Resistive Transition Research Articles

Spatial behavior in a Mott insulator near the voltage-driven resistive transition

We develop a real space theory of the voltage bias driven transition from a Mott insulator to a correlated metal. Within our Keldysh mean field approach the problem reduces to a self-consistency scheme for the charge and spin profiles in this open system. We solve this problem for a two dimensional antiferromagnetic Mott insulator at zero temperature. The charge and spin magnitude is uniform over the system at zero bias, but a bias $V$ leads to spatial modulation over a lengthscale $\xi(V)$ near the edges. $\xi(V)$ grows rapidly and becomes comparable to system size as $V$ increases towards a threshold scale $V_c$. The linear response conductance of the insulator is zero with the current being exponentially small for $V \ll V_c$. The current increases rapidly as $V \rightarrow V_c$. Beyond $V_c$, we observe an inhomogeneous low moment antiferromagnetic metal, and at even larger bias a current saturated paramagnetic metal. We suggest an approximate scheme for the spectral features of this nonequilibrium system.

Discontinuous plastic flow in superconducting multifilament composites

Modern superconducting intermetallic materials (e.g. NbTi, Nb3Sn) are used to build conductors composed of a matrix and the superconductor strands. One of the most popular materials for matrix is copper, because of its excellent physical and mechanical properties at extremely low temperatures. Ductile OFE copper stabilizes, on one hand, the mechanical response of brittle superconductor strands and, on the other hand, takes over the electrical charge in case of quench (resistive transition). Thus, the composite structure of modern conductors used to build the coils of superconducting magnets is fully justified. Such a composite structure results in common deformation of the matrix and the strands when winding the coils and during the operation, when the coils are subjected to the prestress and to the Lorentz forces at extremely low temperatures (liquid or superfluid helium). When the loads are large enough, the copper-superconductor strands composite is subjected to inelastic deformation, including moderately large plastic strains. It is known, that copper and superconductor strands exhibit the so-called discontinuous plastic flow (DPF) at extremely low temperatures, that results in abrupt drops of stress against strain of different amplitude and frequency. In order to describe correctly the behaviour of composite superconductors at extremely low temperatures, a constitutive model of DPF has been developed and applied to both components: matrix and strands. The results of numerical analysis are compared with the experiments, carried out in dedicated cryostat containing liquid helium and the relevant instruments.

Effects of Carbon Doping on Trapped Magnetic Field of MgB$_{2}$ Bulk Prepared by in-situ Hot Isostatic Pressing Method

We report the effects of carbon doping on the trapped field properties of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulks doped with graphite (C) and B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> C, which were prepared by an in-situ hot isostatic pressing method. The trapped fields, BT's were degraded by the graphite and B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> C doping above 15K, which was predominantly due to the lowered T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> by the C substitution. However, the slope of BT(T) and the irreversibility line, Birr(T), determined from the resistive transitions indicated that the BT of the graphite-doped bulk was expected to exceed that of the pristine bulk below 15 K. Contrary to the literature by other groups, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> C did not enhance the vortex pinning properties.

Simulation of the Thermal Performance of HTS Coated Conductors for HVDC SFCL

Within the EU-funded project FastGrid a resistive superconducting fault current limiter for DC-application is actually under development. To reduce substantially the amount of deployed superconducting tape an increase of voltage per length in the limitation case is needed. Moreover, the resistive transition (quench) should be fast and uniform. In the present work, the thermal behavior of three different architectures of coated conductors are investigated by means of transient simulations. The first architecture is composed by an additional Hastelloy shunt layer, which is supposed to avoid overheating of the conductor during fault limitation. The other architectures include layers of silver and copper as stabilizers. Our parameter study including the geometries of the different layers and the inhomogeneity of the critical current density of the superconducting tape shall lead to an optimized tape layout. First comparisons with experiment indicate, that, with the first architecture, electric field strength up to 100 V/m should be within reach.

Stable and Tunable Current-Induced Phase Transition in Epitaxial Thin Films of Ca2RuO4.

