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In this study, green indium phosphide (InP) quantum dots (QDs) were synthesized using a tris(dimethylamino)phosphine ((DMA)3P) phosphorus source and applied to electroluminescent quantum light-emitting diodes (QLEDs). The (DMA)3P precursor is safer and more cost-effective than the conventional tris(trimethylsilyl)phosphine. The emission peak of the InP QDs was shifted to the green region from the red by replacing the conventional zinc precursor ZnCl2 with ZnI2. The surface reaction rate was limited using ZnI2 in the core formation step, yielding small-sized QDs to achieve green emission. In addition, with the optimal ZnSeS intermediate shell and outer shell, the maximum quantum yield of 67.5% with a narrow full width at half maximum of 46 nm was achieved for the (DMA)3P-based green-emitting InP@ZnSeS/ZnS QDs. QLEDs were demonstrated with the (DMA)3P-based green InP QDs, and their efficiency was maximized by optimizing the Mg doping ratios in the electron transport layer (ETL) of ZnMgO. The maximum external quantum efficiency of 1.68% and current efficiency of 4.79 cd/A were achieved with an optimal doping ratio of 12.5% ZnMgO for the (DMA)3P-based green InP QLEDs. This study demonstrates that safer (DMA)3P phosphide source-based green InP QDs are effective in achieving low-cost InP QLEDs.

In this study, multishelled InP-based quantum dots (QDs) were synthesized using a phosphorus source tris(dimethylamino)phosphine [(DMA)3P] and were applied to solution-processed QD light-emitting d...

Graphene-like quantum dots (GQDs) doped with magnetic ions are described in accordance with the mixed Ising model. The magnetic properties of this system are discussed within the framework of the effective field theory with correlations. The numerical results produced several types of phase diagrams with different exchange couplings and anisotropies. Certain unique features, such as reentrant phenomena, were found within a particular range of parameters. We concluded that GQDs doped with magnetic ions have the potential to adjust their performance and effectively enlarge the scope of application.

We study the transport properties of a quantum dot (QD) fabricated by a quantum anomalous Hall insulator. It is found that energy levels of the QD are quantized due to the quantum confinement effect, which leads to the appearance of the resonant-tunnelling phenomenon at low temperature. We also find that topological edge states form around the boundary of the QD, coexisting with the bulk states inside the QD. The electron transmission through the channels of the edge and bulk states drives the Fano interference, manifested as the asymmetric lineshape of the linear conductance spectrum. In addition, the spin polarization of this system is present. It shows that the spin-polarized current can be realized even in the absence of the external magnetic field, because of the breaking the time-reversal symmetry.

Recently, two-dimensional (2D) materials, especially transition-metal dichalcogenides (TMDCs), have attracted extensive interest owing to their potential applications in optoelectronics. Here, we demonstrate a hybrid 2D-zero-dimensional (0D) photodetector, which consists of a single-layer or few-layer molybdenum disulfide (MoS2) thin film and a thin layer of core/shell zinc cadmium selenide/zinc sulfide (ZnCdSe/ZnS) colloidal quantum dots (QDs). It is worth mentioning that the photoresponsivity of the hybrid 2D-0D photodetector is 3 orders of magnitude larger than the TMDC photodetector (from 10 to 104 A W-1). The detectivity of the hybrid structure detector is up to 1012 Jones, and the gain is up to 105. Due to an effective energy transfer from the photoexcited QD sensitizing layer to MoS2 films, light absorption is enhanced and more excitons are generated. Thus, this hybrid 2D-0D photodetector takes advantage of high charge mobility in the MoS2 layer and efficient photon absorption/exciton generation in the QDs, which suggests their promising applications in the development of TMDC-based optoelectronic devices.

We investigate the Aharonov-Bohm (AB) effect in the parallel double-quantum-dot structure, by introducing an additional s-wave superconductor to couple to the quantum dots. It is found that the AB oscillation of the electron tunneling is different from the superconductor-absent result. Meawhile, the local and crossed Andreev reflections exhibit their special oscillation behaviors, with the change of the local magnetic flux. This means that the AB effect plays an important role in manipulating the complicated quantum transport through this system. We believe that this work can be helpful for understanding the AB oscillation in the presence of Andreev reflection processes.

