Evidence for High-Temperature Superconductivity in Doped Laser-Processed Sr-Ru-O (original) (raw)

Specific-Heat Evidence of the First-Order Superconducting Transition in Sr2RuO4

Journal of the Physical Society of Japan, 2014

We investigate the specific heat of ultra-pure single crystals of Sr 2 RuO 4 , a leading candidate of a spin-triplet superconductor. We for the first time obtained specific-heat evidence of the first-order superconducting transition below 0.8 K, namely divergent-like peaks and clear hysteresis in the specific heat at the upper critical field. The first-order transition occurs for all in-plane field directions. The specific-heat features for the first-order transition are found to be highly sensitive to sample quality; in particular, the hysteresis becomes totally absent in a sample with slightly lower quality. These thermodynamic observations provide crucial bases to understand the unconventional pair-breaking effect responsible for the first-order transition.

Multiple superconducting transitions in theSr3Ru2O7region ofSr3Ru2O7-Sr2RuO4eutectic crystals

Physical Review B, 2008

We report superconducting properties of Sr 3 Ru 2 O 7-Sr 2 RuO 4 eutectic crystals, consisting of the spin-triplet superconductor Sr 2 RuO 4 with a monolayer stacking of RuO 2 planes and the metamagnetic normal metal Sr 3 Ru 2 O 7 with a bilayer stacking. Although Sr 3 Ru 2 O 7 has not been reported to exhibit superconductivity so far, our AC susceptibility measurements revealed multiple superconducting transitions occurring in the Sr 3 Ru 2 O 7 region of the eutectic crystals. The diamagnetic shielding essentially reached the full fraction at low AC fields parallel to the c axis. However, both the shielding fraction and the onset temperature are easily suppressed by AC fields of larger than 0.1 mT-rms and no anomaly was observed in the specific heat. Moreover, the critical field curves of these transitions have a positive curvature near zero fields, which is different from the upper critical field curve of the bulk Sr 2 RuO 4. These facts suggest that the superconductivity observed in the Sr 3 Ru 2 O 7 region is not a bulk property. To explain these experimental results, we propose the scenario that stacking RuO 2 planes, the building block of superconducting Sr 2 RuO 4 , are contained in the Sr 3 Ru 2 O 7 region as stacking faults.

Suppression of superconductivity by crystallographic defects in epitaxial Sr[sub 2]RuO[sub 4] films

Applied Physics Letters, 2001

Epitaxial Sr 2 RuO 4 thin films grown by pulsed-laser deposition from high-purity ͑99.98%͒ Sr 2 RuO 4 targets on ͑001͒ LaAlO 3 were found to be not superconducting down to 0.4 K. Structural disorder is believed to be responsible. A correlation was observed between higher resistivity ratios in electrical transport measurements and narrower x-ray diffraction rocking curve widths of the Sr 2 RuO 4 films. High-resolution transmission electron microscopy revealed that the dominant structural defects, i.e., the defects leading to the observed variation in rocking curve widths in the films, are ͕011͖ planar defects, with a spacing comparable to the in-plane superconducting coherence length of Sr 2 RuO 4. These results imply that minimizing structural disorder is the key remaining challenge to achieving superconducting Sr 2 RuO 4 films.

Higher-T_{c} superconducting phase in Sr_{2}RuO_{4} induced by uniaxial pressure

Physical Review B, 2010

We have investigated uniaxial pressure effect on superconductivity of pure Sr 2 RuO 4 , whose intrinsic superconducting transition temperature T c is 1.5 K. It was revealed that a very low uniaxial pressure along the c axis, only 0.2 GPa, induces superconductivity with the onset T c above 3 K. The present results indicate that pure Sr 2 RuO 4 has two superconducting phases with T c = 1.5 K and with varying T c up to 3.2 K. The latter phase exhibits unusual features and is attributable to anisotropic crystal distortions beyond the elastic limit.

Transition into a low temperature superconducting phase of unconventional pinning in Sr2RuO4

Physica B: Condensed Matter, 1999

We have found a sharp transition in the vortex creep rates at a temperature T * = 0.05T c in a single crystal of Sr 2 RuO 4 (T c = 1.03 K) by means of magnetic relaxation measurements. For T < T * , the initial creep rates drop to undetectable low levels. One explanation for this transition into a phase with such extremely low vortex creep is that the low-temperature phase of Sr 2 RuO 4 breaks time reversal symmetry. In that case, degenerate domain walls separating discreetly degenerate states of a superconductor can act as very strong pinning centers.[1]

Evaluation of Spin-Triplet Superconductivity in Sr2RuO4

Journal of the Physical Society of Japan, 2012

This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2 RuO 4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr 2 RuO 4. After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr 2 RuO 4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr 2 RuO 4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr 2 RuO 4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr 2 RuO 4 .

Spatial Development of Superconductivity in the Sr 2 RuO 4 –Ru Eutectic System

Journal of the Physical Society of Japan, 2009

We have clarified how the enhanced superconductivity, often referred to as the 3-K phase superconductivity, develops in the Sr 2 RuO 4 -Ru eutectic system. From the detailed ac and dc susceptibility measurements on well-characterized crystals, we revealed strongly anisotropic shielding, governed by the direction of the screening current dominated within the RuO 2 plane rather than by the orientation of the Ru lamellae. The onset temperature of the 3-K phase superconductivity probed by diamagnetic screening is as high as 3.5 K. The temperature dependence of the diamagnetic shielding above around 2 K is well ascribed by the interfacial screening around each Ru lamella. Below around 2 K, the rapid development of the shielding fraction as well as its peculiar response to ac and dc magnetic fields are explained by the formation of the Josephson network consisting of inter-lamellar supercurrents.

Change in oxygen concentration in Sr 2 RuO 4 single crystals after laser processing

2011

In order to check the possibility of realization of high-temperature superconductivity in strontium ruthenate, we studied experimentally the influence of laser radiation on single-crystal samples of Sr2RuO4. Results obtained by the technique of electron-probe X-ray microanalysis showed an enhancement of the oxygen concentration in the near-surface layer of samples, which may most probably be caused by the change in the

Normal-state and superconducting properties of Sr2RuO4

Journal of Low Temperature Physics

We discuss some of the current issues on the copper-free layered perovskite superconductor Sr2Ru04, for which a sharp transition at Tc = 1.2 K has been reproducibly obtained. The normal state is character&ed as an essentially twodimensional Fermi liquid, and the coherent interlayer transport is established only at low temperatures. The cylindrical Fermi surface observed by de Haas-van Alphen experiments is consistent with other thermodynamic and transport properties. Although the specific heat jump across Tc confirms the bulk superconductivity, the large residual T-linear term which correlates with the variation in T c is unusual and suggestive of unconventional pairing.

Spin-Triplet Superconductivity in Sr2RuO4 Probed by Andreev Reflection

Physical Review Letters, 2000

The superconducting gap function of Sr2RuO4 was investigated by means of quasiparticle reflection and transmission at the normal conductor-superconductor interface of Sr2RuO4-Pt point contacts. We found two distinctly different types of dV /dI vs V spectra either with a double-minimum structure or with a zero-bias conductance anomaly. Both types of spectra are expected in the limit of high and low transparency, respectively, of the interface barrier between a normal metal and a spin-triplet superconductor. Together with the temperature dependence of the spectra this result strongly supports a spin-triplet superconducting order parameter for Sr2RuO4. 74.70.Dd, 71.20.Lp, 73.40.Jn, 74.80.Fp