We perform tunneling spectroscopy of Sr 2 RuO 4 searching for the edge states peculiar to topological superconductivity. Conductance spectra obtained on Sr 2 RuO 4 /Au junctions fabricated using in situ process show broad humps indicating the successful detection of a-axis edge of 1.5K phase. Three types of peak shape are detected: domelike peak, split peak and two-step peak. By comparing the experiments with predictions for unconventional superconductivity, these varieties are shown to originate from multiband chiral p-wave symmetry with weak anisotropy of pair amplitude. The broad hump in conductance spectrum is a direct manifestation of the edge state peculiar to the chiral p-wave superconductivity.Since the discovery of the ruthenate superconductor Sr 2 RuO 4 (SRO) [1], the symmetry of the pair potential has been a topic of hot debate. The high anisotropy of transport properties indicates the quasi-two-dimensional electronic states of this compound. Nuclear magnetic resonance [2] and muon spin resonance experiments [3] suggest spin triplet pairing states with broken 1

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The switching dynamics of current-biased Bi2Sr2CaCu2O 8+δ intrinsic Josephson junctions (IJJs) was studied to clarify the effect of d-wave superconductivity and the stack structure on the switching properties. High quality IJJs were fabricated, and then the temperature dependence of the switching probability distribution was measured for the first and second switchings. Although the standard deviation of the distribution detected for both switchings showed similar saturation characteristics with decreasing temperature, the temperature at saturation was about 13 times higher for the second switching than for the first switching. The properties of the first switching can be explained in terms of a conventional underdamped JJ, that is, macroscopic quantum tunneling below the crossover temperature, and thermal activation with quality factor of 70±20 above the crossover temperature. In contrast, the relatively higher effective temperature for the second switching evaluated from the switching probability distribution suggests a dominant thermal activation process under the influence of the self-heating effect even at sufficiently low temperature.

Sr2RuO4 is one of the most promising candidates of a topological superconductor with broken time-reversal symmetry, because a number of experiments have revealed evidences for a spin-triplet chiral p-wave superconductivity. In order to clarify the time-reversal symmetry of Sr2RuO4, we introduce a novel test that examines the invariance of the Josephson critical current under the inversion of both the current and magnetic fields, in contrast to the detection of a spontaneous magnetic field employed in past experiments. Analyses of the transport properties of the planar and corner Josephson junctions formed between Sr2RuO4 and Nb reveal the time-reversal invariant superconductivity, most probably helical p-wave, of Sr2RuO4. This state corresponds to a yet-to-be confirmed topologicalcrystallinesuperconductivity that can host two Majorana edge modes at the surface protected by crystalline mirror symmetry. arXiv:1907.03939v2 [cond-mat.supr-con]

The c-axis transport properties of a high-pressure synthesized PrFeAsO0.7 single crystal are studied using s-shaped junctions. Resistivity anisotropy of about 120 detected at 50 K shows the presence of strong anisotropy in the electronic states. The obtained critical current density for the c-axis of 2.9*10^5 A/cm^2 is two orders of magnitude larger than that in Bi2Sr1.6La0.4CuO6+d. The appearance of a hysteresis in the current-voltage curve below T_c is the manifestation of the intrinsic Josephson effect similar to that in cuprate superconductors. The suppression of the critical current-normal resistance (I_cR_n) product is explained by an inspecular transport in s_pm-wave pair potential.Comment: 8 pages, 2 figure

Tunneling conductance spectra of normal metal/insulator/superconductor (N/I/S) junctions are calculated to determine the potential of tunneling spectroscopy in investigations of topological superconductivity. Peculiar feature of topological superconductors is the formation of gapless edge states in them. Since the conductance of N/I/S junctions is sensitive to the formation of these edge states, topological superconductivity can be identified through edge-state detection. Herein, the effects of Fermi surface anisotropy and an applied magnetic field on the conductance spectra are analyzed to gather indications that can help to identify the topological nature of actual materials.Comment: 17pages, 1 table, 6 figures, submitted to Physica

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field.

Clarifying the chiral domains structure of superconducting Sr2RuO4 has been a long-standing issue in identifying its peculiar topological superconducting state. We evaluated the critical current Ic versus the magnetic field H of Nb/Sr2RuO4 Josephson junctions, changing the junction dimension in expectation of that the number of domains in the junction is controlled. Ic(H) exhibits a recovery from inversion symmetry breaking to invariance when the dimension is reduced to several microns. This inversion invariant behavior indicates the disappearance of domain walls; thus, the size of a single domain is estimated at approximately several microns.