Temperature-independent Resistance Research Articles

The interplay between anomalous metallic and superconducting states tuned by disorder in thin flakes of Kagome metal KV3Sb5

Recently, V-based Kagome metals have attracted intense attention due to the coexistence of their topological nontrivial electronic structure, charge density wave, and superconductivity. Here, we report the fabrication and physical investigations of single-crystalline thin flakes of the Kagome metal KV3Sb5. For samples with a thickness of , Berezinskii–Kosterlitz–Thouless type behavior is revealed by the temperature dependent resistance and voltage–current data, which indicates the presence of two-dimensional superconductivity. Meanwhile, a temperature-independent resistance behavior is observed in a wide field region, supplying the hallmark of the anomalous metallic (AM) state. Importantly, by comparing the interplay between the superconducting and AM states of two samples with different levels of disorder, a striking competitive evolution with the external field between these two states is uncovered.

Emergence of High-Temperature Superconducting Phase in Pressurized La3Ni2O7 Crystals

The recent report of pressure-induced structural transition and signature of superconductivity with T c ≈ 80 K above 14 GPa in La3Ni2O7 crystals has garnered considerable attention. To further elaborate this discovery, we carried out comprehensive resistance measurements on La3Ni2O7 crystals grown in an optical-image floating zone furnace under oxygen pressure (15 bar) using a diamond anvil cell (DAC) and cubic anvil cell (CAC), which employ a solid (KBr) and liquid (glycerol) pressure-transmitting medium, respectively. Sample 1 measured in the DAC exhibits a semiconducting-like behavior with large resistance at low pressures and gradually becomes metallic upon compression. At pressures P ⩾ 13.7 GPa we observed the appearance of a resistance drop of as much as ∼ 50% around 70 K, which evolves into a kink-like anomaly at pressures above 40 GPa and shifts to lower temperatures gradually with increasing magnetic field. These observations are consistent with the recent report mentioned above. On the other hand, sample 2 measured in the CAC retains metallic behavior in the investigated pressure range up to 15 GPa. The hump-like anomaly in resistance around ∼ 130 K at ambient pressure disappears at P ⩾ 2 GPa. In the pressure range of 11–15 GPa we observed the gradual development of a shoulder-like anomaly in resistance at low temperatures, which evolves into a pronounced drop of resistance of 98% below 62 K at 15 GPa, reaching a temperature-independent resistance of 20 μΩ below 20 K. Similarly, this resistance anomaly can be progressively shifted to lower temperatures by applying external magnetic fields, resembling a typical superconducting transition. Measurements on sample 3 in the CAC reproduce the resistance drop at pressures above 10 GPa and realize zero resistance below 10 K at 15 GPa even though an unusual semiconducting-like behavior is retained in the normal state. Based on these results, we constructed a dome-shaped superconducting phase diagram and discuss some issues regarding the sample-dependent behaviors on pressure-induced high-temperature superconductivity in the La3Ni2O7 crystals.

Assessment of Temperature-Independent Resistance against Bacterial Wilt Using Major QTL in Cultivated Tomato (Solanum lycopersicum L.).

Bacterial wilt (Ralstonia solanacearum) is a devastating disease of cultivated tomato resulting in severe yield loss. Since chemicals are often ineffective in controlling this soil-borne pathogen, quantitative trait loci (QTL) conferring host resistance have been extensively explored. In this study, we investigated effects of ambient temperature and major QTL on bacterial wilt resistance in a collection of 50 tomato varieties. The five-week-old seedlings were inoculated using the race 1 (biovar 4 and phylotype I) strain of R. solanacearum and placed at growth chambers with three different temperatures (24 °C, 28 °C, and 36 °C). Disease severity was evaluated for seven days after inoculation using the 1–5 rating scales. Consistent bacterial wilt resistance was observed in 25 tomato varieties (R group) with the means of 1.16–1.44 for disease severity at all three temperatures. Similarly, 10 susceptible varieties with the means of 4.37–4.73 (S group) were temperature-independent. However, the other 15 varieties (R/S group) showed moderate levels of resistance at both 24 °C (1.84) and 28 °C (2.16), while they were highly susceptible with a mean of 4.20 at 36 °C. The temperature-dependent responses in the R/S group were supported by pairwise estimates of the Pearson correlation coefficients. Genotyping for three major QTL (Bwr-4, Bwr-6 and Bwr-12) found that 92% of varieties in the R group had ≥ two QTL and 40% of varieties in the R/S group had one or two QTL. This suggests that these QTL are important for stability of resistance against bacterial wilt at high ambient temperature. The resulting 25 varieties with temperature-independent resistance will be a useful resource to develop elite cultivars in tomato breeding programs.

