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Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Wed, 10 May 2023

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1.Correlations of spin splitting and orbital fluctuations due to 1/f charge noise in the Si/SiGe Quantum Dot

Authors:Marcin Kępa, Łukasz Cywiński, Jan A. Krzywda

Abstract: Fluctuations of electric fields can change the position of a gate-defined quantum dot in a semiconductor heterostructure. In the presence of magnetic field gradient, these stochastic shifts of electron's wavefunction lead to fluctuations of electron's spin splitting. The resulting spin dephasing due to charge noise limits the coherence times of spin qubits in isotopically purified Si/SiGe quantum dots. We investigate the spin splitting noise caused by such process caused by microscopic motion of charges at the semiconductor-oxide interface. We compare effects of isotropic and planar displacement of the charges, and estimate their densities and typical displacement magnitudes that can reproduce experimentally observed spin splitting noise spectra. We predict that for defect density of $10^{10}$ cm$^{-2}$, visible correlations between noises in spin splitting and in energy of electron's ground state in the quantum dot, are expected.

2.Giant spin Nernst effect in a two-dimensional antiferromagnet due to magnetoelastic coupling-induced gaps and interband transitions between magnon-like bands

Authors:D. -Q. To, C. Y. Ameyaw, A. Suresh, S. Bhatt, M. J. H. Ku, M. B. Jungfleisch, J. Q. Xiao, J. M. O. Zide, B. K. Nikolic, M. F. Doty

Abstract: We analyze theoretically the origin of the spin Nernst and thermal Hall effects in FePS3 as a realization of two-dimensional antiferromagnet (2D AFM). We find that a strong magnetoelastic coupling, hybridizing magnetic excitation (magnon) and elastic excitation (phonon), combined with time-reversal-symmetry-breaking, results in a Berry curvature hotspots in the region of anticrossing between the two distinct hybridized bands. Furthermore, large spin Berry curvature emerges due to interband transitions between two magnon-like bands, where a small energy gap is induced by magnetoelastic coupling between such bands that are energetically distant from anticrossing of hybridized bands. These nonzero Berry curvatures generate topological transverse transport (i.e., the thermal Hall effect) of hybrid excitations, dubbed magnon-polaron, as well as of spin (i.e., the spin Nernst effect) carried by them, in response to applied longitudinal temperature gradient. We investigate the dependence of the spin Nernst and thermal Hall conductivities on the applied magnetic field and temperature, unveiling very large spin Nernst conductivity even at zero magnetic field. Our results suggest FePS3 AFM, which is already available in 2D form experimentally, as a promising platform to explore the topological transport of the magnon-polaron quasiparticles at THz frequencies.

3.Dissipation and diffusion in one-dimensional solids

Authors:Harshitra Mahalingam, Ben Andrew Olsen, Aleksandr Rodin

Abstract: Using a nonperturbative classical model for ionic motion through one-dimensional (1D) solids, we explore how thermal lattice vibrations affect ionic transport properties. Based on analytic and numerical calculations, we find that the mean dissipation experienced by the mobile ion is similar to that of the non-thermal case, with thermal motion only contributing stochastic noise. A nonmonotonic dependence of drag on speed, predicted in earlier work, persists in the presence of thermal motion. The inverse relation between drag and speed at high speeds results in non-Fickian diffusion dominated by L\'{e}vy flights. This suppression of drag at high speeds, combined with enhanced activation frequency, improves the particle mobility at high temperatures, where typical particles move faster.

4.Dark axisymmetric plasma modes in partially gated two-dimensional electron gas disk

Authors:M. V. Cheremisin

Abstract: The transition from ungated to completely gated disk-shaped two-dimensional gas is studied under extension of the central gate spot. We investigate axisymmetric plasmon excitations spectra which show interchange between neighboring modes caused by abrupt change of carriers screening at the gate boarder. This behavior is totally unexpected within simple scenario of sub-gate gap varying [A.L.Fetter, Phys.Rev.B 33, 5221 (1986)]. Our results provide the accurate identification of axisymmetric plasmon modes recently observed in experiment.

5.Voltage-tunable giant nonvolatile multiple-state resistance in interlayer-sliding ferroelectric h-BN engineered van der Waals multiferroic tunnel junction

