sts in a superconducting junction and the ac-josephson...
TRANSCRIPT
Freie Universität Berlin FKF-MPG 20.Nov.2013 1/22
STS in a superconducting
junction
and the
ac-Josephson
effect: A new type of spectroscopy
Klaus Klaus BaberschkeBaberschkeInstitut fInstitut füür Experimentalphysikr Experimentalphysik
Freie UniversitFreie Universitäät Berlint Berlin Arnimallee 14 DArnimallee 14 D--14195 Berlin14195 Berlin--Dahlem Dahlem
GermanyGermany
e-mail: [email protected]://www.physik.fu-berlin.de/~bab
1.
Quasi particle tunneling2.
Josephson effect = pair tunneling, dc, ac
3.
Our ac Josephson spectroscopy (~30 years ago)4.
Proposal for a new ac Josephson UHV-LT-STS
Freie Universität Berlin FKF-MPG 20.Nov.2013 2/22
Rev.Sci.Inst.84,22903(2013)
Single electron
tunneling
(quasi particle)
Freie Universität Berlin FKF-MPG 20.Nov.2013 3/22
2Δ
=3.5 kB
TC
; U
mV 10 K 860 µeV
That’s what w
e do NOT discussKondo-resonance on TTF-TCNQ/Au(111) PRL 101, 217203 (2008)
S-S junction N-N junction
Freie Universität Berlin FKF-MPG 20.Nov.2013 4/22
Coupled
superconductors
SIS, SNS
L,R
2
= , Cooper pair density
order parameter
We used : N = Au + rare earth
You may use: I = molecule monolayer
Freie Universität Berlin FKF-MPG 20.Nov.2013 5/22
dc
-Josephson
effect
= pair tunneling
J0
h = 2T (L
R
)1/2
Φ0
= hc/2e
210-7
G cm2
Overlap of L
and R
.
pair wave fct. leads to a tunnel current of Cooper pairs.
*
This leads to flux quantization and Fresnel interference pattern
–
not discussed today.
It’s a new particle with 2e , 2m and S=0
with Bose statistic.
is one macroscopic
wave fct
for all Cooper pairs.*
Freie Universität Berlin FKF-MPG 20.Nov.2013 6/22
Tunnel junction
+ voltage
= ac
Josephson
effect
J = J0
sin(ΔΘ-2eVt/h) hν
= 2eV
483.6 MHz 1µV
NS1 S2
V
eVt 212
Freie Universität Berlin FKF-MPG 20.Nov.2013 7/22
Our
ac
Josephson
spectroscopy
We
worked
with
a tip
and film thickness of r and d of few
µm, R
0.5 Ω
ac-Josephson
effect as MW-generator
and current
as detector
Freie Universität Berlin FKF-MPG 20.Nov.2013 8/22
Proof for a good Josephson junction:
Fraundofer
diffraction pattern:
I ≈
cos
(πΦ/Φ0
)
Freie Universität Berlin FKF-MPG 20.Nov.2013 9/22
VRi
RVi c
tot 2
2
Freie Universität Berlin FKF-MPG 20.Nov.2013 10/22
For ac Jospheson
effects
see standard literature
books by
P. G. de Genne
1964
M. Tinkham
1996
A. Barone
1982
Rf-driven
Junctions Shapiro
steps
Photon-assisted
tunneling
Freie Universität Berlin FKF-MPG 20.Nov.2013 11/22
483,6 MHz = 1V
Gd3+
=> 8S7/2 => 2S+1 = 8
Crystal field
splitting
cubic
or
lower
symmetry
Freie Universität Berlin FKF-MPG 20.Nov.2013 12/22
Hyperfine splitting of Au 167Er, S + I = F = 3 and 4
ΔEtheo
= 2.87 GHz ; Vres
= 5.4(2) µV, νres
=2.6(1) GHz
Freie Universität Berlin FKF-MPG 20.Nov.2013 13/22
Proposal for new ac Josephson UHV-LT-STSFe3+ S=5/2
Fe3+ or Fe2+,
HS or LS,finally there will be some ZFS within the (2S+1) manifold
Molecular monolayer and superconductingtip and substrate crystal,e.g. Pb.
Freie Universität Berlin FKF-MPG 20.Nov.2013 14/22
3dn-energy scheme and magnetism of the Fe-ion
Dramatic change of ligand
field upon coadsorption
of oxygen.
Gambardella et al. 2009, Bernien
et al. 2009
Unperturbed eg
, t2g
eigenstatesare no good.
“zero field splitting”
≡
CEF
Fe 3+,2+
S= 5/2, 3/2, 1/2S= 2, 1, 0
Freie Universität Berlin FKF-MPG 20.Nov.2013 15/22
Zero field splitting:For Cr3+
=> S=3/2, in Al2
O3
--------------------------------For Fe3+
=> S=5/2Splitting in E±1/2
, E±3/2
,E±5/2
ΔE = 2D, 4DRange 5 to 40 GHz, Bittl
paper
Freie Universität Berlin FKF-MPG 20.Nov.2013 16/22
LZ • SZ
+L •
S
L±
• S+_
The
orbital moment
is
quenched in cubic
symmetry
2-
LZ
2-
= 0,
but
not
for
tetragonal symmetry
Freie Universität Berlin FKF-MPG 20.Nov.2013 17/22
1. Magnetic anisotropy energy = f(T)
2. Anisotropic magnetic moment
f(T)
B (G)
100
100 20000
500
300
300
M (G
)
[111]
[100]
Ni[100]
[111]
0.1 GL ~~
K. Baberschke, Lecture Notes in Physics, Springer 580, 27 (2001)
LS4µB
anisotropic
µL
MAE
MAE µL Bruno (‘89)
g|| - g
= ge (
-|| )
D= gge
Magnetic Anisotropy Energy (MAE) and anisotropic µL
Orbital magnetic
moments
are
small, but
all important
Freie Universität Berlin FKF-MPG 20.Nov.2013 18/22
Freie Universität Berlin FKF-MPG 20.Nov.2013 19/22
100µV
48 GHz
Freie Universität Berlin FKF-MPG 20.Nov.2013 20/22
variable frequencies
0.5 –
50 GHz are
needed
to measure CFS with
and without
magnetic
fields
Freie Universität Berlin FKF-MPG 20.Nov.2013 21/22
Freie Universität Berlin FKF-MPG 20.Nov.2013 22/22
Alexander Schnegg
et al.Phys. Chem. Chem. Phys., 11, 6820 (2009)
Frequency
domain
Fourier
transform
THz-EPR
on single molecule
magnets
using
coherent
synchrotron
radiation
Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool …. at the BESSY II storage ring …
in a frequency range from
5 cm-1
up to 40 cm-1
… together with first measurements on the SMM Mn12
Ac where ΔMS
= ±1 spin transition
was studied …. Thank you
Freie Universität Berlin FKF-MPG 20.Nov.2013 23/22