4,171 research outputs found
Entanglement renormalization of anisotropic XY model
The renormalization group flows of the one-dimensional anisotropic XY model
and quantum Ising model under a transverse field are obtained by different
multiscale entanglement renormalization ansatz schemes. It is shown that the
optimized disentangler removes the short-range entanglement by rotating the
system in the parameter space spanned by the anisotropy and the magnetic field.
It is understood from the study that the disentangler reduces the entanglement
by mapping the system to another one in the same universality class but with
smaller short range entanglement. The phase boundary and corresponding critical
exponents are calculated using different schemes with different block sizes,
look-ahead steps and truncation dimensions. It is shown that larger truncation
dimension leads to more accurate results and that using larger block size or
look-ahead step improve the overall calculation consistency.Comment: 5 pages, 3 figure
-valley electron factor in bulk GaAs and AlAs
We study the Land\'e -factor of conduction electrons in the -valley of
bulk GaAs and AlAs by using a three-band model
together with the tight-binding model. We find that the -valley -factor
is highly anisotropic, and can be characterized by two components,
and . is close to the free electron Land\'e factor but
is strongly affected by the remote bands. The contribution from remote
bands on depends on how the remote bands are treated. However, when
the magnetic field is in the Voigt configuration, which is widely used in the
experiments, different models give almost identical -factor.Comment: 4 pages, 1 figure, To be published in J. App. Phys. 104, 200
Cascaded acceleration of proton beams in ultrashort laser-irradiated microtubes
A cascaded ion acceleration scheme is proposed by use of ultrashort
laser-irradiated microtubes. When the electrons of a microtube are blown away
by intense laser pulses, strong charge-separation electric fields are formed in
the microtube both along the axial and along the radial directions. By
controlling the time delay between the laser pulses and a pre-accelerated
proton beam injected along the microtube axis, we demonstrate that this proton
beam can be further accelerated by the transient axial electric field in the
laser-irradiated microtube. Moreover, the collimation of the injected proton
beam can be enhanced by the inward radial electric field. Numerical simulations
show that this cascaded ion acceleration scheme works efficiently even at
non-relativistic laser intensities, and it can be applied to injected proton
beams in the energy range from 1 to 100 MeV. Therefore, it is particularly
suitable for cascading acceleration of protons to higher energy.Comment: 13 pages, 4 figure
Decoherence and relaxation in the interacting quantum dot system
In this paper we study the low temperature kinetics of the electrons in the
system composed of a quantum dot connected to two leads by solving the equation
of motion. The decoherence and the relaxation of the system caused by the gate
voltage noise and electron-phonon scattering are investigated. In order to take
account of the strong correlation of the electrons in this system, the
quasi-exact wave functions are calculated using an improved matrix product
states algorithm. This algorithm enables us to calculate the wave functions of
the ground state and the low lying excited states with satisfied accuracy and
thus enables us to study the kinetics of the system more effectively. It is
found that although both of these two mechanisms are proportional to the
electron number operator in the dot, the kinetics are quite different. The
noise induced decoherence is much more effective than the energy relaxation,
while the energy relaxation and decoherence time are of the same order for the
electron-phonon scattering. Moreover, the noise induced decoherence increases
with the lowering of the dot level, but the relaxation and decoherence due to
the electron-phonon scattering decrease.Comment: Minor revision. Add journal referenc
Magnetic Incommensurability in Doped Mott Insulator
In this paper we explore the incommensurate spatial modulation of spin-spin
correlations as the intrinsic property of the doped Mott insulator, described
by the model. We show that such an incommensurability is a direct
manifestation of the phase string effect introduced by doped holes in both one-
and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin
susceptibility in momentum space are in agreement with the neutron-scattering
measurement of cuprate superconductors in both position and doping dependence.
In particular, this incommensurate structure can naturally reconcile the
neutron-scattering and NMR experiments of cuprates.Comment: 12 pages (RevTex), five postscript figure
Coexistence of Itinerant Electrons and Local Moments in Iron-Based Superconductors
In view of the recent experimental facts in the iron-pnictides, we make a
proposal that the itinerant electrons and local moments are simultaneously
present in such multiband materials. We study a minimal model composed of
coupled itinerant electrons and local moments to illustrate how a consistent
explanation of the experimental measurements can be obtained in the leading
order approximation. In this mean-field approach, the spin-density-wave (SDW)
order and superconducting pairing of the itinerant electrons are not directly
driven by the Fermi surface nesting, but are mainly induced by their coupling
to the local moments. The presence of the local moments as independent degrees
of freedom naturally provides strong pairing strength for superconductivity and
also explains the normal-state linear-temperature magnetic susceptibility above
the SDW transition temperature. We show that this simple model is supported by
various anomalous magnetic properties and isotope effect which are in
quantitative agreement with experiments.Comment: 7 pages, 4 figures; an expanded versio
Urban energy exchanges monitoring from space
One important challenge facing the urbanization and global environmental change community is to understand the relation between urban form, energy use and carbon emissions. Missing from the current literature are scientific assessments that evaluate the impacts of different urban spatial units on energy fluxes; yet, this type of analysis is needed by urban planners, who recognize that local scale zoning affects energy consumption and local climate. However, satellite-based estimation of urban energy fluxes at neighbourhood scale is still a challenge. Here we show the potential of the current satellite missions to retrieve urban energy budget, supported by meteorological observations and evaluated by direct flux measurements. We found an agreement within 5% between satellite and in-situ derived net all-wave radiation; and identified that wall facet fraction and urban materials type are the most important parameters for estimating heat storage of the urban canopy. The satellite approaches were found to underestimate measured turbulent heat fluxes, with sensible heat flux being most sensitive to surface temperature variation (-64.1, +69.3 W m-2 for ±2 K perturbation); and also underestimate anthropogenic heat flux. However, reasonable spatial patterns are obtained for the latter allowing hot-spots to be identified, therefore supporting both urban planning and urban climate modelling
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