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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
Spin-Wave Gaps in La2CuO4
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)
Spin-Wave Gaps in 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.
)
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)
Spin-Wave Gaps in 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.
)
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
Field Induced Spin Reorientation
(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
Field Induced Spin Reorientation
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
Field Induced Spin Reorientation
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
dTN / dHb ~ -4 K / T
0
1
0 100 200 300In
tens
ity
T (K)
TN
► I(T) peaked at TN
► (T) > 0 at all temperatures
XY
DM
Field Induced Spin Reorientation
TN
Field Induced Spin Reorientation
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
dTN / dHb ~ -4 K / T
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