Graphene quantum dots (GQDs) are known to display tunable photoluminescence (PL) proprieties by functional modification. Here, yellow fluorescence amino-functionalized GQDs (af-GQDs) were synthesized using high-softening point asphalt as precursor and ammonia as nitrogen source, and the mechanism of fluorescence enhancement by nitrogen-containing functional groups is also discussed in detail. The photoluminescence quantum yield (QY) of the resultant GQDs increased from 4.7% to 13.8% after the amino-hydrothermal treatment. Transmission electron microscopy (TEM) images showed that the af-GQDs have more uniform size distribution than GQDs. PL and ultraviolet–visible spectrum (UV–Vis) suggested that two types of electron transitions namely π-π∗ and n-π∗ occurred intrinsically in GQDs, and n-π∗ transition of functional groups was more prominent in af-GQDs. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated that reduction reactions occurred on the surface of GQDs, and nitrogen functional groups were introduced into GQDs during the amino-hydrothermal treatment process. Ultraviolet photoelectron spectroscopy (UPS) results confirmed that the energy level of the highest occupied molecular orbit increased from 6.98 to 7.26 eV. The amide and amino groups were considered to contribute to the fluorescence enhancement of GQDs. Furthermore, the af-GQDs were used as effective fluorescent sensing probes to detect Fe3+ ions, which have a high sensitivity, good selectivity, and superior detection limit of 0.51 nM, indicating their promising application in trace Fe3+ ion detection.

Edge and bulk energy levels can coexist in a quantum dot (QD) made of a topological insulator. Interference effect will occur between bulk and edge levels and also between degenerate edge levels. It can be observed in the transport behavior. For the former, it acts as Fano interference with edge and bulk levels contributing continuous and resonant transport channels, respectively. Generally speaking, Fano interference can be realized in a two-armed junction with a single QD or a one-armed junction with at least two QDs. But here it is realized in a one-armed junction with a single QD. As for the interference between degenerate edge levels, it leads to a spin and space dependent scattering process. Spin of an incident electron will either be conserved or rotate about an axis for transmitting into different leads. It is determined by the local spin polarization of edge levels and the accumulated phase in transport paths in the QD. It may be used in the design of a spin field-effect transistor.

In this Letter, red-emitting multi-shelled indium phosphide (InP) quantum dots (QDs) were synthesized using the safe phosphorus precursor tris(dimethylamino)phosphine ( ( D M A ) 3 P ). The long-chain ligands of oleylamine (OAm) in the ( D M A ) 3 P phosphide source-based InP QDs were partially exchanged with short-chain ligands of phenethylamine (PEA) in the core formation process, and the resulting InP QDs were applied to quantum dot light-emitting diodes (QLEDs). The short-chain ligands of PEA with the π -conjugated benzene ring improved the charge transport and electrical conduction of the QLEDs with ( D M A ) 3 P phosphide source-based InP QDs. The PEA-engineering of InP QDs improved their maximum quantum yield from 71% to 85.5% with the full-width at half-maximum of 62 nm. Furthermore, the maximum external quantum efficiency of QLEDs with the PEA-engineered InP QDs improved from 1.9% to 3.5%, and their maximum power efficiency increased from 2.8 to 6.0 lm/W. This Letter demonstrates that engineering the core formation process with the short-chain ligands of PEA provides an efficient and facile way to improve the charge transport and electrical conduction in ( D M A ) 3 P phosphide source-based InP QLEDs for electroluminescent devices.

We theoretically investigate the Kondo effect of a T-shaped triple-quantum-dot structure, by means of the numerical renormalization group method. It is found that at the point of electron-hole symmetry, the system's entropy has opportunities to exhibit three kinds of transition processes for different interdot couplings, with the decrease of temperature. This leads to the different pictures of the Kondo physics, including the three-stage Kondo effect. Next when the electron-hole symmetry is broken or the structural parameters are changed, the Kondo resonance can also be observed in the conductance spectrum. However, it shows alternative dependence on the relevant quantities, i.e., the Coulomb interaction and interdot couplings. All these phenomena exhibit the abundant and interesting Kondo physics in this system. We believe that this work can be helpful for further understanding the Kondo effect in the triple-quantum-dot structures., To be published in Physical Review B

