1,439 research outputs found
Monte Carlo simulation method for Laughlin-like states in a disk geometry
We discuss an alternative accurate Monte Carlo method to calculate the
ground-state energy and related quantities for Laughlin states of the
fractional quantum Hall effect in a disk geometry. This alternative approach
allows us to obtain accurate bulk regime (thermodynamic limit) values for
various quantities from Monte Carlo simulations with a small number of
particles (much smaller than that needed with standard Monte Carlo approaches).Comment: 13 pages, 6 figures, 2 table
Hypernetted-chain study of broken rotational symmetry states for the = 1/3 fractional quantum Hall effect and other fractionally filled Landau levels
We investigate broken rotational symmetry (BRS) states for the fractional
quantum Hall effect (FQHE) at 1/3-filling of the valence Landau level (LL).
Recent Monte Carlo calculations by Musaelian and Joynt [J. Phys.: Condens.\
Matter {\bf 8}, L105 (1996)] suggest that Laughlin's state becomes unstable to
a BRS state for some critical finite thickness value. We study in detail the
properties of such state by performing a hypernetted-chain calculation that
gives results in the thermodynamic limit, complementing other methods which are
limited to a finite number of particles. Our results indicate that while
Laughlin's state is stable in the lowest LL, in higher LLs a BRS instability
occurs, perhaps indicating the absence of FQHE at partial fillings of higher
LLs. Possible connections to the newly discovered liquid crystalline phases in
higher LLs are also discussed.Comment: 7 pages including 3 eps figure
Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6
The compound SmB is the best established realization of a topological
Kondo insulator, in which a topological insulator state is obtained through
Kondo coherence. Recent studies have found evidence that the surface of SmB
hosts ferromagnetic domains, creating an intrinsic platform for unidirectional
ballistic transport at the domain boundaries. Here, surface-sensitive X-ray
absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS)
spectra are measured at the Sm N-edge, and used to evaluate electronic
symmetries, excitations and temperature dependence near the surface of cleaved
samples. The XAS data show that the density of large-moment atomic multiplet
states on a cleaved surface grows irreversibly over time, to a degree that
likely exceeds a related change that has recently been observed in the surface
4f orbital occupation
Scattering of Phonons by a Vortex in a Superfluid
Recent work gives a transverse force on an isolated moving vortex which is
independent of the normal fluid velocity, but it is widely believed that the
asymmetry of phonon scattering by a vortex leads to a transverse force
dependent on the relative motion of the normal component and the vortex. We
show that a widely accepted derivation of the transverse force is in error, and
that a careful evaluation leads to a much smaller transverse force. We argue
that a different approach is needed to get the correct expression.
\pacs{67.40.Vs,67.57.Fg,47.37.+q,47.32.Cc}Comment: 4 page
Weak charge form factor and radius of 208Pb through parity violation in electron scattering
We use distorted wave electron scattering calculations to extract the weak
charge form factor F_W(q), the weak charge radius R_W, and the point neutron
radius R_n, of 208Pb from the PREX parity violating asymmetry measurement. The
form factor is the Fourier transform of the weak charge density at the average
momentum transfer q=0.475 fm. We find F_W(q) =0.204 \pm 0.028 (exp) \pm
0.001 (model). We use the Helm model to infer the weak radius from F_W(q). We
find R_W= 5.826 \pm 0.181 (exp) \pm 0.027 (model) fm. Here the exp error
includes PREX statistical and systematic errors, while the model error
describes the uncertainty in R_W from uncertainties in the surface thickness
\sigma of the weak charge density. The weak radius is larger than the charge
radius, implying a "weak charge skin" where the surface region is relatively
enriched in weak charges compared to (electromagnetic) charges. We extract the
point neutron radius R_n=5.751 \pm 0.175 (exp) \pm 0.026 (model) \pm 0.005
(strange) fm$, from R_W. Here there is only a very small error (strange) from
possible strange quark contributions. We find R_n to be slightly smaller than
R_W because of the nucleon's size. Finally, we find a neutron skin thickness of
R_n-R_p=0.302\pm 0.175 (exp) \pm 0.026 (model) \pm 0.005 (strange) fm, where
R_p is the point proton radius.Comment: 5 pages, 1 figure, published in Phys Rev. C. Only one change in this
version: we have added one author, also to metadat
A significant improvement in the superconducting properties of MgB2 by co-doping with graphene and nano-SiC
The effects of graphene (G) and nanosilicon carbide (SiC) co-doping on the superconducting properties of MgB2 were studied using bulk samples. SiC remains one of the best dopants which can significantly improve the high field performance, while graphene is emerging as a new dopant for MgB2, which can improve the zero field critical current density (Jc). The superconducting properties characterized by Jc, the intergrain connectivity, and the critical fields were significantly improved by the use of both SiC and graphene as dopants
The Onset of Anisotropic Transport of Two-Dimensional Electrons in High Landau Levels: An Isotropic-to-Nematic Liquid Crystal Phase Transition?
The recently discovered anisotropy of the longitudinal resistance of
two-dimensional electrons near half filling of high Landau levels is found to
persist to much higher temperatures T when a large in-plane magnetic field B||
is applied. Under these conditions we find that the longitudinal resistivity
scales quasi-linearly with B||/T. These observations support the notion that
the onset of anisotropy at B||=0 does not reflect the spontaneous development
of charge density modulations but may instead signal an isotropic-to-nematic
liquid crystal phase transition.Comment: 5 pages, 4 figure
Magnus and Iordanskii Forces in Superfluids
The total transverse force acting on a quantized vortex in a superfluid is a
problem that has eluded a complete understanding for more than three decades.
In this letter I propose a remarkably simple argument, somewhat reminiscent of
Laughlin's beautiful argument for the quantization of conductance in the
quantum Hall effect, to define the superfluid velocity part of the transverse
force. This term is found to be . Although
this result does not seem to be overly controversial, this thermodynamic
argument based only on macroscopic properties of the superfluid does offer a
robust derivation. A recent publication by Thouless, Ao and Niu has
demonstrated that the vortex velocity part of the transverse force in a
homogeneous neutral superfluid is given by the usual form . A combination of these two independent results and the required
Galilean invariance yields that there cannot be any transverse force
proportional to the normal fluid velocity, in apparent conflict with
Iordanskii's theory of the transverse force due to phonon scattering by the
vortex.Comment: RevTex, 1 Encapsulated Postscript figur
Modeling FETCH Observations of 2005 May 13 CME
This paper evaluates the quality of CME analysis that has been undertaken
with the rare Faraday rotation observation of an eruption. Exploring the
capability of the FETCH instrument hosted on the MOST mission, a four-satellite
Faraday rotation radio sounding instrument deployed between the Earth and the
Sun, we discuss the opportunities and challenges to improving the current
analysis approaches.Comment: 33 pages, 24 figure
Acoustic Energy and Momentum in a Moving Medium
By exploiting the mathematical analogy between the propagation of sound in a
non-homogeneous potential flow and the propagation of a scalar field in a
background gravitational field, various wave ``energy'' and wave ``momentum''
conservation laws are established in a systematic manner. In particular the
acoustic energy conservation law due to Blokhintsev appears as the result of
the conservation of a mixed co- and contravariant energy-momentum tensor, while
the exchange of relative energy between the wave and the mean flow mediated by
the radiation stress tensor, first noted by Longuet-Higgins and Stewart in the
context of ocean waves, appears as the covariant conservation of the doubly
contravariant form of the same energy-momentum tensor.Comment: 25 Pages, Late
- …