High Critical Field Research Articles

Violation of the orbital depairing limit in a nonunitary state: High-field phase in the heavy fermion superconductor UTe2

A theoretical study is reported on the origin of an extremely high upper critical field $\ensuremath{\sim}70$ T observed in ${\mathrm{UTe}}_{2}$ with the transition temperature ${T}_{\mathrm{c}}=1.6$--2 K, which exceeds the conventional orbital depairing limit set by the Fermi velocity and ${T}_{\mathrm{c}}$ for a superconductor (SC) in the clean limit. We investigate possible violation of the orbital limit in terms of a spin-triplet nonunitary state, which is effectively coupled to the underlying magnetization induced by an external field. This produces the reduced internal field by canceling it via magnetization. We formulate a theory within the Ginzburg-Landau framework to describe this orbital limit violation and analyze experimental data on the upper critical fields for various field orientations in ${\mathrm{UTe}}_{2}$. We show that the orbital limit violation for a spin-triplet SC, as well as the Pauli-Clogston limit violation for a spin-singlet SC, constitutes a complete and useful framework for examining the high field physics of superconductors in the clean limit.

Surface-phase superconductivity in a Mg-deficient V-doped MgTi2O4 spinel

Around 50 years ago, ${\mathrm{LiTi}}_{2}{\mathrm{O}}_{4}$ was reported to be the only spinel oxide to exhibit a superconducting transition with the highest ${T}_{c}\ensuremath{\approx}13.7$ K. Recently, ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ has been found to be another spinel oxide to reveal a superconducting transition with ${T}_{c}\ensuremath{\approx}3$ K, however, its superconducting state is realized only in thin film superlattices involving ${\mathrm{SrTiO}}_{3}$. We find that a V-doped ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{2}{\mathrm{O}}_{4}$ phase, which gets stabilized as a thin surface layer on top of a nearly stoichiometric and insulating V-doped ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ bulk sample, exhibits high-temperature superconductivity with ${T}_{c}\ensuremath{\approx}16$ K. The superconducting transition is also confirmed through a concomitant sharp diamagnetic transition immediately below ${T}_{c}$. The spinel phase of the superconducting surface layer is conformed through grazing-incidence x-ray diffraction and micro-Raman spectroscopy. A small shift of the sharp superconducting transition temperature ($\ensuremath{\sim}4$ K) with the application of a high magnetic field (up to 9 T) suggests a very high critical field for the system, $\ensuremath{\sim}25$ T. Thus, V-doped ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{2}{\mathrm{O}}_{4}$ exhibits the maximum ${T}_{c}$ among spinel superconductors and also possesses a very high critical field.

Tutorial: Metalorganic chemical vapor deposition of β-Ga2O3 thin films, alloys, and heterostructures

β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor with a bandgap energy of ∼ 4.8 eV and a predicted high critical electric field strength of ∼8 MV/cm, enabling promising applications in next generation high power electronics and deep ultraviolet optoelectronics. The advantages of Ga2O3 also stem from its availability of single crystal bulk native substrates synthesized from melt, and its well-controllable n-type doping from both bulk growth and thin film epitaxy. Among several thin film growth methods, metalorganic chemical vapor deposition (MOCVD) has been demonstrated as an enabling technology for developing high-quality epitaxy of Ga2O3 thin films, (AlxGa1−x)2O3 alloys, and heterostructures along various crystal orientations and with different phases. This tutorial summarizes the recent progresses in the epitaxial growth of β-Ga2O3 thin films via different growth methods, with a focus on the growth of Ga2O3 and its compositional alloys by MOCVD. The challenges for the epitaxial development of β-Ga2O3 are discussed, along with the opportunities of future works to enhance the state-of-the-art device performance based on this emerging UWBG semiconductor material system.

