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 Neel Institute, Grenoble, France J.Marcus
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
sLLL
NbSe3
Sample configuration
σ║/σ┴ =103-104
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
-300 -200 -100 0 100 200 3000.8
1
10
50
4.2K 6K 8K 10K 12K 14K 16K 18K 20K 22K 24K 26K 28K 30K 32K 35K 40K 45K 50K 55K 60K 65K 70K 75K 80K 85K 90K 95K 100K 105K 110K 115K 120K 125K 130K 135K 140K 145K 150K 160K 170K
dI/d
V (
kOhm
-1)
V (mV)
NbSe3 N1
-150 -100 -50 0 50 100 150 V (mv)
0 50 100 1500.0
0.5
1.0
1.5
S(T
)/S(1
60K
)
T (K)
# 1
21
22
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.522
24
26
282
1
21/3
dI/d
V (
kOh
m-1)
V/21
T=100 K
Vt
4.2К 170КYu.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.
Q Q
2KF 2KF
perfect imperfect
H=0 H
R.V. Coleman et al. PRL 1985
A. Bjelis, D. Zanchi, G. Montambeaux PR B 1996, cond-mat /1999
also have shown the possibility to increase Tp by magnetic field.
L.P. Gor’kov and A.G. Lebed 1984
C.A. Balseiro and L.M. Falicov 1984, 1985
Magnetic field destroys ungapped pockets
Magnetic field improves nesting condition and thus can increase CDW gap
Zeeman splitting effect on CDW ordering
-kF kF
2BH
(k)
Q0(H=0)
0
Q
Q
In a zero field the CDW state is degenerated with respect to spin up and spin down configurations. Magnetique field release degeneration due to Zeeman shift. As a result, Q CDW vector increases while Q decreases Q > Q0 > Q Hence a CDW state with a fixed Q0 tends to be destroyed with field
In a zero field the CDW state is degenerated with respect to spin up and spin down configurations. Magnetic field releasess degeneration
due to Zeeman splitting. As a result Q CDW vector increases with field while Q decreases Q > Q0 > Q Therefore a CDW state with a fixed Q0 tends to be destroyed with field.
One can expect the interplay between orbital and Pauli effects at high fields of the scale 2BH ~ kTp. . For NbSe3 with Tp =60K that requires experiments at fields ~50T
Experiments at pulsed magnetic field (see also p. 29 at poster session)
LNCMP, Toulouse
S w eep cu rren t
~50ms
F ie ld s ta rt
F ie ld fin ish
55T
0.5ms Start DAC, 3 ADC
Stop DAC, 3 ADC
kth tr . p u lse
~350ms
Full measurement time 500ms
H
I
~60ms
1000 IV
t
t
V
I, dI/dV
Fm=2MHz 1 0 0 0 p o in ts in IV fo r H k
+Im ax
-Im ax
H m ax
High speed acquisition system
Field-induced gap. 3D picture. T=65 K
-3 -2 -1 0 1 2 3
-2
-1
0
1
2
3
4+2
1
+22
-2
dI/d
V (
kOhm
-1)
V/22(0)
45K 50K 55K 61K 65K
NbSe3 #3
H=2T-2
1
40 50 60 70 80 900100200300400500600700800900100011001200
40 50 60 70 80 90
260280300320340360380400420440460480500
Rd0
(O
hm)
T(K)
NbSe3 #3
H//a*=53.4T
H=0
40 45 50 55 60 65 70 75 80 85 900.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4NbSe
3 #3
2/2 2(4
.2K
)
T (K)
Induced CDW gap above Peierls transition temperature
H=0
H=35T
0 10 20 30 40 500.0
0.2
0.4
0.6
0.8
1.0
1.2
2/
2(4.
2K
)
H (T)
45K 50K 55K 61K 65K 71K 76K 83K
NbSe3 mesa #3
2=0Амплитуда
щелевого пика = 0
Phase diagram. Interplay of orbital and Pauli effects.
