Correlating Josephson supercurrents and Shiba states in quantum spins unconventionally coupled to superconductors

AbstractLocal spins coupled to superconductors give rise to several emerging phenomena directly linked to the competition between Cooper pair formation and magnetic exchange. These effects are generally scrutinized using a spectroscopic approach which relies on detecting the in-gap bound modes arising from Cooper pair breaking, the so-called Yu-Shiba-Rusinov (YSR) states. However, the impact of local magnetic impurities on the superconducting order parameter remains largely unexplored. Here, we use scanning Josephson spectroscopy to directly visualize the effect of magnetic perturbations on Cooper pair tunneling between superconducting electrodes at the atomic scale. By increasing the magnetic impurity orbital occupation by adding one electron at a time, we reveal the existence of a direct correlation between Josephson supercurrent suppression and YSR states. Moreover, in the metallic regime, we detect zero bias anomalies which break the existing framework based on competing Kondo and Cooper pair singlet formation mechanisms. Based on first-principle calculations, these results are rationalized in terms of unconventional spin-excitations induced by the finite magnetic anisotropy energy. Our findings have far reaching implications for phenomena that rely on the interplay between quantum spins and superconductivity.

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Atomic resolution characterisation of interface structures by Electron Energy Loss Spectroscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010014871x ◽

1993 ◽

Vol 51 ◽

pp. 576-577

Author(s):

N. D. Browning ◽

M. M. McGibbon ◽

M. F. Chisholm ◽

S. J. Pennycook

Keyword(s):

High Resolution ◽

Energy Loss ◽

Electron Energy ◽

Electron Energy Loss Spectroscopy ◽

Imaging Technique ◽

Atomic Scale ◽

Atomic Resolution ◽

Reference Image ◽

The Impact ◽

Electron Energy Loss

The recent development of the Z-contrast imaging technique for the VG HB501 UX dedicated STEM, has added a high-resolution imaging facility to a microscope used mainly for microanalysis. This imaging technique not only provides a high-resolution reference image, but as it can be performed simultaneously with electron energy loss spectroscopy (EELS), can be used to position the electron probe at the atomic scale. The spatial resolution of both the image and the energy loss spectrum can be identical, and in principle limited only by the 2.2 Å probe size of the microscope. There now exists, therefore, the possibility to perform chemical analysis of materials on the scale of single atomic columns or planes.In order to achieve atomic resolution energy loss spectroscopy, the range over which a fast electron can cause a particular excitation event, must be less than the interatomic spacing. This range is described classically by the impact parameter, b, which ranges from ~10 Å for the low loss region of the spectrum to <1Å for the core losses.

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Seasonality and Dynamics of Atmospheric Teleconnection from the Tropical Indian Ocean and the Western Pacific to West Antarctica

Atmosphere ◽

10.3390/atmos12070849 ◽

2021 ◽

Vol 12 (7) ◽

pp. 849

Author(s):

Hyun-Ju Lee ◽

Emilia-Kyung Jin

Keyword(s):

Indian Ocean ◽

Rossby Wave ◽

Tropical Indian Ocean ◽

Western Pacific ◽

Tropical Region ◽

Formation Mechanisms ◽

West Antarctica ◽

Background Flow ◽

The Impact ◽

The Western Pacific

The global impact of the tropical Indian Ocean and the Western Pacific (IOWP) is expected to increase in the future because this area has been continuously warming due to global warming; however, the impact of the IOWP forcing on West Antarctica has not been clearly revealed. Recently, ice loss in West Antarctica has been accelerated due to the basal melting of ice shelves. This study examines the characteristics and formation mechanisms of the teleconnection between the IOWP and West Antarctica for each season using the Rossby wave theory. To explicitly understand the role of the background flow in the teleconnection process, we conduct linear baroclinic model (LBM) simulations in which the background flow is initialized differently depending on the season. During JJA/SON, the barotropic Rossby wave generated by the IOWP forcing propagates into the Southern Hemisphere through the climatological northerly wind and arrives in West Antarctica; meanwhile, during DJF/MAM, the wave can hardly penetrate the tropical region. This indicates that during the Austral winter and spring, the IOWP forcing and IOWP-region variabilities such as the Indian Ocean Dipole (IOD) and Indian Ocean Basin (IOB) modes should paid more attention to in order to investigate the ice change in West Antarctica.

