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Yu.Latyshev

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Interlayer tunneling spectroscopy of NbSe3 and graphite
at high magnetic fields
Yu.I. Latyshev
Institute of Raduio-Engineering and Electronics RAS, Mokhovaya 11-7,
Moscow 125009
In collaboration with
А.P. Оrlov, A.Yu. Latyshev
IREE RAS, Moscow
A.A. Sinchenko
Moscow Eng. Physical Institute
А.V. Irzhak
Moscow Inst. of Steel and Alloys
P. Monceau, Th. Fournier
J.Marcus
Neel Institute, Grenoble, France
D. Vignolles
LNCMP, Toulouse, France
OUTLINE
1. Introduction to interlayer tunneling in layered
superconductors and charge density wave materials.
2. CDW gap spectroscopy at high magnetic field in NbSe3.
3. Graphite. Nanostractures fabrication with focused ion
beam.
4. Pseudogap.
5.
Interlayer tunneling spectroscopy of Landau levels.
6. Behaviour in high magnetic fields.
7. Conclusions.
Interlayer tunneling in layered HTS and
CDW materials
Layered crystalline structure
?║/?┴ =103-104
NbSe3
LL
s
Sample
configuration
Bi-2212. Gap/pseudogap spectroscopy
Yu.I. Latyshev et al.ISS Conf. 1999, Physica C,
2001; V.M. Krasnov et al. PRL, 2000, 2001
Spectroscopy of CDW gap and intragap states. NbSe3
4 .2 K
50
6K
1.5
8K
10K
28
16K
1.0
18K
2?1/3
20K
24K
0.5
26K
28K
32K
35K
0.0
0
2? 1
50
100
T (K )
150
40K
45K
50K
55K
60K
65K
70K
75K
80K
85K
90K
95K
-1
22K
dI/dV (kOhm )
S (T )/S (1 6 0 K )
14K
30K
10
2?1
T=100 K
12K
2? 2
-1
d I/d V (k O h m )
NbSe3 N1
# 1
Vt
26
24
100K
105K
110K
115K
120K
125K
130K
135K
1
0 .8
140K
145K
150K
-35000
-1
-2
-1 0 0
-1-5000
0
15000
V (m
V )v)
V (m
4.2К? 170К
210000
310500
160K
170K
22
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
V/2?1
Yu.I. Latyshev, P. Monceau, S. Brazovskii, A.P. Orlov, Th.
Fournier, PRL 2005, 2006
1. CDW gap spectroscopy in high magnetic
fields
Anomalously high magnetoresistance in NbSe3 . Orbital effect on partly
gapped CDW state.
Magnetic field
destroys ungapped
pockets
C.A. Balseiro and
L.M. Falicov 1984,
1985
L.P. Gor?kov and
A.G. Lebed 1984
R.V. Coleman et al. PRL 1985
Q
Q
2KF
2KF
H
perfect
H=0
imperfect
Magnetic field improves nesting
condition and thus can increase CDW
gap
A. Bjelis, D. Zanchi, G.
Montambeaux PR B 1996,
cond-mat /1999
also have shown the possibility
to increase Tp by magnetic
field.
Zeeman splitting effect on CDW ordering
?(k)
In a zero field the CDW state is
In a zero field th e C D W state is
with
respect
sp in to spin up
ect to
erated w ith resp
d eg endegenerated
w n ? ? ?? configurations.
in d odown
d spspin
u p ? ? an
and
co n fig u ratio n s.
Q
Magnetic field releasess degeneration
Q 0 (H = 0)
2?BH
Q
-k F
0
kF
M ag n etiq u e field release
due
to Zeeman splitting. As a result Q
d eg en eratio n d u e to Z eem an
CDW
vector
with field while
lt, Qincreases
A s a resu
sh ift.
?? C D W
creases w h ile Q ? ?
v ecto
Q??r indecreases
d ecreases
Q > Q0 > Q??
Q ?? > Q 0 > Q ??
Therefore
a CDW
fix ed with a fixed
w ith astate
ce a C D W state
H en
beyed
destroyed
with field.
