Showing papers on "Conductance published in 2019"
TL;DR: Observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance are reported.
Abstract: Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold a great promise for topological quantum computing. Due to its particle-antiparticle equivalence, an MZM exhibits robust resonant Andreev reflection and 2e2/h quantized conductance at low temperature. By utilizing variable-tunnel-coupled scanning tunneling spectroscopy, we study tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance. In contrast, no such plateau behaviors were observed on either finite energy Caroli-de Genne-Matricon bound states or in the continuum of electronic states outside the superconducting gap. This unique behavior of the zero-mode conductance reaching a plateau strongly supports the existence of MZMs in this iron-based superconductor, which serves as a promising single-material platform for Majorana braiding at a relatively high temperature.
104 citations
TL;DR: In this paper, the authors show that analog and binary conductance modulation can be achieved in a Pt/HfO2/TiOx/Ti VCM cell by varying the operation conditions.
Abstract: The utilization of bipolar-type memristive devices for the realization of synaptic connectivity in neural networks strongly depends on the ability of the devices for analog conductance modulation under application of electrical stimuli in the form of identical voltage pulses. Typically, filamentary valence change mechanism (VCM)-type devices show an abrupt SET and a gradual RESET switching behavior. Thus, it is challenging to achieve an analog conductance modulation during SET and RESET. Here, we show that analog as well as binary conductance modulation can be achieved in a Pt/HfO2/TiOx/Ti VCM cell by varying the operation conditions. By analyzing the switching dynamics over many orders of magnitude and comparing to a fully dynamic switching model, the origin of the two different switching modes is revealed. SET and RESET transition show a two-step switching process: a fast conductance change succeeds a slow conductance change. While the time for the fast conductance change, the transition time, turns out to be state-independent for a specific voltage, the time for the slow conductance change, the delay time, is highly state-dependent. Analog switching can be achieved if the pulse time is a fraction of the transition time. If the pulse time is larger than the transition time, the switching becomes probabilistic and binary. Considering the effect of the device state on the delay time in addition, a procedure is proposed to find the ideal operation conditions for analog switching.
81 citations
TL;DR: Single antibodies, such as anti-Ebola IgG, can be detected electrically when they bind a peptide epitope tethered to electrodes, with no background signal from molecules that do not bind specifically, providing a method for forming reliable contacts to proteins, and for the specific detection of single molecules.
Abstract: Proteins are widely regarded as insulators, despite reports of electrical conductivity. Here we use measurements of single proteins between electrodes, in their natural aqueous environment to show that the factor controlling measured conductance is the nature of the electrical contact to the protein, and that specific ligands make highly selective electrical contacts. Using six proteins that lack known electrochemical activity, and measuring in a potential region where no ion current flows, we find characteristic peaks in the distributions of measured single-molecule conductances. These peaks depend on the contact chemistry, and hence, on the current path through the protein. In consequence, the measured conductance distribution is sensitive to changes in this path caused by ligand binding, as shown with streptavidin-biotin complexes. Measured conductances are on the order of nanosiemens over distances of many nanometers, orders of magnitude more than could be accounted for by electron tunneling. The current is dominated by contact resistance, so the conductance for a given path is independent of the distance between electrodes, as long as the contact points on the protein can span the gap between electrodes. While there is no currently known biological role for high electronic conductance, its dependence on specific contacts has important technological implications, because no current is observed at all without at least one strongly bonded contact, so direct electrical detection is a highly selective and label-free single-molecule detection method. We demonstrate single-molecule, highly specific, label- and background free-electronic detection of IgG antibodies to HIV and Ebola viruses.
63 citations
TL;DR: In this paper, the authors reported that UV-ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude.
Abstract: We report that UV-ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV-ozone-treated TiO2 anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO2 anatase thin films results in a 2% increase of the average power conversion efficiency (PCE) of methylammonium lead iodide-based perovskite solar cells. PCE values up to 19.5% for mesoporous solar cells are realized. The additional UV-ozone treatment results in a reduced number of oxygen vacancies at the surface, inferred from X-ray photoelectron spectroscopy. These oxygen vacancies at the surface act as charge carrier traps and hinder charge extraction from the adjacent material. Terahertz measurements indicate only minor changes of the bulk conductance, which underlines the importance of UV-ozone treatment to control surface-based defects.
