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

非技术摘要 许多先进技术的关键部分，例如量子计算元件，其尺寸我们没有有用的模型来描述相关物理；尺寸通常称为细观，即介于纳米和宏观之间。 在最小的长度尺度上，例如原子，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保持多长时间。 然而，当我们考虑更复杂的系统时，例如量子位、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或系统如何从一种状态转变到另一种状态或它可以保持激发态多长时间的理解。 首席研究员开发了一个由一侧只有 200 个原子的磁性纳米/介观粒子组成的模型系统，以发展这一重要的物理学。 在这个模型系统中，磁性状态、北极和南极（NS）的方向可以通过连接到每个颗粒的四根电线测量的颗粒的电特性来确定。 颗粒非常小，以至于 NS 方向会因热噪声而波动。 了解 NS 方向如何随时间变化（受热能或温度的影响）与该长度尺度上的突出物理问题直接相关。 此外，纳米/介观尺度粒子是解决与我们理解介观尺度物理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提供了美国高科技公司所需的劳动力。技术摘要该研究使用首席研究员研究小组开发的独特模型系统探索介观系统和其他介观现象的动力学。 动力学重点是对阿伦尼乌斯定律的探索，该定律尚未针对具有复杂反转过程的系统进行测试，另一个重点是对随机共振 (SR) 的研究。 首席研究员 (PI) 开发的技术可以解决这两个长期存在的物理问题。 这包括制造小至 50 nm 的单个磁性颗粒，并连接四个非磁性引线，用于各向异性磁阻的四个终端电阻测量。 PI 之前的研究测量了单个纳米/中尺度磁性粒子中的随机电报噪声 (RTN)，以及单个 RTN 振荡器如何组合产生 1/f 噪声。 对于阿累尼乌斯研究，两种状态的平均 RTN 停留时间是作为分隔状态和温度的能量势垒的函数来测量的。 能量势垒通过施加直流磁场来控制。 将数据与预测模型进行比较。 对于 SR 研究，表现出 RTN 的单个点受到小的交流磁场的影响。 交流场不足以驱动磁化穿过能量景观，从而产生 RTN。 然而，热噪声可以实现状态之间的转换，这是 SR 的核心。 探索磁化响应作为交流场强度、温度、粒子能垒的函数，测试了 SR 模型。该奖项反映了 NSF 的法定使命，并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，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.