scanning tunneling microscopy - tsinghua university
TRANSCRIPT
Scanning Tunneling Microscopy
陈曦清华大学物理系
• Quantum Tunneling
• A Brief History of Microscopy
• Invention of STM
• STM Instrumentation
• Scanning Tunneling Spectroscopy
1Quantum Tunneling
Transmission rate:
Quantum Mechanical Tunneling
V(x)
E
x1 x2
T = exp
�2
Zx2
x1
p2m(V (x) � E)
~ dx
!
Three earliest examples (1928):
• α decay (Gamow)
• Field ionization of hydrogen (Oppenheimer)
• Field emission from metal surface (Fowler & Nordheim)
Quantum Mechanical Tunneling
α decay
Quantum Mechanical Tunneling
ln ⌧ = � lnA +12⇡B
pEk
U(r)
rU0
Ek
Field Ionization
Quantum Mechanical Tunneling
+
-eFx
Field Emission
Quantum Mechanical Tunneling
J =
pEF W
EF + W
e3F 2
2⇡hWexp
�8⇡
p2mW 3/2
3heF
!
Fowler-Nordheim formula
W
0
EF
W+EF-eFx
Quantum Mechanical Tunneling
1973 Nobel Prize in Physics
L Esaki
I Giaever
B D Josephson
p
n
N SΔ
V
Quantum Mechanical Tunneling
To be able to measure a tunneling current the two metals must be spaced no more than about 100Å apart, and we decided early in the game not to attempt to use air or vacuum between the two metals because of problems with vibration. ...... After a few months we hit on the correct idea: to use evaporated metal films and to separate them by a naturally grown oxide layer.
Nobel lecture, I Giaever, 1973
Quantum Mechanical Tunneling between Metals
Insulator
Empty Band
Filled Band
Partially
Filled Band
Metal
Energy GapFermi Level EF
Quantum Mechanical Tunneling between Metals
Density of States (DOS):
The number of states per
interval of energy at an
energy level
DOS of 3D free electrons
DOS
EEF
E =~2k2
2m
Quantum Mechanical Tunneling between Metals
Density of States (DOS):
The number of states per
interval of energy at an
energy level
DOS of 2D free electrons
DOS
EEF
E =~2k2
2m
Quantum Mechanical Tunneling between Metals
Density of States (DOS):
The number of states per
interval of energy at an
energy level
DOS of 2D Dirac electrons
DOS
EEF
E = ~vF k
ED
E
kx ky
Tunneling between two metals
Quantum Mechanical Tunneling between Metals
No tunneling current
Quantum Mechanical Tunneling between Metals
Tunneling between two metals
V
V
I ⇠ e�2d
d
=p
2m(W � E)~
�d ⇠ 1A ! I reduced by 10
Quantum Mechanical Tunneling between Metals
Tunneling spectroscopy
Tunneling probabilityV
Ew(E) / DOS(E)
Quantum Mechanical Tunneling between Metals
Tunneling spectroscopy
V I I+∆IV
∆V
Quantum Mechanical Tunneling between Metals
V
∆V
I∆I
⇓
⇓�I / DOS(V ) · �V
dI(V )dV
/ DOS(V )
w(E) / DOS(E)
Quantum Mechanical Tunneling between Metals
Tunneling: an approach to measure DOS
Example: Coulomb interaction + disorder ⇒ DOS ~ E1/2 at EFAl’tshuler & Aronov (1979)
Al
Al2O3
Ge1-xAux
McMillan & Mochel (1981)
Quantum Mechanical Tunneling between Metals
Pb
MgO
Mg
Giaever, Hart & Megerle (1962)
Inelastic Electron Tunneling Spectroscopy (IETS)
Inelastic excitations in barrier
Pb
Al2O3
Al
1 ML Molecules
Jaklevic & Lambe (1966)
4.2 K
B C
Inelastic Electron Tunneling Spectroscopy (IETS)
dI(V )dV
/ DOS(V )
Number of available tunneling channels at V
V
dI/dV: change of current after V is increased by dV