Quantum-dots-doped covalent organic frameworks in a molecularly imprinted network (QDs-doped COFs@MIP) were developed for detection of nereistoxin (NRT)-related insecticide in tap water. The preparation of QDs-doped COFs@MIP was easy to accomplish via one-pot synthesis at room temperature. QDs-doped COFs@MIP quenched by targeting thiosultap due to the photoinduced charge transfer. A Brunauer–Emmett–Teller surface area of 186.20 m2 g−1 and a maximum adsorption capacity of 771 mg g−1 of the QDs-doped COFs@MIP exhibited good selectivity and adsorption capacity. Direct fluorescence determination was established over the range 5–100 μg L−1 (R2 = 0.9959) with a detection limit of 1.60 μg L−1. Furthermore, 86.5–106.5% recoveries of spiked tap water were achieved. The determination system was feasible for tracing the NRT-related insecticide with high accuracy and good repeatability and reproducibility.

Electron transport through the quantum-dot system with ferromagnetic leads is theoretically investigated, by introducing one Majorana bound state (MBS) to be side-coupled with the dot. It is shown that even for the ferromagnetic leads, the zero-bias conductance is manifested as a peak. However, its magnitude becomes more adjustable, especially when the dot suffers from the external magnetic field and superconducting proximity effect. The other notable result is that the magnetoresistance displays interesting characteristics in this system, which is related to the interplay between the magnetization direction of the MBS and other structural parameters. We believe that this work can be helpful in presenting the MBS-assisted transport behaviors in quantum-dot systems.

We evaluate the quantum transport through one mesoscopic circuit with its embedded quantum dot coupled to the Majorana bound states (MBSs) at the ends of one topological-superconductor nanowire . The calculation results show that when the MBSs co-couple to the dot, antiresonance effect has an opportunity to take place, and the antiresonance point is related to the inter-MBS coupling. Moreover, once the dot-MBS coupling strengths are equal to each other, the Fano effect takes place, manifested as the Fano lineshape in the transmission-function spectrum. The results in this work can provide new information for the understanding of the MBS-contributed quantum transport through quantum-dot systems.

We construct one mesoscopic circuit in which one quantum dot couples to one DIII-class topological superconductor and one s-wave superconductor, in addition to its connection with the metallic lead. And then, the Andreev reflection current in the metallic lead is evaluated. It is found that the two kinds of superconductors drive the Andreev reflection in the constructive manner. Next as finite superconducting phase difference is taken into account, the Andreev reflection oscillates in period π 2 , and it can be suppressed in the low-energy region if the superconducting phase difference is ( n + 1 2 ) π 2 (n ∈ Integer). Such a result is almost independent of the increase of the intradot Coulomb interaction. Therefore, this structure can assist to realize the manipulation of the Andreev reflection. Also, the result in this work provides useful information for understanding the property of the DIII-class topological superconductor.

We theoretically investigate the electronic transport through a parallel-coupled multi-quantum-dot system, in which the terminal dots of a one-dimensional quantum-dot chain are embodied in the two arms of an Aharonov–Bohm interferometer. It is found that in the structures of odd(even) dots, all their even(odd) molecular states have opportunities to decouple from the leads, and in this process antiresonance occurs which are accordant with the odd(even)-numbered eigenenergies of the sub-molecule without terminal dots. Next when Majorana zero modes are introduced to couple laterally to the terminal dots, the antiresonance and decoupling phenomena still co-exist in the quantum transport process. Such a result can be helpful in understanding the special influence of Majorana zero mode on the electronic transport through quantum-dot systems.

Commercial photodetectors have been dominated by bulk silicon (B-Si) due to the maturity of Si technology. However, its relatively poor mobility has impeded B-Si from high-performance applications. Herein, we demonstrate that tin dioxide quantum dots (SnO2-QDs) coupled with graphene produce a Schottky junction with B-Si to drastically promote the performance of the SnO2-QDs/graphene/B-Si Schottky photodetector. This hybrid device is sensitive to broadband illumination covering the UV-vis-NIR region and shows high responsivity of 967.6 A W−1 (nearly 4 orders higher than that of commercial B-Si Schottky photodetectors), with corresponding external quantum efficiency of 2.3 × 105% and detectivity of 1.8 × 1013 Jones. In addition, the hybrid device manifests fast rise and decay times of 0.1 and 0.23 ms, respectively. These figures-of-merit are among the best values of the recently reported B-Si Schottky photodetectors. We also established that the superior performances are attributed to the strong light absorption of the hybrid structure and increased built-in potential of the graphene/B-Si Schottky junction, which allows efficient separation of photoexcited electron–hole pairs. These findings pave the way toward the rational design of optoelectronic devices through the synergetic effects of 2D materials with 0D and 3D semiconductors.

