U.S. technology stocks sold off on Tuesday, as investors grew concerned about high valuations for artificial intelligence companies and prepared for Nvidia's earnings this week. The tech-heavy Nasdaq index fell about 1.8 percent at the start of the day, and the S & P 500 fell about 1.2 percent. Companies at the heart of this year's AI boom have become the biggest losers on Wall Street at this stage. Nvidia (NVDA. O) fell 3.5 percent at one point, Microsoft (MSFT. O), Amazon (AMZN. O) and Meta...