Owing to the recent discovery of the current-induced metal-insulator transition and unprecedented electronic properties of the concomitant phases of calcium ruthenate Ca2RuO4, it is emerging as an important material. To further explore the properties, the growth of epitaxial thin films of Ca2RuO4 is receiving more attention, as high current densities can be applied to thin-film samples and the amount can be precisely controlled in an experimental environment. However, it is difficult to grow high-quality thin films of Ca2RuO4 due to the easy formation of the crystal defects originating from the sublimation of RuO4; therefore, the metal-insulator transition of Ca2RuO4 is typically not observed in the thin films. Herein, a stable current-induced metal-insulator transition is achieved in the high-quality thin films of Ca2RuO4 grown by solid-phase epitaxy under high growth temperatures and pressures. In the Ca2RuO4 thin films grown by ex situ annealing at >1200 °C and 1.0 atm, continuous changes in the resistance of over 2 orders of magnitude are induced by currents with a precise dependence of the resistance on the current amplitude. A hysteretic, abrupt resistive transition is also observed in the thin films from the resistance-temperature measurements conducted under constant-voltage (variable-current) conditions with controllability of the transition temperature. A clear resistive switching by the current-induced transition is demonstrated in the current-electric-field characteristics, and the switching currents and fields are shown to be very stable. These results represent a significant step toward understanding the high-current-density properties of Ca2RuO4 and the future development of Mott-electronic devices based on electricity-driven transitions.

Low-Frequency Imaginary Impedance at the Superconducting Transition of 2H - NbSe2

The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature T$_c$. A superconductor exactly at T$_c$ is thus very sensitive to all kinds of thermal perturbations, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizeable imaginary impedance at frequencies of order of tens of Hz at the resistive transition of single crystals of the layered material 2H-NbSe$_2$. We explain the result using models developed for transition edge sensors. By measuring under magnetic fields and at high currents, we find that the imaginary impedance is strongly influenced by the heat associated with vortex motion and out-of-equilibrium quasiparticles.

Inhibition of Wnt/β-catenin pathway reverses multi-drug resistance and EMT in Oct4+/Nanog+ NSCLC cells

Cancer drug resistance and epithelial-mesenchymal transition (EMT), a critical process of cancer invasion and metastasis, have recently been associated with the existence of cancer stem cells (CSCs). However, there are no appropriate CSC-markers of non-small cell lung cancer (NSCLC)-associated drug resistance and EMT. It is unknown if and how the drug-resistant and EMT phenotypes in NSCLC cells link to specific stemness-related pathways. Here, we found a significant elevated expression of both Oct4 and Nanog in gefitinib-resistant NSCLC cells, which displayed multi-drug resistance (MDR) properties and exhibited EMT phenotype. Ectopic co-expression of Oct4/Nanog empowered NSCLC cells with cancer stem cell properties, including self-renewal, drug resistance, EMT and high tumorigenic capacity. Following molecular mechanism investigation indicated Oct4/Nanog-regulated drug resistance and EMT change through Wnt/β-catenin signaling activation. Moreover, silencing β-catenin abrogated Oct4/Nanog-mediated MDR and EMT process in NSCLC cells. Our findings propose Wnt/β-catenin pathway as a promising therapeutic target for the treatment of progression and metastasis of NSCLC with CSC-like signatures and epithelial-mesenchymal transition phenotype.

Self-powered forest fire alarm system based on impedance matching effect between triboelectric nanogenerator and thermosensitive sensor

Abstract As worldwide forest fire frequently causes a serious threat to forest resources and global climate change, novel early forest fire monitoring and detection technologies are urgently required to explore. Herein, a self-powered forest fire alarm system (FFAS) is proposed by coupling thermosensitive effect and triboelectric effect as an aim of effective forest fire monitoring and detecting. The FFAS is fabricated as a self-powered early forest fire monitoring and detection system by connecting a spherical free-standingmode triboelectric nanogenerator (S-TENG) as power source with polydopamine-modified graphene oxide (P-GO) as thermosensitive sensor and commercial LEDs as alarm. When encountering an open fire or abnormal high temperature the thermosensitive sensor based on P-GO can be in-situ thermally reduced, inducing an obvious transition in electrical resistance. Thus, the output voltage of S-TENG can be tuned by the impedance matching effect between special output characteristics of TENG and working status of thermosensitive sensor, and then can directly light up the LEDs as alarm. Furthermore, the FFAS achieves a low temperature response (160 °C), rapid response time (~3 s), and especially no external power supply. Consequently, the FFAS based on impedance matching effect between TENG and thermosensitive sensor would provide a real-time, rapidly responsive, and self-powered monitoring strategy for the early forest fire warning and detection.

Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov State with Segmented Vortices in the BCS-BEC-Crossover Superconductor FeSe.

We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35T applied parallel to the ab plane. At low temperatures, the upper critical field μ_{0}H_{c2}^{ab} shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at μ_{0}H^{*}≈24 T well below μ_{0}H_{c2}^{ab}, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe.

Study of TES Detector Transition Curve to Optimize the Pixel Design for Frequency-Division Multiplexing Readout

Superconducting transition-edge sensors (TESs) are highly sensitive detectors. Based on the outstanding performance on spectral resolution, the X-ray integral field unit (X-IFU) instrument on-board athena will be equipped with a large array of TES-based microcalorimeters. For optimal performance in terms of the energy resolution, it is essential to limit undesirable nonlinearity effects in the TES detector. Weak-link behavior induced on the TES by superconducting leads is such a nonlinearity effect. We designed and fabricated smart test structures to study the effect of the superconducting leads on the intrinsic transition curve of our TiAu-based TES bilayer. We measured and analyzed the resistance versus temperature transition curves of the test structures. We found relations of long-distance proximity effects with TES length and different lead materials. Based on these results, we can redesign and further optimize our TES-based X-ray detectors.

Electrical Resistivity and Structure of Cu-Pb Alloy during Cooling Process

The variations of electrical resistivity and cooling curve for monotectic Cu-Pb alloy have been measured from liquid state to ambient temperature. The structural transitions were discussed during cooling process. And the correlations between the variations of electrical resistivity, heat and structural transitions were also investigated. The linear relationship between the electrical resistivity and temperature curves in liquid state means there is no structural change in liquid Cu-Pb alloy. And during the solidification process, the electrical resistivity and cooling curves change with the occurrence of new phases.

Structure and properties of barrier-free MgB2 composite wires made by internal magnesium diffusion process

Barrier-free MgB2 wires with four different metallic sheaths, Nb, Fe, Ni and stainless steel, respectively, were fabricated by the internal magnesium diffusion into boron process. It was shown that mechanical strength of metallic sheath affects the B powder density and consequently also the kinetics of MgB2 phase formation. While no interaction has been found at the MgB2/Nb interface after final heat treatment at 650 °C/30 min, reaction layers of 0.8–5.0 μm were created in wires with the other sheaths. Different shapes of the resistive transitions have been observed due to differences in the boron densification and consequent Mg diffusion kinetics, which affect the purity of the created MgB2 phase. Electrical measurements have shown the highest current densities for the mechanically softest Nb sheathed wire and the lowest ones for SS sheathed wire. This is attributed to worsened diffusion of magnesium into highly densified boron powder inside the mechanically strong metallic sheath. Thermal stability is related to the electrical and thermal conductivity of the metallic sheath, which is the worst for stainless steel and the best one for Nb.

Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields

We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 um to 1000 um and film thicknesses d ~ 4-6 nm and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T*(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest the presence of a highly conducting region that is dominating the electric transport in narrow bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.

Resistive switching studies in VO2 thin films

The hysteretic insulator-to-metal transition of VO2 is studied in detail for pulsed laser deposition grown thin films on TiO2 substrates, under variation of temperature and applied bias currents. This system is of interest for novel electronics based on memristive concepts, in particular as the resistive transition in these films occurs close to room temperature. Multiple, stable resistance states can be set controllably in the temperature range of the hysteretic phase transition by tailored temperature sweeps or by Joule heating induced by current pulses.