The Kondo effect in the T-shaped double-quantum-dot structure is theoretically investigated, by considering different adjustments of the quantum dot levels. It is shown that when the quantum dot levels are shifted to the electron–hole symmetry point, the two-stage Kondo effect can be induced at the limit of weak interdot coupling. However, with the increase of interdot coupling, the interdot antiferromagnetic correlation modifies the Kondo effect efficiently, leading to the destruction of the conductance plateau. If the dot levels are detuned, the low-temperature entropy transition will exhibit new results and complicated transport behaviors occur. The reason also arises from the competition between the Kondo effect and the interdot antiferromagnetic correlation. We believe that these results are helpful for the further understanding of the Kondo physics in the T-shaped double-dot structure.

We theoretically study the transport properties in the T-shaped double-quantum-dot structure, by considering the dot in the main channel to be coupled to the Majorana bound state (MBS) at one end of the topological superconducting nanowire. It is found that the side-coupled dot governs the effect of the MBS on the transport behavior. When its level is consistent with the energy zero point, the MBS contributes little to the conductance spectrum. Otherwise, the linear conductance exhibits notable changes according to the inter-MBS coupling manners. In the absence of inter-MBS coupling, the linear conductance value keeps equal to e 2/2h when the level of the side-coupled dot departs from the energy zero point. However, the linear conductance is always analogous to the MBS-absent case once the inter-MBS coupling comes into play. These findings provide new information about the leakage effect of MBSs in quantum-dot structures.

Quantum dots (QDs) have attracted broad attention due to their special optical properties and promising prospect in medical and biological applications. However, the process of QDs on cell membrane is worth further investigations because such process may lead to harmful effects on organisms and also important for QD application. In this study, adhesion of amino- and carboxyl-coated CdTe QDs (A-QDs and C-QDs) on cell membrane and the subsequent internalization are studied using a series of endocytosis-free model membranes, including giant and small unilamellar vesicles, supported lipid bilayers and giant plasma membrane vesicles (GPMVs). The adhered QD amounts on model membranes are quantified by a quartz crystal microbalance. The CdTe QD adhesion on model membranes is governed by electrostatic forces. Positively charged A-QDs adhere on GPMV surface and passively penetrate the plasma membrane via endocytosis-free mechanism, but negatively charged C-QDs cannot. Rat basophilic leukemia (RBL-2H3) cells are exposed to CdTe QDs to monitor the QD internalization process. Both A- and C-QDs are internalized by RBL-2H3 cells mainly via endocytosis. CdTe QDs do not accumulate on the plasma membrane of living cells due to the fast endocytosis and the weakened electrostatic attraction in biological medium, resulting in low chance of passive penetration. The suspended cells after trypsin digestion take more QDs than the adherent cells. A-QDs cause lower cell viability than C-QDs, probably because the approach of positively charged QDs to cells is favored and the smaller aggregates of A-QDs.

We investigate the Andreev reflection in a parallel mesoscopic circuit with Majorana bound states (MBSs). It is found that in such a structure, the Andreev current can be manipulated in a highly efficient way, by the adjustment of bias voltage, dot levels, inter-MBS coupling, and the applied magnetic flux. Besides, the dot-MBS coupling manner is an important factor to modulate the Andreev current, because it influences the period of the conductance oscillation. By discussing the underlying quantum interference mechanism, the Andreev-reflection property is explained in detail. We believe that all the results can assist to understand the nontrivial role of the MBSs in driving the Andreev reflection.

