532 research outputs found
Ultra-Low-Temperature Growth of High-Integrity Gate Oxide Films by Low-Energy Ion-Assisted Oxidation
Collective Oscillations of Vortex Lattices in Rotating Bose-Einstein Condensates
The complete low-energy collective-excitation spectrum of vortex lattices is
discussed for rotating Bose-Einstein condensates (BEC) by solving the
Bogoliubov-de Gennes (BdG) equation, yielding, e.g., the Tkachenko mode
recently observed at JILA. The totally symmetric subset of these modes includes
the transverse shear, common longitudinal, and differential longitudinal modes.
We also solve the time-dependent Gross-Pitaevskii (TDGP) equation to simulate
the actual JILA experiment, obtaining the Tkachenko mode and identifying a pair
of breathing modes. Combining both the BdG and TDGP approaches allows one to
unambiguously identify every observed mode.Comment: 5 pages, 4 figure
Dynamical Susceptibility in KH2PO4-type Crystals above and below Tc
The time dependent cluster approximation called the path probability method
(PPM) is applied to a pseudo-spin Ising Hamiltonian of the Slater-Takagi model
for KH2PO4-type hydrogen-bonded ferroelectrics in order to calculate the
homogeneous dynamical susceptibility above and below the ferroelectric
transition temperature. Above the transition temperature all the calculations
are carried out analytically in the cactus approximation of the PPM. Below the
transition temperature the dynamical susceptibility is also calculated
accurately since the analytical solution of spontaneous polarization in the
ferroelectric phase can be utilized. When the temperature is approached from
both sides of the transition temperature, only one of relaxation times shows a
critical slowing down and makes a main contribution to the dynamical
susceptibility. The discrepancy from Slater model (ice-rule limit) is discussed
in comparison with some experimental data.Comment: 8 pages, 10 figure
Coreless vortex formation in a spinor Bose-Einstein condensate
Coreless vortices were phase-imprinted in a spinor Bose-Einstein condensate.
The three-component order parameter of F=1 sodium condensates held in a
Ioffe-Pritchard magnetic trap was manipulated by adiabatically reducing the
magnetic bias field along the trap axis to zero. This distributed the
condensate population across its three spin states and created a spin texture.
Each spin state acquired a different phase winding which caused the spin
components to separate radially.Comment: 5 pages, 2 figure
Exact Eigenstates and Magnetic Response of Spin-1 and Spin-2 Vectorial Bose-Einstein Condensates
The exact eigenspectra and eigenstates of spin-1 and spin-2 vectorial
Bose-Einstein condensates (BECs) are found, and their response to a weak
magnetic field is studied and compared with their mean-field counterparts.
Whereas mean-field theory predicts the vanishing population of the zero
magnetic-quantum-number component of a spin-1 antiferromagnetic BEC, the
component is found to become populated as the magnetic field decreases. The
spin-2 BEC exhibits an even richer magnetic response due to quantum correlation
between 3 bosons.Comment: 5 pages, no figures. LaTeX20
Josephson Current between Triplet and Singlet Superconductors
The Josephson effect between triplet and singlet superconductors is studied.
Josephson current can flow between triplet and singlet superconductors due to
the spin-orbit coupling in the spin-triplet superconductor but it is finite
only when triplet superconductor has , where and
are the perpendicular components of orbital angular momentum and spin angular
momentum of the triplet Cooper pairs, respectively. The recently observed
temperature and orientational dependence of the critical current through a
Josephson junction between UPt and Nb is investigated by considering a
non-unitary triplet state.Comment: 4 pages, no figure
Transmission and Reflection of Collective Modes in Spin-1 Bose-Einstein Condensate
We study tunneling properties of collective excitations in spin-1
Bose-Einstein condensates. In the absence of magnetic fields, the total
transmission in the long wavelength limit occurs in all kinds of excitations
but the quadrupolar spin mode in the ferromagnetic state. The quadrupolar spin
mode alone shows the total reflection. A difference between those excitations
comes from whether the wavefunction of an excitation corresponds to that of the
condensate in the long wavelength limit. The correspondence results in the
total transmission as in the spinless BEC.Comment: 6 pages, 5 figure
A fabrication guide for planar silicon quantum dot heterostructures
We describe important considerations to create top-down fabricated planar
quantum dots in silicon, often not discussed in detail in literature. The
subtle interplay between intrinsic material properties, interfaces and
fabrication processes plays a crucial role in the formation of
electrostatically defined quantum dots. Processes such as oxidation, physical
vapor deposition and atomic-layer deposition must be tailored in order to
prevent unwanted side effects such as defects, disorder and dewetting. In two
directly related manuscripts written in parallel we use techniques described in
this work to create depletion-mode quantum dots in intrinsic silicon, and
low-disorder silicon quantum dots defined with palladium gates. While we
discuss three different planar gate structures, the general principles also
apply to 0D and 1D systems, such as self-assembled islands and nanowires.Comment: Accepted for publication in Nanotechnology. 31 pages, 12 figure
Fragmented and Single Condensate Ground States of Spin-1 Bose Gas
We show that the ground state of a spin-1 Bose gas with an antiferro-
magnetic interaction is a fragmented condensate in uniform magnetic fields. The
number fluctuations in each spin component change rapidly from being enormous
(order ) to exceedingly small (order 1) as the magnetization of the system
increases. A fragmented condensate can be turned into a single condensate state
by magnetic field gradients. The conditions for existence and the method of
detecting fragmented states are presented.Comment: 4 pages, no figure
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