Conductance Fluctuations Research Articles

Coherent Hole Transport in Selective Area Grown Ge Nanowire Networks.

Holes in germanium nanowires have emerged as a realistic platform for quantum computing based on spin qubit logic. On top of the large spin–orbit coupling that allows fast qubit operation, nanowire geometry and orientation can be tuned to cancel out charge noise and hyperfine interaction. Here, we demonstrate a scalable approach to synthesize and organize Ge nanowires on silicon (100)-oriented substrates. Germanium nanowire networks are obtained by selectively growing on nanopatterned slits in a metalorganic vapor phase epitaxy system. Low-temperature electronic transport measurements are performed on nanowire Hall bar devices revealing high hole doping of ∼1018 cm–3 and mean free path of ∼10 nm. Quantum diffusive transport phenomena, universal conductance fluctuations, and weak antilocalization are revealed through magneto transport measurements yielding a coherence and a spin–orbit length of the order of 100 and 10 nm, respectively.

Correlated carrier dynamics in a superconducting van der Waals heterostructure

A study of Berezinskii–Kosterlitz–Thouless transitions in clean, layered two-dimensional superconductors promises to provide insight into a host of novel phenomena like re-entrant vortex-dynamics, underlying unconventional metallic phases, and topological superconductivity. In this Letter, we report the study of charge carrier dynamics in a novel two-dimensional superconducting van der Waals heterostructure comprising of monolayer MoS2 and few-layer NbSe2 (∼15 nm). Using low-frequency conductance fluctuation spectroscopy, we show that the superconducting transition in the system is percolative. We present a phenomenological picture of different phases across the transition correlating with the evaluated noise. The analysis of the higher order statistics of fluctuation reveals non-Gaussian components around the transition indicative of long-range correlation in the system.

Magnetotransport due to conductivity fluctuations in non-magnetic ZrTe2 nanoplates

Transition metal dichalcogenides with nontrivial band structures exhibit various fascinating physical properties and have sparked intensive research interest. Here, we perform systematic magnetotransport measurements on ZrTe2 nanoplates prepared by mechanical exfoliation. We reveal that the negative longitudinal magnetoresistivity observed in the strong field region in the presence of parallel electric and magnetic fields could stem from conductivity fluctuations caused by excess Zr in the nanoplates. In addition, the parametric plot, which shows the planar Hall resistivity as a function of the in-plane anisotropic magnetoresistivity, has an ellipse-shaped pattern with a shifted orbital center, which further strengthens the evidence for the conductivity fluctuations. Our work provides some useful insights into transport phenomena in topological materials.

Coherent Structures at the Interface between Water Masses of Confluent Rivers

The paper presents the results of field measurements and numerical modeling of the influence of various factors on the formation of coherent structures in the confluence zone of the Sylva and Chusovaya rivers, which are dammed by the Kamskaya Hydroelectric Power Station (HPS). A characteristic feature of the measured parameters in the zone under study is that they experience both seasonal fluctuations and fluctuations of much higher frequency associated with intraday regulation of the HPS operation. These intraday fluctuations give rise to coherent structures with periodicity T~2–10 min, which manifest themselves in the fluctuations of the specific electrical conductivity of water. The flow velocity also experiences significant fluctuations with a sufficiently wide frequency spectrum, although the characteristic period of its fluctuations is less than the period of electrical conductivity fluctuations and is equal to ~1 min. In order to study the features of the formation of such structures, numerical simulation was carried out within the framework of the three-dimensional approach. Calculations were performed for a 300-meter-long stretch of the Chusovaya River, which is located downstream of the confluence of Chusovaya and Sylva rivers and is the site of the Chusovskoy water intake of Perm city. It was found that the intraday irregularity of HPS operation gives rise to the occurrence of vortex structures in this layer, leading to the temporal variation of concentration at a given point of space and the formation of the wave structure of the concentration field at different moments of time. Time period and spatial scale of such vortex structures depend on the ratio of velocities of water masses and difference in their mineralization and, accordingly, in densities. Moreover, the period of fluctuations is proportional to the ratio of flow velocities. These estimations are of fundamental importance for the implementation of stable selective intake of water with required consumer properties under conditions of intraday irregularity of hydroelectric power station operation.

