This work was supported by U.S. Department of Energy
Grant No. DE-FG02-09ER16072, and used resources of the
National Energy Research Scientific Computing Center, a
DOE Office of Science User Facility supported by the Office
of Science of the U.S. Department of Energy under Contract
Publisher StatementThis is a copy of an article published in the Physical Review B American Physical Society Publications. ©2014 American Physical Society.
PublisherAmerican Physical Society