After a nice run higher, one analyst moves to the sidelines.Specialty materials company ATI (ATI -11.14%) has been flying high this year, with the shares up more than 40% since Feb. 1.At least one Wall Street analyst believes that momentum is likely to stall from here. Shares of ATI were down about 10% as of 10:45 a.m. ET Friday after the stock was downgraded to neutral.A strong surge subsides?ATI, formerly known as Allegheny Technologies, is a maker of high-performance materials and advanced metal alloys u ...