CAREER: Excitons, electron-hole plasmas, and electron-hole liquids in the time domain

非技术性总结这个职业奖支持在二维材料中发现的新型相变的理论和计算研究和教育。相变在我们周围很常见;例如，在水的沸腾中，或者在水蒸气冷凝成雨的逆过程中。在某些半导体材料中，可能发生非常相似的相变。当暴露在连续激光束的能量下时，材料中的电子从正常的量子态被激发到另一个量子态。然而，处于新状态的受激电子感觉到它留下的“空穴”的有效吸引力，即它曾经所在的地方。如果足够的电子被泵入激发态，它们-以及它们的空穴对应物-可以经历气体到液体类型的相变。这种相变，虽然其成分是电子和空穴，但具有与水中发现的相变相似的特性。然而，一个显着的区别是，这发生在超快的时间尺度（纳秒），它涉及驱动激光。重要的是，由于这些成分明显是量子物体，因此出现了许多令人兴奋和有趣的特性。所讨论的材料形成二维薄片，这意味着它们可以被纳入柔性电子产品中。最重要的是，现在有可能在纳秒内将它们的行为从简单的半导体（通常是透明材料）转换为金属和反射的物体。这在太阳光收集和通过光子学绕过摩尔定律方面具有很有前途的应用。该项目涉及算法和软件的大量开发，并将以开源代码的形式向社区传播。除了研究之外，该CAREER奖还将通过与美国物理教师协会（AAPT）合作，将他们成功的“Bootstrap for Computational Modeling in Physics First”研讨会转化为远程学习课程，支持美国STEM教育的改善。该研讨会将计算建模集成到8年级和9年级的物理课程中，并且通常亲自参加。远程学习版本的开发将使更多的参与者受益，特别是来自农村地区的参与者，因为农村地区可能无法随时参加长时间的面对面讲习班。由于计算在STEM工作场所中发挥着越来越大的作用，因此早期的准备和接触将提高学生的整体能力。这个版本的研讨会将首先部署在北卡罗来纳州，并将通过AAPT在全国范围内进一步传播。技术总结这个职业奖支持超快平衡相变的理论和计算调查的研究和教育。该研究小组将研究在室温下过渡金属二硫属化物中发生的高光激发时向电子空穴液体（EHL）的转变。由于相变的超快性质，时域方法是至关重要的。该项目将确定创建和维持EHL的条件，其对外部刺激和邻近耦合紧急订单的反应，其可调性，以及其运输和转移动力学。该项目通过对电子-空穴液体的理解，可以将其应用于太阳光收集、光子学绕过摩尔定律等新的装置中。该项目通过非平衡态科学的理论研究和计算方法开发，为高影响力科学提供了机会。这个问题的一个重要方面是，它必须在时域中解决，而不是诉诸通常的平衡分析技术。PI将通过非平衡多体理论和与实验界的合作来解决这一挑战。研究小组将考虑不依赖遍历性的非平衡相变的概念，通过在时域中的对称性破缺状态下进行自洽计算。通过这些方法，研究团队将重新评估我们如何看待量子材料中的非平衡过程和相变，并打破对平衡概念的依赖。整个项目中创建的算法和软件将以开源代码的形式向社区传播。除了研究之外，该CAREER奖还将通过与美国物理教师协会（AAPT）合作，将他们成功的“物理学计算建模Bootstrap”研讨会转化为远程学习课程，以支持美国STEM教育的改进。该研讨会将计算建模集成到8年级和9年级的物理课程中，并且通常亲自参加。远程学习版本的开发将使更多的参与者受益，特别是来自农村地区的参与者，因为农村地区可能无法随时参加长时间的面对面讲习班。由于计算在STEM工作场所中发挥着越来越大的作用，因此早期的准备和接触将提高学生的整体能力。这个版本的研讨会将首先部署在北卡罗来纳州，并将通过AAPT在全国范围内进一步传播。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

NONTECHNICAL SUMMARYThis CAREER award supports theoretical and computational research and education in a new type of phase transition found in two-dimensional materials. Phase transitions are commonly found around us; for example, in the boiling of water, or in the reverse process of condensing water vapor into rain. In some semiconducting materials, a remarkably similar phase transition may occur. When exposed to the energy a continuous laser beam, electrons in the material get excited from their normal quantum state into another. However, the excited electron in its new state feels an effective attraction to the "hole" it left behind, i.e. the place where it used to be. If enough electrons get pumped into the excited state, they - and their hole counterparts - can undergo a gas-to-liquid-type phase transition. This phase transition, although its constituents are electrons and holes, has characteristics similar to the one found in water. However, a significant difference is that this happens on ultrafast time-scales (nanoseconds), and it involves a driving laser. Importantly, because the constituents are manifestly quantum objects, a host of exciting and interesting properties arise.The materials in question form two-dimensional sheets, which means they may be incorporated into flexible electronics. On top of this, there is now the possibility of switching their behavior within nanoseconds from being a straightforward semiconductor (which are typically transparent materials) to being an object that is metallic and reflecting. This has promising applications for solar-light harvesting and for bypassing Moore's law through photonics. The project involves substantial development of algorithms and software, which will be disseminated to the community as open-source code.In addition to the research, this CAREER award will support the improvement of STEM education in the U.S. by partnering with the