Yoseph Imry
It is shown that nanoparticles made of low $T_c$ superconductors have large diamagnetic response at temperatures several orders of magnitude above $T_c$. Most features of the recently observed Giant diamagnetism of Au nanorods are explained in terms of superconducting fluctuations, except for the huge magnitude of the effect.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
继续探索
The magnetic susceptibility of an ensemble of clean metallic nanoparticles is shown to change from paramagnetic to diamagnetic one with the onset of spin-orbit interaction. The effect is quantified on the basis of symmetry analysis with the help of the random matrix theory. In particular, the magnetic susceptibility is investigated as the function of symmetry breaking parameter representing magnetic flux in the crossover from symplectic to unitary and from orthogonal to unitary ensembles. Corresponding analytical and numerical results provide a qualitative explanation to the experimental data …
Zero resistance, diamagnetism (Meissner effect) and the energy gap in the excitation spectrum are the fundamental attributes of superconductivity. In nanoparticles with characteristic size 10 nm superconductivity is suppressed by the quantization of the electron energy spectrum. In narrow quasi-1D superconducting channels thermal fluctuations enable zero resistance only at temperatures noticeably below the critical temperature Tc, while quantum fluctuations suppress the dissipationless electric current in ultra-narrow superconducting nanowires even at temperatures close to T=0. Here we demonst…
In this work we study the effect of engineered disorder on the local magnetic response of proximity coupled superconducting island arrays by comparing scanning Superconducting Quantum Interference Device (SQUID) susceptibility measurements to a model in which we treat the system as a network of one-dimensional (1D) superconductor-normal metal-superconductor (SNS) Josephson junctions, each with a Josephson coupling energy $E_J$ determined by the junction length or distance between islands. We find that the disordered arrays exhibit a spatially inhomogeneous diamagnetic response which, for low l…
An important question in the physics of superconducting nanostructures is the role of thermal fluctuations on superconductivity in the zero-dimensional limit. Here, we probe the evolution of superconductivity as a function of temperature and particle size in single, isolated Pb nanoparticles. Accurate determination of the size and shape of each nanoparticle makes our system a good model to quantitatively compare the experimental findings with theoretical predictions. In particular, we study the role of thermal fluctuations (TF) on the tunneling density of states (DOS) and the superconducting e…
We report low-temperature magnetisation measurements on a large number of purified ropes of single wall carbon nanotubes. In spite of a large superparamagnetic contribution due to the small ferromagnetic catalytical particles still present in the sample, at low temperature ($T < 0.5K$) and low magnetic field ($H < 80 Oe$), a diamagnetic signal is detectable. This low temperature diamagnetism can be interpreted as the Meissner effect in ropes of carbon nanotubes which have previously been shown to exhibit superconductivity from transport measurements.
We review interaction effects in chaotic metallic nanoparticles. Their single-particle Hamiltonian is described by the proper random-matrix ensemble while the dominant interaction terms are invariants under a change of the single-particle basis. In the absence of spin-orbit scattering, the non-trivial invariants consist of a pairing interaction, which leads to superconductivity in the bulk, and a ferromagnetic exchange interaction. Spin-orbit scattering breaks spin-rotation invariance and when it is sufficiently strong, the only dominant nontrivial interaction is the pairing interaction. We di…
The presence of spin-orbit scattering within an aluminum nanoparticle affects measurements of the discrete energy levels within the particle by (1) reducing the effective g-factor below the free-electron value of 2, (2) causing avoided crossings as a function of magnetic field between predominantly-spin-up and predominantly-spin-down levels, and (3) introducing magnetic-field-dependent changes in the amount of current transported by the tunneling resonances. All three effects can be understood in a unified fashion by considering a simple Hamiltonian. Spin-orbit scattering from 4% gold impuriti…
