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Terahertz (THz) plasma oscillations represent a potential path to implement ultrafast electronic devices and circuits. Here, we present an approach to generate on-chip THz signals that relies on plasma-wave stabilization in nanoscale transistors with specific structural asymmetry. A hydrodynamic treatment shows how the transistor asymmetry supports plasma-wave amplification, giving rise to pronounced negative differential conductance (NDC). A demonstration of these behaviors is provided in InGaAs high-mobility transistors, which exhibit NDC in accordance with their designed asymmetry. The NDC onsets once the drift velocity in the channel reaches a threshold value, triggering the initial plasma instability. We also show how this feature can be made to persist beyond room temperature (to at least 75 °C), when the gating is configured to facilitate a transition between the hydrodynamic and ballistic regimes (of electron-electron transport). Our findings represent a significant step forward for efforts to develop active components for THz electronics.

To broaden the scope of van der Waals 2D magnets, we report the synthesis and magnetism of covalent 2D magnetic Cr$_2$Te$_3$ with a thickness down to one-unit-cell. The 2D Cr$_2$Te$_3$ crystals exhibit robust ferromagnetism with a Curie temperature of 180 K, a large perpendicular anisotropy of 7*105 J m-3, and a high coercivity of ~ 4.6 kG at 20 K. First-principles calculations further show a transition from canted to collinear ferromagnetism, a transition from perpendicular to in-plane anisotropy, and emergent half-metallic behavior in atomically-thin Cr$_2$Te$_3$, suggesting its potential application for injecting carriers with high spin polarization into spintronic devices.

The differential conductance of graphene is shown to exhibit a zero-bias anomaly at low temperatures, arising from a suppression of the quantum corrections due to weak localization and electron interactions. A simple rescaling of these data, free of any adjustable parameters, shows that this anomaly exhibits a universal, temperature- (T) independent form. According to this, the differential conductance is approximately constant at small voltages (V kBT/e), while at larger voltages it increases logarithmically with the applied bias. For theoretical insight into the origins of this behaviour, which is inconsistent with electron heating, we formulate a model for weak-localization in the presence of nonequilibrium transport. According to this model, the applied voltage causes unavoidable dispersion decoherence, which arises as diffusing electron partial waves, with a spread of energies defined by the value of the applied voltage, gradually decohere with one another as they diffuse through the system. The decoherence yields a universal scaling of the conductance as a function of eV/kBT, with a logarithmic variation for eV/kBT > 1, variations in accordance with the results of experiment. Our theoretical description of nonequilibrium transport in the presence of this source of decoherence exhibits strong similarities with the results of experiment, including the aforementioned rescaling of the conductance and its logarithmic variation as a function of the applied voltage.

In this study, the electrostatically induced quantum confinement structure, quantum point contact, has been realized in p-type trilayer tungsten diselenide-based van der Waals heterostructure with modified van der Waals contact method with degenerately doped transition metal dichalcogenide crystals. Clear quantized conductance and pinch-off state through the one-dimensional confinement were observed by dual-gating of split gate electrodes and top gate. Conductance plateaus were observed at step of 0.5 $\times$ 2e$^{2}$/h at zero and high magnetic field in addition to quarter plateaus at a finite bias voltage condition indicating the signature of spin-polarized quantum point contact realization., Paper:25 pages and 4 figures, SI: 13 pages and 10 figures, accepted for publication in Nano Letters

Mesoscopic conductance fluctuations are a ubiquitous signature of phase-coherent transport in small conductors, exhibiting universal character independent of system details. In this Letter, however, we demonstrate a pronounced breakdown of this universality, due to the interplay of local and remote phenomena in transport. Our experiments are performed in a graphene-based interaction-detection geometry, in which an artificial magnetic texture is induced in the graphene layer by covering a portion of it with a micromagnet. When probing conduction at some distance from this region, the strong influence of remote factors is manifested through the appearance of giant conductance fluctuations, with amplitude much larger than e^{2}/h. This violation of one of the fundamental tenets of mesoscopic physics dramatically demonstrates how local considerations can be overwhelmed by remote signatures in phase-coherent conductors.