Authors:Xinlong Dong, Xuemin Shen, Xiaowen Sun, Yuhao Bai, Zhi Yan, Xiaohong Xu

Abstract: Multiferroic tunnel junctions (MFTJs) based on two-dimensional (2D) van der Waals heterostructures with sharp and clean interfaces at the atomic scale are crucial for applications in nanoscale multi-resistive logic memory devices. The recently discovered sliding ferroelectricity in 2D van der Waals materials has opened new avenues for ferroelectric-based devices. Here, we theoretically investigate the spin-dependent electronic transport properties of Fe$_3$GeTe$_2$/graphene/bilayer-$h$-BN/graphene/CrI$_3$ (FGT/Gr-BBN-Gr/CrI) all-vdW MFTJs by employing the nonequilibrium Green's function combined with density functional theory. We demonstrate that such FGT/Gr-BBN-Gr/CrI MFTJs exhibit four non-volatile resistance states associated with different staking orders of sliding ferroelectric BBN and magnetization alignment of ferromagnetic free layer CrI$_3$, with a maximum tunnel magnetoresistance (electroresistance) ratio, i.e., TMR (TER) up to $\sim$$3.36\times10^{4}$\% ($\sim$$6.68\times10^{3}$\%) at a specific bias voltage. Furthermore, the perfect spin filtering and remarkable negative differential resistance effects are evident in our MFTJs. We further discover that the TMR, TER, and spin polarization ratio under an equilibrium state can be enhanced by the application of in-plane biaxial strain. This work shows that the giant tunneling resistance ratio, multiple resistance states, and excellent spin-polarized transport properties of sliding ferroelectric BBN-based MFTJs indicate its significant potential in nonvolatile memories.

6.Dynamical bulk boundary correspondence and dynamical quantum phase transitions in higher order topological insulators

Authors:T. Masłowski, N. Sedlmayr

Abstract: Dynamical quantum phase transitions occur in dynamically evolving quantum systems when non-analyticities occur at critical times in the return rate, a dynamical analogue of the free energy. This extension of the concept of phase transitions can be brought into contact with another, namely that of topological phase transitions in which the phase transition is marked by a change in a topological invariant. Following a quantum quench dynamical quantum phase transitions can happen in topological matter, a fact which has already been explored in one dimensional topological insulators and in two dimensional Chern insulators. Additionally in one dimensional systems a dynamical bulk boundary correspondence has been seen, related to the periodic appearance of zero modes of the Loschmidt echo itself. Here we extend both of these concepts to two dimensional higher order topological matter, in which the topologically protected boundary modes are corner modes. We consider a minimal model which encompasses all possible forms of higher order topology in two dimensional topological band structures. We find that DQPTs can still occur, and can occur for quenches which cross both bulk and boundary gap closings. Furthermore a dynamical bulk boundary correspondence is also found, which takes a different form to that in one dimension.

7.Eigenmodes of magnetic skyrmion lattices

Authors:Louise Desplat, Bertrand Dupé

Abstract: We explore the interplay between topology and eigenmodes by changing the stabilizing mechanism of skyrmion lattices (skX). We focus on two prototypical ultrathin films hosting an hexagonal (Pd/Fe/Ir(111)) and a square (Fe/Ir(111)) skyrmion lattice, which can both be described by an extended Heisenberg Hamiltonian. We first examine whether the Dzyaloshinkskii-Moriya, or the exchange interaction as the leading energy term affects the modes of the hexagonal skX of Pd/Fe/Ir(111). In all cases, we find that the lowest frequency modes correspond to internal degrees of freedom of individual skyrmions, and suggest a classification based on azimuthal and radial numbers $(l,p)$, with up to $l=6$, and $p=2$. We also show that the gyration behavior induced by an in-plane field corresponds to the excitation of $l=1$ deformation modes with varying radial numbers. Second, we examine the square lattice of skyrmions of Fe/Ir(111). Its stabilization mechanism is dominated by the 4-spin interaction. After relaxation, the unit cell does not carry a topological charge, and the eigenmodes do not correspond to internal skyrmion deformations. By reducing the 4-spin interaction, the integer topological charge is recovered, but the charge carriers do not possess internal degrees of freedom, nor are they separated by energy barriers. We conclude that a 4-spin dominated Hamiltonian does not yield skyrmion lattice solutions, and that therefore, a nontrivial topology does not imply the existence of skyrmions.

8.Investigation of Spin-Wave Dynamics in Gyroid Nanostructures

Authors:Mateusz Gołębiewski, Riccardo Hertel, Vitaliy Vasyuchka, Mathias Weiler, Philipp Pirro, Maciej Krawczyk, Shunsuke Fukami, Hideo Ohno, Justin Llandro

Abstract: A new concept in magnonics studies the dynamics of spin waves (SWs) in three-dimensional nanosystems. It is a natural evolution from conventionally used planar systems to explore magnetization configurations and dynamics in 3D nanostructures with lengths near intrinsic magnetic scales. In this work, we perform broadband ferromagnetic resonance (BBFMR) measurements and micromagnetic simulations of nanoscale magnetic gyroids - a periodic chiral structure consisting entirely of chiral triple junctions. Our results show unique properties of the network, such as the localization of the SW modes, evoking their topological properties, and the substantial sensitivity to the direction of the static magnetic field. The presented results open a wide range of applications in the emerging field of 3D magnonic crystals and spintronics.