Band flattening at the Fermi level as a precursor of quantum electron crystallization

自1911年发现超导性以来，建造室温超导体一直是人们的梦想。 在相当长的一段时间里，观察到超导性的最高温度保持在23 K（或-250 C）;然而，在1986年，高温超导体被发现，超导性在高压下可以达到138 K（或-135 C），最近甚至可以达到203 K（-70 C）。 目前，室温超导性最有希望的候选者是所谓的“平带材料”（即，在某些动量范围内，电子的能量不依赖于它们的动量的材料）。 PI和他的团队最近在硅锗量子威尔斯阱中发现了这种行为，并正在对这种材料进行研究。 拟议的活动提供了独特的机会，以培养学生在新技术的尖端当今的能力。 东北大学以其标志性的合作学习（“co-op”）教育而闻名，该教育为学生提供了在学习期间进行实践体验学习的机会。在这个程序中，PI有一个显着的记录，在培养本科生和研究生在他的laborator.Technical AbstractThe拟议的工作是一个实验努力，明确建立平坦的二维电子系统中的电子带，可能是至关重要的建设室温超导。 该小组打算研究硅锗量子威尔斯前所未有的质量开发的PI？s组，以及ZnO基异质结构的可比质量。 在过去，PI的团队通过传输方法观察到硅锗量子威尔斯中的能带平坦化。 然而，热力学特性，如电子光谱，只能通过热力学测量可靠地获得。 PI和他的团队打算使用PI中已有的技术？在东北大学的实验室测量热力学磁化和二维系统中电子的热电势。 第一种方法得到电子的能量平均有效质量;第二种方法得到费米能级上的有效质量。 在极低的电子密度极限下，费米能级上能量平均质量的饱和和质量的发散是电子带变平的标志。 该小组还打算调查量子维格纳晶体形成在这些超净系统中作为这种效应的直接后果。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Non-Technical AbstractConstruction of room-temperature superconductors has been a dream since the discovery of the superconductivity in 1911. For quite a while, the highest temperature, at which superconductivity was observed, remained at 23 K (or -250 C); however, in 1986, high-temperature superconductors were discovered with superconductivity surviving up to 138 K (or -135 C) and, more recently, even up to 203 K (-70 C) under high pressure. Presently, the most promising candidates for room-temperature superconductivity are the so-called 'flat-band materials' (i.e., the materials in which the energy of electrons does not depend on their momentum in some range of momenta). The PI and his team have recently discovered such behavior in silicon-germanium quantum wells and are pursuing the investigation of this material. The proposed activities offer unique opportunities to train students in novel technologies at the cutting edge of present-day capabilities. Northeastern University is famous for it's signature cooperative learning ('co-op') education, which affords students the opportunity for hands-on experiential learning during their studies. Within this program, the PI has a remarkable record in training undergraduate and graduate students in his laboratory.Technical AbstractThe proposed work is an experimental effort to unequivocally establish the flattening of the electronic band in the two-dimensional electron systems that may be vital for the construction of the room temperature superconductivity. The team intends to study silicon-germanium quantum wells of unprecedented quality developed by the PI?s group, as well as ZnO-based heterostructures of comparable quality. In the past, the band flattening in silicon-germanium quantum wells was observed by transport methods by the PI's team. However, the thermodynamic characteristics, like the spectrum of electrons, can only be reliably obtained by thermodynamic measurements. The PI and his team intend to use the techniques already available in the PI?s laboratory at Northeastern University to measure the thermodynamic magnetization and the thermopower of the electrons in two-dimensional systems. The first method yields the energy-averaged effective mass of the electrons; the second method yields the effective mass on the Fermi level. The saturation of the energy-averages mass and the divergence of the mass at the Fermi level in the limit of very low electron densities is the hallmark of the flattening of the electron band. The group also intends to investigate the quantum Wigner crystal formation in these ultra-clean systems as a direct consequence of this effect.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.