2007 Fiscal Year Final Research Report Summary
Quantum Phase Transition of Triangular Spin Tube
| Project/Area Number |
18340096
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Condensed matter physics II
|
|---|
| Research Institution | Tohoku University |
|---|
Principal Investigator |
NOJIRI Hiroyuki Tohoku University, Tohoku University, Institute for Materials Research, Professor (80189399)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
OSHIMA Yugo Institute for Materials Research, 金属材料研究所, Assistant Professor (10375107)
FURUKAWA Yuji Hokkaido University, Graduate School of Science, Assistant Professor (50280863)
|
|---|
| Project Period (FY) |
2006 – 2007
|
| Keywords | Chirality / Quantum Spin / Quantum Phase Transition / Ultra-low temperature / High Magnetic Field / Molecular Magnet |
|---|
| Research Abstract |
The purpose of the research is to investigate the magnetic excitation and the quantum phase transition of a triangular spin nano-tube:[CuCl_2tachH]_3Cl]Cl_2:the first quantum spin tube found by us. In the specific heat at ultra-low temperature, we found complex excitations made of two components. The first one is a gapped excitation, which can be fitted by an Ising chain model. The second one is a gap-less excitation with a small density of state. The result indicates that two types of excitations coexist in a spin tube. The origin of the gapped excitation is the excitation of spin chirality holding the Ising nature. This may be associated with the ordering of spin chirality at low temperature. The second excitation is caused by a spin wave like excitation, however, the fraction of this is only 25 % or less of that of a spin chain. It shows that the ground state of the present spin tube is gapless with considerable renormalization of energy.
To investigate the phase diagram of spin tube, we made a D-substituted sample and succeeded in modulating the exchange coupling in the chain direction. It is found that the exchange coupling in increased by 7 % by D-substitution. The origin of the modulation is the suppression of proton tunneling in hydrogen bonds connecting neighboring triangles in chain direction. In NMR, no magnetic anomaly is found down to very low temperature and the good separation between the tubes are confirmed.
The present investigation indicates the variety of magnetic properties in a quantum spin tube, which is caused by the existence of two degrees of freedom: spin and spin chirality.
|
