Dynamics of Mesoscopic Systems Developed with a Tunable Individual Particle Model System

许多先进技术的关键部分，如量子计算元件，都是我们没有有用的模型来描述相关物理的尺寸;尺寸通常被称为中尺度，即介于纳米和宏观之间。 在最小的长度尺度上，比如原子，我们有模型来计算电子如何在能级之间跃迁，以及它们可以在激发态或高能态停留多久。 然而，当我们考虑更复杂的系统时，例如量子比特，聚合物或塑料动力学以及生物过程，增加的复杂性限制了我们对系统动力学的理解，或者系统如何从一种状态过渡到另一种状态，或者它可以保持在激发态多久。 首席研究员开发了一个由磁性纳米/中尺度粒子组成的模型系统，每侧小至200个原子，以开发这一重要的物理学。 在这个模型系统中，磁状态，北，南极（NS）的方向可以确定由四根导线连接到每个粒子测量的粒子的电特性。 粒子是如此之小，NS取向波动从热噪声。 了解NS方向如何随时间变化，受热能或温度的影响，直接关系到这个长度尺度上的突出物理问题。 此外，纳/中尺度粒子是解决与我们对中尺度物理学的理解有关的其他突出物理问题的理想模型系统。 这项研究是由研究生和本科生进行的，作为他们在经济上重要的先进技术和物理技术培训的一部分。 这些训练有素的学生提供劳动力所需的美国的高科技公司。技术abstractThe研究探讨了中尺度系统和其他中尺度现象的动力学使用一个独特的模型系统开发的首席研究员的研究小组。 动力学的重点是探索的阿克里尼乌斯定律，已被测试的系统与复杂的逆转过程和其他重点是随机共振（SR）的调查。 这两个长期存在的物理问题都可以通过首席研究员（PI）开发的技术实现。 这包括制造小至50 nm的单个磁性颗粒，并连接四个引线，用于测量各向异性磁阻的四个端子电阻。 PI先前的研究已经测量了单个纳米/中尺度磁性粒子中的随机电报噪声（RTN），以及单个RTN振荡器如何联合收割机产生1/f噪声。 对于Arabius研究，两种状态中的每一种的平均RTN停留时间被测量为分离状态和温度的能量势垒的函数。 能量势垒由直流磁场的应用控制。 将数据与预测模型进行比较。 对于SR研究，将表现出RTN的单个点置于小的交流磁场中。 交流磁场不足以驱动磁化通过能量景观，从而产生RTN。 热噪声，但是，可以使状态之间的过渡，这是在SR的心脏。探索作为交流磁场大小，温度，粒子能量屏障的功能的磁化响应测试SR的模型。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 abstract The key piece of many advanced technologies, such as quantum computing elements, are of a size for which we do not have useful models to describe the relevant physics; the size is commonly referred to as meso, that is between nano and macro. At the smallest length scales, such as atoms, we have models to calculate how the electrons transition between energy levels and how long they can stay in excited or high energy states. However, as we consider more complex systems, such as quantum bits, polymer or plastics dynamics, and biological processes, the added complexity has limited our understanding of the dynamics of the system or how the system transitions from one state to another or how long it can stay in an excited state. The Principal Investigator has developed a model system consisting of magnetic nano/mesoscale particles as small as 200 atoms on a side to develop this important physics. In this model system, the magnetic state, the orientation of the North and South poles (NS) can be determined by the electrical properties of the particles measured by four wires attached to each particle. The particles are so small that the NS orientation fluctuates from thermal noise. Understanding how the NS directions change with time, influenced by the thermal energy or temperature, is directly related to the outstanding physics questions at this length scale. In addition, the nano/mesoscale particles are an ideal model system for other outstanding physics questions related to our understanding of mesoscale physics. The research is conducted by both graduate students and undergraduates as part of their technical training in economically important advanced technologies and physics. These trained students provide the workforce needed by America’s high technology companies.Technical abstractThe research explores the dynamics of mesoscale systems and other mesoscale phenomena using a unique model system developed by the Principal Investigator’s research group. The dynamics focus is an exploration of the Arrhenius law that has been untested for systems with complex reversal processes and the other focus is an investigation of stochastic resonance (SR). Both of these long standing physics questions are within reach with the technology developed by the Principal Investigator (PI). This consists of the manufacture of individual magnetic particles as small as 50nm with four nonmagnetic leads attached for four terminal resistance measurements of the anisotropic magnetoresistance. Previous research by the PI has measured random telegraph noise (RTN) in individual nano/mesoscale magnetic particles and how individual RTN oscillators can combine to produce 1/f noise. For the Arrhenius studies, the average RTN dwell times for each of the two states is measured as a function of both the energy barrier separating the states and temperature. The energy barrier is controlled by the application of a dc magnetic field. The data are compared to predictive models. For the SR research a single dot exhibiting RTN is subjected to a small ac magnetic field. The ac field is not sufficient to drive the magnetization through the energy landscape giving rise to the RTN. The thermal noise, however, can enable the transition between states, which is at the heart of SR. Exploring the response of the magnetization as functions of ac field magnitude, temperature, particle energy barriers tests the models of SR.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.