Nonequilibrium dynamics of superconductors Ryo Shimano Cryogenic - - PowerPoint PPT Presentation

Ryo Shimano Cryogenic Research Center and Department of Physics University of Tokyo Nonequilibrium dynamics of superconductors

(1) Introduction (2) Photoexcitation in s-wave superconductor (3) Higgs mode in a s-wave superconductor NbN (4) Higgs mode in d-wave cuprate superconductors (5) Photoinduced metastable phase

Outline

Keiichiro Nasu,

• Rep. Prog. Phys. 67, 1607(2004)

Concept of Photoinduced Phase Transition

Yutaka Toyozawa,

• J. Phys. Soc. Jpn. 50, 1861(1981)

Dynamical localization

• N. Tsuji, T, Oka, P. Werner, and H . Aoki
• Phys. Rev. Lett 106, 236401(2011)
• T. Ishikawa et al., Nat. Commun.5, 5528(2014)

Interaction Quench

Photocreation of Berry phase

# realized in cold atoms: “Experimental realization of the toplological Haldane model with ultracold Fermions”, G. Jotzu et al., Nature 515, 237 (2014)

• rbital

lattice spin charge light THz

Superconductor

collective modes(Higgs, N-G) competing order, hidden phase pairing symmetry（p,d,.. ） light-induced superconductivity photocontrol

Light-control of ferroelectricity Light-control of magnetism Ultrafast control of multiferroics

electromagnon, skirmion

Floquet Engineering

control of topological number higher order harmonics generation

Nonequilibrium

Towards artificial light-control of quantum material

Time resolved spectroscopy ARPES XRD Electron Diffraction Terahertz Advanced Light Source/Probe Advanced light source Intense THz pulse mid-IR fs~as optical pulse

+

10

11

10

12

10

13

10

14

10

15

300nm 3mm 30mm 300mm 3mm

THz

30nm

10

16

1010

3cm

109

30cm

GHz Far-IR Mid-IR Microwave・・・Submillimeter wave N-IR UV visible PHz plasmon in doped semiconductors, pseudo gap (High Tc SCs) 4meV 40meV 0.4eV 4eV 40eV 0.4meV 40meV 4meV antiferromagnetic resonance phonons, molecular vibrations carrier scattering rate g

Elementary excitations in condensed matter systems

exciton ionization energy

2DBCS (Tc=10K)

1THz=4meV=300mm=33cm-1~50K

THz generation by femtosecond laser pulse Simultaneous measurements of amplitude and phase of E-field Determination of complex refractive Index without uisng Kramers-Kronig relation Time-resoved probe for ultrafast transient phenomena Imaging applications

Nonlinear crystal （ZnTe, GaP,GaAs,…)

Waveform and power spectrum

THz time-domain spectroscopy

10

• M. Ashida, Jpn.J.Appl.Phys.47, 8221 (2008)

A

gate optical pulse~10fs

THz time-domain spectroscopy

• J. Hebling et al., Opt. Express 10, 1161 (2002).
• J. Hebling et al., J. Opt. Soc. Am. B 25, B6 (2008).

Nonlinear crystal χ(2) (pm/V) ngr

800nm

nph

THz

GaP 25 3.67 3.34 ZnTe 69 3.13 3.27 LiNbO3 168 2.25 4.96

tilted pulse-front method THz generation from LiNbO3 : tilted pulse-front method

Intense THz pulse generation from LiNbO3

Large X(2), but large phase mismatch

0.8 0.4 0.0

• 0.4

Electric Field (MV/cm) 10 8 6 4 2 Delay Time (ps) 1.0 0.5 0.0 Intensity (arb. units) 3 2 1 Frequency (THz) LiNbO3 λ/2 grating wire grid×3 PM parabolic mirror (PM) PM GaP balanced photo detector Si×6 λ/4 Wollaston prism gate

(a)

f=80 f=-40 f=80

(b) (c)

• S. Watanabe, N. Minami, and R.Shimano,
• Opt. Express 19, 1528 (2011).

Intense THz pulse generation

• J. Hebling et al.,
• Opt. Express 10, 1161 (2002).

