arXiv subjects

Roberto Mantovan

Publications and source records attributed to Roberto Mantovan.

6 recordsLinked to original sources

arXiv2026

Terahertz magneto-photocurrents in the topological insulator Bi$_2$Se$_3$ probe its topological surface states

We study ultrafast magneto-photocurrents in a three-dimensional topological insulator. For this purpose, we excite (In$_r$Bi$_{1-r}$)$_2$Se$_3$ thin films with a femtosecond laser pulse in the presence of an external magnetic field $B_{\text{ext}}$ up to 0.3 T parallel to the film plane. The resulting in-plane photocurrent is measured by detecting the emitted terahertz (THz) electromagnetic pulse. It scales linearly with $B_{\text{ext}}$ and is perpendicular to $B_{\text{ext}}$. Strikingly, for $r\ge$4%, we observe an abrupt photocurrent reduction, which is strongly correlated with the Indium-induced quenching of the topological surface states. The rise time, decay time and amplitude of the THz magneto-photocurrent can consistently be explained by a scenario in which optically excited spin-polarized electrons propagate toward the film surface where the accumulated spin is converted into an in-plane charge current due to spin-velocity locking. Our results are highly relevant for contact-free probing of spin-charge conversion in systems with paramagnetic rather than spontaneous magnetic order.

cond-mat.mes-hall↗

arXiv2025

Atomic-scale Origin of Interfacial Dzyaloshinskii--Moriya Interaction in Pt/Fe/Au

Recent results show remarkable interfacial--Dzyaloshinskii--Moriya interaction (i-DMI) in magnetic heterostructures composed of relatively thick Fe thin films ($\gg 1$ nm). To investigate its origin, we present a thorough magnetic characterization of the SiO$_2$/${}^{57}\mathrm{Fe}$($t$)/Au and SiO$_2$/Pt/${}^{57}\mathrm{Fe}$($t$)/Au heterostructures ($t = 1.6$ - $2.2$ nm). An i-DMI constant of $D_s^{\mathrm{Pt}} = 0.43\,\mathrm{mJ\,m^{-2}}$ is extracted for the Pt/Fe/Au system, as probed by wavevector-resolved Brillouin light scattering spectroscopy. Ferromagnetic resonance and conversion electron M\"ossbauer spectroscopy indicate that significant surface anisotropy is present in Pt/Fe/Au, and that an interfacial Fe fraction ($\sim18$) exhibits tilted magnetization ($\sim25^\circ$ out of plane) and an enhanced hyperfine field, correlating with the stronger i-DMI.

cond-mat.mtrl-sci↗

arXiv2025

Transition Metal Dichalcogenide 1T$'$-MoTe$_2$ Nanoscale Films as Spin Pumping Platforms

Transition metal dichalcogenides (TMDs) have emerged as a promising class of materials for spintronics, with the aim of promoting efficient spin-charge conversion (SCC) in TMD/ferromagnet (FM)-based devices. The MoTe$_2$ semimetal with distorted orthorhombic crystal structure in the 1T$'$ phase has gathered particular attention due to its high spin-orbit coupling and reconfigurability as a type-II Weyl semimetal close to room temperature. Here, we report on the role of chemically grown 1T$'$-MoTe$_2$ thin films in inducing SCC in 1T$'$-MoTe$_2$/FM heterostructures as measured at room temperature. Ferromagnetic resonance (FMR) and electrically detected spin-pumping FMR measurements performed on 1T$'$-MoTe$_2$/Co/Au and 1T$'$-MoTe$_2$/Au/Co/Au heterostructures reveal a spin-mixing conductance value of up to $\sim1.6 \times 10^{20}~\mathrm{m^{-2}}$ and a spin Hall angle of $1.7\%$. These findings position MoTe$_2$ thin films as a competitive spin-charge conversion option compared to other functional materials (e.g., heavy metals, topological insulators), highlighting their potential for future applications in spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Probing the quantum metric of 3D topological insulators

