Institute of Materials Science, University of Tsukuba

1
THz emission using Bi2Sr2CaCu2O8d intrinsic
junctions
University of Tsukuba
21st Century COE (Center of Excellence)
Program Promotion of Creative Interdisciplinary
Materials Science for Nobel Functions
K. Kadowaki, I. Kakeya, Y. Kubo, M. Kohri, S.
Kawamata, and T. Yamamoto and M. Tachiki

• Institute of Materials Science, University of
  Tsukuba
• 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573
• JAPAN
• University of Tokyo

Presented at the 5th International Symposium on
the Intrinsic JosephsonEffect in High Tc
Superconductors, 17-19, July, 2006, Institute of
Physics, London, UK.
2
Outline
1. Introduction
Intrinsic Josephson junction
2. Basic interest in Josephson physics
3. What is the intrinsic Josephson effect? _at_
multi-branch in I-V characteristics
_at_oscillation of the flow-resistance _at_
lock-in transition
4. Radiation theory
5. experiments
6. summary
2
3
Bi2Sr2CaCu2O8d Single crystals
Important characteristics
Bi-2212 order parameter y
Rocking Curve
Single Crystal
y 2
Intrinsic inhomogeneity
3
4
Intrinsic Josephson Junction
Atomic Scale Josephson Junction
Single crystal
In a unit cell
4
5
Josephson physics (I)

• Essentially Single layer Property
• ac Josephson effect

Theory B. D. Josephson, Phys. Lett. 1, 251 (1962).
Experiments (Indirect) S. Shapiro, PRL 11, 80
(1963), S. Shapiro, et al., Rev. Mod. Phys. 36,
223 (1964), I. Giaever, PRL 14, 904
(1965). Direct measurements I. K. Yanson, V. M.
Svistunov and I. M. Dmitrenko, ZhETF, 48, 976
(1965), D. N. Langenberg, et al., PRL 15, 294
(1965).
6
5
6
Josephson vortices in Bi2212
L
3. Josephson plasma frequency wp
6
7
Short vs. long junctions
Single-junctions
Mostly short junction limit (lJL)

• dc SQUID and Fraunhofer interference effects
• ac Josephson effect
• Josephson plasma
• Fiske Resonance

Multi-junctions
Long junction limit (lJL)
Josephson plasma resonance in parallel fields
What is different from single junction?
7
8
Evidence for Intrinsic Josephson Effects
1. Direct observation of multi-branches in I-V
characteristics
2. Oscillatory behavior of the Josephson
vortex flow resistance as functions of both
field and current.
3. Lock-in behavior of the Josephson vortex
flow resistance both rab and rc.
8
9
Oscillatory Behavior of rc as a function of H
due to Josephson vortex flow
1. Period H0f0/ws for square or
H0 f0/2ws for triangular
2. The amplitude and the shape depend
strongly on the current I.
3. The threshold field also depends on the
shape of the sample edge pinning.
4. Beat of two periods appears at the
transition region.
5. The shift of the periodicity is found
9
10
Josephson Vortex Flow
Superconducting CuO2 plane
Josephson vortex
Triangular lattice
10
11
Quantum diffraction in a short Josephson junction

