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At least 145 records · Page 8

An antiferromagnetic diode effect in even-layered MnBi 2 Te 4

In a p–n junction, the separation of positive and negative charges leads to diode transport, in which charge flows in only one direction. Non-centrosymmetric polar conductors are intrinsic diodes that could be of use in the development of nonlinear applications. Such systems have recently been extended to non-centrosymmetric superconductors, and the superconducting diode effect has been observed. Here, in this paper, we report an antiferromagnetic diode effect in a centrosymmetric crystal without directional charge separation. We observed large second-harmonic transport in a nonlinear electronic device enabled by the compensated antiferromagnetic state of even-layered MnBi 2 Te 4 . We show that this antiferromagnetic diode effect can be used to create in-plane field-effect transistors and microwave-energy-harvesting devices. We also show that electrical sum-frequency generation can be used as a tool to detect nonlinear responses in quantum materials.

electronic properties and materials↗

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

Abstract In recent years there has been an increasing effort in improving the performance of Nb 3 Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields ( H Irr and H c2 , respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb 3 Sn grains and HfO 2 nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb 3 Sn. H c2 (0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb 3 Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5–4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb 3 Sn closer to the requirements necessary for FCC realization.

36 MATERIALS SCIENCE↗

Visualizing heterogeneous dipole fields by terahertz light coupling in individual nano-junctions

The challenge underlying superconducting quantum computing is to remove materials bottleneck for highly coherent quantum devices. The nonuniformity and complex structural components in the underlying quantum circuits often lead to local electric field concentration, charge scattering, dissipation and ultimately decoherence. Here we visualize interface dipole heterogeneous distribution of individual Al/AlO$_{x}$/Al junctions employed in transmon qubits by broadband terahertz scanning near-field microscopy that enables the non-destructive and contactless identification of defective boundaries in nano-junctions at an extremely precise nanoscale level. Our THz nano-imaging tool reveals an asymmetry across the junction in electromagnetic wave-junction coupling response that manifests as hot (high intensity) vs cold (low intensity) spots in the spatial electrical field structures and correlates with defected boundaries from the multi-angle deposition processes in Josephson junction fabrication inside qubit devices. The demonstrated local electromagnetic scattering method offers high sensitivity, allowing for reliable device defect detection in the pursuit of improved quantum circuit fabrication for ultimately optimizing coherence times.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Neutron scattering study of the kagome metal Sc 3 Mn 3 Al 7 Si 5

Sc 3 Mn 3 Al 7 Si 5 is a rare example of a correlated metal in which the Mn moments form a kagome lattice. The absence of magnetic ordering to the lowest temperatures suggests that geometrical frustration of magnetic interactions may lead to strong magnetic fluctuations. We have performed inelastic neutron scattering measurements on Sc 3 Mn 3 Al 7 Si 5 , finding that phonon scattering dominates for energies from ~20–50 meV. These results are in good agreement with ab initio calculations of the phonon dispersions and densities of states, and as well reproduce the measured specific heat. A weak magnetic signal was detected at energies less than ~10 meV, present only at the lowest temperatures. The magnetic signal is broad and quasielastic, as expected for metallic paramagnets.

36 MATERIALS SCIENCE↗

Enhancing spectroscopy and microscopy with emerging methods in photon correlation and quantum illumination

Quantum optics has led to important advancements in our ability to prepare and detect correlations between individual photons. Its principles are increasingly translated into nanoscale characterization tools, furthering methods in spectroscopy, microscopy and metrology. Here, in this Review, we discuss the rapid progress in this field driven by advanced technologies of single-photon detectors and quantum-light sources, including time-resolved single-photon counting cameras, superconducting nanowire single-photon detectors and entangled photon sources of increasing brightness. We emphasize emerging applications in super-resolution microscopy, measurements below classical noise limits and photon-number-resolved spectroscopy—a powerful paradigm for the characterization of nanoscale electronic materials. We conclude by discussing key technological challenges and future opportunities in materials science and bionanophotonics alike.

Tsao, Chieh [University of California, Berkeley, C↗

Imaging the electronic and magnetic structure of topological-superconductor proximity systems (Final Report)

The primary goals of the projects supported by this grant involved developing methods to detect and control electronic states that can aid in the construction of quantum-information devices, including quantum computers. Two types of materials are needed to create these electronic states: superconductors and topological insulators. The interplay of the quantum mechanics of these materials can give rise to elusive states known as Majorana fermions. Majorana Fermions have incredible potential for quantum technology; they can in principle encode quantum information non-locally, and can thus form the basis of especially robust qubits – the basic building blocks of quantum computers. A centerpiece goal of this work was to develop a Majorana detection tool called a Scanning Majorana Microscope. This tool was successfully developed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Magnetic flux trapping in hydrogen-rich high-temperature superconductors

