shiro kawabata - higher school of economics · s. kawabata, y. tanaka, a. golubov, a. s. vasenko...
TRANSCRIPT
Physics of superconductor/ferromagnet junctions
Shiro Kawabata National Institute of Advanced Industrial Science & Technology (AIST), JAPAN
Seminar at HSE Russia, Sep. 23rd 2016
Research field: Overview
Superconducting electronics
Quantum informationSpintronics
Rashba effect
Anti-weak localization
Circuit QED
Electron cooling
Odd-frequency paring
MQT & MQCTHz
Spin entanglement
Quantum metamaterial
Single molecular magnet
Synchronization
NV-centerTopological insulator
Weyl & Dirac semimetal
Quantum annealing
Quantum coding theory
Quantum feedback theory
Proximity effect
Quantum physics
Nonlinear Physics
Condensed matter theory
Nonlinear optical devices
THz generator
Spin transistor Magnetic sensor
Electron refrigerator
Nonvolatile memory
Current standard
Quantum annealing
From basic to application
Phase slip
Collaboration with Dr. Vasenko (2010~)S. Kawabata, A. S. Vasenko, A. Ozaeta, F. S. Bergeret & F. W. J. Hekking "Heat transport and electron cooling in ballistic normal-metal/spin-filter/superconductor junctions" Journal of Magnetism and Magnetic Materials 383 (2015) 157
A. S. Vasenko, S. Kawabata, A. Ozaeta, A. Golubov, F. S. Bergeret & F. W. J. Hekking "Detection of small exchange fields in S/F structures" Journal of Magnetism and Magnetic Materials 383 (2015) 175
S. Kawabata, A. Ozaeta, A. S. Vasenko, F. W. J. Hekking & F. S. Bergeret "Efficient electron refrigeration using superconductor/spin-filter devices" Appl. Phys. Lett. 103 (2013) 032602
A. S. Vasenko, A. Ozaeta, S. Kawabata, F. W. J. Hekking & F. S. Bergeret "Andreev current and subgap conductance of spin-valve SFF structures" J Supercond. Nov. Mag. 26 (2013) 1951
S. Kawabata, Y. Tanaka, A. Golubov, A. S. Vasenko & Y. Asano "Spectrum of Andreev bound states in Josephson junctions with a ferromagnetic insulator" J Supercond. Nov. Mag. 324 (2012) 3467
S. Kawabata, Y. Tanaka, A. A. Golubov, A. S. Vasenko, S. Kashiwaya & Y. Asano "Tunneling Hamiltonian description of the atomic-scale 0-π transition in superconductor/ferromagnetic- insulator junctions", Physica C 471 (2011) 1199
A. S. Vasenko, S. Kawabata, A. Golubov, M. Y. Kupriyanov, C. Lacroix, F. S. Bergeret & F. W. J. Hekking "Current-voltage characteristics of tunnel Josephson junctions with a ferromagnetic interlayer" Phys. Rev. B 84 (2011) 024524
A. S. Vasenko, S. Kawabata, A. Golubov & F. W. J. Hekking, ”Dissipative current in SIFS Josephson junctions" Physica C 470 (2010) 863
Contents
1.Superconducting spintronics with Ferromagnetic Metals
- Josephson effect & Proximity effect- Josephson π junction - Applications- Long range triplet Josephson effect
2. Superconducting spintronics with Ferromagnetic Insulators
- Ferromagnetic insulator & Spin-filtering effect - Atomic scale 0-π transition - Experiments - Applications 3. Summary
Josephson junction
I
φDriving force = phase difference in the macroscopic
wave function
Weakly coupled two superconductors
DC Josephson effect
I = IC sin�
⇥ = �1 � �2
�ei�1 �ei�2
Josephson current (= tunneling of cooper pairs)
DC current can flow without bias voltage
Ic: Critical current
π-junction in S/FM/S systems
FM : Ferromagnetic Metal (Fe, Co, ...)Exchange field
Buzdin, Rev. Mod. Phys. 77 (05) 935
Pair-amplitude oscillation
Non-zero momentum due to the spin exchange splitting in FMs
Josephson Current I = −IC sinφ = IC sin(⇥ + �)
π-junctionI/IC
φ
0-junction0.0 0.5 1.0 1.5 2.0
-1.0
-0.5
0.0
0.5
1.0
I = +IC sin�
I = �IC sin�
Conventional
