Date: 18-Dec-2019 Time: 10:00 am
Venue: Conference Hall 320
Speaker: Dr. Takahiro Misawa (Institute for Solid State Physics, University of Tokyo)
Accurate numerical methods for treating quantum many-body systems are expected to play important roles for clarifying the nature of novel quantum phases such as high-Tc superconductors and topological materials. Recently, we have developed a method that combines ab initio derivations of the low-energy effective Hamiltonians for real materials and accurate analyses of the obtained low-energy effective Hamiltonians. By using this method, we can clarify electronic structures of real materials in a non-empirical way. In this seminar, I will explain the details of this method and show its applications to high-Tc superconductivities in iron-based superconductors [1,2], cuprates [3,4], and interfaces of the cuprates . As a result, we find that the effective attractive interactions induced by the enhancement of the uniform charge susceptibility stabilize the superconductivities both in the iron-based superconductors and the cuprates. This result offers a useful guideline for designing superconductors with higher transition temperatures.
I will also show our recent studies on the quantum transport phenomena in topological materials. Based on the real-time evolution of the wave functions, we have developed a numerical method for treating quantum transport phenomena in topological materials [6,7]. Using the method, we analyze the spin-charge conversions and spin switching in a topological Dirac semimetal attached to a ferromagnetic insulator . As a result, we show that the charge current induced by the precessing magnetization is semi-quantized, i.e., it depends only on the distance between the two Dirac points in momentum space and hardly depends on the disorder strength. We also show that the electric field applied to the topological Dirac semimetal exerts a spin torque on the local magnetization in the ferromagnetic insulator via the exchange interactions and this torque can reverse the direction of the magnetization in the ferromagnetic insulator. Our study demonstrates that the topological Dirac semimetal offers a less-dissipative platform for spin-charge conversion and spin switching .
 T. Misawa, K. Nakamura, and M. Imada, Phys. Rev. Lett. 108, 177007 (2012).
 T. Misawa and M. Imada, Nat. Commun. 5, 5738 (2014).
 M. Hirayama, T. Misawa, et al., Phys. Rev. B 99, 24515 (2019).
 T. Ohgoe, M. Hirayama, T. Misawa, et al., arXiv:1902.00122.
 T. Misawa et al., Sci. Adv. 2, e1600664 (2016).
 T. Misawa, R. Nakai, and K. Nomura, Phys. Rev. B 100, 155123 (2019).
 T. Misawa and K. Nomura, arXiv:1907.10459.
About the speaker:
Dr. Takahiro Misawa is a theoretical physicist working in the field of strongly correlated electron systems with a special focus on the high-temperature superconductivities induced by the electronic correlations. He is a Principle Investigator of Professional Development Consortium for Computational Materials Scientists (PCoMS) in Institute for Solid State Physics, University of Tokyo, Chiba, Japan since 2016.
He completed his Bachelor degree from University of Tokyo (2004) and obtained Master degree from University of Tokyo in 2006. He earned a PhD in Engineering from Department of Applied Physics, University of Tokyo in 2008. He worked as a Postdoctoral Fellow (2008-2009) and later as a Research Associate (2009-2016) in Professor Masatoshi Imada’s Group at Department of Applied Physics, University of Tokyo. In 2016, he moved to Institute for Solid State Physics, University of Tokyo as a Principle Investigator.
Dr. Misawa’s expertise in high-temperature superconductivities in iron-based superconductors and cuprates superconductors, quantum transport phenomena in topological materials, exotic quantum phases in frustrated magnets, and development of open-source software packages for strongly correlated electrons systems.