Ion energy dependence of dry etch damage depth in Ga2O3 Schottky rectifiers

The β-polytype of Ga2O3 has a high critical electric field strength (∼8 MV.cm−1) and can be grown as large diameter (6 in.) single crystal boules by inexpensive melt-growth techniques. This makes it promising for next generation power electronics and solar-blind UV photodetectors. Since wet etching is not feasible for patterning such devices due to the chemical inertness of Ga2O3, attention is focused on dry etching, with the attendant issue of surface modification due to chemical or ion-induced changes. In this work, we demonstrate that dry etch damage in β-Ga2O3 is manifested by a reduction in near-surface carrier concentration, possibly due to the introduction of Gav acceptor states. The depth to which the carrier density is affected depends on the interplay between ion energy and etch rate, with faster etch rates reducing the depth of the remaining damaged region. The maximum damage depth observed experimentally from capacitance-voltage profiling on Schottky rectifiers was ∼ 110 nm, well beyond the range of the ions in the Inductively Coupled Plasmas and emphasizing that rapid diffusion of point defects occurs into the sample during the etch step. Using Schottky rectifier structures as a platform to understand the effect of dry etch damage on device parameters, we found that on-state resistance was more affected than ideality factor or breakdown voltage, with a large increase (5x) for ion energies ≥ 325 eV. Reverse current density characteristics showed the presence of trap-assisted space-charge-limited conduction in the damaged layers. The implications for high power rectifier fabrication are discussed.

Combustion synthesis of high-performance high-entropy dielectric ceramics for energy storage applications

High-entropy dielectric ceramics have demonstrated a promising prospect for applications in energy storage recently. However, most high-entropy dielectrics synthesized by conventional solid-state reaction (SSR) method demonstrated unsatisfactory performance for energy storage. Therefore, it is meaningful to develop a feasible way to fabricate high-performance high-entropy dielectric ceramics. Herein, high-entropy (Sr0.6Bi0.2Na0.2)(Ti1-xZrx/2Alx/4Nbx/4)O3 ceramics are prepared by a solution combustion synthesis (SCS) method. The SCS fabricated ceramics (x = 0.25) demonstrate a high recoverable energy density of ∼4.46 J/cm3 at a high critical electric field of 520 kV/cm, a high energy efficiency ∼88.52%, a large power density of ∼176.65 MW/cm3 (at 400 kV/cm), an ultrafast discharge time of ∼48 ns, and a high Vikers hardness of ∼7.09 GPa. The key energy storage parameters are much better than those of the samples prepared by the SSR method owing to the absence of unexpected impurity phases, and the refined grain size at the submicrometer scale in our SCS fabricated high-entropy ceramics. The study provides a facile way to fabricate high-performance high-entropy dielectric ceramics for energy storage, indicating that the SCS routine is notably advantageous for preparing high-entropy dielectric energy ceramics.

A flux-tunable YBa2Cu3O7 quantum interference microwave circuit

Josephson microwave circuits are essential for the currently flourishing research on superconducting technologies, such as quantum computation, quantum sensing, and microwave signal processing. To increase the possible parameter space for device operation with respect to the current standards, many materials for superconducting circuits are under active investigation. Here, we present the realization of a frequency-tunable, weakly nonlinear Josephson microwave circuit made of the high-temperature cuprate superconductor YBa2Cu3O7 (YBCO), a material with a high critical temperature and a very high critical magnetic field. An in situ frequency-tunability of ∼300 MHz is achieved by integrating a superconducting quantum interference device (SQUID) into the circuit based on Josephson junctions directly written with a helium ion microscope (HIM). Our results demonstrate that YBCO-HIM-SQUID microwave resonators are promising candidates for quantum sensing and microwave technology applications.

Anisotropic enhancement of lower critical field in ultraclean crystals of spin-triplet superconductor candidate UTe2

The paramagnetic spin-triplet superconductor UTe$_2$ has attracted significant attention because of its exotic superconducting properties including an extremely high upper critical field and possible chiral superconducting states. Recently, ultraclean single crystals of UTe$_2$ have become available, and thus measurements on these crystals are crucial to elucidate the intrinsic superconducting properties. Here, we report the thermodynamic critical field $H_{\rm c}$, the lower critical field $H_{\rm c1}$, and the upper critical field $H_{\rm c2}$ at low fields of these high-quality single crystals. From the comparison of the anisotropies in $H_{\rm c1}$ and $H_{\rm c2}$, we find that the experimental $H_{\rm c1}$ values with the magnetic field along $b$- and $c$-axes are anomalously enhanced, showing unusual low-temperature upturns. We propose an effect of the strong Ising-like ferromagnetic fluctuations on the vortex line energy as the origin of the anisotropic enhancement of $H_{\rm c1}$.

