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!