∝
Inelastic Electron Tunneling Spectroscopy (IETS)
dI/d
VV
Elastic tunneling
Inelastic Electron Tunneling Spectroscopy (IETS)
Inelastic tunneling: additional tunneling channels
E0
d2 I/d
V2
V
dI/d
V
V
E0
2A Brief History of Microscopy
Development of Microscopy
ItalySpectacles
JanssenFirst Microscope
Roman Glass, Lenses
1st Century 14th Century 1590 1665 1676
Leeuwenhoek Bacteria
Hooke: English father of microscopy
Leeuwenhoek: father of microscopy
Development of Microscopy
Lister Spherical
Aberration
1830 1878 1932
ZernikePhase contrastMicroscopeNobel 1953
1933
RuskaNobel 1986
Development of Microscopy
Atomic Era of Microscopy
1951 Oct. 11, 1955 1970
Erwin W. Müller
STEM image of Th atoms
Albert Crewe
1981 STM
3Invention of STM
Gerd Binnig Heinrich RohrerIBM Research Laboratory, Zurich, Switzerland
Nobel Prize in Physics, 1986
Gerd Binnig: superconductivityHeinrich Rohrer: superconductivity, Kondo, phase transitionChristoph Gerber: joined IBM in 1966, worked with HR, craftsmanly, inventor of AFM
“...... gave us the courage and lightheartedness to start something which should not have worked in principle”
None in microscopy or surface science
Motivation: Local study of growth and electrical properties of thin insulating layers as tunneling junctions
Goal: not to build a microscope, but to perform spectroscopy locally on an area less than 100 Å in diameter
Contact over insulating film
Instead of scanning tip in contact over a surface, a small gap of a few angstroms was maintained and controlled by the
tunneling current
Not only a local spectroscopic probeBut spectroscopic and topographic imaging
Profilometer
1978
March 16, 1981 First demonstration of vacuum tunneling
Si(111) 7x7 (1982) 1998
Main instrumental problems:
How to avoid mechanical vibrations that move tip and sample
against each other?
How strong are the forces between tip and sample?
How to move a tip on such a fine scale?
How to move the sample on a fine scale over long distances?
How to avoid strong thermally excited length fluctuations of
sample and tip?
Vibration isolation
1st generationsuperconducting levitation
2st generationspring
2st generationspring
Tip movementThe continuous deformation of piezomaterial in the angstrom and sub-angstrom range was established only later by the tunneling experiments themselves.
Piezoelectric Materials
Scanning and rough positioning
AFM, atomic force microscopy
BEEM, ballistic electron emission microscopy
EFM, electrostatic force microscope
FMM, force modulation microscopy
KPFM, kelvin probe force microscopyMFM, magnetic force microscopy
MRFM, magnetic resonance force microscopy
NSOM, near-field scanning optical microscopy
PFM, piezo force microscopy
PTMS, photothermal microspectroscopy/microscopySAP, scanning atom probe
SCM, scanning capacitance microscopy
SECM, scanning electrochemical microscopy
SGM, scanning gate microscopy
SICM, scanning ion-conductance microscopySThM, scanning thermal microscopy
SVM, scanning voltage microscopy
SHPM, scanning Hall probe microscopy
SSM, scanning SQUID microscope
Scanning
Probe
Family
Who is who: Don Eigler
