temperature dependent photoemission studies of optimally ......alexei fedorov...
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Alexei [email protected]
Temperature Dependent Photoemission Studiesof Optimally Doped Bi2Sr2CaCu2O8
/ crossover from normal to superconducting state in (π ,0) direction /
Physics Department, BNL:
A. V. FedorovT. VallaP. D. Johnson
Division of Materials Science, BNL:
Q. Li
School of Physics, University of New South Wales:
G. D. Gu
Superconductivity Research Laboratory, ISTEC:N. Koshizuka
Supported by the Department of Energy under DE-AC02-98CH10886
Reference: A.V. Fedorov et al., Phys. Rev. Lett. 82, 2179 (1999)
Bin
ding
Ene
rgy
(eV
)
Binding Energy (eV)
EF
EF
EF
EDC
a) 293 K
b) 14 KT = 14 K
hν = 21.22 eV
0.1
0.2
0.1
0.10.2
~ 30 meV
Electron momentum along (π ,0)
Bi2Sr2CaCu2O8
/ “resolution-limited” peak in superconducting state /
P.J. White et al., cond mat/9901348/Stanford University/
M.R. Norman et al., PRL 79, 3506 (1997)/Argonne National Laboratory/
Bi2Sr2CaCu2O8+δ , photoemission near (π ,0)/ influence of temperature, doping and impurities /
Experimental details:
Air-lock chamber with samples has been never backed over 100oC
Samples cleaved in situ
Samples mounted on an open-cycle He cryostat
~ 10< TEMPERATURE (K)< ~450
Temperature monitored with a help of OMEGA CY7 sensor
Typically it takes six hours to get angle-resolved spectra for tentemperatures
Photon energy: 21.22 eV
No effects of sample “aging” have been detected
Photoelectron SpectrometerSES-200: 200 millimeters hemispherical deflector capable of multichannel detection in emission angle and kinetic energy
Example of angle resolved data:hν = 21.22 eV /He I radiation/Cu(111), bulk bands and sp surface state
Presently located at the undulator beamline U13UB at the National Synchrotron Light Source
Binding Energy (eV)
Em
issi
on a
ngle
EF4.0 2.0
Energy resolution ~ 10 meVAngle resolution ~ 0.2 o
Base pressure ~ 2× 10-11 Torr
Sample quality/ samples produced by floating zone method, TC = 91 K /
a) Resistivity measurements
Temperature (K)90
0.5
100 110
Res
istiv
ity
b) Umklaps in ΓΥ direction
Binding Energy (eV)EF
Em
issi
on a
ngle
0
46 K
64 K
95 K
103 K
K//
(π,0
)
0.75
1.0
Binding Energy (meV)
EF50100
Bi2Sr2CaCu2O8/present study/
EF50100 150
S
D
b) EDC`s along 0.75 ΓΜ
“sharp peak” does not movewith temperature;it appears in the spectraabove TC
“dip” does move towards theFermi level at ~ TC
a) band structure
Bi2Sr2CaCu2O8/angle-integrated data/
Binding energy (meV)EF50100150
22 K46 K
64 K
83.5 K
88 K
90 K
93 K
95 K
98.5 K
103 K
∆
Sharp peak:remains at the samebinding energy ~ 40 meV;its width is constant,intrinsic width ~ 14 meV;it disappears at temperatureswell above TC
Binding Energy (meV)
Dip /leading edge of the broad peak/:moves away from EF at TC⇒ gap opens;gap rapidly saturates if temperature islowered below TC
EF200400
Fermi level of Goldmeasured at 20 K/resolution 8 meV/
Fits to the data/ 0.5o angle cuts at 0.75ΓΜ/ /
T = 103 K
95 K
46 K
Temperature (K)
20 40 60 80 100 6020 40 80 100
Temperature (K)
∆(m
eV)
0
10
20
30
0In
tens
ity (a
rb. u
nits
)
Conclusions
a) gap versus temperature b) sharp peak versus temperature
It`s grate to have an instrument like that!
TC< TTC< T
Pseudogap behavior in …K.Ishida et al., Phys. Rev. B 58, R5960 (1998)
Optimal doping: T* = 130 K