Nonmagnetic Sn doping effect on the electronic and magnetic properties of antiferromagnetic topological insulator MnBi[formula omitted]Te[formula omitted

We investigated the effect of nonmagnetic Sn doping on the electronic and magnetic properties of antiferromagnetic topological insulator MnBi2Te4. We observe that the Sn doping reduces out-of-plane antiferromagnetic (AFM) interactions in Mn1−xSnxBi2Te4 for up to 68% of Sn concentration and above, the system is found to be a paramagnetic. In this way, the anomalous Hall effect observed at a very high critical field of 7.8 T in MnBi2Te4 is reduced to 2 T at 68% of Sn doping. Electrical transport measurements suggest that all compositions are metallic in nature, while the low temperature resistivity is sensitive to the AFM ordering and to the doping-induced disorder. Hall effect study demonstrates that Sn actually dopes electrons into the system, thus, enhancing the electron carrier density almost by two orders at 68% of Sn. In contrast, SnBi2Te4 is found to be a p-type metal. Angle-resolved photoemission spectroscopy (ARPES) studies show that the topological properties are intact at least up to 55% of Sn doping as the Dirac surface states are present near the Fermi level. But in SnBi2Te4 we are unable to detect the surface states due to heavy hole doping. Thus, the Sn doping significantly affects the electronic and magnetic properties of MnBi2Te4.

Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers

Nb and its compounds are widely used in quantum computing due to their high superconducting transition temperatures and high critical fields. Devices that combine superconducting performance and spintronic non-volatility could deliver unique functionality. Here we report the study of magnetic tunnel junctions with Nb as the heavy metal layers. An interfacial perpendicular magnetic anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO heterostructures. The tunneling magnetoresistance was evaluated in junctions with different thickness combinations and different annealing conditions. An optimized magnetoresistance of 120% was obtained at room temperature, with a damping parameter of 0.011 determined by ferromagnetic resonance. In addition, spin-transfer torque switching has also been successfully observed in these junctions with a quasistatic switching current density of 7.3 times ;10^{5} A/cm2.

Exchange field enhanced upper critical field of the superconductivity in compressed antiferromagnetic EuTe2

Understanding the interplay between superconductivity and magnetism has been a longstanding challenge in condensed matter physics. Here we report high pressure studies on the C-type antiferromagnetic semiconductor EuTe2 up to 36.0 GPa. A structural transition from the I4/mcm to the C2/m space group is identified at ~16 GPa. Superconductivity is observed above ~5 GPa in both structures. In the low-pressure phase, magnetoresistance measurements reveal strong couplings between the local moments of Eu2+ and the conduction electrons of Te 5p orbits. The upper critical field of superconductivity is well above the Pauli limit. While EuTe2 becomes nonmagnetic in the high-pressure phase and the upper critical field drops below the Pauli limit. Our results demonstrate that the high upper critical field of EuTe2 in the low-pressure phase is due to the exchange field compensation effect of Eu2+ and the superconductivity in both structures may arise in the framework of the Bardeen-Cooper-Schrieffer theory.

Strikingly reduced critical field in Ti-doped Kagomé YMn6Sn5.6Ti0.4 single crystal with large topological Hall effect

The Kagomé layered YMn6Sn6 alloy reveals large anomalous and topological Hall effects, implying tremendous application potential in spintronics devices. However, high critical magnetic field (the applied field corresponding to topological hall resistivity maximum) is likely to be a stumbling block to its practical application. In this work, a series of YMn6Sn6-xTix (x = 0, 0.4, 0.8, 1, 1.2) single crystals were prepared, in which the substitution of Ti for Sn sites is adopted to modify the exchange interaction between Mn layers in YMn6Sn6 alloy. The magnetic configurations and topological Hall effect are controlled resultantly. For YMn6Sn5.6Ti0.4 alloy, especially, the critical field reduces strikingly to less than 1T from near 4T or even higher [Sci. Adv. 6 (2020) eabe2680, https://doi.org/10.1126/sciadv.abe2680 and Phys. Rev. B 103 (2021) 014416, https://link.aps.org/doi/10.1103/PhysRevB. 103.014416]. What is more important, the topological Hall resistivity still remains relatively large value, ∼0.706 μΩ∙cm. In addition, large anomalous Hall conductivity of 55.7 Ω−1cm−1 is obtained in YMn6Sn5.6Ti0.4.

