2017 Fiscal Year Annual Research Report
| Project/Area Number |
16J07545
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| Research Institution | The University of Tokyo |
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Principal Investigator |
張 驍驍 東京大学, 工学系研究科, 特別研究員(DC1)
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| Project Period (FY) |
2016-04-22 – 2019-03-31
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| Keywords | Weyl semimetal / Dirac semimetal / monopole / Luttinger liquid / magnetoelastic / localization / Coulomb interaction |
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| Outline of Annual Research Achievements |
We revised the manuscript on the ultrasonic phenomena in a chiral magnet inhabited by emergent magnetic monopoles connected by skyrmion tubes. It was accepted and published in New. J. Phys.
Our second topic related to Weyl semimetals is the phenomenon under a strong external magnetic field. We study both noncentrosymmetric and time-reversal symmetry breaking Weyl semimetals with the Coulomb interaction. The three-dimensional bulk system is reduced to many mutually interacting quasi-one-dimensional wires. Each strongly correlated wire can be approached within the Tomonaga-Luttinger liquid formalism. Including impurity scatterings, we inspect the localization effect, the temperature dependence of electrical resistivity, and the effect of a large number of Weyl points in realistic materials.
We further question the Weyl system from another viewpoint, where the excitonic instability is inspected. We show, by a fully iterative self-consistent mean-field calculation, how the noninteracting Weyl semimetal is modified in the presence of the Coulomb interaction. The chiral symmetry breaking occurs at strong enough interactions and the internode interband excitonic pairing channel is found to be significant. In the resultant interacting phase, finite band Chern number jumps in the three-dimensional momentum space are retained, indicating the robustness of the topologically nontrivial features.
We also start to work on several other topics. One is the quantum tunneling and interference with dissipation. The second is the scattering problem of Weyl electrons under simple potentials.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The progress is beyond the plan made one year ago. The project on the ultrasonic phenomena in a three-dimensional skyrmion/monopole chiral magnet system is fully completed, submitted, revised, and published. The major project in my plan about one-dimensional quantum liquid induced by a magnetic field applied to a Weyl semimetal system is also published. We successfully construct the correct Tomonaga-Luttinger theory associated with the Weyl system and include the impurity effect such as localization. The temperature dependence also helps to connect with experiments. Besides, we manage to inspect the same Weyl semimetal system from a different point of view. We use an iterative self-consistent mean-field method to unambiguously identify the correct order parameters induced by the Coulomb interaction and as well find the topologically nontrivial feature of the resultant gap-opened phase. Lastly, we further start to work on other topics to be continued in the next fiscal year.
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| Strategy for Future Research Activity |
Our major focus can be regarded as the phenomena related to real-space and momentum-space monopoles in various condensed matter systems. In current status of solid-state research, the former is represented by defects in magnetic skyrmion systems while the latter is genuinely realized by the Weyl semimetals. We reckon it as a promising research topic in the future. And in the light of our experience till now, we indeed hope to think more along this line. The main theme will combine topology and interaction.
In the following fiscal year, we plan to perform or finish at least three projects. One is the quantum tunneling and interference of a spin system in the presence of dissipation. The quantized spin actually resembles the quantum geometry of a Dirac monopole. We will also calculate the scattering problem of Weyl electrons under simple potentials. The interesting point lies in the semi-classical limit of large quantum numbers, which resembles the geometric optics. The third is the finite size effect of Dirac/Weyl semimetals, which is motivated by the latest fabrication of devices with confined geometries.
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