BEGIN:VCALENDAR VERSION:2.0 PRODID:-//linuxsoftware.nz//NONSGML Joyous v1.4//EN BEGIN:VEVENT SUMMARY:Transport thought a critical magnetic quantum dot away from equili brium DTSTART:20260407T123000Z DTEND:20260407T140000Z DTSTAMP:20260806T021102Z UID:e627aa78-cb76-4d60-96b9-6f7367313ee2 SEQUENCE:2 CREATED:20260327T095502Z DESCRIPTION:LINK(+)In this thesis\, we investigate non-equilibrium phase t ransitions in a voltage-biased magnetic quantum dot\, a minimal model rele vant 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 ou t-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 the orem 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 po wer-law-correlated noise\, and close to it\, such as a crossover from firs t- to second-order transitions. Near criticality\, we obtain a stochastic equation description for the order parameter dynamics\, with a microscopic ally derived effective free energy that captures this crossover. Our metho ds show that any finite bias permits a controlled semiclassical descriptio n\, even beyond the effective-temperature regime. Using this framework\, w e show that fluctuations can stabilize metastable configurations in the st rongly driven regime\, revealing a subtle interplay between out-of-equilib rium noise and dissipation. Overall\, our results help clarify how bias-in duced driving and dissipation can shape classical and quantum criticality. LAST-MODIFIED:20260327T095521Z LOCATION:Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online URL:http://df.vps.tecnico.ulisboa.pt/pt/eventos/transport-thought-a-critic al-magnetic-quantum-dot-away-from-equilibrium/ X-ALT-DESC;FMTTYPE=text/html:

LINK(+)

In this thesis\, we investigate non-equilibrium phase transitions in a voltage-biased magnetic quantum dot\, a minimal mo del relevant to spintronic devices near criticality. Using a Keldysh path- integral approach\, we develop an effective theory for the dot'\;s col lective degrees of freedom under finite bias\, $V$\, connecting equilibriu m and out-of-equilibrium regimes. We build a phase diagram for the system& #x27\;s steady-state magnetization\, and find an open quantum critical poi nt 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 t he 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 c rossover from first- to second-order transitions. Near criticality\, we ob tain a stochastic equation description for the order parameter dynamics\, with a microscopically derived effective free energy that captures this cr ossover.

Our methods show that any finite bias permits a control led semiclassical description\, even beyond the effective-temperature regi me. Using this framework\, we show that fluctuations can stabilize metasta ble configurations in the strongly driven regime\, revealing a subtle inte rplay between out-of-equilibrium noise and dissipation. Overall\, our resu lts help clarify how bias-induced driving and dissipation can shape classi cal and quantum criticality.

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