We explore the electrical characteristics of TiS3 nanowire field-effect transistor (FETs), over the wide temperature range from 3 to 350 K. These nanomaterials have a quasi-one-dimensional (1D) crystal structure and exhibit a gate-controlled metal-insulator transition (MIT) in their transfer curves. Their room-temperature mobility is ∼20-30 cm2/(V s), 2 orders of magnitude smaller than predicted previously, a result that we explain quantitatively in terms of the influence of polar-optical phonon scattering in these materials. In the insulating state (

We demonstrate an unusual manifestation of coherent scattering for electron waves in mesoscopic quantum point contacts, in which fast electron dynamics allows the phonon system to serve as a quasistatic source of disorder. The low-temperature conductance of these devices exhibits a giant ($\ensuremath{\gg}2{e}^{2}/h$) zero bias anomaly (ZBA), the features of which are reproduced in a nonequilibrium model for coherent scattering from the ``frozen'' phonon disorder. According to this model, the ZBA is understood to result from the in situ electrical manipulation of the phonon disorder, a mechanism that could open up a pathway to the on-demand control of coherent scattering in the solid state.

In this study, we fabricated quantum point contacts narrower than 100 nm by using an electrostatic potential to open the finite bandgap by applying a perpendicular electric field to bilayer graphene encapsulated between hexagonal boron nitride sheets. The conductance across the quantum point contact was quantized at a high perpendicular-displacement field as high as 1 V/nm at low temperature, and the quantization unit was 2e2/h instead of mixed spin and valley degeneracy of 4e2/h. This lifted degeneracy state in the quantum point contact indicates the presence of valley polarized state coming from potential profile or effective displacement field in one-dimensional channel.

We demonstrate a novel form of thermally-assisted hysteresis in the transfer curves of monolayer MoS2 FETs, characterized by the appearance of a large gate-voltage window and distinct current levels that differ by a factor of ∼102. The hysteresis emerges for temperatures in excess of 400 K and, from studies in which the gate-voltage sweep parameters are varied, appears to be related to charge injection into the SiO2 gate dielectric. The thermally-assisted memory is strongly suppressed in equivalent measurements performed on bilayer transistors, suggesting that weak screening in the monolayer system plays a vital role in generating its strongly sensitive response to the charge-injection process. By exploiting the full features of the hysteretic transfer curves, programmable memory operation is demonstrated. The essential principles demonstrated here point the way to a new class of thermally assisted memories based on atomically thin two-dimensional semiconductors.

Although semiconductor to metal phase transformation of MoTe$_{2}$ by high-density laser irradiation of more than 0.3 MW/cm$^{2}$ has been reported, we reveal that the laser-induced-metal (LIM) phase is not the 1T' structure derived by a polymorphic-structural phase transition but consists instead of semi-metallic Te induced by photo-thermal decomposition of MoTe$_{2}$. The technique is used to fabricate a field effect transistor with a Pd/2H-MoTe$_{2}$/LIM structure having an asymmetric metallic contact, and its contact properties are studied via scanning gate microscopy. We confirm that a Schottky barrier (a diffusion potential) is always formed at the Pd/2H-MoTe$_{2}$ boundary and obstacles a carrier transport while an Ohmic contact is realized at the 2H-MoTe$_{2}$/LIM phase junction for both n- and p-type carriers., Comment: 18 pages, 4 figures, accepted for publication in Nanotechnology

Rapid (nanosecond-scale) electrical pulsing is used to study drift-velocity saturation in graphene field-effect devices. In these experiments, high-field pulses are utilized to drive graphene's carriers on time scales much faster than that on which energy loss to the underlying substrate can occur, thereby allowing the observation of the highest saturation velocities reported to date. In a dramatic departure from the behavior exhibited by conventional metals and semiconductors, as the electron or hole density is reduced toward the charge-neutrality point, the drift velocity is found to reach values comparable to the Fermi velocity itself. Corresponding current densities are as large as 10(9) A/cm(2), similar to the values reported for carbon nanotubes and for graphene-on-diamond transistors. In essence, our approach of rapid pulsing allows us to "free" graphene from the deleterious influence of its substrate, revealing a pathway to achieve the superior electrical performance promised by this material. The usefulness of this approach is not merely limited to graphene but should extend also to a broad variety of two-dimensional semiconductors.

Energy relaxation of hot carriers in graphene is studied theoretically and experimentally at low temperatures, where the loss rate may differ significantly from that predicted for electron---phonon interactions. We show here that plasmons, important in the relaxation of energetic carriers in bulk semiconductors, can also provide a pathway for energy relaxation in transport experiments in graphene. Reflecting the linear nature of graphene's bands, we obtain a total loss rate to plasmons that is independent of carrier density. This results in energy relaxation times whose dependence on temperature and density closely matches that reported experimentally.

