FRANKFURT (Reuters) -The head of T-Mobile U.S., the fast-growing and profitable subsidiary of Germany's Deutsche Telekom, is due to step aside before the end of his current contract, German newspaper Handelsblatt reported on Monday. Handelsblatt reported Mike Sievert, who has headed the mobile operator since 2020, wanted to take a break and that Chief Operating Officer Srini Gopalan, until recently head of Deutsche Telekom's Germany business, was a leading candidate to succeed him.