  This study aims to understand how undergraduate physics majors develop an
interest in specific subfields. We examine interest formation through the lens
of Social Cognitive Career Theory (SCCT) by exploring four key SCCT constructs:
learning experiences, self-efficacy, outcome expectations, and proximal
environmental influences. We conducted 27 interviews with physics majors across
various years of study between 2020 and 2022. Our first research question
analyzes SCCT constructs to provide detailed insights into the interest
formation of various subfields of physics. Examining these constructs, we
better understand the factors influencing students' preferences toward specific
subfields. Our findings indicate that positive class experiences and
experimental opportunities significantly impacted students' interest in
different subfields of physics. This understanding helped us explore
significant variations in interest formation between astrophysics and
biomedical physics in Research Question 2. By understanding how students decide
about their interests, we can provide valuable insights for physics departments
and career guidance professionals.
