SOP

(Final draft)

Statement of Purpose

Nam, Kee Hwan

 

In the future, I will be a physicist who will be one of the most creative scientists. I want to study solid state physics. I studied particle physics, which deals with pure quantum mechanical system and worked in a laboratory which uses extremely strong laser and generates high energy particles. What I notice from the experiences is that I like to find practical to objects that I apply theories that I learned and found. Solid state physics is appropriate for the purpose because it is easily verified by relatively smaller scale experiments than particle physics and high power laser science as well as knowledge in particle and laser physics is still effective and useful. Moreover, semiconductor devices and their derived applications are becoming more and more important for the modern world, so I can contribute to progressing information technology. My interest is to apply theoretical method to solid state materials and confirm it from experiments in order to understand their physical characteristics.

My first research was neutrino phenomenology and particle detector development in master’s course. In neutrino physics, I studied massive neutrinos and their mixing parameters. According to a number of neutrino oscillation experiments, the interaction eigenstates of neutrinos are not the mass eigenstates as well as neutrinos must have non-zero masses. This mixing is similar structure  to but much larger than that of quark sector. I assumed a model so called “complex quark-lepton complementarity” and derived the parameters from the model. The model is based on two ideas. One of them is that theoretical frame explaining quark sector, Cabbibo-Kobayashi-Maskawa matrix, is very similar to that of neutrino sector, Pontecorvo-Maki-Nakagawa-Sakata matrix. The matrices are factorized to three elementary rotation matrices(Eulerian rotation matrices) and one complex phase matrix. The other is that each sum of angles corresponding to the same elementary matrix in two mixing matrices is almost pi/4. This is called quark-lepton complementarity. Because two matrices describes rotation in 3-dimensional complex space, the complementarity can be generalized to the 3-dimensional complex space. In the 3-dim complex space, one of the eigenvectors of the matrix can be taken as the axis of rotation. After taking the axis, we can determine rotation angles of two matrices around the axis. My argument is two angles have relation similar to Pythagorean theorem. The relation acts as a constraint to mixing angles, so unknown mixing parameters can be derived. The results were published in Journal of The Korean Physical Society.

In particle detector project, my task was to design detector chamber and to simulate electric field and particle trajactory. The chamber was type of multiwire proportional chamber. I made the chamber design with a computer aided design software. The chamber was operated in vacuum because high voltage was assigned to multi-wire and poor vacuum might cause to air breakdown.  To calculate electric field, relaxation method to solve laplace equation were employed. After the calculation, I made simulation code of trajactory of charged particle induced by cosmic rays in the field. This result was presented in autumn meeting of The Korean Physical Society at October 2006, and published in Journal of The Korean Physical Society after I had graduated from the course.

The second research was ultra-high power laser expreiment. When I was in Advanced Photonics Research Institute, I participated in extremely intensive laser application experiments, which were particle acceleration and secondary radiation generation. In the experiments, my major tasks were to operate detectors and to analyse obtained signal. When a target is irradiated by extremely intensive and short laser pulse, charged particles are accelerated and secondary lights like water window x-ray and x-ray laser are generated by interaction between laser and plasma. To distinguish particle species, we developed Time-of-flight spectrometer and Thomson parabola spectrometer. In the development, I did assemble, examine, calibrate, and operate the detectors and wrote program code to diagnose characteristics of particles: energy, current, temperature, divergence, and spectrum. Another part of my tasks was to produce ultra-thin film of a few nm thickness to use as laser target. I made the film with spin-coating method from an organic polymer and multi-layer film of the polymer and metal with plasma enhanced chemical vapor deposition devices. The film was used as a target to accelerate heavy ions with relativistic kinetic energy. Some of the results have been published and others are submitted to a journal and reviewing.

As shown above, I am good at dealing with physical problems by mathematical and computational methods because I have experienced laboratories of both of theory and experiment. Even though portion for me to perform works related to solid state physics is small, my experience is benefit because when I try to solve a problem, it will allow me to approach different sight of view to traditional ways. Hence, I would propose and perform experiments to prove my theories and arguments.

