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:20260816T065736Z UID:e627aa78-cb76-4d60-96b9-6f7367313ee2 SEQUENCE:1 CREATED:20260327T095448Z 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 scal ing at finite and. At weak drive\, we extend the fluctuation–dissipatio n 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 oscillati ng power-law-correlated noise\, and close to it\, such as a crossover from first- to second-order transitions. Near criticality\, we obtain a stocha stic equation description for the order parameter dynamics\, with a micros copically derived effective free energy that captures this crossover. Our methods show that any finite bias permits a controlled semiclassical descr iption\, even beyond the effective-temperature regime. Using this framewor k\, we show that fluctuations can stabilize metastable configurations i n the strongly driven regime\, revealing a subtle interplay between out-of -equilibrium noise and dissipation. Overall\, our results help clarify how bias-induced driving and dissipation can shape classical and quantum crit icality. LAST-MODIFIED:20260327T095448Z LOCATION:Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online URL:http://df.vps.tecnico.ulisboa.pt/en/events/transport-thought-a-critica l-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 fluctu ation–dissipation theorem to identify an effective temperature that gove rns the transition. At strong drive\, this description breaks down: we unc over intrinsically non-equilibrium features\, both away from criticality\, such as oscillating power-law-correlated noise\, and close to it\, such a s a crossover from first- to second-order transitions. Near criticality\, we obtain a stochastic equation description for the order parameter dynami cs\, with a microscopically derived effective free energy that captures th is crossover.

Our methods show that any finite bias permits a co ntrolled semiclassical description\, even beyond the effective-temperature regime. Using this framework\, we show that fluctuations can stabilize metastable configurations in the strongly driven regime\, revealing a sub tle interplay between out-of-equilibrium noise and dissipation. Overall\, our results help clarify how bias-induced driving and dissipation can shap e classical and quantum criticality.

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