Statement of Purpose

Behrad Nikzad — PhD in Physics (Experimental Condensed Matter)

The closed-cycle cryostat in our lab at Sharif University of Technology broke three weeks before the measurement that would decide my master's thesis. The cold head had failed, replacement parts faced a months-long import delay, and my tungsten ditelluride devices were degrading in storage. With my advisor's blessing, I spent those three weeks rebuilding the thermal link myself: machining a copper braid coupling, re-indium-sealing the radiation shield, and writing a PID loop to stabilize the second stage at 4.2 kelvin with hardware never designed for it. The measurement that followed — a clean set of magnetoresistance curves showing the anisotropy we had predicted — went into my thesis. The repair went into my formation as an experimentalist. I learned that in condensed matter physics, the instrument is not the background of the science; often it is the science. I am applying to your PhD program to practice that craft at the level your laboratories make possible.

My path to low-temperature transport ran through theory first. As an undergraduate in physics at Sharif, I spent a summer at the Institute for Research in Fundamental Sciences on a computational project, calculating band structures of twisted bilayer graphene near the magic angle. The project produced a poster and a working knowledge of tight-binding methods, but its lasting effect was a question I could not simulate away: which of these exquisite theoretical features survive contact with a real device, with its strain, disorder, and imperfect gates? That question sent me to an experimental group for my master's.

My thesis focused on magnetotransport in exfoliated tungsten ditelluride flakes. I fabricated devices end to end — mechanical exfoliation, electron-beam lithography at a shared national facility, and contact deposition — and measured longitudinal and Hall resistivity down to 4 kelvin and up to 9 tesla. The central result, a systematic study of thickness-dependent magnetoresistance anisotropy across eleven devices, is under review at a peer-reviewed journal with me as first author. Along the way I built the lab's measurement automation in Python, cutting a full field-and-temperature sweep from three days of supervised work to an overnight run; three current students use that code.

I am applying to your program because its Quantum Materials Group works exactly at the junction that formed my question: transport and thermodynamic probes of two-dimensional and topological materials, backed by instrumentation that is out of reach in my current environment — dilution refrigerators reaching millikelvin temperatures, high-field magnets, and an in-house nanofabrication cleanroom that closes the loop between device design and measurement within days rather than months. The group's recent emphasis on strain-tunable devices speaks directly to the disorder-versus-intrinsic-behavior question my thesis left open. I am equally drawn to the program's structure: the first-year laboratory rotations would let me add scanning-probe experience to my transport background, and the weekly joint seminar between experimental and theoretical condensed matter groups reflects how I already like to work — I have kept one foot in tight-binding calculations precisely so I can argue with theorists in their own language.

During the PhD I want to pursue transport studies of engineered two-dimensional heterostructures at millikelvin temperatures, with a particular interest in how controlled strain and twist reshape correlated phases. My preparation is honest but uneven: I bring strong device fabrication, measurement automation, and a proven ability to keep imperfect equipment producing data; I need training in ultra-low-temperature technique and advanced probe methods, which is precisely what your facilities and faculty offer.

My longer-term aim is a research career in quantum materials, in academia or a national laboratory, ideally helping build experimental capacity in places where a broken cold head still costs a student three weeks. Those three weeks taught me more than any course; I would now like to learn what a laboratory looks like when the instruments work — and to earn the skill to push them past their specifications.