3,144 research outputs found
Light Mediated Superconducting Transistor
Bose-condensation of mass-less quasiparticles (photons) can be easily
achieved at the room temperature in lasers. On the other hand, condensation of
bosons having a non-zero mass requires usually ultra-low temperatures.
Recently, it has been shown that polaritons, which are half-light-half-matter
quasi-particles, may form condensed states at high temperatures (up to 300K).
Polaritons composed by electron-hole pairs coupled to confined light modes in
optical cavities may form a Bardeen-Cooper-Schriefer (BCS) superfluid. We
propose a new transistor based on stimulated scattering of electron-hole pairs
into the BCS polariton mode. A pn-junction embedded inside an optical cavity
resonantly emits light into the cavity mode. If the cavity mode energy slightly
exceeds the band-gap energy, it couples with electron-hole pairs with zero
centre of mass wave-vector but non-zero wave-vector of relative motion. This
creates a super-current in the plane of the structure. In an isotropic case,
its direction is chosen by the system spontaneously. Otherwise, it is pinned to
the external in-plane bias. We calculate the phase diagram for the
electron-hole-polariton system.Comment: 11 pages, 3 figure
Quantum Interference Controls the Electron Spin Dynamics in n-GaAs
Manifestations of quantum interference effects in macroscopic objects are
rare. Weak localization is one of the few examples of such effects showing up
in the electron transport through solid state. Here we show that weak
localization becomes prominent also in optical spectroscopy via detection of
the electron spin dynamics. In particular, we find that weak localization
controls the free electron spin relaxation in semiconductors at low
temperatures and weak magnetic fields by slowing it down by almost a factor of
two in -doped GaAs in the metallic phase. The weak localization effect on
the spin relaxation is suppressed by moderate magnetic fields of about 1 T,
which destroy the interference of electron trajectories, and by increasing the
temperature. The weak localization suppression causes an anomalous decrease of
the longitudinal electron spin relaxation time with magnetic field, in
stark contrast with well-known magnetic field induced increase in . This
is consistent with transport measurements which show the same variation of
resistivity with magnetic field. Our discovery opens a vast playground to
explore quantum magneto-transport effects optically in the spin dynamics.Comment: 8 pages, 3 figure
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