• Quantum diffraction effect Fraunhofer pattern

11
12
Quantum Interference effect

• Interference Effect
• DC SQUID

12
13
Angular Dependence of rc Lock-in behavior
Micrometer sized sample
Sub-mm sized sample
Josephson vortex flow resistance
Kadowaki Mochiku, Physica B194-196, 2239 (1994)
Due to Josephson vortex flow
13
14
Angular dependence of Lock-in Angle
Magnetic field dependence
M ? H
(Dq ) ? 1/H
qmax
H
Length dependence
torque energycreation energy of a pancake
Hc1
MHl(Dq)2 const.
(Dq )2 ? 1/l
14
15
Josephson vortex flow resistancemagnetic field
dependence(I)
T60 K
higher
H lower
T 60 K, I 11.4 mA
T 60 K, I 11.4 mA
15
16
Josephson vortex flow resistancemagnetic field
dependence (II)
T75 K
higher
H lower
T 75 K, I 11.4 mA
T 75 K, I 11.4 mA
16
17
Josephson vortex flow resistancemagnetic field
dependence (III)
Dq vs. H
Dq vs. 1/H
17
18
Length dependence
T 60 K, J50 A/cm2
18
19
Temperature dependence
Dq as a function of temperature
Hsin(Dq/2)H? as a function of temperature
19
20
Sample Engineering
FIB Machining
Definition of junction dimensions
Micron sized Josephson junction after FIB cutting
20
21
Samples
w width
t thickness
l length
Range of dimensions
l 5.5117.8 mm w 1.8310.3 mm t 0.141.99 mm
More samples have been measured
21
22
Josephson Plasma Resonance
Josephson plasma energy
In-plane superconducting gap
Schematic view of the superconducting planer
junction a thin insulating barrier layer with
dielectric constant e sandwiched by two
superconducting layers A and B with the phases j
A and j B, respectively.
P. W. Anderson, Lectures on The Many-Body
Problem (vol. II), edited by E. R. Caianiello,
Academic press, 1964, p113.
22
23
Dispersion relation
Plasma Modes in a Superconductor
Anderson-Higgs-Kibble Mechanism
23
24
Josephson plasma experiments and main results
refer to I. Kakeya, et al., Phys. Rev. B72
(2005) 014540.
24
25
Theory of Josephson plasma for Josephson vortex
states
vs
Josephson vortex
vs
after T. Koyama, Phys. Rev. B68 (2003) 224505.
25
26
Fiske resonance (I)
Evidence for the collective excitation of the
plasma mode confined in a sample by motion of
Josephson vortices
Dimension 7.22 mm x 2.83 mm x 0.92 mm
26
27
Fiske resonance (II)
27
28
Fiske Resonance (III)
After S. M. Kim et al., PRB 72 1405054 (2005)
28
29
Fiske resonance (IV)
29
30
Fiske resonance (V)
Langenberg et al., Phys. Rev. Lett.,15, 294-297
(1965)
Paterno and Nordman, J. Appl. Phys., 49,
2456-2460 (1978)
30
31
Fiske resonance (VI)
Single layer josephson junction
Standing wave with open ends
Geometrical resonance
31
32
Fiske resonance (VII)

• The first peak shows non-periodic feature
  especially at low fields.
• Global tendency Vp is decreasing with increasing
  field.
• For small samples, Fiske step is overlapping
  (reason for the oscillation)
• Peak position at a given field does not depend on
  sample.
• V/N 0.2 mV corresponds to w/2p 96.4 GHz
• Similar behavior to LT mode in JPR

32
33
Josephson radiation

• Essentially Multi-layer property
• Something more Tachikis proposal

New Mechanism! Nonlinear Effect
N. B.

• Bukaevskii, Koshelev, et al. preprint,
• predicting high power radiation
  W/cm2

33
34
Principle of THz generation using intrinsic
Josephson junctions
Generation of Josephson vortex flow by external
dc current I
Generating Josephson plasma by nonlinear flow
of Josephson vortices
Formation of standing waves of Josephson plasma
Emission of THz radiation
Josephson plasma Oscillating super currents
EM waves
34
35
The THz waves
THz waves lie between visible light and
radio-waves a kind of electromagnetic waves
Dead zone, unexplored region
THz Waves frequency1012-1013 Hz wave length 300
-30 mm
THz region
35
36
Why THz is interesting?

• Scientific interests
• Electromagnetic radiation sources at THz region
  by making use of Josephson plasma excitation
• Continuous, coherent, tunable, high power, high
  efficiency electromagnetic waves.
• Interest in applications
• imaging(healthcare, medical treatments,
  diagnosing, security issues, environmental
  problems, etc.)
• Medicine, food hygiene, communication, automatic
  navigation, etc.

THz ? Frequency of molecular vibrations
36
37
THz applications and the influence

• imaging

(after Tochigi-NIKON)
(after Prof. Kawase)
37
38
Tachikis theory (I)

• Numerical analysis of nonlinear plasma wave
  equations by the earth simulator (M. Tachiki,
  Phys. Rev. B71 (2005) 134515.)

38
39
Tachikis Theory (II)
39
40
Tachikis Theory (III)
40
41
THz Experiments

• Fabrication of intrinsic Josephson junctions by
  using FIB (Focused Ion Beam)

FIB engineered single crystal Bi2Sr2CaCu2O8d
Operating circuit
intrinsic micro- Josephson junctions
MgO substrate
41
42
Detection experiments

• A bolometer method integrating all energies

The radiating direction is expected to be
reversed by reversing the
current
I
heating
current magnetic field
THz waves
directions.
voltmeter
current
V
I -
42
43
Experiments and data
Kadowaki, et al., Physica C (accepted) Kadowaki,
et al, Sci. and Technol. Adv. Mater. 6, 589
(2005).

