Transport thought a critical magnetic quantum dot away from equilibrium

Fri, 27 Mar 2026 09:55:22 +0000

Terça-feira, 7 de Abril 2026 das 12:30 às 14:00

Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online

In this thesis, we investigate non-equilibrium phase transitions in a voltage-biased magnetic quantum dot, a minimal model relevant to spintronic devices near criticality. Using a Keldysh path-integral approach, we develop an effective theory for the dot's collective degrees of freedom under finite bias, $V$, connecting equilibrium and out-of-equilibrium regimes. We build a phase diagram for the system's steady-state magnetization, and find an open quantum critical point when , with fluctuations that diverge with in contrast with power-law scaling at finite and.

At weak drive, we extend the fluctuation–dissipation theorem to identify an effective temperature that governs the transition. At strong drive, this description breaks down: we uncover intrinsically non-equilibrium features, both away from criticality, such as oscillating power-law-correlated noise, and close to it, such as a crossover from first- to second-order transitions. Near criticality, we obtain a stochastic equation description for the order parameter dynamics, with a microscopically derived …

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Transport thought a critical magnetic quantum dot away from equilibrium