Eschrig, Phys. Today 64 (11) 43
Cooper pair in S/FM hybrids
| �⇥⇤
| ⇥�⇤
Cooper pair in S
| ⇤⇥⌅ � e�ix�p| ⇤⇥⌅
| ⇥⇤⌅ � eix�p| ⇥⇤⌅
Cooper pair in F eix�p| ⇥⇤⌅ � e�ix�p| ⇤⇥⌅
| ⇥⇤⌅ � | ⇤⇥⌅
�p =2Eex
�vF
Re⇥ = cos(�px)Spatial oscillation (FFLO Oscillation)
Proximity effect in S/FM hybrids
Order parameter oscillations
Proximity decay
Proximity decay
D: Diffusion constantEex: Exchange energy
Dirty limit
T: Temperature
Weides, Martin P. (2006) Josephson tunnel junctions with ferromagnetic interlayer. PhD thesis, Universität zu Köln.
VOLUME 86, NUMBER 11 P H Y S I C A L R E V I E W L E T T E R S 12 MARCH 2001
FIG. 2. (Top) Schematic cross section of the sample. (Center)Typical I-V characteristic. (Bottom) Magnetic field dependenceof the critical current Ic for the junction with Cu0.5Ni0.5 anddF ! 14 nm.
alloy thickness, showed a small hysteresis loop with acoercive field of about 8 mT and a saturation moment of0.07mB!Ni atom. We found no significant difference be-tween single layers and trilayers, from which we concludethat also in the junctions the alloy layer is ferromagneticand that a supercurrent can be sustained even through aferromagnetic layer. Figure 3 shows Ic"T # in zero mag-netic field for two junctions with dF ! 22 nm [17]. Thecurve marked (a) shows that Ic increases with decreasingtemperature, goes through a maximum, returns to zero,and rises again sharply. For all data points, it was ascer-tained that the zero-field value was the maximum value forIc. The curve marked (b) shows the same characteristicbehavior although the zero value for Ic lies at a differenttemperature. In this case Ic"H# characteristics were mea-sured at three different temperatures to ascertain that Ic
FIG. 3. Critical current Ic as a function of temperature T fortwo junctions with Cu0.48Ni0.52 and dF ! 22 nm [17]. Inset: Icversus magnetic field H for the temperatures around the cross-over to the p state as indicated on curve b: (1) T ! 4.19 K,(2) T ! 3.45 K, (3) T ! 2.61 K.
was determined correctly. The data, shown in the inset ofFig. 3, prove that the Ic"T # oscillations are not associatedwith residual magnetic inductance changes which wouldchange the position of the central peak. It is important torealize that the phase difference in zero applied field isuniform in the plane of the junction, either 0 or p . TheFraunhofer pattern will not shift when the phase turns from0 to p , but the zero-field Ic goes from positive to negative.In a current-driven experiment, this leads to the sharp cuspobserved in Ic"T #. The p state can also be demonstratedby the thickness dependence of the effect. Shown inFig. 4a is a series of measurements for junctions of differ-ent thicknesses in the range 23 to 27 nm. At 23 nm onlypositive curvature is visible, an inflection point is observedfor 25 nm, a maximum for 26 nm, and the full cusp nowat 27 nm. Figure 4b shows a set of calculations based onthe formalism of the quasiclassical Usadel equations [18],with reasonable parameters for Eex and dF!j!, wherej! ! $h̄D!"2pkBTc#%1!2. They qualitatively demonstratehow the crossover moves into the measurement windowupon increasing the F-layer thickness. Quantitatively, thethickness dependence in the calculations is much weakerthan in the experiments. Parameters such as the spin flipscattering length probably also play a role. Still, the ap-pearance of the crossover is mimicked correctly. If weestimate it around dF!2pjF2 & 0.4 0.5, it follows thatjF2 & 10 nm, as expected for the low magnetic momentand justifying the assumption of dirty limit conditions.