American Association of Physics Teachers (AAPT) to turn their successful "Bootstrap for Computational Modeling in Physics First" workshop into a distance-learning course. The workshop integrates computational modeling into 8th and 9th grade physics courses, and is typically attended in person. The development of a distance-learning version will enable reaching a much larger set of participants, in particular from rural areas which may not have ready access to long in-person workshops. Since computation is playing an increasingly larger role in the STEM workplace, earlier preparation and exposure will improve students' overall capabilities. This version of the workshop will initially be deployed in North Carolina, and will be further disseminated through AAPT across the country.TECHNICAL SUMMARYThis CAREER award supports research and education in theoretical and computational investigations of ultrafast out-of-equilibrium phase transitions. The research team will study the transition into an electron-hole liquid (EHL) that occurs at room temperature upon high photoexcitation in transition-metal dichalcogenides. Due to the ultrafast nature of the phase transition, time-domain approaches are critical. This project will determine the conditions for creating and sustaining the EHL, its response to external stimuli and proximity-coupled emergent orders, its tunability, and its transport and transfer dynamics. This understanding will enable the use of the electron-hole liquid in novel devices, and, in particular, in applications for solar-light harvesting and for bypassing Moore's law through photonics.The project exploits an opportunity for high-impact science through theoretical study and computational method development for nonequilibrium science. One essential aspect of the problem is that it must be tackled in the time domain, rather than resorting to the usual equilibrium analytic techniques. The PI will address this challenge through nonequilibrium many-body theory and through collaboration with the experimental community. The research team will consider the concept of a nonequilibrium phase transition without reliance on ergodicity by performing self-consistent calculations in the broken-symmetry states in the time domain. Through these approaches, the research team will re-evaluate how we think about nonequilibrium processes and phase transitions in quantum materials, and break the reliance on equilibrium concepts. The algorithms and software created throughout the project will be disseminated to the community as open-source code.In addition to the research, this CAREER award will support the improvement of STEM education in the U.S. by partnering with the American Association of Physics Teachers (AAPT) to turn their successful "Bootstrap for Computational Modeling in Physics First" workshop into a distance-learning course. The workshop integrates computational modeling into 8th and 9th grade physics courses, and is typically attended in person. The development of a distance-learning version will enable reaching a much larger set of participants, in particular from rural areas which may not have ready access to long in-person workshops. Since computation is playing an increasingly larger role in the STEM workplace, earlier preparation and exposure will improve students' overall capabilities. This version of the workshop will initially be deployed in North Carolina, and will be further disseminated through AAPT across the country.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.