Stay informed with free updatesSimply sign up to the Equities myFT Digest -- delivered directly to your inbox.Tech stocks fell sharply on Monday as advances by Chinese artificial intelligence start-up DeepSeek cast doubt on whether the US could sustain its leadership in AI by spending billions of dollars on chips.DeepSeek has attracted increasing attention from investors since the company last week released its latest large language AI model showing a comparable performance to those of US rivals...