James Millstein, a banker at Lazard, joined the Treasury Department on Monday in the newly created role of senior restructuring officer, The Financial Times reported. The newspaper, citing a memo Mr. Millstein sent to friends, said the restructuring banker will be assisting Treasury Secretary Timothy F. Geithner in “working out” some of the government’s existing investments in banks and other financial institutions while helping it structure new investments. Prior to becoming an investment banker, Mr. Millstein spent 20 years practicing bankruptcy law at Cleary Gottlieb.