Nanoconfined SnS2 in robust SnO2 nanocrystals building heterostructures for stable sodium ion storage

Transition-metal dichalcogenides are emerging as a class of attractive host materials for Na+ insertion, owing to its high theoretical specific capacity, whereas the intrinsic low conductivity and huge volume fluctuations during deep cycles severely restrict their practical applications. Heterostructure engineering can not only optimize ion transport kinetics to boost rate property but confine mechanical degradation by participation of the second phases. In order to cushion the internal stress and dramatic volume variations induced by the large radius of Na+, herein we introduced a more robust material (SnO2) to construct CC@SnS2/SnO2 heterostructure for sodium-ion batteries (SIBs). The experimental and density functional theory calculations indicate that compressive stress at the heterogeneous interface can effectively buffer the sodiation-induced internal strain by 10%, further maintain the structural stability and improve the cycling performances. Meanwhile, the involvement of inert SnO2 phase, which effectively alleviate the serious volume expansion caused by the active SnS2 upon an extensive sodiation/desodiation process. As expected, the CC@SnS2/SnO2 composite exhibits high reversible capacity (694.7 mAh g−1 at 0.2 A g−1) and long-term cycling retention (78.3% after 100 cycles). Our work inspire a pathway of the selection of heterogeneous materials toward a highly stable SIBs anode.

Regional Differences in Sympathetic Nerve Activity Are Generated by Multiple Arterial Baroreflex Loops Arranged in Parallel.

In this review, by evaluating the responses during freezing, rapid eye movement (REM) sleep, and treadmill exercise, we discuss how multiple baroreflex loops arranged in parallel act on different organs to modulate sympathetic nerve activity (SNA) in a region-specific and coordinated manner throughout the body. During freezing behaviors, arterial pressure (AP) remains unchanged, heart rate (HR) persistently decreases, renal SNA (RSNA) increases, and lumbar SNA (LSNA) remains unchanged. The baroreflex curve for RSNA shifts upward; that for LSNA remains unchanged; and that for HR shifts to the left. These region-specific changes in baroreflex curves are responsible for the region-specific changes in RSNA, LSNA, and HR during freezing. The decreased HR could allow the heart to conserve energy, which is offset by the increased RSNA caused by decreased vascular conductance, resulting in an unchanged AP. In contrast, the unchanged LSNA leaves the muscles in readiness for fight or flight. During REM sleep, AP increases, RSNA and HR decrease, while LSNA is elevated. The baroreflex curve for RSNA during REM sleep is vertically compressed in comparison with that during non-REM sleep. Cerebral blood flow is elevated while cardiac output is decreased during REM sleep. To address this situation, the brain activates the LSNA selectively, causing muscle vasoconstriction, which overcomes vasodilation of the kidneys as a result of the decreased RSNA and cardiac output. Accordingly, AP can be maintained during REM sleep. During treadmill exercise, AP, HR, and RSNA increase simultaneously. The baroreflex curve for RSNA shifts right-upward with the increased feedback gain, allowing maintenance of a stable AP with significant fluctuations in the vascular conductance of working muscles. Thus, the central nervous system may employ behavior-specific scenarios for modulating baroreflex loops for differential control of SNA, changing the SNA in a region-specific and coordinated manner, and then optimizing circulatory regulation corresponding to different behaviors.

Modulating electronic structure of metal-organic frameworks derived zinc manganates by oxygen vacancies for superior lithium storage

Electronic structure manipulation of transition metal oxides in crystal lattices renders as a prevailing methodology for high-performance Lithium-ion battery (LIB) electrodes. Thereinto, oxygen defective oxides can self-adaptively regulate the electronic property and active sites to reconcile the subpar electronic conductivity and substantial volume fluctuation. Herein, a conceptual protocol for constructing oxygen vacancies enriched ZnMn2O4 derived from various Zn-Mn-based Metal-organic frameworks (MOFs) is proposed as versatile anode materials towards lithium storage. Experimental implementation and theoretical calculation systematically unravel that the enriched OV is conducive to boosted electronic conductivity, extra active sites, preferable Li+ adsorption, and accelerated diffusion kinetics of OV-ZMOs. As expected, all the OV-ZMOs derived from dicarboxybenzene-, tricarboxybenzene-, and isonicotinic-based Zn-Mn-MOFs (BDC-OV-ZMO, BTC-OV-ZMO, and IN-OV-ZMO) achieve exalted electrochemical performance with superior specific capacity, distinguished rate capacity, and pre-eminent cyclability. This work envisions a conceptual vacancy protocol for MOF-derived electrode materials for LIBs.

Quantum Signatures in Quench from Chaos to Superradiance.

