Excitation of collective modes in a quantum flute

Physical review. B, Condensed matter (Impact Factor: 3.66). 02/2012; 85(24). DOI: 10.1103/PhysRevB.85.245114
Source: arXiv

ABSTRACT We use a generalized master equation (GME) formalism to describe the
non-equilibrium time-dependent transport of Coulomb interacting electrons
through a short quantum wire connected to semi-infinite biased leads. The
contact strength between the leads and the wire is modulated by out-of-phase
time-dependent potentials which simulate a turnstile device. We explore this
setup by keeping the contact with one lead at a fixed location at one end of
the wire whereas the contact with the other lead is placed on various sites
along the length of the wire. We study the propagation of sinusoidal and
rectangular pulses. We find that the current profiles in both leads depend not
only on the shape of the pulses, but also on the position of the second
contact. The current reflects standing waves created by the contact potentials,
like in a wind musical instrument (for example a flute), but occurring on the
background of the equilibrium charge distribution. The number of electrons in
our quantum "flute" device varies between two and three. We find that for
rectangular pulses the currents in the leads may flow against the bias for
short time intervals, due to the higher harmonics of the charge response. The
GME is solved numerically in small time steps without resorting to the
traditional Markov and rotating wave approximations. The Coulomb interaction
between the electrons in the sample is included via the exact diagonalization
method. The system (leads plus sample wire) is described by a lattice model.

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    ABSTRACT: A Generalized Master Equation (GME) is used to study the thermoelectric currents through a quantum dot in both the transient and steady-state regime. The two semi-infinite leads are kept at the same chemical potential but at different temperatures to produce a thermoelectric current which has a varying sign depending on the chemical potential. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method. We observe a saw-teeth like profile of the current alternating with plateaus of almost zero current. Our calculations go beyond the linear response with respect to the temperature gradient, but are compatible with known results for the thermopower in the linear response regime.
    Physica E Low-dimensional Systems and Nanostructures 03/2013; 53. · 1.86 Impact Factor


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