Who is who: Wilson Ho
Who is who: Roland Wiesendanger
Who is who: Seamus Davis
4STM Instrumentation
V
IV: 10 μV ~ 1 V I : pA ~ nA
Pre-amplifier
+
109 Ω
IV
GainNoise levelBand width
dI/dV: Lock-in amplifier
excitation
experimental system
response
+noise
singnal
+noisetransducer
dc+acexcitation
experimental system
response
+noise singnal+noise
transducer
reference
output
~
x
low-pass filterV+v
I
~
I = I(V + v cos !t) = I(V ) +
dI(V )
dVv cos !t
⇥ cos (!t + �)
I(V ) cos (!t + �) +
dI
dVv(cos (2!t + �) + cos �)/2
= I(V ) cos (!t + �) +
1
2
dI
dVv cos (2!t + �) +
1
2
dI
dVv cos �
1
2
dI
dVv cos �
low pass filter
X-Y scanning
Z motion
Feedback
Z
I
Piezoelectricity
V
x
x+δx
z+δzz
�z = d33V
�x = (x/z)d31V
d ~ 1 Å/V
Lead Zirconate Titanate:PbTiO3+PbZrO3
EBL#2:
d33=3.80 Å/V
d31=-1.73 Å/V
P
Vz
Tube scanner
δL=d31VzL / t ~ 10 Å/V
t
Lz
Vy
Tube scanner
δx=2√2 d31VxL2 / πDt ~10 Å/V
t
L
y
-Vy
Vx -Vx
D
x
X-Y
ZLow sensitivity
Higher spatial resolutionMore invulnerable to noise
Smaller scanning range
Scanning range ~ micron
Sensitivity: displacement per volt
Resonance frequenciesScanning speed
Z
X-Yx-y control
z control
Electronics
feedbackPre-amp
image
Tip approach
Earlier time:mechanical mechanism vibration, thermal leak
shear piezo
V
δx=d15V1 mm: 103~104 steps
HexagonalPrism
Force
ExteriorShell
PositionDetector
Shear PiezoStack
Pan Type
Besocke Type
Vibration noise
General rules:
Low noise environment
Vibration isolation
Rigid design
Vibration noise
Low noise environment:
Basement with solid foundation
Turn off mechanical pumps, turbo pumps, etc
Acoustic-isolation room
Without solid foundation
With solid foundation
Vibration noise
Vibration isolation and rigid design
1
1
2
Vibration noise
Vibration isolation and rigid design
Vibration noise
Vibration isolation and rigid design
UHV STM-Clean Surcace
High vacuum: 10-7 to 10-9 torrUltra high vacuum: < 10-9 torr
Mean free path• 10-9 torr: 105 m• 10-10 torr: 106 m• 10-11 torr: 107 m
Monolayer formation time• 10-9 torr: 103 s• 10-10 torr: 104 s• 10-11 torr: 105 s ~ days
Cryogenic STM
• Investigate phenomena only at low temperature
• Higher energy resolution
• Low thermal drift
• Slow down dynamics
Cryogenic STM
Higher energy resolution
Tip
kBTA level on
Sample
peak width @10K
dI/dV 3.5kBT 3 meV
d2I/dV2 5.4kBT 5 meV
Cryogenic STM
Low thermal drift
ΔL=α(T)·L·ΔT 0.01Å stability
10-5K fluctuation @ 300K
10-2K fluctuation @ 4K
0
10
20
50 100 150 200 250
Al
Cu
SS
Ti
Temperature (K)
Line
ar e
xpan
sion
coe
ffici
ent (
10-6
K-1
)
Cryogenic STM
Cryostats:
LN2: 77 K
LHe: 4.2 K
He-3: ~0.3 K
Dilution: ~10 mK
He-3 Dilution
Cryogenic STM
He-3 Cryostats
He3 pot
1K pot
Sorptionpump
He3 vessel
Cryogenic STM-Continuous Flow
• Variable T• Rapid cooling down• Compact• High LHe consumption• No magnet
Cryogenic STM-Bath Cryostat
Top loading• Conventional• Magnet• Ultra low temperature• Bulky
Cryogenic STM-Bath Cryostat
Bottom loading• Low LHe
consumption• Compact
Ultra low temperature STM
Y. J. Song, et al, RSI 81, 121102 (2010)
1.0 m 10 mK 15 T @NIST
Tsinghua
Ultra low temperature STM
1.0 m 10 mK 15 T @NIST 1.52 m 1.52 m
1.41 m
1.17 m dia.
