Conductance Peak Research Articles

Электрон-фотонные взаимодействия в условиях размерного ограничения проводимости в полупроводниковых одиночных квантово-размерных частицах в межэлектродном нанозазоре

For quantum-size particles of the InSb, PbS, HgSe, CdSe semiconductors, a model of competition of dimensional quantum restrictions and blocking with a single-electron current and Coulomb restriction, as well as heating electrons with an electric field of the light wave, is proposed. This made it possible to explain the highly multiplicity (up to two orders of order) of a change in photoconductivity observed in conditions of tunnel conductivity, and in the conditions of the сonfinition - the absence of inter-zone and inter-level photoconductivity. The resonant current peaks of quantum conductivity observed on the V-I characteristics when irritating with light of any wavelength (in the interval of 0.4–1.2 µm) are reset or shifted towards smaller voltage values. The energy minimum recorded in this case is estimated as 100 meV. The results can be useful in resolving issues of application in uncooled IR detectors, including single-photon registration.

Identifying Majorana bound states at quantum spin Hall edges using a metallic probe

We study the conductance afforded by a normal-metal probe which is directly contacting the helical edge modes of a quantum spin Hall insulator (QSHI). We show a $2e^2/h$ conductance peak at zero temperature in QSHI-based superconductor--ferromagnet hybrids due to the formation of a single Majorana bound state (MBS). In a corresponding Josephson junction hosting a pair of MBSs, a $4e^2/h$ conductance peak is found at zero temperature. The conductance quantization is robust to changes of the relevant system parameters and, remarkably, remains unaltered with increasing the distance between probe and MBSs. In the low temperature limit, the conductance peak is robust as the probe is placed within the localization length of MBSs. Our findings can therefore provide an effective way to detect the existence of MBSs in QSHI systems.

CONDUCTIVITY OF SOLID FLUORIDE-CONDUC­TING PHASES BaxPb0.86-xSn1.14F4

This work presents the results of research of complex solid fluoride ion conducting phases based on lead and tin fluorides. Structure and conductive properties of solid solutions based on PbSnF4 were investigated. Series of samples were synthesized with replacement of lead cations with barium cations in structure of Pb0.86Sn1.14F4 in the concentration range of 0 ≤x ≤0.86. The barium cation has a larger radius and does not have a stereoactive lone pair of electrons, which can have a significant contribution to the conductivity of the synthesized phases and the characteristics of fluoride ion transportation in them.
 It was established that with partial or complete replacement of lead cations with barium cations in the fluoride ion conducting phases in Pb0.86Sn1.14F4 solid solutions of BaxPb0.86‑xSn1.14F4 , where x takes the values 0 ≤x ≤0.86 are formed. The symmetry of the crystal lattice of the synthesized phases in the concentration range of 0 ≤x ≤0.43 corresponds to the structural type of β-PbSnF4 (space group P4/ nmm). Farther increase in the content of barium fluoride cause their crystal lattice to rearrange and approach the structural type of BaSnF4 with preservation of the space group symmetry. The conductive properties of the synthesized phases were investigated.
 We register increase in conductivity of samples bound to increase of barium cation content in the range of 0 ≤x ≤0.43. After reaching peak in conductivity of samples it gradually lowers with increase of barium cation content in the range of 0.43 ≤x ≤0.86.
 The fluoride ion conducting phase Pb0.43Ba0.43Sn1.14F4, isostructural to β-PbSnF4, in comparison with the currently known fluoride-conducting phases has have the highest electrical conductivity in a wide temperature range. Its conductivity is almost two orders of magnitude higher than that of β-PbSnF4 and is 0.12 S/cm at 373 K. With 19FNMR method, it was determined that electrical conductivity is mainly provided by internodal fluorine anions, which are localized between layers of barium and stanium cations. The transfer numbers for fluorine anions in the synthesized phases correspond to the theoretical ones.