THz generation from LiNbO3 : tilted pulse-front method

100kV/cm →700kV/cm Tight focusing with small PM

E=6MV/cm→B=2T

Development laser-based table top THz pulse generation

6 5 4 3 2 1

Peak E-field (MV/cm)

2016 2014 2012 2010 2008

Year

DAST (EPFL) Two color air plasma (UTokyo) (MIT) (UTokyo) (Kyoto) LiNbO3+Metamatel. (MIT) Two color air plasma with mid-IR pump (AALS) LiNbO3

(1) Introduction (2) Photoexcitation in s-wave superconductor (3) Higgs mode in a s-wave superconductor NbN (4) Higgs mode in d-wave cuprate superconductors (5) Photocontrol of superconductors

Outline

Two constraints: Total electron density Total QP density μ* model Gap eq.

• C. S. Owen et al., Phys. Rev. Lett. 28, 1559 (1972).





s k s s

N c c

, k k †



 

s k q s

N N f

, k

   

1 *

exp 1



   m 

k s

E fk

 

 

*

2 1 tanh 2 1 m  

 

  

 k k k

E E d V N

c c

   

 

n n   D D  D D

2 2 3

Super-to-normal transition by quasiparticle injection

First order like transition

Experiments in 1970’s

Experiments in 1990’s: THz spectroscopy

SDW gap dynamics in quasi-1D organic conductor

• M. Beck et al., Phys. Rev. Lett. 107, 177007 (2011).

Optical pump and THz probe experiment in a s-wave superconductor NbN

Near infrared excitation

① hot electron excitation by near infrared light ② relaxation of hot electrons through high energy emission ③ Cooper pair breaking by phonons ④ gradual suppression of superconductivity

Energy DOS Near IR Hot electron phonon

T*

THz pumping: high density QP injection at the gap edge

・direct injection of QPs at the gap edge ・nonequilibrium SC state dynamics

Energy DOS

THz pulse

THz pump THz probe experiment

balanced detection gate pump THz (LiNbO3) sample wire grid wire grid Si probe THz (ZnTe) ZnTe Si

THz pump and THz probe in NbN

THz pump and THz probe dynamics

Barankov and Levitov, PRL 96, 230403 (2006)

 

k k

b  ), ( ), (

eff

t t D   D  

Quench Problem:

rapid switching of the orientation of bk

eff faster than the response

time of the pseudospin

Collective precession of the pseudospin = order parameter oscillation (Higgs mode)

Order parameter change induced by external perturbation = change in the orientation of bk

eff

k k k

σ b σ  

eff

2 dt d

)) ( ) ( ( ) ( ) ( t i t V t i t

y x k k k

     D    D



Order parameter dynamics in the BCS approximation

THz pump and THz probe dynamics

THz pump and THz probe dynamics

・What is this overshooting signal? Higgs?

(1) Introduction (2) Photoexcitation in s-wave superconductor (3) Higgs mode in a s-wave superconductor NbN (4) Higgs mode in d-wave cuprate superconductors (5) Photocontrol of superconductors

Outline

BCS theory: the nonzero order parameter

) ' , ( ) ( Δ

' ' '

  

  



k k c

c V

k

k k k

θ i θ i

e c c ce c



 

† †

,

breaks the invariance of the gauge transformation

History

Energy dispersion of BCS Bogoliubov quasipartice Energy dispersion of particle and antiparticle

http://www.nobelprize.org/

The dispersion of the quasiparticle

1957 BCS theory of superconductor (Bardeen, Cooper&Schrieffer) 1958 Prediction of amplitude mode in superconductors (Anderson) 1960 Theory of spontaneous symmetry breaking (Nambu) 1960-61 Nambu-Goldstone theorem 1963-66 Anderson-Higgs mechanism(Anderson, Higgs)

Goldstone Theorem

amplitude mode When spontaneous symmetry breaking occurs, massless collective mode with respect to the order parameter appears

ReΨ ImΨ Free Energy

phase mode

（ Nambu-Goldstone mode）

In particle physics: such a massless Nambu-Goldstone boson has never been observed. Instead, massive gauge bosons (W, Z) were found. Is N-G theorem wrong? E k