Anomalous metals: From “failed superconductor” to “failed insulator”

Resistivity saturation is found on both superconducting and insulating sides of an "avoided" magnetic-field-tuned superconductor-to-insulator transition (H-SIT) in a two-dimensional In/InOx composite, where the anomalous metallic behavior cuts off conductivity or resistivity divergence in the zero-temperature limit. The granular morphology of the material implies a system of Josephson junctions (JJs) with a broad distribution of Josephson coupling EJ and charging energy EC, with an H-SIT determined by the competition between EJ and EC. By virtue of self-duality across the true H-SIT, we invoke macroscopic quantum tunneling effects to explain the temperature-independent resistance where the "failed superconductor" side is a consequence of phase fluctuations and the "failed insulator" side results from charge fluctuations. While true self-duality is lost in the avoided transition, its vestiges are argued to persist, owing to the incipient duality of the percolative nature of the dissipative path in the underlying random JJ system.

The Resistance Responses of Potato Plants to Potato Virus Y Are Associated with an Increased Cellular Methionine Content and an Altered SAM:SAH Methylation Index.

Plant-virus interactions are frequently influenced by elevated temperature, which often increases susceptibility to a virus, a scenario described for potato cultivar Chicago infected with potato virus Y (PVY). In contrast, other potato cultivars such as Gala may have similar resistances to PVY at both normal (22 °C) and high (28 °C) temperatures. To elucidate the mechanisms of temperature-independent antivirus resistance in potato, we analysed responses of Gala plants to PVY at different temperatures using proteomic, transcriptional and metabolic approaches. Here we show that in Gala, PVY infection generally upregulates the accumulation of major enzymes associated with the methionine cycle (MTC) independently of temperature, but that temperature (22 °C or 28 °C) may finely regulate what classes accumulate. The different sets of MTC-related enzymes that are up-regulated at 22 °C or 28 °C likely account for the significantly increased accumulation of S-adenosyl methionine (SAM), a key component of MTC which acts as a universal methyl donor in methylation reactions. In contrast to this, we found that in cultivar Chicago, SAM levels were significantly reduced which correlated with the enhanced susceptibility to PVY at high temperature. Collectively, these data suggest that MTC and its major transmethylation function determines resistance or susceptibility to PVY.

Influence of Alkaline-Earth-Metal Substitutions on the Bismuth Ruthenate Structure: Bi2-xA'xRu2O6O'1-y (A' = Mg, Ca, Sr).

Solid solutions with the formula of Bi2-xA'xRu2O7-y (A' = Mg, Ca, Sr; 0 ≤ x ≤ 0.2 for Mg, 0 ≤ x ≤ 1 for Ca, and 0 ≤ x ≤ 0.5 for Sr) have been synthesized and characterized. The crystal structures for these phases are found to be in the pyrochlore family, crystallizing in the cubic space group Fd3̅m with complex A/A' cation coordination environments. The Bi cation is found to be off-center from the ideal position because of a lone-pair distortion, while the positions of the substituted A' cations vary based on the size and ionicity. The neutron structure refinements reveal a similar propensity to off-center regarding Ca and Sr, while Mg features the largest static displacement of up to 0.48 Å. Interestingly, this is one of only two known pyrochlores with Mg2+ located in an 8-coordinated site. The average Ru oxidation state for each substitution is found to increase, and charge compensates for the lower divalent A' substitution. The solid solutions show temperature-independent resistance across the series with small changes in magnitude that scale with the amount of substitution, while displaying Pauli paramagnetic behavior throughout.

A −40 °C to 120 °C, 169 ppm/°C Nano-Ampere CMOS Current Reference

This brief presents a nano-ampere CMOS current reference (CCR) for low power application with a wide temperature range from −40°C to 120°C. The current reference is generated by the division of a temperature-independent voltage and resistance in a simple way. The low temperature-independent voltage is generated based on the threshold voltage difference between two same-type NMOS transistors with different channel lengths working in the subthreshold region, while the temperature-independent resistance is made up by two poly resistors, whose temperature coefficients are opposite. By designing a low voltage to allow for a small resistance, the CCR circuit takes a small chip area while generating nano-ampere current. The proposed CCR circuit was implemented in a standard 0.18- ${\mu }\text{m}$ CMOS process and its active area is 0.054 mm2. Among the measured 10 samples, the average output current is 11.6 nA and the average temperature coefficient is 169 ppm/°C.

Helical Edge Transport in Millimeter-Scale Thin Films of Na3Bi.

