A physics professor at a Philadelphia university has pleaded not guilty to charges he gave U.S. technology secrets to China.

Temple University professor Xi Xiaoxing is an expert on superconductivity, which is the ability to conduct electricity without resistance. A superconducting thin film could be key in making computer circuits that work faster.

The 47-year-old entered his plea Thursday. He is free on $100,000 bail and surrendered his passport.

He is a naturalized U.S. citizen born in China.

Prosecutors say he schemed to provide secrest in exchange for prestigious appointments for himself.

Xi's lawyer, Peter Zeidenberg, successfully defended an Ohio woman in a Chinese spying case. Zeidenberg says Xi will be exonerated.

Xi was chairman of the university's physics department until his arrest. He remains a faculty member.