Low Critical Current Density Research Articles

Design and Comparison of Diamond‐ and Sapphire‐Based NbN KIDs for Fusion Plasma Polarimetric Diagnostics

Design and characterization measurements performed on kinetic inductance detectors (KIDs) produced on sapphire and polycrystalline diamond substrates are presented. Designed as part of a nuclear fusion polarimetric diagnostic, the foreseen plasma‐probing frequency of the final devices is 1.3 THz with a maximum response time under 10 ms and cross‐polarization target accuracy of 1%. These detectors are based on superconducting micro‐resonators that undergo de‐tuning upon absorption of radiation. The main characteristics of the devices include polarization sensitiveness and lumped‐elements multi‐pixel configuration produced from photo‐lithographed niobium nitride (NbN) thin films. The direct current (DC) and microwave characterization measurements highlight large differences in the thin film quality, with the superconductor deposited on diamond showing reduced critical temperature, lower critical current density, and increased values of the kinetic inductance. This difference is likely due to the higher lattice constant and thermal expansion coefficient mismatch between film and substrate in the case of diamond, with the different surface finish quality of the crystalline samples available also playing a role. The devices on both substrates show a bolometric response to THz radiation that fulfills the requirement guidelines and represent a good starting point to optimize the design for the application at hand.

Grafting of Lithiophilic and Electron‐Blocking Interlayer for Garnet‐Based Solid‐State Li Metal Batteries via One‐Step Anhydrous Poly‐Phosphoric Acid Post‐Treatment

AbstractGarnet‐based solid‐state Li‐metal batteries (GSSBs) have the merits of high energy density and high safety. However, the realization of a stable and well‐matched Li|garnet interface for GSSBs remains challenging due to electron leakage and lithiophobic Li2CO3 impurity. To address these issues, herein, new surface chemistry is reported that converts the undesired Li2CO3 contaminant into an ultra‐thin lithium polyphosphate (Li‐PPA) layer through anhydrous polyphosphoric acid ‐induced in situ substitution reaction without damaging the water‐sensitive garnet electrolyte. In particular, the Li‐PPA interlayer not only facilitates the homogenous spreading of molten Li but also creates a robust electron‐blocking shield to suppress Li dendrite formation. As a result, the assembled Li symmetric cell exhibits a low interfacial impedance (4 Ω cm2) and high critical current density (1.8 mA cm−2) at 25 °C, which enables the cell to continuously cycle over 2500 h at 0.2 mA cm−2. Furthermore, the GSSBs paired with LiFePO4 deliver a high capacity of 149.3 mAh g−1 at 1 C and maintain 92.3% of the initial capacity after 500 cycles and can be used for solar energy storage, suggesting the feasibility of this interfacial engineering strategy for GSSBs.

Enhanced Spin–Orbit Torque Performances in PtRu–Co–PtRu–Ni–Ru-Based Spintronic Devices

The Pt80Ru20 alloy has been testified to be a satisfying heavy metal layer (HM) in spin–orbit torque (SOT)-induced spintronic devices with a relatively high-spin Hall angle (θDL) and a low critical current density. In this work, the Pt80Ru20–Co–Ni (xNi nm)–Ru multilayers are first prepared to find the field-free SOT-induced switching by the direct coupling of out-of-plane and in-plane ferromagnetic (FM) layers. A low in-plane assist field of −20 Oe and some optimized SOT performances are observed in the devices with xNi = 0.4 and 0.8 nm, respectively. To further enhance the performances of the devices, a 0.6 nm thin Pt80Ru20 layer is inserted between two FM layers. In the Pt80Ru20–Co–Pt80Ru20–Ni (tNi nm)–Ru multilayers, the energy consumption decreases dramatically and a higher θDL of 0.156 is obtained in the device with tNi = 0.8 nm. More importantly, the field-free current-induced magnetization switching is realized in the device with tNi = 1.4 nm. Furthermore, the interfacial Dzyaloshinskii–Moyria Interaction (DMI) can be weakened by the thin insertion as well. Our results reveal that the PtRu-based spintronic devices with enhanced SOT performances and field-free SOT-driven switching can be a promising candidate in the application of SOT-induced spintronic devices.

