51,783 research outputs found
Spin-3/2 physics of semiconductor hole nanowires: Valence-band mixing and tunable interplay between bulk-material and orbital bound-state spin splittings
We present a detailed theoretical study of the electronic spectrum and Zeeman
splitting in hole quantum wires. The spin-3/2 character of the topmost
bulk-valence-band states results in a strong variation of subband-edge g
factors between different subbands. We elucidate the interplay between quantum
confinement and heavy-hole - light-hole mixing and identify a certain
robustness displayed by low-lying hole-wire subband edges with respect to
changes in the shape or strength of the wire potential. The ability to address
individual subband edges in, e.g., transport or optical experiments enables the
study of holes states with nonstandard spin polarization, which do not exist in
spin-1/2 systems. Changing the aspect ratio of hole wires with rectangular
cross-section turns out to strongly affect the g factor of subband edges,
providing an opportunity for versatile in-situ tuning of hole-spin properties
with possible application in spintronics. The relative importance of cubic
crystal symmetry is discussed, as well as the spin splitting away from
zone-center subband edges.Comment: 16 pages, 12 figures, RevTe
Study of 0- phase transition in hybrid superconductor-InSb nanowire quantum dot devices
Hybrid superconductor-semiconducting nanowire devices provide an ideal
platform to investigating novel intragap bound states, such as the Andreev
bound states (ABSs), Yu-Shiba-Rusinov (YSR) states, and the Majorana bound
states. The competition between Kondo correlations and superconductivity in
Josephson quantum dot (QD) devices results in two different ground states and
the occurrence of a 0- quantum phase transition. Here we report on
transport measurements on hybrid superconductor-InSb nanowire QD devices with
different device geometries. We demonstrate a realization of continuous
gate-tunable ABSs with both 0-type levels and -type levels. This allow us
to manipulate the transition between 0 and junction and explore charge
transport and spectrum in the vicinity of the quantum phase transition regime.
Furthermore, we find a coexistence of 0-type ABS and -type ABS in the same
charge state. By measuring temperature and magnetic field evolution of the
ABSs, the different natures of the two sets of ABSs are verified, being
consistent with the scenario of phase transition between the singlet and
doublet ground state. Our study provides insights into Andreev transport
properties of hybrid superconductor-QD devices and sheds light on the crossover
behavior of the subgap spectrum in the vicinity of 0- transition
The Spin--Symmetry of the Quark Model
Corrections to the exact heavy--quark symmetry results are expected to follow
the mass effect of the heavy--quark. We show, by an explicit
calculation, that there is something other than the mass effect that suppresses
the breaking of the spin symmetry
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Concatenated LDPC-TCM coding for reliable storage in multi-level flash memories
In this paper, we present an efficient fault tolerant solution for multi-level per cell (MLC) flash memory that concatenates trellis coded modulation (TCM) with an outer low-density parity-check (LDPC) code. Traditional flash coding systems employ simple hard-decisions based codes, such as Bose-Chaudhuri-Hocquenghem (BCH) codes, that can correct a fixed, specified number of errors. Thanks to the Bahl, Cocke, Jelinek, and Raviv (BCJR) algorithm, the TCM decoder within the proposed design can provide soft decisions which make it possible to use the more powerful LDPC codes. Moreover, the error-correction performance is further improved since TCM can decrease the raw error rate of MLC and hence relieve the burden of outer LDPC code. The effectiveness of concatenated LDPC-TCM systems has been successfully demonstrated through computer simulations
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