As I understand, you would like to have separate variables for each entry, rather than storing them in the cell arrays as you have done above, and you would like those variables to be automatically generated based on the name of the input file.
You can do this using the "eval" command, though it is generally discouraged because it's inefficient and can be difficult to debug. That issue is elaborated upon in this past Answers post: https://www.mathworks.com/matlabcentral/answers/143-how-do-i-make-a-series-of-variables-a1-a2-a3-a10
For example, you could instead generate fields of a structure and populate that:
>> varname = matlab.lang.makeValidName(source_files(k).name(1:end-4));
>> myData.(varname) = xlsread(fullfile(source_dir,source_files(k).name), 'A:A');
The first line is to ensure that you define allowable variable names: http://www.mathworks.com/help/matlab/ref/matlab.lang.makevalidname.html
If you are set on automatic variable generation, you could do that using "eval":
>> varname = matlab.lang.makeValidName(source_files(k).name(1:end-4));
>> eval([varname '= xlsread(fullfile(cd, source_dir,source_files(k).name),'...
char(39) 'A:A' char(39) ');']);
However, as noted above, I would encourage you to explore other options. You may find the following documentation to provide some useful suggestions: http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html