Although nitrogen-doped graphene quantum dots (N-doped GQDs) have been widely studied for their unique properties and promising applications, large scale synthesis of N-doped GQDs has been rarely reported. Besides, the formation mechanism was always explained simply. Herein we report a facile one-step gram-scale approach to prepare N-doped GQDs by polymerization of nitrilotriacetic acid (NTA) under high temperature and pressure in a nitrogen environment. A mechanism, which is rooted in the chemical properties of NTA and consists of dehydration and nucleophilic addition, has been proposed to explain the formation of N-doped GQDs step by step. Utilizing this method, the change in the structure, functional groups and FL properties can be explained intuitively and clearly. Because of the significant difference in ethanol solubility between the raw material and product, N-doped GQD powder with a purity higher than 99% can be easily obtained by a dissolution–centrifugation–drying–dissolution–freeze drying process without a tedious dialysis process. 1.38 grams of N-doped GQDs could be prepared from 3 grams of NTA. The 46% synthetic yield is higher than that obtained using a large majority of methods reported so far. With the introduction of an N atom, the N-doped GQDs showed bright blue fluorescence (FL) under 365 nm ultraviolet (UV) light, exhibiting a quite high quantum yield of 45.8%. A short preparation time, the low cost of the raw materials, a simple preparation process, high synthetic yield, high quantum yield and a facile purification method make this approach promising in the industrial production of N-doped GQDs. Besides, the N-doped GQDs were used as handwriting FL ink in the form of aqueous and oil-like ink, and used in a fountain pen and ball pen respectively. The words written with FL ink showed strong contrast under daylight and UV light, and no obvious change can be observed after long-term high temperature treatment, indicating that the N-doped GQDs have obvious practicability and good stability as an FL ink.

Significant progresses made in the performance of quantum dot (QD) light-emitting diodes have often been associated with basic changes in QD synthesis, particularly with respect to composition and structure. Here we show that the absolute photoluminescence (PL) quantum yield (QY) of QD can reach 88% with a full width of 21 nm at half-maximum (FWHM) when an optimal thickness is chosen for the outer shell of alloyed, graded core/shell QDs. Thicker shell QD-LEDs with a maximum current efficiency of 56.6 cd A−1, an external quantum efficiency of 14.8%, and a brightness of 62 000 cd m−2 are demonstrated. Green emitting QDs of CdSe@ZnS/ZnS with this optimal thickness is also most resistant to photo-stimulated degradation by UV exposure. Only a 7% loss in PL intensity results even after more than 400 hours of exposure to harsh conditions of 85 °C and 85% relative humidity.

We investigate the Dicke-Josephson effect in a superconductor/triple-quantum-dot/superconductor junction in which the central dot is coupled to the superconductors. It is found that the Dicke effect can modulate the Josephson effect in a nontrivial way. In the noninteracting case, the Dicke effect induces a subpeak in the supercurrent spectrum around the energy zero point. When intradot interactions are taken into account, the role of the Dicke effect changes completely. Namely, it tends to suppress the π-phase current near the position of electron-hole symmetry. With the increase of the Coulomb strength, it has an opportunity to reverse the current direction. We thus conclude that the Dicke-Josephson effect is also an important part in describing the Josephson effect in coupled-dot junctions.

We investigate the Andreev reflection in a parallel double quantum dot structure, by considering one metallic lead coupled to one $s$-wave superconductor through the quantum dots. It is found that if an arm of this system provides the reference channel for the Andreev reflection, the Fano line shapes will have opportunities to appear in the linear conductance spectra and can be reversed by adjusting the dot level or local magnetic flux. To present the underlying physics, we obtain the Fano form of the linear conductance expression. Despite the complicated structural parameters, the property of the Fano effect is clearly shown. We believe that the results of this work will help us to understand the Fano interference in the Andreev reflection process.

By considering Majorana zero modes to laterally couple to the quantum dot, we evaluate the thermoelectric effect in one single-dot system. The calculation results show that if one Majorana zero mode couples to the dot, the thermoelectric effect will exhibit its change, but the thermoelectric efficiency cannot be enhanced apparently. However, the thermoelectric effect can be efficiently strengthened when two Majorana zero modes are introduced simultaneously. We believe that the findings in this work provide an alternative method for the detection of Majorana bound state., 8 pages, 7 figures, submitted to PRB

We study the eigenenergies of a one-dimensional quantum-dot chain with its each dot side coupling to two additional dots. It is found that when the $\mathcal{P}T$-symmetric complex potentials are introduced to the side-coupled dots, the eigenlevel degeneracy is broken. However, further increasing the complex potentials induces a kind of two-degree degeneracy of the eigenlevels. This is accompanied by the $\mathcal{P}T$-symmetry breaking, with the appearance of the complex part of the eigenlevels. These changes exactly affect the quantum transport properties of the chain. First, in the case of weak $\mathcal{P}T$-symmetric complex potentials, a group of transmission function peaks arise at the center of the transmission function spectrum. When the eigenlevel degeneracy takes place, the degenerated eigenlevels decouple from the leads and the corresponding peaks disappear in the transmission function spectra. We believe that this work provides helpful information for a better understanding of the eigenenergies and quantum transport properties in non-Hermitian systems.