A final remark concerns qualitative and quantitative re-producibility. Qualitatively, the cusps can be observed forcertain thickness intervals in all sample batches with fer-romagnetic layers which are presently fabricated, both for
2429
VOLUME 86, NUMBER 11 P H Y S I C A L R E V I E W L E T T E R S 12 MARCH 2001
FIG. 2. (Top) Schematic cross section of the sample. (Center)Typical I-V characteristic. (Bottom) Magnetic field dependenceof the critical current Ic for the junction with Cu0.5Ni0.5 anddF ! 14 nm.
alloy thickness, showed a small hysteresis loop with acoercive field of about 8 mT and a saturation moment of0.07mB!Ni atom. We found no significant difference be-tween single layers and trilayers, from which we concludethat also in the junctions the alloy layer is ferromagneticand that a supercurrent can be sustained even through aferromagnetic layer. Figure 3 shows Ic"T # in zero mag-netic field for two junctions with dF ! 22 nm [17]. Thecurve marked (a) shows that Ic increases with decreasingtemperature, goes through a maximum, returns to zero,and rises again sharply. For all data points, it was ascer-tained that the zero-field value was the maximum value forIc. The curve marked (b) shows the same characteristicbehavior although the zero value for Ic lies at a differenttemperature. In this case Ic"H# characteristics were mea-sured at three different temperatures to ascertain that Ic
FIG. 3. Critical current Ic as a function of temperature T fortwo junctions with Cu0.48Ni0.52 and dF ! 22 nm [17]. Inset: Icversus magnetic field H for the temperatures around the cross-over to the p state as indicated on curve b: (1) T ! 4.19 K,(2) T ! 3.45 K, (3) T ! 2.61 K.
was determined correctly. The data, shown in the inset ofFig. 3, prove that the Ic"T # oscillations are not associatedwith residual magnetic inductance changes which wouldchange the position of the central peak. It is important torealize that the phase difference in zero applied field isuniform in the plane of the junction, either 0 or p . TheFraunhofer pattern will not shift when the phase turns from0 to p , but the zero-field Ic goes from positive to negative.In a current-driven experiment, this leads to the sharp cuspobserved in Ic"T #. The p state can also be demonstratedby the thickness dependence of the effect. Shown inFig. 4a is a series of measurements for junctions of differ-ent thicknesses in the range 23 to 27 nm. At 23 nm onlypositive curvature is visible, an inflection point is observedfor 25 nm, a maximum for 26 nm, and the full cusp nowat 27 nm. Figure 4b shows a set of calculations based onthe formalism of the quasiclassical Usadel equations [18],with reasonable parameters for Eex and dF!j!, wherej! ! $h̄D!"2pkBTc#%1!2. They qualitatively demonstratehow the crossover moves into the measurement windowupon increasing the F-layer thickness. Quantitatively, thethickness dependence in the calculations is much weakerthan in the experiments. Parameters such as the spin flipscattering length probably also play a role. Still, the ap-pearance of the crossover is mimicked correctly. If weestimate it around dF!2pjF2 & 0.4 0.5, it follows thatjF2 & 10 nm, as expected for the low magnetic momentand justifying the assumption of dirty limit conditions.
A final remark concerns qualitative and quantitative re-producibility. Qualitatively, the cusps can be observed forcertain thickness intervals in all sample batches with fer-romagnetic layers which are presently fabricated, both for
2429
Ryazanov et al, PRL 86 (2001) 2427 Kontos et al, PRL 89 (2002) 137007
Oboznov, Ryazanov, Buzdin (06), Bell, Blamire (06), Weides, Goldobin, Kleiner(06), Birge(09), ...
