Characteristics of the wavelength of ripples on icicles

It is known that the wavelength of the ripples on icicles in nature is of centimeter-scale. Such study on morphological instability of ice-water interface during ice growth from flowing supercooled water film with one side being a free surface has recently been made [K. Ueno, Phys. Rev. E 68, 021603 (2003)]. This is a first theoretical study taking into account the influence of the shape of the water-air surface on the growth condition of infinitesimal disturbances of the ice-water interface. A simpler formula to determine the wavelength of the ripples than that in the previous paper is derived. It seems that the wavelength of ripples is insensitive to the water supply rates, diameters of the icicles and surrounding air temperatures. The details of dependence of the wavelengh of ripples on these parameters are investigated.Comment: 15 pages, 6 figure

Mechanism of hopping transport in disordered Mott insulators

By using a combination of detailed experimental studies and simple theoretical arguments, we identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca$_{2-x}$Sr$_x$RuO$_4$ near the metal-insulator transition. The hopping exponent $\alpha$ shows a systematic evolution from a value of $\alpha=1/2$ deeper in the insulator to the conventional Mott value $\alpha=1/3$ closer to the transition. This behavior, which we argue to be a universal feature of disordered Mott systems close to the metal-insulator transition, is shown to reflect the gradual emergence of disorder-induced localized electronic states populating the Mott-Hubbard gap.Comment: 5 pages, 3 figures, To be published in Physical Review Letter

Phase transition in the 3 Kelvin phase in the eutectic Sr2RuO4-Ru

The inhomogeneous 3-Kelvin (3K) phase of the eutectic Sr2RuO4 with Ru inclusions nucleates superconductivity at the interface between Ru and Sr2RuO4. The structure of the interface state and its physical properties are examined here. Two superconducting phases are identified between the transitions to the bulk phase at 1.5K and to the 3K phase. The nucleation of the 3K phase results in a state conserving time reversal symmetry, which generates an intrinsically frustrated superconducting network in samples with many Ru inclusions. At a lower temperature (>1.5K), a discontinuous (first order) transition to an interface state breaking time reversal symmetry is found leading to an unfrustrated network phase. It is shown that this phase transition located at a temperature between 1.5 and 3K would yield the anomalous property that the critical current in such a network depends on the sign of the current, reproducing recent experimental observations.Comment: This paper has been withdrawn by the authors. 5 pages, 6 figure

Quasi-particle Density in Sr2RuO4 Probed by means of the Phonon Thermal Conductivity

The thermal conductivity of Sr2RuO4 along the least conducting direction perpendicular to the RuO2 plane has been studied down to 0.3 K. In this configuration the phonons remain the dominant heat carriers down to the lowest temperature, and their conductivity in the normal state is determined by the scattering on conduction electrons. We show that the phonon mean free path in the superconducting state is sensitive to the density of the quasi-particles in the bulk. An unusual magnetic field dependence of the phonon thermal conductivity is ascribed to the anisotropic superconducting gap structure in Sr2RuO4.Comment: 14 pages, 6 eps figures, Latex. This article corresponds to the reference 25 of Phys. Rev. Lett. vol.86 page2649-2652 (2001) and cond-mat/010449

Morphological instability of the solid-liquid interface in crystal growth under supercooled liquid film flow and natural convection airflow

Ring-like ripples on the surface of icicles are an example of morphological instability of the ice-water interface during ice growth under supercooled water film flow. The surface of icicles is typically covered with ripples of about 1 cm in wavelength, and the wavelength appears to be almost independent of external temperature, icicle radius, and volumetric water flow rate. One side of the water layer consists of the water-air surface and growing ice is the other. This is one of the more complicated moving phase boundary problems with two interfaces. A recent theoretical work [K. Ueno, Phys. Rev. E 68, (2003) 021603] to address the underlying instability that produces ripples is based on the assumption of the absence of airflow around icicles. In this paper, we extend the previous theoretical framework to include a natural convection airflow ahead of the water-air surface and consider whether the effect of natural convection airflow on the wavelength of ripples produced on an ice surface is essential or not.Comment: 19 pages, 5 figure

Pressure-Tuned Collapse of the Mott-Like State in Ca_{n+1}Ru_nO_{3n+1} (n=1,2): Raman Spectroscopic Studies

