Upload
eleanore-norris
View
246
Download
0
Embed Size (px)
Citation preview
Landau level properties of two prototypical bilayer graphenes
邱裕煌,何彥宏,林明發
成功大學 物理系
Introduction
Tight-binding Model
Results and Discussions
Conclusions
1/33
hybridization of atomic orbitals
2/33
various dimensionality
3/33
achievement of few-layered sheets
Mechanical exfoliation of highly oriented pyrolytic graphite Science 306, 666 (2004)Epitaxial growth on silicon carbide Science 312,1191 (2006) 4/33
stacking consequence
Bernal stacking5/33
AA
Simple hexagonalstacking
low-energy bands: monolayer & bilayer
Science 313, 951 (2007)
6/33
angle-resolved photoelectron spectroscopy (ARPES)
7/33
Landau quantization
8/33
2DEG
experimental observation of Landau levels in graphene
1. Quantum Hall conductivity2. Scanning tunneling spectroscopy3. Magnetooptical transmission (excitations between Landau levels)
Nature 438, 197 (2005)
Nat. Phys. 3, 623 (2007) PRL 97, 266405 (2006)9/33
Tight-binding model Phys. Rev. 109, 272 (1958)
γ0
γ1 γ3 γ4
γ0
bilayer Bernal graphene
monolayer graphene
10/33γ6
zero-gap semiconductor
semimetal
1
0
1, exp
R
r
RR
R
R
k r ik r r RN
G A d r R
ei G
A R
G
r R d
The Bloch function
Ref: J. M. Luttinger, Phys. R
: Peierls phas
s in a static m
ev. 84, 8
agneti
1
c fiel
e
4
d
~8 1
:
17 ( 9
��������������
��������������
��������������
������������� �
����������������������������������������������������������������� �����
51)
2
2
,
1exp
2
1
2
R R
R
k k k k
i k R k R ie G G
RRRR
R
RR
H k r
Pik R V r R
mN
H H
e HN
PH r R V r
i
m
G
R
e
����������������������������
��������������
��������������������������������������� ���
��������������������������������������� ���
����������������������������
������������� �
��������������
��������������
����������������������������������������������������� ���
��������������
������������� �
1
0
1 2
0
0
50 4.1356 10
For a graphene monolayer, 79000 T through
a hexagon area.
Define 79000 / , is related to the dimensi
The flux quantum
R R
B B
G G R R A R R R d
hTm
e
R T B R
����������������������������������������������������������������������������������������������������������������
onality
of the Hamiltonian matrix.
For monolayer graphene, the dimensionality is 4 .
For bilayer graphene, the dimensionality is 8 .B
B
R
R
12/33
ˆB ; A (0, ,0)Bz Bx
Monolayer graphene
13/33
γ0
nE B
14/33
15/33
18/33
Optical absorption function
Velocity matrix element
', is derived by gradient approximation.h hM
',
2 ', , , , ', ' 1
, 1,2
[ ] . .B
h h
R h hi M j M k i Mk B j M kM M
i j
M
H h c
2', '', ' 1
',0
', ', ', ',0 3 4
', ', ',0 3
' , '
Monolayer:
[ ] . .
= ( )
AB-bilayer:
( )+ ( )+ ( )
AA-bilayer:
( )+ ( )
LL wavefunction:
BRh h h hk Mk B M kM M
h h
h h h h h h h h
h h h h h h
n n n n
M A B A H B h c
M
M M M M
M M M
Monolayer
1, 1
c vn n n
AB-bilayer
AB-bilayer
Selection rules
1 1
2 1
2
2
1
2 1,1
0,
,
0
1
2
1
,2
c
c v
v
v
v
c
c
n n
n
n n
n
n n
16/33
Selection rules
'1
'2 2
1
1
1,
,1
1h
h
h
hn n
n n
17/33
Conclusions:
1. Two prototypes of bilayer graphenes, AA- and AB-stacking bilayer graphenes, exhibit different Landau level spectra, which reflect the fact that the magneto-electronic properties strongly depend on the stacking configurations.2. The Landau wave functions of AA- and AB-stacking bilayer graphenes show dissimilar features and the dissimilarities are reflected in the magneto-optical absorption spectra, such as the distinct selection rules and different field-dependent absorption frequencies.
33/33
Thanks for your attention!