Antiferromagnetic Resonances

1
Antiferromagnetic Resonances and Lattice
Electronic Anisotropy Effects in Detwinned
La2-xSrxCuO4 Crystals
Adrian Gozar
G. Blumberg B. Dennis

Crystals Yoichi Ando Seiki Komyia
CRIEPI, Japan
A. Gozar et al. Phys. Rev. Lett. 04
2
What is (detwinned) La2-xSrxCuO4 ?
T(K)
HTT
adapted from B. Keimer et al. PRB 46, 14034 92
500
HTT (tetragonal)
400
LTO (orthorhombic)
300
200
100
AF
SC
0.2
0.1
0.02
x(Sr)
3
Swapping the Crystal Axes with Magnetic Field
La1.99Sr0.01CuO4 TN 210K
A.N. Lavrov Nature 02
4
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

5
Antiferromagnetic Order in La2-xSrxCuO4 (x ? 0.02)
only in the LTO phase
6
Spin-Wave Gaps in La2CuO4
La2CuO4
C.J. Peters PRB 88
Neutron Scattering
7
Spin-Wave Gaps in La2CuO4
1 meV 8 cm-1
La2CuO4
C.J. Peters PRB 88
Neutron Scattering
Raman Scattering
8
Spin-Wave Gaps in La2CuO4
b
1 meV 8 cm-1
Raman Scattering
Experiment
9
Spin-Wave Gaps in La2CuO4
b
1 meV 8 cm-1
Raman Scattering
Experiment
10
Magnetic Field Induced Raman Modes in La2CuO4
T (K)
300
200
100
0
H // b
11
Field Induced Spin Reorientation
(A) T 10 K
? Spin-Wave calculation is consistent (up to 5)
with the dispersion of the XY gap
B. Keimer Z. Phys. 93
? ?XY 5.5 meV (44 cm-1)
? For H // b ? d ?DM / d Hb lt 0 ? one expects
a magnetic field induced transition
c
12
Field Induced Spin Reorientation
(A) T 10 K
? Spin-Wave calculation is consistent (up to 5)
with the dispersion of the XY gap
B. Keimer Z. Phys. 93
? ?XY 5.5 meV (44 cm-1)
? For H // b ? d ?DM / d Hb lt 0 ? one expects
a magnetic field induced transition
(B) T 300 K
? TN (La2CuO4) 310 K dTN / dHb -1K/T
c
300 K
?DM
strong H // b
d ? 0 ? 0
13
Field Induced Spin Reorientation
T (K)
300
200
100
0
H // b
9 T
14
Field Induced Spin Reorientation
La2CuO4
La1.99Sr0.01CuO4
TN
TN (La1.99Sr0.01CuO4) 210 K
dTN / dHb -4 K / T
15
Field Induced Spin Reorientation
La1.99Sr0.01CuO4
TN
TN (La1.99Sr0.01CuO4) 210 K
dTN / dHb -4 K / T
16
Field Induced Spin Reorientation
La1.99Sr0.01CuO4
H 0
TN
c
net ferromagnetic moment
b
TN (La1.99Sr0.01CuO4) 210 K
dTN / dHb -4 K / T
17
Lattice Electronic Anisotropy - La2-xSrxCuO4
c
T 10 K
1
2
(aa)
x 0
(bb)
b
a
Raman response (rel. units)
18
Local Structure at x 1/8 Sr Doping
La2-x-yNdySrxCuO4 T 10 K
(cc) polarization
1
2
A. Gozar PRB 03
19
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