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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring

Abstract In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24%–28%, peaking at ∼40%) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to ≈46° ± 12° rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of 0.94, and an inclination of 150°. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Terahertz electric-field-driven dynamical multiferroicity in SrTiO 3

The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO 3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein–de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Polarization Angle Swings in Blazars Detected in the Millimeter-wave with the South Pole Telescope

We present the first systematic search for electric vector position angle (EVPA) swings in the millimeter-wave (mm-wave) emission of blazars, using five years of observations from the South Pole Telescope SPT-3G camera at 95 and 150 GHz, and investigate their connection to gamma-ray flares. Of the 168 bright sources in the ~1500 square degrees SPT-3G Main Field, eight have sufficient polarization signal-to-noise for reliable EVPA measurement, four of which have continuous Fermi LAT gamma-ray detections. We detect EVPA swings in all four gamma-ray-active blazars and in none of the remaining four, consistent with the established connection between EVPA swings and high-energy emission seen at optical wavelengths. The observed swing amplitudes and rotation rates are smaller than those found in optical studies, consistent with mm-wave EVPA variability being slower than at shorter wavelengths. Random walk simulations of the polarization angle using a multi-cell model fail to reproduce both the number, amplitude, and duration of the observed swings, suggesting that this mechanism is insufficient to explain the observed swing population. Analysis of EVPA variability on one-week timescales is consistent with the anti-correlation between polarization degree and EVPA rotation rate previously observed at optical wavelengths. Of the 14 detected swings, eight are within 30 days of a gamma-ray flare. While many individual swing-flare associations are found to have a very low probability of happening by chance, the full ensembles of 95 and 150 GHz swing time lags with respect to gamma-ray flares are found to be consistent with random coincidence.

Simpson, A. [Chicago U., Astron. Astrophys. Ctr.; ↗
DOE OSTI2020

Out-of-plane carrier spin in transition-metal dichalcogenides under electric current

Significance Although out-of-plane current-induced spin polarization (CISP) is important for perpendicular-magnetization reorientation, and it has been realized by the crystalline symmetry breaking, its material examples are relatively fewer compared with in-plane CISP in Rashba systems. With the help of intrinsic spin–orbit coupling, an intriguing out-of-plane CISP is designed in transition-metal dichalcogenides by the symmetry breaking in the spin space, which provides opportunities for out-of-plane magnetization rotation and electric control of valley splitting. Moreover, the spin polarization is associated with valley-dependent responses to electric current and adds a dimension, valley degree of freedom, to the study of CISP. The symmetry argument and non-Rashba effective model also helps to illuminate these physics and broaden the scope of the CISP.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Faraday effect in collisional magnetized plasmas

Faraday rotation is a valuable diagnostic tool for investigating laboratory and astrophysical plasmas, but it has almost exclusively been treated in the collisionless limit (despite the non-negligible role of Coulomb collisions in many laboratory plasmas). Here, we show that Faraday rotation can occur in collisional plasmas and that the usual effect is curiously altered by collisions. Namely, an initially linearly polarized light wave—propagating parallel to a uniform magnetic field—becomes elliptically polarized in the collisional plasma, and collisional absorption of the wave also occurs. Moreover, the ellipticity and rotation angle are quantifiably sensitive to the fidelity of the collisional transport coefficients. As we will demonstrate with particle-in-cell EPOCH simulations, these effects offer a stringent diagnostic tool for benchmarking multi-scale plasma simulation codes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Mapping causal pathways with structural modes fingerprint for perovskite oxides

Abstract Causality is innate to the determination of the fundamental mechanism controlling any physical phenomena. However, combining causality within the standard practices of computational modelling to understand structure-functionality connections is extremely rare. This work proposes a fingerprint based on key structural modes for ABO 3 -type perovskite oxides and its derivatives, combined with causal models, for predicting Kohn–Sham energies. Our study of causal models captures the inherent coupling between structural modes such as rotation, tilt and antiferroelectric displacements, responsible for phase transition, polarization, magnetization and metal–insulator transition, exhibited by these materials. Although developed for modelling specific functionality, this method is universally applicable to derive other functionalities and even different material classes while tracking hidden causal mechanisms via structural distortions.