In a zero-dimensional superconductor, quantum size effects(QSE) not only set the limit to superconductivity, but are also at the heart of new phenomena such as shell effects, which have been predicted to result in large enhancements of the superconducting energy gap. Here, we experimentally demonstrate these QSE through measurements on single, isolated Pb and Sn nanoparticles. In both systems superconductivity is ultimately quenched at sizes governed by the dominance of the quantum fluctuations of the order parameter. However, before the destruction of superconductivity, in Sn nanoparticles we…
Discrete energy levels of ultrasmall metallic grains are extracted in single-electron-tunneling-spectroscopy experiments. We study the response of these energy levels to an external magnetic field in the presence of both spin-orbit scattering and pairing correlations. In particular, we investigate $g$-factors and level curvatures that parametrize, respectively, the linear and quadratic terms in the magnetic-field dependence of the many-particle energy levels of the grain. Both of these quantities exhibit level-to-level fluctuations in the presence of spin-orbit scattering. We show that the dis…
We have investigated the spectrum of discrete electronic states in single, nm-scale Al particles incorporated into new tunneling transistors, complete with a gate electrode. The addition of the gate has allowed (a) measurements of the electronic spectra for different numbers of electrons in the same particle, (b) greatly improved resolution and qualitatively new results for spectra within superconducting particles, and (c) detailed studies of the gate-voltage dependence of the resonance level widths, which have directly demonstrated the effects of non-equilibrium excitations.
Nanoparticles of NbC produced by laser ablation in liquid: a study of structural, magnetic and superconductivity properties
采用液相激光烧蚀法合成超导NbC纳米颗粒，发现其表现出超导与磁性共存的独特性质，该现象源于纳米尺度下表面积与体积比的大幅增加。
We have investigated the conduction over a wide range of temperature of $λ$ DNA molecules deposited across slits etched through a few nanometers thick platinum film. The slits are insulating before DNA deposition but contain metallic Ga nanoparticles, a result of focused ion beam etching. When these nanoparticles are superconducting we find that they can induce superconductivity through the DNA molecules, even though the main electrodes are non superconducting. These results indicate that minute metallic particles can easily transfer charge carriers to attached DNA molecules and provide a poss…
We investigate transport and magnetotransport properties of binary networks composed of superconducting (MgB2) and ferromagnetic (CrO2 or LSMO) nanoparticles. While for the LSMO/MgB2 system a single percolation threshold is observed, for CrO2/MgB2 binary composites an anomalously high resistance state with two distinct percolation thresholds corresponding to conductor-insulator and superconductor-insulator transitions is found. The existence of this double percolation effect becomes possible when the interface conductance between the two different constituents is suppressed and the condition f…
There exists a variety of proposals to transform a conventional s-wave superconductor into a topological superconductor, supporting Majorana fermion mid-gap states. A necessary ingredient of these proposals is strong spin-orbit coupling. Here we propose an alternative system consisting of a one-dimensional chain of magnetic nanoparticles on a superconducting substrate. No spin-orbit coupling in the superconductor is needed. We calculate the topological quantum number of a chain of finite length, including the competing effects of disorder in the orientation of the magnetic moments and in the h…
We demonstrate the operation of low-noise nano superconducting quantum interference devices (SQUIDs) based on the high critical field and high critical temperature superconductor YBa$_2$Cu$_3$O$_7$ (YBCO) as ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have been patterned by focused ion beam milling. This allows to precisely define the lateral dimensions of the SQUIDs so as to achieve large magnetic coupling between the nanoloop and individual MNPs. By means of focused electron beam induced de…
A double percolation transition is identified in a binary network composed of nanoparticles of magnesium diborade superconductor and chromium oxide half-metallic ferromagnet. Anomalously high-resistance or insulating state, as compared to the conducting or superconducting states in single-component systems of either constituent, is observed between two distinct percolation thresholds. This double percolation effect, which is especially pronounced at liquid helium temperatures, is controlled by composite volume fraction and originates from the suppressed interface conduction and tunneling betwe…
扫码添加微信好友，提出您的宝贵建议 👇
💡 备注请填写：网站反馈
发表机构由 AI 从论文文本抽取，如发现错误，欢迎反馈修正建议。