134 research outputs found
Tracking the energies of one-dimensional subband edges in quantum point contacts using dc conductance measurements
The semiconductor quantum point contact has long been a focal point for
studies of one-dimensional electron transport. Their electrical properties are
typically studied using ac conductance methods, but recent work has shown that
the dc conductance can be used to obtain additional information, with a
density-dependent Land\'{e} effective g-factor recently reported [T.-M. Chen et
al, Phys. Rev. B 79, 081301 (2009)]. We discuss previous dc conductance
measurements of quantum point contacts, demonstrating how valuable additional
information can be extracted from the data. We provide a comprehensive and
general framework for dc conductance measurements that provides a path to
improving the accuracy of existing data and obtaining useful additional data. A
key aspect is that dc conductance measurements can be used to map the energy of
the 1D subband edges directly, giving new insight into the physics that takes
place as the spin-split 1D subbands populate. Through a re-analysis of the data
obtained by Chen et al, we obtain two findings. The first is that the 2-down
subband edge closely tracks the source chemical potential when it first begins
populating before dropping more rapidly in energy. The second is that the 2-up
subband populates more rapidly as the subband edge approaches the drain
potential. This second finding suggests that the spin-gap may stop opening, or
even begin to close again, as the 2-up subband continues populating, consistent
with recent theoretical calculations and experimental studies.Comment: Published version available at
http://iopscience.iop.org/0953-8984/23/36/362201 15 pages, 3 figure
Signatures of tunable Majorana-fermion edge states
Chiral Majorana-fermion modes are shown to emerge as edge excitations in a
superconductor--topological-insulator hybrid structure that is subject to a
magnetic field. The velocity of this mode is tunable by changing the
magnetic-field magnitude and/or the superconductor's chemical potential. We
discuss how quantum-transport measurements can yield experimental signatures of
these modes. A normal lead coupled to the Majorana-fermion edge state through
electron tunneling induces resonant Andreev reflections from the lead to the
grounded superconductor, resulting in a distinctive pattern of
differential-conductance peaks.Comment: (13 pages, Accepted for publication in New Journal of Physics, an
extension of and expansion on our previous work arXiv:1210.4057). arXiv admin
note: text overlap with arXiv:1210.405
Reply to Comment on "Strongly Correlated Fractional Quantum Hall Line Junctions"
In two recent articles [PRL 90, 026802 (2003); PRB 69, 085307 (2004)], we
developed a transport theory for an extended tunnel junction between two
interacting fractional-quantum-Hall edge channels, obtaining analytical results
for the conductance. Ponomarenko and Averin (PA) have expressed disagreement
with our theoretical approach and question the validity of our results
(cond-mat/0602532). Here we show why PA's critique is unwarranted.Comment: 1 page, no figures, RevTex
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