42 ENGINEERING↗
DOE OSTI2023

Timing of pulsars in the globular cluster omega centauri

We present the timing of the first five millisecond pulsars discovered in the globular cluster Omega Centauri and the discovery of a pulsar with a spin period of 3.68 ms. With a timing baseline of ~3.5 yr we are able to measure the derivative of the spin frequency ($\dot{\nu }$) for the first five pulsars. Upper limits on the pulsar line-of-sight acceleration are estimated and compared with predictions based on analytical models of the cluster. We find that PSRs J1326-4728B and D show large negative accelerations, which are in tension with the minimum acceleration predicted by analytical models. We searched for pulsed γ-ray signals using 14.3 yr of data from the Fermi Large Area Telescope. Although we found no evidence for γ-ray pulsations, PSRs J1326-4728A, B, C, and E are associated with X-ray sources. This suggests that the observed γ-ray emission from Omega Centauri is likely caused by the emission of the ensemble of MSPs. Finally, the linearly polarized emission from PSR J1326-4728A yields a rotation measure of -18 ± 8 rad m -2 .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Finite-Temperature Quantum Matter with Rydberg or Molecule Synthetic Dimensions

Synthetic-dimension platforms offer unique pathways for engineering quantum matter. We compute the phase diagram of a many-body system of ultracold atoms (or polar molecules) with a set of Rydberg states (or rotational states) as a synthetic dimension, where the particles are arranged in real space in optical microtrap arrays and interact via dipole-dipole exchange interaction. Using mean-field theory, we find three ordered phases—two are localized in the synthetic dimension, predicted as zero-temperature ground states, and one is a delocalized phase. We characterize them by identifying the spontaneously broken discrete symmetries of the Hamiltonian. We also compute the phase diagram as a function of temperature and interaction strength for both signs of the interaction. For system sizes with more than six synthetic sites and attractive interactions, we find that the thermal phase transitions can be first or second order, which leads to a tricritical point on the phase boundary. Furthermore, by examining the dependence of the tricritical point and other special points of the phase boundary on the synthetic dimension size, we shed light on the physics for thermodynamically large synthetic dimension.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Beam and Spin Optics Simulation Tutorials, Using Zgoubi Exercises and Solutions 2 - RHIC Run 22 Spin Transparency Experiment

High electron and ion polarizations are paramount design requirements for the future Electron Ion Collider (EIC) at BNL. A “spin transparency” mode of operation, inherited from the “figure-8” ring design [1], allows preservation and control of electron and ion spin polarization in a collider or storage ring [2, 3]. It makes the ring lattice “invisible” to the spin and allows for polarization control by small quasi-static magnetic fields with practically no effect on beam orbital parameters. Beam polarization can then be fully controlled by small adjustments of snake axis orientation (a few degrees) and snake strengths (a few percent); polarization orientation at IPs can be controlled without spin rotators, spins can be adiabatically flipped without the need of ac magnets. The transparent spin mode has been demonstrated in simulations [2] for the purpose of being tested experimentally during RHIC Run 22. This experiment was aimed at providing data to validate the principles. Yellow RHIC ring (Fig. 1.1) was configured in the transparent spin mode by aligning the axes of its two helical snakes (located respectively in the 3 o’clock and 9 o’clock sextants) parallel to the longitudinal axis. Experiment goals and expected results, ad hoc procedures and hardware requirements, are addressed in Refs. [2, 3].

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Nanoscale Ferroelectric Control of Novel Electronic States in Layered Two-Dimensional Materials (Final Report)

