6,255 research outputs found
Tunable few electron quantum dots in InAs nanowires
Quantum dots realized in InAs are versatile systems to study the effect of
spin-orbit interaction on the spin coherence, as well as the possibility to
manipulate single spins using an electric field. We present transport
measurements on quantum dots realized in InAs nanowires. Lithographically
defined top-gates are used to locally deplete the nanowire and to form
tunneling barriers. By using three gates, we can form either single quantum
dots, or two quantum dots in series along the nanowire. Measurements of the
stability diagrams for both cases show that this method is suitable for
producing high quality quantum dots in InAs.Comment: 8 pages, 4 figure
Experimental set-up for detecting blood pressure, heart rate, and lymphocyte redistribution in the running rat
An experimental set--up for detecting lymphocyte redistribution blood pressureand heart rate in the running rat is presented.The design is based 011 caterisation of the carotid anery which previously has been described. The design offers direct access to the blood stream making it possible to examine different cells and biochemical parameters.Furthermore, eontinnusly monitorering of blood pressure and heart rate both at rest and during exercise is described
Magnetic excitations in coupled Haldane spin chains near the quantum critical point
Two quasi-1-dimensional S=1 quantum antiferromagnetic materials, PbNi2V2O8
and SrNi2V2O8, are studied by inelastic neutron scattering on powder samples.
While magnetic interactions in the two systems are found to be very similar,
subtle differences in inter-chain interaction strengths and magnetic anisotropy
are detected. The latter are shown to be responsible for qualitatively
different ground state properties: magnetic long-range order in SrNi2V2O8 and
disordered ``spin liquid'' Haldane-gap state in PbNi2V2O8.Comment: 15 figures, Figs. 5,9, and 10 in color. Some figures in JPEG format.
Complete PostScript and PDF available from
http://papillon.phy.bnl.gov/publicat.ht
Calorons, instantons and constituent monopoles in SU(3) lattice gauge theory
We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge
configurations at non-zero temperature and compare periodic and anti-periodic
temporal boundary conditions for the fermions. It is demonstrated that for the
different boundary conditions often the modes are localized at different
space-time points and have different sizes. Our observations are consistent
with patterns expected for Kraan - van Baal solutions of the classical
Yang-Mills equations. These solutions consist of constituent monopoles and the
zero-modes are localized on different constituents for different boundary
conditions. Our findings indicate that the excitations of the QCD vacuum are
more structured than simple instanton-like lumps.Comment: Remarks added. To appear in Phys. Rev.
Testing the self-duality of topological lumps in SU(3) lattice gauge theory
We discuss a simple formula which connects the field-strength tensor to a
spectral sum over certain quadratic forms of the eigenvectors of the lattice
Dirac operator. We analyze these terms for the near zero-modes and find that
they give rise to contributions which are essentially either self-dual or anti
self-dual. Modes with larger eigenvalues in the bulk of the spectrum are more
dominated by quantum fluctuations and are less (anti) self-dual. In the high
temperature phase of QCD we find considerably reduced (anti) self-duality for
the modes near the edge of the spectral gap.Comment: Remarks added, to appear in Phys. Rev. Let
Electronic Structure of Atoms in Magnetic Quadrupole Traps
We investigate the electronic structure and properties of atoms exposed to a
magnetic quadrupole field. The spin-spatial as well as generalized time
reversal symmetries are established and shown to lead to a two-fold degeneracy
of the electronic states in the presence of the field. Low-lying as well as
highly excited Rydberg states are computed and analyzed for a broad regime of
field gradients. The delicate interplay between the Coulomb and various
magnetic interactions leads to complex patterns of the spatial spin
polarization of individual excited states. Electromagnetic transitions in the
quadrupole field are studied in detail thereby providing the selection rules
and in particular the transition wavelengths and corresponding dipole
strengths. The peculiar property that the quadrupole magnetic field induces
permanent electric dipole moments of the atoms is derived and discussed.Comment: 17 pages, 13 figures, accepted for publication in PR
Locality and topology with fat link overlap actions
We study the locality and topological properties of fat link clover overlap
(FCO) actions. We find that a small amount of fattening (2-4 steps of APE or 1
step of HYP) already results in greatly improved properties compared to the
Wilson overlap (WO). We present a detailed study of the localisation of the FCO
and its connection to the density of low modes of . In contrast to
the Wilson overlap, on quenched gauge backgrounds we do not find any dependence
of the localization of the FCO on the gauge coupling. This suggests that the
FCO remains local in the continuum limit. The FCO also faithfully reproduces
the zero mode wave functions of typical lattice instantons, not like the Wilson
overlap. After a general discussion of different lattice definitions of the
topological charge we also show that the FCO together with the Boulder charge
are likely to satisfy the index theorem in the continuum limit. Finally, we
present a high statistics computation of the quenched topological
susceptibility with the FCO action.Comment: 19 pages, LaTe
Numerical Study of the Antiferrromagnetic Spin Chain with Bond Alternation
We study the quantum spin chain with bond alternation {\cal H}=\sum _i
(1-(-1)^i\delta)\vect{S}_i\cdot \vect{S}_{i+1} by the density matrix
renormalization group method recently proposed by Steven R. White
(\PRL{69}{3844}{1993}). We find a massless point at .
We also find the edge states in the region under the open
boundary condition, which disappear in the region . At the
massless point, the spin wave velocity is and the central
charge is . Our results indicate that a continuous phase
transition occurs at the massless point accompanying
breaking of the hidden symmetry.Comment: 9 pages and 1 PostScript figure, Revtex 3.0 (Minor corrections in
TEX-file format to remove possible compilatory troubles.
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