Single-electron transport in electrically tunable nanomagnets

We study a single-electron transistor (SET) based upon a II-VI semiconductor quantum dot doped with a single-Mn ion. We present evidence that this system behaves like a quantum nanomagnet whose total spin and magnetic anisotropy depend dramatically both on the number of carriers and their orbital nature. Thereby, the magnetic properties of the nanomagnet can be controlled electrically. Conversely, the electrical properties of this SET depend on the quantum state of the Mn spin, giving rise to spin-dependent charging energies and hysteresis in the Coulomb blockade oscillations of the linear conductance.     

Single-electron pumping in a ZnO single-nanobelt quantum dot transistor

Diluted magnetic semiconductors(DMSs)have traditionally been employed to implement spin-based quantum computing and quantum information processing.However,their low Curie temperature is a major hurdle in their use in this field,which creates the necessity for wide bandgap DMSs operating at room temperature.In view of this,a single-electron transistor(SET)with a global back-gate was built using a wide bandgap ZnO nanobelt(NB).Clear Coulomb oscillations were observed at 4.2 K.The periodicity of the Coulomb diamonds indicates that the Coulomb oscillations arise from single quantum dots of uniform size,whereas quasi-periodic Coulomb diamonds correspond to the contribution of multi-dots present in the ZnO NB.By applying an AC signal to the global back-gate across a Coulomb peak with varying frequencies,single-electron pumping was observed;the increase in current was equal to the production of electron charge and frequency.The current accuracy of about 1%for both single-and double-electron pumping was achieved at a high frequency of 25 MHz.This accurate single-electron pumping makes the ZnO NB SET suitable for single-spin injection and detection,which has great potential for applications in quantum information technology.     

Single-electron transistors fabricated with sidewall spacer patterning

We have implemented a sidewall spacer patterning method for novel dual-gate single-electron transistor (DGSET) and metal–oxide–semiconductor-based SET (MOSET) based on the uniform SOI wire, using conventional lithography and processing technology. A 30 nm wide silicon quantum wire is defined by a sidewall spacer patterning method, and depletion gates for two tunnel junctions of the DGSET are formed by the doped polycrystalline silicon sidewall. The fabricated DGSET and MOSET show clear single-electron tunneling phenomena at liquid nitrogen temperature and insensitivity of the Coulomb oscillation period to gate bias conditions. On the basis of the phase control capability of the sidewall depletion gates, we have proposed a complementary self-biasing method, which enables the SET/CMOS hybrid multi-valued logic (MVL) to operate perfectly well at high temperature, where the peak-to-valley current ratio of Coulomb oscillation severely decreases. The suggested scheme is evaluated by SPICE simulation with an analytical DGSET model, and it is confirmed that even DGSETs with a large Si island can be utilized efficiently in the multi-valued logic.     

Graphene based single molecule nanojunction

We introduce the ab-initio framework for zigzag-edged graphene fragment based single-electron transistor (SET) operating in the Coulomb blockade regime. Graphene is modeled using the density-functional theory and the environment is described by a continuum model. The interaction between graphene and the SET environment is treated self-consistently through the Poisson equation. We calculate the charging energy as a function of an external gate potential, and from this we obtain the charge stability diagram. Specifically, the importance of including re-normalization of the charge states due to the polarization of the environment has been demonstrated.     

First-Principles Study of Ultrathin Single-Walled Nanotube-Based Single-Electron Transistor for Fast-Switching Applications

Physics of the Solid State - This work presents modeling and functioning of nanotube island single-electron transistor (SET), through first-principles approach based on density functional theory...     

Single-electron transistor with an island formed by several dopant phosphorus atoms

We present the results of an experimental study of electron transport through individual phosphorus dopants implanted into a silicon crystal. We developed an original technique for single-electron transistor fabrication from silicon-on-insulator material with an island formed by single phosphorus atoms. The proposed method is based on well-known CMOS compatible technological processes that are standard in semiconductor electronics and may be used in most research groups. The large Coulomb blockade energy value of the investigated single-electron transistor (～20 meV) allows one to observe single-electron effects in a wide temperature range up to 77 K. We measured and analyzed stability diagrams of fabricated experimental structures. We demonstrated a single-electron transistor with controllable electron transport through two to three phosphorus dopants only.     

Dynamics and dissipation induced by single-electron tunneling in carbon nanotube nanoelectromechanical systems

We demonstrate the effect of single-electron tunneling (SET) through a carbon nanotube quantum dot on its nanomechanical motion. We find that the frequency response and the dissipation of the nanoelectromechanical system to SET strongly depends on the electronic environment of the quantum dot, in particular, on the total dot capacitance and the tunnel coupling to the metal contacts. Our findings suggest that one could achieve quality factors of 10(6) or higher by choosing appropriate gate dielectrics and/or by improving the tunnel coupling to the leads.     

Analysis of Co-Tunneling Current in Fullerene Single-Electron Transistor

Single-electron transistors (SETs) are nano devices which can be used in low-power electronic systems. They operate based on coulomb blockade effect. This phenomenon controls single-electron tunneling and it switches the current in SET. On the other hand, co-tunneling process increases leakage current, so it reduces main current and reliability of SET. Due to co-tunneling phenomenon, main characteristics of fullerene SET with multiple islands are modelled in this research. Its performance is compared with silicon SET and consequently, research result reports that fullerene SET has lower leakage current and higher reliability than silicon counterpart. Based on the presented model, lower co-tunneling current is achieved by selection of fullerene as SET island material which leads to smaller value of the leakage current. Moreover, island length and the number of islands can affect on co-tunneling and then they tune the current flow in SET.     

