Superconductor V3Si Research Articles

Yu–Shiba–Rusinov states induced by single Fe atoms on reconstructed compound superconductor V[formula omitted]Si

Reconstructed surfaces of the A15-compound superconductor V3Si(100) that are possibly induced by the segregation of bulk impurities serve as platforms to study the dependence of Yu–Shiba–Rusinov states induced by a single Fe atom on the adsorption site. Their number, energy and electron–hole asymmetry vary strongly with the atomic environment of the Fe atom. These variations are indicative of different Fe d-orbitals being active in the site-dependent exchange coupling with the substrate Cooper pairs. Spatially resolved spectroscopy gives rise to a short decay length of the Yu–Shiba–Rusinov states and thereby suggests the three-dimensional character of the scattering process underlying the bound states.

Martensitic transformation in V3Si single crystal: 51V NMR evidence for coexistence of cubic and tetragonal phases

The Martensitic transformation (MT) in A15 binary-alloy superconductor V3Si, though studied extensively, has not yet been conclusively linked with a transition to superconductivity. Previous NMR studies have mainly been on powder samples and with little emphasis on temperature dependence during the transformation. Here we study a high-quality single crystal, where quadrupolar splitting of NMR spectra for 51V allowed us to distinguish between spectra from transverse chains of V as a function of temperature. Our data revealed that (1) the MT is not abrupt, but rather there is a microscopic coexistence of pre-transformed cubic phase and transformed tetragonal phase over a few K below and above Tm, while (2) no pre-transformed phase can be found at Tc, and (3) the Martensitic lengthening of one axis occurs predominantly in a plane perpendicular to the crystal growth axis, as twinned domains.

Magnetic field induced enlargement of the regime of critical fluctuations in the classical superconductor V3Si from high-resolution specific heat experiments

We present high-resolution specific heat data from a high-purity single crystal of the classical superconductor V3Si, which reveal tiny lambda-shape anomalies at the superconducting transition superimposed onto the BCS specific heat jump in magnetic fields of 2 T and higher. The appearance of these anomalies is accompanied by a magnetic-field-induced broadening of the superconducting transition. We demonstrate, using scaling relations predicted by the fluctuation models of the 3d-XY and the 3d-lowest-Landau-level (3d-LLL) universality class that the effect of critical fluctuations becomes experimentally observable due to of a magnetic field-induced enlargement of the regime of critical fluctuations. The scaling indicates that a reduction of the effective dimensionality due to the confinement of quasiparticles into low Landau levels is responsible for this effect.

Field Dependence of the Vortex Core Size in a Multiband Superconductor

The magnetic field dependence of the vortex core size in the multiband superconductor NbSe2 has been determined from muon spin rotation measurements. The spatially extended nature of the quasiparticle core states associated with the smaller gap leads to a rapid field-induced shrinkage of the core size at low fields, while the more tightly bound nature of the states associated with the larger gap leads to a field-independent core size for fields greater than 4 kOe. A simple model is proposed for the density of delocalized core states that establishes a direct relationship between the field-induced reduction of the vortex core size and the corresponding enhancement of the electronic thermal conductivity. We show that this model accurately describes both NbSe2 and the single-band superconductor V3Si.

Shrinking Magnetic Vortices inV3Sidue to Delocalized Quasiparticle Core States: Confirmation of the Microscopic Theory for Interacting Vortices

We report muon spin rotation measurements on the conventional type-II superconductor V3Si that provide clear evidence for changes to the inner structure of a vortex due to the delocalization of bound quasiparticle core states. The experimental findings described here confirm a key prediction of recent microscopic theories describing interacting vortices. The effects of vortex-vortex interactions on the magnetic and electronic structure of the vortex state are of crucial importance to the interpretation of experiments on both conventional and exotic superconductors in an applied magnetic field.

Heat conduction in the vortex state of NbSe2: evidence for multiband superconductivity.

The thermal conductivity kappa of the layered s-wave superconductor NbSe2 was measured down to T(c)/100 throughout the vortex state. With increasing field, we identify two regimes: one with localized states at fields very near H(c1) and one with highly delocalized quasiparticle excitations at higher fields. The two associated length scales are naturally explained as multiband superconductivity, with distinct small and large superconducting gaps on different sheets of the Fermi surface. This behavior is compared to that of the multiband superconductor MgB2 and the conventional superconductor V3Si.

Investigation of the BCS density of states on a conventional superconductor by high-resolution photoelectron spectroscopy

Abstract The superconducting phase transition of the conventional A15 superconductor V3Si occurs at a transition temperature of Tc=17.1 K. According to the BCS theory, the zero-temperature gap width in the electronic density of states (DOS) is given by 1.75kBTc=2.5 meV, a value which is by a factor of the order of ten smaller than for High Temperature Superconductors (HTSC). We have investigated the DOS on polycrystalline V3Si surfaces by photoemission spectroscopy (PES) with an instrumental energy resolution of 3 meV (monochromatized He I). For the first time in photoemission spectra on a conventional superconductor, we could clearly detect the opening of a gap around the Fermi level and the signatures of the BCS DOS on this energy scale. A quantitative analysis of the data — based on a least-squares modelation by the theoretical BCS DOS — is in excellent agreement with the results of other experimental methods.

Magnetic penetration depth in V3Si and LiTi2O4 measured by μSR

Muon spin relaxation (μSR) studies have been performed in the normal spinel LiTi2O4 and the A-15 superconductor V3Si to measure the magnetic penetration depth λ. The relaxation rateσ(T) ∝ 1/λ2 in field-cooled measurements shows a sharp increase belowTc followed by saturation at low temperatures in both systems. This feature implies an isotropic energy gap without anomalous zeros, and most likelys-wave pairing. The low temperature penetration depth λ(T → 0) is determined to be 2100A for LiTi2O4 and 1300A for V3Si respectively. Assuming a clean limit relationσ ∝ λ−2 ∝ns/m*, we derive the Fermi temperatureTF ∝ns/2/3m* from the relaxation rateσ and the Sommerfeld constantγ asTF ∝ σ3/4γ−1/4. Unlike conventional superconductors, both LiTi2O4 and V3Si have a large ratio ofTc/TF ≈ 0.01, only slightly smaller than those ratios in more exotic superconductors.

On Unstable Directions of Dislocations in the Intermetallic Compound V3Si

AbstractThe angular dependence of the reciprocal elastic energy of a straight dislocation in the superconductor V3Si has been computed for different temperatures and slip systems taking elastic anisotropy into account. Regions of instability have been found which depend on temperature. Crystallographic slip planes may be unstable against climb.

Submillimeter–far-infrared spectroscopy in the liquid and solid states with a tunable optically pumped laser*

The design and spectroscopic application of a submillimeter–far-infrared (FIR) optically pumped tunable laser are described. Driven by 15–25 W of power from a cw CO2 laser, the FIR system gave milliwatts of power between 96 and 1217 μm. The pumped media were methyl alcohol (CH3OH) and 1,1-difluoroethylene (CH2CF2). The laser spectrometer was used to measure the transmission of liquid H2O, the bulk semiconductor GaAs, the epitaxial semiconductor InAs, and the high-temperature superconductor V3Si. In general, the laser system gave vastly improved signal-to-noise ratios, reduced stray light problems, and increased penetration power relative to more conventional FIR spectrometers. The laser results agreed extremely well with results from conventional spectrometers except where the narrowness of the laser line produced interference effects.