PhD Mid-term Seminar Series

CIC nanoGUNE Seminars

Speaker

Nuria Santervás, Erlaitz Gómez

When

2025/02/03
11:00

Place

CIC nanoGUNE Seminar room, Tolosa Hiribidea 76, Donostia-San Sebastian

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Nuria Santervás: Excess Energy and Countercurrents After a Quantum Kick

Motivated by the dynamics of non-equilibrium quantum systems, this talk examines the behavior of interacting quantum particles subjected to a sudden onset of motion. Specifically, I will analyze a system under a static external potential that is "kicked" into motion at a constant velocity, v. This scenario is experimentally relevant to the study of Migdal's sudden jolt [1], a well known effect in particle detection, where an atomic nucleus recoils after a collision with a neutron or dark matter particle. I will discuss a generalization of this framework that serves as a useful reference for time-dependent simulations and provides potential inspiration for experiments in optical lattices, where controlled quantum kicks could be realized. For a system initially in a stationary state, the excess energy at any time after the kick is equal to v·⟨P⟩(t), where P is the total momentum of the system. If the system is finite and remains bound, the long time average of the excess energy tends to Mv², where M is the total mass of the system. For macroscopic solid systems, a current counter to the motion of the potential arises when electrons are partially left behind. First principles calculations confirm the appearance of such countercurrents in both an insulator and a metal.

Erlaitz Gómez:  Improving the output signal of Magnetoelectric Spin-Orbit logic devices

The MagnetoElectric Spin-Orbit (MESO) device architecture is a promising energy-efficient solution for integrating spin logic into the existing electronics industry [1]. The information of the logic state is stored in the magnetization of a nanoscale ferromagnetic (FM) element, that can be reversed (i.e. write the logic state) via ME coupling. To read the logic state, a spin-polarized current is created by flowing a charge current through the ferromagnet into a material with spin-orbit coupling (SO), where it is converted by the inverse spin Hall effect (ISHE) into a transverse voltage with two well-defined states depending on , being the difference between those two states. The spin to charge conversion in such devices must be efficient enough so that can switch the writing module of another cascaded MESO unit and perform logic operations. In this regard, there have been demonstrations of a scaling law for in FM/SO ohmic interface devices, that prove the importance of using SO materials with high spin Hall efficiency while also highlighting the current shunt across FM and spin backflow in the interface as limiting factors for the growth of [2]. In this talk, I will discuss how using an insulating MgO barrier as a spin injection layer in CoFeB/MgO/Ta nanostructures can improve the output signal in comparison to ohmic FM/SO interfaces, showing the nanofabrication process developed to integrate such tunnel barriers into devices for magnetic state readout.

References