Method that returns reference to value created in the method?

I have a struct that contains references to two different values. There's two constructors - one that takes a reference for each value, and one that only takes a reference to one of the values while assigning a default to the other.

My problem is assigning that default. See the code below:

struct Foo<'t> {
    a: &'t String,
    b: &'t String,
}

impl<'t> Foo<'t> {
    fn new(a: &'t String, b: &'t String) -> Foo<'t> {
        Foo { a, b }
    }

    fn new_with_default_b(a: &'t String) -> Foo<'t> {
        Foo {
            a,
            b: &String::from("default"),
        }
    }
}

This does not compile:

error[E0515]: cannot return value referencing temporary value
  --> src/lib.rs:12:9
   |
12 | /         Foo {
13 | |             a,
14 | |             b: &String::from("default"),
   | |                 ----------------------- temporary value created here
15 | |         }
   | |_________^ returns a value referencing data owned by the current function

Is it possible to fix this?