Complex search tasks within academic digital libraries go beyond simple lookup. They are open-ended, multi-faceted, with ill-defined information needs, requiring cognitive processing of the encountered information and learning. Academic digital library searchers often use exploratory search strategies for complex search tasks. However, the present academic digital library search interfaces provide limited support for exploratory browsing activities, which is a crucial step that supports learning during the exploratory search process. The present research addresses this issue by designing and implementing a novel search interface called KLink Search, to support exploratory browsing activities via two new features: visually linked keywords and interactive workspace. KLink Search leverages information visualization principles to enable interactive information retrieval in academic digital libraries. A controlled laboratory study was conducted with 32 participants to gather evidence for the value of KLink Search compared to a Baseline interface. The data analysis results show that the participants reported higher degrees of perceived ease-of-use, usefulness, satisfaction, and knowledge gain after using KLink Search for complex search tasks. Further, they spend more time searching for information and saving a highly relevant set of documents at the end of the tasks when using KLink Search. These results depict the value of providing lightweight visual additions to the existing academic digital library search interfaces to support exploratory browsing activities effectively.