4.30 m 5.60 m
3.12 m
110t
1.91 m3.05 m
0.56 m
6t
Ultra low temperature STM
Mixing Chamber
SSMC connectors
Heat exchanger
ICP
Heat exchanger
Still
1K pot condenser
IVC
Volume for 250 L
Magnetic bore
Baffles
JT condenser
Shields (Still & ICP)
Ag clamping ring
plastic guide
SPM receptacle
Mixing Chamber(MC)
Ag extension rods
1K pot
Still
ICP
SSMCconnectors
JT loop
precoolingheat exchanger
thermal anchor
strain relief grooves
STM Tip
Chemistry of tungsten• WO2 and WO3
• WO3 soluble in strong base• Oxide reduced to metal
Etching tungsten tip• AC etching: blunt but less oxide• DC etching: sharp but more oxide• Optimal procedure: AC+DC+Strong acid
Tip etcher
DC etching
STM Tip
1.5kV
1.5mA e-
Ar+
Ar+ Ar+
Ar+
Ar+
~ 1kV
12uA
Repeated cycles of heating and self-sputtering in vacuum to remove oxide and sharpen tip
STM Tip
400Vkeep I < 20uA 5 min
e-A
HV field emission in vacuum to remove oxide
STM Tip
LV field emission in vacuum to fix blunt, multiple tip
5 ~ 10V 1 sec
e-
STM Tip
Controlled crash to sharpen tip
Sample
Single crystal metal: sputter+anneal
180V
9V
0-2kV 0-2kV
A
Ar
Sample
Single crystal metal: sputter+anneal
Sample
Sample holder
e-
HV
Pyrometer
Sample
Single crystal metal
Au(110) Cu(100) Pt(111) 250 nm x 250 nm
Sample
Silicon
I
Flash to 1200ºC
Sample
Cleaving BiO
SrO
CuO2
Ca
CuO2
SrO
BiO
BiO
SrO
CuO2
Ca
CuO2
SrO
BiO
Sample
Thin film growthHeater
Knudsen Cells
RHEED Gun
RHEED Screen
LN2Shroud
Sample
Thin film growth10 nm
I
II
Bi2Te3
KFe2Se2
5Scanning Tunneling Spectroscopy
dI(V )dV
/ DOS(V )
Looking for structures (peak, dip, step) in dI/dVSpectroscopic imaging
-13.6 eV
-3.4 eV
-1.5 eVd
p
s
Electron orbitals of H atom
50 meV
100 meV
150 meV
300 meV
200 meV
xy
EnergySpectroscopic imaging
Electronic States-Landau Quantization
Conventional 2DES
En = ~!c
✓n +
12
◆
H =1
2m(p + eA)2 H = vF [(p + eA) ⇥ �] · z
En = ED + sgn(n)vF
p2eB~|n|
n=0 1 2 3
Massless Dirac fermion
n=0 1 2 E E
Graphene
Electronic States-Landau Quantization
Miller, et al, Science 324, 924 (2009)
Electronic States-Landau Quantization
TI: Bi2Se3
-300 -250 -200 -150 -100 -50 0 50Sample Bias (mV)
0 T
dI/d
V (
a.u
.)
0
1
2
3
4
Dirac Point
Fermi level
1 T2 T
3 T
4 T
5 T
6 T
7 T
8 T
9 T
10 T
11 T
En ⇠p
nB
LL0 independent of B
��
��
��
�
�
�
�
�
��
���7���7
��7��7
� � � � � �� ��√nB
(QHUJ\��P
H9�
Electronic States-Landau Quantization
Electronic States-Quantum Confinement
Sub-band of Pb /Si(111)
EF
0.5
1.0
1.5Bind
ing
ener
gy (
eV)
Γ K
24 ML
Bind
ing
ener
gy
Wave vector
Wave vector
Van Hove Singularity
-1.0 -0.5 0.0 0.5 1.0 1.5
20ML
dI/d
V (a
rb. u
nits
)
Sample Bias(V)
21ML
19ML18ML17ML16ML15ML14ML13ML12ML11ML
22ML
STSQuantum confinement in thin film
Electronic States-Quantum Confinement
Building confined systems by manipulation
Electronic States-Quantum Confinement
Quantum corral
Eigler, et al, Science 262, 218 (1993)
9Å offcenter
Circle’scenter
Openterrace
-0.6 -0.4 -0.2 0.0 0.2 0.4Voltage (V)
dI/d
V (
10-1
0 oh
m-1
)
9
8
7
6
5
4
3
2
1
0
l=0 (hard wall model)l=1l=2
Peaks at circle’s centerExtra peaks 9Å off center
0.6
0.4
0.2
0.0
-0.2
-0.4
Ener
gy r
elat
ive
to E
F(eV
)
nl / Jl(knl⇢)eil�
Enl = ~2k2nl/2m⇤
Electronic States-Quantum Confinement
Atomic chainHo et al, Science 297, 1853 (2002)
NiAl
AuA B
FED
C
Au3
AuAu7
Au13 Au15 Au20
Electronic States-Quantum Confinement
Atomic chain
-8 -4 0 4 8Wave Vector (10 m )9 -1
m = 0.5 meff e0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ene
rgy
(eV
)
1.0eV
1.2eV
1.3eV
1.4eV
1.6eV
1.8eV
1.9eV
2.0eV
2.2eV
2.4eV
n=1
n=2
n=3
n=4
Electronic States-Molecules
1 2 3
4 6
8 9 7
1 2
dI/d
V (a
.u.)