Experiments
3
aspect ratio of the sub-micron patterned device.23 In thiscase the applied field required to modulate the IC doesnot significantly affect the magnetization of the Py, andthe IC(H) is symmetric about zero field. The good fit tothe ideal ‘Fraunhofer’ pattern indicates a uniform currentflow in the junction. Relatively smaller junctions, whichrequire larger fields to modulate the IC , were found toshow hysteresis which we associate with changes in thePy domain structure and magnetization. Net magneticinduction present in the barrier is known to shift theIC(H) pattern away from H = 0 and reduce the IC atzero field from its true maximum value.24 To avoid falsely
FIG. 3: IC(H) modulation for a device demagnetized at 4.2 Kfor a 2 nm thick Py barrier. Device dimension in the directionperpendicular to the applied field ∼ 1.06 µm. Line is a bestfit to a ‘Fraunhofer’ function.
small values of IC , the films were demagnetized at 4.2K, as well as the IC(H) pattern being directly measuredwhere possible, (for devices with ICRN > 2 µV). In somecases however, the offset of the maximum IC from H = 0could not be removed. The cause of this is ascribed toshape anisotropy in the sub-micron devices which pro-vides an additional demagnetizing field which may pre-vent the formation of a flux-closed domain structure inthe barrier.
The variation of ICRN (dPy) is shown in Fig. 4.Other devices showed much larger JC values, but showedstrongly distorted or no IC(H) modulation, implyingshorting around the edges of the junctions due to rede-posited material during device fabrication. For dPy > 8nm the devices showed some reduction of the differentialresistance around zero current bias, but did not show ameasurable supercurrent at T = 4.2 K, (this was alsothe case in several devices with dPy = 7 and 8 nm). Nore-entrant ICRN was observed up to dPy = 12 nm. Itis clear that there is a strong suppression of ICRN forincreasing dPy, but despite some scatter in the data ofFig. 4 for each set of devices with constant dPy, the de-cay is clearly not purely exponential. A component of
FIG. 4: Characteristic voltage ICRN , as a function of Pythickness at T = 4.2 K. Dashed and solid lines are two fits toEq. (1), as described in the text.
this non-monotonic change may be associated with theslightly different preparation methods of the 2, 4 and 6nm thick barriers, or run to run variation in the system.For example for dPy = 3 nm, the fully in-situ depositionmay imply a higher quality and larger ICRN , howeverthis is inconsistent with the same comparison betweenthe samples with dPy = 4, 5 and 6 nm. Therefore thevariation in ICRN would seem to be a true effect associ-ated with the oscillatory induced superconducting orderparameter in the Py layer.