In this DOE Early Career project “Nanoscale Ferroelectric Control of Novel Electronic States in Layered Two-Dimensional Materials,” the PI’s group has combined ferroelectric field effect with nanoscale domain imaging and writing to design the electronic and optical properties of two-dimensional (2D) van der Waals materials, including graphene and transition metal dichalcogenides MoS2 and ReS2. The van der Waals materials have been prepared into field effect transistor (FET) devices with ferroelectric gates. Through domain patterning in a ferroelectric polymer PVDF-TrEF top-gate via conductive atomic force microscopy, the team has created programmable Schottky junctions in monolayer MoS 2 , where both barrier height and I-V rectifying polarity can be reconfigured. The transport anisotropy of monolayer to few-layer ReS 2 has been mapped out by defining the entire channel into an insulating state and creating nanoscale conducting paths along different directions through domain writing in the ferroelectric top-gate. The result shows that the conductivity along and perpendicular to the Re-chain can differ by >5.5x10 4 . Theoretical modeling points to the band origin of the transport anomaly and reveals the emergence of a flat band in few-layer ReS 2 . The interfacial epitaxial relation between ReS 2 and PVDF-TrFE further promotes the formation of close-packed, highly ordered PVDF-TrFE nanowires with width of 35 nm and 10 nm. Nonvolatile modulation of quantum Hall effect has been achieved in graphene FETs with a ferroelectric oxide Ba 0.4 Sr 0.6 TiO 3 back-gate. Scattering from the remote surface optical phonon in Ba 0.4 Sr 0.6 TiO 3 limits the room temperature mobility of graphene to be about 3x10 4 cm 2 /Vs. Steep-slope switching has been achieved in MoS 2 FETs back-gated by polycrystalline Pb(Zr,Ti)O 3 , which signals a static-state negative capacitance mode without involving an additional dielectric layer. Piezoresponse force microscopy studies show that the sub-threshold swing can be well correlated with the domain wall density in Pb(Zr,Ti)O 3 . The team also observes an unconventional filtering effect of the second harmonic generation response at the MoS 2 /Pb(Zr,Ti)O 3 heterointerface, which can be accounted for by the alignment between one of the polar axes of MoS 2 and the chiral dipole rotation at the surface of domain wall in Pb(Zr,Ti)O 3 . The research supported by this DOE grant has significantly advanced the fundamental understanding and functional design of ferroelectric/2D van der Waals heterostructures for their implementation towards energy applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Anisotropic light-tailored RKKY interaction in two-dimensional 𝑑-wave altermagnets

Altermagnets are known in spintronics for their intrinsic spin-splitting and unconventional magnetic responses, particularly to magnetic impurities. However, effectively controlling the magnetic exchange interactions in altermagnets is challenging for practical applications. Here, in this work, we propose using circularly polarized light to tune the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional 𝑑-wave altermagnets. Using the real-space retarded Green's functions approach, our results show that while the Heisenberg and Ising exchanges dominate, a notable Dzyaloshinskii–Moriya (DM) interaction also plays a key role. Furthermore, the inherent strength of altermagnetism imprints chirp-like signatures into the magnetic responses, which can be dynamically tuned via light. We mainly demonstrate that gate-induced Rashba spin-orbit coupling is essential in response to light—light selectively and anisotropically adjusts the DM interaction without affecting the other exchanges. Our findings further indicate that rotating the altermagnet by 45° relative to the light's polarization direction generates a Dirac-like dispersion and different DM interactions. We finally extract critical thresholds where light reverses DM interactions along one axis or balances both in-plane components. The anisotropic light-driven control of RKKY interactions in altermagnets not only highlights their unique properties but also opens new avenues for engineering tailored magnetic characteristics in spintronic applications.

altermagnetism↗
DOE OSTI2025

Prototypes of Nonrelativistic Spin Splitting and Polarization in Symmetry Broken Antiferromagnets

Antiferromagnets that break both space-time reversal and translation-spin-rotation symmetries were recently predicted [L.-D. Yuan, Z. Wang, J.-W. Luo, E. I. Rashba, and A. Zunger, Phys. Rev. B 102, 014422 (2020)] to possess splitting between the otherwise spin-degenerate energy bands even without the relativistic spin-orbit coupling (SOC). Here, we point out that such nonrelativistic spin splitting (NRSS)—in particular, “spin splitting type 4” (SST-4) symmetry-broken antiferromagnets—can be divided into subgroups having distinct patterns of spin splitting and spin textures, depending on additional auxiliary symmetries of spin interconversion and polarity. These SST-4 subgroups include the 𝛼-type (no spin-interconverting symmetry) having spin splitting at the Brillouin zone center, as well as the 𝛽 subgroup in which a rotation symmetry is applied and determines the alternating spin texture and the 𝛾 subgroup having exclusively reflection spin-interconverting symmetry. Unlike ferrimagnets, the 𝛼-type compounds are shown to have tiny net magnetization at finite temperature and thus avoid the adverse effect of the stray field. The 𝛼 and 𝛽 subgroups can be either polar or nonpolar, whereas the 𝛾 subgroup is polar only, providing a basis for possible switching by external fields. The combination of NRSS-enabling and auxiliary symmetries is used here as a filter for identifying previously synthesized compounds as specific prototypes. Their characteristic splitting and spin polarization are calculated by density functional theory to the benefit of potential future experimental testing. Interesting results are as follows: (i) SOC-independent NRSS can exceed the magnitude of the SOC-induced Rashba and Dresselhaus spin splitting in semiconductors. (ii) Examples of predicted 𝛼-type insulating compounds include BiCrO 3 (nonpolar) and Mn 2 ⁢ScSbO 6 (polar), the latter having spin splitting of 158 meV and 160 meV in the valence and conduction bands, respectively. (iii) The 𝛽-type (Cu 2 ⁢Y 2 ⁢O 5 and FeF 2 ) and 𝛾-type compounds (Mn 4 ⁢Nb 2 ⁢O 9 and FeScO 3 ) are distinguished both by their auxiliary symmetries and polarity. The spin textures of 𝛾-type compounds are mirror reflected with spin degeneracy of the wave vectors on that mirror. These observations will likely broaden the experimental playing field of NRSS physics significantly.