Free Energy

Re

Y

Im

Y

Y0 massive amplitude mode massive gauge boson

Anderson-Higgs mechanism

Local gauge transformation

Anderson-Higgs mechanism

“Anderson-Higgs mechanism” or “ Brout-Englert-Higgs mechanism” “ABEGHHK'tH mechanism “ [for Anderson, Brout, Englert, Guralnik, Hagen, Higgs, Kibble and 't Hooft]

amplitude mode E k phase mode

（ Nambu-Goldstone mode）

Z,W boson, p-mesons, plasmon

Massive gauge boson(photon) eating N-G mode in superconductors

Meissner-Ochsenfeld effect 1933 T>Tc T<Tc Meissner Anderson “Plasmons, Gauge Invariance, and Mass”

• Phys. Rev. 130, 439 (1963)

Mass of transverse component of photon E k 2D Higgs mode

single particle excitations

plasmon

PRB 1958

Theoretical investigations: quantum quench problem

Quenching the interaction U(t) much faster than τΔ ~ ℏ/Δ （Δ:order parameter）

Volkov et al., Sov. Phys. JETP 38, 1018 (1974). Barankov et al., PRL 94, 160401 (2004). Yuzbashyan et al., PRL 96, 230404 (2006). Gurarie et al., PRL 103, 075301 (2009). Podolsky, PRB84, 174522 (2011).

• A. P. Schnyder et al., PRB84, 214513 (2011)
• N. Tsuji et al., PRB 88,165115 (2013).
• N. Tsuji et al., PRL 110, 136404 (2013).

Theoretical studies for dynamics of nonequilibrium BCS state after nonadiabatic excitation Emergence of order parameter oscillation (Higgs mode)

Free energy

ReΨ

Higgs mode in superconductors: NbSe2

BCS-CDW coexistent compound

• R. Sooryakumar and M. V. Klein, PRL 45, 660 (1980).

P.B. Littlewood and C. M. Varma, PRL 47, 811 (1982). M.-A. Measson, et al., PRB 89, 060503 (2014). For a recent review:

• D. Pekker and C. M. Varma, Annual Review of Condensed Matter Physics 6, 269 (2015)

Instead of quenching the interaction,…

Energy DOS

2D(0) 2D(T)

Energy DOS EF Cooper pair quasiparticle photon hn The gap (order parameter) is determined self-consistently with the quasiparticle distribution f ()

Quasiparticle injection by ultrafast optical pulse

• T. Papenkort, V. M. Axt, and T. Kuhn,
• Phys. Rev. B76, 224522 (2007).

tpump< D1

Order parameter oscillation after instantaneous excitation near the gap edge

1.5 1.0 0.5 0.0 2.0 1.5 1.0 0.5 0.0 6x10

3

4 2 2.0 1.5 1.0 0.5 0.0

THz pump and THz probe experiment in NbN

Nb0.8Ti0.2N film (12nm)/Quartz TC = 8.5 K, 2Δ(T=4 K) = 3.0 meV = 0.72 THz

response time : tD  D-1 ~ 2.8 ps

Re σ (Ω-1cm-1) real-part

• ptical conductivity

Frequency (THz)

9K 4K 8K 6K 7K

Intensity (arb. units) pump pulse power spectrum Frequency (THz)

5K

Sample

Center frequency 0.7THz～2D

pulse width: tpump ~ 1.5 ps

tpump/tD ～0.57

< 1 nonadiabatic excitation condition THz pump pulse

10 8 6 4 2

Delay Time (ps) Pump Electric Field (arb. units) temporal waveform

gate LiNbO3 sample wire grid×3 wire grid ZnTe ZnTe balanced detection

pump THz pulse probe THz pulse

electro-optic sampling

tilted pulse-front scheme

Pump Probe wire-grid polarizer wire-grid polarizer sample x y z tpp

Pump ： Epump//x Probe： Eprobe//y tpp: pump-probe delay Transmitted probe THz electric field: Free space EO sampling tgate: gate pulse delay

THz pump and THz probe experiment in NbN

Detection of order parameter dynamics

Temperature dependence of the probe E-field without pump We fixed the gate delay at tgate=t0 and measure the pump-probe delay dependence Eprobe(tgate)

Probe Electric Field Eprobe (arb. units) Gate Delay Time tgate (ps) tgate=t0

At tgate=t0, the change in Eprobe is proportional to the change in the order parameter Δ.

