3,069 research outputs found
Gate-controlled superconductivity in diffusive multiwalled carbon nanotube
We have investigated electrical transport in a diffusive multiwalled carbon
nanotube contacted using superconducting leads made of Al/Ti sandwich
structure. We find proximity-induced superconductivity with measured critical
currents up to I_cm = 1.3 nA, tunable by gate voltage down to 10 pA. The
supercurrent branch displays a finite zero bias resistance which varies as R_0
proportional to I_cm^-alpha with alpha=0.74. Using IV-characteristics of
junctions with phase diffusion, a good agreement is obtained with Josephson
coupling energy in the long, diffusive junction model of A.D Zaikin and G.F.
Zharkov (Sov. J. Low Temp. Phys. 7, 184 (1981)).Comment: 5 pages, 4 figure
Influence of topological excitations on Shapiro steps and microwave dynamical conductance in bilayer exciton condensates
The quantum Hall state at total filling factor in bilayer systems
realizes an exciton condensate and exhibits a zero-bias tunneling anomaly,
similar to the Josephson effect in the presence of fluctuations. In contrast to
conventional Josephson junctions, no Fraunhofer diffraction pattern has been
observed, due to disorder induced topological defects, so-called merons. We
consider interlayer tunneling in the presence of microwave radiation, and find
Shapiro steps in the tunneling current-voltage characteristic despite the
presence of merons. Moreover, the Josephson oscillations can also be observed
as resonant features in the microwave dynamical conductance
Assessing T cell clonal size distribution: a non-parametric approach
Clonal structure of the human peripheral T-cell repertoire is shaped by a
number of homeostatic mechanisms, including antigen presentation, cytokine and
cell regulation. Its accurate tuning leads to a remarkable ability to combat
pathogens in all their variety, while systemic failures may lead to severe
consequences like autoimmune diseases. Here we develop and make use of a
non-parametric statistical approach to assess T cell clonal size distributions
from recent next generation sequencing data. For 41 healthy individuals and a
patient with ankylosing spondylitis, who undergone treatment, we invariably
find power law scaling over several decades and for the first time calculate
quantitatively meaningful values of decay exponent. It has proved to be much
the same among healthy donors, significantly different for an autoimmune
patient before the therapy, and converging towards a typical value afterwards.
We discuss implications of the findings for theoretical understanding and
mathematical modeling of adaptive immunity.Comment: 13 pages, 3 figures, 2 table
Quantum jumps on Anderson attractors
In a closed single-particle quantum system, spatial disorder induces Anderson
localization of eigenstates and halts wave propagation. The phenomenon is
vulnerable to interaction with environment and decoherence, that is believed to
restore normal diffusion. We demonstrate that for a class of experimentally
feasible non-Hermitian dissipators, which admit signatures of localization in
asymptotic states, quantum particle opts between diffusive and ballistic
regimes, depending on the phase parameter of dissipators, with sticking about
localization centers. In diffusive regime, statistics of quantum jumps is
non-Poissonian and has a power-law interval, a footprint of intermittent
locking in Anderson modes. Ballistic propagation reflects dispersion of an
ordered lattice and introduces a new timescale for jumps with non-monotonous
probability distribution. Hermitian dephasing dissipation makes localization
features vanish, and Poissonian jump statistics along with normal diffusion are
recovered.Comment: 6 pages, 5 figure
Signatures of many-body localization in steady states of open quantum systems
Many-body localization (MBL) is a result of the balance between
interference-based Anderson localization and many-body interactions in an
ultra-high dimensional Fock space. It is usually expected that dissipation is
blurring interference and destroying that balance so that the asymptotic state
of a system with an MBL Hamiltonian does not bear localization signatures. We
demonstrate, within the framework of the Lindblad formalism, that the system
can be brought into a steady state with non-vanishing MBL signatures. We use a
set of dissipative operators acting on pairs of connected sites (or spins), and
show that the difference between ergodic and MBL Hamiltonians is encoded in the
imbalance, entanglement entropy, and level spacing characteristics of the
density operator. An MBL system which is exposed to the combined impact of
local dephasing and pairwise dissipation evinces localization signatures
hitherto absent in the dephasing-outshaped steady state.Comment: 6 pages, 3 figure
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