Charli XCX Explores New Avant-Pop Direction with Sophie at SXSW

A year ago, Charli XCX seemed like the future of pop music, ready to one day outrace Katy Perry and One Direction with her punk-rock approach to “Break the Rules,” “Breaking Up” and the rest of 2014’s Sucker. Then the 23-year-old singer-songwriter vetoed the plan and started over, stripping out…