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Electronic properties of heterojunctions between metallic and semiconducting single-wall carbon nanotubes are investigated. Ineffective screening of the long-range Coulomb interaction in one-dimensional nanotube systems drastically modifies the charge transfer phenomena compared to conventional semiconductor heterostructures. The length of depletion region varies over a wide range sensitively depending on the doping strength. The Schottky barrier gives rise to an asymmetry of the I-V characteristics of heterojunctions, in agreement with recent experimental results by Yao et al. and Fuhrer et al. Dynamic charge buildup near the junction results in a steplike growth of the current at reverse bias. PACS numbers: 71.20.Tx, 73.30. + y Single-wall carbon nanotubes (SWNTs) are giant linear fullerene molecules which can be studied individually by methods of nanophysics [1]. Depending on the wrapping of a graphene sheet, SWNTs can either be one-dimensional (1D) metals or semiconductors with the energy gap in subelectronvolt range [2,3]. While metallic nanotubes can play a role of interconnects in future electronic circuits, their semiconducting counterparts can be used as basic elements of switching devices. An example is the field effect transistor on semiconducting SWNT operating at room temperature [4].Of particular interest are all-nanotube devices [5]. The simplest can be fabricated by contacting two SWNTs with different electronic properties. The SWNTs can be seamlessly joined together by introducing topological defects (pentagon-heptagon pairs) into the hexagonal graphene network [6]. The resulting on-tube junction generically has the shape of a kink. Electronic properties of such junctions have been investigated theoretically (see, e.g., Refs. [7] and [8]) within the model of noninteracting electrons.Electron transport in nanotube heterojunctions has been studied in two recent experiments. Yao et al. treated junctions in SWNTs with kinks [9] whereas Fuhrer et al. explored contacts of crossed nanotubes [10]. Both groups observed nonlinear and asymmetric I-V characteristics resembling that of rectifying diodes. On one hand, the rectifying behavior can be naturally interpreted in terms of Schottky barriers (SBs). On the other hand, formation of a SB might be surprising since one expects no charge transfer in junctions between two SWNTs made of the same material.A possible reason for the charge transfer might be the doping of the nanotubes forming the heterojunction [11]. The doping can be caused by introduction of dopant atoms into the nanotubes or by charge transfer from metallic electrodes. In the latter case the doping strength can also be controlled by the gate voltage. It is important to mention that screening of the Coulomb interaction is ineffective in one-dimensional nanotubes. For this reason the effect of the doping is long ranged: the density of the transferred charge decays slowly with the distance from the electrodes and might be appreciable at the heterojunction [12].The long-range Coulomb interact...

The phase Hamiltonian of armchair carbon nanotubes at half filling and away from it is derived from the microscopic lattice model by taking the long-range Coulomb interaction into account. We investigate the low-energy properties of the system using the renormalization group method. At half filling, the ground state is a Mott insulator with a spin gap, in which bound states of electrons are formed at different atomic sublattices. [S0031-9007(98)