All in all, I was a generalist who is experienced in many fields: particle, plasma, optics, and even nuclear physics and in various methodologies: theoretical, computational, and experimental researches. Now, I want to proceed a specialized physicist studying solid state material. Explaining my academic objectives concretely, I want to find mathematical structure to understand matters, to compute its physical properties using computational tools such as density functional theory if there is no analytic solution, and to prove it from experiments. My experiences will be helpful to research because broad experiences should give me creative ideas and solutions for the unsolved problems. I can prove my proficiency in practical research. I want to be a physicist indeed. I am finding a teacher to lead me a professional physicist and believe the teacher is in Universeity of Texas at Austin.

i. First paragraph ? Describe the general areas of research that interest you and why. (This is
helpful for a committee to determine which professors should read your application.)

1) Quantum optics

What I concern and am interested in is quantumoptics and its application. The major part of my experience is what I was atAdvanced Photonics Research Institute, which is largest among the institute tostudy optics and photonics in Korea. I installed instruments, analyzed results,and searched literatures related to high field laser plasma experiments. Onthis basis, it is natural for me to be interested in photonics. I think quantumoptics is the only remained way to make breakthrough the limited scientificknowledge because most of what we made are worked by the law ofelectromagnetism. In other words, the electromagnetism rules human life.

 

2) Solid state physics

Semiconductor device rules the world andbecomes more and more important nowadays. To reveal physical laws to explainproperties of solid state devices seems almost to be completed but many thingsto discover are still remained. I want to study solid state physics in yourdepartment. Specially, my interest is to apply theoretical method to solidstate material in order to found proper physical laws. Though I am involved totheoretical physics, I am well trained to experimental way as well.

ii. Second paragraph and Third paragraph ? Descibe some research projects that you worked on.
Tell us what you found, what you learned, what approaches you tried. It’s fine to say that you
were unable to prove what you wanted or to solve your problem.

My first research experience was neutrino phenomenology and particle detector development in master’s course. The results were published in Journal of Korean Physics Society at 2006. The research was performed with my advice proffesor. In neutrino physics, I studied massive neutrinos and their mixing parameters. I assumed a model so called “quark-lepton complementarity” and derived the parameters from the model. In particle detector project, my job was detector chamber design, electric field simulation, and the team leader. I made chamber design with AutoCAD design program. Electric field simulation was performed with a program written in C by ourselves. I advanced my leadership by this.

Second, I worked at Mindalive co., Ltd., which is a company to develop and serve education program for gifted children in science and mathematics. When I was in the company, my task was to review contents in educational games and textbooks. Moreover, my position was as a communication bridge between program developers and contents designers.

The last major experience was ultra-high power laser expreiment. When I was in APRI, I participated in four kinds of high power laser application, which are proton acceleration, electron acceleration, high order harmonic generation, and X-ray laser holography. Because I was a technical assistant, major tasks assigned to me were high vacuum system operation, optical path alignment, particle detection and diagnostic system operation, experimental result analysis, and development of computer programs to support experiments and their analyses. Minor tasks were also assigned, such as computing cluster management, radiation safety management and thin semiconductor film fabrication. From these, what I get are various. For example, I learnt using techniques of actual tools, analyzing vast amount of data, basic and advanced optics with laser, and difference between theory and experiment in real situation.

All in all, in any case my tasks included theory, experiment, and computer simulation. My experieces will be helpful to research in any case because wide range of experiences should give me creative idea and solutions for the given problems.

iii. Fourth paragraph ? Tell us why you feel you need a Ph.D.. Look back to section 2 and explain
what in there appealed to you.

As I was a child, I wanted to be a scientist, specially a physicist. If I get Ph.D., I will advance my research topic. I am a very curious boy. Asking and answering questions about nature and science make me happy and excited. More exactly, I would like to study the field with theoretical methods. Natural scientists have two ways to research: theory and experiment. I think to reveal mathematical structure in the nature is to give us more practical knowledge and suggest which way for us to choose progress the science. Moreover, because I have well experienced as an experimentalist, I can propose theories to get along with experiments.

iv. Fifth paragraph ? Tell us why you want to come to CMU.Whom might you like to work with?
What papers have you looked at from CMU that you enjoyed reading? What will CMU teach
you?