67 research outputs found
Type II superconductivity in SrPd2Ge2
Previous investigations have shown that SrPd2Ge2, a compound isostructural
with "122" iron pnictides but iron- and pnictogen-free, is a conventional
superconductor with a single s-wave energy gap and a strongly three-dimensional
electronic structure. In this work we reveal the Abrikosov vortex lattice
formed in SrPd2Ge2 when exposed to magnetic field by means of scanning
tunneling microscopy and spectroscopy. Moreover, by examining the differential
conductance spectra across a vortex and estimating the upper and lower critical
magnetic fields by tunneling spectroscopy and local magnetization measurements,
we show that SrPd2Ge2 is a strong type II superconductor with \kappa >>
sqrt(2). Also, we compare the differential conductance spectra in various
magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit
type II superconductor in the gapless region. This way we demonstrate that the
type II superconductivity is induced by the sample being in the dirty limit,
while in the clean limit it would be a type I superconductor with \kappa\ <<
sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B
85, (2012)).Comment: 9 pages, 4 figure
Josephson Coupling through a Quantum Dot
We derive, via fourth order perturbation theory, an expression for the
Josephson current through a gated interacting quantum dot. We analyze our
expression for two different models of the superconductor-dot-superconductor
(SDS) system. When the matrix elements connecting dot and leads are featureless
constants, we compute the Josephson coupling J_c as a function of the gate
voltage and Coulomb interaction. In the diffusive dot limit, we compute the
probability distribution P(J_c) of Josephson couplings. In both cases, pi
junction behavior (J_c < 0) is possible, and is not simply dependent on the
parity of the dot occupancy.Comment: 9 pages; 3 encapsulated PostScript figure
Single gap superconductivity in beta-Bi2Pd
beta-Bi2Pd compound has been proposed as another example of a multi-gap
superconductor [Y. Imai et al., J. Phys. Soc. Jap. 81, 113708 (2012)]. Here, we
report on measurements of several important physical quantities capable to show
a presence of multiple energy gaps on our superconducting single crystals of
beta-Bi2Pd with the critical temperature Tc close to 5 K. The calorimetric
study via a sensitive ac technique shows a sharp anomaly at the superconducting
transition, however only a single energy gap is detected. Also other
characteristics inferred from calorimetric measurements as the field dependence
of the Sommerfeld coefficient and the temperature and angular dependence of the
upper critical magnetic field point unequivocally to standard single s-wave gap
superconductivity. The Hall-probe magnetometry provides the same result from
the analysis of the temperature dependence of the lower critical field. A
single-gapped BCS density of states is detected by the scanning tunneling
spectroscopy measurements. Then, the bulk as well as the surface sensitive
probes evidence a standard conventional superconductivity in this system where
the topologically protected surface states have been recently detected by ARPES
[M. Sakano et al., Nature Comm. 6, 8595 (2015)] .Comment: 7 pages, 4 figures, 1 tabl
Frictional drag between quantum wells mediated by fluctuating electromagnetic field
We use the theory of the fluctuating electromagnetic field to calculate the
frictional drag between nearby two-and three dimensional electron systems. The
frictional drag results from coupling via a fluctuating electromagnetic field,
and can be considered as the dissipative part of the van der Waals interaction.
In comparison with other similar calculations for semiconductor two-dimensional
system we include retardation effects. We consider the dependence of the
frictional drag force on the temperature , electron density and separation
. We find, that retardation effects become dominating factor for high
electron densities, corresponding thing metallic film, and suggest a new
experiment to test the theory. The relation between friction and heat transfer
is also briefly commented on.Comment: 14 pages, 4 figure
Thermalization of One-Dimensional Electron Gas by Many-Body Coulomb Scattering
Quantum wires are peculiar in the sense that binary electron-electron collisions cannot thermalize energy distribution of the electrons in the same subband. We show that such thermalization occurs through many-body Coulomb scattering. We consider one-dimensional electron gas described by Newton equations of motion with many-body Coulomb forces. These equations are solved by molecular dynamics technique. Thermalization of the non-equilibrium distribution towards Maxwell function is demonstrated for a single-subband GaAs wire
Teshil-i lisan-i İngilizi
Darülfünun-I Osmanî İngilizce Muallimi Oxford Darülfünundan Mezun Profesör Mister Evenesi Tarafından Bi't-Tedkik Dar-I Mezkur Programına Kabul Olunmuşdur.
Eserde "Marmara Üniversitesi Fen-Edebiyat Fakültesi Kütüphanesi" Mührü Vardır
Study of Tip-Induced Ti-Film Oxidation in Atomic Force Microscopy Contact and Non-Contact Mode
Local anodic oxidation of metals using scanning probe techniques is mostly used for fabrication of isolated gates. The high-resistance oxide created in such a manner divides a thin metallic film into isolated regions. The tip-induced metallic oxide has not so far been used in nanolithography processes as a masking material. The aim of this contribution is to study the technological potential of a TiO mask prepared by the local anodic oxidation of a Ti film. Such a mask can be used to complete a nanotechnology process using atomic force microscopy, which can be easily combined with standard optical lithography techniques. We have found that the insulating properties of the oxides prepared in contact and non-contact modes differ strongly - they represent an energy barrier of 200 meV and 400 meV, respectively
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