Alexei Fedorovalexei@solids.phy.bnl.gov

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