citr provides functions and an RStudio addin to search a BibTeX-file, create, and insert formatted Markdown citations into the current document.
Until citr is on CRAN you can install it from this GitHub repository:
devtools::install_github("crsh/citr")
Once citr is installed you should find the addin in the menus.
You can also define a keyboard shortcut to call the addin.
The following call searches a BibTeX-file and creates formatted Markdown citations for the results.
library("citr")
md_cite("foo 2016", bib_file = "references.bib")
md_cite() searches author, year, title, and journal fields of your references.
If you are interested in other handy addins take a look at this list. There you can find other useful addins, such as the word count addin.