青木 伸之

Using an approach that allows us to probe the electronic structure of strongly pinched-off quantum point contacts (QPCs), we provide evidence for the formation of self-consistently realized bound states (BSs) in these structures. Our approach exploits the resonant interaction between closely coupled QPCs, and demonstrates that the BSs may give rise to a robust confinement of single spins, which show clear Zeeman splitting in a magnetic field. © 2007 The American Physical Society.

We have established a novel manipulation technique using a glass-micro capillary under a high-resolution CCD microscope so far. Two isolated multi-wall carbon nanotubes (MWNTs) are settled to form a well-aligned cross structure. Recently, we have tried to develop a fine manipulation system using a scanning probe microscope with a silicon cantilever. Therefore, thinner high-quality MWNTs (∼10 nm in diameter) can be utilized in this system. At the junction, we have observed weak localization and Fano-like-effect, zero bias anomaly whose traces were visible even at room temperature with thick MWNTs (∼100 nm in diameter). On the other hand, with thinner high-quality MWNTs (∼10 nm in diameter), we have observed also anomalous I-V characteristic and Altshuler-Aronov-Spivak-like magneto-oscillations at low temperature in the nano-space transport. © 2007 American Institute of Physics.

We report on the electrical properties of Field-Effect Transistors (FETs) based on C60 nano-whiskers (C60 NWs). The C60 NWs-FETs exhibits n-channel, normally-on, properties and the carrier mobility is estimated to be almost 2 × 10-2 cm2/Vs under vacuum conditions at room temperature. We also report on C60 NWs-FET characteristics with low work-function source and drain (Mg) electrodes. The carrier mobility of Mg-electrode device is slightly higher than that of the Au-electrode one. © 2007 American Institute of Physics.

We observe novel behavior in the non-linear conductance of semiconductor quantum wires near pinch-off. In this regime, their low-temperature (<1K) differential conductance increases dramatically from zero to a value above 2e2/h. This enhancement depends strongly on temperature, in-plane magnetic field, and wire length. Our results suggest that this resonance is related to the formation of a novel many-body state in the quantum wires near pinch-off. © 2007 American Institute of Physics.

Recently, there are many interests on electronics nano-device applications based on carbon nano-tubes (CNT). We have studied the low temperature transport properties due to the crossing of two multi walled carbon nano-tubes (MWNTs). Especially, there exists a peak structure in the zero bias anomalies of the I-V characteristics of the crossing and this is found to be very sensitive to change of temperature, magnetic field and source drain voltage. Fano resonance like behavior has been observed in the central structure of the zero bias anomaly.[1,2] With radio wave irradiations in the microwave-region, the central part of the anomaly is found to respond strongly. It can be connected to new CNT applications for extremely small sized microwave detection. Also, we have observed quantum coherent transport in MWNT and hybrid devices using MWNT and single walled carbon nano-tube (SWNT). In such nano-scaled electronic devices, there exist crossing points as a quantum dot or quantum point contact. The origin of the sensitivity in the crossing may be associated with the quantum nature in the transport through localized or conductive states in the CNT However, such sensitiveness is unstable, it may also be sensitive to the thermal cycling in the low temperature transport measurements. Since it must be originated to the nano-scaled structure changes in CNT, we must carefully clarify on the nature of the structural defects in the CNT In the quantum device applications, such as microwave detection and so on, it should be noted that there exist certain degradations preventing the coherent properties in low temperature transports which is strongly related to the device performance. The details of the results of recent experiments in MWNT and SWNT, will be discussed based on quantum transport device performances. © 2007 IEEE.

We have investigated quantum structures, such as narrow wires, single or coupled quantum dots (QDs), and quantum point contact (QPC), in order to clarify the origin of the chaotic and fractal behavior in their transport properties. Chaotic behavior in the electrical transport in QD and QPC has been studied in the low temperature magneto-resistance (MR), and by use of scanning gate microscopy (SGM). The quantum structures are fabricated using hetero-junction semiconductors. The low temperature MR has been measured using a 3He cryostat or dilution refrigerator with magnetic fields up to 8 T. We discuss the relation between the narrow constrictions in these structures and chaotic scatterings observed in the MR and SGM.

Various techniques are developed to implement ambient scanning gate microscopy (SGM) as a tool for the characterization of organic-thin-film field-effect transistors (OFETs). OFETs comprising copper phthalocyanine have been investigated by this technique and their SGM response has been observed only at the edges of the metal electrodes, thereby providing visualization of the Schottky barrier at the boundary between the organic channel and the metal electrode. © 2007 American Institute of Physics.

