Antiferromagnetic Resonances and Lattice & Electronic Anisotropy Effects

Antiferromagnetic Resonancesand

Lattice & Electronic Anisotropy Effectsin Detwinned La2-xSrxCuO4 Crystals

Crystals: Yoichi Ando & Seiki Komyia

Adrian Gozar #

G. Blumberg & B. Dennis

CRIEPI, Japan

#

A. Gozar et al. Phys. Rev. Lett. ‘04

Cu2+

O2-

La3+

What is (detwinned) La2-xSrxCuO4 ?

100

200

300

400

500

x(Sr)0.20.1

T(K)

AF SC

LTO(orthorhombic)

HTT(tetragonal)

0.02

adapted from B. Keimer et al. PRB 46, 14034 ‘92

HTT

a

bb

a

Y.Horibe PRB ‘00

LTO

a

b

c

b = 5.4 Ab - a ~ 0.05 A

R.J. Birgeneau PRL ‘87

Swapping the Crystal Axes with Magnetic Field

A.N. LavrovNature ‘02

room temperature

1 mmc

a(b)a(b)

b b

La1.99Sr0.01CuO4

TN ~ 210K

strong magneto-elastic coupling

net ferromagnetic moment ?

H ~ 14 T

H

In a magnetic field H // CuO2 planesthe b orthorhombic axis follows the

direction of the external field

Outline

Long Range Antiferromagnetic Order in La2-xSrxCuO4

Magnetic Field Dependent Raman Data in La2-xSrxCuO4

x(Sr) 0.01 low energy magnetic excitations

► anisotropic dispersions of spin wave gaps ► in H 11 T observation of magnetic field induced spin ordering (H // b-axis)

Strong Lattice and Electronic Anisotropies ► detwinned La2-xSrxCuO4 x(Sr) 0.03

► CuO6 tilt disorder at x(Sr) = 1/8 doping in (La,Nd)2-1/8Sr1/8CuO4

a

b

c

Antiferromagnetic Order in La2-xSrxCuO4 (x 0.02)

CuO2

planec

b

J

d

(3/4,1/4)

R. ColdeaPRL ’01

(1/2,0)(0,0)

Excitations

0 k

(k)

XY ~ m(2J)1/2

DM ~ md

ab

c

Cu2+

Spin Hamiltonian

B. Keimer Z. Phys ’93

2D Heisenberg

J ~ 140 meV

‘XY’ exchangeanisotropy

/ J ~ 10-4

‘DM’ Dzyaloshinskii-Moriya

d / J ~ 7 10-3 only in the LTO phase

Spin-Wave Gaps in La2CuO4

0 k

(k)

XY ~ m(2J)1/2

DM ~ md

Neutron Scattering

T = 80 K

C.J. Peters PRB ’88

~ 2 meV

Raman Scattering

10 15 20 25Raman shift (cm-1)

1

0

Ram

an r

espo

nse

(rel

. u.

)

1 meV ~ 8 cm-1

La2CuO4

10 15 20 25

0 T466.89

H || c(RL) pol.

Raman shift (cm-1)

1

0

Ram

an r

espo

nse

(rel

. u.

)

0 k

(k)

XY ~ m(2J)1/2

DM ~ md

Neutron Scattering

T = 80 K

Raman Scattering

C.J. Peters PRB ’88

1 meV ~ 8 cm-1


La2CuO4

CuO2

planec

b

H T. Thio PRB ’90

0 3 6 9

H || a

H || c

H || b

14

16

18

20

22

Ene

rgy

(cm

-1)

H (Tesla)


10 15 20 25

0 T466.89

H || c(RL) pol.

Raman shift (cm-1)

1

0

Ram

an r

espo

nse

(rel

. u.

)

Raman Scattering

1 meV ~ 8 cm-1

a

b

c

Experiment

b

2D Spin-Wave Model

0 3 6 9H (Tesla)

DM = 17.0 cm-1

XY

DM

CuO2

planec

0 3 6 9

H || a

H || c

H || b

14

16

18

20

22

Ene

rgy

(cm

-1)

H (Tesla)


10 15 20 25

0 T466.89

H || c(RL) pol.

Raman shift (cm-1)

1

0

Ram

an r

espo

nse

(rel

. u.

)

Raman Scattering

1 meV ~ 8 cm-1

a

b

c

Experiment

b

0 10 20 30 400

4

8

Raman shift (cm-1)

x = 0

x = 0.01

x = 0.02

x = 0.03

(ab) T = 10 K

0 10 20 30 400

10

20

(RR)

10 K

230 K9 6

0 T 9

0 T

6

Raman shift (cm-1)

300 K

9

6

0 T

Ram

an r

espo

nse

(rel

. u.

)

11 T

4

7x = 0

Magnetic Field Induced Raman Modes in La2CuO4

T (K)

0H // b

300

200

100

a

b

c

0 10 20 30 400

10

20

(RR)

10 K

230 K9 6

0 T 9

0 T

6

Raman shift (cm-1)

300 K

9

6

0 T

Ram

an r

espo

nse

(rel

. u.