• Direct observation of the radiation power

Josephson vortices moving towards the
detector (more power)
Josephson vortices moving against the
detector (less power)
Substrate
Detector
Sample
Detector and sample configuration
43
44
Experimental results (I)
Current reversal experiments
Total energy
radiation energy

heat
?
5
0.1 mW
P5 mW/10mm2 50 W/cm2
44
45
Experimental results (II)
Magnetic field reversal experiments
Samples so far studied
Evidence for Radiation!?
3-6 difference in power around 1 T by reversing
magnetic field
45
46
Experimental results (III)
46
47
Experimental results (IV)
47
48
Experimental results (V)
48
49
New experimental setup

• InSb hot electron detector
• spectrometer

Spectrometer 220,000 cm-1
Power Reduction
D diameter of the window of the detector 4
mm R distance between sample and detector 1 m
D4 mm
THz waves
reduction factor
current
r1 m
I
heating
H
1 mW power
1 pW
Sample
(Assuming no extra losses)
V
Superconducting Split Magnet
current
voltmeter
I -
49
50
Impedance Mismatching
50
51
Future plans

• Fundamental studies
• Frequency spectrum, improving sensitivity,
  stability, temperature and field dependences,
  etc.
• Development of high sensitivity spectrometer
• Magnetic field up to several T
• Temperature 4.2300 K(stable within a few mK)
• Angular setting small precision
  goniometer(accuracy1/1000 degree)
• Wave lengths 1mm0.1 cm
• Development of detectors
• integrated detectors bolometers (Si
  bolometer)
• InSb hot electron detectors
• others array of detectors for imaging
• Antennas and wave guides
• Communications, imaging, etc.

51
52
Summary (I)

• A beautiful evidence for the intrinsic Josephson
  junctions was shown.
• The lock-in angle Dq has been studied as
  functions of temperature, magnetic field, current
  and angle with respect to the ab-plane.
• The experimental evidence ((Dq ) ? 1/H, (Dq )2 ?
  1/l) can be explained by the energy balance
  between magnetic anisotropy and formation energy
  of a pancake vortex.
• It is intriguing to note that Josephson vortex
  flow resistance can be controlled by introducing
  only a few pancake vortices.

52
53
Summary (II)

• The new principle of THz generation is proposed
  and examined.
• The third light
• The radiation has superior properties to the ones
  obtained by conventional semiconductor devices.
• Radiation in THz frequencies is very useful to
  detect and to identify specific molecules,
  polymers, proteins, etc. because the vibration
  frequencies match with them. This opens a wide
  range of applications such as quantum
  electronics, environmental monitoring, drug
  manufacturing, medical care and diagnosing,
  security issues, etc.
• Developing new technologies for measurements and
  analyses creates new industrial activities.

53
54
Acknowledgements

• This work has been supported by
• the 21st Century Program, Promotion of Creative
  Interdisciplinary Materials Science for Novel
  Functions and
• the Core-to-Core Program Integrated Action
  Initiative, Nano-Science and Technology in
  Superconductivity.

Thank you.
54
55
High Quality Single Crystals

• Importance of identical stacking of Josephson
  junctions

Laue photo
Single Crystal
Rocking Curve
46
56
Surface Study
Low Temperature STM
Room Temperature AFM
47
57
STM Study(J. C. Davis group, Berkeley, USA)
15 nm x 15 nm square Constant current
topograph T4.2 K, I100 pA
130 nm x 130 nm square Zero-bias conductance nap
E. W. Hudson, et al., Science 285 88 1999.
48
58
Low Temperature STM Study (I)
K. Sakai, Osaka University
Hoogenboom, et al., Univ. of Geneva
49
59
Low Temperature STM Study (II)
B. M. Hoogenboom, et al., Physica C391 (2003)
376-380.
50
60
Diffraction Image of Abrikosov Vortex Lattice
Observation of Bragg Reflection by Small Angle
Neutron Diffraction Technique
4 K
55 K
75 K
51
61
THz applications and the influence

• Wide range of applications
• Quantum electronics, communications, etc.
• Environmental analyses
• Drug manufactures
• Medical cares
• Diagnosing
• Security issues
• etc.
• Creating new technologies
• Development of new industries

44