Grounded In Theory – Michele Governale

Story by Ruth Beran Michele Governale InterfaceWalking into Associate Professor Michele Governale’s office at Victoria University, it’s hard to miss the big whiteboard with equations scribbled in red pen. “These things have been written by my students and co-workers,” Governale explains. “At the moment there is no one complete thing, there are many.” It’s a testament to how the theoretical physicist operates. “Some people might think that a theoretical physicist works on his own, closed in his office. That’s not the case. I think interactions are very important. Robust discussions often.” Governale is often engrossed in numerous projects at a time. “If you ask me what research I like most, it’s always the last,” he says. “This is what keeps you going.” Governale’s research primarily looks at low dimensional systems. These could be 1, 2 or 3 dimensional nanostructures where electrons are confined in their movement. Within these systems he is interested in the quantum effects that occur at low temperatures, where the spins of electrons are manipulated by both electrical and magnetic fields; a technology known as spintronics. Another interest for Governale is the effects of electrostatic (or Coloumb) interactions between particles. “It’s basically the standard repulsion between charged particles,” he says. “When particles start to interact it makes problems challenging but it can also give striking effects, so it’s often an important ingredient to get unexpected effects.” Governale studied electronic engineering in Pisa, Italy but realised that his passion was for physics. He completed his PhD in Germany on quantum dots and quantum wire nanoelectronic devices. One of his current MacDiarmid Institute funded PhD students, Stephanie Droste, is also working on quantum dots. In particular she’s looking at fluctuations of electric current in nanoscale systems coupled to superconductors. Droste is drawn to superconductors because when electrons are confined in a quantum dot in the presence of both a strong electrostatic interaction, and superconductivity, an interesting competition between the two phenomena results. Governale is also working on a project that has an intriguing history tracing back to an Italian physicist called Ettore Majorana, a student of Enrico Fermi—the discoverer of nuclear fission. “Majorana disappeared in thin air,” says Governale. “Somehow he boarded a ferry and nobody knows what happened to him. There are a lot of theories of what happened to Ettore Majorana.” Before he disappeared, Majorana postulated that you could have fermions that are their own anti-particles, so called Majorana fermions. Fermions are matter particles and include electrons, quarks and neutrinos. However, if the particle is charged it cannot be its own anti-particle. This eliminates all matter particles except the neutrino, but just like Majorana himself, these Majorana fermions haven’t yet been found. In order to prove or disprove the existence of Majorana fermions, particle physicists will need to use a particle accelerator like the Large Hadron Collider, and there are already several groups competing with each other to find the smoking gun signature of decay that will detect Majorana fermions. “In this, we could steal a march on the particle physicists because we can create our own zoo of quasi-particles including Majorana fermions, even if they turn out not to exist freely in the universe,” says Governale. He is also quick to point out that theorists don’t always explain experiments once they have been done. “Often theorists can lead you and propose new structures, new ideas, new devices, new experiments. In this case, it’s a completely theory-led project,” he says. “Often theorist’s dreams become reality after a certain delay.” While most of Governale’s work is done with just pen and paper, he does sometimes use computer software to help. Although the idea is not to simply get a curve on the computer. “What you try to do is have the minimal non-trivial model,” he says. “To get an analytic expression that will tell you, if I change this parameter, this will happen.” To achieve this, all unnecessary complications of reality are stripped, leaving a non-trivial model to explain the effect. “But of course,” Governale points out, “reality is complicated.” Once a minimal non-trivial model is developed its results can be compared to experiments, and the model tweaked if needed. To this end Governale is collaborating with other MacDiarmid Institute researchers like Ben Ruck and Joe Trodahl on rare earth nitride systems and superconductivity. With new appointments in the Institute Governale says it’s an exciting time to be at Victoria University. He adds to a ‘critical mass of theorists’ at the MacDiarmid Institute, with Ulrich Zuelicke, Nicola Gaston, and Shaun Hendy. “We call it the theory think tank. Basically the onestop shop for theoretical modelling in New Zealand,” he explains. “I think theory can be quite important in the MacDiarmid Institute, both helping answer questions the experimentalists might have but also leading, in terms of proposing new, functional devices.”

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