The driven-dissipative Dicke model features normal, superradiant, and lasing steady states that may be regular or chaotic. We report quantum signatures of chaos in a quench protocol from the lasing states. Within the framework of a classical mean-field perspective, once quenched, the system relaxes either to the normal or to the superradiant state. Quench from chaos, unlike quench from a regular lasing state, exhibits erratic dependence on control parameters. In the quantum domain, this sensitivity implies an effect that is similar to universal conductance fluctuations.

Detecting Magnetic Permeability and Electrical Conductivity Fluctuations in Metallic Ferromagnetic Sheets through the Shielding Effect

In this report, a method is proposed for determining the fluctuations of physical and structural properties in metallic ferromagnetic samples by magnetic scanning. The method is based on the shielding of a circular loop electromagnetic field source using a ferromagnetic and metallic sheet. The shielding of the electromagnetic field depends on the field frequency and amplitude as well as the electrical conductivity and magnetic permeability of the sheet. The proposed method does not require winding around the sheet. The experimental AC shielding results are reported.

Effect of high pressure on temperature dependences of the resistivity in the ab-plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals

In the present work, we investigated the influence of high hydrostatic pressure up to 11 kbar on the conductivity in the basal ab-plane of medium-doped with praseodymium (x≈0.23) single-crystal Y1-xPrxBa2Cu3O7-δ samples. It was determined that, in contrast to the pure YBa2Cu3O7-δsamples with the optimal oxygen content, the application of high pressure leads to the formation of phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. Possible mechanisms of the effect of Pr doping and high pressure on the two-step resistive transition to the superconducting state are discussed. It was determined that in the normal state, the conductivity is metallic and is limited by phonons scattering (Bloch-Grüneisen regime) and defects. The fluctuation conductivity is considered within the Lorentz-Doniach model. Hydrostatic pressure, accompanied by a decrease in anisotropy, leads to a decrease in the residual and phonon resistances. Debye temperature and coherence length are independent of pressure. The applicability of the McMillan formula in the presence of significant anisotropy is discussed.

Ultrasmall metal (Fe, Co, Ni) nanoparticles strengthen silicon oxide embedded nitrogen-doped carbon superstructures for long-cycle-life Li-ion-battery anodes

A universal electrospray-carbonization approach to prepare ternary metal/SiO x /nitrogen-doped carbon (NC) superstructures is proposed, where metal (Fe, Co, Ni, CoNi, FeNi, FeCo and FeCoNi) and small SiO x nanoparticles (NPs) are homogeneously distributed in NC matrix. Metal greatly promotes the electrochemical activity and stability of the SiO x system, which can be considered as high-performance Li-ion-battery anodes. • Metal/SiO x /nitrogen-doped carbon superstructures are designed as LIB anodes. • Nitrogen-doped carbon inhibits the gathering of SiO x and relieves its strain. • Ultrasmall Ni nanoparticles and nitrogen-doped carbon improve the kinetics of SiO x . • The strategy to prepare multiple SiO x - or metal-based composites is universal. For silicon oxides (SiO x ) as a prospective Li-ion-battery anode material, the low inherent conductivity and huge volume fluctuation during cycling immensely limit their electrochemical performance. Herein, a universal electrospray-carbonization approach to prepare ternary metal/SiO x /nitrogen-doped carbon (NC) superstructures is proposed. Accordingly, metal (Fe, Co, Ni, CoNi, FeNi, FeCo and FeCoNi) nanoparticles (NPs) and small SiO x NPs derived from rice husks (RHs) are homogeneously distributed in the NC matrix. Metal (Fe, Co, Ni) NP-embedded NC frameworks avoid the accumulation, increase the conductivity and accommodate adequent volume expansion of SiO x NPs. This results in an enhanced rate capability and excellent cycle stability upon cycling. Besides, Ni/SiO x /NC (NSC) superstructures with ultra-small Ni NPs can exhibit better electrochemical kinetics for fast diffusion of ions and charge transfer and cyclability than Co/SiO x /NC (CSC) and Fe/SiO x /NC (FSC) composites. When NSC superstructures are employed as lithium-ion battery (LIB) anodes, superior specific capacities of 757.5 mA h g −1 at the 200th cycle, as well as superb long cyclability with discharge capacities of 665.0 mA h g −1 for 500 cycles at 500 mA g −1 and 116.3 mA h g −1 at the 5000th cycle, even at 10 A g −1 , are achieved. Furthermore, the easy and general approach for preparing multiple SiO x -, metal- or alloy-based superstructures paves the way for designing high-performance rechargeable batteries and electrocatalysts.