We can compare the behavior of these junctions tothe non-epitaxial evaporated junctions of Blum et al.8,with the structure Nb/Cu/Ni/Cu/Nb. In that case ameasurable critical current at T = 4.2 K was observedup to a Ni thickness of 9 nm - similar to the present data.Due to the relatively small number of data points and thescatter, it is difficult to accurately fit this non-monotonicdecay. We model the data using
ICRN ∝ | sin(2EexdF /!vF )|/(2EexdF /!vF ) , (1)
where vF is the Fermi velocity of Py, and Eex the ex-change energy.1,8 These two parameters have recentlybeen measured25 in Py as Eex = 135 meV and vF =2.2±0.2×105 ms−1 (for the majority spin). The lines inFig. 4 correspond to Eex = 95 meV, with both vF = 2.2and 2.1 × 105 ms−1, to indicate the degree of variationthe error in vF causes. The agreement between the dataand the model is not ideal, however for an order of mag-nitude estimate it is clear that the fit is acceptable. Theperiod of oscillation of ICRN (dF ) is given by π!vF /Eex,and can therefore be estimated to be of the order of 5 nm,again similar in magnitude to the 5.4 nm value obtainedby Blum et al.8
For the previously mentioned Ni junctions8, a max-imum IC ∼ 20 mA was observed at T = 4.2 K in10 × 10 µm2 devices for a 1 nm thick Ni barrier, giv-
Nb/CuNi/NbTemperature dependence FM thickness dependence
Nb/PdNi/Nb
Applications of π junctions
Quiet QubitSuperconductor ring with single π-junction
Bulaevskii, Kuzii & Sobyanin, JETP Lett. 25 (1977) 291
Spontaneous circulating current
Provides natural and precisely-degenerate quantum two-level system
WITHOUT applying external magnetic field
�0/2��0/2
Quiet flux qubitYamashita, Takahashi, Maekawa, PRL 95 (05) 097001
Robust to the fluctuation of external fields
Note: usual flux qubit (0-junction ring): External flux bias is needed
Blatter et al, PRB 63 (01) 174511 Ioffe et al, Nature 398 (99) 679
single-valued nature→
π junction circuits
Classical logic circuit Quantum logic circuit
Phase qubitFlip flop
Feofanov Ustinov, et al, Nature Phys. 6 (2010) 593
Rabi oscillationScalable
Ortlepp et al, Science 312 (2006) 1495
SF hybrid memory: Beak et al., Nature Comm. 5(2014)3888
Drawback of FM for quantum applications
How to avoid?→Ferromagnetic INSULATORS (FIs)!
FM is a metal→Low energy quasiparticle excitation →Strong damping & decoherence
FI based superconducting spintronics for quantum applications
DOS: FM vs FI
FM: Co, Fe, Ni,…
E
FI: Eu chalcogenides (EuO, EuSe), Spinel ferrites(NiFe2O4),
Oxides (LMO, LBMO, LCMO)...
EF
Moodera, Santos & Nagahama J. Phys.: Cond. Mat. 19(2007)165202
Ferromagnetic insulatorEu chalcogenides
→Spin filter
EF
5d
4f
5d
4f
EF
5d
4f
5d
4f
www.webelements.com
Spin filtering effectG. Printz, Phys. Today No.4 (1995)58.
Ec
Ec
Ferromagnetic Semiconductor :EuSe, EuS
Ec
EcPRL 61(‘88)637, 70(’93)853
S
Reflection
Transmission
FS S
S FS S
Meservey & Tedrow, Phys. Rep. 238 (1994) 173
Experiments:Eu chalcogenides (EuO, EuSe),
Spinel ferrites(NiFe2O4), Oxides (LaMnO, LBMO, LCMO)...
Spin-selective tunneling = Spin filter
FI
FIN N
NNSince the transmission probability depends exponentially on the barrier height, a highly-spin polarized current is generated by the barrier.