An experimental set-up to probe the quantum transport through a single atomic$$/$$molecular junction at room temperature

Understanding the transport characteristics at the atomic limit is the prerequisite for futuristic nanoelectronic applications. Among various experimental procedures, mechanically controllable break junction (MCBJ) is a well-adopted experimental technique to study and control atomic or molecular scale devices. Here, we present the details of developing a piezo-controlled table-top MCBJ set-up, working at ambient conditions, along with the necessary data acquisition technique and analysis of the data. We performed the conductance experiment on a macroscopic gold wire, which exhibits a quantised conductance plateau upon pulling the wire. Conductance peak up to ~ 20G0 (G0 = 2e2\(/\)h where e is the electronic charge and h is the Planck’s constant) could be resolved at room temperature. A well-known test bed molecule, 4,4′-bipyridine, was introduced between the gold electrodes and the conductance histogram exhibits two distinctive conductance peaks, confirming the formation of a single molecular junction, in line with the previous reports. This demonstrates that our custom-designed MCBJ set-up can measure the quantum transport of a single molecular junction at ambient conditions.

Physiological Study of Ethephon- and ACC-Induced Fruitlet and Leaf Abscission in Peach Trees Under Different Conditions of Temperature

The effect of temperature on the ability of 2-chloroethylphosphonic acid (ethephon, ETH) and the 1-aminocyclopropane carboxylic acid (ACC) to induce ethylene production in fruitlets and abscission of fruitlets and leaves when applied at postbloom (~15 mm fruit diameter) was studied using 5-year-old ‘Sweet Lady’/Rootpac-20 peach [Prunus persica (L.) Batsch] trees kept in pots in environment-controlled growth rooms. ETH at 150 mg L−1 and ACC at 500 mg L−1 effectively thinned peaches. Increasing the temperature from 10 to 20 °C pronounced the ETH-induced fruit and leaf abscission and the ACC-induced leaf abscission and decreased stomatal conductance in leaves. However, the ACC thinning effect was not affected by increasing temperature, as well as ETH- and ACC-induced ethylene production in fruitlets and in the quantum yield of PSII photochemistry. Changes in ethylene peak in fruitlets and stomatal conductance in leaves were related to the abscission response.

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Achieving glass-like lattice thermal conductivity in PbTe by AgBiTe2 alloying

Here, we report the thermal transport properties of lead telluride (PbTe)1−x(AgBiTe2)x (x = 0.05 and 0.15) alloys. It is found that the prominent peak in lattice thermal conductivity at 15 K for PbTe disappears after forming solid solution with AgBiTe2, exhibiting a typical glass-like thermal transport behavior. The high energy phonons are scattered by the point defects induced by cationic disorder, while the appearance of soft vibrational modes arises from Ag atoms acting like Einstein oscillators (ΘE1 = 5.4 K, ΘE2 = 67.3 K), which substantially affects the lattice thermal conductivity. Further with nanostructuring, the mid-frequency phonons are scattered by the high-density disc-like Ag2Te precipitates. As a result, an ultralow lattice thermal conductivity (≤1.0 W m−1 K−1) for (PbTe)0.85(AgBiTe2)0.15 is obtained, which is the lowest value ever reported to date for the PbTe-based TE materials. Our work highlights a synthetic route to achieve glass-like lattice thermal conductivity in PbTe over the entire temperature range.

Strategically improving electrical conductivity of reduced graphene oxide through a series of reduction processes

Current work aims at producing reduced graphene oxide(rGO) with highest possible conductivity, starting with graphene oxide(GO) produced by electrochemical exfoliation(ECE) of graphite rod salvaged from C-type primary batteries. Six single-step reduction process were used to reduce GO in the first stage. Following that, most effective three reduction methods, namely water-based reduction(W), hydrothermal reduction(H), and microwave reduction(MW), were used in two combinations (W-H-MW and W-MW-H). The conductivity of rGO(W-H-MW) and rGO(W-MW-H) is 43.78Sm−1 and 28.33Sm−1 respectively with rGO(W-H-MW) having highest conductivity of all selected reduction methods. It is also found that sequence of reduction processes has a big impact on the final product's conductivity, ID/IG ratio, and XRD peak intensity. Characterization by XRD, XPS, TEM, FEG-SEM, FTIR, Raman etc. is used to discuss the findings. Chemical structure, morphology and specific surface area of rGO(W-H-MW) are compared to those of GO and their influence on bulk conductivity of rGO’s are discussed.