w ith
estro
to b e dto
ten
Q 0Q
0 d stends
field
One can expect the interplay between orbital and Pauli effects at high
fields of the scale 2?BH ~ kTp. . For NbSe3 with Tp =60K that
requires experiments at fields ~50T
Experiments at pulsed magnetic field (see also p. 29
at poster session)
H
LNCMP, Toulouse
55T
Hmax
Field
start
~60ms
~350ms
Field
finish
t
I
+Imax
Start
DAC,
3 ADC
0.5ms
Full measurement time 500ms
1000 IV
Sweep current
I, dI/dV
-Imax
~50ms
kth
tr. pulse
V
Fm=2MHz
1000 points
in IV for Hk
High speed acquisition system
Stop
DAC,
3 ADC
t
Field-induced gap. 3D picture. T=65 K
N bSe3 #3
-? ? 2
H=2T
4
-2 ? 1
45K
50K
55K
61K
65K
+2?2
+2?1
-1
d I/d V (kO h m )
3
2
1
0
-1
-2
-3
-2
-1
0
V /2 ? 2 (0 )
1
2
3
Induced CDW gap above Peierls transition temperature
1.4
NbSe3 #3
1.2
1100
H//a*=53.4T
1000
900
0.8
0.6
0.4
800
0.2
700
0.0
40
600
500
50
60
70
T(K)
80
90
65
70
75
80
85
90
H=35T4 5 K
50K
55K
61K
65K
71K
76K
83K
H=0
1 .0
0 .8
0 .6
2
0
60
2
100
55
N b S e 3 m e sa # 3
300
200
50
1 .2
400
H=0
45
T (K)
? / ? (4 .2 K )
40
2?/2?2(4.2K)
1200
Rd0 (Ohm)
500
480
460
440
420
400
380
360
340
320
300
280
260
1.0
NbSe3 #3
0 .4
А м плитуда
? =0
2
щ елевого
пика
=0
0 .2
0 .0
0
10
20
30
H (T )
40
50
Phase diagram. Interplay of orbital and Pauli effects.
Field induceed
CDW state
Non-monotonic behaviour of Tp(H) is defined
by interplay between orbital and Pauli effects
on CDW pairing. Orbital effect is realized in
improving of nesting condition and, thus, in
increase of ?? and Tp, while Zeeman splitting
tends to destroy CDW pairing.
Experimental crossover field corresponds to
H ? 30T,
2?BH0 ? kTp
That is consistent with calculatons of Zanchi,
Bjelis, Montambeau PRB 1996 for the case of
moderate imperfection parameter (valid for
NbSe3)
?BH0 / (2?Tp) ? 0.1 or
For Tp = 61 K that corresponds to H0 ? 30T
2. Interlayer tunneling
spectroscopy of graphite
Questions:
1. Is there interlayer correlation?
2. Is that possible to observe Dirac fermion
features by interlayer tunneling technique?
3. Which is the inter-graphene behaviour in
high magnetic fields?
Fabrication of nanostructures
FIB microetching method
Yu.I. Latyshev, T. Yamashita, et al. Phys. Rev. Lett., 82 (1999) 5345.
S.-J. Kim, Yu.I.Latyshev, T. Yamashita, Supercond. Sci. Technol. 12 (1999) 729.
FIB
FIB machine
40 nm
Seiko Instruments Corp. SMI-9000(SP)
Ga+ ions 15-30 kV
Beam current : 8pA ? 50 nA
Minimal beam diameter: 10nm
D am aged
region
60 nm
Stacked structures fabricated from layered materials by FIB methods
NbSe3 single crystals are thin whiskers with a thickness of 1-3 ?m, a width
of 20 ?m and a length of about 1 mm
a)
b)
c)
d)
Figure 2. (a-c) Stages of the double sided FIB processing technique for
fabrication of the stacked structure; (d) SEM image of the structure. The
structure sizes are 1? x 1? x 0.02 - 0.3?
Yu. I. Latyshev et al. Supercond.Sci.Techn. 2007
Pseudogap in graphite
Interlayer tunneling in graphite mesas
M1
G1
G ra p h ite
G ra p h ite m e s a # 1
4 .2 K
7K
10K
15K
20K
30K
50K
80K
110K
150K
200K
250K
1 7 .5
1 .2
1 7 .0
-1
d I/d V (kO h m )
R /R T = 3 0 0 K
1 .0
0 .8
0 .6
0 .4
0 .2
0
50
100
150
200
250
300
T (K )
At 300K ?? ? 0.2 ?? cm, ?// ? 50 ??
cm, ?? /?// ~ 4000
1 6 .5
1 6 .0
1 5 .5
1 5 .0
1 4 .5
1 4 .0
-1 0 0 -8 0 -6 0 -4 0 -2 0
At 4.2K ?? /?// ~ 30 000
20
V (m V )
Mesa sizes; 1?m x 1?m x 0.02-0.03?
We found an evidence of pseudogap
formation in graphite below T0 =30K.
Vpg ? 10-15 mV
0
Vpg ? 3.5 kT0 !?
Yu.I.Latyshev, A.P.Orlov, A.Yu.
Latyshev,Th. Fournier, J. Marcus and P.
