872 research outputs found
Density Functional Theory of Multicomponent Quantum Dots
Quantum dots with conduction electrons or holes originating from several
bands are considered. We assume the particles are confined in a harmonic
potential and assume the electrons (or holes) belonging to different bands to
be different types of fermions with isotropic effective masses. The density
functional method with the local density approximation is used. The increased
number of internal (Kohn-Sham) states leads to a generalisation of Hund's first
rule at high densities. At low densitites the formation of Wigner molecules is
favored by the increased internal freedom.Comment: 11 pages, 5 figure
Flow of 3He-B through Narrow Channels
The critical current Jc of superfluid 3He-B through 0.8-μm-diam channels has been measured. For small currents the pressure difference ΔP=0 along the flow channels within the resolution, implying small or zero dissipation. ΔP grows rapidly with increasing current above Jc; a clear transition to dissipative flow is thus observed. The temperature dependence of Jc indicates that the superfluid density and the critical temperature are reduced inside the narrow flow channels.Peer reviewe
Interaction of Lamb modes with two-level systems in amorphous nanoscopic membranes
Using a generalized model of interaction between a two-level system (TLS) and
an arbitrary deformation of the material, we calculate the interaction of Lamb
modes with TLSs in amorphous nanoscopic membranes. We compare the mean free
paths of the Lamb modes with different symmetries and calculate the heat
conductivity . In the limit of an infinitely wide membrane, the heat
conductivity is divergent. Nevertheless, the finite size of the membrane
imposes a lower cut-off for the phonons frequencies, which leads to the
temperature dependence . This temperature dependence
is a hallmark of the TLS-limited heat conductance at low temperature.Comment: 9 pages, 2 figure
Enhancement of the optomechanical coupling and Kerr nonlinearity using the Josephson capacitance of a Cooper-pair box
We propose a scheme for enhancing the optomechanical coupling between microwave and mechanical resonators by up to seven orders of magnitude to the ultrastrong coupling limit in a circuit optomechanical setting. The tripartite system considered here consists of a Josephson junction Cooper-pair box that mediates the coupling between the microwave cavity and the mechanical resonator. The optomechanical coupling can be modified by tuning the gate charge and the magnetic flux bias of the Cooper-pair box which in turn affect the Josephson capacitance of the Cooper-pair box. We additionally show that with a suitable choice of tuning parameters, the optomechanical coupling vanishes and the system purely exhibits a cross-Kerr type of nonlinearity between the cavity and the mechanical resonator. This allows the system to be used for phonon counting
Critical current of 3He-A in narrow channels
The critical current Jc of superfluid 3He-A in 0.8-μm-diam channels has been measured by the observation of the pressure difference along the channels versus the mass current. During warming Jc was found to decrease by about 30% at TBA(cyl) and by another 30% at TBA; TBA(cyl) is the reduced B→A transition temperature in the narrow flow channels, with TBA(cyl)TBA=0.92 at 27.4 bars. Above TBA a second dissipative mechanism was observed at lower currents. These features are believed to be associated with the ends of the channels.Peer reviewe
Magnetic phases of one-dimensional lattices with 2 to 4 fermions per site
We study the spectral and magnetic properties of one-dimensional lattices
filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a
generalized Hubbard model that takes account all interactions on a lattice
site, and solve the many-particle problem by exact diagonalization. We find an
intriguing magnetic phase diagram which includes ferromagnetism, spin-one
Heisenberg antiferromagnetism, and orbital antiferromagnetism.Comment: 8 pages, 6 figure
Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of Liquid 3He below 10 mK
The Helsinki temperature scale, used earlier in measurements of the heat capacity of liquid 3He (1-10 mK), is compared with the National Bureau of Standards (NBS) noise and nuclear-orientation temperature scale. The superfluid transition temperature (Tc) of 3He at zero pressure and the superconductive transition temperatures of tungsten and beryllium were used as fixed points. Tc on the NBS scale was found to be 1.025 ± 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support the Helsinki data on the heat capacity of 3He.Peer reviewe
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