A two-dimensional topological insulator (2DTI) has an insulating bulk and helical edges robust to nonmagnetic backscattering. While ballistic transport has been demonstrated in micron-scale 2DTIs, larger samples show significant backscattering and a nearly temperature-independent resistance of unclear origin. Spin polarization has been measured, however the degree of helicity is difficult to quantify. Here, we study 2DTI few-layer Na3Bi on insulating Al2O3. A nonlocal conductance measurement demonstrates edge conductance in the topological regime with an edge mean free path ∼100 nm. A perpendicular magnetic field suppresses spin-flip scattering in the helical edges, resulting in a giant negative magnetoresistance (GNMR) up to 80% at 0.9 T. Comparison to theory indicates >96% of scattering is helical spin scattering significantly exceeding the maximum (67%) expected for a nonhelical metal. GNMR, coupled with nonlocal measurements, thus provides an unambiguous experimental signature of helical edges that we expect to be generically useful in understanding 2DTIs.

Modeling Low-TC Transition-Edge Sensors Made of NS Bilayers: The Specific Interface Resistance

One way of making a transition-edge sensor (TES) is by utilizing the proximity effect, in which the $$T_{C}$$ of a superconducting film is reduced with a normal metal film in metallic contact. The $$T_{C}$$ of a bilayer TES can be estimated by solving the Usadel equations with given boundary conditions. The classical boundary conditions of a bilayer include a specific interface resistance being temperature-independent. In this paper, we will introduce a temperature-dependent specific interface resistance. By fitting the measured $$T_{C}$$ data of Ir/Au bilayers from the literature to a $$T_{C}$$ calculation model, we will compare the fit parameters and fit errors with the temperature-dependent specific interface resistance described in this work and with the classical temperature-independent specific interface resistance.

Anomalous metallic phase in tunable destructive superconductors

Multiply connected superconductors smaller than the coherence length show destructive superconductivity, characterized by reentrant quantum phase transitions driven by magnetic flux. We investigate the dependence of destructive superconductivity on flux, transverse magnetic field, temperature, and current in InAs nanowires with a surrounding epitaxial Al shell, finding excellent agreement with mean-field theory across multiple reentrant transitions. Near the crossover between destructive and nondestructive regimes, an anomalous metal phase is observed with temperature-independent resistance, controlled over two orders of magnitude by a millitesla-scale transverse magnetic field.

Mobile metallic domain walls in an all-in-all-out magnetic insulator.

Magnetic domain walls are boundaries between regions with different configurations of the same magnetic order. In a magnetic insulator, where the magnetic order is tied to its bulk insulating property, it has been postulated that electrical properties are drastically different along the domain walls, where the order is inevitably disturbed. Here we report the discovery of highly conductive magnetic domain walls in a magnetic insulator, Nd2Ir2O7, that has an unusual all-in-all-out magnetic order, via transport and spatially resolved microwave impedance microscopy. The domain walls have a virtually temperature-independent sheet resistance of ~1 kilohm per square, show smooth morphology with no preferred orientation, are free from pinning by disorders, and have strong thermal and magnetic field responses that agree with expectations for all-in-all-out magnetic order.

Enhancement in Quality Factor of SRF Niobium Cavities by Material Diffusion

An increase in the quality factor of superconducting radiofrequency cavities is achieved by minimizing the surface resistance during processing steps. The surface resistance is the sum of temperature independent residual resistance and temperature/material dependent Bardeen-Cooper-Schrieffer (BCS) resistance. High temperature heat treatment usually reduces the impurities concentration from the bulk niobium, lowering the residual resistance. The BCS part can be reduced by selectively doping non-magnetic impurities. The increase in quality factor, termed as Q-rise, was observed in cavities when titanium or nitrogen thermally diffused in the inner cavity surface.

Temperature Dependence of IPRT and SPRT Self-Heating: Does Working with $${{\varvec{W}}}$$ W Really Help?

Platinum resistance thermometers (PRTs) are capable of providing reliable measurements at the millikelvin level, and are widely used in both industry and research applications. However, the intrinsic thermal noise associated with their resistance requires the use of a measurement current of typically around a milliampere to determine their resistance. Unfortunately, this same current also dissipates heat into the thermometer element, causing the well-known “self-heating” effect of typically a few millikelvins. Performing measurements in terms of the ratio to the resistance at the ice point provides some level of cancelation of this error around this temperature: If the thermal resistance between the sensor and environment were constant, this cancelation would work over a much wider temperature range. However, there is little evidence on the effectiveness of this strategy in practice. This paper reports on an extensive set of systematic measurements of the self-heating of six standard platinum resistance thermometers (SPRTs) and six industrial platinum resistance thermometers (IPRTs) of different designs, as a function of temperature, over the range from $$-190~^{\circ }\mathrm{C}$$ to $$420\,^{\circ }\mathrm{C}$$ , in a range of intercomparison baths and blocks. The measurements show that PRT self-heating varies from being almost constant with temperature to being nearly proportional to temperature. The assumption of a roughly temperature-independent thermal resistance is thus not justified in general. The results allow estimation of appropriate uncertainty terms for SPRT and IPRT self-heating for the two scenarios of “working in $$R$$ ” and “working in $$W$$ .”