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, 2BH0 kTp
That is consistent with calculatons of Zanchi, Bjelis, Montambeau PRB 1996 for the case of moderate imperfection parameter (valid for NbSe3)
BH0 / (2Tp) 0.1 or
For Tp = 61 K that corresponds to H0 30T
60
65
70
75
80
85
0 10 20 30 40 50 60
H (T)
T (
K)
#3 #4
NbSe3
Field induced CDWField induceed CDW state
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.
40 nm
60 nm Damaged
region
FIB
FIB machine
Seiko Instruments Corp. SMI-9000(SP)Ga+ ions 15-30 kV Beam current : 8pA – 50 nAMinimal beam diameter: 10nm
Stacked structures fabricated from layered materials by FIB methods
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
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
Pseudogap in graphite
Interlayer tunneling in graphite mesas
0 50 100 150 200 250 300
0.2
0.4
0.6
0.8
1.0
1.2
R
/RT
=300K
T (K)
M1 G1
Graphite
-100 -80 -60 -40 -20 0 20 40 60 80 10014.0
14.5
15.0
15.5
16.0
16.5
17.0
17.5
dI/d
V (
kOh
m-1
)
V (mV)
4.2K 7K 10K 15K 20K 30K 50K 80K 110K 150K 200K 250K
Graphite mesa #1
We found an evidence of pseudogap formation in graphite below T0 =30K.
Vpg 10-15 mV Vpg 3.5 kT0 !?Yu.I.Latyshev, A.P.Orlov, A.Yu. Latyshev,Th. Fournier, J. Marcus and P. Monceau 2007
At 300K 0.2 cm, // 50 cm, /// ~ 4000
At 4.2K /// ~ 30 000
Mesa sizes; 1m x 1m x 0.02-0.03
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 hc[|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
2.643m
4m
5m
6m
7m
8m
9m
10m
11m
V (mV)200-200 -100 0 100
6 6
0.410.470.540.610.690.770.870.971.081.201.341.491.651.822.022.232.462.702.92
7.805m
1.943m
2.5m
3m
3.5m
4m
4.5m
5m
5.5m
6m
6.5m
7m
7.5m
V (mV)200-200 -100 0 100
G #1 N30 G #3 N 20
We found Landau quantization from interlayer tunneling transitions
-1<->1, -2<->2 consistent with STM and magneto-transmission data
Spectra are well reproducible, peak position does not dependent on N
аnother selection rule: |n| = 0valid for coherent tunnеling
0 1 2 3
-100
-50
0
50
100
Graphite
V
(m
V)
H (T)
#1 #3
Comparison of the 1st level energy for two samples
V H1/2
typical for Dirac fermions
Comparison with STM and magneto transmission data
Transitions -1<->1, -2<->2, -3<->3 observed are consistent with STM and
magneto-transmission data. VF = 108 cm/s, En (nH)1/2
0 1 2 3 4 5 6-400
-300
-200
-100
0
100
200
300
400
Mag.trans 2x(01) STM 2x(01) STM 2x(02) Inter.tunn -11 Inter.tunn -22 Inter.tunn -33
V
(m
V)
H(T)
Graphite #1
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 axisD. Yoshioka and H. Fukuyama, J. Phys. Soc. Jpn. 50, 725 (1981).
We attempted to find CDW gap above 30 T
0 5 10 15 20 25 30 35 40 45 50 55 600
200
400
600
800
1000
1200
R (
Ohm
)
H (T)
G1 G3
Graphite mesa
T=1.4K
Effect nearly disappeared for 20 graphene layers
Pseudogap at graphite at high fields Yu.L., A.P. Orlov, D. Vignolles, P. Monceau 06-07
-600 -400 -200 0 200 400 600
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.7510T
14T
21T
25T
28T
14T
21T
25T
28T
dI/d
V (
kOh
m-1)
V (mV)
dI/dU11(sm)Graphite #1
10T
T=4.2K
Pseudogap appears above 20T, Vpg 150 mV
Remarkable features:
(1) increase of tunnel conductivity with field
(2) field induced PG
???
10 15 20 25 30 35 40 45 50 55-400
-300
-200
-100
0
100
200
300
400
V
(m
V)
H (T)
Graphite #1
Field dependence of pseudogap value
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 10-15 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.
