Kavli—Bermuda Triangle - Kavli Institute at Cornell

Kavli—Bermuda Triangle - Kavli Institute at Cornell

An Integrated Approach to
Creating New Quantum Materials
Darrell G. Schlom
Department of Materials Science and Engineering
Kavli Institute at Cornell for Nanoscale Science
Our Integrated Approach
Photoemission
Spectroscopy
(Shen)
Scanning
Tunneling
Microscopy (Davis)
MBE Growth (Schlom)
Creating New Materials
(SrTiO3)30
(BaTiO3)1
(SrTiO3)30
BaTiO3 / SrTiO3
STEM (Muller)
MBE ≈ Atomic Spray Painting
Evolution of MBE
1st
University MBE
Cornell,
1978
1st MBE
Al Cho at Bell Labs, 1972
Production
MBE
Today
(courtesy of TRW)
Evolution of Electronic Materials
e- KE
Nuclei KE
e- / Nuclei Int.
e- / e- Int.
Nuclei / Nuclei Int.
Electrons act like independent particles!
Complex Electronic Materials
La1-xCaxMnO3
Superconductivity
e- KE
Nuclei KE
e- / Nuclei Int.
e- / e- Int.
Nuclei / Nuclei Int.
Electrons are entangled and act collectively
Imaging Electronic Structure
survey
x 10
2
X-ray Photoemission of Gold
4f
20
CPS
15
4d
10
5
4s
4p
Courtesy of Jon Shu
1000
800
600
Binding Energy (eV)
400
200
0
P roduced w ith Cornell Site Licens e
chemical fingerprinting
oxidation states of atoms Core
Photoemission (global)
Spectroscopic Imaging
STM (local)
Electrons
Valence Electrons
controls all thermodynamic properties:
electrical properties, thermal conductivity,
magnetism, superconductivity, etc.
Our Integrated Approach
Photoemission
Spectroscopy
(Shen)
Scanning
Tunneling
Microscopy (Davis)
MBE Growth (Schlom)
Examples
n = 2
n = 3
n = 4
n = 5
n = 1
n = ∞
…
Mother of all
Cuprate Superconductors
Srn+1RunO3n+1 Phases
Superconductivity
!
Ferromagnetism
n = 1
n = 2
n = 3
n = ∞
Our Integrated Approach (today)
Srn+1RunO3n+1 Phases
Sr2RuO4
Single Layer
• Spin-triplet
Superconductor
(possibly
chiral p-wave)
• Analogous to
cuprates, but clean
Damascelli et al., PRL 85, 5194
(2000)
Sr3Ru2O7
Bilayer
• Metamagnetic
quantum phase
transition
• Electronic
nematic
Tamai et al., PRL 101, 026407
(2008)
SrRuO3
∞-layer
• Itinerant
Ferromagnet
• Large effective mass
m* / mDFT ≈ 4
• Does not cleave
Electronic Structure of SrRuO3
SrRuO3
(n = ∞)
kz
ky (Å-1)
DFT Majority
DFT Minority
(0,p)
(p,p)
(0,0)
― DFT
Majority
― DFT
Minority
k (Å-1)
x
ky
kx
DFT: David J. Singh, JAP 79, 4818 (1996)
Map Parameters:
hn = 40.8 eV, EF ± 5 meV, T = 10 K, 2-fold symmetrized
Cuprate Superconductors
Ca2–xNaxCuO2Cl2
Single Layer
• Well-understood
electronic structure
• Relatively low Tc
(28 K)
• Can only be grown in a
narrow doping range
Bi2Sr2CaCu2O8
Bilayer
• Complex crystal
structure
(incommensurate
superstructure)
• Extensively studied by
ARPES, STM
x = 0.12
K.M. Shen et al., Science 307, 901
(2005)
Asensio et al., PRB 67, 014519
(2003)
SrCuO2
∞-layer
• Simplest Structure
• Only cuprate
superconductor that
can be doped with
holes or electrons
• Does not cleave
Different Electronic Structure
10% Electron Doping
(p,p)
(0,0)
10% Hole Doping
(p,p)
(0,0)
K.M. Shen et al., Science 307, 901
(2005)
In electron-doped, additional
weight at (p,0) and suppressed
intensity ( hot spots )
demonstrate stronger coupling
to antiferromagnetism
Our Integrated Approach (future)
Spectroscopic Imaging STM
Spectroscopic
Imaging STM
(Davis)
Spectroscopic Imaging STM measures
local Electronic Structure
Our Integrated Approach
Photoemission
Spectroscopy
(Shen)
Spectroscopic
Imaging
STM (Davis)
MBE Growth (Schlom)