The Majorana-induced Andreev reflection is theoretically investigated, by considering the case of ferromagnetic lead to couple to it via one quantum dot. We find that for the ferromagnetic lead, the Majorana zero mode (MZM) still causes the resonant Andreev reflection at the low-bias limit, even when finite Zeeman splitting appears in the quantum dot. However, the magnetoresistance exhibits interesting properties, and its magnitude and sign depend on the magnetization-direction difference between the ferromagnetic lead and the MZM, especially in the presence of Zeeman effect in the dot. We believe that these findings can be helpful in understanding the MZM-driven Andreev reflections modulated by the ferromagnetic lead.

The Majorana-induced Andreev reflection is theoretically investigated, by considering an additional quantum dot coupled to the normal metallic lead. We find that the quantum dot takes variable effect on the zero-bias conductance induced by the Majorana zero mode. The non-superconducting dot with zero-energy level can suppress the Andreev reflection. Otherwise, the quantum dot only changes the width of the Andreev reflection peak around the zero-bias point with its magnitude equal to 2 e 2 h . Alternatively for the Majorana nonzero mode, the effect of quantum dot becomes dominant, including the zero-bias result. Our findings provide new insights for understanding the Andreev reflection driven by the Majorana modes in experiment.

We investigate the Andreev reflection in the heterostructure formed by the indirect coupling between the metallic lead and Majorana zero mode (MZM) via one quantum dot which suffers from the electron-phonon interaction. Our calculation results show that at the zero-temperature limit, the MZM-governed zero-bias conductance value is independent of the electron-phonon interaction. However at finite temperature, the electron-phonon interaction exacerbates the suppression of the magnitude of zero-bias conductance. We believe that the results in this work can help to further differentiate the signature of the MZM in the Andreev reflection process.

Graphene quantum dots (GQDs) have been synthesized by different chemical methods in recent years. For conventional chemical methods, it is inevitable to introduce a large amount of impurities in the preparation process. Long time of dialysis process increases the time cost extremely. Herein, we report a one-step solvothermal method for synthesizing GQDs with the application of hydrogen peroxide in N, N-Dimethylformamide (DMF) environment, which completely avoids the use of concentrated sulphuric acid and nitric acid to treat raw material and introduces no impurity in whole preparation process simultaneously for the first time. Pure GQDs can be obtained after evaporation/redissolution and filtration process with a strong blue emission at 15% quantum yield. This solvothermal method, not requiring dialysis process and complicated equipments, exhibits simple, eco-friendly and low time-cost properties. Besides high quantum yields, the as-prepared GQDs also show good photoluminescence stability in different pH conditions. The optical properties, morphology and structure of GQDs were studied by various equipments, implying potential application in biomedical fields and electronic device.

We investigate the Josephson effect in a superconductor/triple-quantum-dot/superconductor junction in which the central dot is coupled to the superconductors. It is found that the supercurrent exhibits rich 0–π phase translations due to the interplay between interdot spin and electron correlations. Moreover, when the side dots are half-occupied, the nonlocal spin correlation between them, i.e., ferromagnetic or antiferromagnetic, coincides well with the supercurrent phase. We thus consider such a system to be a promising candidate for controlling the nonlocal magnetic configuration based on the Josephson effect.

We investigate the Andreev transports through a double-dot Y-shaped junction with Majorana zero mode. It is observed that the additional direct coupling between the dots plays a nontrivial role in manipulating the Andreev transports. Due to its existence, finite magnetic flux can be introduced through this structure to adjust the local and crossed Andreev reflections in different ways. As a result, changing the interdot coupling is able to enhance the crossed Andreev reflection and weaken the local one at the same time in both the linear and nonlinear transport regions. Such a work can be helpful for controlling the Andreev transport behaviors related to Majorana bound state.