Assessing the critical current density of all-solid-state Li metal symmetric and full cells

All-solid-state Li metal batteries (Li-ASSBs) have drawn much attention in recent years owing to their potential in achieving high energy densities. However, the low critical current density (CCD) of Li-ASSBs at room temperature remains a major bottleneck which limits the prospects for commercialization. Most studies reported so far have demonstrated CCDs significantly lower than conventional lithium-ion batteries, along with a lack of consistency across such reports. While these CCD inconsistencies can be attributed to variations in pressure, temperature, and solid electrolyte chemistry, crucial parameters often omitted in the literature, such as the fabrication pressure used and duration for which it is applied, both of which are required to achieve good contact between Li metal and the solid electrolyte. Here, the relationship between the fabrication pressure contact hold time of Li metal versus CCD is reported, thus elucidating the effect of controlled Li deformation on the CCD. The CCDs for symmetric and full cell architectures are also evaluated, where the effect of volumetric expansion and associated changes in cell stack pressure are examined. Finally, a constant pressure cell design is introduced to mitigate the negative effects of volume change during cycling, allowing the Li-ASSB to achieve higher CCDs at room temperature.

Efficient Tuning of the Spin-Orbit Torque via the Magnetic Phase Transition of FeRh.

The understanding and control of the spin-orbit torque (SOT) are central to antiferromagnetic spintronics. Despite the fact that a giant SOT efficiency has been achieved in numerous materials, its efficient tuning in a given material has not been established. Materials with magnetic phase transitions (MPTs) offer a new perspective, as the SOT efficiency may vary significantly for the different magnetic orderings across the transition, and the transition itself can be readily tuned by various control parameters. This work reports that the SOT efficiency of a FeRh-based perpendicular magnetized heterostructure can be significantly tuned by varying the temperature across the MPT. The SOT efficiency exhibits a temperature hysteresis associated with the first-order nature of the MPT, and its value in the ferromagnetic phase is seen to be enhanced by ∼450%, simply by a lowering of temperature to drive FeRh into the antiferromagnetic phase. Furthermore, current-induced magnetization switching can be achieved without an assistant magnetic field for both ferromagnetic and antiferromagnetic FeRh, with a low critical switching current density for the latter. These results not only directly establish FeRh as an efficient spin generator but also present a strategy to dynamically tune SOT via varying the temperature across MPTs.

Enhancement of lithium argyrodite interface stability through MoO2 substitution and its application in lithium solid state batteries

A recently developed sulfide solid electrolyte in lithium solid-state batteries has a low critical current density, which can cause battery failure. Therefore, the metal oxide substitution in the Li-argyrodite structure was considered as a strategy to enhance the interface stability. In this work, the interface stability of the Li-argyrodites was improved using metal and oxygen substitution in the P- and S-sites of the Li6PS5Cl structure; furthermore, their structural and electrochemical performances were evaluated. For this study, the MoO2 substituted argyrodite (0 ≤ x ≤ 0.2) was synthesized using a high-energy ball-milling process. Structural analysis revealed that impurity phases occurred when x was over 0.05; this indicated the solubility limit of the metal oxide substitution. The ionic conductivity analysis demonstrated that Li6PS5Cl-MoO2-0.05 electrolyte maintained an ionic conductivity of 4.16 mS cm−1. Additionally, the Li6PS5Cl-MoO2-0.05 composition exhibited a higher critical current density (0.55 mA cm−2) than that of Li6PS5Cl (0.20 mA cm−2). It should be further noted that the electrochemical performances were examined against lithium as a reference.

Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: Structural, strain, magnetic, and spin transport properties

Single-crystal europium iron garnet (EuIG) thin films epitaxially strain-grown on gadolinium gallium garnet (GGG)(100) substrates using off-axis sputtering have strain-induced perpendicular magnetic anisotropy (PMA). By varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe) composition ratios in the films to tailor the film strains. The films exhibited an extremely smooth, particle-free surface with roughness as low as 0.1 nm as observed using atomic force microscopy. High-resolution x-ray diffraction analysis and reciprocal space maps showed in-plane epitaxial film growth, very smooth film/substrate interface, excellent film crystallinity with a small full width at half maximum of 0.012$^{\circ}$ in the rocking curve scans, and an in-plane compressive strain without relaxation. In addition, spherical aberration-corrected scanning transmission electron microscopy showed an atomically abrupt interface between the EuIG film and GGG. The measured squarish out-of-plane magnetization-field hysteresis loops by vibrating sample magnetometry in conjunction with the measurements from angle-dependent x-ray magnetic dichroism demonstrated the PMA in the films. We have tailored the magnetic properties of the EuIG thin films, including saturation magnetization ranging from 71.91 to 124.51 emu/c.c. (increase with the (Eu/Fe) ratios), coercive field from 27 to 157.64 Oe, and the strength of PMA field ($H_\bot$) increasing from 4.21 to 18.87 kOe with the in-plane compressive strain from -0.774 to -1.044%. We have also investigated spin transport in Pt/EuIG bi-layer structure and evaluated the real part of spin mixing conductance to be $3.48\times10^{14} {\Omega}^{-1}m^{-2}$. We demonstrated the current-induced magnetization switching with a low critical switching current density of $3.5\times10^6 A/cm^2$, showing excellent potential for low-dissipation spintronic devices.

A liquid cathode/anode based solid-state lithium-sulfur battery

Solid-state lithium sulfur batteries constantly suffer from a poor interfacial compatibility between solid-state cathode/anode and electrolyte, and low critical current density of Li metal anode (< 3 mA cm−2). Here, a concept of a liquid cathode/anode based, room-temperature, solid-state lithium sulfur battery with low impedance electrode/electrolyte interfaces is presented. Due to an extremely stable liquid-solid interface with a high compatibility and unique properties of liquid alloy, the liquid Li-amalgam anode based symmetric cells show a superior electrochemical performance, and no internal short circuit occurs as they run at 55.6 mA cm−2 for 10,000 cycles. Liquid Li2S8 polysulfide catholyte can afford a high active material loading (≥135.2 mg mL−1) and has a good contact with the solid-sate electrolyte. The cathode/anode and electrolyte are tightly welded together by the liquid-solid interfaces, and the resulting cells show high performance and good structural stability during cycling.

The Influence of Surface Chemistry on Critical Current Density for Garnet Electrolyte

AbstractGarnet‐based solid state lithium batteries have attracted a lot of attention due to their potential advantages in safety and energy density. However, the high electrode–electrolyte interfacial resistance and low critical current density (CCD) related with lithium dendrite penetration have seriously hindered their further development and practical application. Here, for garnet‐type solid electrolyte, the surface Li2CO3, interlayer species, lithium wettability, interfacial impedance, and CCD are systematically investigated. It turns out that Li2CO3‐free garnet electrolyte is intrinsically lithiophilic, and the interfacial impedance is mainly affected by the amount of surface Li2CO3. In addition, the CCD values are manipulated by the interfacial impedance rather than the apparent Li wettability. This study provides a comprehensive understanding about the interrelationships among surface chemistry, lithium wettability, interfacial impedance, and critical current density for garnet‐type solid electrolytes.

