current-driven metamorphosis of electronic structures in...
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Current-driven metamorphosis of electronic structures
in two-dimensional 1T-TaS2 crystals
Masaro Yoshida1,2 & Yoshihiro Iwasa1,2
1RIKEN CEMS, Japan2Department of Applied Physics, The University of Tokyo, Japan
1
Current switching to a metastable electronic phase in thin 1T-TaS2.
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).
M. Yoshida et al. PRB 95, 121405(R) (2017).
M. Yoshida et al. Nano Lett. (2017). See my poster!
Discovery of a hidden crystal phase by making 2Ha-TaS2 into the thin flakes.
Plenty of room at the “2D” 2
Explore novel phases in 2D materials with interacting electrons.
Purpose
B. Radisavljevic et al.
Nat. Nano. (2011).
MoS2Graphene
2004 2005
“2D material”
MoS2
BSCCO
NbSe2
K. S. Novoselov et al.
PNAS (2005)
Year
K. S. Novoselov et al.
Science (2004)
2011~ 2014~
1T-TaS2
NbSe2
M. Yoshida et al.
Sci. Rep. (2014).
N. E. Staley et al. PRB (2009).
X. Xi et al. Nat. Nano. (2015).
A. W. Tsen et al. Nat. Phys. (2016).
M. Yoshida et al. APL (2016).….
Graphene FET.QHE…
Any layered material can be 2D.
MoS2 FET.Superconductivity.
J. T. Ye et al. Science (2012). CDW, superconductivity….Phase transition.
Target materials: 2Ha-TaS2 & 1T-TaS2.
Explore novel phases in 2D materials 3
1T-TaS22Ha-TaS2
Explore hidden crystal phase by thinning the bulk crystal.
Explore metastable electronic phaseby current injection.
r(W
cm
)
T (K)
C
NC
IC
10
5
03002001000
r(x
10
-4W
cm
)
T (K)
IC
Normal
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).M. Yoshida et al., PRB 95, 121405(R) (2017).
M. Yoshida et al., Nano Lett. (2017).Details in my poster!
TaS
S
1.0
0.8
0.6
0.4
0.2
0.0
3
2
1
03002001000
R(T
)/R
(30
0 K
)
T (K)
RH
(x1
0-4
cm
3/C
)
Two-dimensional 2Ha-TaS2 crystal (Details in my poster!) 4
2Ha: Trigonal prisms.1T: Octahedrons. 4Hb/6R: Mixture.
M. Yoshida et al. Nano Lett. (2017).
1.0
0.8
0.6
0.4
0.2
0.0
3
2
1
03002001000
2Ha-type flake
New-type flake
A new polymorph was discovered by thinning the 2Ha bulk crystal.
Inte
nsity (
arb
. units)
40393837
20 0 8 (deg)2 (deg)
008
Inte
nsity (
arb
. units)
40393837
20 0 8 (deg)
Normal
CDW
2Ha crystal
Scotch Tape0.5cm 2μm
E = 12.4 keVSPring-8
Polymorphism in TaS2 bulk crystals
Explore novel phases in 2D materials 5
1T-TaS22Ha-TaS2
Explore hidden crystal phase by making the bulk crystal into the 2D.
Explore metastable electronic phaseby current injection.
r(W
cm
)
T (K)
C
NC
IC
10
5
03002001000
r(x
10
-4W
cm
)
T (K)
IC
Normal
TaS
S
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).M. Yoshida et al., PRB 95, 121405(R) (2017).
M. Yoshida et al., Nano Lett. (2017).Details in my poster!
r(W
cm)
T (K)
Two-dimensional 1T-TaS2 crystal 6
High TLow T
C NC IC
1T-TaS2 : CDW system
Supercooling the NC state by thinning.
Bulk
C: Commensurate CDW
NC: Nearly commensurate CDW
IC: Incommensurate CDW
M. Yoshida et al., Sci. Rep. 4, 7302 (2014).Y. Yu et al., Nat. Nanotech. (2015).
A. W. Tsen et al., PNAS (2015)…
C
NC
IC
NCThin
Thick
C
NC
E Thin
1 K/min
Nonvolatile current switching in 1T-TaS2 thin crystals 7
A. W. Tsen et al., PNAS (2015).
M. Yoshida et al., Sci. Adv.
1, e1500606 (2015).
