Environmental Engineering Reference
In-Depth Information
4.3.2
Ballistic Thermal-Transport Properties in 2D
Three-Terminal Quantum Structures
Note that two preceding cases only consider the ballistic phonon
transport in the two-terminal dielectric systems. Recently, various
three-terminal junctions have emerged as building blocks in the
formation of nanoscale electronic devices. Some applications of
three-terminal junctions are proposed based on the theoretically
investigated properties of electron transport [87, 88]. For the
electronic transport in three-terminal system, it has become well
known that the third terminal can be used to apply a gate voltage
and thus compatibly control the electric current in the channel
built by the two other terminals by using the gate as a voltage
probe [87]. More recently, phonon transport properties in three-
terminal systems have drawn increasing attentions due to the
potential applications in thermal devices. As shown in Fig. 4.5, for
anasymmetric
y
-branchthree-terminaljunction[89],onefindsthat
in the low frequency region, where the two lowest phonon modes
can be excited, there exist obvious mode splitting behaviors in such
structure. For instance, the incoming zero mode mostly transports
into an outgoing lead with the same thickness to the incident lead
(namely region B), while the 1
th
mode mostly enters into the
other lead (namely region A). Similar mode splitting behaviors can
be also observed in this case for the higher incident frequency.
These interesting properties can be well understood as a result
of the resonant coupling between the incident lead and different
outgoing leads. In addition, Ming
et al.
presented a study of the
thermal properties of three-terminal mesoscopic dielectric systems
in the nonlinear response regime at low temperature [90]. It is
demonstrated that when temperatures
T
L
and
T
R
are applied to
the left and right lead of a symmetric three-terminal system in
push-pull fashion with
T
L
=
T
R
, the temperature of the central
lead is always higher than (
T
L
+
/
2. Similar phenomenon
can be also observed for an asymmetric three-terminal system.
According to Eq. 4.2, these are analytically explained by making the
Taylor expansion for the Bose-Einstein distribution function. There
should be no thermal rectification in two-terminal mesoscopic
dielectric system, since the transmission coe
cient of ballistic
T
R
)