Ferromagnetic Oxide
La2BaCuO5
First principle LSDA+U calculation
Vex � 0.34eV
↑band
↓band
Eyert et al, Europhys. Lett. 31 (1995) 385
Mizuno et al, Nature 345 (1990) 788
Oxide ferromagnet
Both bands (hybridized Cu-d & O-p) are split
FI based superconducting spintronicsSpin-filter Josephson effect
Macroscopic quantum tunneling (MQT)
Atomic-scale 0-pi transition
Qubit
Electron refrigerator & Heat device
Majorana fermion & Topological qubit (S/QSHI/FI junction)
Kashiwaya & Tanaka Physica 274 (1997) 357 Kawabata & Asano, Int. J. Mod. Phys. 23 (2009) 4320 Senapati, Blamire & Barber, Nature Mat. 10 (2011) 849 Experiment Pal, Barber, Robinson & Blamire, Nature Comm. 5(2014)3340 Experiment
Kawabata, Asano, Tanaka, Golubov & Kashiwaya, Phys. Rev. Lett. 104 (2010) 117002
Kawabata, Tanaka, Golubov, Vasenko, Kashiwaya & Asano, Physica C 471 (2011) 1199Kawabata, Asano, Tanaka & Kashiwaya, Physica E 42 (2010) 1010Kawabata, Asano, Low Temp. Phys. 36 (2010) 915 REVIEW
Kawabata, Kashiwaya, Asano, Tanaka & Golubov, Phys. Rev. B 74 (2006) 180502(R)
Kawabata, Kashiwaya, Asano & Tanaka, Physica C 427-438 (2006) 136
Kawabata, Asano, Tanaka, Kashiwaya & Golubov, Physica C 468 (2008) 701Kawabata & Golubov, Physica E 40 (2007) 386
Kawabata, Kashiwaya, Asano, Tanaka & Golubov, Phys. Rev. B 74 (2006) 180502(R)
Kawabata, Vasenko, Ozaeta, Bergeret, & Hekking, JMMM 383 (2015) 157Kawabata, Ozaeta, Vasenko, Hekking & Bergeret, Appl. Phys. Lett. 103 (2013) 032602
Vasenko, Kawabata, Golubov, Kupriyanov, Lacroix, Bergeret & Hekking, Phys. Rev. B 84 (2011) 024524
Sau, Lutchyn, Tewari & Das Sarma, Phys. Rev. Lett. 104 (2010) 040502Alicia, Repts. Prog. Phys. 75 (2012) 076501 REVIEW
Massarotti, Pal, Rotoli, Longobardi, Blamire & Tafuri, Nature Comm. 6 (2015) 8376 Experiment
SN FI I
Q̇
V
Giazotto et al., Appl. Phys. Lett. 105 (2016) 062602Linder & Bathen, Phys. Rev. B 93 (2016) 224509
Josephson effect through FIs Atomic scale 0-pi transition
Superconductor Superconductor (BCS)Ferromagnetic insulator
1 ...... ...j = 0 LF
m = 1
m = W
...
Tight binding BdG calculation
Bogolibov de-Gennes eq.
Andreev levels
Josephson current IJ(�) =2e
��
n
⇤⇥n(�)⇤�
f(⇥n)
⇥n(�)
Exchange energy VexEF Vexg
g=Vex-8t: Band gap
FI layer numberJosephson critical current
0 junction
π junction
1 2 3 4 5 6 7 8
1
1
10�1
10�2
10�3
10�3
10�2
10�1
FI layer number = EVEN2 4
0 junction 0 junction
FI layer number = ODD
1 3
π junction π junction
1 2 3 4 5 6 7 8
IC < 0
IC > 0
|IC
(n)/
I C(1
)|Josephson current
LF
Kawabata et al., Phys. Rev. Lett. 104(2010)117002
EVEN
ODD
IJ = IC sin�
Atomic scale 0-π transition
Origin of πfor the tunneling limitIC � T �
⇤ T⇥ g � t
VexEFg
t4
∴π-junction
∴ Ic<0
T� � �t
g< 0
T� � +t
g> 0
Transmission coefficient of an electron through FI barrier
S FI S
S FI S
Spin-dependent sign changeelectron
electron | �⇥
| �⇥ �| ⇥⇤
| �⇥
|��� � |��� � (|��� � |���)Cooper pair
Kawabata et al., PRL104(10)117002