Quantum transport in a quantum point contact of InGaAs has been successfully visualized using a low temperature scanning gate microcopy. The images involves three kinds of features: (i) conductance fluctuations due to quantum interference, (ii) characteristic peaks corresponding to the propagating mode, (iii) a static-peak pattern observed just before the pinch-off condition. Furthermore, the fluctuations in the image reveal that the area distribution has a peak at around 2.5 × 104 nm2 and follows Gaussian unitary ensemble. It is consistent with a distribution of frequency components of the magneto conductance fluctuations of the quantum point contact. © 2007 American Institute of Physics.

A pure and solvate C60 nanowhisker (NW) has been synthesized in N2 environment so as to study the C60-NW-based field effect transistor (FET) characteristics using X-ray diffraction, atomic-force microscopy, and scanning electron microscopy. The FET has been worked even at the solvate condition, and shows the highest on/off ratio in the various conditions. The crystalline structure changes from a highly-oriented hexagonal structure to a disordered face centered cubic structure after evaporating the solvent with an introduction of high-density dislocations and gate-independent carriers in C60 NWs. It is found that the solvate C60-NW FET shows a clear improvement of on/off ratio, however we need an appropriate solvent in order to improve the mobility. © 2007 IEEE.

We have investigated the dependence of the 0.7 feature in a quantum point contact on variation of a back-gate voltage, which is used to control the density of the two-dimensional electron gas in its reservoirs. In measurements at 1.8 K, we analyze the dependence of the transconductance to carefully extract the variation of the 0.7 feature with electron density. © 2006 Elsevier B.V. All rights reserved.

Direct visualization of quantum transport within the constriction of a quantum point contact (QPC) has been obtained using scanning gate microscopy (SGM). The SGM operates at 0.3 K using a PtIr-coated piezolever. Transmission through the QPC shows conductance quantization in units of 2 e2/h at 6 K; however, the plateaus are washed out by quantum fluctuations at 280 mK. Interference patterns within the QPC were observed by scanning the tip above the QPC. This is attributed to the presence of a random disorder potential. Near the pinch-off voltage, the technique allows us to directly image the disorder potential. At high magnetic fields, we observe quantized plateaus in the images, which may indicate a direct visualization of the edge states. © 2006 Elsevier B.V. All rights reserved.

We present significant electrical conductivity responses of the pelletized as-prepared and oxidized (ox-) single-wall carbon nanohorns (SWNHs) on adsorption of CO2 and O2. The morphological and pore structures of both pelletized SWNHs were examined by transmission electron microscopy (TEM) and nitrogen adsorption isotherm, leading to explicit evidences of the formation of nanoscale windows on the wall by oxidation. The SWNH and ox-SWNH induced a semiconducting behavior, strongly responded to CO2 and O2 adsorptions, and each exhibited n-type- and p-type-like conductivities. The electrical conductivity increase and decrease for CO 2 and O2 adsorption, respectively, were observed for SWNH, whereas ox-SWNH showed a marked electrical conductivity drop on CO2 adsorption and almost no change on O2 adsorption. The dramatically different electrical conductivity response of ox-SWNH is presumed to be ascribed to the annihilation of pentagons in the single graphene wall by oxidation. © 2006 American Chemical Society.

Quantum transport of an array of quantum billiards is investigated as a function of the coupling strength of the quantum point contacts that connect the individual billiards. A fractal analysis of the measured magneto-conductance fluctuations is used as a novel non-invasive probe of two characteristic energy scales of the energy level spectrum-the average energy level spacing and average energy level broadening. This analysis reveals a marked transition in the coherent area of the array as the coupling between the billiards is increased and the array evolves into a combined quantum system. © 2005 Elsevier B.V. All rights reserved.

We report the characterization of electrical properties for multi-walled carbon nanotubes (MWNTs) synthesized by the arc-discharge method, as to the difference of characteristics between two diameters of 10 nm and 100 nm. In a result of Raman spectrums, we have observed clear radial-breathing-mode peak at approximately 255 cm-1, which corresponds in turn to an innermost diameter of ∼2 nm in the MWNT, and shows a good agreement with the TEM image of diameter of the thin MWNT. The results of two- and fourterminal measurements of the thin MWNTs show a power-law behavior as expected for the Tomonaga-Luttinger liquid model. The power-law exponent, α ∼ 0.4, seems consistent with the one-dimensional nature of the transport in these structures. We have also investigated the thick MWNTs. © 2006 IOP Publishing Ltd.