Dynamics after the THz pump pulse

THz pump-induced change in the probe E-field δEprobe(tgate=t0)

8 6 4 2

• 2
• 4

1 nJ/cm

2

9.6 8.5 7.9 7.2 6.4 5.6 4.8 4.0

τpump/τΔ=0.57

Change of Probe Electric Field δEprobe(tgate=t0) (arb. units) Pump-probe Delay Time tpp (ps)

Order parameter dynamics

Pump Intensity (nJ/cm2)

Frequency (THz)

8 6 4 2

• 2
• 4

1 nJ/cm

2

9.6 8.5 7.9 7.2 6.4 5.6 4.8 4.0

0.6 0.4 0.2 0.0 10 8 6 4

Pump-probe Delay Time tpp (ps) Change of Probe Electric Field δEprobe(tgate=t0) (arb. units) U Δ Δ∞ Δ0 f = 2Δ∞

f 2Δ∞

• R. Matsunaga et al., PRL111, 057002 (2013)

2D-scan of THz pump and THz probe measurement

5 4 3 2 1

• 1
• 2
• 3

2.0 1.5 1.0 0.5 5 4 3 2 1

• 1
• 2
• 3

2.0 1.5 1.0 0.5 3x10

4

2 1 6x10

4

5 4 3 2 1 2.0 1.5 1.0 0.5 w/o pump 0.9 ps 1.3 ps 1.7 ps 2.1 ps 2.5 ps 2x10

4

1 2.0 1.5 1.0 0.5 w/o pump 0.7 ps 1.1 ps 1.5 ps 1.9 ps 2.3 ps (a) σ1 (ω) (Ω-1 cm-1) (b) σ2 (ω) (Ω-1 cm-1) σ1 (ω) (Ω-1 cm-1) σ2 (ω) (Ω-1 cm-1) Pump-Probe Delay Time tpp (ps) Pump-Probe Delay Time tpp (ps) Frequency ω (THz) Frequency ω (THz) Frequency ω (THz) Frequency ω (THz) (c) (d)

44

Time evolution of conductivity spectrum σ1(ω; tpp)

Higgs mode in larger gap samples τpump/τΔ≲1

1.5 1.0 0.5 0.0 2.0 1.5 1.0 0.5 0.0

Frequency (THz) Intensity (arb. units)

2 1 8 6 4 2 0.40 0.35 8 6 4 2 nJ/cm

2

100 90 77 δEprobe(tgate=t0) (arb. units)

f = 0.98 THz

τpump/τΔ=0.81 tpp (ps) 2Δ0=1.1 THz

1 8 6 4 2 8 6 4 2 0.06 0.05

nJ/cm

2

115 90 63

tpp (ps)

f = 1.34 THz

τpump/τΔ=0.98

δEprobe(tgate=t0) (arb. units)

2Δ0=1.3 THz

2D

• 0.1

0.0 12 10 8 6 4 Pump-Probe Delay Time (ps) Data Power-law fit Exponential fit

δEprobe (arb. units)

exponential decay t= 1.3 ps power-law decay

b = 0.71

Tc=15K, 2Δ(T=4K)=1.3THz

c2= 3.6×10-4 c2= 2.8×10-4

f=1.35 THz

Power law decay

Volkov et al., Sov. Phys. JETP 38, 1018 (1974). Yuzbashyan et al., PRL 96, 097005 (2006). Weak coupling case (BCS)

Dynamics in the coherent excitation regime

tpp (ps)

Pump pulse waveform Epump (arb. units)

1 8 6 4 2 8 6 4 2 0.06 0.05

nJ/cm

2

115 90 63

δEprobe(tgate=t0) (arb. units)

What is happening during the irradiation of AC driving field?