Toward 100% Spin–Orbit Torque Efficiency with High Spin–Orbital Hall Conductivity Pt–Cr Alloys

5d transition metal Pt is the canonical spin Hall material for efficient generation of spin–orbit torques (SOTs) in Pt/ferromagnetic layer (FM) heterostructures. However, for a long while with tremendous engineering endeavors, the damping-like SOT efficiencies (ξDL) of Pt and Pt alloys have still been limited to ξDL < 0.5. Here we present that with proper alloying elements, particularly 3d transition metals V and Cr, a high spin–orbital Hall conductivity (σSH ≈ 6.5 × 105 (ℏ/2e) Ω–1 m–1) can be developed. Especially for the Cr-doped case, an extremely high ξDL ≈ 0.9 in a Pt0.69Cr0.31/Co device can be achieved with a moderate Pt0.69Cr0.31 resistivity of ρxx ≈ 133 μΩ cm. A low critical SOT-driven switching current density of Jc ≈ 3.2 × 106 A cm–2 is also demonstrated. The damping constant (α) of the Pt0.69Cr0.31/FM structure is also found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall high σSH, giant ξDL, moderate ρxx, and reduced α of such a Pt–Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.

Fast‐Charging Solid‐State Lithium Metal Batteries: A Review

Nowadays solid‐state lithium metal batteries (SSLMBs) catch researchers’ attention and are considered as the most promising energy storage devices for their high energy density and safety. However, compared to lithium‐ion batteries (LIBs), the low ionic conductivity in solid‐state electrolytes (SSEs) and poor interface contact between SSEs and electrodes counteract some advantages of SSEs. As a result, SSLMBs show high energy density but low critical current density and slow charging speed. Herein, the recent progress and proposed strategies for fast‐charging SSLMBs are reviewed. In the second part of this review, various strategies for improving SSE performance in fast‐charging batteries are comprehensively highlighted. In the third part, various rational structure design schemes benefitting fast‐charging batteries are discussed. Finally, the development of fast‐charging SSLMBs is concluded and prospected. It is believed that the combination of fast‐charging times and SSLMBs is rather competitive for next‐generation, high energy density, high safety, and high charging rate energy storage devices.

Enhanced critical current density of Garnet Li7La3Zr2O12 solid electrolyte by incorporation of LiBr

Cubic garnet Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolytes have a strong potential to allow solid-state lithium-ion to become the next-generation energy storage systems and for addressing the safety issues. However, the applications of LLZO solid electrolytes are seriously limited by the relatively low critical current density of LLZO. In this study, we introduce lithium bromide (LiBr) with a low melting point as the sintering aid to prepare a high-performance garnet with high ionic conductivity, high relative density, and excellent critical current density. The prepared LLZO solid electrolyte with a LiBr concentration of 0.15 ( x LiBr–LLZO with x = 0.15 mol) exhibited a high ionic conductivity of 7.62 × 10 −4 S cm −1 at 25 ℃ with an excellent relative density of 96.27%. The critical current density (CCD) of the symmetric Li | 0.15LiBr–LLZO | Li cell was 1.0 mA cm −2 at 25 ℃. Furthermore, this cell can stably operate for 1000 h under a current density of 0.3 mA cm −2 . In addition, quasi-solid-state batteries of Li | LiFePO 4 with 0.15LiBr–LLZO electrolyte delivered excellent capacity retention (141.1 mAh g − 1 ; ∼89.7%) after 300 cycles, excellent rate performance, high coulombic efficiency and cycling stability. Furthermore, Li | LiNi 0.8 Co 0.1 Mn 0.1 O 2 with 0.15LiBr–LLZO electrolyte could run normally with high coulombic efficiency (>99%). These research results show that the solid-state batteries developed using 0.15LiBr–LLZO electrolyte are highly promising for the practical applications.