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Endothelial k-RasV12 Expression Induces Capillary Deficiency Attributable to Marked Tube Network Expansion Coupled to Reduced Pericytes and Basement Membranes

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvbaha.121.316798 ◽

2021 ◽

Author(s):

Zheying Sun ◽

Scott S. Kemp ◽

Prisca K. Lin ◽

Kalia N. Aguera ◽

George E. Davis

Keyword(s):

Protein Kinase ◽

Basement Membrane ◽

Arteriovenous Malformations ◽

Network Formation ◽

Tube Formation ◽

Small Gtpase ◽

Basement Membranes ◽

Formation Mechanisms ◽

Lumen Formation ◽

The Impact

Objective: We sought to determine how endothelial cell (EC) expression of the activating k-Ras mutation, k-RasV12, affects their ability to form lumens and tubes and interact with pericytes during capillary assembly Approach and Results: Using defined bioassays where human ECs undergo observable tubulogenesis, sprouting behavior, pericyte recruitment to EC-lined tubes, and pericyte-induced EC basement membrane deposition, we assessed the impact of EC k-RasV12 expression on these critical processes that are necessary for proper capillary network formation. This mutation, which is frequently seen in human ECs within brain arteriovenous malformations, was found to markedly accentuate EC lumen formation mechanisms, with strongly accelerated intracellular vacuole formation, vacuole fusion, and lumen expansion and with reduced sprouting behavior, leading to excessively widened tube networks compared with control ECs. These abnormal tubes demonstrate strong reductions in pericyte recruitment and pericyte-induced EC basement membranes compared with controls, with deficiencies in fibronectin, collagen type IV, and perlecan deposition. Analyses of signaling during tube formation from these k-RasV12 ECs reveals strong enhancement of Src, Pak2 (P21 [RAC1 (Rac family small GTPase 1)] activated kinase 2), b-Raf (v-raf murine sarcoma viral oncogene homolog B1), Erk (extracellular signal–related kinase), and Akt activation and increased expression of PKCε (protein kinase C epsilon), MT1-MMP (membrane-type 1 matrix metalloproteinase), acetylated tubulin and CDCP1 (CUB domain-containing protein 1; most are known EC lumen regulators). Pharmacological blockade of MT1-MMP, Src, Pak, Raf, Mek (mitogen-activated protein kinase) kinases, Cdc42 (cell division cycle 42)/Rac1, and Notch markedly interferes with lumen and tube formation from these ECs. Conclusions: Overall, this novel work demonstrates that EC expression of k-RasV12 disrupts capillary assembly due to markedly excessive lumen formation coupled with strongly reduced pericyte recruitment and basement membrane deposition, which are critical pathogenic features predisposing the vasculature to develop arteriovenous malformations.

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Magnetic and defect probes of the SmB6 surface state

Science Advances ◽

10.1126/sciadv.aau4886 ◽

2018 ◽

Vol 4 (11) ◽

pp. eaau4886 ◽

Cited By ~ 14

Author(s):

Lin Jiao ◽

Sahana Rößler ◽

Deepa Kasinathan ◽

Priscila F. S. Rosa ◽

Chunyu Guo ◽

...