We demonstrate DNA field effect transistor (DNA-FET) using multiwalled carbon nanotube (MWNT) as nano-structural source and drain electrodes. The MWNT electrodes have been fabricated by focused ion-beam bombardment (FIBB). A very short channel, approximately 50 nm, was easily formed between the severed MWNT. The current-voltage (I-V) characteristics of DNA molecules between the MWNT electrodes showed hopping transport property. We have also measured the gate-voltage dependence in the I-V characteristics and found that poly DNA molecules exhibits p-type conduction. The transport of DNA-FET can be explained by two hopping lengths which depend on the range of the source-drain bias voltages. © 2006 IOP Publishing Ltd.

We have investigated the non-linear transport properties of split-gate quantum wires of various channel lengths. In this report, we present results on a resonant enhancement of the non-linear conductance that is observed near pinch-off under a finite source-drain bias voltage. The resonant phenomenon exhibits a strong dependence on temperature and in-plane magnetic field. We discuss the possible relationship of this phenomenon to the spin-polarized manybody state that has recently been suggested to occur in quasi-one dimensional systems. © 2006 IOP Publishing Ltd.

C60 nano-whiskers (C60 NWs) have been synthesized by a method of liquid-liquid interfacial precipitation using a system of C 60-saturated m-xylene and isopropyl alcohol, and a C60 nano-whisker based field-effect transistor (C60 NW-FET) has been fabricated by a manipulator with use of a glass micro-capillary. The transport of the C60 NW-FET exhibits n-channel normally on properties and their carrier mobility is estimated to be 2.5 × 10-2 cm 2/Vs in vacuum at room temperature. © 2006 IOP Publishing Ltd.

Two types of quantum point contacts have been studied by low temperature scanning gate microscopy. In addition to the usual bright spot, which corresponds to a large conductance change at the constriction, ring structures are observed near the center of the quantum point contact. The ring diameter shrinks with increasing base conductance when the side gate voltage is changed. The rings are thought to relate to the observation of impurity potentials in the constriction region. © 2006 IOP Publishing Ltd.

We fabricate field-effect transistors (FETs) based on C 60 nanowhiskers (C 60 NWs) and investigate their structural and electrical properties. Thermally annealed C 60 NWs show x-ray powder-diffraction spectra that are consistent with a similar fee structure to that of C 60 bulk crystals, although with a slightly reduced lattice constant (a = 13.9 Å). The C 60 NW-FETs exhibit n-channel, normally-on, properties (or FETs) and their carrier mobility is estimated to be 2 × 10 -2 cm 2/V s under vacuum conditions at room temperature. © 2006 American Institute of Physics.

We report on a remarkable resonance in the differential conductance of long quantum point contacts (QPCs) that is observed as a precursor to regular quantized transport. This effect is increasingly pronounced in longer QPCs, in which the differential conductance may resonantly exceed 2e2/h. From a study of the experimental characteristics of this feature, we suggest that it may be associated with the formation of a well-resolved energy gap that opens dynamically as a result of enhanced many-body interactions in long QPCs. ? 2006 The American Physical Society.

Polycrystalline In2 O3 films with high crystallinity were prepared by annealing the amorphous In2 O3 films deposited at room temperature by using dc/rf sputtering method. General electronic behaviors of both these amorphous and polycrystalline films have been investigated by means of Hall effect and resistivity measurements at temperatures between 4.2 and 300 K. For the amorphous films, ionized impurity scattering dominates the electronic transport, and Hall mobility agrees well with the theory of degenerate semiconductors with divalent impurity scattering centers. On the other hand, the conduction mechanism of the polycrystalline films is governed dominantly by phonon scattering, since these films exhibit a clearly positive temperature coefficient of resistivity with the maximum Hall mobility of 150 cm2 V s at 300 K and 230 cm2 V s at 4.2 K, with little change in carrier concentration between these temperatures. Conductivity of both the amorphous and polycrystalline films is found to show a linear relationship in a double-logarithmic plot against carrier concentration between 4× 1015 and 5× 1020 cm-3, a typical behavior of the impurity semiconductors with parabolic conduction band. For each set of films with the same thermal history, Hall mobility is found to vary on a convex upward curve with respect to carrier concentration. This behavior suggests a general and strong correlation of the structural defects introduced upon deposition and localization of conduction electrons with electron mobility, which led to a proposition of three categories for temperature coefficient of resistivity with major transport mechanisms of phonon scattering, divalent impurity scattering, and weak localization, respectively. © 2006 American Institute of Physics.