49 citations
TL;DR: In this article, a quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor a topological superconducting phase, the elementary excitations of which (i.e. Majorana fermions) can form topological qubits upon non-Abelian braiding operations.
Abstract: A quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor a topological superconducting phase, the elementary excitations of which (i.e. Majorana fermions) can form topological qubits upon non-Abelian braiding operations. A recent transport experiment interprets the half-quantized two-terminal conductance plateau as the presence of chiral Majorana fermions in a millimeter-size QAH-Nb hybrid structure. However, there are concerns about this interpretation because non-Majorana mechanisms can also generate similar signatures, especially in a disordered QAH system. Here, we fabricated QAH-Nb hybrid structures and studied the QAH-Nb contact transparency and its effect on the corresponding two-terminal conductance. When the QAH film is tuned to the metallic regime by electric gating, we observed a sharp zero-bias enhancement in the differential conductance, up to 80% at zero magnetic field. This large enhancement suggests high probability of Andreev reflection and transparent interface between the magnetic topological insulator (TI) and Nb layers. When the magnetic TI film is in the QAH state with well-aligned magnetization, we found that the two-terminal conductance is always half-quantized. Our experiment provides a comprehensive understanding of the superconducting proximity effect observed in QAH-superconductor hybrid structures and shows that the half-quantized conductance plateau is unlikely to be induced by chiral Majorana fermions.
49 citations
TL;DR: In this paper, the authors show that the charged mode is much faster than the neutral mode on quantum Hall edges at large filling factors, and the edge may remain out of equilibrium in thermal conductance experiments.
Abstract: Since the charged mode is much faster than the neutral modes on quantum Hall edges at large filling factors, the edge may remain out of equilibrium in thermal conductance experiments This sheds light on the observed imperfect quantization of the thermal Hall conductance at $\ensuremath{
u}=8/3$ and can increase the observed thermal conductance by two quanta at $\ensuremath{
u}=8/5$ Under certain unlikely but not impossible assumptions, this might also reconcile the observed thermal conductance at $\ensuremath{
u}=5/2$ with not only the PH-Pfaffian order but also the anti-Pfaffian order
44 citations
TL;DR: In this article, an electrochemical metallization memristor based on Zr0.5Hf0/Pt and an active Cu electrode with quantum conductance and neuromorphic behavior has been reported.
Abstract: An electrochemical metallization memristor based on Zr0.5Hf0.5O2 film and an active Cu electrode with quantum conductance and neuromorphic behavior has been reported in this work. After electroforming in the Cu/Zr0.5Hf0.5O2/Pt device, linear conductance characteristics in low resistance states were found and the stepwise changes of conductance with the order of G0 ((=2e2)/h) multilevel states were obtained by varying pulse amplitude, width and adjacent-pulse time interval, which is beneficial for backpropagation learning algorithms belonging to deep neural networks, essentially using memristors as vector–matrix multiplication accelerators in image processing. The gradual resistance tuning served as the basis of memory and learning. Under the coactivity of pre- and post-synaptic spikes, bidirectional long-term Hebbian plasticity modulation was realized. The temporal difference, spike rate and size of the top and bottom electrode pulse voltage can strongly affect the sign and degree of Hebbian plasticity. Moreover, the quantum conductance phenomenon was ascribed to interstitial Cu in the dielectric layer forming single- and multi-atom chains. The results can provide multilevel storage and next-generation parallel neuromorphic computing architecture, promoting the development of functional plastic electronic synapses.
43 citations
TL;DR: In this paper, a charge transfer complex with tetracyanoethylene (TCNE) was proposed to increase charge transport efficiency in long and poorly conductive molecular wires, with important repercussions in single-entity thermoelectronics and spintronics.
Abstract: Interference features in the transmission spectra can dominate charge transport in metal–molecule–metal junctions when they occur close to the contact Fermi energy (EF). Here, we show that by forming a charge-transfer complex with tetracyanoethylene (TCNE) we can introduce new constructive interference features in the transmission profile of electron-rich, thiophene-based molecular wires that almost coincide with EF. Complexation can result in a large enhancement of junction conductance, with very efficient charge transport even at relatively large molecular lengths. For instance, we report a conductance of 10−3G0 (∼78 nS) for the ∼2 nm long α-quaterthiophene:TCNE complex, almost two orders of magnitude higher than the conductance of the bare molecular wire. As the conductance of the complexes is remarkably independent of features such as the molecular backbone and the nature of the contacts to the electrodes, our results strongly suggest that the interference features are consistently pinned near to the Fermi energy of the metallic leads. Theoretical studies indicate that the semi-occupied nature of the charge-transfer orbital is not only important in giving rise to the latter effect, but also could result in spin-dependent transport for the charge-transfer complexes. These results therefore present a simple yet effective way to increase charge transport efficiency in long and poorly conductive molecular wires, with important repercussions in single-entity thermoelectronics and spintronics.