We investigate the Josephson effect in a triple-quantum-dot ring in which only one dot is coupled to the superconductors, by performing the numerical renormalization group calculations. As a result, two kinds of Josephson phase transitions arise. One is the phase transition accompanied by the sharp change of the current direction, whereas the other phase transition is only accompanied by the smooth change of the current direction. Our analysis shows that in this structure, the phase transitions are determined by the variation of interdot spin correlations. The geometry of triple-dot ring induces various spin-correlation modes, leading to the complicate phase transitions. What's notable is that a spin singlet can form between the two lateral dots, which is decoupled from the main channel of this structure. It is certain that such a structure provides an alternative proposal to manipulate the spin correlation between the lateral dots.

We present the influence of an interacting quantum dot on the fractional Josephson effect in the junction constructed by two topological superconducting wires where Majorana zero modes exist. It is found that the intradot Coulomb interaction plays a nontrivial role in adjusting the magnitude and direction of the Josephson current. Moreover, despite the change of coupling manner between the two Majorana zero modes, appropriate Coulomb strengths are able to induce the occurrence of normal Josephson effect. With these results, the influence of one quantum dot on the fractional Josephson effect can be understood.

A simple technique to prepare graphene quantum dots (GQDs) by the hydrothermal reaction of graphene oxide (GO) sheets with hydrogen peroxide is presented. Complete removal of the hydrogen peroxide after reaction was achieved by catalytic dialysis with manganese oxide. By varying the reaction time, the particle sizes of GQDs could be controlled, leading to variations in the photoluminescence. The prepared GQDs produced stable green and blue photoluminescence. The nanostructure of the prepared GQDs was characterized and discussed in relation to its preparation procedures and behaviours of photoluminescence. The mechanism of the reaction was also discussed.

We present a detailed analysis about the changes of the orbital electron-correlation effects in one quantum-dot circuit, by considering finite couplings between the quantum dots and Majorana zero modes (MZMs). It is found that the dot-MZM couplings complicate the orbital-Kondo effect, because the orbital correlation occurs between the localized states in the quantum dots and the continuum hybridized states induced by the indirect metal-MZM couplings. When two of such correlation exist in pair, they have an opportunity to induce a long-range RKKY correlation, which is related to the MZMs. Further investigation shows that this RKKY interaction leads to the anomalous fractional Josephson effect. Our work can be helpful in clarifying the influence of MZM on the orbital electron correlation effects.

We investigate the influences of the electron-phonon interaction on the transport properties of one quantum-dot system with a side-coupled Majorana zero mode (MZM). Our calculation results show that at the zero-temperature limit, the MZM-governed zero-bias conductance value can be magnified, dependent on the interplay between electron-phonon interaction and dot-MZM coupling. In the case of finite temperature, the electron-phonon interaction makes leading contributions to the suppression of the magnitude of zero-bias conductance. We believe that this work can be helpful for understanding the signature of the MZM in electron transport through mesoscopic circuits., 9 pages 7 figures

With the help of the numerical renormalization group method, we theoretically investigate the Josephson phase transition in a parallel junction with one quantum dot embedded in each arm. It is found that in the cases of appropriate dot levels and symmetrical dot-superconductor couplings, the Josephson phase transition will be suppressed. This is manifested as the fact that with the enhancement of the electron correlation, the supercurrent only arrives at its ${\ensuremath{\pi}}^{\ensuremath{'}}$ phase but cannot enter its $\ensuremath{\pi}$ phase. Moreover, when the dot levels are detuned, one ${\ensuremath{\pi}}^{\ensuremath{'}}$-phase island appears in the phase diagram. Such a result is attributed to the interplay among the Kondo effect, RKKY effect, and the Cooper pairing correlation. We believe that this work can be helpful in understanding the special roles of the correlation mechanisms of the parallel junction in driving the Josephson phase transition.

We investigate the electron transport through a quantum dot connected with two ferromagnetic leads, by coupling one Majorana doublet laterally to the quantum dot. It is found that Majorana doublet keeps the value of zero-bias conductance to be independent of the shift of structural parameters, including dot level, relative lead-magnetization direction, and magnetic field on the dot. Even in the cases of asymmetric dot-lead couplings, the zero-bias conductance is weakly dependent on the relative lead-magnetization direction. On the other hand, when Majorana doublet is replaced by Majorana singlet, the zero-bias conductance value becomes sensitive to the structural parameters. Via analyzing the respective particle motion processes, the different influences of Majorana doublet and singlet are explained. We believe that this work can be helpful for understanding the peculiar properties of Majorana doublet.

