Nature:物理学家设计出导电接近光速的二维材料

诸平

UCI physicist Jing Xia (right, with graduate student Alex Stern) calls the fiber-optic Sagnac interferometer he built the most sensitive magnetic microscope in the world. He compares it to a telescope that an ornithologist in Irvine could use to inspect the eye of a bird in New York. Credit: Steve Zylius / UCI

据加州大学欧文分校(University of California, Irvine，UCI)2017年4月26日提供的消息，下面照片上的右边一位就是该校的物理学家夏晶(Jing Xia音译），而另一位是研究生亚历克斯·斯特恩（Alex Stern），夏晶声称他已经建造出世界上最敏感的磁力显微镜即光纤萨尼亚克干涉仪（Sagnac interferometer ）。将其比作一架在欧文的鸟类学家可以用其来检查纽约一只鸟眼睛的望远镜。

加州大学欧文分校(University of California, Irvine)和其他地方的物理学家，已经制造出新的突破电和磁属性的二维量子材料,可以用其来构建未来的量子计算机及其他等先进的电子产品。

2017年4月份，有3个独立的研究已经在本月的《自然》（Nature）, 《科学进展》（Science Advances）以及《自然材料》（Nature Materials）杂志上发表,美国UCI的研究人员和加州大学伯克利分校（UC Berkeley）、劳伦斯伯克利国家实验室（Lawrence Berkeley National Laboratory）、普林斯顿大学（Princeton University）,中国复旦大学以及美国马里兰大学（University of Maryland）的研究人员合作开发出二维态新材料后对其物理性质进行研究，确定它们可以将计算机速度和功率推进到新的高度。更多信息请浏览

Cheng Gong, Lin Li, Zhenglu Li, Huiwen Ji, Alex Stern, Yang Xia, Ting Cao, Wei Bao, Chenzhe Wang, Yuan Wang, Z. Q. Qiu, R. J. Cava, Steven G. Louie, Jing Xia, Xiang Zhang. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. Nature, 2017, DOI: 10.1038/nature22060. Published online: 26 April 2017.

Abstract

The realization of long-range ferromagnetic order in two-dimensional van der Waals crystals, combined with their rich electronic and optical properties, could lead to new magnetic, magnetoelectric and magneto-optic applications^{1, 2, 3, 4}. In two-dimensional systems, the long-range magnetic order is strongly suppressed by thermal fluctuations, according to the Mermin–Wagner theorem⁵; however, these thermal fluctuations can be counteracted by magnetic anisotropy. Previous efforts, based on defect and composition engineering^{6, 7, 8, 9, 10}, or the proximity effect, introduced magnetic responses only locally or extrinsically. Here we report intrinsic long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers, as revealed by scanning magneto-optic Kerr microscopy. In this magnetically soft, two-dimensional van der Waals ferromagnet, we achieve unprecedented control of the transition temperature (between ferromagnetic and paramagnetic states) using very small fields (smaller than 0.3 tesla). This result is in contrast to the insensitivity of the transition temperature to magnetic fields in the three-dimensional regime. We found that the small applied field leads to an effective anisotropy that is much greater than the near-zero magnetocrystalline anisotropy, opening up a large spin-wave excitation gap. We explain the observed phenomenon using renormalized spin-wave theory and conclude that the unusual field dependence of the transition temperature is a hallmark of soft, two-dimensional ferromagnetic van der Waals crystals. Cr2Ge2Te6 is a nearly ideal two-dimensional Heisenberg ferromagnet and so will be useful for studying fundamental spin behaviours, opening the door to exploring new applications such as ultra-compact spintronics.