Pohl founded solid-state physics at Göttingen. Color in alkali halides stems from vacancy defects called F-centers. Irradiation makes diamond and sodium chloride crystals conductive. Pohl and Gudden observed photoelectric effects in bulk insulators. Pohl and Hilsch created 1938 three-electrode transistor in potassium bromide crystal. Pohl published 54 articles and three books by World War I. Pohl directed 1st Physical Institute during Göttingen's golden physics age with Franck and Born. Pohl wrote influential three-volume physics textbooks used into modern editions. Pohl supported Ohain's private jet propulsion experiments. Pohl aided bee color perception studies with Kühn. Nevill Mott named Pohl father of solid-state physics. Pohl trained 55 PhD students including 17 future professors. Pohl rejected Nazi regime and aided resistance contacts. Pohl demonstrated X-ray diffraction early and worked on photoelectric effects. Pohl's institute stayed small but internationally renowned post-war.