Investors have bought billions of euros in German treasury notes that pay negative interest—meaning the purchasers agreed to pay a small fee for the privilege of lending the German government their money. […] Germany auctioned €3.34 billion ($4.3 billion) Wednesday in two-year notes at an average yield of minus 0.07 percent. Rates are very low all over, and German debt is considered ultra-safe, so security-minded investors are paying for safety. Expectation the European Central Bank will buy bonds has also driven down yields, which move opposite to prices. And the small negative yield on the notes is still a better...