Scanning Tunneling Microscopy of CeTe3

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Scanning Tunneling Microscopy of CeTe3

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Scanning Tunneling Microscopy of CeTe3 Stuart
Tessmer Collaborators Aleksandra
Tomic?, Christos Malliakas, Hyunjeong Kim,
Mercouri Kanatzidis, Simon Billinge Michigan
State University, East Lansing, MI
48824 Research supported by the National
Science Foundation grant No DMR03-05461.
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Charge Density Waves in Complex Materials

• Delicate relationship between electronic,
  magnetic and
• structural effects
• Recently discovered in high temperature
  superconductors

A 'checkerboard' electronic crystal state in
lightly hole-doped Ca2-xNaxCuO2Cl2
J.C. Davis Group, Nature 430, 1001-1005, Aug.
26, 2004
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Charge Density Waves
CDWs arise from electron-lattice effect in
metals atomic position shifts ? charge density
variations

• Metal without CDW

• Introduced periodic lattice
• deformation and CDW
• Example
• 1D Metal with half-filled band
• ?CDW?/kF2a

- - - -
q 2kF
EF--------------------------
DCDW
CDW is commensurate
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Structure of CeTe3

• 1-dimensional, room temperature CDW
• occurs in square Te net
• Nature of CDW is not well characterized
• We use STM to study the CDW in CeTe3

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CDW periodicity with respect to atomic lattice
? Commensurate
? Incommensurate Uniformly
? Incommensurate Locally commensurate
with domain walls
commensurate
domain wall
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STM Technique

• Based on quantum
• mechanical tunneling
• Tip-sample separation
• d less than 1 nm
• Current I e-2kd

Our Microscope
Achieves atomic-scale spatial resolution
Tunneling sensitive to electronic
structure Ideal CDW probe

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STM Results CDW modulations oriented at 45 to
the net
Itun 0.6 nA Vbias100 mV
3 nm

• Fourier transform useful in characterizing
  nature of CDW
• In case of discommensurate CDW, satellite peaks
  in Fourier
• transform occur in vicinity of principal peaks

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Significance of satellite peaks
?CDW?IC(x)M(x)
M(x)?fnei(nkDx) ?CDW(x)f0?IC(x)
f1?IC(x)ei(kDx) Peaks in FT occur at kIC
(fundamental), kICkD (satellite), Difference
in wave vectors of main peak and corresponding
satellite, gives the domain size. Understand
this as the beating pattern of two closely
spaced wave vectors (k1 and k2) where net
result are beats with wave vector k k1-k2

See Thomson et al, PRB 49, 16899 (1994)
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Fourier Transform of the STM data (27 x 27 nm)

• Peaks L correspond to
• square Te-net
• CDW peaks at 45 to Te-
• net
• - fundamental and 1st
• harmonic peaks labeled 1
• and 3
• - satellite peaks observed,
• labeled 2 and 4
• Peak 5 corresponds to the
• diagonal of Te-net

ky
kx
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Fourier Transform of the STM data (27 x 27 nm)

• Peaks L correspond to
• square Te-net
• CDW peaks at 45 to Te-
• net
• - fundamental and 1st
• harmonic peaks labeled 1
• and 3
• - satellite peaks observed,
• labeled 2 and 4
• Peak 5 corresponds to the
• diagonal of Te-net

ky
kx
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STM results

• STM images show
• robust CDW
• Fourier transform
• has satellite peaks
• indicating
• discommensurations
• Commensurate
• domain size 2?/ kD
• ? 38Å

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Comparison to X-Ray Scattering PDF Method

• The blue line bond-length
• distribution obtained from the PDF
• The red line bond-length
• distribution from the crystallographic
• model
• Crystallographic model gives
• Gaussian distribution coming from
• continuous distribution of Te-Te
• distances in incommensurate CDW
• Local structural model has bimodal
• distribution ? locally commensurate
• CDW
• Crossover at 27Å

Nearest-neighbor bond length distribution in the
Te nets
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Summary

• CeTe3 has a robust 1-dimensional, room
  temperature CDW
• in a Te-net
• STM images in real space shows a large CDW
  modulation
• Satellite peaks in the Fourier transforms
  indicate
• discommensurate CDW with characteristic domain
  size of
• ? 38Å

Arrangements of short bonds used in the PDF
modeling. Discommensurations occur as defects of
this pattern.
H. J. Kim, et al., cond-mat/0602361, PRL
(in-press).