Superconductivity Achieved in Nanowires Via 5.5m/mT Domain Wall Modulation

Researchers have demonstrated that superconductivity within semiconductor nanowires can be powerfully modulated by magnetic textures. Nandi, Estrada Saldaña, and Vekris, from the Niels Bohr Institute and Stanford University, alongside colleagues including Turley, Zhang, and Liu, reveal superconductivity in aluminium shells surrounding indium arsenide/europium sulphide nanowires only when the europium sulphide exhibits a multi-domain magnetic state. This finding, achieved through scanning SQUID magnetometry and transport measurements, is significant because it proves the magnetic texture is reconfigurable with minimal external fields , even moving a magnetic domain wall at 5.5m/mT with sub-mT fields. Such precise control over magnetism along a nanowire opens exciting possibilities for developing novel topological, Andreev spin, logic, and memory devices.

Magnetic texture drives superconductivity in nanowires by modulating

Scientists have demonstrated a direct link between magnetic texture and superconductivity in a one-dimensional InAs/EuS/Al nanowire heterostructure, revealing a pathway to manipulate superconducting regions using magnetic fields. The research team achieved this breakthrough by fabricating full-shell nanowires, epitaxially growing layers of Europium Sulfide and Aluminium around an Indium Arsenide core, and then employing scanning Superconducting Quantum Interference Device (SQUID) magnetometry alongside transport measurements. This approach allowed them to observe superconductivity within the Aluminium shell only when the Europium Sulfide layer exhibited a multi-domain magnetic state, confirming predictions of both domain wall superconductivity and multi-domain-averaged superconductivity. The study unveils that the magnetic texture of the Europium Sulfide is not static, but is dynamically reconfigurable with minor adjustments to the external magnetic field.
Experiments show the team successfully moved a well-defined magnetic domain wall along the nanowire at approximately 5.5μm/mT using sub-mT fields, indicating that any associated localised superconducting region could also be repositioned with precision. Scanning SQUID magnetometry provided detailed spatial mapping of the magnetic texture, confirming its position-dependent nature and responsiveness to external stimuli. This ability to control the magnetic texture opens up possibilities for creating movable superconducting regions within the nanowire, a crucial step towards advanced device functionalities. The work establishes a clear correlation between the EuS magnetic domain state and the emergence of superconductivity in the Al shell, absent in the saturated single-domain state, and provides direct evidence for the mechanisms of both domain wall superconductivity and multi-domain-averaged superconductivity.

This breakthrough reveals a novel platform for manipulating superconductivity at the nanoscale, potentially enabling the development of topological qubits, Andreev spin qubits, and innovative superconducting logic and memory devices. The researchers fabricated nanowires with epitaxial superconducting shells, combining strong spin-orbit coupling with proximity effects and gate tunability. By adding a ferromagnetic layer, they introduced a Zeeman shift that, while typically suppressing superconductivity, can be locally overcome by magnetic texture control. Because Cooper pairs extend over a coherence length, superconductivity can survive where the averaged Zeeman field is suppressed, such as near magnetic domain walls or in multi-domain states where net magnetization averages to zero. The team’s findings demonstrate that controlled manipulation of these magnetic textures along the nanowire can be used to engineer and reposition superconducting regions, paving the way for future applications in quantum technologies and beyond.

Nanowire Magnetism Characterised by Scanning SQUID Imaging

Scientists investigated the interplay between magnetism and superconductivity in one-dimensional InAs/EuS/Al nanowires, employing a combination of scanning SQUID magnetometry and four-probe differential resistance measurements. The research team fabricated full-shell nanowires and characterised their magnetic properties using a scanning SQUID, achieving a spatial resolution sufficient to map magnetic textures and identify domain walls. Magnetometry images were acquired at 4.2 K, and the normalised axial magnetic moment, mz, was calculated from these images to construct hysteresis loops, revealing a coercive field, Hc, of −3.5 mT where the magnetic moment became zero. Further imaging of another nanowire at fields exceeding Hc revealed the evolution of the initial domain into multiple smaller domains, indicative of nanoscale magnetic structures.

To probe superconductivity, the study pioneered four-probe differential resistance, dV/dI, measurements at 30 mK, recognising the Al shell’s critical temperature was below 1 K and a quasi-1D Meissner response would be weak at higher temperatures. Experiments employed a multi-contact transport device, focusing on 700nm segments labelled A and B, with current sourced between contacts 1 and 6 and voltage measured between 2 and 3. The team measured dV/dI as a function of applied magnetic field, Ha, observing a normal-state resistance, Rn, of 0.5 kΩ throughout most field sweeps. Zero-field-cooled measurements on segment A revealed a low-resistance region near zero field, disappearing at an annihilation field, Hann, of approximately 10 mT, suggesting a superconducting phase.