The surface states of 3D topological insulators possess geometric structures that imprint distinctive signatures on electronic transport. A prime example is the Berry curvature, which controls, for instance, electric frequency doubling via its higher order moments. In addition to the Berry curvature, topological surface states are expected to exhibit a nontrivial quantum metric, which plays a key role in governing nonlinear magnetotransport. However, its manifestation has yet to be experimentally observed and controlled in 3D topological insulators. Here, we provide evidence for a nonlinear response activated by the quantum metric of the topological surface states of Sb$_2$Te$_3$. We measure a time-reversal odd, nonlinear magnetoresistance that is independent from the temperature and the scattering time below 30 K, and is thus of intrinsic geometrical origin. This quantum metric magnetoresistance can be controlled by tuning the contributions of the top and bottom topological surface states by voltage gating. Our measurements thus demonstrate the existence and tunability of quantum geometry-induced transport in topological phases of matter and provide strategies for designing novel functionalities in topological devices.

cond-mat.mes-hall↗

arXiv2025

Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures

Three-dimensional topological insulators possess topologically protected surface states with spin-momentum locking, which enable spin-charge-current interconversion (SCI) by the inverse Edelstein effect (IEE). However, it remains experimentally challenging to separate the surface-related IEE from the bulk-type inverse spin Hall effect (ISHE). Here, we search for distinct time-domain signatures of the two SCI phenomena in a $\mathcal{F}$|TI model stack of a ferromagnetic-metal layer $\mathcal{F}$ (Co and Fe) and a topological-insulator layer TI (Bi$_2$Te$_3$, SnBi$_2$Te$_4$ and Bi$_{1-x}$Sb$_x$ with $x$ = 0.15 and 0.3), where the focus is on Bi$_2$Te$_3$. A femtosecond laser pulse serves to induce a transient spin voltage $\mu_s^{\mathcal{F}}$ in $\mathcal{F}$ and, thus, drive an ultrafast spin current out of $\mathcal{F}$. SCI results in a transverse charge current with a sheet density $I_c$ that is detected by sampling the emitted terahertz electric field. Analysis of the dynamics of $I_c(t)$ vs time $t$ relative to $\mu_s^{\mathcal{F}}(t)$ reveals two components with distinct time scales: (i) a quasi-instantaneous response and (ii) a longer-lived response with a relaxation time of 270 fs, which is independent of the chosen $\mathcal{F}$ material. Component (i) is consistently ascribed to the ISHE. In contrast, we interpret component (ii) as a signature of interfacial spin accumulation and the IEE at the $\mathcal{F}$/Bi$_2$Te$_3$ interface, with a fraction of $< 10^{-2}$ of the incident spins participating. This assignment is fully consistent with respect to its dynamics and magnitude. We rate other possible signal contributions, such as spin trapping in intermediate states, as less likely. Our results show that the femtosecond dynamics of photocurrents provide important insights into the mechanisms of spin transport and SCI in $\mathcal{F}$|TI stacks.

cond-mat.mes-hall↗

arXiv2021

Large spin-to-charge conversion at room temperature in extended epitaxial Sb2Te3 topological insulator chemically grown on Silicon

Spin-charge interconversion phenomena at the interface between magnetic materials and topological insulators (TIs) are attracting enormous interest in the research effort towards the development of fast and ultra-low power devices for the future information and communication technology. We report a large spin-to-charge conversion efficiency in Au/Co/Au/Sb2Te3/Si(111) heterostructures based on Sb2Te3 TIs grown by metal organic chemical vapor deposition on 4 inches Si(111) substrates. By conducting room temperature spin pumping ferromagnetic resonance, we measure an inverse Edelstein Effect length λIEE up to 0.75 nm, a record value for 3-dimensional chalcogenide-based TIs heterostructures. Our results open the path toward the use of chemical methods to produce TIs on large area Si substrates and characterized by highly performing spin-charge conversion, thus marking a milestone toward future technology-transfer.

cond-mat.mtrl-sci↗