antiferromagnets↗
DOE OSTI2025

Polarization-separated double-imaging spectroscopy for weakly-ionized plasma diagnostics

Laser Thomson scattering, which provides thermal properties of electrons, has been extensively utilized in plasma diagnostics. However, being a non-resonant linear light scattering technique, it often encounters several challenges in weakly-ionized plasma diagnostics due to spectral overlap with different scatterings induced from other existing species, including Mie, Rayleigh, and rotational Raman scatterings. To address this challenge, we propose an imaging spectroscopy technique, polarization-separated double-imaging spectroscopy (PoDIS), which selectively separates specific scatterings based on their polarization characteristics. Using an atmospheric plasma jet as a plasma source for demonstration, we show that PoDIS can effectively separate rotational Raman and Thomson scatterings from a superimposed spectrum without prior knowledge or assumptions about the thermal properties of neutrals or electrons. This separation enables independent fitting of the rotational Raman and Thomson scattering spectra, allowing for precise determination of the thermal properties of neutral particles and electrons separately.

Bak, Junhwi [Texas A&M University, College Station↗
DOE OSTI2025

Nanoscale Quantum Imaging of Field-Free Deterministic Switching of a Chiral Antiferromagnet

Recently, unconventional spin-orbit torques (SOTs) with tunable spin generation have opened new pathways for designing novel magnetization control for cutting-edge spintronics innovations. A leading research thrust is to develop field-free deterministic magnetization switching for implementing scalable and energy favorable magnetic recording and storage, which have been demonstrated in conventional ferromagnetic and antiferromagnetic material systems. Here, in this work, we extend this advanced magnetization control strategy to chiral antiferromagnet Mn 3 ⁢Sn using spin currents with out-of-plane canted polarization generated from low-symmetry van der Waals (vdW) material WTe 2 . Numerical calculations suggest that dampinglike SOT of spins injected perpendicular to the kagome plane of Mn 3⁢ Sn serves as a driving force to rotate the chiral magnetic order, while the fieldlike SOT of spin currents with polarization parallel to the kagome plane provides the bipolar deterministicity to the magnetic switching in the absence of an external magnetic field. We further introduce scanning quantum microscopy to visualize nanoscale evolutions of Mn 3 ⁢Sn magnetic domains during the field-free switching process, corroborating the exceptionally large magnetic switching ratio up to 90%. Our results highlight the opportunities provided by hybrid SOT material platforms consisting of noncollinear antiferromagnets and low-symmetry vdW spin source materials for developing next-generation spintronic logic devices.

2-dimesional systems↗
DOE OSTI2023

Design of high polarization low switching barrier hybrid improper ferroelectric perovskite oxide superlattices

Hybrid improper ferroelectricity is a useful tool to design ABO 3 /A'BO 3 polar superlattices from non polar building blocks. In this study, we have designed high polarization-low switching barrier hybrid improper ferroelectric superlattices with efficient polarization, and polarization-magnetization switching properties above room temperature, using density functional theory and ab initio molecular dynamics simulations. Superlattices with a chemical formula of (AAlO 3 ) m /(A'AlO 3 ) n , where m/n = 1/1, 1/3, 3/1, 1/5 and 5/1, A, A' = Lanthanide and Y cations are considered to outline the design principles behind polarization switching and (LaFeO 3 ) 3 /(CeFeO 3 ) 1 is investigated for polarization-magnetization switching. We find that the unconventional switching paths via out-of-phase rotation Q R- (a 0 a 0 c - ) and tilt precession QTP always yield lower switching barrier compared to those via in-phase rotation Q R+ (a 0 a 0 c + ) and tilt QT (a - a - c 0 ) of BO 6 octahedra. Results from ab initio molecular dynamics simulations estimate the temperature at which the lowest energy barrier can be overcome. Furthermore, it is possible to tune the polarization switching barrier by tuning the tolerance factor, A,A' cation radius mismatch and super lattice periodicity. For switching via Q R- , the switching barrier varies exponentially with rotation angle, indicating how high switching barrier is expected for systems, away from cubic symmetry. We provide a recipe to overcome such a bottleneck by tuning superlattice periodicity. Finally, we have proposed the multiferroic device application concept through a proposed polarization-temperature hysteresis loop and magnetization switching.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Deployment of POLARBEAR-2b

