ElectronPhonon Coupling in Charge Density Wave ZrTe3

1
Electron-Phonon Coupling in Charge Density Wave
ZrTe3

• Moritz Hoesch,
• Alexey Bosak, Alessandro Mirone, Michael Krisch
• European Synchrotron Radiation Facility ESRF
• Helmuth Berger École Polytechnique Fédérale de
  Lausanne, Suisse
• Dmitry Chernyshov Swiss-Norwegian Beamlines at
  ESRF

2
ZrTe3 crystal structure and resistivity
resistivity anomaly along a and
c anisotropy ra / rb 1 rc / ra 10
prismatic (ZrTe3)8 chains along b
TCDW 63 K, QCDW (1/14 0 1/3 )
S. Takahashi et al. Journal de Physique 6 (1983)
C3-1733 D.J. Eaglesham et al. J.Phys. C 17 (1984)
L697
Te Te chains along a
3
anomalous feature in the diffuse scattering
diffuse scattering at SNBL BM01A reconstructed
a-c plane MAR345 image plate detector
T 295 K (4.7 TCDW)
T 80 K (1.3 TCDW)
(h0l)-plane
(h0l)-plane
4
dispersion across qCDW
5
temperature evolution of the Kohn anomaly
mean field theory
observation close to
giant Kohn anomaly leads to the lattice
instability.
6
origin of the diffuse scattering intensity
IXS intensities from fit vs diffuse scattering
intensity
diffuse scattering is dominated by non-phonon
scattering --gt onset of order contributes
strongly to diffuse scattering
7
diffuse scattering around qCDW
T gt TCDW sharpening up of diffuse scattering
T lt TCDW growth of intensity of
superstructure reflection
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power law exponents
T lt TCDW growth of intensity of
superstructure reflection
T gt TCDW sharpening up of diffuse scattering
intensity
width
inverse correlation length -gt ? 0.85 0.2
order parameter -gt ß 0.13 0.03
TDS-regime
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conclusions

• ZrTe3 shows a soft-mode driven Peierls
  transition.
• Electron-phonon coupling leads to a Kohn Anomaly
  (KA) at high temperatures.
• The coupling occurs in the mostly transverse
  acoustic phonon along qCDW.
• The KA becomes giant and leads to the lattice
  instability as TCDW is approached.
• Fluctuating CDW-order leads to enhanced diffuse
  scattering around qCDW.
• The CDW order is three-dimensional with finite
  correlation along c (out-of-plane).
• The order parameter increases rapidly away from
  TCDW with a small power law
  ?CDW with power law 1/8 and intensity
  with ß 0.13 0.03.
• Transition is close to (blurred) first order
  transition, like (TaSe4)2I or blue bronze.

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the CDW superstructure
LDA calculation of the Fermi surface C. Felser et
al. J. Mater Chem 8, 1787
colors Fermi velocity
convergent beam electron diffraction at 50 K D.J.
Eaglesham et al. J.Phys. C 17 (1984)
L697 chemical modulation A vanishes with
time (no observed with x-rays) CDW-modulation
B qCDW (1/14 0 1/3)
CDW nesting vector
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Fermi surface map (ARPES)
two
hv 45.2 eV lin. polarized T 160 K
Two quasi 1-dim. Fermi-surfaces (a) hybridized
Zr 4d along b (b) Te 5px along a

M. Hoesch, X. Cui, K. Shimada (Hiroshima Univ.)
unpublished data, see also T. Yokoya et al., PRB
71 (2005) 140504R.
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lattice dynamics at room temperature
Inelastic x-ray scattering, resolution DE 3.2
meV
ZrTe3 phonon dispersions along a and b three
kinds of modes are observed - collective
acoustic phonons - bending and torsion modes
of the chains - optical modes of Te - atoms
Raman data A. Zwick, M.A. Renucci, A. Kjekhus,
J. Phys. C Solid State Phys. 13 (1980) 5603.
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comparison TDS vs IXS
x 10-4
inelastic x-ray scattering (IXS) measures S(Q, w)
and gives w
thermal diffuse scattering (TDS) measures S(Q)
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survey of momentum space
diffuse scattering at SNBL BM01A T 295
K tomographic single crystal diffractometer
MAR345 image plate detector
wheres the soft mode?
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IXS spectrometer schematic
DQ (nm-1)
DE (meV)
reflection
0.05
5.5
(8 8 8)
3.0
(9 9 9)
1.7
(11 11 11)
0.15
0.9
(13 13 13)