Cuevas & Fogelstrom PRB 64(01)104502Zhao, et al., PRB 70(04)124510
π junction
Origin of π
S FI (single layer) SCooper pair
|�in⌅ =1⇧2
(| ⇥⌅| ⇤⌅ � | ⇤⌅| ⇥⌅)
Spin-dependent sign changeelectron
electron | �⇥
| �⇥ �| ⇥⇤
| �⇥
|�out⇧ ⇥ � (| ⇤⇧| ⌅⇧ � | ⌅⇧| ⇤⇧)
= �|�in⇥-1
FI (LF layers)
…|�in⌅ =
1⇧2
(| ⇥⌅| ⇤⌅ � | ⇤⌅| ⇥⌅)
π-junctionEven LF
Odd LF
0-junctionIC < 0IC > 0
|�out⇤ ⇥ (�1)LF |�in⇤-1 -1 -1 -1 -1 -1
π-junction
VexEF
FI
…|�in⌅ =
1⇧2
(| ⇥⌅| ⇤⌅ � | ⇤⌅| ⇥⌅) |�out⇤ ⇥ (�1)LF |�in⇤-1 -1 -1 -1 -1 -1
εF
Δp p
E
ε↑
ε↓
2Eex
FM
Finite center of mass momentum due to the exchange splitting
Spin-dependent phase shift
0
4
2 � 0 � 0 � 0 � 0
g[/t
]
LF
Robustness of the atomic scale 0-π transitionExchange splitting: g
Temperature: T
Magnetization configuration
Order parameter symmetry s-wave JJ & d-wave c-axis JJ
(Colinear)
FI layer
High-Tc layer
High-Tc layer
LaLb
Ferro (uniform)
Anti-ferro
Dimensionality (1D, 2D, & 3D)
DOS asymmetry
EF
Nakamura, Souma, Ogawa & Kawabata, Physics Procedia 27 (2012) 308
Kawabata, Asano, Tanaka, Golubov & Kashiwaya, Phys. Rev. Lett. 104 (2010) 117002Kawabata, Tanaka, Golubov, Vasenko, Kashiwaya & Asano, Physica C 471 (2011) 1199
Kawabata, Asano, Tanaka & Kashiwaya, Physica E 42 (2010) 1010Kawabata & Asano, Low Temp. Phys. 36 (2010) 915
Experiments
ExperimentsSpin-filter Josephson effect
Fraunhofer pattern & Pure 2nd harmonics
Pal, Barber, Robinson & Blamire, Nature Comm. 5(2014)3340
EF
5d
4f
5d
4f
EF
5d
4f
5d
4f
Josephson current !
NbN/Spin-filter(GdN)/NbN
Senapati, Blamire & Barber, Nature Mat. 10 (2011) 849
Macroscopic quantum tunneling (MQT)Massarotti, Pal, Rotoli, Longobardi, Blamire & Tafuri, Nature Comm. 6 (2015) 8376
Theory: Kawabata, et al., Phys. Rev. B 74 (2006) 180502(R)
Applications
Quantum application
Coherent π-qubit Electron refrigerator
Highly coherent flux qubit Highly efficient cooler for quantum devices
Kawabata, Kashiwaya, Asano, Tanaka & Golubov, Phys. Rev. B 74 (2006) 180502(R) Kawabata, Ozaeta, Vasenko, Hekking & Bergeret, Appl. Phys. Lett. 103 (2013) 032602
SN FI I
Q̇
V
Other applications:Topological qubit: Sau, Lutchyn, Tewari & Das Sarma, Phys. Rev. Lett. 104 (2010) 040502Heat transistor: Giazotto et al., Appl. Phys. Lett. 105 (2016) 062602Spin caloritronics: Linder & Bathen, Phys. Rev. B 93 (2016) 224509
SummarySuperconductor spintronics based on
ferromagnetic insulators
Josephson effect : Atomic scale 0-π transition Macroscopic Quantum Tunneling
Applications : Coherent qubit & Efficient electron refrigerator
Ferromagnetic-insulator based superconducting-spintronics would be useful for future QUANTUM & COOLING businesses.
REVIEW: Kawabata & Asano, Low Temp. Phys. 36 (2010) 915Kawabata, Asano, Tanaka, Golubov & Kashiwaya, Phys. Rev. Lett. 104 (2010) 117002
Kawabata, Ozaeta, Vasenko, Hekking & Bergeret, Appl. Phys. Lett. 103 (2013) 032602
Kawabata, Kashiwaya, Asano, Tanaka & Golubov, Phys. Rev. B 74 (2006) 180502(R)
SN FI I
Q̇
V
Kawabata, Vasenko, Ozaeta, Bergeret, & Hekking, JMMM 383 (2015) 157