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Finite bias evolution of bosonic insulating phase and zero bias conductance in boron-doped diamond: A charge-Kondo effect
摘要： We report novel transport features in heavily boron-doped nanocrystalline diamond films, in particular an anomalous resistance peak near to the superconducting transition temperature and a strong zero bias conductance peak in the differential current-voltage spectra. The shape of the resistance-temperature curves near the critical temperature is seen to be strongly influenced by both magnetic field and bias current. As the bias current is lowered, the resistance peak becomes more pronounced, whereas when the magnetic field is varied the peak shifts towards lower temperatures. The resistance upturn shows a quadratic temperature dependence as expected for a Kondo transition. We find that a number of transport features such as resistance peak height, zero bias conduction peak height and width scale according to a power law dependence. We interpret these features as a result of a charge-Kondo effect where hole dopants act as degenerate Kondo impurities by opening additional pseudo-spin scattering channels.
关键词： bosonic insulating phase,zero bias conductance peak,charge-Kondo effect,boron-doped diamond,superconductivity
更新于2025-09-23 15:23:52
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Diluted Oxide Interfaces with Tunable Ground States
摘要： The metallic interface between two oxide insulators, such as LaAlO3/SrTiO3 (LAO/STO), provides new opportunities for electronics and spintronics. However, due to the presence of multiple orbital populations, tailoring the interfacial properties such as the ground state and metal-insulator transitions remains challenging. Here, an unforeseen tunability of the phase diagram of LAO/STO is reported by alloying LAO with a ferromagnetic LaMnO3 insulator without forming lattice disorder and at the same time without changing the polarity of the system. By increasing the Mn-doping level, x, of LaAl1?xMnxO3/STO (0 ≤ x ≤ 1), the interface undergoes a Lifshitz transition at x = 0.225 across a critical carrier density of nc = 2.8 × 1013 cm?2, where a peak TSC ≈255 mK of superconducting transition temperature is observed. Moreover, the LaAl1?xMnxO3 turns ferromagnetic at x ≥ 0.25. Remarkably, at x = 0.3, where the metallic interface is populated by only dxy electrons and just before it becomes insulating, a same device with both signatures of superconductivity and clear anomalous Hall effect (7.6 × 1012 cm?2 < ns ≤ 1.1 × 1013 cm?2) is achieved reproducibly. This provides a unique and effective way to tailor oxide interfaces for designing on-demand electronic and spintronic devices.
关键词： anomalous Hall effect,2D electron liquid,oxide interfaces,superconductivity,metal-insulator transitions
更新于2025-09-23 15:23:52
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[Advances in Imaging and Electron Physics] || superconductors and magnetic electron lenses
摘要： The use of superconductors seems a logical step if one wants to make iron-free magnetic lenses or to reduce the dimensions of conventional lenses since, when decreasing the coil size, the current density is increased. In the 1960s and 1970s, research mainly concentrated on the applicability of superconductors to magnetic electron lenses, and took place on a relatively large scale. This is reviewed in Section 2, after a general introduction into superconductivity in Section 1. Superconducting lenses and microscopes did not become popular due to their inconvenient operation and the lack of interest in high-voltage electron microscopy. High-voltage microscopy has been one of the main reasons for working on strong magnetic lenses and, consequently, on the utilization of superconductors. In 1986, with the discovery of high-temperature superconductivity, discussion on the applicability of superconductors to magnetic electron lenses was reopened. In the past, one of the most serious disadvantages in operating superconducting lenses had been related to the use of liquid helium refrigeration, so high-T c superconductors might be employed to overcome this problem, because their cooling demands are much more relaxed. However, especially during the first years of high-Tc superconductivity, despite their high operating temperatures, the materials themselves seemed extremely unfriendly, as they were brittle, sensitive to water, unstable, and difficult to produce. Fortunately, most of these disadvantages have now disappeared and the discussion concerning their utilization assumes a more fundamental character in the sense that most of the properties of the high-Tc materials are known, though a sound theoretical basis has not yet been defined. The properties of high-T c superconductors are the subject of Section 3. The question whether high-Tc superconductors are more appropriate for applications in particle optics than their classical counterparts was considered to be an interesting research topic. Therefore, this work was started as a feasibility study to the use of high-temperature superconductors in particle optics. Most short-term applications in this field were expected to exploit the high current density of these materials at temperatures above liquid helium, so this work concentrated on magnetic lenses as one of the most straightforward high current density applications. Since conventional iron circuit lenses are already used to their limits, as set by the saturation of the ferromagnetic circuit, significant improvements are to be expected only from iron-free lenses or highly saturated pole piece lenses. Their performance is restricted by the current density allowed in the windings and, further, for the iron-free lens, by the attainable mechanical tolerances, since, in the absence of iron, a lack of axial symmetry in the windings directly results in parasitic aberrations. For making small iron free lenses, high-Tc thin films are potentially interesting candidates, as they possess a high current density and can be patterned very accurately using lithographic techniques. Advantages to be expected from thin film lenses are smaller dimensions and better optical properties. An overview of fabrication techniques for high-Tc thin films is given in Section 4. The first attempt to make a coil in a superconducting thin film, using co-evaporated YBa2Cu3O7?x films, is the subject of Section 5. A thin film has to be patterned with some form of spiral in order to obtain a coil. Therefore, thin film lenses basically do not possess full axial symmetry. The relationship between the geometry of a flat coil and its optical properties is given in Section 6. The geometry of a feasible thin film lens element, along with its corresponding optical properties, is given in Section 7 while the technology used to fabricate this lens element is the subject of Section 8. Finally, based upon the work presented here, Section 9 treats the potential applicability of high-Tc superconductors in instruments that employ particle beams.
