摘要
该工作利用扫描SQUID显微镜研究了分子束外延生长在LSAT衬底上的最优掺杂无限层镍酸盐Nd1−xEuxNiO2（x=0.25）薄膜的局域超流密度与磁结构。同时进行的直流磁强计和交流磁化率成像显示，超导与弱磁织构共存，且超导态在空间上高度不均匀：接近超导转变时出现稳健的条纹状超导增强，并伴有光晕状缺陷响应及条纹间顺磁区域。这些结果表明，竞争磁相是导致该最优掺杂NENO样品超导转变异常展宽的主要因素；理解这种超导增强机制可能为提升此类材料的超导温度提供途径。
材料
本批次暂无数据。
方法
本批次暂无数据。
关键词
本批次暂无数据。
亮点
本批次暂无数据。
结论
本批次暂无数据。
主要论断
- Optimally doped NENO exhibits a robust stripe-like enhancement of superconductivity near Tc, indicating a highly non-uniform superfluid density.
- 证据: AC susceptibility maps show a periodic stripe pattern with period ≈12.3±0.5 μm by direct measurement.,FFT analysis gives a spatial frequency of 0.079 μm^-1, corresponding to a 12.5 μm period.,Stripes appear from ≈8.8 K to 11.1 K and persist under temperature cycling and small out-of-plane fields.
- A weak intrinsic magnetic texture coexists with superconductivity in NENO.
- 证据: DC magnetometry maps show magnetic texture above Tc and when superconductivity is suppressed by small out-of-plane fields.,Vortex contribution is estimated to be at least an order of magnitude weaker than the observed magnetic signal.,HAADF-STEM and STEM-EELS show no nanoparticle inclusions or secondary phases that could explain the magnetic response.
- Competing magnetic order or electronic phase separation is the primary contributor to the broad superconducting transition.
- 证据: The global superconducting transition is broad, from about 8 K to 22 K.,Paramagnetic regions appear between superconducting stripes, and halo-like regions indicate local pair-breaking.,Local transition temperature varies by as much as 1.8 K within 100 μm.,Structural and chemical probes show no corresponding periodic inhomogeneity.
- The sample edge hosts an enhanced superconducting response.
- 证据: A heightened diamagnetic response at the sample edge remains detectable up to ≈13.4 K.,The highest local transition temperature in approach curves was found near the sample edge.
- The ≈12 μm stripe modulation is distinct from known nickelate charge density waves and is not due to SQUID scan artifacts.
- 证据: Nickelate charge density waves typically have ~three-unit-cell periodicity (≈1 nm), orders of magnitude smaller than the observed ≈12 μm period.,Non-periodic stripes of similar signal strength are also observed independently of the periodic array.,Stripes are detected on a second sample and their orientation relative to the sample edge varies between samples.
研究流程
- sample_preparation — Optimally doped NENO thin films were synthesized on LSAT and reduced to the infinite-layer phase for local magnetic and superconducting characterization.
- 材料: Nd1−xEuxNiO2 (NENO, x=0.25) thin films; commercial LSAT (001) substrates; metallic Al capping layer
- 方法: molecular beam epitaxy (MBE); substrate cleaning with activated oxygen; in situ topotactic reduction using a 2–3 nm Al capping layer
- 观察: NENO films grown on LSAT; infinite-layer structure obtained after topotactic reduction; Al capping oxidizes to Al2O3 and remains on the film surface
- initial_bulk_characterization — Macroscopic measurements show superconductivity with a broad transition and a hysteretic magnetic response, motivating local probes.
- 材料: NENO films on LSAT
- 方法: PPMS transport measurements; MPMS magnetization measurements; zero-field-cooled and field-cooled scans; magnetic field sweeps
- 观察: broad superconducting transition from about 8 K to 22 K; magnetic moment increases as temperature decreases from 100 K; small ZFC/FC hysteresis; no bulk diamagnetic drop in MPMS
- scanning_SQUID_microscopy — Local SSM imaging reveals coexisting magnetic texture and a highly non-uniform, stripe-patterned superconducting state in NENO.
- 材料: NENO film; LSAT substrate; vacuum reference
- 方法: scanning SQUID microscopy (SSM); simultaneous DC magnetometry and AC susceptometry; piezoelectric raster scanning; zero-field cooling; substrate or vacuum subtraction; low-pass filtering of magnetometry
- 观察: weak magnetic texture coexisting with superconductivity; halo-like point-defect responses at low temperature; stripe-like enhancement of diamagnetic response with period ≈12.3–12.9 μm; paramagnetic regions between stripes; edge-enhanced superconductivity; stripes persist under temperature cycling and small magnetic fields
- susceptibility_approach_curves — Approach curves confirm spatially varying effective penetration depth and local Tc, indicating a non-uniform superconducting and magnetic response.
- 材料: NENO film; LSAT substrate
- 方法: height-dependent susceptibility approach curves; fitting to Kirtley-Kogan thin-film diamagnetic and paramagnetic responses
- 观察: effective penetration depth minimum ≈4.05 μm at 6.5 K and approaches infinity past 10 K; transition between diamagnetic and paramagnetic phases between 9.5 K and 10.4 K; model fails in the intermediate regime; local transition temperature varies by as much as 1.8 K within 100 μm
- structural_elemental_characterization — Structural and elemental probes rule out gross structural or chemical inhomogeneity and secondary-phase nanoparticles as the cause of the stripes.
- 材料: NENO lamella prepared by FIB; NENO film surface
- 方法: SEM; HAADF-STEM; STEM-EELS; EDS; FIB lamella preparation; PCA noise reduction for EELS
- 观察: smooth film surface without scratches or cracks; epitaxial growth and atomically flat film-substrate interface; no inclusions or secondary phases; uniform elemental composition at atomic scale; no periodic structural feature matching the ≈12 μm stripes
- data_analysis_and_interpretation — The observed stripe and magnetic textures are intrinsic electronic and magnetic phenomena consistent with mesoscopic phase separation, not instrumental or structural artifacts.
- 材料: SSM images; transport and magnetization data; STEM/EELS data
- 方法: cross-sectional analysis; Fast Fourier Transform (FFT); comparison across samples and positions; vortex-strength estimation; phase-separation interpretation
- 观察: FFT peak at 0.079 μm^-1 corresponding to a 12.5 μm period; stripe orientation varies between samples but is consistent within a sample; magnetic texture spatially correlates with susceptibility stripes; vortex contribution estimated at least an order of magnitude weaker than the observed magnetic signal