2,162 research outputs found
Correlating the nanostructure of Al-oxide with deposition conditions and dielectric contributions of two-level systems in perspective of superconducting quantum circuits
This work is concerned with Al/Al-oxide(AlO)/Al-layer systems which are
important for Josephson-junction-based superconducting devices such as quantum
bits. The device performance is limited by noise, which has been to a large
degree assigned to the presence and properties of two-level tunneling systems
in the amorphous AlO tunnel barrier. The study is focused on the
correlation of the fabrication conditions, nanostructural and nanochemical
properties and the occurrence of two-level tunneling systems with particular
emphasis on the AlO-layer. Electron-beam evaporation with two different
processes and sputter deposition were used for structure fabrication, and the
effect of illumination by ultraviolet light during Al-oxide formation is
elucidated. Characterization was performed by analytical transmission electron
microscopy and low-temperature dielectric measurements. We show that the
fabrication conditions have a strong impact on the nanostructural and
nanochemical properties of the layer systems and the properties of two-level
tunneling systems. Based on the understanding of the observed structural
characteristics, routes are derived towards the fabrication of
Al/AlO/Al-layers systems with improved properties.Comment: 28 pages, 4 figure
Cloud Chamber: A Performance with Real Time Two-Way Interaction between Subatomic Particles and Violinist
âCloud Chamberâ - a composition by Alexis Kirke, Antonino Chiaramonte, and Anna Troisi - is a live performance in which the invisible quantum world becomes visible as a violinist and subatomic particle tracks interact together. An electronic instrument was developed which can be âplayedâ live by radioactive atomic particles. Electronic circuitry was developed enabling a violin to create a physical force field that directly affects the ions generated by cosmic radiation particles. This enabled the violinist and the ions to influence each other musically in real time. A glass cloud chamber was used onstage to make radioactivity visible in bright white tracks moving within, with the tracks projected onto a large screen
Antiferromagnetic phase of the gapless semiconductor V3Al
Discovering new antiferromagnetic compounds is at the forefront of developing
future spintronic devices without fringing magnetic fields. The
antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully
synthesized via arc-melting and annealing. The antiferromagnetic properties
were established through synchrotron measurements of the atom-specific magnetic
moments, where the magnetic dichroism reveals large and oppositely-oriented
moments on individual V atoms. Density functional theory calculations confirmed
the stability of a type G antiferromagnetism involving only two-third of the V
atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray
diffraction and transport measurements also support the antiferromagnetism.
This archetypal gapless semiconductor may be considered as a cornerstone for
future spintronic devices containing antiferromagnetic elements.Comment: Accepted to Physics Review B on 02/23/1
Combined effect of nonmagnetic and magnetic scatterers on critical temperatures of superconductors with different gap anisotropy
The combined effect of nonmagnetic and magnetic defects and impurities on
critical temperatures of superconductors with different gap anisotropy is
studied theoretically within the weak coupling limit of the BCS model. An
expression is derived which relates the critical temperature to relaxation
rates of charge carriers by nonmagnetic and magnetic scatterers, as well as to
the coefficient of anisotropy of the superconducting order parameter on the
Fermi surface. Particular cases of d-wave, (s+d)-wave, and anisotropic s-wave
superconductors are briefly discussed.Comment: 5 pages, Te
Nanoscale sensing based on nitrogen vacancy centers in single crystal diamond and nanodiamonds : achievements and challenges
Powered by the mutual developments in instrumentation, materials and theoretical descriptions,
sensing and imaging capabilities of quantum emitters in solids have significantly increased in the past
two decades. Quantum emitters in solids, whose properties resemble those of atoms and ions, provide
alternative ways to probing natural and artificial nanoscopic systems with minimum disturbance and
ultimate spatial resolution. Among those emerging quantum emitters, the nitrogen vacancy (NV)
color center in diamond is an outstanding example due to its intrinsic properties at room temperature
(highly-luminescent, photo-stable, biocompatible, highly-coherent spin states). This review article
summarizes recent advances and achievements in using NV centers within nano- and single crystal
diamonds in sensing and imaging. We also highlight prevalent challenges and material aspects for
different types of diamond and outline the main parameters to consider when using color centers as