关键词： magnetic electron lenses,High-Tc superconductors,thin films,capacitive alignment,lens design,YBa2Cu3O7?x,superconductivity,electron microscopy
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Hangzhou, China (2018.8.13-2018.8.17)] 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Bottom up Nano-integration Technique for the Fabrication of Novel Superconducting Quantum Interference Devices Based on Granular Superconducting Diamond
摘要： The report is focused on the fabrication and characterization of nano-necklaces created from individual nanostructures namely heavily boron-doped superconducting nano-diamond grains and BIISCO whiskers. The production of nanostructures from individual nano-diamonds is done using 3D mechanical nano-manipulation and nano-assembling based on new generation shape memory alloy composite nanotweezers. Quantum transport of such nano-necklaces will be probed in order to study the confinement effects on superconductivity and other related quantum effects. This bottom-up nano-integration technique thus demonstrates a niche fabrication route for the realization of novel complex nanostructured quantum rings which may be of use for quantum information technologies.
关键词： nanodiamonds,bottom-up paradigm,carbon based nanomaterials,nanogripper,shape memory effect,nano-manipulation,superconductivity
更新于2025-09-23 15:23:52
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Grain boundaries and tilt angle-dependent transport properties of 2D Mo2C superconductor
摘要： Grain boundaries (GBs) of graphene and molybdenum disulfide have been extensively demonstrated to have strong influence on their electronic, thermal, optical and mechanical properties. 2D transition metal carbides (TMCs), known as MXenes, are a rapidly growing new family of 2D materials with many fascinating properties and promising applications. However, the GB structure of 2D TMCs and the influence of GB on their properties still remain unknown. Here, we used aberration-corrected scanning transmission electron microscopy combined with electrical measurements to study the GB characteristic of highly crystalline 2D Mo2C superconductor, a newly emerging member of 2D TMC family. 2D Mo2C superconductor shows unique tilt angle-dependent GB structure and electronic transport properties. Different from the reported 2D materials, the GB of 2D Mo2C shows peculiar dislocation configuration or sawtooth pattern depending on the tilt angle. More importantly, we found two new periodic GBs with different periodic structure and crystallographic orientations. Electrical measurements on individual GBs show that GB structure strongly affects the transport properties. In the normal state, an increasingly stronger electron localization behavior is observed at the GB region with increasing tilt angle. In the superconducting state, the magnitude of the critical current across the GBs is dramatically reduced, associated with local suppression of superconductivity at GBs. These findings provide new understandings on the GB structure of 2D TMCs and the influence of GB on 2D superconductivity, which would be helpful for tailoring the properties of 2D TMCs through GB engineering.
关键词： dislocations,MXene,2D materials,grain boundaries,superconductivity
更新于2025-09-23 15:22:29
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Stages of the Excitation Relaxation in a Superconductor after the Impact of a Femtosecond Laser Pulse Taking into Account the Momentum Distribution of Quasiparticles
摘要： A theoretical model is formulated for the description of the nonequilibrium state of a superconductor on the basis of the nonequilibrium distribution function of phonons and quasiparticles on a finite momentum lattice convenient for numerical simulation. The simulation is performed under conditions of pulsed optical impact demonstrating the role of excess quasiparticles in suppressing the order parameter and the main stages of the relaxation process in the absence of electric current.
关键词： superconductivity,kinetics simulation,nonequilibrium processes,ultrashort laser pulse
更新于2025-09-23 15:21:01
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Exposes its Excitonic Character
摘要： Recent experiments suggest that excitonic degrees of freedom play an important role in precipitating the charge density wave (CDW) transition in 1T-TiSe2. Through systematic calculations of the electronic and phonon spectrum based on density functional perturbation theory, we show that the predicted critical doping of the CDW phase overshoots the experimental value by 1 order of magnitude. In contrast, an independent self-consistent many-body calculation of the excitonic order parameter and renormalized band structure is able to capture the experimental phase diagram in extremely good qualitative and quantitative agreement. This demonstrates that electron-electron interactions and the excitonic instability arising from direct electron-hole coupling are pivotal to accurately describe the nature of the CDW in this system. This has important implications to understand the emergence of superconductivity within the CDW phase of this and related systems.
