11,506 research outputs found
Emerging magnetism and electronic phase separation at titanate interfaces
The emergence of magnetism in otherwise nonmagnetic compounds and its
underlying mechanisms have become the subject of intense research. Here we
demonstrate that the nonmagnetic oxygen vacancies are responsible for an
unconventional magnetic state common for titanate interfaces and surfaces.
Using an effective multiorbital modelling, we find that the presence of
localized vacancies leads to an interplay of ferromagnetic order in the
itinerant t2g band and complex magnetic oscillations in the
orbitally-reconstructed eg-band, which can be tuned by gate fields at oxide
interfaces. The magnetic phase diagram includes highly fragmented regions of
stable and phase-separated magnetic states forming beyond nonzero critical
defect concentrations.Comment: 5 pages, 4 figure
How Large is the Intrinsic Flux Noise of a Magnetic Flux Quantum, of Half a Flux Quantum and of a Vortex-Free Superconductor?
This article addresses the question whether the magnetic flux of stationary
vortices or of half flux quanta generated by frustrated superconducting rings
is noisy. It is found that the flux noise generated intrinsically by a
superconductor is, in good approximation, not enhanced by stationary vortices.
Half flux quanta generated by -rings are characterized by considerably
larger noise.Comment: 11 pages, 3 figures. in: A. Bussmann-Holder, H. Keller (Eds.) High Tc
Superconductors and Related Transition Metal Oxides, Springer, 237-242; also
to be published in: Journal of Superconductivity (2007
A Flexible Network Approach to Privacy of Blockchain Transactions
For preserving privacy, blockchains can be equipped with dedicated mechanisms
to anonymize participants. However, these mechanism often take only the
abstraction layer of blockchains into account whereas observations of the
underlying network traffic can reveal the originator of a transaction request.
Previous solutions either provide topological privacy that can be broken by
attackers controlling a large number of nodes, or offer strong and
cryptographic privacy but are inefficient up to practical unusability. Further,
there is no flexible way to trade privacy against efficiency to adjust to
practical needs. We propose a novel approach that combines existing mechanisms
to have quantifiable and adjustable cryptographic privacy which is further
improved by augmented statistical measures that prevent frequent attacks with
lower resources. This approach achieves flexibility for privacy and efficency
requirements of different blockchain use cases.Comment: 6 pages, 2018 IEEE 38th International Conference on Distributed
Computing Systems (ICDCS
Dynamic Freeze-In: Impact of Thermal Masses and Cosmological Phase Transitions on Dark Matter Production
The cosmological abundance of dark matter can be significantly influenced by
the temperature dependence of particle masses and vacuum expectation values. We
illustrate this point in three simple freeze-in models. The first one, which we
call kinematically induced freeze-in, is based on the observation that the
effective mass of a scalar temporarily becomes very small as the scalar
potential undergoes a second order phase transition. This opens dark matter
production channels that are otherwise forbidden. The second model we consider,
dubbed vev-induced freeze-in, is a fermionic Higgs portal scenario. Its scalar
sector is augmented compared to the Standard Model by an additional scalar
singlet, , which couples to dark matter and temporarily acquires a vacuum
expectation value (a two-step phase transition or `vev flip-flop'). While
, the modified coupling structure in the scalar
sector implies that dark matter production is significantly enhanced compared
to the phases realised at very early times and again
today. The third model, which we call mixing-induced freeze-in, is similar in
spirit, but here it is the mixing of dark sector fermions, induced by non-zero
, that temporarily boosts the dark matter production rate.
For all three scenarios, we carefully dissect the evolution of the dark sector
in the early Universe. We compute the DM relic abundance as a function of the
model parameters, emphasising the importance of thermal corrections and the
proper treatment of phase transitions in the calculation.Comment: 26 pages, 11 figures, v2: matches journal version, change to the
value of a benchmark coupling in section II, impact of thermal masses
increase
Large and Small Polaron Excitations in La2/3(Sr/Ca)1/3MnO3 Films
We present detailed optical measurements of the mid-infrared (MIR)
excitations in thin films of La2/3Sr1/3MnO3 (LSMO) and La2/3Ca1/3MnO3 (LCMO)
across the magnetic transition. The shape of the excitation at about 0.2 eV in
both samples is analyzed in terms of polaron models. We propose to identify the
MIR resonance in LSMO as the excitation of large polarons and that in LCMO as a
small polaron excitation. A scaling behavior for the low-energy side of the
polaronic MIR resonance in LSMO is established
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