Youth and science

Nguyen Danh Tung: "JINR is known in Vietnam"

This year, two JINR employees from the Socialist Republic of Vietnam Nguyen Van Thiep and Nguyen Danh Tung defended their dissertations for the degree of candidate of physical and mathematical sciences. Nguyen Danh Tung defended his thesis on "Charge fluctuations and superconductivity in strongly correlated electronic systems" on 26 April. Today, we introduce a young BLTP employee to the readers of our weekly.

Please, state as briefly as possible the essence of your dissertation paper.

The essence of my dissertation is to study the impact of interactions in materials on the properties of high-temperature superconducting materials, especially on the superconducting temperature. Electronic spin-spin interactions, Coulomb interactions between electrons, electron-lattice vibrations (or electron-phonon interactions) and other interactions have been discovered in high-temperature superconducting materials. These interactions are different for different materials depending on their composition and structure. They play different roles, influencing the superconducting temperature of the material. The dissertation examines the relationship between interactions in high-temperature superconducting materials and superconducting properties, especially superconducting temperature.

Previously, Professor N.M.Plakida (BLTP) and other scientists showed that spin-spin fluctuations play an important role in the superconductivity temperature, but little attention was paid to other interactions. In my thesis, we extend the previous model to include Coulomb and electron-phonon interactions, and study how they affect the properties of high-temperature superconducting materials. The main results of the thesis show that Coulomb interaction and electron-phonon interaction also play a role in superconducting properties, however, compared to spin-spin fluctuations, their contribution is very small and spin-spin fluctuations play an important role in the mechanism of superconductivity.

Why did you choose theoretical physics and the topic of superconductivity?

I like mathematics and physics because they are logical. However, physics is closer to us and appears everywhere in our lives. I wanted to know why physical phenomena occur and how physics can be applied to life, so I chose physics. It would be very interesting if we could use mathematics to calculate in physics and predict what will happen in the future, that is why I really love theoretical physics. The topic of superconductivity has interested me since my second year at university because of new phenomena and applications, especially in high-speed trains. When I was at university, I was particularly fascinated by a lecture on "airways" (we can make objects float in the air, influenced by the wind from the airways). Similar lectures can be found at: https://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/24.12.html.

I thought that the same thing would happen with the "magnetic track" because two identical poles would repel each other. Then my friend and I bought a lot of magnets and made a "magnetic track", hoping that magnetic trains would travel along it. However, this was not successful. Afterwards, I read about superconducting materials and how they could be used in high-speed trains and I became very interested. When I arrived in Dubna, I did not know what topic I would study next, for it largely depended on my supervisor. And it turned out to be a great success for me as Professor Plakida that became my supervisor, was an expert in superconductivity, I followed this topic and my dream of researching superconductivity came true.

How popular is physics in Vietnam today? What is the competition for entering the universities for physics departments or physics specialties? What university did you graduate from?

Today, in Vietnam many people know about natural sciences (mathematics, physics, chemistry). Students have a basic knowledge of the physical phenomena around us, they understand why things happen the way they do (such as, Newton's law, electric current, others). There are even excellent students in Vietnam that have won international prizes in physics. I can say that mathematics and physics are very popular in our country and people are interested in these subjects. Competitions for entering the universities are held annually. For physics departments or physics specialties, the entrance score is very high. Students need to score about 9 out of 10 points in each of the three subjects (mathematics, physics, chemistry). Sometimes some applicants that score 9.5 out of 10 in each subject may fail.

I graduated from Hanoi Normal University. Every year, the physics department at my university selects 90 students from all over the country. Of these, only 14 gifted students are selected for a special group through additional exams. At the end of each academic year, these students undergo competitive testing that weeds out the weak. I graduated from such a group.

How did you learn about JINR? Why did you decide to work at BLTP?

When I received my master's degree from the Institute of Physics of the Vietnam Academy of Science and Technology (VAST), I began preparing documents for my PhD application. At the same time, Professor Le Hong Khiem that at that time was the Plenipotentiary Representative of the Government of Vietnam at the Joint Institute, told my supervisor in Vietnam about the cooperation programme between VAST and JINR. He wanted to find students to work at JINR as part of this cooperation. Then my supervisor asked me what I thought about this project and whether I wanted to work in Russia. JINR is well known in Vietnam, many famous Vietnamese scientists worked there. I thought this was a great opportunity to work and prepare my dissertation, so I decided to fly to Dubna.

What do you know about your compatriot, student of N. N. Bogolyubov, theoretical physicist, academician Nguyen Van Hieu that worked at JINR in the 1950s-1960s?

In Vietnam, Professor Nguyen Van Hieu is considered the number one scientist and most people know him. He made a major contribution to the development of physics research institutes. He had many students and today, they are leading physics professors in Vietnam. I represent the younger generation of scientists, I know Professor Nguyen Van Hieu mainly from colleagues, from books, newspapers and television. He published numerous papers on various topics in theoretical physics. His publications are still included in books today. I met and talked with Professor Nguyen Van Hieu several times. He was a very open, sociable and warm person. He was loved and respected by many.

How do you remember Nikolay Plakida? Did you communicate with him outside of work?

Before meeting Professor N.M. Plakida, I heard from my colleagues that he was a famous and excellent theoretical physicist. I thought he was a strict person that was difficult to communicate with. However, he turned out to be open and friendly. I asked him to become my supervisor and he agreed. Then he helped me to prepare the documents required for the work at BLTP. Gradually, while working with him, I began to treat him as my close relative... He was the author of many publications in both Russian and English. He never rushed to conclusions, he fully thought through every aspect of the problem. He was a good teacher, knew how to help students to understand difficult points and felt whether his students understood him or not. When his students had a clear understanding of a topic, he directed them to more complex things.

Most of the time we just talked about work. From time to time he asked me about my family, about my friends and about Vietnam. In the last days of his life, he did not stop working hard. I remember he told me that he would help me to prepare the required documents for my defense and asked me to wait for his call. However, he never called because he was hospitalized, unable to speak and later, he died. In my deep heart, I wanted him to take part in the graduation ceremony. To my regret, this will no longer happen...

What are your future scientific plans? Are they associated with JINR?

I want to continue working at JINR for several years; I still have a lot to learn at BLTP. My goal is to make as many publications as possible. In addition, if possible, I would like to contribute as much as I can to the cooperation between JINR and VAST.

The work of a theoretical physicist is sedentary. Do you play any sports?

Yes, the work of a theoretical physicist is sedentary. We have to sit in front of a computer all day long and carry out analytical or numerical calculations and write articles. Sometimes, I play table tennis. This sport can be practiced both indoors and outdoors, in summer and winter. If I have time, I like to run and just walk along the river bank to relax and get some fresh air.

What are your wishes to your laboratory colleagues and all JINR employees in 2024?

First of all, I would like to thank Directorate of BLTP for creating favorable conditions for the preparation of my dissertation. I would also like to thank my supervisors, colleagues, family and friends for their support. I wish everyone health, happiness and all the best. And Happy New Year 2024!

Olga TARANTINA,
photo by Elena PUZYNINA