Visualization of quantum interference patterns has been obtained within a quantum point contact using scanning gate microscopy. The area distribution of the interference pattern is shown to be consistent with the interference area obtained from the magnetoconductance fluctuations of a quantum point contact. Both distributions follow the Gaussian unitary ensemble, corresponding to chaotic behavior. The interference is caused by the random potential fluctuations within the channel, which is modified by the tip-induced potential. ? 2006 American Institute of Physics.

Integer quantum Hall edge states have been imaged in the constriction region of a quantum point contact fabricated in an InGaAs heterostructure at high magnetic fields using low-temperature scanning gate microscopy (SGM). Features in the SGM images grew wider and deeper as side gates squeezed the constriction. Furthermore, clear plateaus corresponding to the depopulation of edge states were observed. We propose a model for these images based on the variation of the local confinement potential induced by the tip. ? 2005 The American Physical Society.

We have studied to try on direct measurement of electron transport between DNA molecules by means of carbon nanotube (CNT) as a nano-electrode. The CNT electrodes were fabricated by focused ion beam bombardment (FIBB). Very short channel having about 50nm gap was easily formed between the severed CNT. Poly (dG)-poly (dC) DNA molecules containing identical base pairs were positioned between the CNT nano-electrodes by electrostatic trapping method. The current-voltage (I-V) characteristics showed a very short hopping distance of 3.8 Å and were similar to the distance between general base pairs (∼3.4 Å) of poly (dG)-poly (dC) DNA molecules. We also measured the gate-voltage dependence in the I-V characteristics and found that poly (dG)-(dC) DNA molecules exhibited p-type conduction. It confirms that the current seems to flow really through the DNA molecules. © 2005 American Institute of Physics.

We have studied transport properties in the low-temperature magnetoresistance through the ballistic narrow path restricted by a short width metallic gate on the 2 dimentional electron gas (2DEG) system. An alternate and systematic variation between a Lorentzian line fitting and a cusp-like line fitting in the zero-field peaks has been observed, as sweeping the gate voltage. It indicates a possibility of existence of chaotic and regular paths on the short gated ballistic/tunneling transport. We will discuss on the quantum chaos behavior on the systematic variation between the Lorentzian and the cusp-like peakshape based on the disordered path system under the short gate. © 2005 American Institute of Physics.

We have studied the electrical transport property of the coupled Quantum Point Contacts. That resonance peak structure has appeared in conductance of the detector QPC by forming of local spin moment in swept QPC. We find that resonance peak depends on the one-dimensional density of states in detector QPC. We will discuss the consistency with theoretical model using Anderson Hamiltonian. © 2005 American Institute of Physics.

A fractal analysis is used to characterize magnetoconductance fluctuations in an open, coupled quantum-dot array. The fractal dimension is combined with the empirical parameter Q as a probe of the energy level spectrum in the array, and a coupling transition is identified as a function of the number of modes in the coupling quantum point contact. © 2005 American Institute of Physics.

Superconducting properties in multi-walled carbon nanotubes (MWNTs) have been studied due to an interest on the flux field effect transistor applications. We have prepared a sample of a lope or bundle of MWNTs contacted with Indium metal at the both ends and observed a clear decrease in the magneto-resistance near the transition temperature of the Indium metal. This behavior has been expected to arise from superconducting precursor or the fluctuation effects near the transition temperature. © 2005 American Institute of Physics.

Transport property of crossed two multiwall carbon nanotubes has been investigated through low temperature measurement. We have succeeded to obtain the essential transport characteristics at the junction by means of the four-terminal measurement, where the conductance showed no Tomonaga-Luttinger liquid behabior, but showed almost metallic transport corrected by weak localization. © 2005 American Institute of Physics.

We have fabricated a cross-linked structure of multi-walled carbon nanotube(MWNT) in order to observe Fano-resonance in quantum coherent nano-devices. We can observe a certain distorted line shape in the zero-bias anomaly of the I-V characteristics for the cross-linked MWNT in wide temperature range. Especially, at low temperatures near 4.2K, the resonance peak can be observed to be similar to Fano resonance line shape. © 2005 American Institute of Physics.

