Dear Professor XX,
I was a graduate student with DrXXX at the University of XXX working on XXX,
YYY to be more specific.
I am writing this letter to inquire about the possibility of receiving a
supportive letter from you toward my Green Card application in the United
States. The application requires me to provide evidences showing my area of
research has a high impact and my research has contributed to the scientific
community.
One way to prove this is providing supporting letters from distinguished
researchers, such as you, in my research field. Since one of my works has
been cited by your elegant work on the function of XXX published in XXX,
your evaluation and recommendation of my research and scientific
contribution would be a great support to my application.
Thank you for your kind consideration in this matter and I would be happy to
send you a draft, or any additional information you may need. Kindly see
the attached pdf version of my CV for your reference.
I look forward to hearing from you.
Best wishes,
ZZZ