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第７回ＣＯＥ(自己組織系物理)セミナー (通算12回)
| “The Secret Order of the Cuprates” |
| 講 師 |
Prof. J.C.Davis, Dept. of Physics, Cornell University, Ithaca, NY14853, USA. |
| 日 時 |
2004年11月19日（金） 13:30-15:00pm |
| 場 所 |
早稲田大学理工学部62号館W棟大会議室(62W-107) |
| 講演の概要 |
High temperature superconductivity appears upon strong hole-doping of the CuO2 crystal planes in the cuprates. But, at low hole-densities, many other unprecedented electronic phenomena are also observed. A ‘hidden’ electronic state at low hole-doping, has been proposed to explain this situation.
Scanning tunneling microscopy (STM) studies have played a key role in searches for this state. They reveal that destruction of superconductivity in Bi2Sr2CaCu2O8 (Bi-2122), whether by high magnetic fields1, by exceeding the critical temperature Tc2, or by strong underdoping3, results in a very similar set of effects. These include a checkerboard pattern of quasi-periodic electronic structure modulations (with periods between 4a0 and 5a0). But underdoped Bi-2212 has such intense crystal and electronic disorder at the nanoscale3 that identifying any ‘hidden’ electronic state is impossible.
Instead, in collaboration with Prof. Hidenori Takagi of Tokyo University, we recently began STM studies of a different cuprate material Ca2-xNaxCuO2Cl2. It is a beautifully simple crystal with only one CuO2 plane in the unit cell, and can be very lightly doped. As envisaged by Anderson and Ong4, the approach of the Mott insulating state at light doping should be signalled by a characteristic tunnelling spectrum in which electron extraction probabilities greatly exceed those for injection. Spectra measured on lightly doped Ca2-xNaxCuO2Cl2 surfaces are in very good agreement. I will describe our ‘wavefunction imaging’ studies of this material which reveal an unprecedented 4a0X4a0‘checkerboard’ electronic crystal state5 with intricate atomic scale structure.
Finally, I will discuss proposals for the identity of this state, ranging from a charge-ordered insulator to a bosonic 2e supersolid, along with their implications for high-Tc superconductivity.
J. E. Hoffman et al , Science 295, 466 (2002).
M. Vershinin et al ,Science 303, 1995 (2004).
K. McElroy et al , Cond/mat 0404005
P.W. Anderson & P. Ong, Cond/mat 0405518
T. Hanaguri et al , Nature 430, 1001 (2004).
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| 紹介教員 |
松田梓 |
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