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Electric Field Control of 2D Materials
Yoshi Iwasa
Univ Tokyo & RIKEN
IMPACT 2016 August 23-September 2, 2016Cargèse, Corsica, France
Acknowledgements
AP, Univ Tokyo
Y. Saito,W. ShiF. QinM. YoshidaY. Nakagawa,J. T. Ye→GroningenY. Kasahara→KyotoM. Nakano
IMR, Tohoku Univ
T. Nojima
RIKEN CEMSD. HashizumeT. KikitsuD. Inoue
Reshef Tenne
Alla Zak
Theoretical supportRIKEN CEMS & U Tokyo
N. NagaosaM. EzawaS. HoshinoR. Wakatsuki
Electric field effects in 2D materials
3
100 ~ 101 nm100 ~ 101 mm
Longitudinal electric field Transverse electric field
E ~ 104 MV/cm
J = 1 ~ 100 MA/cm2. E ~ 107 MV/cm
e.g. Current switching
in 1T-TaS2.
R(k
W)
V (V)
M. Yoshida et al. Sci. Adv. (2015).
A. W. Tsen et al. PNAS (2015).
I. Vaskivskyi et al. Nat. Commun. (2016).
J. T. Ye et al. Nat. Mater. (2010).
K. S. Novoselov et al. Science (2004).
B. Radisavljevic et al. Nat. Nanotech. (2011).
Gate-induced superconductivity
Monolayer transistor
e.g.
Small volume!
substrate substrate
E E
Field effect transistor Nonlinear transport
OUTLINE
(1) Transverse electric field effect
1-1 Electric double layer transistor (EDLT)
1-2 A new aspect as a 2D superconductor
1-3 Superconductivity in inorganic nanotubes
(2) Longitudinal electric field effect
2-1 Thinning effect in 1T-TaS2
2-2 Nonvolatile current switching
Basic Ideas
Helmholtz’s electric double layer (1853)
--+
-++-
+
Ele
ctr
osta
tic P
ote
ntia
l
+ --
+ --
+
+
-
-
-
-
+
+
+
+
EDL( ~1 nm ) Hermann von Helmholtz
(1821-1894)
Electric Double Layer (EDL)
at interfaces between electronic and ionic conductors
Electrochemical cell
Pt Pt
Electric Double Layer
electrochemical interface
similar to solid heterointerface
High electric field x 100
high density charge x 100
EDLC (super capacitor)
Versatile
n2D (cm–2)
107 109 1011 1013 1015105
Semiconductor MetalElectronic phase transition
FET Electric Double Layer Transistor (EDLT)
Insulator
From FET to EDLT (Electric Double Layer Transistor)
Ge J. Bardeen, Nobel Lecture (1956)
ISFET P. Bergveld: IEEE Trans. Biomed. Eng. BM17, 70 (1970).
Si A. Tardella, and J.-N. Chazalviel: Phys. Rev. B 32, 2439 (1985).
H. S. White, G. P. Kittlesen , M. S. Wrighton: J. Am. Chem. Soc. 106, 5375 (1984).
Y. Harima, T. Eguchi, K. Yamashita: Synth. Met. 95, 69 (1998).
M. Krüger, M. R. Buitelaar, T. Nussbaumer, C. Schönenberger, and L. Forró: Appl.
Phys. Lett. 78, 1291 (2001).
S. Rosenblatt, Y. Yaish, J. Park, J. Gore, V. Sazonova, and P. L. McEuen: Nano Lett.
2, 869(2002).
M. Taniguchi and T. Kawai, Appl. Phys. Lett. 85, 3298 (2004).
H. Shimotani, G. Diguet, Y. Iwasa: Appl. Phys. Lett. 86, 022104 (2005).
M. J. Panzer, C. R. Newman, and C. D. Frisbie: Appl. Phys. Lett. 86, 103503 (2005).
D. Nilsson and M. Berggren, Adv. Mater. 17, 353 (2005).
Conducting polymers
Carbon nanotube transistors
Organic transistors
Early works on Ge and Si
History of semiconductor-electrolyte interfaces
M. Krüger et al., APL (2001)
Carbon nanotube EDLTs
S. Rosenblatt, Nano Lett. (2002).
Single-walledMulti-walled
Characteristics of ZnO-EDLT
10
n-type transistor operation
20
15
10
5
0
2
0
I D (
mA
)Le
ak c
urr
ent
(mA
)
0 0.8 1.6 2.4 3.2Gate voltage (V)
VDS = 0.1 V
Transfer curve
0 0.2 0.4 0.6 0.8 1
120
80
40
0
Drain voltage (V)
I D(m
A)