Recent discoveries of superconductivity in various hydrides at high pressures have shown that a critical temperature of superconductivity can reach near-room-temperature values. However, experimental studies are limited by high-pressure conditions, and electrical transport measurements have been the primary technique for detecting superconductivity in hydrides. Here we implement a non-conventional protocol for the magnetic measurements of superconductors in a SQUID magnetometer and probe the trapped magnetic flux in two near-room-temperature superconductors H 3 S and LaH 10 at high pressures. Contrary to traditional magnetic susceptibility measurements, the magnetic response from the trapped flux is almost unaffected by the background signal of the diamond anvil cell due to the absence of external magnetic fields. The behaviour of the trapped flux generated under zero-field-cooled and field-cooled conditions proves the existence of superconductivity in these materials. We reveal that the absence of a pronounced Meissner effect is associated with the very strong pinning of vortices inside the samples. This approach can also be a tool for studying multiphase samples or samples that have a low superconducting fraction at ambient pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Design of a Superconducting Magnetic Suspension System for a Liquid Helium Flow Experiment

We discuss a preliminary design for a superconducting magnetic suspension system for measurement of drag on rotationally symmetric bodies in liquid helium. Superconducting materials are a natural choice for liquid helium studies, since temperatures are well below most critical temperatures, so that the resulting heat load is negligible. Also, due to its diamagnetic properties, a superconducting model (for example made or coated with Nb) is inherently stable against disturbances. Issues which we consider include model placement during initial cool-down, maintaining placement during anticipated drag and lift forces, and force measurement. This later can be achieved by a passive technique, where the body is allowed to deflect under the influence of drag from its neutral position. The resulting shift in flux is detected via a superconducting pickup coil. The pickup coil may be connected either to a SQUID, or a secondary loop wound around a Hall probe. Both options are discussed. The objective of this work is to gain a better understanding of the nature of turbulent fields in normal and superfluid helium for potential application to problems in classical high Reynolds number turbulence.

Smith, Michael R.↗

SERAPH: Wavelike Dark Matter Searches with SRF Cavities

Haloscopes consisting of a microwave cavity with a high quality factor (Q) connected to low-noise electronics have been deployed to detect wavelike axions and dark photons. But the dark matter mass is unknown, so haloscopes must be tunable to search through the photon coupling vs. mass parameter space. Therefore, the scan rate for haloscope experiments is a crucial figure of merit and is proportional to the cavity’s quality factor. State-of-the-art experiments like ADMX currently use copper cavities with 𝑄∼80000. However, implementing superconducting cavities with 𝑄∼1010 can increase the instantaneous scan rate by possibly a factor of 105.This presentation will report progress on the SERAPH experiment, a family of superconducting haloscopes being developed by the Superconducting Quantum Materials and Systems (SQMS) Center. In this presentation, I will first discuss the principles behind operating a haloscope whose bandwidth is much narrower than the dark matter halo energy distribution. I will then describe the first SERAPH experiments implementing a 1.3 GHz Niobium cavity with an ultra-high quality factor (Q~1010) that has achieved the best sensitivity and deepest exclusion to wavelike dark photon dark matter by almost an order of magnitude. Next, I will discuss progress on the next phase of SERAPH, which will search dark photon dark matter using a widely-tunable SRF cavity (4-7 GHz). I will finally describe plans for subsequent SERAPH experiments to search for dark photons and axions with tunable SRF cavities tolerant to multi-Tesla magnetic fields and quantum sensors that subvert the Standard Quantum Limit.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

SERAPH: Wavelike Dark Matter Searches with SRF Cavities

Haloscopes consisting of a microwave cavity with a high quality factor (Q) connected to low-noise electronics have been deployed to detect wavelike axions and dark photons. But the dark matter mass is unknown, so haloscopes must be tunable to search through the photon coupling vs. mass parameter space. Therefore, the scan rate for haloscope experiments is a crucial figure of merit and is proportional to the cavity’s quality factor. State-of-the-art experiments like ADMX currently use copper cavities with 𝑄∼80000. However, implementing superconducting cavities with 𝑄∼1010 can increase the instantaneous scan rate by possibly a factor of 105. This presentation will report progress on the SERAPH experiment, a family of superconducting haloscopes being developed by the Superconducting Quantum Materials and Systems (SQMS) Center. In this presentation, I will first discuss the principles behind operating a haloscope whose bandwidth is much narrower than the dark matter halo energy distribution. I will then describe the first SERAPH experiments implementing a 1.3 GHz Niobium cavity with an ultra-high quality factor (Q~1010) that has achieved the best sensitivity and deepest exclusion to wavelike dark photon dark matter by almost an order of magnitude. Next, I will discuss progress on the next phase of SERAPH, which will search dark photon dark matter using a widely-tunable SRF cavity (4-7 GHz). I will finally describe plans for subsequent SERAPH experiments to search for dark photons and axions with tunable SRF cavities tolerant to multi-Tesla magnetic fields and quantum sensors that subvert the Standard Quantum Limit.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Magnet Architectures and Active Radiation Shielding Study (MAARSS)

