STUDY OF HIGH TEMPERATURE SUPERCONDUCTORS WITH ANGLE-RESOLVED ...

126 Pages·2003·5.03 MB·English

SLAC-624

STUDY OF HIGH TEMPERATURE SUPERCONDUCTORS WITH
ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY

Pavel Valer’evich Bogdanov

Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
Stanford University, Stanford, California 94309

SLAC-Report-624
December 2001

Prepared for the Department of Energy
under contract number DE-AC03-76SF00515

Printed in the United States of America. Available from the National Technical
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________________________________________
* Ph.D. thesis, Stanford University, Stanford, CA 94309.
STUDY OF HIGH TEMPERATURE
SUPERCONDUCTORS
WITH ANGLE-RESOLVED PHOTOEMISSION
SPECTROSCOPY
a dissertation
submitted to the department of applied physics
and the committee on graduate studies
of stanford university
in partial fulfillment of the requirements
for the degree of
doctor of philosophy
Pavel Valer’evich Bogdanov
December 2001
I certify that I have read this dissertation and that, in
my opinion, it is fully adequate in scope and quality as a
dissertation for the degree of Doctor of Philosophy.
Zhi-Xun Shen
(Principal Adviser)
I certify that I have read this dissertation and that, in
my opinion, it is fully adequate in scope and quality as a
dissertation for the degree of Doctor of Philosophy.
Sebastian Doniach
I certify that I have read this dissertation and that, in
my opinion, it is fully adequate in scope and quality as a
dissertation for the degree of Doctor of Philosophy.
Martin Greven
Approved for the University Committee on Graduate
Studies:
iii
Abstract
The Angle Resolved Photoemission Spectroscopy (ARPES) recently emerged as a
powerful tool for the study of highly correlated materials. This thesis describes the
new generation of ARPES experiment, based on the third generation synchrotron
radiation source and utilizing very high resolution electron energy and momentum
analyzer. This new setup is used to study the physics of high temperature supercon-
ductors. New results on the Fermi surfaces, dispersions, scattering rate and super-
conducting gap in high temperature superconductors are presented.
iv
Acknowledgements
Iwouldliketothankmyadvisor,Zhi-XunShen,forhismanysuggestionsandconstant
support during my years in graduate school. His insight led to the research in Bi2212
compound, which I originally considered too well researched and not very promising.
However experience proved me wrong, and we were able to discover phonon energy
scale in Bi2212, observe bilayer splitting and more. I would also like to acknowledge
thehelpofZahidHussain, myBerkeleyadvisor, whohelpedmesettleattheLawrence
Berkeley National Laboratory and whose support I could always count on. I am also
very grateful to Xingjiang Zhou. Him and Scot Kellar were essential for making
HERS endstation at the Advanced Light Source possible and were very helpful with
experiments and data analysis. Alessandra Lanzara joined the group in a later part
of my graduate term, but she became an essential part of Bi2212 research. She was
the driving force in phonon interpretation of the data, and I enjoyed every moment
of our collaboration. Over the years, all members of the Berkeley group became my
friends, and it helped to make the long PhD experience enjoyable.
I would also like to acknowledge the support of Julia and my parents. Their
presence helped me not to give up in times of trouble and stay focused.
I also wish to thank Er Dong Lu, Wan Li Wong, and Jonathan Denlinger. I want
to acknowledge the support of the ALS stuff, in particular the work of Noel Kellog
and Ed Wang, who helped make HERS endstation a functioning reality.
Finally, I’d like to acknowledge my many group mates from Stanford- Peter Ar-
mitage, Stuart Friedman, Anton Puchkov, Filip Ronning, Donglai Feng, Zhengyu
v
Wang, Anne Matsuura - whom I worked with extensively in my early years at Stan-
ford, as well as other group members - Jeff Harris, Changyoung Kim, Donghui Lu,
Kyle Shen, Paul White, Teppei Yoshida and Tchnag-Uh Nahm. And of course lots of
thanksgoestoGloriaBarnesandMarilynGordon, whosavedusallfrombureaucratic
nightmares. Thank you all!
Stanford, California Pavel Bogdanov
vi
Contents
Abstract iv
Acknowledgements v
1 Introduction 1
2 Angle Resolved Photoemission Spectroscopy (ARPES). Theory and
experiment. 3
2.1 Historical Developments . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 How to do a correct experiment . . . . . . . . . . . . . . . . . . . . . 5
2.3 How to analyze ARPES data (MDCs vs EDCs) . . . . . . . . . . . . 9
3 HERSendstationat Beamline10.0.0.1oftheAdvancedLightSource 16
3.1 Beamline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2 Endstation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.3 Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4 High Temperature Supercoductors and ARPES 25
4.1 History of the problem . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 High Temperature Superconductivity . . . . . . . . . . . . . . . . . . 26
4.3 ARPESstudyofHighTemperatureSuperconductivity-Outlineofthis
thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5 Fermi Surface Studies: Bi2212 system 32
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
vii
5.2 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6 Fermi Surface Studies: LSCO - Model Stripe Compound 42
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.2 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
6.3 The Nd-LSCO results at the critical doping x = 0.12 . . . . . . . . . 47
6.4 Optimally doped (x = 0.15) Nd-LSCO and pure LSCO results . . . . 54
6.5 x = 0.22 pure LSCO results . . . . . . . . . . . . . . . . . . . . . . . 58
7 Dispersions in Bi2212 and other cuprates - observation of electron-
phonon coupling. 62
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.2 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.3 Bi Sr CaCu O results . . . . . . . . . . . . . . . . . . . . . . . . . 64
2 2 2 8
7.4 Ubiquity of the effect in cuprates . . . . . . . . . . . . . . . . . . . . 70
7.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
8 Study of scattering rate anisotropy at the Fermi surface of Bi2212. 75
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
8.2 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
8.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 77
9 Study of superconducting gap in Bi2212. 85
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
9.2 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
9.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 87
10 Future directions. 94
10.1 Fermi Surface Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
10.2 Energy Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
10.3 Mapping Gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
viii
A Preliminarystudy ofthesuperconducting gapfromPbdoped Bi2212
along the two resolved Fermi surfaces 96
A.1 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Bibliography 101
ix
List of Figures
2.1 Panel a) shows a typical photo electron emission setup, with syn-
chrotron light hitting the sample, and with a hemispherical analyzer
scanning the electron energy. The bottom panel illustrates the ideal
spectra for direct processes. Panel b) shows more realistic situation,
where the resulting spectra is complicated by inelastically scattered
electrons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Figure shows near Fermi edge spectra of La .48Nd .4Sr .12 collected
1 0 0
in analyzer angle mode with the integration of all spectra under iden-
tical conditions except for different photon flux (beamline resolution)
settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Panela)showsangle-resolvednearFermiedgespectrafromLuNi B C
2 2
with beamline resolution set to 15 meV. Panels b)-d) correspond to
beamline resolution settings of 7 meV, 5 meV and 4 meV respectively. 7
2.4 In this figure we plot simulated ARPES spectra for a Fermi liquid
spectral function. Here β is equal to 1 in panel a) and to 7 in panel
b). E −0.1K is the line corresponding to MDC derived dispersion. It
is plotted in blue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5 In panel a) solid line corresponds to MDC fits for β 1 and 7 cases.
Broken line represents EDC fit for β = 1, dash represents EDC fit for
β = 7. Panel b) shows EDCs for the angular interval −7 < angle < 1
for β = 1. Panel c) shows EDCs for the same angular interval as in b)
for β = 7 case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
x