From Hopkins and Rutgers: “Between two worlds: Exotic insulator may hold clue to key mystery of modern physics”
Dec 6, 2016
Scientists experiment with material that straddles world of classical physics and hidden quantum realm
Experiments using laser light and pieces of gray material the size of fingernail clippings may offer clues to a fundamental scientific riddle: what is the relationship between the everyday world of classical physics and the hidden quantum realm that obeys entirely different rules?
N. Peter Armitage
“We found a particular material that is straddling these two regimes,” said N. Peter Armitage, an associate professor of physics at Johns Hopkins University who led the research for the paper just published in the journal Science. Six scientists from Johns Hopkins and Rutgers University were involved in the work on materials called topological insulators, which can conduct electricity on their atoms-thin surface, but not in their insides.
Topological insulators were predicted in the 1980s, first observed in 2007, and have been studied intensively since. Made from any number of hundreds of elements, these materials have the capacity to show quantum properties that usually appear only at the microscopic level, but here appear in a material visible to the naked eye.
The experiments reported in Science establish these materials as a distinct state of matter “that exhibits macroscopic quantum mechanical effects,” Armitage said. “Usually we think of quantum mechanics as a theory of small things, but in this system quantum mechanics is appearing on macroscopic length scales. The experiments are made possible by unique instrumentation developed in my laboratory.”
In the experiments reported in Science, the elements bismuth and selenium make up dark gray material samples—each a few millimeters long and of different thicknesses—that were hit with “THz” light beams that are invisible to the unaided eye. Researchers measured the reflected light as it moved through the material samples and found indicators of a quantum state of matter.
Specifically, they found that as the light was transmitted through the material, the wave rotated a specific amount, which is related to physical constants that are usually only measurable in atomic scale experiments. The amount matched predictions of what would be possible in this quantum state.
The results add to scientists’ understanding of topological insulators, but also may contribute to the larger subject that Armitage says is the central question of modern physics: what is the relationship between the macroscopic classical world, and the microscopic quantum world from which it arises?
Scientists since the early 20th century have struggled with the question of how one set of physical laws governing objects above a certain size can co-exist alongside a different set of laws governing the atomic and subatomic scale. How does classical mechanics emerge from quantum mechanics, and where is the threshold that divides the realms?
Those questions remain to be answered, but topological insulators could be part of the solution.
“It’s a piece of the puzzle,” said Armitage, who worked on the experiments along with Liang Wu, who was a graduate student at Johns Hopkins when the work was done; Maryam Salehi of the Rutgers University Department of Material Science and Engineering; and Nikesh Koirala, Jisoo Moon, and Sean Oh of the Rutgers University Department of Physics and Astronomy.
See the full article here .
Rutgers, The State University of New Jersey, is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.
The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”
The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”
What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.