)

11 T

4

7x = 0(A) T = 10 K

► Spin-Wave calculation is consistent (up to 5%) with the dispersion of the XY gap

B. KeimerZ. Phys. ’93

► XY ~ 5.5 meV (44 cm-1)

► For H // b d DM / d Hb < 0 one expects a magnetic field induced transition

c

(B) T = 300 K

► TN (La2CuO4) = 310 K & dTN / dHb ~ -1K/T

CuO2

plane

c

b

H = 0strongH // b

Field Induced Spin Reorientation

0 4 8 120

5

10

15

Ene

rgy

(cm

-1)

H (T)

0 10 20 30 400

10

20

(RR)

10 K

230 K9 6

0 T 9

0 T

6

Raman shift (cm-1)

300 K

9

6

0 T

Ram

an r

espo

nse

(rel

. u.

)

11 T

4

7x = 0


(A) T = 10 K

► Spin-Wave calculation is consistent (up to 5%) with the dispersion of the XY gap

(B) T = 300 K

B. KeimerZ. Phys. ’93

► XY ~ 5.5 meV (44 cm-1)

► For H // b d DM / d Hb < 0 one expects a magnetic field induced transition

► TN (La2CuO4) = 310 K & dTN / dHb ~ -1K/T

c

strongH // b

300 K

d ≠ 0 = 0

DM

is this a ‘regular’ spin-flop like transition ?

(continuous) spin reorientation in the (bc) plane


T (K)

0 H // b

300

200

100

a

b

c

9 T

0 10 20 30 40 500

10

20

Ram

an r

espo

nse

(re

l. u.

)

Raman shift (cm-1)

295 K

230

170110

10

200

0 10 20 30 40 500

10

20

Raman shift (cm-1)

180175160145

10 K

10050

Ram

an r

espo

nse

(re

l. u.

)

295275

250

200


0 10 20 30 40 500

10

20

Ram

an r

espo

nse

(re

l. u.

)

Raman shift (cm-1)

295 K

230

170110

10

200

La2CuO4La1.99Sr0.01CuO4

TN (La1.99Sr0.01CuO4) = 210 K

dTN / dHb ~ -4 K / T

TN

0

10

20

30

0 100 200 300

Ene

rgy

(cm

-1)

T (K)

TN

0 10 20 30 40 500

10

20

Raman shift (cm-1)

180175160145

10 K

10050

Ram

an r

espo

nse

(re

l. u.

)

295275

250

200

La1.99Sr0.01CuO4

TN (La1.99Sr0.01CuO4) = 210 K


0

1

0 100 200 300In

tens

ity

T (K)

TN

► I(T) peaked at TN

► (T) > 0 at all temperatures

XY

DM


TN


0 10 20 30 40 500

10

20

Raman shift (cm-1)

180175160145

10 K

10050

Ram

an r

espo

nse

(re

l. u.

)

295275

250

200

La1.99Sr0.01CuO4

TN (La1.99Sr0.01CuO4) = 210 K


TN

H = 0

netferromagnetic

moment

c

b

0

40

80

120

0 100 200 300 400

Lattice & Electronic Anisotropy - La2-xSrxCuO4

x = 0

Ram

an r

esp

on

se (

rel.

un

its)

T = 10 K(aa)(bb)

0

40

80

x = 0.01(aa)(bb)

0

40

80

0 100 200 300 400

x = 0.03

Raman shift (cm-1)

(aa)(bb)

1 2 La/Sr2 1

c

a

b

Local Structure at x ~ 1/8 Sr Doping

La/Sr2 1

0

10

20

30

0 100 200 300 400

Raman shift (cm-1)

LNSCOx ~ 1/8y = 0.4

LSCOx = 0.01

y = 0

LSCOx ~ 1/8y = 0

Ram

an r

espo

nse

(rel

. u.

)

x 0.04

La2-x-yNdySrxCuO4 T = 10 K

1 2

A. Gozar PRB ’03

(cc) polarization

► no signatures of charge super modulation in (cc) polarized Raman spectra - group theory for the LTO phase predicts 5 fully symmetric Raman active modes

► at 1/8 Sr doping there exists substantial disorder in the CuO6 octahedra tilt pattern

50 100 150

Conclusions

Magnetic Excitations

► DM and XY anisotropy induced spin-wave gaps ► For fields H // b observation of magnetic field induced spin reorientation

Low Energy Lattice & Electronic Dynamics ► detwinned La2-xSrxCuO4 x(Sr) 0.03 - about 30% anisotropy in the electronic background - strong phononic anisotropy

► x(Sr) = 1/8 (La,Nd)2-xSrxCuO4

- disorder in the local structure lattice has to be taken into account when discussing possible spin or charge modulation in LaSrCuO

0 10 20 30 400

10

20

(RR)

10 K

230 K9 6

0 T 9

0 T

6

Raman shift (cm-1)

300 K

9

6

0 T

Ram

an

resp

ons

e (

rel.

u.)

11 T

4

7x = 0

0

40

80

0

10

20

30

0 100 200 300 400

Raman shift (cm -1)

LNSCOx ~ 1/8y = 0.4

LSCOx = 0.01

y = 0

LSCOx ~ 1/8y = 0

Ram

an r

espo

nse

(rel

. u.

)

x 0.04

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Antiferromagnetic Resonances and Lattice & Electronic Anisotropy Effects