TRANSVERSE CONDUCTIVITY BEHAVIOR
NbSe3 AT THRESHOLD ELECTRIC FIELD
FOR CDW SLIDING
A. Sinchenko,
National Research Nuclear University MEPhI, Moscow
P. Monceau and T. Crozes
Institut Néel, CNRS, Grenoble
Acknowledgements:
S.A. Brazovskii, S.N. Artemenko, J. Marcus
Outline
• Motivation. Strange transverse effects in the sliding state of CDW.
• Experimental configuration.
• Transverse electric field: why it is important. The temperature
dependence of transverse voltage in NbSe3 in the static state of
CDW.
• Transverse voltage in NbSe3 in the sliding state of CDW:
temperature evolution of transverse voltage; longitudinal and
transverse IV-characteristics. Transverse and longitudinal Shapiro
steps.
• Possible explanations.
• Conclusion.
Strange transverse effects
Field-Effect Modulation of Charge-DensityWave Transport in NbSe3 and TaS3
T.L.Adelman, S.V.Zaitsev-Zotov and R.E.Thorne,
PRL 74, 5264 (1995)
Torsional Strain of TaS3 Whiskers on the ChargeDensityWave Depinning
V.Ya. Pokrovskii, S. G. Zybtsev, and I. G. Gorlova, PRL 98,
206404 (2007)
Regions of negative absolute resistance are observed in the CDW sliding regime
H. S. J. van der Zant, et al., PRL 87, 126401(2001)
Anomalous Asymmetry of Magnetoresistance in NbSe3 Single Crystals
A. A. Sinchenko, et al, JETP Lett., 84, 271 (2006).
What happens in the transverse direction at threshold electric field?
Experimental
NbSe3
Two Peierls transitions at
TP2=59 K and TP1=144 K
2500
R (Ohm)
2000
1500
1000
500
0
0
50
100
150
T (K)
Rtr=Vtr/I
RL=VL/I
200
250
300
w=20 μ
h= 0.1-0.4 μ
potential probes (4,5,6,7)= 3 μ
current probes (2,3,8,9)= 10 μ
d1,2=d2,4=d6,8=d8,10=100 μ
d4,6=50 μ
Transverse electric field: to be important it should exist
4
2
3
6
8
7
9
Measurements of Rtr(T) (where Rtr=Vtr/I)
in NbSe3 in static state. Pairs of contacts 4-5 and
6-7 were used for Vtr, contacts 4-6 and 5-7 for
longitudinal voltage VL measurements.
0
50
100
150
200
250
0.10
0.4
b)
0.05
0.2
Rxx (Ohm)
Rxy (Ohm)
Rtr=Vtr/I (Ohm)
10
0.00
a)
0.0
5
-0.05
-0.2
-0.10
50
100
150
200
250
T (K)
Rtr(T) at variation of the electric field direction
misalignment of potential probes is negligible
0
50
100
150
200
0
250
T (K)
Rtr(T) in the case of complete compensation
of the electric field at T=300 K (Vtr<10-9 V)
(black curve); and RL(T) – blue curve.
R(T+T)
0.05
R(T)
j1
j2
R(T)
R(T)
j0
j0
Rxy (Ohm)
0.00
о – Rtr(T); blue curve – α[RL(T+ΔT)-RL(T)]
at ΔT=0.1 K and α=0.31.
-0.05
Rtr(T)~dRL(T)/dT
-0.10
50
100
150
T (K)
200
Transverse voltage appears as a result of any
inhomogeneouty, impurity or over defects, or
because of fluctuation effects.
A. A. Sinchenko, P. Monceau, and T. Crozes,
JETP Lett., 93, 56 (2011).
Qualitatively the same effect was observed in superconductors. Qualitatively the
same explanation was proposed. A. Segal, M. Karpovski, and A. Gerber, Phys. Rev.
B 83, 094531 (2011).
In real samples the transverse electric field exists always
Φ1
Φ2
Transverse conductivity at sliding state of CDW
For studying properties of the transverse conductivity in
the longitudinal CDW sliding state it is convenient to
have well defined transverse components of the electronic
transport. We used the pair of contacts 2-9 or 3-8 as
current electrodes. The electric field direction is not
strictly parallel to the conducting chains, and a small but
finite transverse component Etr exists simultaneously with
the longitudinal one, EL.
9
The maxima of RL observed below Tp1 and Tp2
decrease as usual . The opposite picture is
observed in Rtr behavior: a strong increase of the
transverse voltage takes place below Tp1 and Tp2
leading to the appearance of transverse resistance
maxima.
0.02 mA
0.10 mA
0.25 mA
0.50 mA
0.75 mA
1.00 mA
1.25 mA
1.50 mA
12
8
4
0
1.5
b)
25
1.5
1.0
20
1.0
0.5
15
I=0.02 mA
10
0.5
Does the change in transverse voltage result from
the current redistribution induced by the CDW
sliding?
RL(Ohm)
7
8
a)
16
RL (Ohm)
6
20
Rtr (Ohm)
3
4
Rtr (Ohm )
2
Temperature dependencies of
longitudinal resistance RL(T) and
transverse Rtr(T) at different currents
5
0.0
0
100
100
150
0.0
0
50
T (K)
T (K)
200
200
300
250
Transverse and longitudinal IVcharacteristics
2
3
55 K
4
6
8
7
9
4
2
3
120 K
0.2
6
8
7
9
Vtr (mV)
0.1
-0.4
-0.2
I (mA)
0.0
0.0
0.2
0.4
-0.1
-0.2
0.004
Vtr (mV)
I (mA)
-0.4
0.000
0.0
-0.004
In contrast to longitudinal IVC, a jump (step) of
transverse voltage takes place at threshold electric field
for CDW sliding. Such type of jump was observed even
in the case when the electric field is oriented strongly
along the chains.