The high field phenomena of inter-valley transfer and avalanching breakdown have long been exploited in devices based on conventional semiconductors. In this Article, we demonstrate the manifestation of these effects in atomically-thin WS2 field-effect transistors. The negative differential conductance exhibits all of the features familiar from discussions of this phenomenon in bulk semiconductors, including hysteresis in the transistor characteristics and increased noise that is indicative of travelling high-field domains. It is also found to be sensitive to thermal annealing, a result that we attribute to the influence of strain on the energy separation of the different valleys involved in hot-electron transfer. This idea is supported by the results of ensemble Monte Carlo simulations, which highlight the sensitivity of the negative differential conductance to the equilibrium populations of the different valleys. At high drain currents (>10 μA/μm) avalanching breakdown is also observed, and is attributed to trap-assisted inverse Auger scattering. This mechanism is not normally relevant in conventional semiconductors, but is possible in WS2 due to the narrow width of its energy bands. The various results presented here suggest that WS2 exhibits strong potential for use in hot-electron devices, including compact high-frequency sources and photonic detectors.

We explore the contributions to the electrical resistance of monolayer and bilayer graphene, revealing transitions between different regimes of charge carrier scattering. In monolayer graphene at low densities, a nonmonotonic variation of the resistance is observed as a function of temperature. Such behaviour is consistent with the influence of scattering from screened Coulomb impurities. At higher densities, the resistance instead varies in a manner consistent with the influence of scattering from acoustic and optical phonons. The crossover from phonon-, to charged-impurity, limited conduction occurs once the concentration of gate-induced carriers is reduced below that of the residual carriers. In bilayer graphene, the resistance exhibits a monotonic decrease with increasing temperature for all densities, with the importance of short-range impurity scattering resulting in a “universal” density-independent (scaled) conductivity at high densities. At lower densities, the conductivity deviates from this universal curve, pointing to the importance of thermal activation of carriers out of charge puddles. These various assignments, in both systems, are made possible by an approach of “differential-conductance mapping”, which allows us to suppress quantum corrections to reveal the underlying mechanisms governing the resistivity.

In recent experiments, we have succeeded to fabricate a h-BN/graphene/h-BN heterostructure showing a good mobility reaching to 8 × 104 cm2/Vs. And then, we observed a transition between conductance fluctuations at low magnetic field less than 0.5 T and regular Shubnikov-de Haas oscillation at higher than the magnetic field. We analyzed the fluctuations compared to that of former graphene samples on SiO 2 layer, especially focused on the amplitude and the carrier density dependence. We will discuss the anomalous behavior breaking the universality in the conductance fluctuations of the bilayer graphene in a quasi-ballistic transport regime.

Clear Shubnikov-de Haas Oscillations have been observed in a high-mobility monolayer graphene sandwiched between two sheets of h-BN. The maximum mobilities of the p- and n-type carriers are 1.2 × 105 cm2/Vs and 1.1 × 105 cm2/Vs at 0.3 K, respectively. The typical effective mass can be estimated as 0.030 and 0.031 in p-type and n-type regions, respectively. The effective mass and the lifetime as a function of the carrier concentration will also be discussed and compared to the values observed in a conventional low-mobility sample using a SiO 2 layer.

The fluctuations in the conductance of graphene that arise from a long-range disorder potential induced by random impurities are investigated with an atomic tight-binding lattice. The screened impurities lead to a slow variation of the background potential and this varies the overall potential landscape as the Fermi energy or an applied magnetic field is varied. As a result, the phase interference varies randomly and leads to fluctuations in the conductance. Recently, experiments have shown that an applied magnetic field produces a remarkable reduction in the amplitude of these conductance fluctuations. We find qualitative agreement with these experiments, and it appears that the reduction in magnetic field of the fluctuations arises from a field induced smoothing of the conductance landscape.

We review recent experiments in which we have used wavefunction coupling between quantum point contacts as an approach to electrically isolate and detect single spins. The physical basis for our experiments is the idea that a well-defined bound state develops in these nanostructures near pinch-off, where the electron density becomes vanishingly low and many-body interactions are consequently enhanced. By coupling the bound state in one point contact to another that serves as a detector, with the nature of this coupling being provided by the mutual wavefunction overlap between the two nanostructures, a Fano resonance is observed in the detector conductance. In this perspective we discuss how this resonance provides an experimental means to characterize the microscopic properties of the bound state that localizes the single spin.

