iTHEMS Weekly News Letter


Dr. Tetsuo Hatsuda's new book,

Dr. Tetsuo Hatsuda's new book, "The Future of 'Useless' Research", will be published on April 9, 2021


Dr. Hatsuda's new book, "The Future of 'Useless' Research", will be published on April 9th, 2021. It is now available for pre-order!

Hot Topic



The annual in-house gathering entitled iTHEMS NOW and NEXT FY2020 was held on March 11th via zoom. The gathering is the occasion we share the current status and future perspectives on our research and organization. In the morning, keynote overview talks were given by Takashi Okada, Hiroyasu Miyazaki, Akinori Tanaka, and Ching-Kai Chiu, followed by the interdisciplinary talk which Don Warren and Catherine Beauchemin jointly presented. During subsequent lunchtime, a special session on the proper practices in conducting scientific researches was taken place. In the session, the participants discussed their research practices in small groups and later shared their discussions with all. The afternoon session was devoted to the progress reports from the working groups and the study groups. This time, we observed a moment of silence in honor of those affected by the 2011 Tohoku earthquake and tsunami during these presentations since it just marked precisely ten years from the calamity. Program Director Hatsuda's remarks concluded the gathering.

Seminar Report

Quantum Matter Seminar by Prof. Jan Budich on March 3, 2021


We are happy to invite Prof. Han Budich from the Dresden University of Technology to give a talk on March 3rd. The topic is Exceptional Topology of Non-Hermitian Systems: from Theoretical Foundations to Novel Quantum Sensors. Prof. Budich started with the review of the topological phases. After the introduction, he introduced the emergence of the exceptional points from non-Hermitian systems. The exceptional points, which are similar to Weyl nodes, possess intrinsic topological properties. Later, he proposed a novel idea of the quantum sensor to probe topological features from non-Hermitian platforms. It is great to have this nice talk.

Upcoming Events


Quantum Matter Seminar

Geometric nonlinear optical effects

March 16 at 17:00 - 18:15, 2021

Prof. Takahiro Morimoto (Associate Professor, Department of Applied Physics, The University of Tokyo)

Time: 5pm ~ 6:15pm (JST); 9am ~ 10:15am (CET)

The responses of materials to high intensity light, i.e., nonlinear optical responses, constitute a vast field of physics and engineering. While geometry and topology has been playing a central role in recent studies of condensed matters, geometrical aspects of nonlinear optical effects have not been fully explored so far. In this talk, I will show a few examples of nonlinear optical effects that have geometrical origins. First, I present that the second-order nonlinear optical effects including the shift-current, a candidate mechanism for recently discovered solar cell action in perovskite materials, has a close relationship to the modern theory of polarization, and is described by the Berry connection of Bloch wave function [1]. I will also discuss how electron correlations can enhance/modify shift current response in inversion broken materials. Next, I show that another second-order nonlinear effect, circular photogalvanic effect (CPGE), is governed by Berry curvature and shows quantization in Weyl semimetals [2]. I will report a recent measurement on chiral multifold fermion RhSi that observed a plateau structure in CPGE which is consistent with the expected quantization [3].

Venue: via Zoom

Event Official Language: English


iTHEMS Math Seminar

The Green-Tao theorem for number fields

March 22 at 16:00 - 18:10, 2021

Dr. Wataru Kai (Assistant professor, Mathematical Institute, Tohoku University)

5, 11, 17, 23, 29 are prime numbers which form an arithmetic progression of length 5. A famous theorem of Ben Green and Terence Tao in 2008 says there are arbitrarily long arithmetic progressions of prime numbers. Algebraic number theorists are also interested in more general numbers like square roots of integers. Recently, Mimura, Munemasa, Seki, Yoshino and I have established a generalization of the Green-Tao theorem in such a direction.

In the first 50 minutes of my talk, I would like to explain some background and technology behind the Green-Tao theorem. In the second half after a break, I explain the concept of number fields to formulate our generalization of their result. I will also discuss how one of the new difficulties, which I call the norm vs length conflict, is handled by a technique called Geometry of Numbers.

*Please contact Keita Mikami or Hiroyasu Miyazaki's mailing address to get access to the Zoom meeting room.

Venue: via Zoom

Event Official Language: English


Math-Phys Joint Seminar

Self-adjoint extension in quantum mechanics and non-Rydberg spectra of one-dimensional hydrogen atom

April 13 at 16:00 - 18:10, 2021

Prof. Takuju Zen (Professor, School of Environmental Science and Engineering, Kochi University of Technology)

We offer a beginner’s guide to the functional-analytical techniques in quantum mechanics, and cover its application to the 1D Coulomb problem. It is shown that the wave function at the diverging point of the Coulomb potential is mathematically described by three-parameter family of generalized connection conditions. A scheme is devised to physically implement the generalized conditions, which provides the way to experimentally realize non-Rydberg spectra in 1D Hydrogen atom.

Part 1, Self-adjoint extension of Hilbert space operator
Part 2, 1D Coulomb problem

Venue: via Zoom

Event Official Language: English

Upcoming Visitor

Dr. Nagisa Hiroshima thumbnail

March 21 - 23, 2021

Dr. Nagisa Hiroshima

Visiting Scientist, iTHEMS / Assistant Professor, Theoretical Physics Group, University of Toyama

Research fields: Dark Matter, High Energy Astrophysics

Visiting Place: RIKEN Wako Campus

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