43 citations
TL;DR: In this article, the Cadmium-doped zinc oxide (CdxZn1−xO) thin films with various Cd dopants (x 0.10, 0.20 and 0.30) were deposited on p-Si wafers via sol-gel spin coating method.
Abstract: We have reported on the electrical and dielectric properties of Al/CdxZn1-xO/p-Si structures. The cadmium-doped zinc oxide (CdxZn1−xO) thin films with various Cd dopants (x = 0.10, 0.20 and 0.30) were deposited on p-Si wafers via sol–gel spin coating method. The admittance (Y = Gm + iωCm) measurements were performed at 1 MHz. The C−2–V plots were used to extract the main electrical parameters such as the diffusion potential (VD), the concentration of acceptor atoms (NA), depletion region width (WD) and barrier height (ΦB). The experimental results reveal that the capacitance increases with higher Cd dopant concentration due to the presence of interfacial charges while an opposite behaviour is observed in conductance. The lower values of conductance in the sample with high Cd content can be attributed to increase in series resistance. The dielectric measurements also confirm the effect of Cd substitution in ZnO on the device performance.
40 citations
TL;DR: The single‐molecule conductance of a series of cumulenes and cumulene analogues, where the number of consecutive C=C bonds in the core is n=1, 2, 3, and 5, is reported.
Abstract: Cumulenes are sometimes described as "metallic" because an infinitely long cumulene would have the band structure of a metal. Herein, we report the single-molecule conductance of a series of cumulenes and cumulene analogues, where the number of consecutive C=C bonds in the core is n=1, 2, 3, and 5. The [n]cumulenes with n=3 and 5 have almost the same conductance, and they are both more conductive than the alkene (n=1). This is remarkable because molecular conductance normally falls exponentially with length. The conductance of the allene (n=2) is much lower, because of its twisted geometry. Computational simulations predict a similar trend to the experimental results and indicate that the low conductance of the allene is a general feature of [n]cumulenes where n is even. The lack of length dependence in the conductance of [3] and [5]cumulenes is attributed to the strong decrease in the HOMO-LUMO gap with increasing length.
37 citations
TL;DR: The present work demonstrates the correlation between optical processes of molecules and quantum transport in their junction, and thus opens up a new avenue for the application of AIE-type molecules in molecular electronics and functional devices.
Abstract: We report an effective modulation of the quantum transport in molecular junctions consisting of aggregation-induced-emission(AIE)-active molecules. Theoretical simulations based on combined density functional theory and rate-equation method calculations show that the low-bias conductance of the junction with a single tetraphenylethylene (TPE) molecule can be completely suppressed by strong electron-vibration couplings, that is, the Franck-Condon blockade effect. It is mainly associated with the low-energy vibration modes, which is also the origin of the fluorescence quenching of the AIE molecule in solution. We further found that the conductance of the junction can be lifted by restraining the internal motion of the TPE molecule by either methyl substitution on the phenyl group or by aggregation, a mechanism similar to the AIE process. The present work demonstrates the correlation between optical processes of molecules and quantum transport in their junction, and thus opens up a new avenue for the application of AIE-type molecules in molecular electronics and functional devices.
TL;DR: A biomimetic submicro-channel with functions of continuously tunable ion rectification and conductance based on thermoresponsive polymer layer-by-layer (LbL) self-assembly that can be applied for on-demand on-off molecule delivery, which was important for disease therapy.
Abstract: A biomimetic conical submicrochannel (tip side ca. 400 nm) with functions of continuously tunable ion rectification and conductance based on thermoresponsive polymer layer-by-layer (LbL) self-assembly is presented. These self-assembled polymers with different layers exhibited a capability to regulate the effective channel diameter, and different ion rectifications/conductance were achieved. By controlling temperature, the conformation and wettability of the assembled polymers were reversibly transformed, thus the ion rectification/conductance could be further adjusted subtly. Owing to the synergistic effect, the ion conductance could be tuned over a wide range spanning three orders of magnitude. Moreover, the proposed system can be applied for on-demand on-off molecule delivery, which was important for disease therapy. This study opens a new door for regulating channel size according to actual demand and sensing big targets with different size with one channel.