A spin–orbit scattering–enhanced high upper critical field at the LaAlO3/KTaO3(111) superconducting interface

Spin–orbit interaction is essential to enhance the in-plane upper critical field of two-dimensional superconductors. Here, we report the LaAlO3/KTaO3 (111) superconducting interface (T c,0 ≈ 0.475 K) with a high in-plane upper critical field (∼1.6 T), which is approximately 1.8 times the Pauli paramagnetic limit. The H T superconducting phase diagram is well-fitted by the Klemm–Luther–Beasley (KLB) theory, and the relevant spin–orbit scattering (SOS) length is approximately 32 nm. Furthermore, normal-state magnetotransport measurements show signatures of weak antilocalization caused by strong spin–orbit coupling in LaAlO3/KTaO3 (111). The spin diffusion length derived from magnetotransport measurements was 40 nm at 2 K, which is comparable with the SOS length. The conformity of the phase diagram with the KLB theory and the consistency of normal state spin diffusion length and superconducting SOS length indicate that the high in-plane upper critical field at the LaAlO3/KTaO3 (111) superconducting interface is enhanced by SOS.

Electron–phonon effects and temperature-dependence of the electronic structure of monoclinic β-Ga2O3

Gallium oxide (Ga2O3) is a promising semiconductor for next-generation high-power electronics due to its ultra-wide bandgap and high critical breakdown field. To utilize its unique electrical properties for real-world applications, an accurate description of its electronic structure under device-operating conditions is required. Although the majority of first-principles models focus on the ground state, temperature effects govern the key properties of all semiconductors, including carrier mobility, band edge positions, and optical absorption in indirect gap materials. We report on the temperature-dependent electronic band structure of β-Ga2O3 in a wide temperature range from T = 0 to 900 K using first-principles simulations and optical measurements. Band edge shifts from lattice thermal expansion and phonon-induced lattice vibrations known as electron–phonon renormalization are evaluated by utilizing the quasi-harmonic approximation and the recently developed “one-shot” frozen phonon method, respectively. Electron–phonon effects and thermal expansion together induce a substantial temperature-dependence on the bandgap, reducing it by more than 0.5 eV between T = 0 and 900 K, larger than that observed in other wide bandgap materials. Key implications, including an increase in carrier concentrations, a reduction in carrier mobilities due to localization of band edge states, and an ∼20% reduction in the critical breakdown field, are discussed. Our prediction of temperature-dependent bandgap matches very well with experimental measurements and highlights the importance of accounting for such effects in first-principles simulations of wide bandgap semiconductors.

Low leakage current and high breakdown voltage of AlGaN/GaN Schottky barrier diodes with wet-etching groove anode

AlGaN/GaN heterojunction epitaxies with wide bandgap, high critical electric field as well as high density and high mobility two-dimensional electron gas have shown great potential applications in the next-generation high-power and high-frequency devices. Especially, with the development of Si-based GaN epitaxial technique with big size, GaN devices with low cost also show great advantage in consumer electronics. In order to improve the rectification efficiency of AlGaN/GaN Schottky barrier diode (SBD), low leakage current and low turn-on voltage are important. The GaN Schottky barrier diode with low work-function metal as anode is found to be very effective to reduce turn-on voltage. However, the low Schottky barrier height makes the Schottky interface sensitive to damage to groove surface, which leads to a high leakage current. In this work, a novel wet-etching technique with thermal oxygen oxidation and KOH corrosion is used to prepare the anode groove, and the surface roughness of groove decreases from 0.57 to 0.23 nm, compared with that of the dry-etching surface of groove. Meanwhile, the leakage current is suppressed from 1.5 × 10<sup>–6</sup> to 2.6 × 10<sup>–7</sup> A/mm. Benefiting from the great corrosion selectively of hot KOH solution to AlGaN barrier layer and GaN channel layer after thermal oxygen oxidation, the spikes of the edge of groove region caused by the nonuniform distribution of plasma in the cavity is improved, and the breakdown voltage of the fabricated AlGaN/GaN SBDs is raised from –1.28 to –1.73 kV.