3
4 5
Sample Bias (V) -2.0 -1.0 0.0 1.0 2.0
9
8 7 6
Bare Ag(100)
C60/Ag(001)-1.7 V 0.02 & 0.41 V 1.62 V
HOMO split LUMO LUMO+1
Theory
Exp
-1.7 V 0 V 0.4 V 1.6 V
Crommie et al, PRL 2003
Electronic States-Kondo
U
ε0
1nmEF
density of states
ener
gy
TK
Γ
1nm
MnNCH
Electronic States-Kondo
Quantum mirage
Eigler, et al, Nature 2000
F1 F2
Electronic States-Standing Wave
Eigler, et al, Nature 363, 524 (1993)
Cu(111)
0 20 40 60 80 100 120
1
3
5
7
9
11
13
Distance (Å)
dI/d
V (
10-9
Ω-1
)
ki kf
q
k=q/2
Electronic States-Standing Wave
400 mV300 mV200 mV100 mV50 mV
K
M
Fourier transform gives the momentum transfer q
q only in Γ-M directions
Backscattering is forbidden in topological insulator
Electronic States-Standing Wave
Backscattering is forbidden in topological insulator
Γ-K
Γ-M
K
M
Electronic States-Standing Wave
Backscattering is forbidden in topological insulator
Γ-K
Γ-M
K
M
E0
d2 I/d
V2
V
dI/d
V
V
E0
Inelastic Electron Tunneling Spectroscopy (IETS)
Inelastic Electron Tunneling Spectroscopy (IETS)
Ho, et al, Science 280, 1732 (1998)
Cu(100)
C2H2 on tip
1 on C2H2 2 on bare surface
358 meV: stretching mode of C2H2
Inelastic Electron Tunneling Spectroscopy (IETS)
358 mV
266 mV 311 mV
Inelastic Electron Tunneling Spectroscopy (IETS)
Cu(111)
CO
dimer
trimer
dI/d
V (
a.u
.)d
2 I/d
V2
(a.u
.)
-40 -20 0 20 40
-40
-20
0
20
40
12C16O13C16O
Sample voltage (mV)
30 35 40
1.5
1.6
1.7
12C16O13C16O
VAC= 2 mVRMS
Sample voltage (mV)
Eigler, et al, Science 298, 1381 (1998)
STM Topography of array of CO dI/dV image at 35.5 mV
Inelastic Electron Tunneling Spectroscopy (IETS)
[001]
[110]
AgFe
e
CO
Tip
e
Single bond formation
Inelastic Electron Tunneling Spectroscopy (IETS)
Ho, et al, Science 286, 1719 (1999)
20
0
-20
d2 I / d
V2 (
nA /
V2 )
280260240220200180
Sample Bias (mV)
Ag
Fe(12C16O)
Fe(12C16O)2
234
236
Identification of bond formation
Inelastic Electron Tunneling Spectroscopy (IETS)
Δ=gµBS·B
Spin flip spectroscopy
dI/d
V
0 Δ-ΔV
Δ~1 mV at 10 T, need He3 fridge
Inelastic Electron Tunneling Spectroscopy (IETS)
H=JS1·S2
Spin flip spectroscopy
dI/d
V
0 J-JV
Inelastic Electron Tunneling Spectroscopy (IETS)
Spin flip spectroscopy
Eigler, et al, Science 308, 466 (2004)
4 5 6 70.4
0.6
0.8
B (T)
6�(m
eV)
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.8
0.9
1.0
Voltage (mV)
B=0B=2.8TB=4.2TB=5.6TB=7T
Sca
led
dl/d
V
0.7
0.8
0.9
1.0
Voltage (mV)
Mn on metal
bare metal