TL;DR: It is demonstrated that imidazole based π–π stacked dimers form strong and efficient conductance pathways in single-molecule junctions using the scanning-tunneling microscope-break junction (STM-BJ) technique and density functional theory-based calculations.
Abstract: We demonstrate that imidazole based π–π stacked dimers form strong and efficient conductance pathways in single-molecule junctions using the scanning-tunneling microscope-break junction (STM-BJ) technique and density functional theory-based calculations. We first characterize an imidazole-gold contact by measuring the conductance of imidazolyl-terminated alkanes (im-N-im, N = 3–6). We show that the conductance of these alkanes decays exponentially with increasing length, indicating that the mechanism for electron transport is through tunneling or super-exchange. We also reveal that π–π stacked dimers can be formed between imidazoles and have better coupling than through-bond tunneling. These experimental results are rationalized by calculations of molecular junction transmission using non-equilibrium Green's function formalism. This study verifies the capability of imidazole as a Au-binding ligand to form stable single- and π-stacked molecule junctions at room temperature.
TL;DR: This analysis shows that the effect on thermal conductance is dominated by the phonon thermalization through anharmonic effects, while elastic phonon transmission and impedance matching play a secondary role, and proposes a strategy to potentially best enhance interfacial thermal transport through solid-solid interfaces by adding nano-engineered, exponentially mass-graded intermediate layers.
Abstract: We propose a strategy to potentially best enhance interfacial thermal transport through solid–solid interfaces by adding nano-engineered, exponentially mass-graded intermediate layers. This exponential design rule results in a greater enhancement than a linearly mass-graded interface. By combining calculations using non-equilibrium Green's functions (NEGF) and non-equilibrium molecular dynamics (NEMD), we investigated the role of impedance matching and anharmonicity in the enhancement in addition to geometric parameters such as the number of layers and the junction thickness. Our analysis shows that the effect on thermal conductance is dominated by the phonon thermalization through anharmonic effects, while elastic phonon transmission and impedance matching play a secondary role. In the harmonic limit, increasing the number of layers results in greater elastic phonon transmission at each individual boundary, countered by the decrease of available conducting channels. Consequently, conductance initially increases with number of layers due to improved bridging, but quickly saturates. The presence of slight anharmonic effects (at very low temperature, T = 2 K) turns the saturation into a monotonically increasing trend. Anharmonic effects can further facilitate interfacial thermal transport through the thermalization of phonons at moderate temperatures. At high temperature, however, the role of anharmonicity as a facilitator of interfacial thermal transport reverses. Strong anharmonicity introduces significant intrinsic resistance, overruling the enhancement in thermal conduction at the boundaries. It follows that at a particular temperature, there exists a corresponding junction thickness at which thermal conductance is maximized.
TL;DR: It is concluded that the light and dark mechanisms are additive, with photoexcited carriers transported without thermal activation for a thickness range of 5-10 nm, and Photostimulated resonant transport potentially widens the breadth of conceivable molecular electronic devices and may have immediate value for wavelength-specific photodetection.
Abstract: Molecular electronic junctions consisting of nitroazobenzene oligomers covalently bonded to a conducting carbon surface using an established “all-carbon” device design were illuminated with UV–vis light through a partially transparent top electrode. Monitoring junction conductance with a DC bias imposed permitted observation of photocurrents while varying the incident wavelength, light intensity, molecular layer thickness, and temperature. The photocurrent spectrum tracked the in situ absorption spectrum of nitroazobenzene, increased linearly with light intensity, and depended exponentially on applied bias. The electronic characteristics of the photocurrent differed dramatically from those of the same device in the dark, with orders of magnitude higher conductance and very weak attenuation with molecular layer thickness (β = 0.14 nm–1 for thickness above 5 nm). The temperature dependence of the photocurrent was opposite that of the dark current, with a 35% decrease in conductance between 80 and 450 K, whi...
07 Oct 2019
TL;DR: The results suggest that it would be helpful to explore different experimental techniques such as recognition tunneling and conditions to help identify the nature of amino-acid-based junctions even further, with the goal to establish a firm platform for their unambiguous recognition by tunneling break-junction experiments.