Coexistence of superconductivity and charge density wave instability in A15-Nb3Sn.

A15-type compound Nb3Sn has attracted much attention due to its relatively high critical temperature and critical field of superconductivity, making it a leading material for superconducting applications. In this study, we investigate the structural instability and superconductivity of Nb3Sn under hydrostatic pressure using first-principles calculations. We determine the electronic properties, phonon dispersion, electron-phonon coupling and the superconducting gap for Nb3Sn at pressures ranging from ambient to 9 GPa. Our results show that a significant electron density is present near the Fermi level due to the van Hove singularity, indicating the strong electron-phonon coupling. The phonon dispersion of Nb3Sn exhibits Kohn anomalies at three different wave vectors at a lower temperature. Moreover, above a pressure of 6 GPa, the charge density wave (CDW) instability disappeared, suggesting that pressure inhibits the CDW phase. The superconducting temperature is predicted to be TC = 18.62 K under ambient conditions, which is well consistent with the experimental results. We find that both the CDW and superconducting orders respond to pressure, with their transition temperatures decreasing as the pressure increases below 6 GPa. Above 6 GPa, the superconducting transition temperature increases slowly with pressure. Our results suggest that the instability in Nb3Sn is driven by the softening of the phonon modes due to the CDW caused by strong electron-phonon coupling. Therefore, the CDW phase and superconducting phase of Nb3Sn coexist at low pressure.

Characterization of epitaxial layers grown on 4H-SiC (0 0 0 −1) substrates

SiC is an excellent semiconductor material that can be used in power semiconductor devices. It has the advantages of high thermal conductivity, stable chemical properties, and high critical breakdown field strength. The active region of a SiC device is usually in the SiC epitaxial layer, so the growth of high-quality SiC epitaxial layers is extremely valuable. In this paper, we investigate the epitaxial growth of SiC on n-type 4° off-axis SiC (0 0 0–1) substrates. We used a horizontal hot-wall chemical vapor deposition apparatus for rapid epitaxy on SiC substrates, using C2H4, and SiHCl3 as precursors and H2 as carrier gas, respectively, and growing at 1350 °C,1400 °C,1450 °C,1500 °C, 1550 °C, 1600 °C for half an hour to get epitaxial layer. The effect of growth temperature on the surface morphology of SiC (0 0 0 –1) epitaxial layer was analyzed and epitaxial layers is characterized by optical microscope, scanning electron microscope, atomic force microscope and Raman scattering instrument, and the growth rate of epitaxial layer was obtained. It is found that the higher growth temperature is helpful to obtain the epitaxial layer with smooth surface and higher content of 4H-SiC under certain pressure, C/Si molar ratio, and following rate of precursor and carrier gas.

Design, fabrication, and characterization of a high-field high-temperature superconducting Bi-2212 accelerator dipole magnet

The use of high-field superconducting magnets has furthered the development of medical diagnosis, fusion research, accelerators, and particle physics. High-temperature superconductors enable magnets more powerful than those possible with Nb-Ti (superconducting transition temperature ${T}_{c}$ of 9.2 K) and ${\mathrm{Nb}}_{3}\mathrm{Sn}$ (${T}_{c}$ of 18.4 K) conductors due to their very high critical field ${B}_{c2}$ of greater than 100 T near 4.2 K. However, the development of high-field accelerator magnets using high-temperature superconductors is still at its early stage. We report the construction of the world's first high-temperature superconducting ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{x}$ (Bi-2212 with ${T}_{c}$ of $\ensuremath{\sim}82\text{ }\text{ }\mathrm{K}$) accelerator dipole magnet. The magnet is based on a canted-cosine-theta design with Bi-2212 Rutherford cables. A high critical current was achieved by an overpressure processing heat treatment. The magnet was constructed from a nine-strand Rutherford cable made from industrial 0.8 mm wires. At 4.2 K, it reached a quench current of 3600 A and a dipole field of 1.64 T in a bore of 31 mm. The magnet did not exhibit the undesirable quench training common in Nb-Ti and ${\mathrm{Nb}}_{3}\mathrm{Sn}$ accelerator magnets. It quenched a dozen times without degradation. The magnet exhibited low magnetic field hysteresis ($<0.1%$) as measured by a cryogenic Hall sensor. It was fast cycled to 1.47 T at $0.54\text{ }\text{ }\mathrm{T}/\mathrm{s}$ without quenches. This work validates the canted-cosine-theta Bi-2212 dipole magnet design, illustrates the fabrication scheme, and establishes an initial performance benchmark.