Sweeping the field from +70 to −70 mT induced superconductivity reappearing at Hn = −13 mT and vanishing at Hann = −18 mT, with reverse sweeps showing similar, though not perfectly symmetric, behaviour. Linecuts of dV/dI at 11, 13, and 17 mT demonstrated suppressed resistance at low bias and finite-bias peaks at 11 and 13 mT, confirming the superconducting state, with a sharper resistance drop at 93 nA at 13 mT. Across six segments in three devices, this consistent phenomenology , reduced resistance, intermediate-bias peaks, and sharp resistance jumps , provided strong evidence for superconductivity confined to a narrow parameter range, correlating with a multi-domain state of the EuS shell identified by magnetometry.

Europium Sulfide Magnetism Controls Nanowire Superconductivity at low

Scientists have demonstrated superconductivity in aluminium shells of InAs/EuS/Al nanowires contingent on the magnetic state of the embedded europium sulfide. Scanning SQUID magnetometry and transport measurements revealed that superconductivity appears only when the EuS is in a multi-domain state, a finding consistent with both domain wall suppression and multi-domain averaged suppression mechanisms. This superconducting behaviour was absent when the EuS was in a saturated single-domain state, establishing a clear link between magnetic configuration and superconducting phase. Experiments using scanning SQUID magnetometry showed the magnetic texture of the EuS is position dependent and can be reconfigured with small changes in the external magnetic field.

The team measured a well-defined domain wall moving at approximately 5.5μm/mT with sub-mT fields, indicating that any associated localised region is similarly movable. This control over magnetic texture along the nanowire opens possibilities for novel devices, including those based on topological principles, Andreev spin physics, logic circuits, and memory storage. Detailed analysis of the magnetometry images revealed that a single magnetic domain in the quasi-1D system exhibits field lines leaving and entering at each end. Imaging two bare nanowires, researchers observed multiple positive and negative lobes in the zero-field-cooled state, confirming a multi-domain configuration with both micron-scale and nanoscale domains.

Sweeping an axial field to +8 mT trained the nanowire into a single domain, evidenced by a single positive and negative lobe at the wire ends. A second domain nucleated at −0.8 mT, and by −2.4 mT, a clear domain separation was observed, with the domain wall moving at the measured rate of 5.5μm/mT. The magnetic moment of the nanowire became zero at a coercive field of −3.5 mT, coinciding with a 3.7μm region of near-zero signal between domains. Four-probe differential resistance measurements at 30 mK confirmed superconductivity in the Al shell, with a normal-state resistance of 0.5 kΩ. A minimum in dV/dI was observed near zero-bias current for |I| ≲ 500 nA, disappearing at an annihilation field of approximately 10 mT. At 11 mT and 13 mT, dV/dI was suppressed at low bias, exhibiting finite-bias peaks signifying the superconducting state, with a resistance minimum at 13 mT and an abrupt drop at a bias current of 93 nA.

Magnetic domains drive nanowire superconductivity at low temperatures

Scientists have demonstrated that superconductivity within an aluminium shell surrounding an indium arsenide/europium sulfide nanowire is intrinsically linked to the magnetic texture of the europium sulfide layer. Measurements using scanning SQUID magnetometry and differential resistance reveal superconducting signatures only when the europium sulfide is in a multi-domain magnetic state, specifically after zero-field cooling and near its coercivity. This superconductivity is absent when the europium sulfide is in a saturated single-domain state, suggesting a direct correlation between magnetic domain configuration and superconducting behaviour. The research supports two potential microscopic mechanisms: superconductivity near magnetic domain walls and multi-domain-averaged superconductivity, though current measurements cannot differentiate between them.

Micromagnetic simulations of the europium sulfide hysteresis corroborate these findings. Furthermore, the magnetic texture can be controlled and reconfigured using small external magnetic fields, enabling the movement of a well-defined domain wall at 5.5m/mT with sub-mT fields. The authors acknowledge a limitation in distinguishing between the two proposed superconducting mechanisms with the present data. These findings are significant as they open avenues for novel device architectures utilising spatially controlled magnetic domain walls. Theoretical work suggests that a mobile domain wall within a Josephson weak link could control the superconducting diode effect, potentially leading to a fast, low-dissipation readout for racetrack memory states. Additionally, the ability to manipulate the superconducting phase locally offers a route to reconfigurable phase control for Andreev spin qubits, potentially improving coherence and scalability. Future research will focus on refining experimental techniques to distinguish between the proposed superconducting mechanisms and exploring the potential of these nanowires in advanced quantum devices.