0.4
Transverse and longitudinal IVcharacteristics
2
3
55 K
4
6
8
7
9
4
2
3
120 K
0.2
6
8
7
9
Vtr (mV)
0.1
-0.4
-0.2
I (mA)
0.0
0.0
0.2
0.4
-0.1
-0.2
0.004
Vtr (mV)
I (mA)
-0.4
0.000
0.0
-0.004
In contrast to longitudinal IVC, a jump (step) of
transverse voltage takes place at threshold electric field
for CDW sliding. Such type of jump was observed even
in the case when the electric field is oriented strongly
along the chains.
0.4
Transverse and longitudinal differential IVcharacteristics
3
-0.3
2.0
6
8
7
9
-0.2
-0.1
0.0
0.1
0.2
-0.4
0.3
16
120 K
-0.2
0.0
0.2
0.4
2.0
15
130 K
1.4
dVtr/dI (Ohm)
14
1.6
dVL/dI (Ohm)
dVtr/dI (Ohm)
1.8
1.8
14
1.6
1.4
13
12
1.2
1.2
1.0
-0.3
12
-0.2
-0.1
0.0
I (mA)
0.1
0.2
0.3
-0.4
-0.2
0.0
I (mA)
0.2
0.4
dVL/dI (Ohm)
4
2
The observed change in transverse conductivity is qualitatively
different from longitudinal one and takes place at a current
lower than that needed for the CDW to slide. So, the jump in
transverse voltage does not result from the current redistribution
induced by the CDW sliding. On the contrary, we can propose
the inverse statement: the change in transverse conductivity
triggers the longitudinal CDW depinning.
Tentative explanation
Under an applied longitudinal electric field, the CDW is deformed
up to a certain critical value, Et1<Et corresponding to the critical
CDW deformation. We assume that at this field the phasing
between the neighbouring chains sharply changes leading to the
destruction of the transverse CDW coherence.
According to (S.N. Artemenko, JETP 84, (1997), 823) the strong
phase difference and the different deformations of the CDW on
neighbouring chains result in different shifts of local chemical
potential at these chains leads to a strong decrease of the
transverse conductivity. The transverse conductivity is a function
of the phase difference between neighboring chains, and this effect
is similar to the tunneling current between two conductors with
charge density waves (S.N. Artemenko and A.F. Volkov, Sov. Phys.
JETP 60, (1984),395).
Is in accordance with
R. Danneau, et al, Phys. Rev.
Lett.89, (2002) 106404.
This current has a term proportional to the cosine of the difference between the
phases. When an external alternating signal acts on the sample, a resonance should
be observed for a fixed Vtr if the frequencies of the external and characteristic
oscillations coincide.
Joint application of dc and rf electrical field ?
Joint application of dc and rf driving fields
-1.5
0.7
-1.0
-0.5
0.0
0.5
1.0
1.5
135 K
49.64 MH
0.7
13.5
16
dVL/dI (Ohm)
dVtr/dI (Ohm)
0.6
0.5
0.4
14
0.6
13.0
0.5
I (mA)
0.4
0.4
0.5
0.6
12.5
0.7
0.3
0.2
-1.5
-1.0
-0.5
0.0
0.5
1.0
Shapiro steps for longitudinal transport appear in the
dVL/dI(I) characteristic as spikes, that corresponds to
voltage steps. On the contrary, for transverse transport
minima in the differential resistance are observed that
corresponds to Shapiro current steps. Without complete
mode locking, Shapiro steps in transverse transport have a
larger amplitude and much more pronounced features.
1.5
I (mA)
dVtr/dI (Ohm)
0.7
-0.5
0.0
0.5
120 K
19.02 MH
50 mV
1.0
19
18
17
0.6
16
0.5
15
0.4
14
0.3
0.2
-1.0
13
-0.5
0.0
I (mA)
0.5
12
1.0
dVL/dI (Ohm)
-1.0
The transverse Shapiro steps precedes the
longitudinal one.
When the CDW slides along one chain but is pinned
along neigbouring chains, or if the CDW moves with
different velocities in different chains, or if the CDW is
pinned but phase slippage takes place, then the phase
varies with time and alternating tunneling current is
generated transversely to the chain direction with a
frequency depending on the longitudinal electric field.
B
I
chain direction
EH
I
c-axis bridg in magnetic field
(Latyshev, Sinchenko, Monceau 2008-2011)
0.08
Ic (mA)
20T
17.5T
15T
12.5T
10T
7.5T
5T
0.0008
0.0004
1.5 K
4.2 K
8.0 K
15.0 K
25.0 K
30.0 K
0.04
0.00
0.05
0.10
-1
1/B (T )
Shapiro steps without CDW sliding
0.0000
-200
0
200
V (mV)
-4
6.0x10
4.0x10
197 MG
1V
1.5 K
-4
F=197 MHz
F=0
3.0x10
-4
2.0x10
-4
20.0 T
17.5 T
15.0 T
12.5 T
10.0 T
-1
dI/dV (Ohm )
T=1.5 K
B=20 T
-1
dI/dV (Ohm )
-1
dI/dV (Ohm )
0.0012
-4
4.0x10
-4
2.0x10
1.0x10
-4
-300
-200
-100
0
V (mV)
100
200
300
-300
0
V (mV)
300
Conclusion
1. At an electric field less than the longitudinal threshold
one for CDW sliding a sharp decrease in transverse conductivity
takes place; that may result from induced phase shifts between CDW
chains.
2. Under the joint application of dc and rf driving fields
pronounced current Shapiro steps in transverse transport have been
observed. The results were tentatively explained in the frame of
Artemenko-Volkov theory .
Thank you very much for attention