This report describes the analysis of several magnetic radiation shield architectures and the spacecraft systems associated with them, such as quench detection, thermal management, and compensation coils. This work was performed as part of the NASA Institute of Advanced Concepts (NIAC) Grant Phase II effort. Because radiation exposure during long duration space missions poses a significant risk for crewed space-flight, Advanced Magnetic Lab, Inc. (AML) and NASA are studying magnetic radiation shielding, which may generate low-mass protection. Recent technological developments in high-temperature superconducting technology suggest the possibility of such shielding. This report analyzes some of the technical difficulties involved in such a system and identifies technology areas where further investment would be warranted. Most analysis was performed on a baseline configuration (8-meter diameter coils, with 1 tesla field). However, a baseline design with an expandable coil configuration (16 meter diameter coils, 1.5 tesla field) has a significant potential to increase shielding efficiency. The magnetic forces on the magnetic shield's components are large enough to require detailed structural design. Analysis of the thermal structural response of a yttrium-barium-copper-oxide (YBCO) high-temperature, superconducting (HTS) tape in a large-scale solenoid magnet showed that structural and thermal performance improved by replacing Hastelloy® with graphene in the tape. Integrating graphene into the high-strength fiber (HSF) support structure brings even greater benefits. The energy stored in a shield system's magnetic field must be safely dissipated if a quench-type failure occurs. Analysis of quench detection by fiber-optic thermal sensing and improvement of quench characteristics using graphene showed quench is manageable. Low-temperature superconductors can quench when subjected to movement, but lab tests of coil expansion testing showed that HTS materials do not quench when subject to the movement associated with coil expansion. Compensation coils are necessary to reduce the magnetic field in the crew habitat. Analysis showed that subdividing the compensation coil into individually controlled sections allows for a robust, adjustable system. AML analyzed the forces on an approaching capsule that were a result of eddy currents in its structure induced by its motion through the magnetic field from the coils. AML also analyzed coil-to-coil forces. Thermal control to maintain the HTS material at a suitable temperature is challenging. The sunshield technology review revealed a greater possibility of thermal insulation of the coils and use of passive cooling. The availability of suitable cryocoolers was also reviewed. A parametric graph estimating mass and shielding effectiveness for strength and thickness was developed, and allows spacecraft designers to assess the tradeoffs of using a magnetic radiation shield.

Spacecraft↗

On the Topotactic Phase Transition Achieving Superconducting Infinite‐Layer Nickelates

Abstract Topotactic reduction is critical to a wealth of phase transitions of current interest, including synthesis of the superconducting nickelate Nd 0.8 Sr 0.2 NiO 2 , reduced from the initial Nd 0.8 Sr 0.2 NiO 3 /SrTiO 3 heterostructure. Due to the highly sensitive and often damaging nature of the topotactic reduction, however, only a handful of research groups have been able to reproduce the superconductivity results. A series of in situ synchrotron‐based investigations reveal that this is due to the necessary formation of an initial, ultrathin layer at the Nd 0.8 Sr 0.2 NiO 3 surface that helps to mediate the introduction of hydrogen into the film such that apical oxygens are first removed from the Nd 0.8 Sr 0.2 NiO 3 / SrTiO 3 (001) interface and delivered into the reducing environment. This allows the square‐planar / perovskite interface to stabilize and propagate from the bottom to the top of the film without the formation of interphase defects. Importantly, neither geometric rotations in the square planar structure nor significant incorporation of hydrogen within the films is detected, obviating its need for superconductivity. These findings unveil the structural basis underlying the transformation pathway and provide important guidance on achieving the superconducting phase in reduced nickelate systems.