sensors. As a novel sensing resource, we highlight the properties of NV centers as light emitting
electrical dipoles and their coupling to other nanoscale dipoles e.g. graphene
Exchange Instabilities in Semiconductor Double Quantum Well Systems
We consider various exchange-driven electronic instabilities in semiconductor
double-layer systems in the absence of any external magnetic field. We
establish that there is no exchange-driven bilayer to monolayer charge transfer
instability in the double-layer systems. We show that, within the unrestricted
Hartree-Fock approximation, the low density stable phase (even in the absence
of any interlayer tunneling) is a quantum ``pseudospin rotated'' spontaneous
interlayer phase coherent spin-polarized symmetric state rather than the
classical Ising-like charge-transfer phase. The U(1) symmetry of the double
quantum well system is broken spontaneously at this low density quantum phase
transition, and the layer density develops quantum fluctuations even in the
absence of any interlayer tunneling. The phase diagram for the double quantum
well system is calculated in the carrier density--layer separation space, and
the possibility of experimentally observing various quantum phases is
discussed. The situation in the presence of an external electric field is
investigated in some detail using the
spin-polarized-local-density-approximation-based self-consistent technique and
good agreement with existing experimental results is obtained.Comment: 24 pages, figures included. Also available at
http://www-cmg.physics.umd.edu/~lzheng/preprint/ct.uu/ . Revised final
version to appear in PR
Pseudogap in the microwave response of YBa_2Cu_3O_{7-x}
The in-plane and out-of-plane surface impedance and microwave conductivity
components of one and the same YBa_2Cu_3O_{7-x} (0.07\le x\le 0.47) single
crystal are determined in the wide ranges of temperature T and carrier
concentration p in CuO_2 planes. The following features of the superfluid
density n_s(T,p)\propto\lambda_{ab}^{-2}(T,p) are observed at T<Tc/2 and
0.078\le p\le 0.16: (i) n_s(0,p) depends linearly on p, (ii) the derivative
|dn_s(T,p)/dT|_{T\to 0} depends on p slightly in the optimally and moderately
doped regions (0.10<p\le 0.16); however, it rapidly increases with p further
lowering and (iii) the latter finding is accompanied by the linear
low-temperature dependence \Delta n_s(T)\propto(-T) changing to \Delta
n_s(T)\propto(-\sqrt{T}). For optimum oxygen content the temperature dependence
of the normalized imaginary part of the c-axis conductivity
\lambda_c^2(0)/\lambda_c^2(T) is found to be strikingly similar to that of
\lambda_{ab}^2(0)/\lambda_{ab}^2(T) and becomes more convex with p lowering.
\lambda_c^{-2}(0,p) values are roughly proportional to the normal state
conductivities \sigma_c(T_c,p) along the c-axis. All these properties can be
treated in the framework of d-density wave order of pseudogap.Comment: 7 pages, 9 figures, presented at EUCAS 2003 (September 14-18),
submitted to SUS
Theory of the c-Axis Penetration Depth in the Cuprates
Recent measurements of the London penetration depth tensor in the cuprates
find a weak temperature dependence along the c-direction which is seemingly
inconsistent with evidence for d-wave pairing deduced from in-plane
measurements. We demonstrate in this paper that these disparate results are not
in contradiction, but can be explained within a theory based on incoherent
quasiparticle hopping between the CuO2 layers. By relating the calculated
temperature dependence of the penetration depth \lambda_c(T) to the c-axis
resistivity, we show how the measured ratio \lambda_c^2(0) / \lambda_c^2(T) can
provide insight into the behavior of c-axis transport below Tc and the related
issue of ``confinement.''Comment: 4 pages, REVTEX with psfig, 3 PostScript figures included in
compressed for
Disorder Effects in Superconductors with Anisotropic Pairing: From Cooper Pairs to Compact Bosons
In the weak coupling BCS-approximation normal impurities do not influence
superconducting T_{c} in significant manner in case of isotropic s-wave
pairing. However, in case of d-wave pairing these are strongly pair-breaking.
This fact is in rather strong contradiction with many experiments on disordered
high-T_{c} superconductors assuming the d-wave nature of pairing in these
systems. With the growth of electron attraction within the Cooper pair the
system smoothly crosses over from BCS-pairs to compact Boson picture of
superconductivity. As pairing strength grows and pairs become compact
significant deviations from universal Abrikosov-Gorkov dependence of T_{c} on
disorder appear in case of d-wave pairing with superconducting state becoming
more stable than in the weak coupling case. As high-T_{c} superconductors are
actually in the intermediate region with Cooper pairs size of the order of few
interatomic lengths, these results can explain the relative stability of d-wave
pairing under rather strong disordering.Comment: 8 pages, 3 figures, RevTeX 3.0, 1 Postscript figure attached,
submitted to JETP Letter
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