Characteristics of Hybrid Nanolubricants for MQL Cooling Lubrication Machining Application

Efficient and effective lubricants have great application prospects in the manufacturing industries. Minimum quantity lubrication (MQL) machining with low flow rate of nanolubricants is investigated for cooling and lubrication during the process. This paper investigates the characterization of graphene-mixed aluminium oxide (G-Al2O3) hybrid nanomixture spent lubricants for MQL machining purposes. The main advantage of this method is to reduce the disposal lubricants to develop high-performance cooling-lubrication by using nanolubricants of G-Al2O3 nanoparticles in different volume composition ratios at a constant 1.0% volume concentration in a base liquid mixture of 40% spent lubricants. Before conducting the measurements of the nanolubricants’ thermal conductivity and dynamic viscosity, the nanolubricants were homogenous and stable. The tribological performance of all ratios was evaluated by using a four-ball wear tribotester machine. The thermal conductivity peak value for the G-Al2O3 hybrid nanolubricant was obtained and the highest enhancement, up to 29% higher than the base liquid solution, was obtained. The dynamic viscosity variation for all ratios was lower than the 40:60 ratio. The properties enhancement ratio suggests that G-Al2O3 hybrid nanolubricants with 1.0% volume concentration aid in the heat transfer, especially for ratios of 60:40 and 20:80. The lowest coefficient of friction (COF) for a ratio of 60:40 was obtained to be 0.064, with 45% enhancement as compared to the base liquid solution. In conclusion, optimum ratios for G-Al2O3 hybrid nanolubricants were determined to be 20:80 and 60:40. Regarding the properties enhancement ratio, the combination of enhanced thermophysical and tribological properties had more advantages for cooling lubrication application.

Band Structure and Quantum Conductance of Surface-unsaturated and Hydrogenated Sb and Bi Monolayer Nanoribbons

Electronic structure and quantum conductance of surface-unsaturated and hydrogenated Sb and Bi monolayer nanoribbons are theoretically investigated by first-principles calculations combined with non-equilibrium Green’s function method. Band structures, electronic transmission spectra and current-voltage curves of these Sb and Bi monolayer derived nanoribbons along zigzag crystallographic orientations are calculated to explore their potential applications in topological nanoelectronics. It is verified that extremely high conductivity under low bias voltage is acquired from the scattering-forbidden topological edge-states of these nanoribbons, as indicated by Dirac-point-like energy dispersion of band-edges near Fermi level, which also provides an evident negative differential conductance under 0.2 ∼ 0.3 V voltage bias when the ballistic conductance peak at Fermi level shifting out of bias window. The present study suggests Sb and Bi monolayers after acquiring chemical stability by hydrogenation are prospective candidates to be applied for ultrahigh power and zero-loss nanotransistors.

Magneto-optical conductivity of nodal link semimetals

Nodal link semimetals as a type of topological semimetals are characterized by the nodal link rings in the Brillouin zone. The magneto-optical conductivity of nodal link semimetals is investigated numerically based on a system with a magnetic field. We find that in the system, the Landau levels (LLs) and magnetic field show a relationship of three halves power, which can lead to an intricate curved LLs. Due to the rich structure of LLs, we divided the LLs into four different regions to calculate the magneto-optical conductivity. We calculated the absorption peaks of longitudinal and Hall conductance of a neutral system and with different chemical potential. We find that the absorption peaks of longitudinal conductance are in a curved background in the whole range of magnetic field. When chemical potential is tuned to pass through the LLs, there are not only the intraband transition but also weak redistributed peaks in the low frequency. From the transition peaks of Hall conductance, we can find that there are several negative peaks because of the striking LLs spectrum structure. This will provide a feasible way to distinguish nodal link semimetals from other materials.