关键词： charge density wave,1T-TiSe2,electron-electron interactions,superconductivity,excitonic instability
更新于2025-09-23 15:21:01
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revealed by high-energy x-ray diffraction
摘要： We explore the evolution of the structural phase transition of (Sr, Ca)3Ir4Sn13, a model system to study the interplay between structural quantum criticality and superconductivity, by means of high-energy x-ray diffraction measurements at high pressures and low temperatures. Our results confirm a rapid suppression of the superlattice transition temperature T ? against pressure, which extrapolates to zero at a critical pressure of ≈1.79(4) GPa. The temperature evolution of the superlattice Bragg peak in Ca3Ir4Sn13 reveals a drastic decrease of the intensity and an increase of the linewidth when T → 0 K and p → pc. Such anomaly is likely associated with the emergence of quantum fluctuations that disrupt the formation of long-range superlattice modulation. The revisited temperature-pressure phase diagram of (Sr, Ca)3Ir4Sn13 thus highlights the intertwined nature of the distinct order parameters present in this system and demonstrates some similarities between this family and the unconventional superconductors.
关键词： high-energy x-ray diffraction,structural phase transition,superconductivity,quantum criticality,quantum fluctuations
更新于2025-09-23 15:19:57
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Structure and transport properties of titanium oxide (Ti2O, TiO1+, and Ti3O5) thin films
摘要： Titanium oxides have partially filled or empty d orbital and are stable at various oxidation states with different structures and unique properties. Here, three kinds of titanium oxide thin films of hexagonal Ti2O metal, cubic TiO1+d superconductor, and monoclinic g-Ti3O5 semiconductor, were successfully grown on a-Al2O3 substrates by a pulsed laser deposition technique, through ablating a pure titanium target under different oxygen pressures. The electrical resistivities of these films increase with increasing oxygen content. The metallic behaviors of Ti bulk and Ti2O film can be described by the Bloch-Grüneisen formula, and the semiconducting behaviors of TiO1+d films in normal state and g-Ti3O5 film obey the variable range hopping and the small polaron hopping conduction mechanisms, respectively. For titanium monoxide TiO1+d (1.05 ≤ 1+d ≤ 1.17) films, increasing oxygen content is accompanied by an increase of disorder, a decrease of electron density of states at the Fermi level, and an enhancement of carrier localization, leading to a suppression of superconductivity.
关键词： Electron energy-loss spectroscopy,Oxygen content,Superconductivity,Transport properties,Titanium oxide thin films,Pulsed laser deposition
更新于2025-09-19 17:15:36
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Imaging the local electronic and magnetic properties of intrinsically phase separated Rb<sub>x</sub>Fe<sub>2-y</sub>Se<sub>2</sub> superconductor using scanning microscopy techniques
摘要： The discovery in 2008 of the iron-based superconducting pnictide and chalcogenide compounds has provided an entirely new family of materials for studying the crucial interplay between superconductivity and magnetism in unconventional superconductors. The alkali-metal-intercalated iron selenide (AxFe2?ySe2, A = alkali metal) superconductors are of particular interest owing to their relatively high transition temperatures of 30 K and the co-existence of the superconducting state with antiferromagnetic ordering. Intrinsic phase separation on the mesoscopic scale is known to occur in “single crystals” of these compounds, adding to the complexity of interpretation of bulk property measurements. In this study, we investigate the local electronic structure and chemistry of RbxFe2?ySe2 crystals using scanning microscopy techniques. Nano-focussed angle-resolved photoemission spectroscopy (NanoARPES) has enabled the band structure of the minority superconducting phase and the non-superconducting matrix to be measured independently and linked to the surface chemistry from the same regions using core-level spectroscopy. Valence band mapping reveals the characteristic microstructure of these crystals, but does not have sufficient spatial resolution to enable the precise morphology of the superconducting phase to be elucidated. Cryogenic magnetic force microscopy (MFM) has shown that the superconducting phase has a fine-scale stripey morphology that was not resolved in the SPEM experiment. The correlation of these findings with previous microstructural studies, bulk measurements and first-principles DFT calculations paves the way for understanding the intriguing electronic and magnetic properties of these compounds.
关键词： RbxFe2?ySe2,phase separation,magnetism,superconductivity,scanning microscopy
更新于2025-09-19 17:15:36