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Band structure of graphene and CNT
Band structure of graphene and CNT
Graphene :
Lattice : 2- dimensional triangular lattice
Two basis atoms
X 축
y 축
1A
3A
2A
1B3B
2B
Bloch State of the π bands
X 축
y 축
1A
3A
2A
1B3B
2B
Three nearest neighbor
Nearest Neighbor Approximation
Multiply on both sides ( )zP r
RHS =
Tight Binding Approximation 에서 Nearest Neighbor Approximation 이라는 것은
Within Nearest Neighbor on site only
B AHC C
X 축
y 축
1A
3A
2A
1B3B
2B
의 nearest neighbor 1A 2A 3A1B
Multiply on both sides
Left=
Right=
A BH C C
3 32 2 3 36 6
2 2
1/ 2
2 20
2 cos( ) 2 cos( )2 2
31 4cos ( ) 4cos( )cos( )
2 2 2
3( , ) 1 4cos( )cos( ) 4cos ( )
2 2 2
y yy y
a aa ai k i ki k i k
x x
x y x
graphenex y y x x
a aH e e k e e k
a a ak k k
a a aE k k k k k
3,
2 3 2x y
a ak k
2 2
,3 3
x yk ka a
2 1,1
3 3k
a
Pass the Fermi point(Dirac point)
( ) 0grahpeneE k
2 1( ,1)
3 3Fermik
a
1 2
2 1
3 3Fermik b b
1a((((((((((((((
2a((((((((((((((
X 축
y 축
X 축
y 축
1b((((((((((((((
2b((((((((((((((
Lattice Reciprocal Lattice
Band Structure of Graphene Dirac point
1 2
4 10 , ( , )
3 3b b fixed
2 1( , )3 3
Band Structure of Graphene
1 2
4 10 , ( , )
3 3b b fixed
( ) ( )graphene grapheneE k E k G ((((((((((((( (
“ - 공간 에서의 주기함수” 를 확인하시기 바랍니다 .k
CNT =
wrapped graphene ribbon
X 축
c
경계조건
y 축
For example,
1/ 2
2 20
3( , ) 1 4cos( )cos( ) 4cos ( )
2 2 2x y y x x
a a aE k k k k k
Subband (n=0) (9,0)0
3( ) 1 4cos( ) 4
2CNT
yE k ak
Subband (n=1)(9,0) 2
0
3( ) 1 4cos( )cos( ) 4cos ( )
2 9 9CNT
yE k ak
0n1n
2n
3n
4n
8n
5n
6n
7n
Low energy effective Hamiltonian near K and K’
Tight-binding π bands, again.
Near K or K’
x x y yH k k
Near K or K’spinor of pseudospin
( )
x x y yH k k
A AH kB B
Mahmut, you have the solution for the spinor
( )
( )when ( ) , Mahmut write the sol.
( )
when ( ) , Mahmut write the sol.
A AH kB B
A kk k
B k
Ak k
B
Bands are doubly degenerate in real spin
With SOC
0
ˆ
ˆ0 0
0 ˆ0
ˆ ˆ = '
x x y y x z
x y z
x y z
H k k S
k ik S
k ik S
H H
In this low-energy Cone region, how and why the
SOC is represented this way?
ˆ 0ˆˆ0
zSOC
z
SH
S
Min et al., PRB74,165310(2006), Kane and Mele, PRL, 95, 226801(2005)
Full 4 component or 8 component solution A bit complicated
Diagonalize in real spin space
Min et al., PRB74,165310(2006), Kane and Mele, PRL, 95, 226801(2005)
ˆ is diagonalized
and as
x x y y x zH k k S
A A
B B
Diagonalize in real spin space
ˆ ˆ =
0 0
0 0
x y
x y
x y
x y
A AH H E
B B
k ikH
k ik
k ik A AE
k ik B B
Diagonalize in real spin space
2 2 2 2
2 2 2
x y
x y
E k k
E k k
Effective Hamiltonian Including the two Fermi point
K and K’ (K’=-K)
, near
, near '
x x y y
x x y y
k k KH
k k K
Without SOC it is not very meaningful
Effective Hamiltonian Including the two Fermi point
K and K’ (K’=-K)
ˆ , 1( ( '))x x y y z zH k k s K K
Why do we need this ? ????
ˆ , 1( ( '))x x y y z zH k k s K K
Why do we need this ?
Near K
ˆ ˆ =
0 0
0 0
x y
x y
x y
x y
A AH H E
B B
k ikH
k ik
k ik A AE
k ik B B
Near K’=-K
ˆ ˆ =
0 0
0 0
x y
x y
x y
x y
A AH H E
B B
k ikH
k ik
k ik A AE
k ik B B