high field mangneto-transport in two-dimensional electron...
TRANSCRIPT
High field magneto-transport on two-dimensional electron gas in LaAlO3/SrTiO3
Ming Yang, Kun Han, Olivier Torresin, Mathieu Pierre, Shengwei Zeng, Zhen Huang, T. V. Venkatesan, Michel Goiran, J. M. D. Coey, Ariando,
and Walter Escoffier
LaAlO3/SrTiO3
Ohtomo
A. Ohtomo and H. Hwang, Nature 427, 423 (2004)
A. Janotti et al., Phys. Rev. B 86,241108(R) (2012)
P. Delugas et al., Phys. Rev. Lett. 106, 166807 (2011)
Both require high magnetic
field.
Electronic subbands of 2DEG derived from
the Ti 3d(t2g) orbitals.
dxz/dyz
Investigate the electronic states of the
2DEG.
Transport properties in LaAlO3/SrTiO3
Sample preparation
Pulsed Laser Deposition: 10 uc LAO deposited on STO substrate
T =740 oC
PO2 = 2x10-3 Torr
f = 1 Hz
Post annealing in air @ 550 oC
Fabricated in National University of Singapore
25um Al wire wedge bonding
L=180 μm
W=50 μm
Measurement under high magnetic field
0.0 0.1 0.2 0.3 0.4 0.50
10
20
30
40
50
60
B (
T)
Duration (s)
Magnetic field: 0-60T Temperature: 1.5-300K Angle: 0-90o Sample size: 4x4mm
14 MJ Capacitor Bank
60T magnet
Also available at LNCMI-T: 70T and 90T down to 300mK
Magneto-transport in LAO/STO
Negative MR:
Kondo effect (A. Joshua et al., PNAS110, 9633 (2013))
Diamagnetic shift (A. McCollam et al., APL Mat 2,022102(2014))
Rashba spin-orbit coupling (M. Diez et al., PRL 115, 016803 (2015))
Positive MR (perpendicular field) to negative MR(parallel field) transition.
Linear Hall effect under magnetic field.
Small oscillations superimpose on Rxx.
Single band?
SdH oscillations
0 10 20 30 40 50 60-50
0
50
100
150
200
250
(STO)
(LAO)10
I
B
(001)
(100)
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 0
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0
(STO)
(LAO)10
I
B
(001)
(100)
0
30
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0
(STO)
(LAO)10
I
B
(001)
(100)
0
30
60
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
(STO)
(LAO)10
I
B
(001)
(100)
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 0
30
60
75
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0
(STO)
(LAO)10
IB
(001)
(100)
0
30
60
75
90
Rxy (
k
)
B (T)
Rxx(0)=1440 Ω
Magneto-transport in LAO/STO
Negative MR:
Kondo effect (A. Joshua et al., PNAS110, 9633 (2013))
Diamagnetic shift (A. McCollam et al., APL Mat 2,022102(2014))
Rashba spin-orbit coupling (M. Diez et al., PRL 115, 016803 (2015))
Positive MR (perpendicular field) to negative MR(parallel field) transition.
Linear Hall effect under magnetic field.
Small oscillations superimpose on Rxx.
Single band?
SdH oscillations
0 10 20 30 40 50 60-50
0
50
100
150
200
250
(STO)
(LAO)10
I
B
(001)
(100)
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 0
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0
(STO)
(LAO)10
I
B
(001)
(100)
0
30
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0
(STO)
(LAO)10
I
B
(001)
(100)
0
30
60
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
(STO)
(LAO)10
I
B
(001)
(100)
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 0
30
60
75
Rxy (
k
)
B (T)
0 10 20 30 40 50 60-50
0
50
100
150
200
250
MR
(%
)
B (T)
T=1.7 K
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0
(STO)
(LAO)10
IB
(001)
(100)
0
30
60
75
90
Rxy (
k
)
B (T)
Rxx(0)=1440 Ω
0.02 0.04 0.06 0.08 0.10
-80
-40
0
40
80
1.68K
1.97K
2.54K
3.15K
4.20K
R
XX (
)
1/B (T)
Single-subband with Rashba effect
Multi-subbands
Non-perfect periodicity of oscillations
SdH oscillations
Effective mass m*=1.9 me heavy carrier : dxz / dyz orbitals
Dingle temperature TD=5.5 K quantum mobility μq~200 cm2/Vs
The average frequency yields the carrier density ~ 1012cm-2, one order of magnitude
lower than the carrier density extracted from the Hall effect.
