92 research outputs found
Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+d
Identifying the mechanism of superconductivity in the high-temperature
cuprate superconductors is one of the major outstanding problems in physics. We
report local measurements of the onset of superconducting pairing in the
high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+d using a
lattice-tracking spectroscopy technique with a scanning tunneling microscope.
We can determine the temperature dependence of the pairing energy gaps, the
electronic excitations in the absence of pairing, and the effect of the local
coupling of electrons to bosonic excitations. Our measurements reveal that the
strength of pairing is determined by the unusual electronic excitations of the
normal state, suggesting that strong electron-electron interactions rather than
low-energy (<0.1 volts) electron-boson interactions are responsible for
superconductivity in the cuprates
Bias dependence of spin transfer torque in Co<sub>2</sub>MnSi Heusler alloy based magnetic tunnel junctions
Heusler compounds are of interest as electrode materials for use in magnetic tunnel junctions (MTJs) due to their half metallic character, which leads to 100% spin polarization and high tunneling magnetoresistance. Most work to date has focused on the improvements to tunneling magnetoresistance that can stem from the use of Heusler electrodes, while there is much less work investigating the influence of Heusler electrodes on the spin transfer torque properties of MTJs. Here, we investigate the bias dependence of the anti-damping like and field-like spin transfer torque components in both symmetric (Co2MnSi/MgO/Co2MnSi) and asymmetric (Co2MnSi/MgO/CoFe) structure Heusler based MTJs using spin transfer torque ferromagnetic resonance. We find that while the damping like torque is linear with respect to bias for both MTJ structures, the asymmetric MTJ structure has an additional linear component to the ordinarily quadratic field like torque bias dependence and that these results can be accounted for by a free electron tunneling model. Furthermore, our results suggest that the low damping and low saturation magnetization properties of Heusler alloys are more likely to lead significant improvements to spin torque switching efficiency rather than their half metallic character
Comparative assessment of sire evaluation by univariate and bivariate animal model for estimation of breeding values of first lactation traits in HF cross cattle
The aim of the present investigation was to study the superiority of bivariate over univariate sire evaluation. Data were collected on 1,988 first parity Karan Fries cows, spread over 31 years. The (co) variance components estimated by using average information restricted maximum likelihood (AIREML) were fitted into univariate and bivariate animal models for prediction of breeding values. Low heritability estimates were obtained for fertility traits ranging from 0.02 (FDPR) to 0.19 (AFC) indicating lesser role of additive gene action in fertility of dairy cattle. Comparative analysis revealed that the breeding values estimated using bivariate animal model had lower error variance and greater range in comparison to univariate animal models. The mean sire breeding values for production traits estimated by bivariate analysis ranged from 3055.50 to 3063.15 kg and were higher compared to the mean sire breeding values estimated by univariate animal model. The inclusion of fertility traits along with production traits improved the differentiating ability of bivariate animal model with respect to the production performance
Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown CrxSb2-xTe3 thin films
This work arises from research funded by the John Fell Oxford University Press Research Fund. LJC-M and LBD acknowledge financial support from EPSRC. LBD acknowledges financial support from the Science and Technology Facilities Council (UK) and AS from the Cambridge Commonwealth Trust.We report the structural, electronic, and magnetic study of Cr-doped Sb2Te3 thin films grown by a two-step deposition process using molecular-beam epitaxy (MBE). The samples were investigated using a variety of complementary techniques, namely, x-ray diffraction (XRD), atomic force microscopy, SQUID magnetometry, magneto-transport, and polarized neutron reflectometry (PNR). It is found that the samples retain good crystalline order up to a doping level of x = 0.42 (in CrxSb2-xTe3), above which degradation of the crystal structure is observed by XRD. Fits to the recorded XRD spectra indicate a general reduction in the c-axis lattice parameter as a function of doping, consistent with substitutional doping with an ion of smaller ionic radius. The samples show soft ferromagnetic behavior with the easy axis of magnetization being out-of-plane. The saturation magnetization is dependent on the doping level, and reaches from ~2 μBto almost 3 μB per Cr ion. The transition temperature (Tc) depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phase-pure films of x = 0.42 ,a Tc of 125 K was determined. Electric transport measurements find surface-dominated transport below ∼10 K. The magnetic properties extracted from anomalous Hall effect data are in excellent agreement with the magnetometry data. PNR studies indicate a uniform magnetization profile throughout the film, with no indication of enhanced magnetic order towards the sample surface.Publisher PDFPeer reviewe
Electronic structure in underdoped cuprates due to the emergence of a pseudogap