POLARBEAR-2b (PB-2b) is the second receiver in the Simons Array, a cosmic microwave background (CMB) polarization experiment. The Simons Array uses dichroic polarization sensitive lenslet-coupled sinuous antennas and transition-edge sensor (TES) bolometers made of superconducting films. These bolometers are read out with frequency multiplexing electronics. PB-2b contains ~7500 detectors in two bands at 90 and 150 GHz with arcminute resolution. The polarization of these detectors is modulated by a cryogenic continuously rotating half-wave plate. PB-2b was installed on its telescope in 2022 in the Atacama Desert at an altitude of 5.2 km. This paper will detail initial readout commissioning, test of a new loopgain monitoring method, and focusing the optics. Work is ongoing to commission the remaining ambient temperature readout electronics, measure detector time constants, and observe with the cryogenic half-wave plate spinning.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Energy-Efficient and Water-Saving Sorbent Regeneration at Near Room Temperature for Direct Air Capture

Here this study reports energy-efficient and water-saving microwave-accelerated regeneration of sorbent (MARS) for dilute carbon capture from the ambient air. The experimental studies indicated that the CO 2 desorption rate from the chemisorbents increased with microwave output under near-isothermal conditions at near room temperature. The reduced activation energy of MARS, i.e., 20–28 kJ/mol, indicated enhanced CO 2 desorption kinetics by microwave-induced rotational–vibrational (rovibrational) coupling transitions, primarily due to the highly polarized feature of the carbamate (CO 2 -PEI). The instant and selective delivery of microwave energy to the targeted polarized C–N bonds at room temperature is particularly advantageous for energy-efficient direct air capture. The experimental results also demonstrated a good working capacity of 0.6–1.4 mmol of CO 2 /g and a promising rapid MARS-DAC process with microwave swing. As it does not require steam regeneration and heat exchanger, a simple MARS process is attractive for CO 2 capture in water-stressed regions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Strain-tuned quantum criticality in electronic Potts-nematic systems

Motivated by recent observations of threefold rotational symmetry breaking in twisted moiré systems, cold-atom optical lattices, quantum Hall systems, and triangular antiferromagnets, we phenomenologically investigate the strain-temperature phase diagram of the electronic 3-state Potts-nematic order. While in the absence of strain the quantum Potts-nematic transition is first-order, quantum critical points (QCP) emerge when uniaxial strain is applied, whose nature depends on whether the strain is compressive or tensile. In one case, the nematic amplitude jumps between two non-zero values while the nematic director remains pinned, leading to a symmetry-preserving metanematic transition that terminates at a quantum critical end-point. For the other type of strain, the nematic director unlocks from the strain direction and spontaneously breaks an in-plane twofold rotational symmetry, which in twisted moiré superlattices triggers an electric polarization. Such a piezoelectric transition changes from first to second-order upon increasing strain, resulting in a quantum tricritical point. Using a Hertz-Millis approach, we show that these QCPs share interesting similarities with the widely studied Ising-nematic QCP. The existence of three minima in the nematic action also leaves fingerprints in the strain-nematic hysteresis curves, which display multiple loops. At non-zero temperatures, because the upper critical dimension of the 3-state Potts model is smaller than three, the Potts-nematic transition is expected to remain first-order in 3D, but to change to second-order in 2D. As a result, the 2D strain-temperature phase diagram displays two first-order transition wings bounded by lines of critical end-points or tricritical points, reminiscent of the phase diagram of metallic ferromagnets. Furthermore, we discuss how our results can be used to unambiguously identify spontaneous Potts-nematic order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