Keyword(s):

Surface States ◽

Scanning Tunneling Spectroscopy ◽

Tunneling Spectroscopy ◽

Scanning Tunneling ◽

Magnetic Impurities ◽

Fundamental Physics ◽

Length Scales ◽

Kondo Insulator ◽

Theoretical Predictions ◽

The Impact

The impact of nonmagnetic and magnetic impurities on topological insulators is a central focus concerning their fundamental physics and possible spintronics and quantum computing applications. Combining scanning tunneling spectroscopy with transport measurements, we investigate, both locally and globally, the effect of nonmagnetic and magnetic substituents in SmB6, a predicted topological Kondo insulator. Around the so-introduced substitutents and in accord with theoretical predictions, the surface states are locally suppressed with different length scales depending on the substituent’s magnetic properties. For sufficiently high substituent concentrations, these states are globally destroyed. Similarly, using a magnetic tip in tunneling spectroscopy also resulted in largely suppressed surface states. Hence, a destruction of the surface states is always observed close to atoms with substantial magnetic moment. This points to the topological nature of the surface states in SmB6 and illustrates how magnetic impurities destroy the surface states from microscopic to macroscopic length scales.

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A water vapor modulated aerosol impact on ice crystal size

10.5194/acp-2017-548 ◽

2017 ◽

Cited By ~ 1

Author(s):

Bin Zhao ◽

Kuo-Nan Liou ◽

Yu Gu ◽

Jonathan H. Jiang ◽

Qinbin Li ◽

...

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

Deep Convection ◽

Significant Negative Correlation ◽

Formation Mechanisms ◽

Strong Positive Correlation ◽

Ice Crystal ◽

Ice Clouds ◽

Dry Conditions ◽

The Impact

Abstract. The interactions between aerosols and ice clouds represent one of the largest uncertainties in global radiative forcing from pre-industrial time to the present. In particular, the impact of aerosols on ice crystal effective radius (Rei), which is a key parameter determining ice clouds' net radiative effect, is highly uncertain due to limited and conflicting observational evidence. Here we investigate the effects of aerosols on Rei under different meteorological conditions using 9-year satellite observations. We find that the responses of Rei to aerosol loadings are modulated by water vapor amount in conjunction with several other meteorological parameters. While there is a significant negative correlation between Rei and aerosol loading in moist conditions, consistent with the Twomey effect for liquid clouds, a strong positive correlation between the two occurs in dry conditions. Simulations based on a cloud parcel model suggest that water vapor modulates the relative importance of different ice nucleation modes, leading to the opposite aerosol impacts between moist and dry conditions. When ice clouds are decomposed into those generated from deep convection and formed in-situ, the water vapor modulation remains in effect for both ice cloud types, although the sensitivities of Rei to aerosols differ noticeably between them due to distinct formation mechanisms. The water vapor modulation can largely explain the difference in the responses of Rei to aerosol loadings in various seasons. A proper representation of the water vapor modulation is essential for an accurate estimate of aerosol-cloud radiative forcing produced by ice clouds.

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Vertically-resolved Characteristics of Air Pollution during Two Severe Winter Haze Episodes in Urban Beijing, China

10.5194/acp-2017-891 ◽

2017 ◽

Author(s):

Qingqing Wang ◽

Yele Sun ◽

Weiqi Xu ◽

Wei Du ◽

Libo Zhou ◽

...

Keyword(s):