VG
(V)3.1
3.0
2.9
2.8
2.7
2.6
Output curve
H. Shimotani et al., Appl. Phys. Lett. 91, 082106 (2007).
Hall effect measurement of EDL
0.8
0.6
0.4
0.2
0
5
4
3
2
1
0
Sheet
conducta
nce (
mS
)
Carr
ier
den
sity (
10
13
cm
–2)
0 0.5 1 1.5 2 2.5 3
Gate voltage (V)
ne = Q = CV
Solvent moleculeIon
- - -
+ + +
C ~ 7.8 mF/cm2
EDL
ZnO
5–5 0
VH/I
D(k
W) 2
1
0
–1
–2
B (T)
0
1.423
VG(V)
thickness of EDL ~ 1 nm
(cf. 15 nF/cm2 for SiO2)
(e = 10 e0 for PEO solvent)
H. Shimotani et al., Appl. Phys. Lett. 91, 082106 (2007).
Insulator-metal transitions in oxide semiconductors
H. Shimotani et al., Appl. Phys. Lett. (2007). R. Misra et al., Appl. Phys. Lett. (2007).
ZnO InOx
Electric field induced superconductivity in SrTiO3
2.5V
3.5V
2.25V
VG = 2V
2.75V
3V
T ( K )
R (
W/
)
SrTiO3
h / e2
100 300200102
0
106
104
Insulator
Metal
K. Ueno et al. Nater Materials (2008).
STO, YBCO: Goldman et al., PRL (2011)LSCO: Bozovic et al., Nature (2011)MoS2: Takagi et al APL (2012)WS2: Morpurgo et al., Nano Lett (2015)PCCO: Ariando, PRB (2014)
ElectrochemicalTaS2: Y. Yu et al., Nat Nano (2015)MoSe2, MoTe2: W. Shi et al. Sci Rep (2015)FeSe: J. Shiogai et al., Nat Phys (2016)
Superconductivity induced by EDLT
Gate induced ferromagnetism
Y. Yamada et al.,
Science, 2011.
S. Shimizu et al.,
PRL, 2013.
CoxTi1-xO2 Pt Co
K. Shimamura et al.,
APL, 2012.
Electric-field induced phase transitions in correlated electron systems
M-I transitions
M. Nakano et al.,
Nature, 2012.
Metal
Insulator
M-COO transitions
T. Hatano, et al.,
Sci. Rep., 2013.
Metal
Insulator
CDW transitions
M. Yoshida, et al.,
Sci. Rep., 2014.
TaS2
Band bending
Conventional
semiconductor
Strongly correlated
system
Band reconstruction
Bulk
EF
Surface
Fundamental question of correlated FETs
EF
Bulk Surface
How
connected ?OR
Ionic conductors as a gate dielectric
8
6
4
2
0C
arri
er d
ensi
ty [
10
14
cm2]
SiO2 Polymer electro-lyte
Ionic liquid
Ionic liquid (low T)
H. T. Yuan et al., Adv. Funct. Mater. 19, 1046 (2009)
N+
CH3
O CH3
CH3
CH3
S
N-
S
O O OO
F F
F
F
F
F
Ionic liquids
Ion gels
DEME TFSI
BF4
ZnO
Polymer electrolytes
KClO4 + (PEO or PEG)
Ionic liquid + block copolymer
Emerging 2D superconductors
MBE-grown CVD-grown mechanically-exfoliated Interface, field effect
Pb-single layer (1L)Science 324, 1314 (2009).Nature Phys. 6, 104 (2014).
In-1L
PRL 107, 207001 (2011).
FeSe-1L
CPL 29, 03742 (2012).
Ga-2L
PRL, 114, 107003 (2015).Science, aaa7154 (2015).
Tl-Pb-1L
PRL 115, 147003 (2015).
BSCCO-1L
Nature Comm. 5, 5708 (2014).
NbSe2-1~2L
Nature Nano. 10, 765 (2015).Nature Phys: 12, 92 (2016).Nature Phys: 12, 139 (2016).Nature Phys: 12, 208 (2016).
ZrNCl-quasi-1L
Nature Mat. 9, 1314 (2010).Science 350, 409 (2015).
Mo2C-1~2L
Nature Mat. 14, 1135 (2015)
MoS2-quasi-1L
Science 338, 1193 (2012).Science 350, 1352 (2015).Nature Phys: 12, 144 (2016).
WS2, MoSe2 etc.
Sci. Rep. 5, 12534 (2015)Nano Lett. 15, 1197 (2015).
LAO/STO
Science 317, 1196 (2007).Nature 456, 624 (2008).
