2015 Fiscal Year Research-status Report
Transport and Thermodynamics in Topological Materials
| Project/Area Number |
15K05140
|
|---|
| Research Institution | Institute of Physical and Chemical Research |
|---|
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)
|
|---|
| Project Period (FY) |
2015-04-01 – 2018-03-31
|
| Keywords | Topological Semimetals / Dirac Semimetals / Weyl Semimetals / Topological SC / Rashba effect / polar semiconductors |
|---|
| Outline of Annual Research Achievements |
During the first year of his project two systems were probed: The topological Dirac semimetal Cd3As2 and the polar superconductor and Rashba system GeTe (both by doping).
Several different elements were dopend into Cd3As2. The main issue during the first year of this project was to settle the growth conditions given that arsenic is a highly toxic element. A new tube furnace was installed. Several safety measures were carried out, too. There was one dpoant which was foundto clearly influence the topological nature of the system. This project is ongoing.
The work on GeTe had already been started before this project was granted. GeTe exhibits a polar (ferroelectric) distortion below approx. 900 K and ferromagnetism is induced upon Mn doping, which also suppresses the ferroelectric distortion. In the rhombohedral phase (up to x ~ 0.12), two competing magnetic phases were found. The ferromagnetic transition temperatures Tc differ by a factor of five to six for x ~0.05. The low-Tc phase was reported in literature and described in an RKKY framework. However, the high-Tc phase was newly found and had not been identified before. The underlying effect is a spinodal decomposition, a spontaneous spatial modulation of the Mn concentration upon cooling leading to Mn-rich islands embedded into a lake of almost pristine GeTe. The switchability bewteen these two magnetic phases was successfully demonstrated, adding a new feature to GeTe system: magnetic phase-change functionality in a bulk ferromagnet. A patent application on this effect is pending.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
During the first year of this project a new furnace was purchased and installed in the lab. The design of the new furnace was closely discussed with the constructing company. Since this was time consuming, meanwhile existing infrastructure was used for growing crystals. Although the handling of the toxic materials containing As was more difficult than it is when using the new furnace, this approach was chosen in order not to delay the progress of this project which successfully worked. A large series of doped Cd3As2 and GeTe batches were grown.
|
| Strategy for Future Research Activity |
During the next fiscal year, the effect of different dopants will be examined. Also several collaborations have been started and will be continued.
Cd3As2: A comprehensive transport study is in progress. The goal is to finish this study and publish the results in the next Fiscal Year. In a collaboration with a group at the University of Tokyo also target materials for pulsed-laser deposition experiments were grown.
GeTe: Beside Mn doping different dopants will be tried out. The base material GeTe is a low charge carrier superconductor with a complicated band structure. It is known that in such systems the superconducting transition temperature depends directly on the charge carrier concentration. For undoped GeTe the superconducting transition temperature is rather low (< 500 mK). Therefore I would like to increase it by changing the charge carrier concentration. Given the polar nature of GeTe, superconductivity achieved upon doping might be unconventional. However, to control the charge carrier concentration is known to be a challenging task, particularily in GeTe, since the charge carriers in this system are due to unintentional self doping, i.e., Ge vacancies. Therefore the defect chemistry in this system has to be probed in detail as well.
|
| Causes of Carryover |
Article costs: During the first year of this project a new tube furnace was purchased. The eventual costs were lower than initially estimated. This was due to changes in the design which were made during the discussion about the precise setup of the furnace with the contracting company.
Travelling costs: The budget for traveling was not used yet. Business trips during last Fiscal Year were not solely related to this project and hence the regular budget of my institute was used instead.
|
| Expenditure Plan for Carryover Budget |
The remaining money will be used during this Fiscal Year. it is planned to install a fume hood in which the new furnace will be moved for safety reasons. This is to prevent any contamination of the enbvironment in case a crystal growth run inculding arsenic fails.
|