Abstract: We studied the electron-transport properties of ten different amino acids and one dimer (di-methionine) using the mechanically controlled break-junction (MCBJ) technique. For methionine and cysteine, additional measurements were performed with the scanning tunneling microscope break-junction (STM-BJ) technique. By means of a statistical clustering technique, we identified several conductance groups for each of the molecules considered. Ab initio calculations revealed that the observed broad conductance distribution stems from the possibility of various binding geometries which can be formed during stretching combined with a multitude of possible conformational changes. The results suggest that it would be helpful to explore different experimental techniques such as recognition tunneling and conditions to help identify the nature of amino-acid-based junctions even further, for example, with the goal to establish a firm platform for their unambiguous recognition by tunneling break-junction experiments.
TL;DR: Investigation of the behavior of pristine graphene and defect engineered graphene membranes for ionic conductance and selectivity concludes that pristine graphene is fairly selective and the conductance is mainly due to protons.
Abstract: Inspired by recent reports on possible proton conductance through graphene, we have investigated the behavior of pristine graphene and defect engineered graphene membranes for ionic conductance and selectivity with the goal of evaluating a possibility of its application as a proton selective membrane. The averaged conductance for pristine chemical vapor deposited (CVD) graphene at pH1 is ∼4 mS/cm2 but varies strongly due to contributions from the unavoidable defects in our CVD graphene. From the variations in the conductance with electrolyte strength and pH, we can conclude that pristine graphene is fairly selective and the conductance is mainly due to protons. Engineering of the defects with ion beam (He+, Ga+) irradiation and plasma (N2 and H2) treatment showed improved areal conductance with high proton selectivity mostly for He-ion beam and H2 plasma treatments, which agrees with primarily vacancy-free type of defects produced in these cases confirmed by Raman analysis.
TL;DR: The large chemical modulation for the meta-connected series is not apparent for the para-series, showing the competition between (i) meta-connectivity quantum interference phenomena and (ii) the ability of the pyrrolic nitrogen to facilitate conductance, that can be modulated by chemical substitution.
Abstract: A key area of activity in contemporary molecular electronics is the chemical control of conductance of molecular junctions and devices. Here we study and modify a range of pyrrolodipyridines (carbazole-like) molecular wires. We are able to change the electrical conductance and quantum interference patterns by chemically regulating the bridging nitrogen atom in the tricyclic ring system. A series of eight different N-substituted pyrrolodipyridines has been synthesized and subjected to single-molecule electrical characterization using an STM break junction. Correlations of these experimental data with theoretical calculations underline the importance of the pyrrolic nitrogen in facilitating conductance across the molecular bridge and controlling quantum interference. The large chemical modulation for the meta-connected series is not apparent for the para-series, showing the competition between (i) meta-connectivity quantum interference phenomena and (ii) the ability of the pyrrolic nitrogen to facilitate conductance, that can be modulated by chemical substitution.
TL;DR: In this paper, trans-Ru(dppe)2 (dppe = 1,2-bis(diphenylphosphino)ethane) was implanted into oligoynyl chains with various number of ethynyl groups to construct Au-molecule-Au junctions using methylthiol (−SMe) as anchoring groups.
Abstract: To unveil the influence of metal coordination on charge transport and length-dependent conductance attenuation in π-conjugated organic molecules, trans-Ru(dppe)2 (dppe = 1,2-bis(diphenylphosphino)ethane) was implanted into oligoynyl chains with various number of ethynyl groups to construct Au–molecule–Au junctions using methylthiol (−SMe) as anchoring groups. The single-molecule conductance measured by I(s) method gave high and low values of conductance. A direct comparison of the conductance indicates that implanting trans-Ru(dppe)2 moiety into π-conjugated oligoynyl chains results in 2.6- to 5.8-fold enhancement of the conductance although the molecular length is increased by ca. 0.25 nm as a result of Ru insertion. More importantly, implanting trans-Ru(dppe)2 moiety into π-conjugated oligoynyl chains alleviates dramatically length-dependent conductance attenuation in view of the much smaller conductance decay constants for ruthenium(II)-implanted molecules (2.6 nm–1 for high value and 2.5 nm–1 for low ...
TL;DR: In this case, the conductance measured between these two fixed points on the antibody does not change with gap size, yielding an estimated electronic decay length >6 nm, long enough that it is not possible to distinguish between an exponential or a hyperbolic distance dependence.
