quantum transport in vdw heterostructures of …quantum transport in vdw heterostructures of...

Quantum transport in vdW heterostructuresof graphene and 2D materials

Tomoki Machida

Institute of Industrial Science, University of Tokyo

June 11, 2015

NPSMP （ISSP, Kashiwa）

OutlineTransfer technique of atomic layersQuantum Hall pnp junctions

Novel magnetoresistance oscillationsCoherent interference in QH edge channels

Graphene/h-BN

Josephson junctionsSupercurrentFraunhofer pattern and Fiske resonance

NbSe2/NbSe2

Magnetic tunnel junctionsMagnetoresistance effect

Fe0.25TaS2/Fe0.25TaS2

Graphene p-n junctions

Klein Tunneling

T=1p n

Negative refractive index

p n p n

Snake States

B

Quantum transport of Dirac fermions

Dirac coneGaplessPseudo spin

Graphene p-n junctions in high B

Landau quantizationQHE

Co-propagating quantum Hall edge channels

p nCounter-circulating quantum Hall edge channels

Novel resistance oscillations

Transfer of atomic layers

graphene

SiO2/Si

Polymer film

graphenePolymer film

GrapheneGraphene

Graphene/h‐BNGraphene/h‐BN

Glass slideh‐BN

SiO2/Sih‐BNh‐BN

h‐BN

SiO2/Si

Graphene on SiO2

SiO2

Si

dangling bond

SiO O

Mobility limited by extrinsic scattering sources

Graphene

Mechanical exfoliation

Surface roughnessDangling bondsCharged impuritySiO2 optical phonon (60 meV)

Graphene on SiO2 v.s. graphene on h-BN

SiO2

Graphene

Si

Hexagonal Boron Nitride Atomically flat surface

Extrinsic scattering sources suppressed

Surface roughnessDangling bondsCharged impuritySiO2 optical phonon (60 meV)

Atomically flat surfaceNo dangling bondsHoneycomb latticeBN optical phonon (100 meV)

BN

TG Graphene

1 m

Graphene

h-BN/SiO2

Back Gate

h-BN

Top Gate

+ + + +

ｰｰｰ

+ +ｰｰ

ｰ

nnn

ppppnp

npn

局所キャリア変調

1.6 K

h-BN / Graphene /h-BN

~ 105 cm2/Vs@RT

Graphene

h-BN/SiO2

Back Gate

h-BN

Top Gate

+ + + +

ｰｰｰ

+ +ｰｰ

ｰ

局所キャリア変調h-BN / Graphene /h-BN

~ 105 cm2/Vs@RT

500 nm

p nn

High quality graphene n-p-n junctions (L > 500 nm)

T = 1.6 K

R (k

)

n-n’-n / n-p-n quantum Hall junctions

n p nn n’ nv v’ v

B

v v’ v

2

1'

hRe

Co-propagating edge channel

n-n’-n / n-p-n quantum Hall junctions

n pB

v v’ v

n n’ nv v’ v

2

1'

hRe

2 2

2 1 2 '' '

h h v vRv v vve e

for fully-mixed QH edge channelsB. Ozyilmaz et al., PRL 99, 166804 (2007).

for adiabatic QH edge channelsF. Amet et al., PRL112, 196601 (2014).

n

2

2 ''

h v vRvve

n-p-n quantum Hall junctions

2

1'

hRe

nn’n

2

1'

hRe

n n’ nv v’ v

for full mixing2

2 1'

hRv ve

n p n

v v’ v for adiabatic2

2 1'

hRv ve

Novel oscillation observed !npn

T = 1.6 K

n-p-n quantum Hall junctions

T = 1.6 K

12 21.7 10 cm

12 21.5 10 cm

12 21.3 10 cm

12 21.1 10 cm

12 20.9 10 cm

12 20.7 10 cm

12 20.5 10 cm

12 20.3 10 cm

B ~ 0.5 T

Aharonov-Bohm effect

1hBe S

Carrier density profile at n-p junctions

n p n


v= 6 v

= -6v

= 0 v=

-2v

= 2


v= 6 v

= -6v

= 0 v=

-2v

= 2

●●●

●●●

x

c

c

= 0 incompressible strip

S

B

S

|nTG|B

B B 1hB

e S 1hB

e S

|nTG|

Local carrier density profile by FEM analysis

Graphene

h-BN/SiO2

Back Gate

h-BN

Top Gate

Graphene

h-BN/SiO2

Back Gate

h-BN

Top Gate

Finite element method(Infolytica Elecnet)

-2

0

2

n (1

012cm

-2)

-100 -50 0 50 100

6

4

2

0

x

(nm

)

86420B (T)

012 2

12 2

12 2

12 2

12 2

12 2

12 2

1.7 10 cm1.5 10 cm1.3 10 cm1.1 10 cm0.9 10 cm0.7 10 cm0.5 10 cm

p

c 0.4

x (nm)

012 2

12 2

12 2

12 2

12 2

12 2

12 2

0.5 10 cm0.7 10 cm0.9 10 cm1.1 10 cm1.3 10 cm1.5 10 cm1.7 10 cm

p


0, ,BW x B n p N (N = 1, 2, …, 10, …)

v= 6 v

= -6v

= 0 v=

-2v

= 2

x

Resistance oscillations

0, ,BW x B n p N

x

v= 6 v

= -6v

= 0 v=

-2v= 2

v= 6 v

= -6v

= 0 v=

-2v= 2 W

(N = 1, 2, …, 10, …)

N = 4

N = 20

Resistance oscillations

x

v= 6 v

= -6v

= 0 v=

-2v= 2

v= 6 v

= -6v

= 0 v=

-2v= 2 W

Novel oscillations in quantum Hall pn junctions

Quantum Hall pnp junctions Magnetic flux quantization in = 0 incompressible strip formed between co-propagating quantum Hall edge channels

0 1.5

n (1012 cm-2)

CalculationExperimentn-p-nn-n’-n

x

v= 6 v

= -6v= 0 v

= -2v= 2

v= 6 v

= -6v= 0 v

= -2v= 2 W

CollaboratorsSatoru Masubuchi, Sei MorikawaRai Moriya, Naoto Yabuki, Miho Arai(Institute of Industrial Science, University of Tokyo)

Takashi Taniguchi, Kenji Watanabe(National Institute of Materials Science)

Keiji Ueno(Saitama University)

SummaryTransfer technique of atomic layersQuantum Hall pnp junctions

Novel magnetoresistance oscillationsCoherent interference in QH edge channels

Graphene/h-BN

Josephson junctionsSupercurrentFraunhofer pattern and Fiske resonance

NbSe2/NbSe2

Magnetic tunnel junctionsMagnetoresistance effect

Fe0.25TaS2/Fe0.25TaS2

quantum transport in vdw heterostructures of …quantum transport in vdw heterostructures of...

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