This researh is focused in unconventional superconductors possessing a pairing symmetry different from the s-wave pairing, an area that is at the center stage of condensed matter physics research. The first goal of the proposed research is to establish the precise pairing symmetries in pure Sr₂RuO₄. There is little doubt that Sr₂RuO₄ is a spin-triplet superconductor. However, whether its precise pairing symmetry is that of the chiral p-wave has not been settled, primarily because the expected gapless chiral surface states have not been observed.

 

Our second goal is to explore the consequences of the unconventional pairing symmetry in these two material systems. If Sr₂RuO₄ is indeed shown to be chiral p-wave or chiral f-wave as described above, novel physical phenomena are expected, which include gapless chiral surface states, domains (originating from the presence of doubly degenerate p-wave, k_x + i k_y and k_x - i k_y, or f-wave, (k_x + i k_y) k_z² and (k_x - i k_y) k_z², states), half-flux-quantum vortices, and Majorana modes.

Our third goal is to study the physics of compounds related to Sr₂RuO₄ , including Sr₃Ru₂O₇ and Ca₃Ru₂O₇ so as to obtain insights into the mechanism of superconductivity in Sr₂RuO₄.

To accomplish these goals we propose to: 1) perform phase-sensitive measurements on the k_z-dependence of the order parameter for Sr₂RuO₄; 2) perform Little-Parks resistance oscillations and scanning SQUID measurements to search for half-flux-quantum flux states; and 3) to perform low temperature transport and thermoelectric transport measurements on Sr₃Ru₂O₇ and Ca₃Ru₂O₇.

Work proposed here is expected to create opportunities for fundamental discoveries and an improved understanding of unconventional superconductivity. In addition, the establishment of half-flux-quantum flux states will pave the way for identifying and making use of localized Majorana modes that will in turn help advance future quantum computing technologies.