The British chip designer Arm looked set to be valued at more than $60bn as it debuted on the Nasdaq stock exchange in the biggest US share listing of the year. Arm set a price of $51 a share, valuing the company at $54.5bn on Wednesday. But as trading began on Thursday morning, investor appetite for the company’s initial public offering (IPO) pushed its share price up 10% to $56.10, valuing the company at just below $60bn. It later rose by as much as 20% up, before settling back at 17% up, giving a valuation of around $64bn. Founded in...