We describe the fabrication of a hybrid nanomagneto-electronic device, consisting of a GaAs/AlGaAs quantum wire that is bridged by a ferromagnetic gate, and study the influence of the nanomagnet fringing fields on the quantum-wire magneto-resistance. The nonplanar gate shows clear single-domain structure in magnetic-force microscopy, and a simple magnetization behavior in an external magnetic field. This behavior is reflected as a hysteretic variation of the quantum-wire magneto-resistance, whose magnitude is found to be consistent with theoretical predictions for ballistic electron transport through a spatially varying magnetic field.

We investigate the classical and quantum dynamics in an array of electron billiards within a magnetic field. The resulting modification of the phase space due to the magnetic field can be directly related to the experimentally observed magneto-resistance. We argue that the behaviour of chaos plays an important role in the transport of such ballistic devices.

We review recent work where we have investigated the non-linear transient response of quantum point contacts (QPCs) using pulsed excitation with sub-nanosecond time resolution. The transient response of these devices is shown to be dominated by a large parallel capacitance that is independent of the QPC conductance and pulse amplitude. These characteristics lead us to suggest that the capacitance is associated with charging of the two-dimensional reservoirs that source and sink current to the QPC. Our investigations also show that the transient conductance of the QPC must develop very quickly as the voltage pulse is applied, at least on a time scale shorter than the fastest rise time (2 ns) used in the experiments. We also find the existence of a characteristic fixed point in the non-linear conductance, at which its value is bias independent. The fixed point appears to correspond to the situation where the unbiased QPC is almost depopulated and can be accounted for by considering the unidirectional population of QPC subbands by the voltage bias. To discuss the behavior of the transient conductance away from the fixed point, we find that it should be necessary to consider the influence of the applied bias on the QPC profile and electron–phonon scattering.

Hot-electron single-photon counters based on long superconducting nanowires are starting to become popular in optical and infrared technologies due to their ultimately high sensitivity and very high response speed. We investigate intrinsic fluctuations in long NbN nanowires in the temperature range of 4.2 K-20 K, i.e. above and below the superconducting transition. These fluctuations are responsible for fluctuation resistivity and also determine the noise in practical devices. Measurements of the fluctuation resistivity were performed at low current densities and also in external magnetic fields up to 5 T. Above the BCS critical temperature Tco the resistivity is well described by the Aslamazov-Larkin (AL) theory for two-dimensional samples. Below Tco the measured resistivity is in excellent agreement with the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory developed for one-dimensional superconductors. Despite that our nanowires of 100 nm width are two-dimensional with respect to the coherence length, our analysis shows that at relatively low current densities the one-dimensional LAMH mechanism based on thermally induced phase slip centers dominates over the two-dimensional mechanism related to unbinding of vortex-antivortex pairs below the Berezinskii-Kosterlitz-Thouless transition.

The amplitude-frequency modulation of oscillations of the magnetoresistance of 2D electrons in an AlSb(δ-Te)/InAs/AsSb(δ-Te) quantum well is studied. In the dependence of the amplitude of the oscillations δ(1/B) T = const, regions of negative Dingle temperature are observed. The anomalies in the dependence δ(1/B) T = const are attributed to the fact that the quantizing magnetic field resonantly induces intersubband electron-electron interaction between the 2D electrons of the ground size-quantization subband and excited subband. The resonance fields B and the times corresponding to the collision-related broadening of the Landau levels are estimated. The concentration threshold of filling of the excited size-quantization subband is established at a level of n s ≈ 8 × 1011 cm−2.

We examine transport through the system of two coupled quantum point contacts. We show that when one of them is driven close to the pinch-off condition, the conductance of the second one exhibits very pronounced peak. The shape of this peak has a Fano form indicating the formation of the localized state in the quantum point contact near the pinch-off. The experimental data are fitted to the Fano expression with determination of parameters involved. More detailed microscopic analysis demonstrates the existence of both symmetric and antisymmetric contributions to the conductance peak.

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.