Monceau 2007
40
60
80
100
Observation of Dirac fermions in
graphite
previous experiments
ARPES on graphite
S.Y. Zhou et al. Nature
Physics, 2006
Landau quantization in graphite from STM G.Li and E.Andrei, Nature Phys. 07
Graphene spectrum
E(k) = ? vF(h/2?) k
Landau quantization
E(n)= sgn n [2e (h/2?) VF2|n|B]1/2
E(n) ? (nB)1/2
Bilayer graphene
E(n)= sgn n h?c[|n|(|n|+1)]2
?c = eB/m*
Fit: vF= 1.07 108 cm/s
as for graphene and for graphite data
from ARPES
For linear E(H) dependence
m* = 0.028 m0
Landau quantization in graphite from magneto-transmission experiment
M. Orlita et al. Phys. Rev. Lett. 2008
selection rule:
?n =? 1,
Interlayer tunneling
our experiments
Landau quantization in graphite (Interlayer tunneling Yu.I.L, A.P. Orlov, D. Viqnolles 07
11.69m
0.41
0.47
0.54
0.61
0.69
0.77
0.87
0.97
1.08
1.20
1.34
1.49
1.65
1.82
2.02
2.23
2.46
2.70
2.92
11m
10m
9m
8m
7m
6m
5m
6
4m
2.643m
-200
-100
0
V (mV)
100
G #1 N?30
We found Landau quantization from
interlayer tunneling transitions
-1<->1, -2<->2 consistent with STM
and magneto-transmission data
200
7.805m
7.5m
7m
6.5m
6m
5.5m
5m
4.5m
4m
3.5m
3m
2.5m
1.943m
-200
-100
0
V (mV)
100
G #3 N ?20
Spectra are well reproducible, peak position
does not dependent on N
аnother selection rule: |?n| = 0
valid for coherent tunnеling
200
Comparison of the 1st level energy for two samples
Graphite
#1
#3
100
V (mV)
50
V ? H1/2
0
typical for Dirac
fermions
-50
-100
0
1
2
H (T)
3
Comparison with STM and magneto transmission data
Graphite #1
400
300
200
Mag.trans 2x(0??1)
STM 2x(0??1)
STM 2x(0??2)
Inter.tunn -1??1
Inter.tunn -2??2
Inter.tunn -3??3
V (mV)
100
0
-100
-200
-300
-400
0
1
2
3
4
5
6
H(T)
Transitions -1<->1, -2<->2, -3<->3 observed are consistent with STM and
magneto-transmission data. VF = 108 cm/s, En ?(nH)1/2
Effects in strong magnetic fields
Graphite at strong fields Yu.I.L., A.P.Orlov, D. Vignolles, P. Monceau 07
Observation H. Ochimizu et al., Phys. Rev. B46, 1986 (1992).
Explanation was related with the CDW formation along the field
axis
D. Yoshioka and H. Fukuyama, J. Phys. Soc. Jpn. 50, 725
(1981).
We attempted to find CDW gap above 30 T
Graphite mesa
1200
T=1.4K
G1
G3
1000
R (Ohm)
800
600
400
200
0
0
5 10 15 20 25 30 35 40 45 50 55 60
H (T)
Effect nearly disappeared for 20
graphene layers
Pseudogap at graphite at high fields Yu.L., A.P. Orlov, D. Vignolles, P. Monceau
06-07
Graphite #1
d
T=4.2K
1.75
-1
dI/dV (kOhm )
1.70
10
10T
28T
1.65
25T
1.60
28T
1.55
21T
25T
1.50
14T
1.45
21T
14T
1.40
1.35
-600
-400
-200
0
200
400
V (mV)
Pseudogap appears above
20T, Vpg ? 150 mV
Remarkable features:
(1) increase of tunnel
conductivity with field
(2) field induced PG
???
60
Field dependence of pseudogap value
400
Graphite #1
300
200
V (mV)
100
0
-100
-200
-300
-400
10
15
20
25
30
35
H (T)
40
45
50
55
No essential field dependence above 25 T
We consider that the big value of the field induced
pseudogap is an indication of some collective excitations
in graphene at high fields
CONCLUSIONS
1.
FIB technique has been adapted for fabrication mesa type structures on
various nanomaterials as HTS materials, CDW layered materials and
graphite.
2.
We found the effect of CDW gap induction by high magnetic field above
Peierls transition temperature. We also found non-monotonic dependence of
Tp(H) which is interpreted as the interplay between orbital and Pauli effects
on CDW ordering.
3.
We found interlayer correllative gap in graphite below 25K with energy of 1015 mV.
4.
Using interlayer tunneling we identified in graphite Landau levels typical for
Dirac fermions in graphene.
5.
We found field induced pseudogap in graphite. The high value of the
pseudogap, 150 mV, points out to its possible origin related with collective
excitations in graphene.
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