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

许多先进技术的关键部分，如量子计算元素，其规模之大，我们没有有用的模型来描述相关的物理；尺寸通常被称为中观，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转换，以及它们能在激发态或高能态停留多长时间。然而，当我们考虑更复杂的系统，如量子比特、聚合物或塑料动力学以及生物过程时，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转变到另一种状态，或者它能保持在激发态多长时间。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，每边只有200个原子，以发展这一重要的物理学。在这个模型系统中，磁态、南北极（NS）的方向可以通过粒子的电学特性来确定，这些粒子通过连接在每个粒子上的四根导线来测量。这些粒子非常小，以致于其NS取向随热噪声而波动。了解NS方向在热能或温度的影响下如何随时间变化，直接关系到这个长度尺度上悬而未决的物理问题。此外，纳米/中尺度粒子是与我们对中尺度物理的理解相关的其他突出物理问题的理想模型系统。这项研究由研究生和本科生共同进行，作为他们在经济上重要的先进技术和物理方面的技术培训的一部分。这些训练有素的学生为美国的高科技公司提供了所需的劳动力。技术摘要：本研究使用由首席研究员研究小组开发的独特模式系统探索中尺度系统和其他中尺度现象的动力学。动力学重点是对具有复杂反转过程的系统尚未测试的Arrhenius定律的探索，另一个重点是随机共振（SR）的研究。这两个长期存在的物理问题都可以通过首席研究员（PI）开发的技术来解决。这包括制造小至50nm的单个磁性颗粒，并连接四个非磁性引线，用于测量各向异性磁电阻的四个终端电阻。PI之前的研究已经测量了单个纳米/中尺度磁性颗粒中的随机电报噪声（RTN），以及单个RTN振荡器如何组合产生1/f噪声。对于阿伦尼乌斯的研究，两种状态的平均RTN停留时间是作为分离状态的能量势垒和温度的函数来测量的。能量势垒由施加直流磁场来控制。将这些数据与预测模型进行比较。在SR研究中，一个显示RTN的单点受到一个小的交流磁场的作用。交流磁场不足以通过能量景观驱动磁化，从而产生RTN。然而，热噪声可以实现状态之间的过渡，这是sr的核心。探索磁化作为交流场大小，温度，粒子能量势垒的函数的响应测试sr模型。这一奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.