949 research outputs found
Fermi's golden rule and the second law of thermodynamics
We present a Gedankenexperiment that leads to a violation of detailed balance
if quantum mechanical transition probabilities are treated in the usual way by
applying Fermi's "golden rule". This Gedankenexperiment introduces a collection
of two-level systems that absorb and emit radiation randomly through
non-reciprocal coupling to a waveguide, as realized in specific chiral quantum
optical systems. The non-reciprocal coupling is modeled by a hermitean
Hamiltonian and is compatible with the time-reversal invariance of unitary
quantum dynamics. Surprisingly, the combination of non-reciprocity with
probabilistic radiation processes entails negative entropy production. Although
the considered system appears to fulfill all conditions for Markovian
stochastic dynamics, such a dynamics violates the Clausius inequality, a
formulation of the second law of thermodynamics. Several implications
concerning the interpretation of the quantum mechanical formalism are
discussed.Comment: thoroughly revised, 30.5 pages, 9 figures, published online in
Foundations of Physic
Field-Effect Devices Utilizing LaAlO-SrTiO Interfaces
Using LaAlO-SrTiO bilayers, we have fabricated field-effect devices
that utilize the two-dimensional electron liquid generated at the bilayers'
{\textit n}-type interfaces as drain-source channels and the LaAlO layers
as gate dielectrics. With gate voltages well below 1\,V, the devices are
characterized by voltage gain and current gain. The devices were operated at
temperatures up to 100\,{\deg}C.Comment: to be published in Applied Physics Letter
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
Quartett formation at (100)/(110)-interfaces of d-wave superconductors
Across a faceted (100)/(110) interface between two d-wave-superconductors the
structure of the superconducting order parameter leads to an alternating sign
of the local Josephson coupling. Describing the Cooper pair motion along and
across the interface by a one-dimensional boson lattice model, we show that a
small attractive interaction between the bosons boosts boson binding at the
interface -- a phenomenon, which is intimately tied to the staggered sequence
of 0- and Pi-junction contacts along the interface. We connect this finding to
the recently observed h/4e oscillations in (100)/(110) SQUIDS of cuprate
superconductors.Comment: 13 pages, 2 figure
Alex M\"uller, the High-Tc Field-Effect Transistor and Electric-Field Gated Quantum Materials
Alex M\"uller and Georg Bednorz are widely recognized for their trailblazing
discovery of high-temperature superconductivity and their groundbreaking
research on SrTiO3. In comparison, their substantial contributions to inventing
the high-Tc superconducting field-effect transistor remain relatively unknown.
Nevertheless, their efforts were crucial in developing the electric field
effect into a valuable tool for studying a broad spectrum of complex materials.
This article provides a brief overview of these developments and of the current
status in this field, with a particular focus on Alex M\"uller's visionary role
in advancing the field following the discovery of high-temperature
superconductivity.Comment: Contribution to a planned memorial issue for K.A. M\"uller by Physica
Large Negative Electronic Compressibility of LaAlO3-SrTiO3 Interfaces with Ultrathin LaAlO3 Layers
A two-dimensional electron liquid is formed at the n-type interface between
SrTiO3 and LaAlO3. Here we report on Kelvin probe microscopy measurements of
the electronic compressibility of this electron system. The electronic
compressibility is found to be negative for carrier densities of
\approx10^13/cm^2. At even smaller densities, a metal-to-insulator transition
occurs. These local measurements corroborate earlier measurements of the
electronic compressibility of LaAlO3-SrTiO3 interfaces obtained by measuring
the capacitance of macroscopic metal-LaAlO3-SrTiO3 capacitors
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