The influence of BaSnO3 artificial pinning centres on the resistive transition of 2G high-temperature superconductor wire in magnetic field

In this work, we present a study of the resistive transition in magnetic field of 2G high-temperature superconductor wire samples with BaSnO3 (BSO) artificial pinning centres (APCs) in a GdBa2Cu3O7−x (GdBCO) superconductor. The GdBCO layer was fabricated by pulsed laser deposition, using production equipment to obtain samples with varied concentrations of APC: 0, 6, 12 and 18 mol% of BSO. Resistive transition curves were measured in the magnetic field range from 0 to 9 T, and magnetic field orientations from B∣∣c (θ = 0°) to B∣∣ab (θ = 90°) with an angle step of 15°. We observed an irreversibility temperature peak at the B∣∣ab orientation. We determined the angular regions where correlated pinning centres dominated and found them to expand with the increase of BSO concentration. The activation energy (Ua) obtained from the lg(ρ/ρ0) against the 1/T plots was almost constant in the whole angular range, with a small peak at B∣∣ab. The activation energy as well as the irreversibility temperature decreased with the increasing doping level, but the Ua(θ) curves looked similar for all samples with APCs. The logarithmic resistivity plot of the undoped sample looked substantially different from those of the APC samples, with a kink and two different slopes corresponding to two regions with different Ua. We discuss that this difference is related to the different pinning landscapes in samples with and without APCs.

Abstract P2-11-09: Characterization of metastatic breast cancer through a novel next generation sequencing platform for hypothesis generation on endocrine resistance

Abstract Introduction: Notwithstanding the increasing efficacy of systemic therapy, metastatic breast cancer (MBC) is still an incurable disease. The prolonged exposure to endocrine therapy will result in acquired resistance with consequent disease progression. Understanding the underlying mechanisms of resistance is therefore crucial for early resistance detection and for treatment choice optimization. The aim of this study was a comprehensive characterization through circulating tumor DNA analysis (ctDNA) for hypothesis generation on endocrine resistance. Methods: This retrospective study analyzed a pilot cohort of 35 metastatic breast cancer (MBC) patients (pts) treated and evaluated for ctDNA at Northwestern University (Chicago, IL). ctDNA was analyzed using the PredicinePLUS™ NGS 180-gene panel (Predicine Inc, CA). Endocrine resistance was defined as a relapse during the first 2 years of adjuvant endocrine therapy or progressive disease within endocrine therapy (ET) for MBC. Associations between clinico-pathological characteristics and gene variants were tested though Fisher’s exact test. Results: The study included 27 hormone receptor positive MBC (HR+) pts, 5 HER2 positive and 1 Triple Negative MBC (TNBC) patient. Among HR+ pts, 24 received ET in previous lines, including 21 cases treated with an aromatase inhibitor (AI)-based backbone, while 14 received an ET association with CDK4/6 inhibitors. Fifteen were classified as endocrine resistant according to clinical criteria. In the subgroup of pts previously treated with AI, the main detectable gene variants wereTP53 (48%), PIK3CA (26%), GNAS (30%), ESR1 (25%), CDH1 (22%), BRCA2(22%), ARID1A (41%) and AR (52%). Notably, TP53 and ESR1 aberrations were mainly polygenic (ESR1:c.1138G&amp;gt;C, c.1261A&amp;gt;C, c.1551G&amp;gt;A c.1607T&amp;gt;C, c.1609T&amp;gt;A, c.1610A&amp;gt;C, c.1610A&amp;gt;G, c.1613A&amp;gt;G, c.172G&amp;gt;A; TP53:c.1024C&amp;gt;T, c.473G&amp;gt;A, c.524G&amp;gt;A, c.536A&amp;gt;G, c.559G&amp;gt;A, c.586C&amp;gt;T, c.587G&amp;gt;C, c.638G&amp;gt;A, c.659A&amp;gt;G, c.713G&amp;gt;A, c.772del), while the main genes showing copy number variations were in BRCA2 (Loss), JAK2 (Loss), PPP2R2A (Loss), RB1 (Loss), SERPINB3 and SERPINB4 (Gain). Moreover, among the totally detected 448 gene variants, only ESR1 mutations were associated with previous AI prescription (P=0.030). Conclusion:The present study offers an insight on the mutational landscape of MBC patients treated with endocrine therapy alone or associated with CDK4/6 inhibitors. ESR1 mutations were confirmed as the predominant resistance factor and were mainly polygenic. New promising targets such as SERPINB3, SERPINB4, ARID1A and AR add new intriguing clues on the potential role of Epithelial to Mesenchymal transition in endocrine resistance and warrant further investigation on a larger, prospective, cohort. Citation Format: Lorenzo Gerratana, Qiang Zhang, Andrew A Davis, Ami N Shah, Jianjun Yu, Shidong Jia, Youbin Zhang, Firas Wehbe, Amir Behdad, Leonidas C Platanias, William J Gradishar, Massimo Cristofanilli. Characterization of metastatic breast cancer through a novel next generation sequencing platform for hypothesis generation on endocrine resistance [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-11-09.

