Recollection of Neil W. Ashcroft by Nandini Trivedi

I met Neil for the last time in June 2018 along with Judith and their son Robert. I happened to be at Cornell to give a couple of blackboard talks at a workshop. We had a lovely conversation on many wide-ranging topics. Neil was his usual self: curious to learn about new topics with that particular quizzical look that I still remember from my graduate student days!

I first met Neil Ashcroft when he taught the condensed matter physics class. I was one of Neil’s graduate students from 1981-1987. It was a time of growth for me: in a new culture, navigating new friends, being by myself far away from friends and family. My research was on disorder and transport, and quantum size effects in nanowires. In my first year of grad school as I was trying to pick an area to research on, I often heard proclamations that everything that had to be discovered had already been discovered. And yet each year there was a major discovery in condensed matter physics: from quasicrystals, fractional quantum Hall effect, award of the Nobel Prize to von Klitzing for the integer quantum Hall effect, weak localization and h/(2e) oscillations, and finally in 1987 the discovery of high temperature superconductivity! And Ken Wilson won his Nobel Prize in 1982 just when he was teaching a statistical physics course on Renormalization group that I was taking!!

One of the challenges I faced in graduate school was focusing on my PhD project with exciting discoveries happening all around. Every time I would bring these up with Neil, he would reiterate the importance of focusing. Learning to balance breadth and depth was an important lesson for my intellectual development during graduate school. It has played a major role in my ability to branch out in so many exciting directions over the course of my career.

I learned many things from Neil—most importantly how to approach a completely new problem: first try dimensional analysis was a mantra he always emphasized. I also learned from him the importance of making simple numerical estimates. I have continued to train my students to keep an eye on these simple but powerful messages. The second important thing I learned from Neil was how to deconstruct a result someone shows you without actually going through the derivation (of course once the dimensions have been checked!) Ashcroft and Mermin has remained my go-to textbook for condensed matter physics in the decades since graduate school.