The phenomenological Green's function developed in the works of Yang, Rice
and Zhang has been very successful in understanding many of the anomalous
superconducting properties of the deeply underdoped cuprates. It is based on
considerations of the resonating valence bond spin liquid approximation and is
designed to describe the underdoped regime of the cuprates. Here we emphasize
the region of doping, , just below the quantum critical point at which the
pseudogap develops. In addition to Luttinger hole pockets centered around the
nodal direction, there are electron pockets near the antinodes which are
connected to the hole pockets by gapped bridging contours. We determine the
contours of nearest approach as would be measured in angular resolved
photoemission experiments and emphasize signatures of the Fermi surface
reconstruction from the large Fermi contour of Fermi liquid theory (which
contains hole states) to the Luttinger pocket (which contains hole
states). We find that the quasiparticle effective mass renormalization
increases strongly towards the edge of the Luttinger pockets beyond which it
diverges.Comment: 11 pages, 9 figure
Deterministic control of magnetic vortex wall chirality by electric field
Concepts for information storage and logical processing based on magnetic domain walls have great potential for implementation in future information and communications technologies. To date, the need to apply power hungry magnetic fields or heat dissipating spin polarized currents to manipulate magnetic domain walls has limited the development of such technologies. The possibility of controlling magnetic domain walls using voltages offers an energy efficient route to overcome these limitations. Here we show that a voltage-induced uniaxial strain induces reversible deterministic switching of the chirality of a magnetic vortex wall. We discuss how this functionality will be applicable to schemes for information storage and logical processing, making a significant step towards the practical implementation of magnetic domain walls in energy efficient computing
Transverse Domain Wall Profile for Spin Logic Applications
Domain wall (DW) based logic and memory devices require precise control and manipulation of DW in nanowire conduits. The topological defects of Transverse DWs (TDW) are of paramount importance as regards to the deterministic pinning and movement of DW within complex networks of conduits. In-situ control of the DW topological defects in nanowire conduits may pave the way for novel DW logic applications. In this work, we present a geometrical modulation along a nanowire conduit, which allows for the topological rectification/inversion of TDW in nanowires. This is achieved by exploiting the controlled relaxation of the TDW within an angled rectangle. Direct evidence of the logical operation is obtained via magnetic force microscopy measurement
Consumer Adoption of Self-Service Technologies in the Context of the Jordanian Banking Industry: Examining the Moderating Role of Channel Types
YesThis study aimed to examine the key factors predicting Jordanian consumers’ intentions and
usage of three types of self-service banking technologies. This study also sought to test if the
impacts of these main predictors could be moderated by channel type. This study proposed a
conceptual model by integrating factors from the unified theory of acceptance and use of
technology (UTAUT), along with perceived risk. The required data were collected from a
convenience sample of Jordanian banking customers using a survey questionnaire. The
statistical results strongly support the significant influence of performance expectancy, social
influence, and perceived risk on customer intentions for the three types of SSTs examined. The
results of the X2 differences test also indicate that there are significant differences in the
influence of the main predictors due to the moderating effect of channel type. One of the key
contributions of this study is that three types of SSTs were tested in a single study, which had
not been done before, leading to the identification of the factors common to all three types, as
well as the salient factors unique to each type
Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors
In the first three years since the discovery of Fe-based high Tc
superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed
light on three important questions. First, STM has demonstrated the complexity
of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle
interference (QPI) imaging and low temperature spectroscopy have shown that the
pairing order parameter varies from nodal to nodeless s\pm within a single
family, FeTe1-xSex. Second, STM has imaged C4 -> C2 symmetry breaking in the
electronic states of both parent and superconducting materials. As a local
probe, STM is in a strong position to understand the interactions between these
broken symmetry states and superconductivity. Finally, STM has been used to
image the vortex state, giving insights into the technical problem of vortex
pinning, and the fundamental problem of the competing states introduced when
superconductivity is locally quenched by a magnetic field. Here we give a
pedagogical introduction to STM and QPI imaging, discuss the specific
challenges associated with extracting bulk properties from the study of
surfaces, and report on progress made in understanding Fe-based superconductors
using STM techniques.Comment: 36 pages, 23 figures, 229 reference
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