A nano-scale C60 field-effect transistor has been fabricated with carbon nanotubes (C60CN-FET). A rope of multi-walled carbon nanotubes has been anchored by metal pads and cut by a focused Ga2+ ion beam ablation. The ablated ends of the rope have been integrated as electrodes into the C60CN-FET, which exhibits an excellent performance of a low-voltage operation, even as small as 100 nm of channel length. The electrodes have been applied also for two-terminal conductance of salmon's DNA. © 2005 American Institute of Physics.

狭い金属ゲート(QPC)を両端に有する開放型量子ドットについて、零磁場近傍の磁気抵抗のピーク形状が、ゲート電圧を変化させることによってローレンツ型とカスプ型が交互に現れる現象が観測された。このローレンツ型とカスプ型が交互に現れる要因としては、QPCによるトンネリング効果と量子ドットによる弱局在の両方が関係しているものではないかと推測され、考察を行った。

A nanoscale C60 field-effect transistor has been fabricated with carbon nanotubes (C60 CNT-FET). A wire of multiwalled carbon nanotube has been anchored by metal pads on a Si wafer, and cut by bombardment with focused Ga2+ ion beam. The cut ends of the wire have been integrated as source-drain electrodes into the C60 CNT-FET, with a vacuum evaporated C60 thin film. The C60 CNT-FET has exhibited an excellent performance of a low-voltage drive operation, without any short-channel effect even at as small as 100 nm of channel length. © 2005 American Institute of Physics.

In recent years, there has been interest in devices created on InGaAs due to the possibility of its use for spintronics. Nonetheless, this material is known for usually presenting some levels of disorder. We have used scanning gate microscopy to study the local potential for an in-plane gated InGaAs quantum point contact and succeeded in obtaining images corresponding to sites where same quantum interference conditions are maintained. Furthermore, we have visualized images of the local potential variations within the confined region near pinch-off condition. ? 2005 American Institute of Physics.

Much attention has been given to sub-1G 0 (=2e 2/h) features in the transmission curve of a quantum point contact (e.g.: 0.5G 0, 0.7G 0). Explanations for this phenomenon have been attributed to many-body interactions such as the Kondo effect or the formation of spin polarized currents. We have used scanning gate microscopy to directly observe the local features of the transport associated with sub-1G 0 structures. Images taken with this technique reveal striking features such as weak localization induced within the constriction as well as the formation of self-consistent potentials in the QPC. ©2005 IEEE.

The variable range hopping (VRH) in a C60 field-effect transistor (FET) was discussed. Investigations show the effect of thermal annealing (TA) at 453 and 498 K, on the conductance in various gate voltages and several source-drain separations. It was observed that the C60FET contains a large single-crystalline grain and there were less amount of grain boundaries. The results show that the density of states in the pseudogap decreases as TA temperature increases.

Fractal behavior in magnetoconductance fluctuations in coupled quantum dots has been studied by means of exact and statistical self-similarity. The fractal dimensions from the different features are not coincident exactly but show the similar gate voltage dependences, where the values increase with increasing negative gate voltage. Moreover, results of statistical fractal dimensions obtained from two types of dot-array samples show the same dependence on the gate voltage variation. It seems a common feature of coupled-dot systems that the fractal dimension increases by decreasing the inter-dot coupling. © 2003 Elsevier B.V. All rights reserved.

We demonstrate the presence of a resonant interaction between a pair of coupled quantum wires, which are realized in the ultra-high mobility two-dimensional electron gas of a GaAs/AlGaAs quantum well. Measuring the conductance of one wire, as the width of the other is varied, we observe a resonant peak in its conductance that is correlated with the point at which the swept wire pinches off. We discuss this behaviour in terms of recent theoretical predictions concerning local spin-moment formation in quantum wires.

We demonstrate the presence of a resonant interaction between a pair of coupled quantum wires, which are formed in the ultrahigh mobility two-dimensional electron gas of a GaAs/AlGaAs quantum well. The coupled-wire system is realized by an extension of the split-gate technique, in which bias voltages are applied to Schottky gates on the semiconductor surface, to vary the width of the two quantum wires, as well as the strength of the coupling between them. The key observation of interest here is one in which the gate voltages used to define one of the wires are first fixed, after which the conductance of this wire is measured as the gate voltage used to form the other wire is swept. Over the range of gate voltage where the swept wire pinches off, we observe a resonant peak in the conductance of the fixed wire that is correlated precisely to this pinchoff condition. In this paper, we present new results on the current- and temperature-dependence of this conductance resonance, which we suggest is related to the formation of a local moment in the swept wire as its conductance is reduced below 2e2/h.

