Wanted: A new phase of matter

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The principles of quantum mechanics are the gateway to a faster and more secure means of computing. These quantum computers are far from reaching their full potential, but they are already one of the 21st-century breakthroughs. To ascend a classic machine into the quantum world, the standard approach relies on quantum bits, so-called qubits. However, qubits are still in development and generally not robust enough to survive the complexities of the everyday world. Many researchers, like IST Professor Kimberly Modic, seek an alternative approach and a new state of matter known as a quantum spin liquid might be the answer.

A quantum spin liquid relies on an intrinsic property of the electrons in the material, the so-called spin. The spin can be thought of as a tiny little arrow, which can point in any direction. The perfect foundation for quantum data transfer is possible when all spins move together as a fluid, just like water – physicists call this behavior “correlated”. This means that the actions of each spin determine the behavior of its neighbors. Think of it as a loose ball pendulum, where the spin information can travel undisturbed throughout the whole medium. Here’s the problem: while scientists theoretically predicted quantum spin liquids in the 1970s, experiments on candidate materials since then have not identified the smoking-gun signature of this new state of matter. In fact, experimentalists don’t know what to look for, which makes the search very difficult. Here’s where Kimberly Modic comes in.

She developed a novel technique to measure the magnetic properties of candidate materials and learn about the interactions between spins. Scientists expected that specific preconditions like extremely cold temperatures or magnetic fields are necessary to observe a quantum spin liquid. With her method, Kimberly Modic modifies both, while continuously scanning her sample’s magnetic behavior for anomalies. “Our technique has one-part-per-billion sensitivity and it completely revolutionizes how we determine the magnetic properties of materials.” Therefore, there is every reason to expect that this new technique will become a mainstream tool for investigating quantum spin liquids.

Currently, ruthenium-trichloride, a dark metallic-looking solid, is one of the prime candidates for a quantum spin liquid. It is one of the most well-studied materials in this context, with new papers attempting to explain its behavior appearing weekly. What’s unique about Kimberly Modic’s recent study is her ability to measure ruthenium-trichloride over a wide range of temperatures and magnetic field strengths. This revealed an anomalous magnetic response; it seems that all complex spin interactions spread out across the material, and the measured spin interaction strength effectively vanishes. This phenomenon is expected from a quantum spin liquid and could be an indicator that ruthenium-trichloride is everything researchers have been hoping for. “We don’t know for sure yet if ruthenium-trichloride is a quantum spin liquid, but it has a very nontrivial magnetic response when subjected to magnetic fields. The fact that we can’t explain this behavior like we could a conventional magnet gives us every reason to dig deeper. This is where things get interesting!”

At IST Austria, Kimberly Modic and her team will use their expertise to investigate quantum spin liquids and other modern quantum materials. “We demonstrated a new capability, as well as a new way to think about spin liquids, but this is just an exciting first step. In a physics-rich system like ruthenium-trichloride, this result just begs for more experiments. It already has us thinking about new ways to enhance the technique and extend it to new classes of 2D materials. One thing that became clear to us during this project is that we need to focus more attention on sample care and preparation.  At IST, we recently purchased a plasma FIB (focused ion beam) that will allow us to control and fully modernize this aspect of our experiments, and we’re looking forward to new directions that will come with this capability. “

Nature physics August issue also featured Professor Kimberly Modic’s research. Click this link to check it out.