2016 Fiscal Year Research-status Report
Transport and Thermodynamics in Topological Materials
| Project/Area Number |
15K05140
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
Kriener Markus 国立研究開発法人理化学研究所, 創発物性科学研究センター, 研究員 (60447919)
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| Project Period (FY) |
2015-04-01 – 2018-03-31
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| Keywords | Topological Insulators / Weyl Semimetals / Rashba Effect / Polar Semiconductors / Superconductivity |
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| Outline of Annual Research Achievements |
The GeTe project was continued: Mn-doping into the rhombohedrally distorted semiconductor GeTe induces ferromagnetism and reduces the rhombohedral distortion. There are two different magnetic phases with very different ferromagnetic transition temperatures Tc. Which phase is realized can be controlled by the heat-treatment of a sample. Optimized annealing conditions were identified and the Tc of bulk samples was enhanced to above 200 K, higher than reported so far for this system. It was also found that controlled-cooled samples exhibit a very inhomogeneous Mn distribution and that several differently distorted phase fractions develop upon annealing and Mn doping: at least two rhombohedral (one weakly, one strongly distorted) and one cubic phase fraction. A clear correlation between high Tc values and the existence of large weakly-distorted phase fractions was revealed.
Other elements were successfully doped and control over the charge carrier concentration achieved. For quenched samples this also allowed control over Tc. However it was not possible to further increase Tc in controlled-cooled samples, two competing effects compensated each other.
Cd3As2: Two collaborations with U Tokyo Labs are ongoing. One is about probing thermoelectrical features in doped Cd3As2 based on my results as well as the consequences of doping on the topological nature of the pure compound (which is a Weyl semimetal). The second collaboration is on topological aspects of thin films (paper submitted)
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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
The sample preparation works well, desired bulk materials can be successfully synthesized in our lab. Also the handling of toxic materials is under control. So far conventional fume hoods are used to handle the growth of the latter materials. In this fiscal year it is planned to buy and install a fume hood which is specially designed to host the earlier bought rotatable tube furnace to allow full use of its properties when growing toxic materials. This will enhance the convenience and safety of the growth process.
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| Strategy for Future Research Activity |
GeTe: The results on charge-carrier control and ferromagnetism in this system will written up and submitted, a few measurements are pending. It is planned to investigate the effect of physical pressure on Mn-doped GeTe. Additional dopants will be probed, so far there is no big step forward in terms of (topological) superconductivity in this system.
As a related but new project, I am planing to work on SnTe-based materials and possibly also the GeTe-SnTe substitution series: SnTe is an experimentally confirmed topological crystalline insulator which also superconducts at low temperatures. Doping, e.g., In into this system is known to enhance the Tc of the superconducting phase as compared to pure SnTe. Depending on the dopant, valence skipping effects are expected to play a role which may enhance superconductivity.
Cd3As2: The project on the topological aspects of the doped bulk system is ongoing. Structural analyses will be carried out to see whether there is any correlation with the experimental results so far obtained from transport measurements. As for the question of the thermoelectrical efficiency of doped Cd3As2, it is planned to measure high-temperature properties as well. The next steps will depend on the outcome.
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| Causes of Carryover |
A fume hood specifically designed for the earlier bought rotatable tube furnace will be purchased this fiscal year. So far conventional fume hoods were used for the growth of toxic materials, however, to allow full use of the functionality of the tube furnace, an independent fume hood is desirable.
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| Expenditure Plan for Carryover Budget |
The remaining funding will be used for the fume hood. Also a software program will be purchased for data analysis.
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[Journal Article] Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1-xMnxTe2016
Author(s)
M. Kriener, T. Nakajima, Y. Kaneko, A. Kikkawa, X.Z. Yu, N. Endo, K. Kato, M. Takata, T. Arima, Y. Tokura, and Y. Taguchi
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Journal Title
Scientific Reports
Volume: 6
Pages: 25748-1 25748-9
DOI
Peer Reviewed / Open Access / Int'l Joint Research / Acknowledgement Compliant
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