SDW) states in all three compounds under zero external magnetic field. The onset of the SDW is extremely sharp, which may indicate a first-order transition. The sublattice magnetization (or SDW amplitude) in the ${\mathrm{PF}}_{6}$ compound exhibits significant reduction with increasing temperature at low temperatures, which demonstrates the existence of collective low-energy excitations, in addition to the single-particle excitations across the SDW gap. The large spin-wave stiffness we observe in this system is incompatible with a Heisenberg model for a localized spin system; this demonstrates the importance of using an itinerant-electron picture to describe the magnetic behavior of this system. The broad distribution of local magnetic fields deduced from the \ensuremath{\mu}SR time spectra is consistent with that expected from an incommensurate SDW. The magnitude of the internal field at T\ensuremath{\rightarrow}0 is approximately the same for the three systems, suggesting a common SDW amplitude in these systems. Transverse-field \ensuremath{\mu}SR measurements in the relaxed-state ${\mathrm{ClO}}_{4}$ system show no visible enhancement of the relaxation rate in the superconducting state down to 0.1 K, providing a lower limit for the superconducting penetration depth ${\ensuremath{\lambda}}_{\mathrm{ab}\ensuremath{'}}$\ensuremath{\geqslant}12 000 \AA{}.

In this paper, we report measurements of the normal-metal-superconductor phase boundary T c (H) in disordered quasiperiodic wire networks. The initially ordered network is an eightfold quasiperiodic array of the type previously constructed by Ammann, and several types of disorder have been introduced. One series of arrays is areally disordered by stretching and contracting individual worm segments in the network, and the resulting phase boundary exhibits a gradual decay of all phase-boundary structure with increasing field. A second series is perturbed by phason disorder, which amounts to the local flipping of small symmetric clusters of tiles and destroys the local ordering inherent in the inflation symmetry of the ordered network

We have made a detailed pressure--magnetic-field--temperature phase diagram study of the organic conductors (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$ and (TMTSF${)}_{2}$${\mathrm{ClO}}_{4}$ in the low temperature regions dominated by the cascade of field-induced spin density wave (FISDW) transitions. The ${\mathrm{PF}}_{6}$ salt shows general agreement with the ``standard model'' for the FISDW and the pressure dependence of its high field insulating state connects nicely with the n=0 SDW. The ${\mathrm{ClO}}_{4}$ salt shows agreement with the standard model only when an anion ordering transition has been suppressed above \ensuremath{\sim}5 kbar.

Lebed predicted striking effects in both the metallic and field-induced spin-density-wave (FISDW) states of quasi-one-dimensional conductors when the orientation of the magnetic field causes commensurate electron motion in the least-conducting plane. We have observed sharp cusplike dips in the normal-state magnetoresistance of (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$ suggesting a giant resonance at the commensurate angles. On entering the FISDW state some of the dips become peaks, others fade, and fractional states appear. Magic angle effects are also prominent in the phase boundary of the FISDW state and in the Hall resistance.

Dynamic light scattering from polymer gels is complicated by the fact that the scattering intensity and its time correlation function change as different parts of a sample are explored. This results from the nonergodicity of the sample---time averages are not the same as ensemble averages, the result of a finite rigidity that leads to constrained inhomogeneities. We demonstrate a direct technique for ensemble averaging (by moving the sample), present the experimental correlation function containing correlations that do not decay with time, and show that the light scattering results from a superposition of static scattering from immobile inhomogeneities and dynamic density fluctuations from ``gel modes.''

Using a multiple light scattering technique and a stabilizing counterflow (i.e., a fluidized bed), we measured the average sedimentation velocity, its variance, and the short-time self-diffusion coefficient in a concentrated hard-sphere suspension. Many-body hydrodynamic interactions slow both the Brownian diffusion and mean sedimentation and provide a novel mechanism for long time dispersion.

We have performed a thermoelectric-power study of the organic conductor (TMTSF) 2 PF 6 which exhibits a type of bulk quantum Hall effect (QHE), resulting from a cascade of magnetic-field- induced spin-density-wave (FISDW) transitions. The FISDW are characterized by a sharp increase in thermopower as the temperature is lowered through the transition temperature, followed by an exponential decrease as temperature approaches zero. This suggest a temperature-dependent gap leading to collective QHE-like transport. Most surprising is the vanishing thermopower in the insulating n=0' state

We report the studies of the elasticity of ${\mathrm{O}}_{60}$ single crystals. For sublimed fcc crystals, Young's modulus has an 8% jump at the first-order transition at 260 K. At \ensuremath{\sim}160 K there is a frequency-dependent elastic anomaly resulting from time dependent stress relaxation. Comparison with rotation rates seen in NMR suggests that the dynamics below 260 K is more complex than jumps between equivalent molecular configurations. Solvent grown monoclinic crystals have a second-order transition at 242 K, while the 160-K glass transition remains unchanged.

We study the effects of hydrodynamic interactions on the diffusion of hard spheres in concentrated suspensions. Using a multiple-light-scattering technique, we measure [H(q)], a weighted average of H(q), a function that characterizes the hydrodynamic interaction. By changing the size of the spheres we probe the particle size dependence of [H(q)] and find reasonable agreement with recent calculations for volume fractions \ensuremath{\varphi}0.45. For large spheres (diameter 2Rg2\ensuremath{\mu}m), [H(q)]\ensuremath{\rightarrow}H(\ensuremath{\infty}) and thus, we measure the short-time self-diffusion coefficient ${\mathit{D}}_{\mathit{s}}$==${\mathit{D}}_{0}$H(\ensuremath{\infty}) where ${\mathit{D}}_{0}$ is the free-particle diffusion coefficient. We find that H(\ensuremath{\infty})=1-1.77(\ifmmode\pm\else\textpm\fi{}0.07)\ensuremath{\varphi} for \ensuremath{\varphi}\ensuremath{\le}0.45. This agrees with the linear (low-concentration) term calculated for short-time self-diffusion. The short-time diffusion coefficient is also found to be continuous across the freezing transition.

The thermopower of the organic superconductor \ensuremath{\kappa}-(BEDT-TTF${)}_{2}$Cu[N(CN${)}_{2}$]Br single crystals has been measured in two crystallographic directions a and c within the most conducting organic donor molecule plane. [Here BEDT-TTF represents bis(ethylenethio)-tetrathiafulvalene.] While the thermopower in the a direction is positive, the thermopower in the c direction is negative. The drastic anisotropy in thermopower reveals that the carriers in the a direction are holelike, whereas the carriers in the c direction are electronlike. A calculation based on the tight-binding electronic band structure is able to describe the temperature dependence of the anisotropic thermopower, but with a much reduced band dispersion.