61T 81T
75T
0.02 0.04 0.06 0.08 0.10
-80
-40
0
40
80
1.68K
1.97K
2.54K
3.15K
4.20K
R
XX (
)
1/B (T)
Single subband +
Rashba SOI
0 1 2 3 4 5 6 7 8
0.00
0.02
0.04
0.06
R
XX/R
0
T (K)
m*=1.9 0.1 me
TD=5.5 0.3 K
SdH oscillations Lifshitz-Kosevich equation:
Effective mass m*=1.9 me heavy carrier : dxz / dyz orbitals
Dingle temperature TD=5.5 K quantum mobility μq~200 cm2/Vs
The average frequency yields the carrier density ~ 1012cm-2, one order of magnitude
lower than the carrier density extracted from the Hall effect.
SdH oscillations with Rashba effect
A. Fête et al., New J. Phys.16, 112002 (2014).
Good fitting of the oscillations for both samples using the effective mass of 1.9me.
The same Rashba constant and g*-factor for both samples and consistent with the literature (3.4E-12eVm and 5.2 respectively).
The carrier density compares with Onsager relation, one order of magnitude lower than the carrier density extracted from the Hall effect.
Landau Levels:
0.02 0.04 0.06 0.08 0.10
-80
-40
0
40
80
1.68K
1.97K
2.54K
3.15K
4.20K
R
XX (
)
1/B (T)
Single subband +
Rashba effect
0 1 2 3 4 5 6 7 8
0.00
0.02
0.04
0.06
R
XX/R
0
T (K)
m*=1.9 0.1 me
TD=5.5 0.3 K
Zeeman term Rashba term
0.04 0.08
-150
-100
-50
0
50
100
experiment
fitting
R
(
)
1/B (T-1)
m*=1.9me
= 5.4510-12
eVm
n = 1.651012
cm-2
g = 5
Sample S1
0.04 0.08
-40
-20
0
20
40
experiment
fitting
Sample S2
m*=1.9me
= 5.4510-12
eVm
n = 2.401012
cm-2
g = 5
1/B (T-1)
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 experimental data
Rxy (
k
)
B (T)
nHall
= 1.451013
cm-2
Multi conduction channels 2-fluids model:
Quantum oscillations Classical transport
dxz dyz dxy
0.04 0.08
-150
-100
-50
0
50
100
experiment data
Rashba fitting
R
(
)
1/B (T-1)
m*=1.9me
= 5.4510-12
eVm
n = 1.651012
cm-2
g = 5
Sample S1
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 experimental data
2 fluids fitting
Rxy (
k
)
B (T)
Two conduction channels with a dominating one
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 experimental data
Rxy (
k
)
B (T)
nHall
= 1.451013
cm-2
Multi conduction channels 2-fluids model:
Quantum oscillations Classical transport
dxz dyz dxy
0.04 0.08
-150
-100
-50
0
50
100
experiment data
Rashba fitting
R
(
)
1/B (T-1)
m*=1.9me
= 5.4510-12
eVm
n = 1.651012
cm-2
g = 5
Sample S1
0 10 20 30 40 50 60-2.5
-2.0
-1.5
-1.0
-0.5
0.0 experimental data
2 fluids fitting
Rxy (
k
)
B (T)
Transport mobility and quantum mobility
Quantum relaxation time
Transport relaxation time
Q(θ) is the probability through a scattering angle θ.
P. T. Coleridge et al., Phys. Rev. B 39,1120(1989).
We assume that the quantum mobility of the in-plane carriers is too small for SdH oscillations.
Carriers far from the interface (dxz/dyz) :
Carriers close to the interface (dxy) :
?
Summary and perspectives
Investigate on the angle dependence of the SdH oscillations with Rashba effect. Investigate on the carrier density dependence (back-gate, top-gate, UV light) to
map the band structure of the LAOSTO interface. STO substrate with different crystalline orientation.
Carriers originate from the dxz/dyz orbitals
Carriers originate from the dxy orbitals
Heavy effective mass Lower carrier density Higher mobility Far from the LAO/STO interface,
less sensitive to scattering at the interface.
Light effective mass? higher carrier density lower mobility Close the LAO/STO interface, more
sensitive to scattering at the interface.
Hypothesis:
Rashba effect
Two-fluids model
Qualitatively consistent with the negative magnetoresistance in parallel field(M. Diez et al., PRL 115, 016803 (2015))
Acknowledgement NUSNNI Group @Singapore & Dublin
LNCMI Group @Toulouse
Thank you!
arXiv:1604.03451