13,870 research outputs found
Quantized circular photogalvanic effect in Weyl semimetals
The circular photogalvanic effect (CPGE) is the part of a photocurrent that
switches depending on the sense of circular polarization of the incident light.
It has been consistently observed in systems without inversion symmetry and
depends on non-universal material details. Here we find that in a class of Weyl
semimetals (e.g. SrSi) and three-dimensional Rashba materials (e.g. doped
Te) without inversion and mirror symmetries, the injection contribution to the
CPGE trace is effectively quantized in terms of the fundamental constants and with no material-dependent parameters. This is so
because the CPGE directly measures the topological charge of Weyl points, and
non-quantized corrections from disorder and additional bands can be small over
a significant range of incident frequencies. Moreover, the magnitude of the
CPGE induced by a Weyl node is relatively large, which enables the direct
detection of the monopole charge with current techniques.Comment: 4+5 pages, 3 figures, published versio
Recommended from our members
Catalina Quesada y Kristine Vanden Berghe, editores. El libro y la vida. Ensayos crÃticos sobre la obra de Héctor Abad Faciolince. Liège; MedellÃn: Presses Universitaires de Liège; Editorial Eafit, 2019. 204 pp.
Catalina Quesada y Kristine Vanden Berghe, editores. El libro y la vida. Ensayos crÃticos sobre la obra de Héctor Abad Faciolince. Liège; MedellÃn: Presses Universitaires de Liège; Editorial Eafit, 2019.
204 pp
q-State Potts model metastability study using optimized GPU-based Monte Carlo algorithms
We implemented a GPU based parallel code to perform Monte Carlo simulations
of the two dimensional q-state Potts model. The algorithm is based on a
checkerboard update scheme and assigns independent random numbers generators to
each thread. The implementation allows to simulate systems up to ~10^9 spins
with an average time per spin flip of 0.147ns on the fastest GPU card tested,
representing a speedup up to 155x, compared with an optimized serial code
running on a high-end CPU. The possibility of performing high speed simulations
at large enough system sizes allowed us to provide a positive numerical
evidence about the existence of metastability on very large systems based on
Binder's criterion, namely, on the existence or not of specific heat
singularities at spinodal temperatures different of the transition one.Comment: 30 pages, 7 figures. Accepted in Computer Physics Communications.
code available at:
http://www.famaf.unc.edu.ar/grupos/GPGPU/Potts/CUDAPotts.htm
Arsenic in drinking water wells on the Bolivian high plain: field monitoring and effect of salinity on removal efficiency of iron-oxides-containing filters
In the rural areas around Oruro (Bolivia), untreated groundwater is used directly as drinking water. This research aimed to evaluate the general drinking water quality, with focus on arsenic (As) concentrations, based on analysis of 67 samples from about 16 communities of the Oruro district. Subsequently a filter using Iron Oxide Coated Sand (IOCS) and a filter using a Composite Iron Matrix (CIM) were tested for their arsenic removal capacity using synthetic water mimicking real groundwater. Heavy metal concentrations in the sampled drinking water barely exceeded WHO guidelines. Arsenic concentrations reached values up to 964 mu g L-1 and exceeded the current WHO provisional guideline value of 10 mu g L-1 in more than 50% of the sampled wells. The WHO guideline of 250 mg L-1 for chloride and sulphate was also exceeded in more than a third of the samples, indicating high salinity in the drinking waters. Synthetic drinking water could be treated effectively by the IOCS- and CIM-based filters reducing As to concentrations lower than 10 mu g L-1. High levels of chloride and sulphate did not influence As removal efficiency. However, phosphate concentrations in the range from 4 to 24 mg L-1 drastically decreased removal efficiency of the IOCS-based filter but had no effects on removal efficiency of the CIM-based filter. Results of this study can be used as a base for further testing and practical implementation of drinking water purification in the Oruro region
Design principles for shift current photovoltaics
While the basic principles and limitations of conventional solar cells are
well understood, relatively little attention has gone toward maximizing the
potential efficiency of photovoltaic devices based on shift currents. In this
work, we outline simple design principles for the optimization of shift
currents for frequencies near the band gap, derived from the analysis of a
general effective model. The use of a novel sum rule allows us to express the
band edge shift current in terms of a few model parameters and to show it
depends explicitly on wavefunctions via Berry connections in addition to
standard band structure. We use our approach to identify two new classes of
shift current photovoltaics, ferroelectric polymer films and single-layer
orthorhombic monochalcogenides such as GeS. We introduce tight-binding models
for these systems, and show that they exhibit the largest shift current
responsivities at the band edge reported so far. Moreover, exploring the
parameter space of these models we find photoresponsivities that can exceed
mA/W. Our results show how the study of the shift current via effective
models allows one to improve the possible efficiency of devices based on this
mechanism and better grasp their potential to compete with conventional solar
cells.Comment: 10 pages, 4 figures, AC and BMF share equal contributions. Published
in Nature Communication
Hispanics in the e-commerce business
This project focuses on developing links between the emerging e-commerce industry and Hispanic owned business community of Haverhill, Massachusetts (US). (Library-derived description)de la Cruz, J. E. (2000). Hispanics in the e-commerce business. Retrieved from http://academicarchive.snhu.eduMaster of Science (M.S.)School of Community Economic Developmen
- …