To clarify the superconducting gap structure of the spin-triplet superconductor Sr2RuO4, the in-plane thermal conductivity has been measured as a function of relative orientations of the thermal flow, the crystal axes, and a magnetic field rotating within the 2D RuO2 planes. The in-plane variation of the thermal conductivity is incompatible with any model with line nodes vertical to the 2D planes and indicates the existence of horizontal nodes. These results place strong constraints on models that attempt to explain the mechanism of the triplet superconductivity.

We present the temperature dependence of the thermal conductivity κ(T ) of the unconventional superconductor Sr2RuO4 down to low temperatures (∼100 mK). In T → 0 K limit we found a finite residual term in κ/T , providing clear evidence for the superconducting state with an unconventional pairing. The residual term remains unchanged for samples with different Tc, demonstrating the universal character of heat transport in this spin-triplet superconductor. The low-temperature behavior of κ suggests the strong impurity scattering with a phase shift close to π/2. A criterion for the observation of universality is experimentally deduced.PACS numbers: 74.20. Rp, 74.25.Fy, 74.70.Pq Through the study of the cuprate superconductor in the last decade, a notable progress has been made in an understanding of the thermodynamic and transport properties of quasi-particles (QP) in unconventional superconductors. One of the important findings is the novel phenomenon called the universal transport, pointed out first by Lee [1]. In an unconventional superconductor with nodes in the superconducting (SC) gap, nonmagnetic impurities suppress the transition temperature (T c ) and induce the finite density of QP states at the Fermi level with the energy width γ imp [2]. The presence of impurities increases both the QP density and the impurity scattering rate, which completely cancel each other [3,4]. In this case the QP transport, such as thermal conductivity (κ), restores the temperature (T ) dependence typical for the normal state (e.g. κ ∝ T ) [5] and becomes independent of impurity concentration. The magnitude of the residual term in κ/T depends only on the QP spectrum near the gap nodes, providing a useful tool for studying the SC order parameter [4].Experimentally, the universal residual term in κ/T at T → 0 K has been reported in optimally-doped high-T c cuprates YBa 2 Cu 3 O 6.9 [6] and Bi 2 Sr 2 CaCu 2 O 8 [7,8].Their residual values are consistent with the d-wave SC gap structure [9]. For non-d-wave gap symmetries, the universal conductivity has never been observed. In contrast, the extrapolated κ/T at T → 0 K of the spin-triplet superconductor UPt 3 [10,11] rapidly increases with the density of defects, showing no universal behavior, and the residual term seems to vanish in zero-disorder limit [11]. The origin of the lack of universality is still unclear, similar to the case of under-doped cuprates [12], and it is strongly desirable to extend studies to other unconventional superconductors.In this respect, of special interest is the study of Sr 2 RuO 4 , a unique quasi-two-dimensional (Q2D) spin triplet superconductor [13,14]. This material has a layered perovskite structure [15] and its electronic state is well described in the Landau-Fermi liquid model [16]. The SC state of Sr 2 RuO 4 (T c = 1.5 K) is chiral with a broken time reversal symmetry [17] and its T c is rapidly suppressed by non-magnetic impurities [18,19]. Views on the SC gap symmetry of Sr 2 RuO 4 changed in time. Early theoretical prediction of the fully ga...

The dependence of in-plane and interplane thermal conductivities of Sr2RuO4 on temperature, as well as magnetic field strength and orientation, is reported. We found no notable anisotropy in the thermal conductivity for the magnetic field rotation parallel to the conducting plane in the whole range of experimental temperatures and fields, except in the vicinity of the upper critical field H(c2), where the anisotropy of the H(c2) itself plays a dominant role. This finding imposes strong constraints on the possible models of superconductivity in Sr2RuO4 and supports the existence of a superconducting gap with a line of nodes running orthogonal to the Fermi surface cylinder.

We have experimentally investigated the control of Marangoni flow around a micro bubble using photothermal conversion. Using a focused laser spot acting as a highly localized heat source on Au nanoparticles/dielectric/Ag mirror thin film enables us to create a micro bubble and to control the temperature gradient around the bubble at a micrometer scale. When we irradiate the laser next to the bubble, a strong main flow towards the bubble and two symmetric rotation flows on either side of it develop. The shape of this rotation flow shows a significant transformation depending on the relative position of the bubble and the laser spot. Using this controllable rotation flow, we have demonstrated sorting of the polystyrene spheres with diameters of 2 lm and 0.75 lm according to their size. V