We study the influence of a normal magnetic field on the 0.7 feature exhibited by quantum point contacts (QPCs). The magnetic field is used to induce the formation of edge states whose spin splitting and spatial separation can be varied directly via the applied field. By appropriate control of the gate voltage, the QPC can be configured so that its conductance is determined by the two spin-resolved edge states of the lowest Landau level, mimicking the two-channel picture that has been suggested in discussions of the 0.7 feature. Under these conditions, a clear 0.7 feature is only observed at weak magnetic fields, where any spin gap is small and the two edge states are strongly overlapping. A similar feature is also seen at high magnetic fields, but only once the temperature is increased such that the thermal energy is comparable to the size of the spin gap. The connection of these results to the processes that lead to the 0.7 feature is discussed.

We investigate the linear transport properties of quantum point contacts (QPCs) whose symmetry is deliberately broken in a controlled manner. The devices that we study consist of a conventional split-gate QPC, which is modified by the inclusion of an additional perturbing gate that is used to modulate the electron density on one side of the device. As the voltage applied to this 'finger gate' is varied, we observe several reproducible features below the last integer plateau, as well as strong modifications of the integer-plateau staircase. Self-consistent calculations, performed for the exact device structure utilized in experiment, suggest that these features are related to the ability of the finger gate to strongly disrupt the symmetry of the QPC, reducing the electron density significantly on one side of the device. We discuss these results within the context of recent models for many-body electron transport in QPCs.

We study the scaling properties of the conductance fluctuations due to quantum interference in linear quantum-dot arrays. The key finding of our study is of a common scaling behaviour of the fluctuations, according to which their amplitude varies in direct proportion to the total conductance of the system, independently of the size of the arrays. We argue that such behaviour is inconsistent with a classical scaling of incoherently coupled dots, but is reasonable for that expected when dephasing arises from the interaction of the quantum system with its external environment.

Magnetotransport measurements on a high-quality InAs/GaSb quantum well show single-period Shubnikov–de Haas (SdH) oscillations at low magnetic fields under dark conditions after initial sample cool down to 4.2 K. However, during and after illumination of the sample with infrared light, a beating pattern is observed in the SdH oscillations, indicating the possible appearance of two sets of Landau levels at low fields. Furthermore, for each condition, the original oscillation pattern persists under the application of a positive (or negative) backgate voltage that increases (or decreases) the two-dimensional electron gas density.

Evidence for dynamical tunneling is observed in studies of the transmission, and wave functions, of a soft-walled microwave cavity resonator. In contrast to previous work, we identify the conditions for dynamical tunneling by monitoring the evolution of the wave function phase as a function of energy, which allows us to detect the tunneling process even under conditions where its expected level splitting remains irresolvable.

Recent work on the role of decoherence in quantum physics has suggested that the quantum to classical decay is governed by a discrete set of pointer states, which are quite stable and uncoupled from other states in the system. We show that the conductance oscillations exhibited by open quantum dots are governed by a discrete set of stable quantum states which have the properties of the pointer states, and which are closely related to trapped classical orbits in the open dot. These states are essentially classical in nature, as evidenced by their energy level spacing, and their decay is apparently in the environment as opposed to within the dots.

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.

We report on the investigation of ballistic magneto-transport in open AlGaAs/GaAs dots and its response to microwaves in the frequency range around 50 GHz . The results allow to distinguish between backscattering peaks and Shubnikov-de-Haas oscillations in the transition range from classical to quantum-mechanical behaviour.

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 2e/sup 2//h.

The description of a quantum dot can be applied to a great variety of structures, some of which are defined by physical characteristics, such as self-assembled dots, and others of which are defined by the imposition of a self-consistent potential applied through confining gates. Indeed, the range of these different types of structures is sufficiently large that no single review can hope to cover them in anything like adequate detail. Yet the application of quantum dots has become important in an equally wide range of technical fields, for both optical and electronics applications. For that reason, we will try to outline the range of quantum dots that can occur, before we limit ourselves to a couple of examples that have proven useful for the investigation of new phenomena in transport physics. Perhaps the largest area of quantum dots (QDs) that has been of interest is self-assembled QDs. Here, we refer to the creation of a QD during a growth process or subsequent annealing process. The leading example is that of InAs or InGaAs QDs, which are created on a GaAs substrate via the Stransky-Krastanov (SK) growth process 1 .

