9 research outputs found
Comment on "Experimental determination of superconducting parameters for the intermetallic perovskite superconductor MgCNi"
In a recent paper (Phys. Rev. {\bf B 67}, 094502 (2003)) Mao et al.
investigated the bias-dependent conductance of mechanical junctions between
superconducting MgCNi and a sharp W tip. They interpreted their results in
terms of 'single-particle tunneling'. We show it is more likely that current
transport through those junctions is determined by thermal effects due to the
huge normal-state resistivity of MgCNi. Therefore no conclusion can be
drawn about the possible unconventional pairing or strong-coupling
superconductivity in MgCNi.Comment: 2 pages, 1 Fig. Comment on Z. Q. Mao et al. (Phys. Rev. {\bf B 67},
094502 (2003)
Current-field diagram of magnetic states of a surface spin valve in a point contact with a single ferromagnetic film
We present a study of the influence of an external magnetic field H and an electric current I on the spin-valve
(SV) effect in point contact between a ferromagnetic thin film (F) and a sharp tip of a nonmagnetic metal (N). To
explain our observations, we propose a model of a local surface SV which is formed in such a N/F contact. In
this model, a ferromagnetic cluster at the N/F interface plays the role of the free layer in this SV. This cluster exhibits
a larger coercive field than the bulk of the ferromagnetic film, presumably due to its nanoscale nature. Finally,
we construct a magnetic state diagram of the surface SV as a function of I and H
Orbital Kondo behavior from dynamical structural defects
The interaction between an atom moving in a model double-well potential and
the conduction electrons is treated using renormalization group methods in
next-to-leading logarithmic order. A large number of excited states is taken
into account and the Kondo temperature is computed as a function of
barrier parameters. We find that for special parameters can be close to
and it can be of the same order of magnitude as the renormalized
splitting . However, in the perturbative regime we always find that
T_K \alt \Delta with a T_K \alt 1 {\rm K} [Aleiner {\em et al.}, Phys.
Rev. Lett. {\bf 86}, 2629 (2001)]. We also find that remains
unrenormalized at energies above the Debye frequency, .Comment: 9 pages, 9 figures, RevTe
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Stimulated emission and absorption of photons in magnetic point contacts
Point contacts between high anisotropy ferromagnetic SmCo5 and normal metal Cu are used to achieve a strong spin-population inversion in the contact core. Subjected to microwave irradiation in resonance with the Zeeman splitting in Cu, the inverted spin population relaxes through stimulated spin-flip photon emission, detected as peaks in the point-contact resistance. Resonant spin-flip photon absorption is detected as resistance minima, corresponding to sourcing the photon field energy into the electrical circuit. These results demonstrate fundamental mechanisms that are potentially useful in designing metallic spin-based lasers
Josephson effect and Andreev reflection in Ba₁₋xNaxFe₂As₂ (x = 0.25 and 0.35) point contacts
I(V) characteristics and their first derivatives of ScS and ScN-type (S is superconductor, c is constriction, N is
normal metal) point contacts (PCs) based on Ba₁₋xNaxFe₂As₂ (x = 0.25 and 0.35) were studied. ScS-type PCs with
S = Nb,Ta, and Pb show Josephson-like resistively shunted I(V) curves with microwave induced Shapiro steps
which satisfy relation 2eV = ω. The IcRN product (Ic is critical current, RN is normal state PC resistance) in these
PCs is found to be up to 1.2 mV. All this data with the observed dependence of the Ic on the microwave power of
ScS PCs with Pb counterelectrode indicates the presence of the singlet s-wave type pairing in Ba₁₋xNaxFe₂As₂.
From the dV/dI(V) curves of ScN-type PCs demonstrating Andreev-reflection like features, the superconducting gap
∆ ratio 2∆/kBTc = 3.6 ± 1 for the compound with x = 0.35 was evaluated. Analysis of these dV/dI(V) at high biases
V, that is well above ∆, testifies transition to the thermal regime in PCs with a voltage increase
Electron-phonon interaction in transition metal diborides TB_2 (T=Zr, Nb, Ta) studied by point-contact spectroscopy
The electron-phonon interaction (EPI) in transition metal diborides TB_2
(T=Zr, Nb, Ta) is investigated by point-contact (PC) spectroscopy. The PC EPI
functions were recovered and the EPI parameters lambda<0.1 were estimated for
all three compounds. Common and distinctive features between the EPI functions
for those diborides are discussed also in connection with the superconductivity
in MgB_2.Comment: V2: minor changes, Ref.[21] added, publ. in PR
ELECTRON TUNNELING I N SUPERCONDUCTORS WITH NONEQUILIBRIUM OCCUPATION OF QUASIPARTICLE STATES
La décroissance de la conduction électrique de jonctions tunnel de plomb hors d'équilibre a été mesurée pour eV ≥ 2Ɗ. Nous avons étudié en détail l'effet de la température, du courant superfluide, de l'excitation des quasiparticules et des conditions de transfert de chaleur sur la fonction de distribution hors d'équilibre de l'énergie des quasiparticules. Nous comparons les résultats expérimentaux aux résultats calculés en utilisant une fonction de distribution hors d'équilibre.The decrease in electrical conductivity of nonequilibrium tunnel junctions of lead has been measured at eV ≥ 2Ɗ. The effect of ambient temperature, superfluid current, methods of quasiparticle excitation and heat transfer conditions on the nonequilibrium part of quasiparticle energy distribution function has been studied in detail. The experimental data are compared to the results calculated using the model nonequilibrium distribution function
Relaxation dynamics in the high-frequency crystal-field spectroscopy of PrNi₅ point contacts
High-frequency point-contact (PC) spectroscopy is used to investigate the relaxation processes kinetics in the intermetallic rare-earth compound PrNi₅. A difference is observed in the spectral response between the conventional low-frequency PC data and the response signal to microwave and farinfrared radiation of PrNi₅-Cu point contacts. This difference is connected with the f-shell electronic levels (CEF levels) and phonon temporal dynamics. The phonon reabsorption contribution to the spectra above the Debye energy decreases for microwave and far-infrared frequencies. However, the crystal-field contribution to the spectra at 4.2 meV is enhanced for high frequencies reflecting the relaxation processes specific for these Fermi-statistics electron excitations. The characteristic frequency for CEF-level relaxation is evaluated as ~200 GHz
Spin-valve effects in point contacts to exchange biased Сo₄₀Fe₄₀B₂₀ films
Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N)
and films of amorphous ferromagnet (F) Сo₄₀Fe₄₀B₂₀ of different thickness, exchange-biased by antiferromagnetic
Mn8₀Ir₂₀ are studied. A surface spin valve effect in the conductance of such F–N contacts is observed. The
effect of exchange bias is found to be inversely proportional to the Сo₄₀Fe₄₀B₂₀ film thickness. This behavior as
well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in
nature to those found in conventional three-layer spin-valves