Identification and validation of powdery mildew (Podosphaera xanthii)-resistant loci in recombinant inbred lines of cucumber (Cucumis sativus L.)

Powdery mildew limits cucumber production worldwide. Most resistant cucumber cultivars become susceptible to powdery mildew at low temperatures. Resistance within a wide temperature range is therefore desirable for cucumber production. We constructed a cucumber genetic linkage map based on a population of 111 recombinant inbred lines derived from a cross between CS-PMR1, with strong and temperature-independent resistance, and Santou, with moderate and temperature-dependent resistance. The map spans 693.0 cM and consists of 296 markers segregating into seven linkage groups; the markers include 289 simple sequence repeats (SSRs), six sequence characterized amplified regions, and one inter simple sequence repeat. Due to the presence of 150 common SSR markers, we were able to compare our map with previously published maps obtained by using populations derived from inter- or intra-variety crosses. We also evaluated powdery mildew resistance of the recombinant inbred lines and identified seven quantitative trait loci (QTL) contributed by CS-PMR1 and two QTL contributed by Santou. Four QTL (pm3.1, pm5.1, pm5.2 and pm5.3) were successfully validated by using populations derived from residual heterozygous lines. Some of the QTL identified in our study are in good agreement with previously published results obtained with materials of different origin. The markers reported here would be useful for introducing high and temperature-independent resistance by accumulation of QTL from CS-PMR1 and Santou.

The influence of the buffer layer architecture on transport properties for BaFe1.8Co0.2As2 films on technical substrates

A low and almost temperature independent resistance in the normal state and an anomalous peak effect within the normal-superconducting transition have been observed in BaFe1.8Co0.2As2/Fe bilayers, prepared on ion beam assisted deposition-MgO/Y2O3 buffered technical substrates. A resistor network array sufficiently reproduces this effect, assuming an increase of the electrical conductance between tape and film with decreasing buffer layer thickness. Based on this model, we evaluated the influence of this effect on the critical current density and successfully reconstructed the superconducting transition of the bilayer.

Thermal activation of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height

This paper investigates the thermal activation behaviour of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height by numerical simulation. The analytical Gaussian distribution model predicted that the I-V-T curves may intersect with the possibility of the negative thermal activation of current, but may be contradictory to the thermionic emission mechanism in a Schottky diode. It shows that the cause of the unphysical phenomenon is related to the incorrect calculation of current across very low barriers. It proposes that junction voltage Vj, excluding the voltage drop across series resistance from the external bias, is a crucial parameter for correct calculation of the current across very low barriers. For correctly employing the thermionic emission model, Vj needs to be smaller than the barrier height ø. With proper scheme of series resistance connection where the condition of Vj > ø is guaranteed, I-V-T curves of an inhomogeneous Schottky diode with a Gaussian distribution of barrier height have been simulated, which demonstrate normal thermal activation. Although the calculated results exclude the intersecting possibility of I-V-T curves with an assumption of temperature-independent series resistance, it shows that the intersecting is possible when the series resistance has a positive temperature coefficient. Finally, the comparison of our numerical and analytical results indicates that the analytical Gaussian distribution model is valid and accurate in analysing I-V-T curves only for small barrier height inhomogeneity.

Rin4 causes hybrid necrosis and race-specific resistance in an interspecific lettuce hybrid.

Some inter- and intraspecific crosses may result in reduced viability or sterility in the offspring, often due to genetic incompatibilities resulting from interactions between two or more loci. Hybrid necrosis is a postzygotic genetic incompatibility that is phenotypically manifested as necrotic lesions on the plant. We observed hybrid necrosis in interspecific lettuce (Lactuca sativa and Lactuca saligna) hybrids that correlated with resistance to downy mildew. Segregation analysis revealed a specific allelic combination at two interacting loci to be responsible. The allelic interaction had two consequences: (1) a quantitative temperature-dependent autoimmunity reaction leading to necrotic lesions, lethality, and quantitative resistance to an otherwise virulent race of Bremia lactucae; and (2) a qualitative temperature-independent race-specific resistance to an avirulent race of B. lactucae. We demonstrated by transient expression and silencing experiments that one of the two interacting genes was Rin4. In Arabidopsis thaliana, RIN4 is known to interact with multiple R gene products, and their interactions result in hypersensitive resistance to Pseudomonas syringae. Site-directed mutation studies on the necrosis-eliciting allele of Rin4 in lettuce showed that three residues were critical for hybrid necrosis.