Dynamo chiral plasma instabilities from charges and oscillations driven by torsion fluctuations

Recently, Barrow et al. showed that chaotic dynamical systems may be obtained from small fluctuations of torsion in cosmological plasmas. Following this idea our goal in this paper is to show analytically that torsion fluctuations in primordial plasmas induce chiral fluctuations, magnetic field fluctuations, dynamo plasma instabilities, as well as rapid oscillations in the chiral plasma. These phenomena are important in plasma relaxation to allow for a plasma dynamo instability to induce a lower electric voltage in plasmas. This phenomenon is induced in Minkowskian plasma physics, but to our knowledge it is proved for the first time in Einstein–Cartan sort of cosmology. In cosmological models where torsion gravity and electromagnetic fields are non-minimally coupled, dynamo instability is obtained when conductivity fluctuations are driven by torsion. Moreover, symmetry breaking of plasmas is shown here to be obtained from conductivity torsion fluctuations, which serves to bypass Zeldovich anti-dynamo theorem, inducing a dynamo onset, as shown recently in domain planar walls [L. Garcia de Andrade, Einstein–Cartan spin-polarised nucleons in domain wall dynamos, Ann Phys. (N.Y.) 432 (2021) 168558.]. Moreover, chiral charge fluctuations are shown to be induced by torsion fluctuations. It is shown that chiral charges may vanish, whereas the effective chiral charges may be driven by torsional fluctuations. It is also shown that dynamo electric field induces a magnetic helicity which oscillates and dynamo action is shown to dominate oscillations. This agrees with the results obtained from loop voltage. Chiral effective charges’ fluctuations are derived to be proportional to the product of anisotropic conductivity and magnetic field fluctuations.

Relating thermal conductivity of soil skeleton with soil texture by the concept of “local thermal conductivity fluctuation”

The thermal conductivity of the soil skeleton λs is an essential parameter from the point of view of the correct assessment of soil overall/effective conductivity. This work introduces the concept of “local thermal conductivity fluctuation” which characterizes the microscale variation of conductivity within the solid phase. It is proposed to link the “local fluctuation” of thermal conductivity λ with the soil texture – the information that is available at the scale of engineering applications. It was possible to relate the skeleton thermal conductivity with the grain size distribution of the soil. Finally, based on a large series of numerical simulations, the paper provides four triangle diagrams (at different organic matter contents: 0%, 2%, 4% and 6%) relating the value of λs with volume fraction of individual soil separates. This result is extremely important from the practical point of view. One can quickly evaluate λs value provided that information on the grain size distribution and organic matter content is available.

Large Linear Magnetoresistance and Evidence of Degeneracy Lifting of Valence Bands in Rhombohedral Phase of Topological Crystalline Insulator SnTe

A comprehensive magnetotransport study on a p‐type single crystal of SnTe topological crystalline insulator is reported, across the cubic‐to‐rhombohedral (R3m) transition atTs≈64 K. SnTe exhibits a large unsaturated linear magnetoresistance (LMR) reaching a value of 42% at 5 K and 8 T for (100) plane. LMR is found to have a direct dependence on the mobility and a detailed analysis shows that it follows the classical Parish‐Littlewood model of conductivity fluctuations arising from macroscopic inhomogeneities of tellurium interstitial atoms. Profound SdH oscillations having aπBerry phase are observed in the rhombohedral (R3m) phase having significantly lower carrier density ≈5.32 × 1011 cm−2at 2 K, which provides direct evidence of protected topological surface states in theR3mphase. The Hall conductivity shows a transformation from one band to two‐band behavior across the structural transition, thus providing an experimental evidence for the degeneracy lifting of bulk valence bands below the cubic symmetry breaking point which is consistent with recent band structure calculations. The overall results indicate that magnetotransport studies can distinctly probe the surface and bulk sensitive properties of SnTe, and can also track the band‐splitting of degenerate bands across the cubic‐to‐rhombohedral (R3m) transition.

The molecular origin of the electrostatic gating of single-molecule field-effect biosensors investigated by molecular dynamics simulations.