Mixing Layer ◽

Urban Site ◽

Formation Mechanisms ◽

Vertical Profiles ◽

Severe Winter ◽

Aerosol Composition ◽

Layer Height ◽

Mixing Layer Height ◽

The Impact ◽

Beijing China

Abstract. We conducted the first real-time continuous vertical measurements of particle extinction (bext), gaseous NO2, and black carbon (BC) from ground level to 260 m during two severe winter haze episodes at an urban site in Beijing, China. Our results illustrated four distinct types of vertical profiles: 1) uniform vertical distributions (37 % of the time) with vertical differences less than 5 %; 2) higher values at lower altitudes (29 %); 3) higher values at higher altitudes (16 %), and 4) significant decreases at the heights of ~ 100–150 m (14 %). Further analysis demonstrated that vertical convection as indicated by mixing layer height, temperature inversion, and local emissions are three major factors affecting the changes in vertical profiles. Particularly, the formation of Type 4 was strongly associated with the stratified layer that was formed due to the interactions of different air masses and temperature inversions. Aerosol composition was substantially different below and above the transition heights with ~ 20–30 % higher contributions of local sources (e.g., biomass burning and cooking) at lower altitudes. A more detailed evolution of vertical profiles and their relationship with the changes in source emissions, mixing layer height, and aerosol chemistry was illustrated by a case study. BC showed overall similar vertical profiles as those of bext (R2 = 0.92 and 0.69 in November and January, respectively). While NO2 was correlated with bext for most of the time, the vertical profiles of bext/NO2 varied differently for different profiles, indicating the impact of chemical transformation on vertical profiles. Our results also showed that more comprehensive vertical measurements (e.g., more aerosol and gaseous species) at higher altitudes in the megacities are needed for a better understanding of the formation mechanisms and evolution of severe haze episodes in China.

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RKKY interaction in topological crystalline insulators

Canadian Journal of Physics ◽

10.1139/cjp-2020-0140 ◽

2020 ◽

Author(s):

Seyyed Hosein Ganjipour

Keyword(s):

Band Structure ◽

Exchange Coupling ◽

Magnetic Impurities ◽

Rkky Interaction ◽

Magnetic Ground State ◽

Magnetic Exchange ◽

Magnetic Exchange Coupling ◽

Spatial Configurations ◽

State Band ◽

Topological Crystalline Insulators

We theoretically study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction between two magnetic impurities embedded on the (001) surface of a topological crystalline insulator (TCI), using the Green’s function method. Highly anisotropic band structure of TCI, gives rise to a highly anisotropic magnetic exchange coupling. We show that the interaction is oscillatory; the amplitude and wavelength of oscillations have angular dependence arising from the anisotropy of the surface state band structure. The spatial configurations of the magnetic impurities can also dramatically change the quality and quantity of the RKKY interaction. We find a strong anisotropy of the exchange interaction and the magnetic ground state of two magnetic adatoms can be tuned by changing the rotational configuration of impurities. It is found that the three types of interactions contribute to the magnetic exchange coupling in the (001) TCI surfaces: the Heisenberg, Dzyaloshinsky-Moriya, and Ising types. Our results will open up a new route toward spintronics based on TCIs.

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Atomic-scale viscoplasticity mechanisms revealed in high ductility metallic glass films

Scientific Reports ◽

10.1038/s41598-019-49910-7 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 3

Author(s):

Hosni Idrissi ◽

Matteo Ghidelli ◽

Armand Béché ◽

Stuart Turner ◽

Sébastien Gravier ◽

...

Keyword(s):

Metallic Glass ◽

Metallic Glasses ◽

Shear Banding ◽

Atomic Scale ◽

Microscopy Imaging ◽

Rate Dependent ◽

Imaging And Spectroscopy ◽

Shear Transformation Zones ◽

The Impact ◽

Glass Films

Abstract The fundamental plasticity mechanisms in thin freestanding Zr65Ni35 metallic glass films are investigated in order to unravel the origin of an outstanding strength/ductility balance. The deformation process is homogenous until fracture with no evidence of catastrophic shear banding. The creep/relaxation behaviour of the films was characterized by on-chip tensile testing, revealing an activation volume in the range 100–200 Å3. Advanced high-resolution transmission electron microscopy imaging and spectroscopy exhibit a very fine glassy nanostructure with well-defined dense Ni-rich clusters embedded in Zr-rich clusters of lower atomic density and a ~2–3 nm characteristic length scale. Nanobeam electron diffraction analysis reveals that the accumulation of plastic deformation at room-temperature correlates with monotonously increasing disruption of the local atomic order. These results provide experimental evidences of the dynamics of shear transformation zones activation in metallic glasses. The impact of the nanoscale structural heterogeneities on the mechanical properties including the rate dependent behaviour is discussed, shedding new light on the governing plasticity mechanisms in metallic glasses with initially heterogeneous atomic arrangement.

