  Studying the factors that influence the quality of physics PhD students'
doctoral experiences, especially those that motivate them to stay or leave
their programs, is critical for providing them with more holistic and equitable
support. Prior literature on doctoral attrition has found that students with
clear research interests who establish an advisor-advisee relationship early in
their graduate careers are most likely to persist. However, these trends have
not been investigated in the context of physics, and the underlying reasons for
why these characteristics are associated with leaving remain unstudied. Using
semi-structured interviews with 40 first and second year physics PhD students,
we construct a model describing the characteristic pathways that physics PhD
students take while evaluating interest congruence of prospective research
groups. We show how access to undergraduate research and other formative
experiences helped some students narrow their interests and look for research
groups before arriving to graduate school. In turn, these students reported
fewer difficulties finding a group than students whose search for an advisor
took place during the first year of their PhD. Lastly, we identify two
characteristic types of students at a higher risk of leaving their programs:
students who enter graduate school with broad interests and struggle to find a
group, and students who join a research group early based on research interest
alone and subsequently encounter issues with a negative mentoring relationship.
This work serves as a major step toward creating a comprehensive model of how
PhD students find a research group, and opens the door for future work to
investigate how factors such as group culture and working environment impact
the search process.