Design and Preparation of Double-Harmonic Piezoelectric Composite Lamination.

In this work, a new type of double-harmonic piezoelectric composite laminated structure is designed. Two bending vibration frequencies are generated by designing the structure with non-equal length and non-equal width, and the response is relatively consistent at the frequency point of the double-harmonic vibration. Firstly, the finite element software ANSYS is used to establish the simulation model of double-harmonic piezoelectric composite lamination. Two bending vibration frequencies are generated by using the non-equal length structure design, and the variation law of the conductance curve with the laminated structure is analyzed. Then, according to this law, the structure is optimized, and a non-equal width structure is further proposed in this work. Different double-harmonic piezoelectric composite laminations are prepared for comparison. The simulation and experimental results show that the value of the corresponding conductance curve at the two vibration frequency points can be increased or reduced by changing the lamination width. Then, the same conductance peak can be obtained to have a relatively consistent response at the double-harmonic frequency point. This will provide a good choice for expanding the transducer bandwidth and developing the broadband energy collector.

Anomalous universal conductance as a hallmark of non-locality in a Majorana-hosted superconducting island

The non-local feature of topological states of matter is the key for the topological protection of quantum information and enables robust non-local manipulation in quantum information. Here we propose to manifest the non-local feature of a Majorana-hosted superconducting island by measuring the temperature dependence of Coulomb blockade peak conductance in different regimes. In the low-temperature regime, we discover a coherent double Majorana-assisted teleportation (MT) process, where any independent tunneling process always involves two coherent non-local MTs; and we also find an anomalous universal scaling behavior, i.e., a crossover from a {[max (T,eV)]}^{6} power-law to a {[max (T,eV)]}^{3} power-law conductance behavior when energy scale increases — in stark contrast to the usual exponential suppression due to certain local transport. In the high-temperature regime, the conductance is instead proportional to the temperature inverse, indicating a non-monotonic temperature-dependence of the conductance. Both the anomalous power law and non-monotonic temperature-dependence of the conductance can be distinguished from the conductance peak in the traditional Coulomb block, and therefore, together serve as a hallmark for the non-local feature in the Majorana-hosted superconducting island.

Effect Of Strain on Optical Conductivity in Monolayer FeCl2

We implemented the density functional theory to study the effect of strain on the optical conductivity in 1T monolayer FeCl2 within the collinear structure. The computational calculation was run based on the Kubo-Greenwood formulation. We showed that the peak of optical conductivity would be shifted by applying strain. This indicates that the optical conductivity is sensitive to the strain. Moreover, we also found that the half-metallicity in the band dispersion disappeared as the lattice parameter was compressed so highly.

Optical Conductivity as a Probe of the Interaction-Driven Metal in Rhombohedral Trilayer Graphene

Study of the strongly correlated states in van der Waals heterostructures is one of the central topics in modern condensed matter physics. Among these, the rhombohedral trilayer graphene (RTG) occupies a prominent place since it hosts a variety of interaction-driven phases, with the metallic ones yielding exotic superconducting orders upon doping. Motivated by these experimental findings, we show within the framework of the low-energy Dirac theory that the optical conductivity can distinguish different candidates for a paramagnetic metallic ground state in this system. In particular, this observable shows a single peak in the fully gapped valence-bond state. On the other hand, the bond-current state features two pronounced peaks in the optical conductivity as the probing frequency increases. Finally, the rotational symmetry breaking charge-density wave exhibits a minimal conductivity with the value independent of the amplitude of the order parameter, which corresponds precisely to the splitting of the two cubic nodal points at the two valleys into two triplets of the band touching points featuring linearly dispersing quasiparticles. These features represent the smoking gun signatures of different candidate order parameters for the paramagnetic metallic ground state, which should motivate further experimental studies of the RTG.