1.5 1.0 0.5 0.0 16 14 12 10 8 6 4 Temperature (K) Electric Field (arb. units) 25 20 15 10 5 Delay Time (ps) monocycle pulse monocolor pulse Intensity (arb. units) 2.0 1.5 1.0 0.5 0.0 Frequency (THz) monocycle pulse monocolor pulse

Coherent excitation regime with multicycle THz pulse

Quasi-monochromatic THz pulse（0.3THz, pulsewidth～13ps）

E-field waveform Power Spectrum

2Δ (THz)

Photon energy vs BCS gap

How does the BCS ground state respond to the strong electromagnetic field with ℏω<2Δ?

ℏω=0.3THz

10 8 6 4 2 Delay Time (ps) 10 8 6 4 2 Pump-Probe Delay Time (ps) 14 K 14.5 K 14.8 K 15.5 K 13 K 12 K 10 K 4 K

Epump |Epump|2 δEprobe (arb. units) ω=0.6THz E=3.5 kV/cm @ peak

Coherent Excitation Regime Experiments

• R. Matsunaga et al., Science 345, 1145 (2014)

2Δ(T)

ω=0.6THz

1 16 14 12 10 8 6 4 Temperature (K) δEprobe (arb. units)

long-term component

• scillating component

16 14 12 10 8 6 4 Temperature (K)

2ω

Anderson’s pseudospin (k  representation

: effective magnetic field for k Anderson, Phys. Rev. 112, 1900 (1958) Pseudospin up : (k, -k) both empty Pseudospin down: (k, -k) both occupied

Time evolution of BCS state= motion of pseudospins under effective magnetic field

) (

BCS     



 Y

k k k k k

c c v u ＋

normal state (T=0) BCS state kF k f kF k f

 

k k k k

σ b σ σ   

eff

2 , i dt d



 

k k k

σ beff

 



   

k k k y x

σ i σ U i " Δ ' Δ Δ

 

k k

b ε , " Δ , ' Δ

eff

  

k, -k empty k, -k occupied

In the presence of EM field (vector potential) z-component of effective magnetic field oscillates at 2 ⇒ precession of Anderson’s pseudospins

z beff

k

σk (εk-A+εk+A)/2

• Δ’

x εk

 

k k

b  , " , '

eff

D  D  

 



   

k k k y x

σ i σ U i " Δ ' Δ Δ

 

. ) ( e 2 ) ( ) ( ) ( 2 2 1

, 4 2 2 2 2 , 4 2 2 ) ( ) (

 

            

   j i t i j i j i j i j i j i t e t e

A O E E k k e A O t A t A k k e



      

k k k k A k A k

Pseudospin dynamics under the presence of vector potential A(t)

 

k k k k

σ b σ σ   

eff

2 , i dt d

Pseudospin dynamics : simulation with BdG equation

THz THG by Higgs mode

Current density

dD(t)～ei2t, A(t) ～ eit

) ( Δ ) ( Δ ) ( ~ 2 1 ) ( ) (

2 linear ) (

t δ t U e t t σ ε e n e t

z t e

A j k v j

k k A k k k A k

           

 

 

London equation for nonlinear current jnl

j (t) ～ ei3t

Does superconductor emit THz third harmonics?

Waveform of the transmitted pulse Power spectrum of the transmitted pulse

12 10 8 6 4 2 Delay Time (ps) 10 K 15.5 K Epump (arb. units)

Tc=15K

10

• 4

10

• 3

10

• 2

10

• 1

10 10

1

10

2

Intensity (arb. units) 2 1 Frequency (THz) 10 K 15.5 K

3ω ω

Efficient THG from superconductor

Nonlinear transmission experiment

5x10

• 2

4 3 2 1 Intensity (arb. units) 2.4 2.2 2.0 1.8 1.6 1.4 1.2 Frequency (THz) 4 K 8 K 10 K 11 K 12 K 13 K 14 K 15.5 K

1 1.2 1.0 0.8 0.6 0.4 1.5 1.0 0.5 0.0

0.8 THz

1 1.2 1.0 0.8 0.6 0.4 1.5 1.0 0.5 0.0

0.3 THz

1 1.2 1.0 0.8 0.6 0.4 1.5 1.0 0.5 0.0

0.6 THz

THG Intensity (arb. untis) Experiment 1 1.2 1.0 0.8 0.6 0.4

0.8 THz 0.6 THz 0.3 THz

T/Tc THG Intensity (arb. untis) Theory 1.2 THz 1.6 THz 0.6 THz 2Δ(T) (THz) T/Tc

Temperature dependence of THG

Experiments with different frequencies

ω=0.3, 0.6, 0.8 THz

THG shows a peak at 2ω=2Δ(T), but not at ω=2Δ(T)! Collective precession of Anderson’s pseudospin resonating with the Higgs mode

