ChargeDensityWave nanowires

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Charge-Density-Wave nanowires
Erwin Slot Mark Holst Herre van der Zant
Sergei Zaitsev-Zotov Sergei Artemenko Robert
Thorne
Molecular Electronics and Devices group
http//med.tn.tudelft.nl/
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submicron CDW devices
etched wires in crystals
nanowires
thin films
junctions/constrictions
5mm
submicron probes
bulk CDW properties studied in detail much less
in known about the microscopic details
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multi-chain nanowires
NbSe3 wires
Ultrasonic cleaving in pyridine
Disperse on substrate with predefined markers
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contacting nanowires
2 mm
E-beam lithography Buffered Hydrofluoric acid (4
sec) Deposition of Ti and Au width 30-300 nm,
thickness 10-50 nm Lowest contact resistance
100 W
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linear resistance measurements
power-law behavior E. Slot et al. Phys. Rev.
Lett. 93 (2004) 176602
reducing cross section
1D CDW dynamics E. Slot et al., Phys. Rev. B 69
(2004)
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threshold field increases as cross section
decreases
T120 K
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1D collective pinning single phase coherent
domain
2D
1D
slope 2/3
evidence of 1D weak collective CDW pinning ET ?
(1/A)2/3
slope 1/2
surface and 2D pinning with ET ? (1/A)1/2 can be
excluded
E. Slot et al., Phys. Rev. B 69 (2004)
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no evidence for single-particle model in IV
characteristics
ET
-ET
pinned
sliding
sliding
10-3 mm2
3 x 10-3 mm2
7 x 10-3 mm2
single-particle expectation
22 x 10-3 mm2
T120 K
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gradual reduction of transition temperatures as
cross section decreases
R/L (kW/mm)
R/L (kW/mm)
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power-law behavior in R(T)
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power-law behavior in I-V(T)
R ? T-a a 2.15 I ? Vb b 4.2
I/Ta1 C sinh(geV/kBT) G(1b/2igeV/pkBT)2
power-law in both I(V) and R(T), and scaling
behavior (bosonic excitations with linear
spectrum) are a fingerprint for 1D transport
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power-law behavior due to uncondensed carriers !
coexistence of power law behavior and sliding
threshold in IVs
no abrupt decrease of nonzero TP1,TP2
R/L (kW/mm)
R/L (kW/mm)
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multiwall carbon nanotubes
Bachtold et al., Phys. Rev. Lett. 87, 166801
(2001)
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and
MWNT
NbSe3

• Both diffusive conductors
• Both interaction between chains
• Both show power-law behaviour
• Both show scaling of I(V)s

Xinluo Zhao et al., Phys. Rev. Lett. 90, 187401
(2003)
7 Å
7 Å
LL and ECBT have the same dependencies on energy
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Environmental Coulomb Blockade
Ingold Nazarov, Single charge tunneling Matveev
Glazman, Phys. Rev. Lett. 70, 990 (1993)
Coulomb blockade is smeared by quantum
fluctuations in the leads
Environment (Z-transmission line)
I(V) ? Vb b 2Z/RQ 1
V
Junction
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nanowire as transmission line
R
L
G
C
V
For NbSe3 nanowire Kinetic inductance L 17
nH/mm (very high!) Capacitance C 10 aF/mm
Z 41 kW ?
1.6RQ
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nanowire with tunnel barrier
LC
V
wL gt R ? h?gt 0.4 meV
measurement
I(V) ? Vb b 2Z/RQ 1 ? 4.2
model
b 4.2
Z 41 kW ? 1.6RQ
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model reproduces dependence of exponents of R(T)
on cross section
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low carrier density (1018 cm-3 30 nm distance
between electrons) and low Fermi energy indicate
the importance of e-e interactions
Environmental Coulomb Blockade
But applicability of ECB is not clear developed
for a single junction

• Alternative model Wigner crystal
• Coulomb energy larger than Fermi energy
• Power-law exponent determined by localization
  length

Data in agreement with general concepts
describing 1D conductors. At present no full
theory describing our system with many channels
and disorder.
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gate effect periodic features are NOT observed
switches occur with pulses on the gate
IVs are switchy when the gate is not grounded
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Conclusions

• As the cross-section of CDW nanowires becomes
  smaller, the Peierls temperature gradually
  decreases and the threshold field increases (1D
  collective pinning)
• Below TP2 NbSe3 nanowires with less than 1000
  chains in total show power-law behavior typical
  for 1D transport
• Data in agreement with general concepts
  describing 1D
• conductors. At present no full theory describing
  our
• system with many channels and disorder
• Role of impurities discussed by Artemenko on
  Monday

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conclusions

• Current conversion occurs through strain-induced
  phase-slip processes (changes on the micron
  scale)
• Importance of strain change in the chemical
  potential (negative resistance)
• Energy spectroscopy in CDW junctions and weak
  links evidence for solitons
• A single phase coherent CDW domain can not be
  described with the single particle model
• Thin NbSe3 nanowires show the characteristics of
  one-dimensional transport (power-law behavior
  low electron density)
• A full microscopic CDW model needed

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gradual reduction of transition temperatures as
cross section decreases
bulk sample
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1D collective pinning
Fukuyama-Lee-Rice Hamiltonian
3D Weak pinning
1D Weak pinning
ET independent on size
ET ? (1/A)2/3