We present a comprehensive analysis about the transport properties of a quantum dot (QD) system with a side-coupled Majorana zero mode. Our calculation result shows that when the coupling manners between the two leads and QDs are identical, the local Andreev reflection and the interlead normal tunneling have the same magnitude at the zero-bias limit. Accordingly, the zero-bias conductance value is always equal to e 2 /2 h , which is exactly one half of the resonant-tunneling conductance. This result is independent of the level number and the level distribution in the single-QD case, and in the coupled-QD case it is irrelevant to the geometry of the QD molecule. The universal transport property is a powerful evidence for the feasibility to detect the MBSs based on a QD circuit. This result also means that the QD condition is not a key factor to achieve the detection. On the other hand, if the decoupling phenomenon appears, the Majorana zero mode may play a trivial role in contributing to the conductance property.

In this work, we study the effect of $\mathcal{PT}$-symmetric complex potentials on the transport properties of one non-Hermitian system, which is formed by the coupling between a triple-quantum-dot molecule and two semi-infinite leads. As a result, it is found that the $\mathcal{PT}$-symmetric imaginary potentials take pronounced effects on transport properties of such a system, including changes from antiresonance to resonance, shift of antiresonance, and occurrence of new antiresonance, which are determined by the interdot and dot-lead coupling manners. This study can be helpful in understanding the quantum transport behaviors modified by the $\cal PT$ symmetry in non-Hermitian discrete systems., Comment: 8 pages, 9 figures

An effective approach to produce graphene quantum dots (GQDs) has been developed, which based on the cutting of graphene oxide (GO) powder into smaller pieces and being reduced by a green approach, using sodium polystyrene sulfonate (PSS) as a dispersant and l-ascorbic acid (l-AA) as the reducing agent, which is environmentally friendly. Then the as-prepared GQDs were further used for the detection of heavy metal ions Pb(2+). This kind of GQDs has greater solubility in water and is more biocompatible than GO that has been reduced by hydrazine hydrate. The few-layers of GQDs with defects and residual OH groups were shown to be particularly well suited for the determination of metal ions in the liquid phase using an electrochemical method, in which a remarkably low detection limit of 7×10(-9)M for Pb(2+) was achieved.

By introducing floating leads to mimic the decoherence mechanism, we study the influence of the decoherence effect on the Fano interference in electron transport through a parallel double quantum dot (QD) structure. We find that when the decoherence effect is incorporated in the resonant channel, the Fano interference can apparently be suppressed, especially in the case of ϕ = π (ϕ is the phase due to the presence of a local magnetic flux). On the other hand, if the decoherence effect is introduced into the nonresonant channel, the Fano antiresonance is independent of the strengthening of the decoherence effect. If the magnetic flux is absent, the Fano antiresonance valley will be widened by the decoherence. When ϕ = π, the Fano lineshape in the conductance spectrum is robust. By analyzing the electron motion is this system, we clarified all the results. We hope that these results will be helpful for relevant experiments.

We discuss the influence of local impurities on the thermoelectric effect in a parallel double quantum dot (QD) structure. It is first found that in this structure, the Fano effect contributes significantly to the enhancement of thermoelectric efficiency, especially in the case of ϕ = π. Next, impurities are introduced to couple to the QDs, respectively. We readily find that regardless of which QD is coupled to a local impurity, the thermoelectric efficiency can be enhanced by the strengthening of impurity–QD coupling. This means that the destruction of the Fano interference is not the necessary condition to suppress the thermoelectric effect. Accordingly, we hope that the numerical results can help to understand the role of impurities in adjusting the thermoelectric properties of the QD structure.

We investigate the Andreev reflections in a single-dot quantum ring with one s-wave superconductor side-coupled to the quantum dot, by considering the presence of local Rashba interaction and magnetic flux. It shows that in this system, the local Rashba interaction induces apparent spin polarizations of the local Andreev reflections, with their directions depending on the Rashba interaction and the lead index, respectively. Nevertheless, the crossed Andreev reflection cannot be polarized, and its magnitude can be adjusted by the threaded local magnetic flux. We propose this structure to be the promising candidate for achieving the manipulation of Andreev reflections.