Field-effect biosensors (bioFETs) offer a novel way to measure the kinetics of biomolecular events such as protein function and DNA hybridization at the single-molecule level on a wide range of time scales. These devices generate an electrical current whose fluctuations are correlated to the kinetics of the biomolecule under study. BioFETs are indeed highly sensitive to changes in the electrostatic potential (ESP) generated by the biomolecule. Here, using all-atom solvent explicit molecular dynamics simulations, we further investigate the molecular origin of the variation of this ESP for two prototypical cases of proteins or nucleic acids attached to a carbon nanotube bioFET: the function of the lysozyme protein and the hybridization of a 10-nt DNA sequence, as previously done experimentally. Our results show that the ESP changes significantly on the surface of the carbon nanotube as the state of these two biomolecules changes. More precisely, the ESP distributions calculated for these molecular states explain well the magnitude of the conductance fluctuations measured experimentally. The dependence of the ESP with salt concentration is found to agree with the reduced conductance fluctuations observed experimentally for the lysozyme, but to differ for the case of DNA, suggesting that other mechanisms might be at play in this case. Furthermore, we show that the carbon nanotube does not impact significantly the structural stability of the lysozyme, corroborating that the kinetic rates measured using bioFETs are similar to those measured by other techniques. For DNA, we find that the structural ensemble of the single-stranded DNA is significantly impacted by the presence of the nanotube, which, combined with the ESP analysis, suggests a stronger DNA-device interplay. Overall, our simulations strengthen the comprehension of the inner working of field-effect biosensors used for single-molecule kinetics measurements on proteins and nucleic acids.

Detailed impedance and electrical studies of Zr4+ doped La0.7Ca0.3 (Mn0.5 Fe0.5) O3 for cathode materials in solid oxide fuel cells

The solid state reaction approach was used to prepare the (La0.7Ca0.3)(Mn0.5Fe0.5)1-xZrxO3 (where × = 0.1 and 0.5) system for use as a cathode in solid oxide fuel cells. The impedance and electrical properties have been investigated. The ac impedance spectra of the samples show a grain boundary contribution to total conductivity and diffusion controlled impedance. A wide range impedance spectroscopy research from 50 to 200 °C revealed both bulk and grain boundary effects. At higher temperatures, oxygen vacancies could be used as ionic charge carriers, indicating an Arrhenius-type thermally activated process. The hopping mechanism for electrical processes in the system was shown by the fluctuation in ac conductivity as a function of frequency.

Correlation between skin conductance measurements and subjective pain scales in children after otolaryngological procedures

Abstract Introduction Pain assessment in children is crucial in managing postoperative analgesia; it is therefore necessary to determine the most accurate tool for assessing pain in children. The aim of this study was to evaluate the correlation between skin conductance measurements and self-reporting pain scales in children after otolaryngology procedures. Materials and methods Thirty-three children (N=33) were assessed for eligibility for the research. Postoperative pain was assessed using the Visual Analogue Scale; the Wong-Baker Faces Pain Rating Scale; the Face, Legs, Activity, Cry, and Consolability scale; and a skin conductance algesimeter. The postoperative pain was measured 1 and 2 hours after the surgery. Results There was no statistically significant correlation between self-reported pain scores and the skin conductance fluctuations in the children studied, regardless of gender or age. A statistically significant correlation was found between the existing subjective pain scales in children. Conclusions The skin conductance measurements do not provide an additional reliable tool for assessing pain in patients after otolaryngological procedures. The existing self-reported pain scales are sufficient to assess postoperative pain in children.

Resistive Switching Devices Producing Giant Random Telegraph Noise

Resistive switching (RS) has been studied for several applications such as information storage and bio-inspired computing, although reliability issues still prevent their massive use. In this work, we present a novel observation of trapping activity that imposes giant random conductance fluctuations, up to 3 orders of magnitude, resembling RTN in RS devices based on TiO2, HfO2 and hexagonal boron nitride (h-BN) under reading voltages (~ 0.1 V). These events appeared reproducible for all the aforementioned RS device types in sequential measurements and under different bias. This behavior is very beneficial to ensure recognition of the device’s two-state in applications such as stochastic computing integrated circuits (ICs).

Statistical studies of Conductance Fluctuations in Quantum Dots

Statistical studies of Conductance Fluctuations in Quantum Dots

Analysis on the Transmission of International Oil Price to China’s Price Index--Based on Granger Causality Network

This paper uses complex network theory and Granger causality method to construct Granger Causality Network among price indices (PIGCN), specifically based on crude oil price and China’s domestic price index from a systematic perspective and provides a statistical physical method to analyze conduction fluctuations. This paper selects four typical price indices in China, including 36 sub price indices as samples for empirical research. Through the analysis of the PIGCN structure, we have analyzed the volatility transmission path of the international crude oil price and Chinese domestic price index, and further revealed the dynamic relationship among the price indices. Also, we have put forward some policy recommendations to better monitor the spread of price fluctuation risks.