Low temperature transport in C60 thin film field-effect transistors has been studied using several samples with various gate voltages. Nearest neighbor hopping and variable range hopping transport have been observed in the low temperature transport measurements. Analyzing the temperature dependence of the transport types, it was found that the electrical properties of the film can be improved by thermally agitated evaporation of C60. © 2004 Elsevier Ltd. All rights reserved.

A multiwall carbon nanotube crossroads has been fabricated by a manipulation technique using a glass microcapillary, and the low temperature transport properties investigated. The two-terminal conductance of an individual tube shows Tomonaga-Luttinger liquid behavior G ∝ Tα at high temperature and dI/dV ∝ Vα at low temperature. However, no evidence of such a power-law behavior is obtained in the four-terminal conductance at the junction, where the conductance shows an almost metallic behavior 'corrected' by weak localization. Weak localization would essentially appear in electron states at the junctions of MWNTs. © Published by Elsevier Ltd.

We have investigated the damage in multi-wall carbon nanotubes (MWNTs) destroyed by electrical breakdown and focused ion beam bombardment (FIBB). The transport properties of a MWNT destroyed by electrical breakdown have been compared with those of a MWNT destroyed by FIBB. Also the Tomonaga-Luttinger transport (TLT) model has been applied to each type of destroyed MWNT. The MWNT destroyed by FIBB showed TLT behavior because of the weak destruction of the remaining walls. However, in the case of MWNTs destroyed by electrical breakdown, three-dimensional variable-range hopping (VRH) was observed in the low temperature transport. This suggests that the local damage has been caused by strong breakdown. There exists a clear difference between the effects of electrical breakdown and FIBB. Wall destruction by FIBB could be applied to control the one-dimensional transport of MWNTs. © Published by Elsevier Ltd.

ESR spectra of MWNTs have been studied with isochronal annealing and temperature dependence down to 100 K. Two closely spaced peaks are observed in the ESR signals. The higher-field signal disappears after thermal annealing at 500°C and can be related to the presence of contaminations and /or defects in the MWNTs. However, the lower-field signal is thought to be associated with free carriers in the carbon nanotube and the transport relaxation time can be expected to decrease roughly by one-third after annealing. This suggests an associated enhancement of the spin-relaxation rate of conduction electrons due to an increase of carrier scatterings in the metallic system, consistent with Elliot's spin relaxation mechanism. © 2003 Elsevier B.V. All rights reserved.

Exactly self-similar, and statistically self-similar, features have been studied in the magneto-conductance of an open quantum-dot molecule. The fractal dimensions determined from the two different features are found to differ significantly from each other. While we do not understand the detailed origins of this difference at present, our results suggest that different physical processes are responsible for the two different types of fractal structure. © 2003 Elsevier B.V. All rights reserved.

Nonlocal resonant interaction between coupled quantum wires was studied. A resonant peak in the conductance that was correlated to the point at which the other wire pinches off was observed by measuring the conductance of one of the wires, as width of the other was varied. A micrograph of the device structure and schematics which illustrated the different measurements was showed.

Electrical transport properties of C60 thin-film field-effect transistor (FET) grown at room temperature was investigated with various gate voltages. The conduction above 260 K and below 200 K can be well explained by a thermal activation model. Especially, it is noted that a strong dependence on the gate voltage appeared for the conduction above 260 K. © 2002 Elsevier Science B.V. All rights reserved.

Fundamental transport mechanism in multi-walled carbon nano-tube has been studied by means of electron spin resonance (ESR) in order to discuss on the transport properties in the tube. After thermal annealing, the transport in the tube shows an ordinal metallic conduction. And the g-value and the line width for the ESR signal are gradually increased after the annealing. This also can be originated from a conduction electron system in the nano-tube. © 2002 Elsevier Science B.V. All rights reserved.

The characteristics of the conductance fluctuations, observed in the low-temperature magnetoresistance of an open quantum-dot molecule formed from a pair of split-gate quantum dots, have been studied. The evolution of these fluctuations suggests a decrease in the typical area for coherent interference with decreasing the coupling strength between the two dot. We discuss this behavior in terms of a transition from multi- to single-dot interference as a function of the inter-dot coupling. Moreover, an existence of interference trajectories which were independent of the dot coupling was also found in our analysis. © 2003 Published by Elsevier Science B.V.