We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca_3Ru_2O_7 (T_N=56 K) and Ca_2RuO_4 (T_N=110 K). The pressure-dependence of the phonon and two-magnon excitations in these materials indicate: (i) a pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P* ~ 55 kbar in Ca_3Ru_2O_7 and P* ~ 5-10 kbar in Ca_2RuO_4, reflecting the importance of Ru-O octahedral distortions in stabilizing the AF insulating phase; and (ii) evidence for persistent AF correlations above the critical pressure of Ca_2RuO_4, suggestive of phase separation involving AF insulator and ferromagnetic metal phases.Comment: 3 figure

Orbital Properties of Sr3Ru2O7 and Related Ruthenates Probed by 17O-NMR

We report a site-separated $^{17}$O-NMR study of the layered perovskite ruthenate Sr$_3$Ru$_2$O$_7$, which exhibits nearly two-dimensional transport properties and itinerant metamagnetism at low temperatures. The local hole occupancies and the spin densities in the oxygen $2p$ orbitals are obtained by means of tight-binding analyses of electric field gradients and anisotropic Knight shifts. These quantities are compared with two other layered perovskite ruthenates: the two-dimensional paramagnet Sr$_2$RuO$_4$ and the three-dimensional ferromagnet SrRuO$_3$. The hole occupancies at the oxygen sites are very large, about one hole per ruthenium atom. This is due to the strong covalent character of the Ru-O bonding in this compound. The magnitude of the hole occupancy might be related to the rotation or tilt of the RuO$_6$ octahedra. The spin densities at the oxygen sites are also large, 20-40% of the bulk susceptibilities, but in contrast to the hole occupancies, the spin densities strongly depend on the dimensionality. This result suggests that the density-of-states at the oxygen sites plays an essential role for the understanding of the complex magnetism found in the layered perovskite ruthenates.Comment: 9 pages, 5 figures, to be published in Phys. Rev.

Multiple first-order metamagnetic transitions and quantum oscillations in ultrapure

We present measurements on ultra clean single crystals of the bilayered ruthenate metal Sr3Ru2O7, which has a magnetic-field-tuned quantum critical point. Quantum oscillations of differing frequencies can be seen in the resistivity both below and above its metamagnetic transition. This frequency shift corresponds to a small change in the Fermi surface volume that is qualitatively consistent with the small moment change in the magnetisation across the metamagnetic transition. Very near the metamagnetic field, unusual behaviour is seen. There is a strong enhancement of the resistivity in a narrow field window, with a minimum in the resistivity as a function of temperature below 1 K that becomes more pronounced as the disorder level decreases. The region of anomalous behaviour is bounded at low temperatures by two first-order phase transitions. The implications of the results are discussed. PACS: 68.35.Rh, 71.27.+a, 72.15.-v, 74.70.PqComment: 12 pages 4 figures, submitte

Magnetic anisotropy of the spin ice compound Dy2Ti2O7

We report magnetization and ac susceptibility of single crystals of the spin ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the charasteristic axes [100] and [110] agree with the expected values for an effective ferromagnetic nearest-neighbor Ising pyrochlore with local anisotropy, where each magnetic moment is constrained to obey the `ice-rule'. At high enough magnetic fields along the [111] axis, the saturated moment exhibits a beaking of the ice-rule; it agrees with the value expected for a three-in one-out spin configuration. Assuming the realistic magnetic interaction between Dy ions given by the dipolar spin ice model, we completely reproduce the results at 2 K by Monte Carlo calculations. However, down to at least 60 mK, we have not found any experimental evidence of the long-range magnetic ordering predicted by this model to occur at around 180 mK. Instead, we confirm the spin freezing of the system below 0.5 K.Comment: 7 pages, 6 figures, submitted to Phys. Rev.

Gap Structure of the Spin-Triplet Superconductor Sr2RuO4 Determined from the Field-Orientation Dependence of Specific Heat

We report the field-orientation dependent specific heat of the spin-triplet superconductor Sr2RuO4 under the magnetic field aligned parallel to the RuO2 planes with high accuracy. Below about 0.3 K, striking 4-fold oscillations of the density of states reflecting the superconducting gap structure have been resolved for the first time. We also obtained strong evidence of multi-band superconductivity and concluded that the superconducting gap in the active band, responsible for the superconducting instability, is modulated with a minimum along the [100] direction.Comment: 4 pages, 4 figure