Spintronics of a nanoelectromechanical shuttle

We consider effects of the spin degree of freedom on the nanomechanics of a single-electron transistor (SET) containing a nanometer-sized metallic cluster suspended between two magnetic leads. It is shown that in such a nanoelectromechanical SET (NEM-SET) the onset of an electromechanical instability leading to cluster vibrations and shuttle transport of electrons between the leads can be controlled by an external magnetic field. Different stable regimes of this spintronic NEM-SET operation are analyzed. Two different scenarios for the onset of shuttle vibrations are found.     

Non-equilibrium spin accumulation in ferromagnetic single-electron transistors

We study transport in ferromagnetic single-electron transistors. The non-equilibrium spin accumulation on the island caused by a finite current through the system is described by a generalized theory of the Coulomb blockade. It enhances the tunnel magnetoresistance and has a drastic effect on the time-dependent transport properties. A transient decay of the spin accumulation may reverse the electric current on time scales of the order of the spin-flip relaxation time. This can be used as an experimental signature of the non-equilibrium spin accumulation. Received 6 May 1998     

Quantum-size effects on the characteristics of single-electron tunneling

Effects of single-electron tunneling charging and Coulomb blockade in a cluster structure (molecular transistor) with regard to the quantization of electron levels in an island electrode are investigated. The spectrum of electrons is calculated for small disk-shaped clusters. Restrictions connected with the Coulomb instability of the cluster and electron relaxation are introduced in the theory. The current gap and its voltage asymmetry are calculated for single-electron transistors based on small gold clusters. The effect of the cluster shape on the current gap is investigated.     

DNA transistor and quantum bit element: Realization of nano-biomolecular logical devices

Based on the theoretical prediction that chemical bonds can act as tunnel junctions in the Coulomb blockade regime, and on the technical ability to coat a DNA strand with metal, we suggest that DNA can be used to built nano-logical devices. We discuss two explicit examples: a single-electron tunneling transistor (SET) and a quantum bit element. These devices would be literally in the nano-meter scale and would be able to operate at room temperature. In addition they would be highly stable and have a self ably property.     

Single-electron transistor spectroscopy of InGaAs self-assembled quantum dots

A single-electron transistor (SET) is used to detect tunneling of single electrons into individual InGaAs self-assembled quantum dots (QDs). By using an SET with a small island area and growing QDs with a low density we are able to distinguish and measure three QDs. The bias voltage at which resonant tunneling into the dots occurs can be shifted using a surface gate electrode. From the applied voltages at which we observe electrons tunneling, we are able to measure the electron addition energies of three QDs.     

Molecular states observed in a single pair of strongly coupled self-assembled InAs quantum dots

Molecular states in a single pair of strongly coupled self-assembled InAs quantum dots are investigated using a sub-micron sized single-electron transistor containing just a few pairs of coupled InAs dots embedded in a GaAs matrix. We observe a series of well-formed Coulomb diamonds with charging energy of less than 5 meV, which are much smaller than those reported previously. This is because electrons are occupied in molecular states, which are spread over both dots and occupy a large volume. In the measurement of ground and excited state single-electron transport spectra with a magnetic field, we find that the electrons are sequentially trapped in symmetric and anti-symmetric states. This result is well explained by numerical calculation using an exact diagonalization method.     

Continuum limit of single-electron tunneling

We consider the continuum limit of the standard model for treating single-electron tunneling (SET) of electrons through a one-dimensional array of tunnel junctions. We show that the formalism reduces to the computation of the motion of overdamped particles undergoing potential gradient flow, with the potential being given by the full interacting free energy of the electrons in the system. We show that the tunneling coefficients in the SET model can be re-interpreted in terms of a diffusion coefficient and a temperature and that therefore the SET problem reduces to a fully self-consistent treatment of overdamped particle diffusion.     

Cross correlations in mesoscopic charge detection

We study a tunnel contact that acts as charge detector for a single-electron transistor(SET) focusing on correlations between the detector current and the current through theSET. This system can be described fully by a Markovian master equation for the SET, whileelectron tunneling in the charge monitor represents a process with a stochastic rate,which can be solved exactly. It turns out that current monitoring is possible as long asthe detector current correlates with the currents through either SET barrier. By contrast,correlations with the effective current according to the Ramo-Shockley theorem are notessential. Moreover, we propose the measurement of the SET barrier capacitances.     

Quantized current of a hybrid single-electron transistor with superconducting leads and a normal-metal island

We discuss the operation of the superconductor–insulator–normal-metal–insulator–superconductor (SINIS) turnstile. This voltage-biased hybrid single-electron transistor (SET) provides current quantization even with only one radio-frequency (rf) control parameter, namely the gate voltage of the single island. We give an overview of the main error mechanisms of the turnstile and consider its feasibility as a quantum current standard. We also present experimental results of pumping with the SINIS structure which show decreased leakage current compared to earlier measurements with the opposite NISIN structure.     

Size-dependent single electron tunneling effect in Au nanoparticles

We investigated single electron tunneling (SET) behavior of dodecanethiol-coated Au nanoparticles of two different sizes (average sizes are 5 nm and 2 nm) using nanogap electrodes, which have a well-defined gap size, at various temperatures. The Coulomb staircases and the Coulomb gap near-zero bias voltage caused by the suppression of the tunneling electrons due to the Coulomb blockade effect were observed in the current-voltage (I-V) curves of both sizes of nanoparticles at a low temperature (10 K). At room temperature, the Coulomb gap was observed only in the I-V curve of the smaller nanoparticles. This result indicates that the charging energy of the smaller nanoparticles is enough to overcome the thermal energy at room temperature. This suggests that it is possible to operate the SET devices at room temperature using the smaller nanoparticles as a Coulomb island.