Theory: N. Tsuji and H. Aoki,

• Phys. Rev. B 92, 064508(2015)
• R. Matsunaga et al.,

Science 345, 1145 (2014)

Free Energy

Re

Y

Im

Y

Y0

Ginzburg-Landau picture

Local gauge transformation

Science 345, 1121 (2014)

Higgs vs Charge Density Fluctuation

• T. Cea, C. Castellani, and L. Benfatto,
• Phys. Rev. B93, 180507 (2016)

BCS with 2D square lattice model Pump polarization dependence BCS mean field: Higgs << Charge density fluctuation

E k 2D Higgs mode

single particle excitations

plasmon

Beyond BCS with retaradtion

• N. Tsuji , Y. Murakami, and H. Aoki, Phys. Rev. B 94, 224519 (2016)

Beyond BCS: When retarded interaction is taken into account, Higgs term can become larger than the charge density fluctuation.

Polarization dependence of THG

Polarization dependence of THG

Polarization of THG is always in parallel with the incident light polarization and its intensity is irrespective to the crystal axis. Higgs mode is the dominant origin of THG → Retardation effect beyond ＢＣＳ

• R. Matsunaga, et al. Phys. Rev. B 96, 020505(R) (2017).

(1) Introduction (2) Photoexcitation in s-wave superconductor (3) Higgs mode in a s-wave superconductor NbN (4) Higgs mode in d-wave cuprate superconductors (5) Photocontrol of superconductors

Outline

Higgs modes in d-wave SC

Barlas and Varma, PRB 87, 054503 (2013)

A1g A2g B2g B1g

Higgs modes in d-wave SC: nonequilibrium

• B. Fauseweh, et al., arXiv:1712.0798

• A. F. Kemper, M. A. Sentef, B. Moritz, J. K. Freericks, and T. P. Deveraux,
• Phys. Rev. B 92, 224517 (2015)
• B. Nosarzewski, B. Moritz, J. K. Freericks, A. F. Kemper,

and T. P. Deveraux et al., arXiv 1609.04080(2016)

Time-resolved ARPES (Theory)

THz pump and optical probe experiments in Bi2Sr2CaCu2Ox

400 200

• 200

5.0 2.5 0.0 Time (ps)

b a Cu-O Sample Time Delay THz Pump Optical Probe (800 nm) θ

10 8 6 4 2 Delay Time (ps) 10 8 6 4 2 Pump-Probe Delay Time (ps) 14 K 14.5 K 14.8 K 15.5 K 13 K 12 K 10 K 4 K

Epump |Epump|2 δEprobe (arb. units) ω=0.6THz E=3.5 kV/cm @ peak

Coherent Excitation Regime Experiments

• R. Matsunaga et al., Science 345, 1145 (2014)

2Δ(T)

ω=0.6THz

1 16 14 12 10 8 6 4 Temperature (K) δEprobe (arb. units)

long-term component

• scillating component

16 14 12 10 8 6 4 Temperature (K)

2ω

Phase diagram of Bi2Sr2CaCu2Ox

• M. Hashimoto et al., Nat. Phys. 10, 483 (2014)

UD OP OD

Transient reflectivity change

300 200 100 Temperature (K) 10 5 Time (ps)

8 4

DR/R (10

• 4)

TC

Cu-O THz Pump

a

Probe

°

Optical Probe

b

Symmetry of the signal

y x Cu O

y +

• +

x EProbe A1g B2g B1g

2.0 1.6 1.2 0.8 0.4 0.0 DRMax/R (10

• 3)

