2,270 research outputs found
The influence of the long-lived quantum Hall potential on the characteristics of quantum devices
Novel hysteretic effects are reported in magneto-transport experiments on
lateral quantum devices. The effects are characterized by two vastly different
relaxation times (minutes and days). It is shown that the observed phenomena
are related to long-lived eddy currents. This is confirmed by torsion-balance
magnetometry measurements of the same 2-dimensional electron gas (2DEG)
material. These observations show that the induced quantum Hall potential at
the edges of the 2DEG reservoirs influences transport through the devices, and
have important consequences for the magneto-transport of all lateral quantum
devices.Comment: 5 pages, 4 figure
Spin-blockade spectroscopy of a two-level artificial molecule
Coulomb and spin blockade spectroscopy investigations have been performed on
an electrostatically defined ``artificial molecule'' connected to spin
polarized leads. The molecule is first effectively reduced to a two-level
system by placing both constituent atoms at a specific location of the level
spectrum. The spin sensitivity of the conductance enables us to identify the
electronic spin-states of the two-level molecule. We find in addition that the
magnetic field induces variations in the tunnel coupling between the two atoms.
The lateral nature of the device is evoked to explain this behavior.Comment: 4 pages, 4 figures; revised version with a minor change in Fig.2 and
additional inset in Fig.3.;accepted by PR
Coulomb and Spin blockade of two few-electrons quantum dots in series in the co-tunneling regime
We present Coulomb Blockade measurements of two few-electron quantum dots in
series which are configured such that the electrochemical potential of one of
the two dots is aligned with spin-selective leads. The charge transfer through
the system requires co-tunneling through the second dot which is in
resonance with the leads. The observed amplitude modulation of the resulting
current is found to reflect spin blockade events occurring through either of
the two dots. We also confirm that charge redistribution events occurring in
the off-resonance dot are detected indirectly via changes in the
electrochemical potential of the aligned dot.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Charge Sensing of an Artificial H2+ Molecule
We report charge detection studies of a lateral double quantum dot with
controllable charge states and tunable tunnel coupling. Using an integrated
electrometer, we characterize the equilibrium state of a single electron
trapped in the doubled-dot (artificial H2+ molecule) by measuring the average
occupation of one dot. We present a model where the electrostatic coupling
between the molecule and the sensor is taken into account explicitly. From the
measurements, we extract the temperature of the isolated electron and the
tunnel coupling energy. It is found that this coupling can be tuned between 0
and 60 micro electron-volt in our device.Comment: 5 pages, 4 figures. Revised version with added material. To be
published in Physical Review
Jack vertex operators and realization of Jack functions
We give an iterative method to realize general Jack functions from Jack
functions of rectangular shapes. We first show some cases of Stanley's
conjecture on positivity of the Littlewood-Richardson coefficients, and then
use this method to give a new realization of Jack functions. We also show in
general that vectors of products of Jack vertex operators form a basis of
symmetric functions. In particular this gives a new proof of linear
independence for the rectangular and marked rectangular Jack vertex operators.
Thirdly a generalized Frobenius formula for Jack functions was given and was
used to give new evaluation of Dyson integrals and even powers of Vandermonde
determinant.Comment: Expanded versio
The origin of switching noise in GaAs/AlGaAs lateral gated devices
We have studied the origin of switching (telegraph) noise at low temperature
in lateral quantum structures defined electrostatically in GaAs/AlGaAs
heterostructures by surface gates. The noise was measured by monitoring the
conductance fluctuations around on the first step of a quantum point
contact at around 1.2 K. Cooling with a positive bias on the gates dramatically
reduces this noise, while an asymmetric bias exacerbates it. We propose a model
in which the noise originates from a leakage current of electrons that tunnel
through the Schottky barrier under the gate into the doped layer. The key to
reducing noise is to keep this barrier opaque under experimental conditions.
Bias cooling reduces the density of ionized donors, which builds in an
effective negative gate voltage. A smaller negative bias is therefore needed to
reach the desired operating point. This suppresses tunnelling from the gate and
hence the noise. The reduction in the density of ionized donors also
strengthens the barrier to tunneling at a given applied voltage. Support for
the model comes from our direct observation of the leakage current into a
closed quantum dot, around for this device. The current
was detected by a neighboring quantum point contact, which showed monotonic
steps in time associated with the tunneling of single electrons into the dot.
If asymmetric gate voltages are applied, our model suggests that the noise will
increase as a consequence of the more negative gate voltage applied to one of
the gates to maintain the same device conductance. We observe exactly this
behaviour in our experiments.Comment: 8 pages, 7 figure
Rodrigues Formula for the Nonsymmetric Multivariable Laguerre Polynomial
Extending a method developed by Takamura and Takano, we present the Rodrigues
formula for the nonsymmetric multivariable Laguerre polynomials which form the
orthogonal basis for the -type Calogero model with distinguishable
particles. Our construction makes it possible for the first time to
algebraically generate all the nonsymmetric multivariable Laguerre polynomials
with different parities for each variable.Comment: 6 pages, LaTe
Rodrigues Formula for Hi-Jack Symmetric Polynomials Associated with the Quantum Calogero Model
The Hi-Jack symmetric polynomials, which are associated with the simultaneous
eigenstates for the first and second conserved operators of the quantum
Calogero model, are studied. Using the algebraic properties of the Dunkl
operators for the model, we derive the Rodrigues formula for the Hi-Jack
symmetric polynomials. Some properties of the Hi-Jack polynomials and the
relationships with the Jack symmetric polynomials and with the basis given by
the QISM approach are presented. The Hi-Jack symmetric polynomials are strong
candidates for the orthogonal basis of the quantum Calogero model.Comment: 17 pages, LaTeX file using jpsj.sty (ver. 0.8), cite.sty,
subeqna.sty, subeqn.sty, jpsjbs1.sty and jpsjbs2.sty (all included.) You can
get all the macros from ftp.u-tokyo.ac.jp/pub/SOCIETY/JPSJ
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