Dynamics of vortex penetration, jumpwise instabilities, and nonlinear surface resistance of type-II superconductors in strong rf fields

We consider the nonlinear dynamics of a single vortex in a superconductor in a strong rf magnetic field ${B}_{0}\phantom{\rule{0.2em}{0ex}}\mathrm{sin}\phantom{\rule{0.2em}{0ex}}\ensuremath{\omega}t$. Using the London theory, we calculate the dissipated power $Q({B}_{0},\ensuremath{\omega})$ and the transient time scales of vortex motion. For the linear Bardeen-Stephen viscous drag force, vortex velocities reach unphysically high values during vortex penetration through the oscillating surface barrier. It is shown that penetration of a single vortex through the ac surface barrier always involves penetration of an antivortex and the subsequent annihilation of the vortex-antivortex pairs. Using the nonlinear Larkin-Ovchinnikov (LO) viscous drag force at higher vortex velocities $v(t)$ results in a jumpwise vortex penetration through the surface barrier and a significant increase of the dissipated power. We calculate the effect of dissipation on the nonlinear vortex viscosity $\ensuremath{\eta}(v)$ and the rf vortex dynamics and show that it can also result in the LO-type behavior, instabilities, and thermal localization of penetrating vortex channels. We propose a thermal feedback model of $\ensuremath{\eta}(v)$, which not only results in the LO dependence of $\ensuremath{\eta}(v)$ for a steady-state motion, but also takes into account retardation of the temperature field around a rapidly accelerating vortex and a long-range interaction with the surface. We also address the effect of pinning on the nonlinear rf vortex dynamics and the effect of trapped magnetic flux on the surface resistance ${R}_{s}$ calculated as a function of rf frequency and field. It is shown that trapped flux can result in a temperature-independent residual resistance ${R}_{i}$ at low $T$ and a hysteretic low-field dependence of ${R}_{i}({B}_{0})$, which can decrease as ${B}_{0}$ is increased, reaching a minimum at ${B}_{0}$ much smaller than the thermodynamic critical field ${B}_{c}$. We propose that cycling of the rf field can reduce ${R}_{i}$ due to rf annealing of the magnetic flux which is pumped out by the rf field from a thin surface layer of the order of the London penetration depth.

Contribution of electron tunneling transport in semiconductor gas sensor

It was found that thin film devices derived from SnO 2 sols by spin-coating method showed unique thermal behavior of electric resistance in air involving a temperature region where resistance was independent of temperature. The temperature independent resistance region extended up to 400 °C, replacing a region of temperature-conventionally dependent resistance, as film thickness increased. Such unique behavior of resistance was observed also for a brush-coated device but not for screen-coated thick film devices or disk-type device, suggesting that the absence of mechanical forces applied during device fabrication favored the occurrence of the unique behavior. It was shown that the unique behavior could be well accounted for by postulating a combination of electron tunneling transport and conventional migration transport. Calculation of tunneling probability based on a simple model allowed estimating that electron tunneling transport can take place between oxide grains with a probability of 0.01 or larger if a gap in between is narrower than 0.01 nm.

Resistive λ-sensors based on ball milled Fe-doped SrTiO 3 nanopowders obtained by self-propagating high-temperature synthesis (SHS)

A series of SrTi 1− x Fe x O 3− δ (STO or STFO) powders, with x ranging from 0 to 0.6, were prepared by self-propagating high-temperature synthesis (SHS) starting from SrO 2, Ti, TiO 2 and Fe. A ball-milling (BM) treatment was subsequently carried out for further structure refinement and size reduction. Morphological and microstructural characteristics of both untreated and ball-milled SHS samples were investigated by SEM and XRD. Screen-printed SrTi 1− x Fe x O 3− δ SHS powders on alumina substrate were investigated for resistive oxygen sensors operating at high operating temperature (450–650 °C). STFO powders have shown better performances with respect to the corresponding undoped STO ones. Moreover, when STFO powders were subjected to BM treatment, both temperature-independent resistance characteristics and sensor response greatly improved. On the basis of the reported data, it can be suggested that the ball milling treatment likely acts: (i) stabilizing the formation of non-equilibrium structures; (ii) decreasing the particle size, increasing surface defects and hence surface reactivity; (iii) favouring the substitution of titanium by iron in the SrTiO 3 perovskite structure.