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Probing Semiconductor/Insulator Heterostructures Through Electron Spin Resonance of Point Defects: Interfaces, Interlayers, and Stress

MRS Proceedings ◽

10.1557/proc-984-0984-mm08-01 ◽

2006 ◽

Vol 984 ◽

Author(s):

A. Stesmans ◽

K. Clémer ◽

P. Somers ◽

V. V. Afanas'ev

Keyword(s):

Electron Spin Resonance ◽

Integrated Circuits ◽

Electron Spin ◽

Point Defects ◽

Atomic Scale ◽

Interface Quality ◽

Si Substrates ◽

Spin Resonance ◽

The Impact

AbstractElectron spin resonance (ESR) spectroscopy has become indispensable when it comes to the characterization on atomic-scale of structural, and correlated, electrical properties of actual semiconductor/insulator heterostructures. Through probing of paramagnetic point defects such as the Pb-type defects, E', and EX as a function of VUV irradiation and post deposition heat treatment, basic information as to the nature, quality, and thermal stability of the interface and interfacial regions can be established. This is illustrated by some specific examples of ESR analysis on contemporary Si/insulator structures promising for future developments in integrated circuits. First the impact of strain on the Si/SiO2 entity will be discussed. Through ESR analysis of thermally oxidized (111)Si substrates mechanically stressed in situ during oxidation, and tensile strained (100)sSi/SiO2 structures, it will be pointed out that in-plane tensile stress in Si can significantly improve the interface quality. Next, ESR results for stacks of (100)Si/SiOx/HfO2 and (100)Si/LaAlO3 are presented, revealing the potential to attain a high quality Si/SiO2 interface for the former and an abrupt, thermally stable interface for the latter.

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An advanced structural characterization of templated meso-macroporous carbon monoliths by small- and wide-angle scattering techniques

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.11.23 ◽

2020 ◽

Vol 11 ◽

pp. 310-322

Author(s):

Felix M Badaczewski ◽

Marc O Loeh ◽

Torben Pfaff ◽

Dirk Wallacher ◽

Daniel Clemens ◽

...

Keyword(s):

Neutron Scattering ◽

Carbon Materials ◽

Pore Space ◽

Atomic Scale ◽

Sorption Behavior ◽

Wide Angle ◽

Large Organic Molecule ◽

Nanoscale Pore ◽

Nanopore Structure ◽

The Impact

This study is dedicated to link the nanoscale pore space of carbon materials, prepared by hard-templating of meso-macroporous SiO2 monoliths, to the corresponding nanoscale polyaromatic microstructure using two different carbon precursors wthat generally exhibit markedly different carbonization properties, i.e., a graphitizable pitch and a non-graphitizable resin. The micro- and mesoporosity of these monolithic carbon materials was studied by the sorption behavior of a relatively large organic molecule (p-xylene) in comparison to typical gas adsorbates (Ar). In addition, to obtain a detailed view on the nanopore space small-angle neutron scattering (SANS) combined with in situ physisorption was applied, using deuterated p-xylene (DPX) as a contrast-matching agent in the neutron scattering process. The impact of the carbon precursor on the structural order on an atomic scale in terms of size and disorder of the carbon microstructure, on the nanopore structure, and on the template process is analyzed by special evaluation approaches for SANS and wide-angle X-ray scattering (WAXS). The WAXS analysis shows that the pitch-based monolithic material exhibits a more ordered microstructure consisting of larger graphene stacks and similar graphene layer sizes compared to the monolithic resin. Another major finding is the discrepancy in the accessible micro/mesoporosity between Ar and deuterated p-xylene that found for the two different carbon precursors, pitch and resin, which can be regarded as representative carbon precursors in general. These differences essentially indicate that physisorption using probe gases such as Ar or N2 can provide misleading parameters if to be used to appraise the accessibility of the nanoscale pore space.

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