14 research outputs found
The two critical temperatures conundrum in LaSrCuO
The in-plane and out-of-plane superconducting stiffness appear to vanish at
different transition temperatures, which contradicts thermodynamical
expectation. In addition, we observe a surprisingly strong dependence of the
out-of-plane stiffness transition on sample width. With evidence from Monte
Carlo simulations, this effect is explained by a crossover from three
dimensions into quasi one dimensional behavior of the finite sample. Due to an
essential singularity at the thermodynamic transition temperature , the
out-of-plane stiffness appears to vanish below by an amount which is
proportional to the inverse width. A fit of our prediction to the data is used
to determine the value of the anisotropy parameter. Analogy to studies of
helium superfluids in nanopores is made
Effects of lattice geometry on thermopower properties of the repulsive Hubbard mode
We obtain the Seebeck coefficient or thermopower , which determines the
conversion efficiency from thermal to electrical energy, for the
two-dimensional Hubbard model on different geometries (square, triangular, and
honeycomb lattices) for different electronic densities and interaction
strengths. Using Determinantal Quantum Monte Carlo (DQMC) we find the following
key results: (a) the bi-partiteness of the lattice affects the doping
dependence of ; (b) strong electronic correlations can greatly enhance
and produce non-trivial sign changes as a function of doping especially in the
vicinity of the Mott insulating phase; (c) near half filling can show
non-monotonic behavior as a function of temperature. We emphasize the role of
strong interaction effects in engineering better devices for energy storage and
applications, as captured by our calculations of the power factor where is the dc conductivity.Comment: 10 pages, 8 figure
Tuning superinductors by quantum coherence effects for enhancing quantum computing
Research on spatially inhomogeneous weakly-coupled superconductors has
recently received a boost of interest because of the experimental observation
of a dramatic enhancement of the kinetic inductance with relatively low losses.
Here, we study the kinetic inductance and the quality factor of a
strongly-disordered weakly-coupled superconducting thin film. We employ a
gauge-invariant random-phase approximation capable of describing collective
excitations and other fluctuations. In line with the experimental findings, in
the range of frequencies of interest, we have found that an exponential
increase of the kinetic inductance with disorder coexists with a still large
quality factor . More interestingly, on the metallic side of the
superconductor-insulator transition, we have identified a range of frequencies
and temperatures, well below the critical one, where quantum coherence effects
induce a broad statistical distribution of the quality factor with an average
value that increases with disorder. We expect these findings to further
stimulate experimental research on the design and optimization of
superinductors for a better performance and miniaturization of quantum devices
such as qubits circuits and microwave detectors.Comment: 15 pages, 10 figure