36 MATERIALS SCIENCE↗

High Fermi velocities and small cyclotron masses in LaAlGe

Here, we report quantum oscillation measurements of LaAlGe, a Lorentz-violating type-II Weyl semimetal with tilted Weyl cones. Very small quasiparticle masses and very high Fermi velocities were detected at the Fermi surface. Whereas three main frequencies have been observed, the angular dependence of two Fermi surface sheets indicates possible two-dimensional (2D) character despite the absence of the 2D structural features such as van der Waals bonds. Such conducting states may offer a good platform for low-dimensional polarized spin current in magnetic RAlGe (R = Ce, Pr) materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Probing magnetic configuration-mediated topological phases via high harmonic generation in MnBi 2 Te 4

Compared to a space group, a magnetic space group is much more complex, as both magnetic structure and magnetic moment direction can change the original symmetries of materials. The interplay between space symmetry and magnetism can generate versatile novel quantum states. However, detecting these topological phases experimentally, achieved through manipulating the magnetic configuration, has been restricted. It is mainly because the intrinsic link between the theory and the available experimental technique remains elusive. Here, we show that high harmonic generation (HHG) can identify these topological quantum states. In this work, we use rhombohedral MnBi 2 Te 4 film as an example, and analyze the symmetry-dependent harmonic order and signal by combining first-principles calculations and time-dependent Liouville equation numerical computations. Our results provide a fundamental basis for using HHG to study the topological quantum phases mediated by various magnetic configurations that can be easily realized by applying an external magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Nematic transitions in iron pnictide superconductors imaged with a quantum gas

The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) uses an atomic Bose–Einstein condensate to measure magnetic fields emanating from solid-state samples. The quantum sensor does so with unprecedented d.c. sensitivity at micrometre resolution, from room to cryogenic temperatures. An additional advantage of the SQCRAMscope is the preservation of optical access to the sample so that magnetometry imaging of, for example, electron transport may be performed in concert with other imaging techniques. Here, we apply this multimodal imaging capability to the study of nematicity in iron pnictide high-temperature superconductors, where the relationship between electronic and structural symmetry breaking resulting in a nematic phase is under debate. We combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface. This enables simultaneous and spatially resolved detection of both bulk and near-surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing local measurements of emergent resistivity anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and structural transitions. More broadly, these measurements demonstrate the SQCRAMscope’s ability to reveal important insights into the physics of complex quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Evidence for a single-layer van der Waals multiferroic

Here we searched for signatures of type-II multiferroic order in ultrathin van der Waals materials, to determine if such a state, comprising coexisting electrical polarization and spin order with strong magnetoelectric effects, could persist down to a single-atomic layer. We reported the first observation of such a state in triangular lattice material NiI 2 . This system has a layered structure and built-in magnetic frustration that promotes a complex magnetic ground state with proper-screw spin helices. The spin helix pattern breaks inversion symmetry and induces electrical polarization via magnetoelectric coupling. We use circular dichroic Raman measurements to directly probe the magneto-chiral ground state and its electromagnon modes originating from dynamic magnetoelectric coupling. Using birefringence and second-harmonic generation measurements, we detect a highly anisotropic electronic state simultaneously breaking three-fold rotational and inversion symmetry. The evolution of the optical signatures as a function of temperature and layer number surprisingly revealed a multiferroic state that persists down to the ultrathin limit of monolayer NiI 2 . These observations establish NiI 2 and transition metal dihalides as a new platform for studying emergent multiferroic phenomena, chiral magnetic textures and ferroelectricity in the 2D limit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Development and performance of a 2.9 Tesla dipole magnet using high-temperature superconducting CORC® wires

Although the high-temperature superconducting (HTS) REBa 2 Cu 3 O x (REBCO, RE-rare earth elements) material has a strong potential to enable dipole magnetic fields above 20 T in future circular particle colliders, the magnet and conductor technology needs to be developed. As part of an ongoing development to address this need, here we report on our CORC® canted cosθ magnet called C2 with a target dipole field of 3 T in a 65 mm aperture. The magnet was wound with 70 m of 3.8 mm diameter CORC® wire on machined metal mandrels. The wire had 30 commercial REBCO tapes from SuperPower Inc. each 2 mm wide with a 30 µm thick substrate. The magnet generated a peak dipole field of 2.91 T at 6.290 kA, 4.2 K. The magnet could be consistently driven into the flux-flow regime with reproducible voltage rise at an engineering current density between 400-550 A mm -2 , allowing reliable quench detection and magnet protection. The C2 magnet represents another successful step towards the development of high-field accelerator magnet and CORC® conductor technologies. The test results highlighted two development needs: continue improving the performance and flexibility of CORC® wires and develop the capability to identify locations of first onset of flux-flow voltage.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Unconventional Hall effect induced by Berry curvature

Berry phase and Berry curvature play a key role in the development of topology in physics and do contribute to the transport properties in solid state systems. In this paper, we report the finding of novel nonzero Hall effect in topological material ZrTe 5 flakes when the in-plane magnetic field is parallel and perpendicular to the current. Surprisingly, both symmetric and antisymmetric components with respect to magnetic field are detected in the in-plane Hall resistivity. Further theoretical analysis suggests that the magnetotransport properties originate from the anomalous velocity induced by Berry curvature in a tilted Weyl semimetal. Our work not only enriches the Hall family but also provides new insights into the Berry phase effect in topological materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