| Project/Area Number |
17540342
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Waseda University |
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Principal Investigator |
MATSUDA Azusa Waseda University, Faculty of Science and Engineering, Professor (40386587)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥300,000)
Fiscal Year 2007: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2005: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | High Tc Superconductivity / Low Temperature STM / Mechanism of Superconductivity / Highly Correlated Electronic System / Impurity Effect / 強相関系 / 層状Cu酸化物 / 層状Co酸化物 / 不均一状態 |
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| Research Abstract |
We have studied highly underdoped Cu oxide high Tbsuperconductors (HTSCs) and the related material that has a highly correlated electronic system, by using a low-temperature scanning tunneling microscope (LTSTM). The goal of the research is to understand the origin of the several anomalous characteristics observed in the underdoped HTSC, such as a pseudogap or spatial inhomogeneity in gap energy.
First, we realized highly underdoped Bi-2212 superconductors with Tcof~20K, by using a special annealing treatment under a reduced oxygen atmosphere as well as a partial substitution of Sr by Bi. LTSTM measurements of this sample and other samples which cover a wide range of doping level revealed following points; (1) we could not fmd any gap-like structure whose energy is proportional to Tc (2) highly oxygen reduced samples, which are near the decomposition line, sometimes give a spatially uniform gap. In addition, if the tunnel spectra with various doping levels including non-superconducting underdoped one were scaled by there gap values, they gave an essentially single spectrum. The point (2) suggests the gap inhomogeneity is related to the existence of excess oxygen.
In this research, we studied the impurity efiect on HTSCs, which also reduces lb down to 0 K. We measured the DOS of the Co substituted Bi-2212 samples with keeping the doping level constant We found either that the pseudogap was developed upon impurity doping. This suggests that the pseudogap is something related to an electron localization other than the development of a hidden order.
Tb study the relation between the pseudogap and the localization, we investigated Bi_2Sr_2Co_2O_x crystals, which show the electron localization at low temperatures. LTSTM measurements revealed that it also has a pseudogap and the STM topography showed the modulation structures which suggest the formation of several charge density waves.
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