TiSe2
Nature 529, 185 (2016)
History of 2D superconductors
Physics of 2D superconductors
ZrNCl-EDLT MoS2-EDLT
Y. Saito et al. Science 350, 409 (2015).
Y. Saito et al., Nature Physics, 12, 144 (2016)J. M. Lu et al., Science 350 1353 (2015)
Enhanced Hc2 by spin-orbit interaction and symmetry breaking
Quantum metallic states
Gate Induced Superconductivity in ZrNCl
R-T Curve Insulator
Ionic liquid
Gate Superconductor
Source
Drain
5 mm
ZrNCl nano device
ZrNCl-EDLT:
Y. Saito et al. Science 350, 409 (2015).
R-T Curves for H and H// (ZrNCl)
Y. Saito et al. Science 350, 409 (2015).
Anisotropy in Hc2 (ZrNCl)
2/10//20
2
020
)/1()0(2
12)(
)/1()0(2
)(
c
scGL
c
c
GL
c
TTd
TH
TTTH
m
m
dSC 1.8 nm
GL(0) 13.1nm
Temperature dependence of Hc2
2D GL model
H
H
ZrNCl 1layer ~ 1 nm
Charge accumulation = monolayer1st principle calculation T. Brumme et al. PRB (2014)
Bulk-LixZrNCl
ZrNCl-EDLT
Amplitudefluctuation
Phase fluctuation
Aslamazov-Larkin
Maki-Thompson
+
BKT transition
Aslamazov-Larkin
Maki-Thompson
+
Superconducting fluctuation near Tc in ZrNCl
Φ = 𝚽𝟎 exp 𝑖𝝓Macroscopic wave function
Tc0
TBKT
Phase FluctuationBKT transition
Amplitude FluctuationAZ+MT analysis
e-
e-
e-
e-e-
e-
e-
e-
Interface (2D) vs bulk (3D) : R(H) -T curve
ZrNCl-EDLT (2D) LixZrNCl (3D Anisotropic)
ZrNCl
2DEGE
LixZrNCl
dsc ~ 1.8 nm
60 nm
Flattening resistance at low temperature
H
Quantum metals in highly-crystalline 2D SCs
ZrNCl-EDLT
Y. Saito et al. Science 350, 409 (2015).
Quantum metal induced by vortex fluctuation due to weak pinning
H
Quantum metals in highly-crystalline 2D SCs
ZrNCl-EDLT
Y. Saito et al. Science 350, 409 (2015).
Quantum metal induced by vortex fluctuation due to weak pinning
H
Cu0.03TaS2 (Zhu et al., J. Phys. Cond. Mater 22, 505704 (2010)
Quantum metals in highly-crystalline 2D SCs
ZrNCl-EDLT
Quantum metal induced by vortex fluctuation due to weak pinning
Hh-BN capped bilayer NbSe2
A. W. Tsen et al. Nature Phys. 12, 208 (2016).
Bose metal
Y. Saito et al. Science 350, 409 (2015).
Quantum metals in highly-crystalline 2D SCs
ZrNCl-EDLT
Quantum metal induced by vortex fluctuation due to weak pinning
HSrTiO3-EDLT
Y. Saito et al. Science 350, 409 (2015).
TBKT
Robust zero-resistance in In monolayer
M. Yamada, T. Hirahara and S. Hasegawa, Phys. Rev. Lett. 110 237001 (2013).
No significant broadening in the MBE grown In monolayermaybe due to the grain boundaries
Gate-induced superconductivity in MoX2
(IL)(IL)(KClO4/PEG)
1.0
0.8
0.6
0.4
0.2
0
Re
sis
tan
ce
(a
rb.u
nit
s)
14121086420
Temperature (K)
MoSe2 MoS2MoTe2
W. Shi et al. Sci Rep 5, 12534 (2015)
Superconductivity in WS2
33
Superconductivity in WS2
IDS – VG Curves R – T Curves (log plot)
o Reversible gate control of intercalation
(potassium -doped)Tc = 8.6 K
10-2
10-1
100
101
102
Rs (
W)
12 3 4 5 6
102 3 4 5 6
1002
T (K)
VG = 6 V
2.0
1.5
1.0
0.5
0.0
Rs (
W)
12840
T (K)
VG = 10 V
0 T
2 T
IntercalationEDLTelectrostatic electrochemical
Cf) S. Jo et al., Nano Lett. 15 1197 (2015)
W. Shi et al. Sci Rep 5, 12534 (2015)
2. Longitudinal electric field effect
34/26
Nonvolatile and Memristive switching
in TaS2
M. YoshidaPII-12Next week
1T-TaS2: Electronic phase transition system
1T-TaS2 : Charge density wave (CDW) system
Ta
S
10-4
10-3
10-2
10-1
3D (
W c
m)
3002001000T (K)
C
NC
IC
S
Ta
C NC IC
High TLow T
Commensurate
Nearly-commensurate
In-commensurate
Thickness dependent phase transitions
102
103
104
105
Rs (
W)
3002001000T (K)
100 nm10
2
103
104
105
Rs (
W)
3002001000T (K)
61 nm
102
103
104
105
Rs (
W)
3002001000T (K)
102
103
104
105
Rs (
W)
3002001000T (K)
42 nm
102
103
104
105
Rs (
W)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
3002001000T (K)
200
150
100
50
0
TC (
K)
101 2 4 6 8
102
Thickness (nm)Bulk
NC
C
C
NC
IC
NC
IC
1 K/min
Abrupt suppression of NC-C transition on cooling. → Consider kinetics.
