1,732 research outputs found
Nonlinear nonequilibrium quasiparticle relaxation in Josephson junctions
Nonequilibrium electrons in superconductors relax and eventually recombine
into Cooper pairs. Relaxation is facilitated by electron-boson interaction and
is accompanied by emission of nonequilibrium bosons. Here I solve numerically a
full set of nonlinear kinetic balance equations for stacked Josephson
junctions, which allows analysis of strongly nonequilibrium phenomena. It is
shown that nonlinearity becomes significant already at very small
disequilibrium. The following new, essentially nonlinear effects are obtained:
(i) At even-gap voltages nonequilibrium bosonic
bands overlap. This leads to enhanced emission of bosons
and to appearance of dips in tunnel conductance. (ii) A new type of radiative
solution is found at strong disequilibrium. It is characterized by the fast
stimulated relaxation of nonequilibrium quasiparticles. A stack in this state
behaves as a light emitting diode and directly converts electric power to boson
emission, without utilization of the ac-Josephson effect. This leads to very
high radiation efficacy and to significant radiative cooling of the stack. The
phenomenon can be used for realization of a new type of superconducting cascade
laser in the THz frequency range.Comment: 4 pages, 4 figures and a supplementar
Phase transitions in Bose-Fermi-Hubbard model in the heavy fermion limit: Hard-core boson approach
Phase transitions are investigated in the Bose-Fermi-Hubbard model in the
mean field and hard-core boson approximations for the case of infinitely small
fermion transfer and repulsive on-site boson-fermion interaction. The behavior
of the Bose-Einstein condensate order parameter and grand canonical potential
is analyzed as functions of the chemical potential of bosons at zero
temperature. The possibility of change of order of the phase transition to the
superfluid phase in the regime of fixed values of the chemical potentials of
Bose- and Fermi-particles is established. The relevant phase diagrams are
built.Comment: 20 pages, 15 figure
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