Submicron Sr0.7Bi0.2TiO3 dielectric ceramics for energy storage via a two-step method aided by cold sintering process

A serials of relaxor ferroelectrics of Sr0.7Bi0.2TiO3 ceramics with different grain sizes were prepared by a conventional sintering (CS) and a two-step cold sintering aided process (CSP) method. The microstructure, dielectric and energy storage performance of the synthesized ceramics were systematically studied. Owing to the involvement of CSP, grain size is reduced to submicrometer scale, and uniform and dense morphology are achieved at a lower sintering temperature compared with the CS method. As a consequence, high critical electric field (420 kV/cm), a good recoverable energy storage density (3.32 J/cm3), and a superior energy efficiency (92.84 %) can be realized for the ceramic via CSP sintered at 1170 °C. Meanwhile, it also exhibits good stability over wide ranges of measuring frequencies and temperatures, and increasing cycles to 107. A high power density (85.46 MW/cm3) is achieved due to a very fast discharge rate (∼61.7 ns). Moreover, the synthesized ceramic demonstrates an ultrahigh hardness of ∼ 8.73 GPa. These results indicate that CSP is a feasible solution to achieve outstanding comprehensive dielectric energy storage performance by utilizing the synergistic effects of grain refinement and densification.

High critical field superconductivity at ambient pressure in MoB2 stabilized in the P6/mmm structure via Nb substitution

Recently it was discovered that, under elevated pressures, MoB$_2$ exhibits superconductivity at a critical temperature, $T_c$, as high as 32 K. The superconductivity appears to develop following a pressure-induced structural transition from the ambient pressure R$\bar{3}$m structure to an MgB$_2$-like P6/mmm structure. This suggests that remarkably high $T_c$ values among diborides are not restricted to MgB$_2$ as previously appeared to be the case, and that similarly high $T_c$ values may occur in other diborides if they can be coerced into the MgB$_2$ structure. In this paper, we show that density functional theory calculations indicate that phonon free energy stabilizes the P6/mmm structure over the R$\bar{3}$m at high temperatures across the Nb$_{1-x}$Mo$_x$B$_2$ series. X-ray diffraction confirms that the synthesized Nb-substituted MoB$_2$ adopts the MgB$_2$ crystal structure. High magnetic field electrical resistivity measurements and specific heat measurements demonstrate that Nb$_{1-x}$Mo$_x$B$_2$ exhibits superconductivity with $T_c$ as high as 8 K and critical fields approaching 6 T.

High upper critical field (120 T) with small anisotropy of highly hydrogen-substituted SmFeAsO epitaxial film

The electronic transport properties of a highly hydrogen-substituted 1111-type SmFeAsO epitaxial film with high critical-temperature (Tc = 45 K) were investigated under high magnetic fields. By using a single-turn magnet generating up to 130 T, we clarified that the upper critical field ({\mu}0Hc2) of SmFeAsO0.65H0.35 is 120 T at the nearly low-temperature limit of 2.2 K for {\mu}0H || ab. The angular dependence of {\mu}0Hc2 revealed that the anisotropic parameter ({\gamma}) around Tc is ~2, which is comparable with that of a practical candidate 122-type BaFe2As2 with lower Tc and much smaller than that of F-substituted SmFeAsO. The small {\gamma} mainly originates from the high hydrogen incorporation. The extremely high {\mu}0Hc2 and small {\gamma}, together with the high Tc and high critical current density, suggest that SmFeAsO1-xHx has high potential for the superconducting electromagnets and cables.