Abstract: Antibodies have two identical binding domains and can therefore form a well-defined conducting bridge by binding a pair of electrodes functionalized with an epitope. The conductance measured between these two fixed points on the antibody does not change with the size of the electrode gap. A second conduction path is via one specific attachment to an epitope and a second nonspecific attachment to the surface of the antibody. In this case, the conductance does change with gap size, yielding an estimated electronic decay length >6 nm, long enough that it is not possible to distinguish between an exponential or a hyperbolic distance dependence. This decay length is substantially greater than that measured for hopping transport in an organic molecular wire.
TL;DR: In this article, the condition on the commensurability of the Fermi momenta of different channels and the strength of the interactions resulting in such remarkable phenomena are explored using Abelian bosonization.
Abstract: We study one-dimensional clean systems with few channels and strong electron-electron interactions. We find that in several circumstances, even when time-reversal symmetry holds, they may lead to two-terminal fractional quantized conductance and fractional shot noise. The condition on the commensurability of the Fermi momenta of the different channels and the strength of the interactions resulting in such remarkable phenomena are explored using Abelian bosonization. Finite temperature and length effects are accounted for by a generalization of the Luther-Emery refermionization at specific values of the interaction strength, in the strongly interacting regime. We discuss the connection of our model to recent experiments in a confined two-dimensional electron gas, featuring possible fractional conductance plateaus, including situations with a zero magnetic field, when time-reversal symmetry is conserved. One of the most dominant observed fractions, with two-terminal conductance equal to $\frac{2}{5}({e}^{2}/h)$, is found in several scenarios of our model. Finally, we discuss how at very small energy scales the conductance returns to an integer value and the role of disorder.
TL;DR: The development of high-speed SICM is presented, where temporal resolution 100-fold higher than that of conventional systems is achieved, together with spatial resolution around 20 nm.
Abstract: Scanning ion conductance microscopy (SICM) can image the surface topography of specimens in ionic solutions without mechanical probe-sample contact. This unique capability is advantageous for imaging fragile biological samples but its highest possible imaging rate is far lower than the level desired in biological studies. Here, we present the development of high-speed SICM. The fast imaging capability is attained by a fast Z-scanner with active vibration control and pipette probes with enhanced ion conductance. By the former, the delay of probe Z-positioning is minimized to sub-10 µs, while its maximum stroke is secured at 6 μm. The enhanced ion conductance lowers a noise floor in ion current detection, increasing the detection bandwidth up to 100 kHz. Thus, temporal resolution 100-fold higher than that of conventional systems is achieved, together with spatial resolution around 20 nm.
TL;DR: In this article, a series of quantized conductance steps within strongly interacting electron waveguides formed at the LaAlO/SrTiO$_3$ interface were observed.
Abstract: The ability to create and investigate composite fermionic phases opens new avenues for the investigation of strongly correlated quantum matter. We report the experimental observation of a series of quantized conductance steps within strongly interacting electron waveguides formed at the LaAlO$_3$/SrTiO$_3$ interface. The waveguide conductance follows a characteristic sequence within Pascal's triangle: $(1, 3, 6, 10, 15, ...)\cdot e^2/h$, where $e$ is the electron charge and $h$ is the Planck constant. The robustness of these steps with respect to magnetic field and gate voltage indicate the formation of a new family of degenerate quantum liquids formed from bound states of $n = 2, 3, 4, ...$ electrons. These experiments could provide solid-state analogues for a wide range of composite fermionic phases ranging from neutron stars to solid-state materials to quark-gluon plasmas.
TL;DR: This work explores the electrical properties of a molecule with bidentate anchor groups, namely 4,4'-(1,4-phenylenebis(ethyne-2,1-diyl))bis(pyridin-2-amine), in both large area devices and at the single molecule level.
Abstract: When a molecule is bound to external electrodes by terminal anchor groups, the latter are of paramount importance in determining the electrical conductance of the resulting molecular junction. Here we explore the electrical properties of a molecule with bidentate anchor groups, namely 4,4′-(1,4-phenylenebis(ethyne-2,1-diyl))bis(pyridin-2-amine), in both large area devices and at the single molecule level. We find an electrical conductance of 0.6 × 10−4G0 and 1.2 × 10−4G0 for the monolayer and for the single molecule, respectively. These values are approximately one order of magnitude higher than those reported for monodentate materials having the same molecular skeleton. A combination of theory and experiments is employed to understand the conductance of monolayer and single molecule electrical junctions featuring this new multidentate anchor group. Our results demonstrate that the molecule has a tilt angle of 30° with respect to the normal to the surface in the monolayer, while the break-off length in the single molecule junction occurs for molecules having a tilt angle estimated as 40°, which would account for the difference in their conductance values per molecule. The bidentate 2-aminepyridine anchor is of general interest as a contact group, since this terminal functionalized aromatic ring favours binding of the adsorbate to the metal contact resulting in enhanced conductance values.