The gate bias dependent evolution of the Coulomb oscillations in a silicon-on-insulator nano-wire transistor is reported. Transport data obtained for a wide range of front- and back-gate bias strongly suggest that multiple quantum dots (QDs) with different potential depths are formed in the nano-wire channel. Our data can be clearly interpreted as arising from the turning on or off of one of these QDs as the back-gate bias is varied. Quantitative calculation based on the model of single-electron tunneling through two parallel QDs is in reasonable agreement with the measured data in the back-gate bias range where the third dot is not activated.

We study the magneto-resistance of a V-grooved GaAs quantum-wire 6eld-e7ect transistor (QWR-FET) realized by selective growth of metalorganic vapor phase epitaxy. At low temperatures, the magneto-resistance of the wire shows reproducible #uctuations resulting from the quantum interference of electrons in the wire. The gate-voltage and temperature dependence of the conductance #uctuations are studied, and the latter reveal evidence for the robust phase coherence of electrons in the V-grooved QWR. ? 2003 Elsevier B.V. All rights reserved.

We discuss the response of a non-locally coupled quantum point contact to the transport properties of a quantum dot. With both structures biased in the tunneling regime, this setup allows for the detection of single-electron charging. We show here that non-local measurements may be used to detect features of the transport through open quantum dots, although the response of the detector to changes in the dot conductance is found to be very much more complicated than that exhibited by tunnel-coupled dots.

We present the results of detailed transport measurements on a silicon-on-insulator (SOI) metal-oxide–semiconductor field-effect transistor (MOSFET) in a wide range of temperature (T, 4.2 K ). The temperature dependence of the threshold voltage and low-field effective mobility (μeff) of the MOSFET is found to be consistent with that of a fully depleted, and strongly localized, MOSFET. The activation energy obtained from the temperature dependence of μeff suggests that the inversion layer is strongly perturbed by the presence of impurities at its back (Si/SiO2) interface. The transport of a 100 nm -wide wire fabricated on the same SOI wafer exhibits oscillatory features and the origin is interpreted as the existence of unintentional Coulomb islands created by back interface impurities.

A many-body model of transport through open quantum dots is formulated. Based upon the idea of an enhanced electron–electron interaction due to a resonantly trapped state, we construct a model interaction term which is peaked at a particular energy. Our studies suggest that the effect of including this peaked interaction is to increase the amplitude of the conductance fluctuations, beyond the value expected from a single-particle treatment. Our calculations thus demonstrate the role of interaction-induced corrections to the transport in these structures.

We discuss the origin of the Shubnikov–de Haas oscillations (SdHO) that are observed in the magneto-resistance of strongly open quantum dots at magnetic fields where the Lorentz force on the electrons allows them to undergo cyclotron motion within the quantum dot. Similar to the discussion of this effect in two-dimensional electron systems, we find that the properties of the SdHOs in the dots are strongly affected by the presence of disorder, which serves to provide coupling between bulk- and edge-like dot eigenstates. As an example of this behavior, we present the results of studies of the SdHO in InAs open quantum dots.

We study the electrical properties of Pt nanowires, formed on SiO2 substrates by focused-ion-beam deposition. Their magneto-resistance shows evidence for weak-antilocalization at temperatures below 10 K , with a phase-breaking length of ∼100 nm , and a temperature dependence suggestive of quasi-one-dimensional interference. Studies of their temperature-dependent resistance at low temperatures reveal a significant contribution due to electron-electron interaction as well as weak anti-localization. A switching behavior in the temporal resistance signals suggests two metastable states exist in local lattice configurations of the systems, which might be the source of saturation of phase-breaking length at low temperatures.

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.

In this report, we review the results of our joint experimental and theoretical studies of electron-interference, and interaction, phenomena in open electron cavities known as quantum dots. The transport through these structures is shown to be heavily influenced by the remnants of their discrete density of states, elements of which remain resolved in spite of the strong coupling that exists between the cavity and its reservoirs. The experimental signatures of this density of states are discussed at length in this report, and are shown to be related to characteristic wavefunction scarring, involving a small number of classical orbits. A semiclassical analysis of this behaviour shows it to be related to the effect of dynamical tunnelling, in which electrons are injected into the dot tunnel through classically forbidden regions of phase space, to access isolated regular orbits. The dynamical tunnelling gives rise to the formation of long-lived quasi-bound states in the open dots, and the many-body implications associated with electron charging at these resonances are also explored in this report.

We discuss the influence of the electron–electron interaction on transport properties of open quantum dot systems. Based on the idea of the Anderson model, we present interaction-induced temperature-dependent corrections to the conductance beyond the single-particle picture.