B=0B=7T
Sca
led
dl/d
V0.8
0.9
1.0Mn on oxide
bare oxide
B=0B=7T
Sca
led
dl/d
V
Voltage (mV)
NiAl(110)
Al2O3Mn
4th layer
3rd layer
2nd layer
1st layer
Inelastic Electron Tunneling Spectroscopy (IETS)
Pb
1st layer
2nd layer
3rd layer
4th layer
5th layer
~60O
Chain
CoPc
Inelastic Electron Tunneling Spectroscopy (IETS)
-40 -20 0 20 40
dI/d
V
Sample Bias (mV)-40 -20 0 20 40-40 -20 0 20 40
Spin flip IETS of spin chains
2 spins 3 spins 4 spins
0.66J
1.37JS = 1/2
J
1.5J
S = 1/2
S = 3/2
S = 1
S = 0
S = 1
S = 0
S = 1
JS = 1/2J = 18 meV
H = J S1 . S2+J S2 . S3H = J S1 . S2 H = J S1 . S2+J S2 . S3+J S3 . S4
11T
5T
1.5T
Sample Bias (mV)17 18 19 20 21 22 23
dI/d
V (a
.u.)
1234567
Inelastic Electron Tunneling Spectroscopy (IETS)
S = 1
S = 0
Sz=-1Sz=0Sz=1
B=0 B=0
Singlet to triplet transition
Inelastic Electron Tunneling Spectroscopy (IETS)
5Å
Anisotropy CuN
Fe
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-10 -8 -6 -4 -2 0 2 4 6 8 10
0.05
0.10
0.15
0.20
dI/d
V (n
A /
mV
)
Voltage (mV)
7T
5T
3T
1T
0T
BBBBBBBB
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-10 -8 -6 -4 -2 0 2 4 6 8 10
0.05
0.10
0.15
0.20
0T
1T
3T
5T
dI/d
V (n
A /
mV
)
Voltage (mV)
7T
1086420-2-4-6-8-10
dI/d
V (
nA
/mV
)
0.05
0.10
0.15
0.20
Voltage (mV)
B ∥ N directionBBBB
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-10 -8 -6 -4 -2 0 2 4 6 8 10
0.05
0.10
0.15
0.20
dI/d
V (n
A /
mV
)
Voltage (mV)
7T
5T
3T
1T
0T
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-10 -8 -6 -4 -2 0 2 4 6 8 10
0.05
0.10
0.15
0.20
0T
1T
3T
5T
dI/d
V (n
A /
mV
)
Voltage (mV)
7T
B ⊥ N direction
1086420-2-4-6-8-10
dI/d
V (
nA
/mV
)0.05
0.10
0.15
0.20
Voltage (mV)
H = gµB
B · S + DS2z
+ E(S2x
� S2y
)
Heinrich, et al, Science 317, 1199 (2007)
D =-1.55 meVE = 0.31 meV
Spin Polarized STM
Tip SampleE E
DOS DOS
emptystates
filledstates
Spin Polarized STM
dI/dV = (dI/dV )0 + (dI/dV )SP MT · MA
Tip SampleE E
DOS DOS
emptystates
filledstates
Spin Polarized STM
1 ML of antiferromagnetic Mn on W
[001]
[011]-
Wiesendanger, et al, Science 288, 1805 (2000)
Spin Polarized STM
Wiesendanger, et al, Science 288, 1805 (2000)
W tip
W tip coated with Fe
[001]
[011]-
Spin Polarized STM
All-spin-based logic operations atom by atom
Readout Output
Bbias Bpulse
Spin Lead Spin Lead
Gate
Input _Input `
JlJisl
J_
J`
Readout Output
B
Wiesendanger, et al, Science 332, 1062 (2011)
CoCoFe
Spin Polarized STM