100 Probe (degree) 30 K 100 K 300 K Pump = 0°

) 2 sin 2 sin 2 cos 2 cos ( 2 1 Re 1 ~ ) , (

) 3 ( ) 3 ( ) 3 ( ) 3 ( ) 3 ( 1

2 1 1

probe pump B probe pump B A pump l pump k ijkl probe j probe i

g g g

E E R R E E R R   c   c c c c        D

Bi2212: D4h point group THz-induced Kerr effect

10 5 Time (ps)

1.5 0.0 DR/R (10

• 4)

B1g 300 200 100 Temperature (K) 10 5 Time (ps)

8 4 DR/R (10

• 4)

Tc A1g Temperature dependence of A1g and B1g

A1g: oscillatory(coherent) component + decay(incoherent) component B1g: only oscillatory(coherent) component

Decomposition into coherent and incoherent part

5.0 2.5 0.0 DR/R (10

• 4)

10 Time (ps)

10 K A1g

Temperature dependence of each component

Doping dependence

A1g signal is always dominant.

Polarization dependence of CDF mean field(BCS) theory with d-wave symmetry

W : 4meV  : 1.5 eV The dominance of A1g signal cannot be explained by CDF. CDF: B1g is dominant THz pump-optical probe

Doping dependence of the oscillating component

A1g signal is attributed to Higgs. B1g is most likely CDF.

200 150 100 50 Temperature (K) 1.0 0.8 0.6 0.4 0.2 0.0 B1g / A1g 0.20 0.10 Doping TC

• K. Katsumi et al., arXiv:1711.04923 (to be published in PRL)

poster presentation

(1) Introduction (2) Photoexcitation in s-wave superconductor (3) Higgs mode in a s-wave superconductor NbN (4) Higgs mode in d-wave cuprate superconductors (5) Photocontrol of superconductors

Outline

• D. Fausti et al.,

Science 331, 189 (2011). La1.675Eu0.2Sr0.125CuO4 Pump (//ab): 15 μm

• S. Kaiser et al.,

PRB 89, 184516 (2014). YBa2Cu3O6.45 Pump (//c): 15 μm

• D. Nicoletti et al.,

PRB 90, 100503(R) (2014). La1.885Ba0.115CuO4 Pump (//c): 800 nm

Photoinduced superconductivity

c-axis spectra of optimally doped La2-xSrxCuO4

1.0 0.8 0.6 0.4 0.2 0.0 Reflectivity 10 8 6 4 2 Photon Energy (meV)

50 K 40 K 30 K 25 K 20 K 15 K 5 K

0.20 0.15 0.10 0.05 0.00 Loss Function 10 8 6 4 2 Photon Energy (meV)

Reflectivity Optical conductivity σ1(ω) Loss function：Im(-1/ε(ω))

Tc = 35.5 K

THz probe

120 80 40  1 (W

• 1cm
• 1)

10 8 6 4 2 Photon Energy (meV)

In equilibrium: only one longitudinal mode

Raw Reflectivity 1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 470 48 7.3 1.4 µJ/cm 2 Energy (meV)

Reflectivity spectra under the 800-nm pump

100 ps

Optical Pump

n neq

800-nm pump: dpump=600nm THz: dTHz ~20 mm

0.2 0.1 0.0 10 8 6 4 2 Loss Function 120 80 40 10 8 6 4 2 Energy (meV) 1 W1cm-1) Energy (meV) 1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 Reflectivity 470 48 7.3 1.4 µ J/cm 2 Energy (meV)

Optical Pump

n

Optical spectra at the surface region under weak excitation

Consistent with optical pump optical probe at t=100ps [ M. Beyer, et al., Phys. Rev. B 83, 214515 (2011). ]. Energy required to destruct SC~14 K/Cu~150 mJ/cm2.

120 80 40

• 40

10 8 6 4 2 1.4 7.3 48 470 µJ/cm

2

120 80 40 10 8 6 4 2 0.2 0.1 0.0 10 8 6 4 2 1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2

Energy (meV) Energy (meV) Reflectivity 1 W1cm-1) Loss Function 2 W1cm-1)

Fitting by two fluid model

 

        



       

2 2

1

n

i

Continuous suppression of the Josephson plasma resonace

Reflectivity spectra under strong excitation

1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 3600 2600 1800 1100 770 µJ/cm2 1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 equil.