Emergence of Interlayer Coherence in Twist-Controlled Graphene Double Layers

We report enhanced interlayer tunneling with reduced linewidth at zero interlayer bias in a twist-controlled double monolayer graphene heterostructure in the quantum Hall regime, when the top (ν_{T}) and bottom (ν_{B}) layer filling factors are near ν_{T}=±1/2,±3/2 and ν_{B}=±1/2,±3/2, and the total filling factor ν=±1 or ±3. The zero-bias interlayer conductance peaks are stable against variations of layer filling factor, and signal the emergence of interlayer phase coherence. Our results highlight twist control as a key attribute in revealing interlayer coherence using tunneling.

Structure Identification for Force-Induced Reaction Using Single-Molecule Conductance Measurement

Structure Identification for Force-Induced Reaction Using Single-Molecule Conductance Measurement

Spin quantum transport in double top-gate system

The quantum transport in an n-type two-dimensional electron gas (2DEG) with a double top gate system is investigated. A propagation matrix method is used to derive the band structure and obtain the conductance of the considered system. The results show that in the presence of the Rashba and the Zeeman interactions, resonance peaks and hole-like bound state structure are formed in the conductance spectra influenced by the gate potential and gate distance. While, under the influence of the Rashba–Dresselhaus and the Zeeman interactions, resonance peaks and inner-mode resonance conductance peaks are formed reflecting the gate potential and the gate distance. Notably, when the Dresselhaus interaction reaches a certain strength, the partial conductance of the spin-preservation internal mode becomes significant. Finally, a simple transcendental equation is found to estimate the energy of a bound state.

Large zero bias peaks and dips in a four-terminal thin InAs-Al nanowire device

We report electron transport studies of a thin InAs-Al hybrid semiconductor-superconductor nanowire device using a four-terminal design. Compared to previous works, thinner InAs nanowire (diameter less than 40 nm) is expected to reach fewer sub-band regime. The four-terminal device design excludes electrode contact resistance, an unknown value which has inevitably affected previously reported device conductance. Using tunneling spectroscopy, we find large zero-bias peaks (ZBPs) in differential conductance on the order of $2e^2/h$. Investigating the ZBP evolution by sweeping various gate voltages and magnetic field, we find a transition between a zero-bias peak and a zero-bias dip while the zero-bias conductance sticks close to $2e^2/h$. We discuss a topologically trivial interpretation involving disorder, smooth potential variation and quasi-Majorana zero modes.

Random matrix theory for the robustness, quantization, and end-to-end correlation of zero-bias conductance peaks in a class D ensemble

We develop a general theory to study strong random quenched disorder effects in systems of experimental relevance in the search for Majorana zero modes in topological superconductors. Using the random matrix theory in a class D ensemble, we simulate the transport properties of random quantum dots by attaching leads, and calculating the differential conductance in the $S$-matrix formalism. To add the concept of the length to the random system so that disordered Majorana nanowires can be simulated by the random matrix theory, we generalize the model of a single quantum dot to a chain of quantum dots by analogy with the superconductor-semiconductor nanowire Majorana platform. We first define a new concept, the robustness of zero-bias conductance peaks, in terms of an effective random Hamiltonian considering the self-energy of leads. We then study the joint distribution for the robustness and zero-bias conductance peaks, and find a strong correlation that the zero-bias conductance peak with stronger robustness is also prone to carry a larger conductance peak near $2{e}^{2}/h$. This trend is more prominent in shorter chains than in longer chains. This is consistent with experimentally observed zero-bias conductance associated with disorder-induced trivial Andreev bound states (the so-called ugly zero-bias peaks). Finally, we study the end-to-end correlation of the disorder-induced zero-bias conductances from two leads by calculating the normalized mutual information, which estimates the degrees of the correlation arising from the trivial zero-bias conductance peaks. Our work provides an estimate of several important metrics used in superconductor-semiconductor experiments to determine the nature of zero-bias conductance peaks, including the robustness, the quantization, and the end-to-end correlation of the trivial zero-bias peaks. Therefore, in order to claim any evidence for the Majorana zero modes, one must establish the observed zero-bias conductance peaks to have considerable statistical significance well beyond what we find in this work to exist for the trivial peaks.