Reversible heat flow through the carbon tube junction

Abstract

Microscopic mechanisms of externally controlled reversable heat flow through the carbon nanotube junctions (NJ) are studied theoretically. Our model suggests that the heat is transfered along the tube section T by electrons (e) and holes (h) moving ballistically in either in parallel or in opposite directions and accelerated by the bias source-drain voltage VSD (Peltier effect). We compute the Seebeck coefficient α, electric σ and thermal κ conductivities and find that their magnitudes strongly depend on VSD and VG. The sign reversal of α versus the sign of VG formerly observed experimentally is interpreted in this work in terms of so-called chiral tunneling phenomena (Klein paradox).PACS numbers: 73.23. Hk, 73.63.Kv, 73.40.Gk Physics of the heat transfer determines functionality, precision and effectiveness of solid state nanocoolers [1,2,3,5] which are environment friendly and have a lot of applications in the experimental physics, nanoelectronics, chemistry, industry and medicine. Therefore exploiting of new thermoelectric materials with high figures of merit Z · T (T being the temperature) attracts a lot of attention. Recently such interest arose toward the carbon nanotube and graphene junctions which electronic properties are highly unconventional [5]. The thermoelectric power experiments [5] addressed single wall carbon nanotube junctions. In Ref.[5] a temperature difference ∆T induced a finite bias voltage ∆V p across the junction which sign changed versus the gate voltage V G . A question here is how that unconventional thermoelectric behavior is related to the intrinsic nature of the carbon nanotube and graphene? It is widely accepted that the charge carrier motion in carbon nanotubes and in graphene is essentially phase-correllated. For such a reason the conducting electrons and holes in that materials behave as relativistic massless 'chiral fermions' (CF) characterized by a 'pseudospin' (see review [6] and references thereis).In this Letter we argue that the phase-correlated thermoelectric transport of charge carriers implicates a voltage-controlled and reversable heat flow through the single wall carbon nanotube junctions (Peltier effect). The enhancement of Z · T in those 1D devices where the charge carriers propagate ballistically occurs due to strong van Hove singularities (VHS). The VHS position is tuned by the gate voltage V G in respect to the Fermi level ε F of the electrodes. When an VHS and ε F match each other, it results in a sufficient density of charge carriers which contribute to the electric conductivity despite the Fermi energy itself is relatively small. A finite gate voltage V G = 0 is not just merely supplies either the electrons or holes into T , but rather creates a potential barrier (U 0 > 0) or well (U 0 < 0) for chiral fermions transmitted across the junction as illustarted in Figs across the junction tilts the chiral barrier and causes the electric charge carriers to accelerate. This means that the energy of the charge carriers changes by δ = eV SD , which inflicts a local...

Quantized magneto-thermoelectric transport in low-dimensional junctions

“…Therefore, we merely regard them as equilibrium Fermi functions f (0) (ε/T C ) = 1/ (exp (ε/T C ) + 1) with a steady state temperature T C . Equations (6) with L th were addressed in Ref. [2] whereas the phonon drag was considered in Refs.…”

“…[2] whereas the phonon drag was considered in Refs. [2,6,8,38]. The phonon drag leads to the non-equilibrium deviation δf pd which in the linear approximation is computed from Eq.…”

“…Furthermore, quantization of transverse electron motion occurs owing to spatial confinement of the electron states inside the narrow stripes. The above phenomena are utilized in the low-dimensional elements of electronic circuits, and also during the thermoelectric cooling and energy generation [5,6].In this Letter we focus on the other aspects of the problem concerning of filtering, spatial separation, redirecting and conversion the different components of the thermal and electric transport. Such the phenomena take place when the d.c. magnetic field B = {0, 0, B z } acts on the crossing of a narrow AM stripe C with the metal stripe N. We examine the microscopic mechanism of controllable redirection and convertion one type of transport to another taking place in such the crossing (C/N-knot), where the electric and heat currents are separated from each other as shown in Fig.…”

Coherent nonlocal transport in quantum wires with strongly coupled electrodes

“…We account for this coupling using the Green's function method 13 . Electronic transport through this structure involves multiple transmission and reflection processes for the electron wave functions, which are solutions of the Dirac equation [17][18][19] . The transmission probability through the shallow barrier along the CNT axis depends on the electron energy E, on gate voltage V G , and on the potential barrier profile U (x).…”

“…Relevant composition rules and calculations details of T P (E, U, V G ) can be found in earlier papers (see, e.g., Refs. 18,19 ). The conductance G = dI/dV 1−2 of section A is computed by using the Landauer-Büttiker formula 13 for the electric current…”