Rs(W
)
M. Yoshida et al.,
Sci. Rep. 4, 7302 (2014).
36
104
105
106
3D (
W c
m)
3002001000
T (K)
104
105
106
3D (
W c
m)
3002001000
T (K)
104
105
106
3D (
W c
m)
3002001000
T (K)
104
105
106
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
10-3
10-2
10-1
3D (
W c
m)
3002001000
T (K)
Cooling-rate-dependent phase transition
1 K/min
0.2 K/min
8 K/min
1 K/min
10 K/min
5 K/min
1 K/min
10 K/min
Thickness = 31 nm 61 nm Bulk
C
NC
IC
C
NC
IC
C
NC
IC
Super-Cooled
NC
37
Phase diagram considering kinetics
10-2
10-1
100
101
QC (
K/m
in)
9
102 3 4 5 6 7 8 9
100Thickness (nm)
200
150
100
50
0
TC (
K)
10-2
10-1
100
101
QC (
K/m
in)
9
102 3 4 5 6 7 8 9
100Thickness (nm)
200
150
100
50
0
TC (
K)
10-2
10-1
100
101
QC (
K/m
in)
9
102 3 4 5 6 7 8 9
100Thickness (nm)
200
150
100
50
0
TC (
K)
10-2
10-1
100
101
QC (
K/m
in)
9
102 3 4 5 6 7 8 9
100Thickness (nm)
200
150
100
50
0
TC (
K)
Bulk
NC-CDW
C-CDW
The ordering kinetics of the transition becomes slow by thinning.
C-CDW
NC-CDWCritical cooling rate
for the occurrence
of the transition
Rc (K/min)
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).
103
104
3002001000T (K)
103
104
3002001000T (K)
Nonvolatile switching from the NC state by Vin-plane
Thickness = 19 nm
1 K/min
225 K
Rs
(Ω)
IC
NC
NC
IC
Vin-plane
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).A. W. Tsen et al. PNAS (2015).
I. Vaskivskyi et al. Nat. Commun. (2016).
103
104
3002001000T (K)
103
104
3002001000T (K)
Multiple metastable state by Vin-plane
103
104
3002001000T (K)
Apply Vin-plane
at T = 165 K
300 K
285 K
260 K
195 K
225 K
Rs
(Ω)
IC
NC
40
Thickness = 19 nm
1 K/minIC
NC Vin-plane
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).
2
1
40030020010005
04003002001000
Rs
(kW
)V
(V)
Time (s)
1.0
0.5x1
03
20010005
02001000
Rs
(kW
)V
(V)
Time (s)
Apply V at T = 90 K
tw = 200 s
tw = 100 ms
Switching to various electronic states
Memristive switing
C
NC
IC
41
Thickness
= 36 nm
The stability of the voltage-induced metastable states
42
Thickness = 19 nm
1 K/min
Apply Vin-plane
at T = 165 K
300 K
285 K
260 K
225 K
195 K
Thickness = 74 nm
1 K/min
Apply Vin-plane
at T = 225 K
The metastable states can also exist in thick crystals, but are fragile.
IC
NC
IC
NC
C
Energy landscapes
C NC
Energ
yE
nerg
y
Bulk
Thin flake
Summary
(1) 2D superconductivity by EDLT
(2) Quantum metallic states under magnetic fields in ZrNCl
(3) Superconductivity in WS2 nanotube/
transport reflecting tublar and chiral structure
New states of matter in 2D materials created by electric fields
Transverse electric field: E ~ 107 V/cm
(1) Many metastable states, possibly semimetallic in TaS2
(2) Non-volatile memristive switching
Longitudinal electric field: E ~ 104 V/cm