18 Nov 2019
TL;DR: In this article, the thermal boundary conductance (TBC) between copper and carbon crystals is controlled, since it can bottleneck the thermal conductivity when reinforcing copper with carbon-crystals fill.
Abstract: Controlling the thermal boundary conductance (TBC) between copper and carbon crystals is important since it can bottleneck the thermal conductivity when reinforcing copper with carbon-crystals fill...
TL;DR: The atomic origin of the conductance features in the single perovskite quantum dot junctions are revealed, and direct evidence of the room-temperature quantum interference effects is presented.
Abstract: The studies of quantum interference effects through bulk perovskite materials at the Angstrom scale still remain as a major challenge. Herein, we provide the observation of room-temperature quantum interference effects in metal halide perovskite quantum dots (QDs) using the mechanically controllable break junction technique. Single-QD conductance measurements reveal that there are multiple conductance peaks for the CH3NH3PbBr3 and CH3NH3PbBr2.15Cl0.85 QDs, whose displacement distributions match the lattice constant of QDs, suggesting that the gold electrodes slide through different lattice sites of the QD via Au-halogen coupling. We also observe a distinct conductance 'jump' at the end of the sliding process, which is further evidence that quantum interference effects dominate charge transport in these single-QD junctions. This conductance 'jump' is also confirmed by our theoretical calculations utilizing density functional theory combined with quantum transport theory. Our measurements and theory create a pathway to exploit quantum interference effects in quantum-controlled perovskite materials.
TL;DR: It is observed that the current levels between the two conductance states are separated by 2 orders of magnitude, but in a real-time measurement, only unidirectional switching behavior from the open to the closed state is observed.
Abstract: We fabricate and characterize vertical molecular junctions consisting of self-assembled monolayers of diarylethene (DAE) contacted by a multilayer graphene (MLG) electrode on the top and gold on the bottom. The DAE molecular junctions show two stable electrical states, a closed state (high conductance) or an open state (low conductance), which are created upon illumination with UV or visible light, respectively. For the Au-DAE-MLG junction structure, we observe that the current levels between the two conductance states are separated by 2 orders of magnitude. However, in a real-time measurement, we observe only unidirectional switching behavior from the open to the closed state.
TL;DR: It is found that DQI is almost entirely overcome by adding a bridging carbonyl, to yield a cross-conjugated fluorenone in meta-connected 1,1'-biphenyl-containing molecules, which contrasts with other π-systems, such as para-connected anthraquinone, where cross- Conjugation results in low conductance.
Abstract: Charge transport is strongly suppressed by destructive quantum interference (DQI) in meta-connected 1,1′-biphenyl-containing molecules, resulting in low electrical conductance. Surprisingly, we have found that DQI is almost entirely overcome by adding a bridging carbonyl, to yield a cross-conjugated fluorenone. This contrasts with other π-systems, such as para-connected anthraquinone, where cross-conjugation results in low conductance.
TL;DR: In this paper, the third generation fluoroquinolone antibiotic drug Levofloxacin hemihydrate (LFH) with the naturally occurring polyol i.e. sorbitol as a function of temperature have been investigated by volumetric, acoustic and conductance methods.
TL;DR: In this paper, the authors investigated the single-molecule electrical conductance of alkane rings connected to gold electrodes and demonstrated that their logarithmic conductances are ocillatory functions of length.
Abstract: We investigate the single-molecule electrical conductance of alkane rings connected to gold electrodes and demonstrate that their logarithmic conductances are ocillatory functions of length. This contrasts with the logarithmic conductances of alkane chains, which decay linearly with length. This non-classical behaviour is attributed to conformational effects in the alkane rings, which tend to be more (less) planar when their branches contain even (odd) numbers of CH2 groups. Surprisingly the conductances of alkane rings with two parallel conductance paths are predicted to be lower then those of the corresponding linear chains with only one conductance path.