Reveal the switching mechanism and the electronic structure of NC* states.
Purpose
C
NC
NC*
T (K)
R(W
)E
CNC
NC*
I. Vaskivskyi et al.,
Sci. Adv. (2015),
Nat. Commun. (2016).
Current switching to the metastable NC*.
Vo
ltag
e (V
)
Current (A)
Vin-plane
E
qIC qH qC
q
G. Liu et al.,
Nat. Nano. (2016).
E
C
NC
NCICVoltage (V)
Cu
rren
t (m
A)
“Hidden state”
103
104
3002001000T (K)
103
104
3002001000T (K)
Switching from NC to NC* states
The persistent metastable NC* state was created.
Thickness = 19 nm
1 K/min
225 K
Rs
(Ω)
IC
NC
NC
IC
Vin-plane
NC*
8
NC
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).
Thickness dependent stability of the NC* state
30020010003002001000
R(T
)/R
(37
0K
)
T (K) T (K)
1 K/min 1 K/min
10 K/min 10 K/min
10 K/min after switching
10 K/min after switching
Thickness = 47nm 83 nm
Thinning-induced slow kinetics makes the metastable states robust.
NC
IC
NC
IC
C C
9
NC
NC*
100
101
102
The NC* state is inherent even in bulk crystals.
8
6
4
2
0
R(T
)/R
(370K
)
86420
E (kV/cm)
Switching mechanism
225 K
NC NC* IC
① Eth for the switching to NC*.
② End of the switching to NC*.
③ Eth for the switching to IC.
8
6
4
2
0
E (
kV
/cm
)
3002001000
T (K)
IC
NC*
NC
Intermediate
10
Thickness = 19 nm
Int.
R/R
(37
0K
)
NC
NC*
IC
8
6
4
2
0
R(T
)/R
(370K
)
86420
E (kV/cm)
Switching mechanismR
/R(3
70
K) 165 K
352 K
IC
NC
NC*
8
6
4
2
0
E (
kV
/cm
)
3002001000
T (K)
Transition from NC* to IC.
:Joule heating.
Transition from NC to NC*.
:Eth∝exp(-T/T0). Depinning of CDW.
102
2
4
6
103
2
4
6
104
E (
V/c
m)
3002001000
T (K)
IC
NC*
NC
K. Maki PRB 33, 2852 (1986).
TNC-IC
11
Sliding of CDW that is strongly pinned by lattice.
Small system size enables us to apply high electric field.
Thickness = 19 nm
IC
NC
NC*
-12
-8
-4
0
RH (
x1
0-3
cm
3/C
)
3002001000
T (K)
10-2
10-1
100
101
(
cm
2/V
s)
3002001000
T (K)
Electronic structure
t = 19 nm
Apply
V at
165 K RH
(x1
0-3
cm
3/C
)
NC
IC
n3
D(c
m-3
)
80
60
40
20
0
RH (
x1
0-3
cm
3/C
)
3002001000
T (K)
Apply V at 90 K
T (K)
(c
m2
V-1
s-1
)
12
1 electron / 1 UC
NC
C
NC*
NC
NC*
NC
C
NC*
NC
NC*
NC
The metastable NC* state is an unprecedented semimetal.
T (K)
E
E
E
RH = (en3D)-1
r-1= en3D
Summary 13
Plenty of room in 2D devices for CDW physics.
1T-TaS22Ha-TaS2
Discovery of new phase stable only in 2D.
1.0
0.5
0.03002001000
T (K)
r/r
(3
00
K)
New2Ha
New
2Ha
R(T
)/R
(370K
)
E (kV/cm)
Slow ordering kinetics. Current phase switching.Sliding of CDW with commensurability.Semimetal.
T (K)
R(W
)
Vin-plane
NC*
C
NC
M. Yoshida et al., Sci. Adv. 1, e1500606 (2015).M. Yoshida et al., PRB 95, 121405(R) (2017).
M. Yoshida et al., Nano Lett. (2017).Details in my poster!