Efficient and controllable magnetization switching induced by intermixing-enhanced bulk spin–orbit torque in ferromagnetic multilayers

Spin–orbit torque induced ferromagnetic magnetization switching brought by injecting a charge current into strong spin–orbit-coupling materials is an energy-efficient writing method in emerging magnetic memories and spin logic devices. However, because of the short spin coherence length in ferromagnetic layers, the interfacial effective spin–orbit torque typically leads to high critical current density for switching thick ferromagnet, which goes against low-power and high-density requirements. Here, we experimentally demonstrate efficient bulk spin–orbit torque-driven perpendicular magnetization switching under relatively low critical current density in thick Pt/Co multilayers with gradient-induced symmetry breaking. Through tuning the thickness gradient of Pt, the spin–orbit torque efficiency and switching chirality can be highly controlled, which also indicates that net spin current arises from gradient. Meanwhile, x-ray absorption spectroscopy results reveal that the atomic intermixing can significantly enhance the spin–orbit torque efficiency through improving the strength of spin–orbit-coupling of Pt. We also establish a micromagnetic model by taking both gradient-induced and intermixing-enhanced spin–orbit torque into account to well describe the experimental observations. This work would blaze a promising avenue to develop novel spin–orbit torque devices for high-performance spintronic memory and computation systems.

An effective solid-electrolyte interphase for stable solid-state batteries

An effective solid-electrolyte interphase for stable solid-state batteries

Exponential reduction in critical current density in Eu1-xCexBa2Cu3O7-δsuperconductors near critical temperature

We have studied how the current-voltage (IV) characteristic below the critical temperature gets affected by electron doping in Eu1-xCexBa2Cu3O7-δ (ECBCO) superconducting systems. The critical current density as a function of T has been extracted in the vicinity but below the critical temperature. Variation of the low critical current density with temperature in the limited range of T has been explained by using an exponential dependence on T. Possibility of the Ambegaokar-Baratoff (AB) to Ginzburg-Landau (GL) crossover has been explored. An exponential nature of the variation in all electron doped superconductors with large angular separation between grain boundaries is attributed to the existence of the vortex fluid state in a narrow range of T.

Pronounced electromigration of GaInSn/Cu interconnects under super low critical current density

Ga-based alloys has been paid increasingly attention as a promising material choice for constructing flexible and stretchable electronics. The interfacial stability of non-bonding GaInSn/Cu interconnect plays a critical role in determining its electrical performance. Here, we report an interesting electromigration phenomenon under current flux and verify the atoms migration through the GaInSn path from cathode to the anode. The critical current density for inducing the room temperature electromigration of Cu/GaInSn/Cu is two orders of magnitude lower than that of other electromigration system. When Ni which has a higher bond strength is employed to substitute Cu anode, due to the small number of intermetallic compounds embryos, the electromigration resistance of anode material is substantially improved. Our findings will provide good insights into the electromigration of Cu/GaInSn/Cu and may offer a critical first step toward the design of high- performance Ga-based soft and stretchable electronics.

Characterization of energy potential in tunable rf-SQUIDs with the classical regime toward precise design of superconducting flux qubit

The detailed characteristics of classical states in a radio-frequency superconducting quantum interference device (rf-SQUID) with well-designed energy-potential shape are investigated at 4.2 K. Using Nb/AlO x standard process which enables precise circuit-parameter implementation, the rf-SQUID is designed in its energy potential. Directions of persistent current can be distinguished in the rf-SQUID we have fabricated. Analyses in circuit simulations indicate the device design based on enough high critical current provides available parameters to construct the device for 10 mK measurement by circuit-parameter scaling. This knowledge may contribute to the precise design of the rf-SQUID for superconducting qubit through device process with lower critical current density.