An Invariable Temperature during the Phase Transition of W Doped VO2 Film

The phase transition temperature of the functional VO2 films was adjusted to near room temperature by the W6+ doping. The V1−xW xO2 (0 ≤ x ≤ 0.04) films were deposited by the one‐step thermal decomposition process (30 min at 793 K) on a sapphire (0001) substrate under inert conditions. The electrical resistivity of the films showed that the ending point of the metal to insulator transition (TCE) of the pure VO2 phase transition, which appeared at ~310 K, was shifted down to ~265 K along with the increased doping level of W. The hysteresis gap between cooling and heating cycles in the plot of temperature vs. electrical resistivity for the films decreased from ~25 to ~2 K by the increased W level. The transition temperature shift and the hysteresis gap decrement were also observed in the measurement of infrared (IR) transmittance near the transition temperature. The degree of IR (1550 nm) transmittance of the VO2 film in the low‐temperature region was decreased from ~80 to ~40% by the W doping, but nearly the same transmittance in the high‐temperature region. Even though the characteristics of the transition in resistivity and transmittance measurements were greatly altered by the W doping, the starting point of the metal to insulator transition (TCS) was nearly constant, TCS ~338 K.

Physics-based model for resistance transition of sputter-deposited silicon oxide films

Abstract This paper proposes a physics-based model to explain the resistance transition of sputter-deposited silicon oxide films. At first, the impact of metallic silicon precipitate inclusions on the resistance transition of silicon oxide films is discussed, and possible chemical structures yielding high-resistance state and low-resistance state are revealed based on chemical reaction energy. Finally, the transient process of resistance transition is theoretically modeled and some important parameters are discussed

Age-related pharmacodynamics in a bumblebee-microsporidian system mirror similar patterns in vertebrates.

Immune systems provide a key defence against diseases. However, they are not a panacea and so both vertebrates and invertebrates co-opt naturally occurring bioactive compounds to treat themselves against parasites and pathogens. In vertebrates, this co-option is complex, with pharmacodynamics leading to differential effects of treatment at different life stages, which may reflect age-linked differences in the immune system. However, our understanding of pharmacodynamics in invertebrates is almost non-existent. Critically, this knowledge may elucidate broad parallels across animals in regard to the requirement for the co-option of bioactive compounds to ameliorate disease. Here, we used biochanin A, an isoflavone found in the pollen of red clover (Trifolium pratense), to therapeutically treat Nosema bombi (Microsporidia) infection in bumblebee (Bombus terrestris) larvae and adults, and thus examine age-linked pharmacodynamics in an invertebrate. Therapeutic treatment of larvae with biochanin A did not reduce the infection intensity of N. bombi in adults. In contrast, therapeutic treatment of adults did reduce the infection intensity of N. bombi This transition in parasite resistance to bioactive compounds mirrors the age-linked pharmacodynamics of vertebrates. Understanding how different life-history stages respond to therapeutic compounds will provide novel insights into the evolution of foraging and self-medication behaviour in natural systems more broadly.

Simple design of memristive counters and their applications in automatic irrigation system

Memristor, a passive circuit element got tremendous research attention for its in-memory computation. In this study, it was identified that controllable resistive state transitions exist within a single memristor. On the basis of this realisation, a simple but unconventional implementation of memristive up and down counters was presented. Furthermore, a dual up-down counter was developed, which can mimic any real-time process variations. To demonstrate its practical application, a counter-based memristive automatic irrigation system was explicated, which provided optimised utilisation of electrical and water resources. The proposed study opens up a new purview in the area of future non-Von Neumann computer architectures and its potential electronic applications.