Shiro Kawabata - Higher School of Economics · S. Kawabata, Y. Tanaka, A. Golubov, A. S. Vasenko &...

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

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, 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

http://link.aps.org/doi/10.1103/PhysRevLett.104.117002

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


SN FI I

Q̇

V

Kawabata, Vasenko, Ozaeta, Bergeret, & Hekking, JMMM 383 (2015) 157


Shiro Kawabata - Higher School of Economics · S. Kawabata, Y. Tanaka, A. Golubov, A. S. Vasenko &...

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