U.S. investors are getting a new way to buy into the memory boom. SK Hynix, the second most valuable company in South Korea, behind only Samsung, is slated to begin trading on the Nasdaq on Friday. The market debut, coinciding with the company's hefty expansion plans for the U.S., comes after a more than sevenfold increase in its stock price over the past year, a rally that's lifted SK Hynix's mar...