Negligible oxygen vacancies, low critical current density, electric-field modulation, in-plane anisotropic and high-field transport of a superconducting Nd0.8Sr0.2NiO2/SrTiO3 heterostructure

The emerging Ni-based superconducting oxide thin films are rather intriguing to the entire condensed matter physics. Here we report some brief experimental results on transport measurements for a 14-nm-thick superconducting Nd0.8Sr0.2NiO2/SrTiO3 thin-film heterostructure with an onset transition temperature of ~9.5 K. Photoluminescence measurements reveal that there is negligible oxygen vacancy creation in the SrTiO3 substrate during thin-film deposition and post chemical reduction for the Nd0.8Sr0.2NiO2/SrTiO3 heterostructure. It was found that the critical current density of the Nd0.8Sr0.2NiO2/SrTiO3 thin-film heterostructure is relatively small, ~4x10^3 A/cm2. Although the surface steps of SrTiO3 substrates lead to an anisotropy for in-plane resistivity, the superconducting transition temperatures are almost the same. The out-of-plane magnetotransport measurements yield an upper critical field of ~11.4 T and an estimated in-plane Ginzburg-Landau coherence length of ~5.4 nm. High-field magnetotransport measurements up to 50 T reveal anisotropic critical fields at 1.8 K for three different measurement geometries and a complicated Hall effect. An electric field applied via the SrTiO3 substrate slightly varies the superconducting transition temperature. These experimental results could be useful for this rapidly developing field.

Efficient Spin-Orbit Torque Generation in Semiconducting WTe2 with Hopping Transport.

Spin-orbit torques (SOTs) from transition metal dichalcogenide systems (TMDs) in conjunction with ferromagnetic materials are recently found to be attractive in spintronics for their versatile features. However, most of the previously studied crystalline TMDs are prepared by mechanical exfoliation, which limits their potentials for industrial applications. Here, we show that amorphous WTe2 heterostructures deposited by magnetron sputtering possess a sizable damping-like SOT efficiency of ξDLWTe2 ≈ 0.20 and low damping constant of α = 0.009 ± 0.001. Only an extremely low critical switching current density of Jc≈ 7.05 × 109 A/m2 is required to achieve SOT-driven magnetization switching. The SOT efficiency is further proved to depend on the W and Te relative compositions in the co-sputtered W100-xTex samples, from which a sign change of ξDLWTe2 is observed. In addition, the electronic transport in amorphous WTe2 is found to be semiconducting and is governed by a hopping mechanism. With the above advantages and rich tunability, amorphous and semiconducting WTe2 serves as a unique SOT source for future spintronics applications.

Fluctuation induced conductivity and pseudogap state studies of Bi1.6Pb0.4Sr2Ca2Cu3O10+\u03b4 superconductor added with ZnO nanoparticles

The major limitations of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductor are weak flux pinning capability and weak inter-grains coupling that lead to a low critical current density and low critical magnetic field which impedes the suppleness of this material towards practical applications. The addition of nanoscales impurities can create artificial pining centers that may improve flux pinning capability and intergranular coupling. In this work, the influences of ZnO nanoparticles on the superconducting parameters and pseudogap properties of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductor are investigated using fluctuation induced conductivity analyses. Results demonstrate that the ZnO nanoparticles addition improves the formation of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ phase significantly. Various superconducting parameters include coherence length along c-axis (ξc(0)), penetration depth (λpd(0)), Fermi velocity (vF), Fermi energy (EF), lower and upper critical magnetic fields (Bc1(0) and Bc2(0) respectively) and critical current density (Jc(0)), are estimated for samples with different amounts of ZnO nanoparticles. It is found that the values of the Bc1(0), Bc2(0), and Jc(0) are improved significantly in the 0.2 wt% ZnO added sample in comparison to the ZnO-free sample. The magnitude and temperature dependence of the pseudogap Δ*(T) is calculated using the local pairs model. The obtained values of Tpair, the temperature at which local pairs are transformed from strongly coupled bosons into the fluctuating Cooper pairs, increases as the added ZnO nanoparticles concentration enhances up to 0.2 wt%. Also, the estimated values for the superconducting gap at T = 0 K (Δ(0)) are decreased from about 26 meV in ZnO-free sample to about 22 meV in 0.2 wt% ZnO added sample and then increases for higher values of additive.