2020 Fiscal Year Research-status Report
Novel Quantum States in Topological Kondo insulators
| Project/Area Number |
18K03511
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| Research Institution | Kyoto University |
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Principal Investigator |
Peters Robert 京都大学, 理学研究科, 講師 (80734293)
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| Project Period (FY) |
2018-04-01 – 2023-03-31
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| Keywords | Kondo insulators / topology / non-Hermiticity / exceptional points / Weyl-semimetals / nonlinear transport / Kondo effect |
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| Outline of Annual Research Achievements |
We performed research on the impact of non-Hermitian properties due to strong correlations on topological Kondo insulators. From previous studies, it has become clear that band structures, including Dirac cones, provide a situation where non-Hermitian phenomena such as exceptional points can easily be observed. Thus, the surface states of topological Kondo insulators, hosting strongly interacting Dirac cones, present ideal conditions. We indeed were able to demonstrate the existence of exceptional points at finite temperatures in the bulk and at the surface of topological Kondo insulators. Contrary to our expectations, the exceptional points at the surface are not created by the surface Dirac cones alone but by a combination of surface and bulk states. This leads to an exciting combination of Dirac cones due to the topological band structure and band touching due to non-Hermicity. Furthermore, the spin texture inherent in the Dirac cones is altered by the exceptional points, which might give an experimental probe to observe exceptional points.
Besides our study about non-Hermitian effects in topological Kondo insulators, we performed a study about topological Weyl-Kondo-semimetal. We analyzed how the Kondo effect destroys the Weyl nodes at finite temperatures resulting in a transition from a metal at high temperatures to a semimetal at low temperatures. Most remarkably, we revealed that the Kondo effect strongly enhances the nonlinear conductivity. We believe that our theoretical study explains a recently observed large nonlinear Hall effect in a Weyl-Kondo-semimetal.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Our research about the interplay of topology and strong correlations in Kondo lattice systems advanced as planned. The calculations about the emergence of exceptional points due to non-Hermiticity in topological Kondo insulators have been finalized and are currently summarized in a forthcoming publication. Furthermore, we finished our calculations about the impact of strong correlations on the nonlinear Hall effect in Weyl-Kondo semimetals.
In summary, the project proceeds as planned, analyzing the interplay of topology and strong correlations in Kondo systems.
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| Strategy for Future Research Activity |
We have started to analyze recent experiments on topological Kondo insulators showing a finite heat conductivity at low temperatures, although the system is charge insulating. These experiments indicate the presence of gapless charge-neutral excitations at low temperatures, which can carry heat but no charge.
Using variational matrix product states, we have started to calculate single-particle and two-particle properties of Kondo insulators in one dimension. We thereby compare different models, including topologically trivial and nontrivial band structures. Besides single-particle properties, we will mainly focus on the study of charge-neutral spin and electron-hole excitations. Furthermore, we will directly calculate heat and charge currents in these models and see under which conditions there is heat transport in the absence of charge transport.
As a second project, we plan to analyze further the metallic state arising at high magnetic fields in topological Kondo insulators. In recent experiments, it has been shown that even this metallic state shows unconventional properties, which were explained by charge-neutral excitations. Using dynamical mean-field theory for a two-dimensional model, we will study single-particle properties for magnetic fields larger than the critical field strength at which the magnetic breakdown occurs. In particular, we will analyze the effect of strong correlations and topologically nontrivial band structure on the quantum oscillations observed in this metallic state.
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| Causes of Carryover |
Due to the Covid-19 pandemic, it was impossible to attend academic conferences. Thus, there were no academic travels last year.
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