Magnetic and Raman response properties in La2CuO4

Marcello Barbosa da Silva Neto

Lara Benfatto

Vladimir Juricic

Cristiane de Morais Smith

Complex Behavior in Correlated Electron SystemsLorentz Center – 08/01 until 08/19 - 2005

 

Magnetism in the cuprates

1 2 2exps s

B

Cc k T

NLSM

Unusual magnetic susceptibility anisotropies

Unexpected hierarchy of T=0 susceptibilities!

ASHCROFT & MERMIN A. Lavrov et al. PRL (‘01)

The field induced mode – FIM

Only ONE magnetic mode for the (ab) and (RL) polarization

configurations of the light

Appearance of a second magnetic

mode for B || b, and ONLY for that orientation, in (RR) configuration

A. Gozar et al., PRL (‘04)

Magnetic anisotropies

Tilting+

SO coupling

Generalized nonlinear Sigma Model

M.B.Silva Neto, L.Benfatto, V.Juricic and C.Morais-Smith, cond-mat/0502588

n || b

D || a

|| c

Magnetic Susceptibility

Traditional UNIFORMsusceptibility

NEW STAGGEREDcontribution!!!!

20,0G M

Comparison with experiment

The electric-dipole Hamiltonian

zS S

TS I

r

E r EEDH 0r r r r r r rK S G S S

Elastic scattering S

,

A BED A BA B

H M S M S

Electric dipole selection rules

L=0

2 z z z zA S I S IM E E f D l l D i E E f D l l D i

L=1

1L

SOH L S

D zD

i

f

l1

1D rY

10

zD rY

One-magnon energy!

T TS I S I

,

E E E EA B A B

a a c cED a c

A B

H S S S S

0 0

0 0

0 0 0

ab

ba

M

M

a

0 0 0

0 0

0 0bc

cb

M

M

c

a b c

a

b

c

The final electric-dipole Hamiltonian

1gB 3gBor (ab) channel or (cb) channel

M.B.Silva Neto and L.Benfatto, cond-mat/0507103

Raman spectroscopy

Backscattering Geometry

Electric field ALWAYS parallel to the ab plane!!!

, ( , ,0)I F a bE E E��������������

0 0 0

0 0

0 0bc

cb

M

M

c

One-magnon Raman Intensity

2 21 A 0, A 0, B a a c cI n

0 0

0 0

0 0 0

ab

ba

M

M

a

A. Gozar et al., PRL (‘04)

Rotation of spin quantization basis – B||b

ˆ ˆL2 b c c b

Dx x

J

��������������

tan c

b

0, , ,b cn

The field induced mode - FIM

0 cos sin

cos 0 0

sin 0 0

ab ab

ba

ba

M M

M

M

a

2 2

2 2

0 0 0

0 sin cos sin cos

0 sin cos sin coscb bc bc cb

cb bc cb bc

M M M M

M M M M

c

Hole doping and spirals

Hole doping – dipolar frustration of the AF background

Anisotropies give robustness to the Neel ground state – DM gap vanishes at 2% - V. Juricic et al. in preparation!

Above 2% instability to a spiral phase

New periodicity!N.Hasselman et al., PRB (‘04)

Topological defects and transport

Doped holes – cores of topological defects

Dynamics of defects is dissipative – bath of magnons

V.Juricic et al., PRL (‘04)

Conclusions

Dzyaloshinskii Moryia interaction accounts for the unusual hierarchy of T=0 susceptibilities and for the anisotropic magnetic response.

It is also responsible for the rotation of the spin quantization basis and appearance of the FIM.

It gives robustness to the Neel ground state and vanishes at 2% where the ground state becomes a spiral.