Discovering a 'rule-breaking' quantum material

“We have experimentally produced high-quality, atomically-thin samples of TaIrTe4 and developed corresponding electronic devices,” 太阳城网赌平台 物理学助理教授 Qiong Ma, 该报告的主要作者. “What's particularly intriguing is our discovery of not just one, but two topological insulating states, beyond the predictions of theory.”

The findings introduce a novel effect that the team calls the dual topological insulator or the dual quantum spin Hall insulator, 马说.

特别瘦, two-dimensional layers of a crystalline material called TaIrTe4, 由钽制成, 铱, 和碲, were the focus of the team of scientists from BC, 麻省理工学院, 哈佛大学, 加州大学洛杉矶分校, 德克萨斯州的一个&M, 田纳西大学, Singapore’s Nanyang Technological University,  the Chinese Academy of Sciences, and Japan’s National Institute for Materials Science.

Each layer is less than 1 nanometer thick—that's over 100,000 times thinner than a strand of human hair. 这些层, 或“雪花," were carefully peeled off from a larger crystal using a simple method involving clear adhesive tape, a Nobel Prize-honored technique used widely in materials science.

“Our investigation aimed to understand how these materials conduct electricity,马说. “Given the minuscule size of these materials, we employed advanced nanofabrication techniques, including photolithography and electron beam lithography, to establish nano-sized electrical contacts.”

马说 the project’s primary objective was to test the theoretical prediction that suggests the thinnest TaIrTe4 layer acts as a two-dimensional topological insulator—also known as a quantum spin Hall insulator—a novel material where its interior is insulating and electricity flows along its boundaries without any energy loss. This unique combination makes these materials a focus of researchers trying to develop future generations of energy-efficient electronic devices.

Through manipulation of specific parameters—referred to as gate voltages—the team found TaIrTe4's transition between the two distinct topological states, 马说. 在这两个例子中, the material exhibits zero electrical conductivity within its interior, while its boundaries remain conductive. Through systematic experimental and theoretical investigation, they determined that these two topological states stem from disparate origins.

The findings, which exceeded the theoretical predictions, surprised the scientists.

“通常, adding electrons to a material increases its conductivity due to the greater number of charge or electricity carriers,马说. “Initially, our system behaved as expected and became more conductive with the addition of electrons. 然而, 超过某一点, adding more electrons unexpectedly turned the interior insulating again, with electrical conduction only at the boundaries and without energy loss, which is exactly again a topological insulating phase just like at the starting point when the interior has no electrons. This transition to a second topological insulating phase is entirely unexpected.”

马说 future work on the discovery includes collaborations with groups skilled in other specialized techniques, 比如纳米级成像探针, to further understand the unexpected behavior.

“We'll also focus on refining our material's quality to improve the already impressive dissipationless topological conduction,马说. “此外, we plan to build heterostructures based on this new material to unlock even more intriguing physical behaviors.”

在太阳城网赌平台, Ma collaborated with Professors of Physics Kenneth Burch and Ziqiang Wang; staff at the University Clean Room; BC post-docs Jian Tang, Zumeng黄, and Zhe Sun; graduate students Thomas Siyuan Ding, 迈克尔Geiwitz, 穆罕默德Shehabeldin, Vsevolod Belosevich, and Yiping Wang; and Zihan Wang, a visiting undergraduate researcher.