• 5 ps

3 14 350 Raw Reflectivity Raw Reflectivity

Excitation fluence dependence at 100 ps

Energy (meV) Energy (meV)

Dynamics

• 60
• 40
• 20

100 80 60 40 20 3600 470 48 7.3 µJ/cm2 200 100

• 100
• 200

5 4 3 2 1 Eprobe(arb.units) Gate Delay tgate (ps) Pump-Probe Delay t (ps) DEprobe(arb.units)

Optical spectra at the surface region under strong excitation

1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 0.2 0.1 0.0 10 8 6 4 2 120 80 40 10 8 6 4 2 120 80 40

• 40

10 8 6 4 2 Energy (meV) Energy (meV) Reflectivity Loss Function 1 W1cm-1) 2 W1cm-1) 3600 2600 1800 1100 770 µJ/cm2

A new longitudinal mode A new transverse mode

SmLa1-xSrxCuO4-δ

• T. Kakeshita et al., Phys. Rev. Lett. 86, 2122 (2001).

Double JPR in T*214

Two longitudinal and one Transverse JPR modes

Double JPR of YBa2Cu3O6.6 under B-field

• K. M. Kojima et al., PRL 89, 247001 (2002).

・Splitting of longitudinal JPR ・Emergence of transverse JPR

Bulaevskii and Clem, PRB 44, 10234 (1991).

Josephson vortex Two kinds of Josephson coupling “multilayer model”

Multilayer model

• D. van der Marel and A. Tsvetkov,
• Czech. J. Phys. 46, 3165 (1996);

PRB 64, 024530 (2001). ω ω

Loss Function σ1

ωL2 ωL1 ωL1 ωL2 ωL1 ωL1 ωL2 ωT

 

          



       

, 2 2

1

j n j j

i

   





j j j

z     MLM 1

Experiments

1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 0.2 0.1 0.0 10 8 6 4 2 120 80 40 10 8 6 4 2 1.0 0.8 0.6 0.4 0.2 0.0 10 8 6 4 2 0.2 0.1 0.0 10 8 6 4 2 120 80 40 10 8 6 4 2 120 80 40

• 40

10 8 6 4 2 120 80 40

• 40

10 8 6 4 2 1100 1800 2600 3600 µJ/cm

2

Calculation

Energy (meV) Energy (meV) Energy (meV) Energy (meV) Reflectivity Reflectivity 1 W1cm-1) 1 W1cm-1) 2 W1cm-1) 2 W1cm-1) Loss Function Loss Function

Fitting by the extended multilayer model in the strong photoexcitation regime

Pump fluence dependence of each JPR modes

8 6 4 2 3 2 1 10 10

1

10

2

10

3

10

4

Pump Intensity (μJ/cm2) dpump (μm) Peak Energy (meV) (a) A B B CuO2 CuO2 CuO2 CuO2 CuO2 CuO2 (c) (b)

L L’ T’

A A

• K. Tomari et al.,arXiv:1712.05086
• H. Niwa, poster presentation

• rbital

lattice spin charge light THz

Superconductor

collective modes(Higgs, N-G) competing order, hidden phase pairing symmetry（p,d,.. ） light-induced superconductivity photocontrol

Light-control of ferroelectricity Light-control of magnetism Ultrafast control of multiferroics

electromagnon, skirmion

Floquet Engineering

control of topological number higher order harmonics generation

Nonequilibrium

Towards light-control of quantum material

National Institute of Communication Technology

• K. Makise
• Y. Uzawa
• H. Terai
• Z. Wang (SIMIT at present)
• Dept. of Phys., Univ. of Tokyo
• H. Aoki
• N. Tsuji (Riken CEMS at present)

Coworkers and Collaborators

• R. Matsunaga
• Y. I. Hamada
• K. Tomita
• K. Tomari
• K. Katsumi

NbN: YBCO:

• Dept. of Phys., Osaka Univ.
• S. Tajima
• K. Lee
• S. Miyasaka

Bi2212: Brookhaven National Lab. R.D. Zhong, J.Schneeloch, G.D. Gu,

• Univ. of Paris Diderot
• Y. Gallais

LSCO:

• D. Song
• H. Eisaki

AIST