Biomedical Engineering Reference
In-Depth Information
Tabl e 7. 5
Degeneracy of the
triple dot system energy
levels as it follows from the
underlying
D
3
symmetry.
Alevel
N
i
is the
i
th excited
level with
N
particles. The
total degeneracy of the level
is the product of its orbital
and spin degeneracies.
From [
22
]
Many-body
energy level
Orbital
degeneracy
Spin
degeneracy
0
1
1
1
0
1
2
2
0
1
1
2
1
2
3
3
0
2
2
4
0
1
3
5
0
2
2
6
1
1
Fig. 7.11
Stationary current for the triple dot I-SET. Coulomb blockade diamonds are visible
at low biases. Ground state and excited state interference blockades are also highlighted. The
temperature is
k
b
T
=
0
.
002
|
b
|
. The other parameters are the same as the ones in Fig.
7.10
.
From [
22
]
we also give the degeneracies of all levels relevant for the blocking states analysis
which will follow. We distinguish between spin and orbital degeneracy since the
latter is the most important for the identification of the blocking states. The total
degeneracy of a level is simply the product of the two.
7.5.2
Excited State Blocking
In Fig.
7.11
we show the stationary current through the triple dot I-SET as a function
of bias and gate voltage. At low bias the current vanishes almost everywhere
due to Coulomb blockade. The particle number is fixed within each Coulomb
diamond by the gate voltage and the zero particle diamond is the first to the
right. The zero current lines running parallel to the borders of the 6-, 4-, and 2-
particle diamonds are instead signatures of ground state interference that involves
an orbitally non-degenerate ground state (with 2-, 4-, and 6-particle) and an orbitally
double-degenerate one (with 3 and 5 particles).
