Degenerate ground-state configurations of the hidden order

Four different types of RA-SHG patterns found by performing local measurements within all of the domains mapped in Fig. 2b. Red lines are fits to the expressions described in the text. The large lobes are shaded pink to emphasize the orientation of each pattern. Schematics of the four degenerate magneto-electric loop-current order configurations are shown below each pattern to illustrate the possible correspondence. The red arrows denote the direction of the toroidal moment Ω in each plaquette.

Members of David Hsieh’s group have discovered an unusual form of matter—not a conventional metal, insulator, or magnet, for example, but something entirely different. This phase, characterized by an unusual ordering of electrons, offers possibilities for new electronic device functionalities and could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity—the ability for some materials to conduct electricity without resistance, even at “high” temperatures approaching –100 degrees Celsius.  Hsieh says the finding emphasizes the importance of developing new tools to try to uncover new phenomena. “This was really enabled by a simultaneous technique advancement,” he says. Furthermore, he adds, these multipolar orders might exist in many more materials. “Sr2IrO4 is the first thing we looked at, so these orders could very well be lurking in other materials as well, and that’s exactly what we are pursuing next. Read the full Caltech media article. The article was published online in Nature Physics on October 26.

Zhao, L. and Torchinsky, D. H. and Chu, H. and Ivanov, V. and Lifshitz, R. and Flint, R. and Qi, T. and Cao, G. and Hsieh, D. (2015) Evidence of an odd-parity hidden order in a spin–orbit coupled correlated iridate. Nature Physics . ISSN 1745-2473. (In Press)