In addition to the excellent suggestions of KM, I think it is very reasonable in solid state physics to have some economic motivation for the research (even loosely). In addition, the work tends to lend itself to collaboration across fields (again, even loosely) in that work you do can benefit engineers or motivate material scientists and solid state chemists. These are both forms of connection to a broader sphere. And...hint, hint play well when searching for funding.
I'm not saying to go overboard or to be plaintive or salesy. But at the same time you need to give people SOME "so what". Don't overhype BUT also don't "hide your light under a bushel". Give people some translation so they can get the "so what".
Your plasmons and solitons and other funky thingamijugs (I know enough about SSP to know that I see terms I don't know!) have the potential to give us better understanding that can lead to improved solar cells, flat panel displays, etc. I don't know the plasmon, but I could use some better solar cells and a cheaper laptop!
Similarly the implicit connections to other fields of science (or I guess subfields of physics). A metallurgist or device designer may have no clue how to do some of the theoretical calcs or superfancy physical measurements, but your fundamental work can motivate the metallurgist to synthesize new intermetallic compounds or the device designer to consider new configurations. And you are actually filling a gap, because these individuals are good at what they do, but not so good at Ashcroft and Mermin (and you are even way past that).
P.s. While this answer is about solid state, many other fields of science have similar economic/social motivations and tangencies to other research. A little bit of this basic context setting should be included in grant appeals, SOPs, website descriptions of your research to attract students, TALKS, and even a sentence or two in the introduction of each science report.
In terms of "how". I would as an exercise, go through and write a couple versions. Maybe one where you do a lot of "because" and one with a moderate amount (you have the "no" control already). The act of sitting down and writing will cause you to find individual bullet points (content) to support a narrative.
I also think there is nothing wrong with showing why a particular interest has aroused. You can do this objectively or personally. I actually wouldn't be so leery about personalizing things, but either way, some rationale is helpful and connects the reader. For example I (one) first was motivated by the desire to improve output property X and thus researched combinations of Y and Z. Subsequent learnings showed me the importance of W. At this point, my interests have moved from pure catalogueing of the output function versus input variables to a microscopic understanding. [Or WHATEVER. But I'm sure that while you worked in this topic, you have learned some things, changed some things, and have a desire to do new things in a different direction. Note, this is a HUMAN story (the evolution of your research direction) that even a biologist can understand. I don't need to know what the plasmon is to get that.]