All-spin-based logic operations atom by atom
1 nm
_
`
0.4 T0
1
10
0
1
0
0
weak coupling between output atom and input α
Spin Polarized STM
Strong coupling between output atom and both inputs: OR
`_
1 10 1 01
0 110 00
-0.39 T
-0.385 T
-2 T
0.75 T
Superconductivity
Perfect diamagnetism
Oct. 26, 1911
No DC resistivity Energy gap
T(K)0 0.5 1.0 1.5 2.0TC
c (m
illijo
ules
/mol
e-K
)
0
1
2
3
4
Al
Phillips, PR 114, 676 (1959)
Superconductivity
Pb
Hg
Nb
NbN
Nb3Sn
V3Si
Nb3Ge
CeCu2Si2 UBe13 UPt3UPd2Al3 CeCoIn5
CNT diamondYbC6
CaC6
CNTCNTPuRhGa5
PuCoGa5
Li@33GPa
YbPd2B2C
K3C60
RbCsC60
[email protected] MgB2
FeAsYBaCuO
BiSrCaCuO
TlBaCaCuOHgBaCaCuO
HgTlBaCaCuO
HgBaCaCuO @30GPa
≈ ≈
≈≈
Liquidhelium
Liquidhydrogen
Liquidneon
Liquidnitrogen
Year
Tem
per
atu
re (
K)
2010200520001995199019851980194019000
10
20
30
40
50
100
150
200
Superconductivity
-6 -4 -2 0 2 4 6
0
10
20
30
40
50 4.2 K
2 K
1.2 K
600 mK
240 mKDiff
eren
tial C
ondu
ctan
ce (
nS)
Sample Bias (mV)
NbSe2 TC = 7.2 K Vortex, 0.25 T, 300 mK
dI/dV map at -0.21 mV
Superconducting gap
Hudson, PhD thesis
Superconductivity
1
l(E)
6 E
gap
Quasi-particles S anti-parallel to m
Sm
U
U = JS · � J > 0
Superconductivity
Impurity induced sub-gap states
5A 5A
0
2
4
6
8
Cr
0 2 4 6-2-4-6Bias (mV)
0
2
4
6
0 2 4 6-2-4-6Bias (mV)
Mn
Si(111)
Pb
Nb tip
0
2
4
6
8
Pb
0 2 4 6-2-4-6Bias (mV)
Mn Cr
dI/d
V
dI/d
V
dI/d
V
Superconductivity
-200 -100 0 100 2000.0
0.5
1.0
1.5
2.0
2.5
Diffe
rent
ial c
ondu
ctan
ce (n
S)
Sample bias (mV)
Zn (nomagnetic) induced bound state in BSCCO
Davis, et al, Nature 403, 746 (2000)
-1.5 mV
Signature of d-wave
Superconductivity
Quasiparticle scattering in BSCCO
Davis, et al, Nature 422, 592 (2003)
kx (2π/a)
k y (2π/
a)
X=(1/2,1/2)M=(0,1/2)
q1
q2q3
q4 q5q6
q7
-1 -1/2 0 1/2 10
1/2
1
q1
q2
q3
q4q5q6q7
qx (2π/a)
q y (2π/
a)∆
3-3 -1 1
2
1
0
d-wave superconductor
nodal point
Superconductivity
0 10 20 30 40 50 60 70 80 900
5
10
15
20
25
30
35
40
θk∆(θ)
(m
eV)
FT-STS (-)FT-STS(+)ARPES
dI/dV image
Superconductivity
Phase separation in KxFe2-ySe2
10 nm
I
II
0 2 4 6 8 10-2-4-6-8-10
1
2
3
4
5
0
Bias (mV)
dI/d
V (
a.u
.)
2Δ1
2Δ2
0.43 V
0 0.2 0.4 0.6-0.2-0.4-0.6Bias (V)
1
2
3
4
5
0
dI/d
V (
a.u
.)
6
KFe2Se2
K2Fe4Se5
Reference books:
• C. J. Chen, Introduction to scanning tunneling microscopy
• J. A. Stroscio & W. J. Kaiser, Scanning tunneling microscopy
• R. Wiesendanger, Scanning probe microscopy and spectroscopy