Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Z19: Drive engineering and topology |
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Sponsoring Units: DCMP Chair: Federico Bocci, University of California Irvine Room: Room 211 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z19.00001: Chiral gauge field in light-driven Dirac electrons in Co3Sn2S2 Naotaka Yoshikawa, Yoshua Hirai, Kazuma Ogawa, Shun Okumura, Kohei Fujiwara, Junya Ikeda, Takashi Koretsune, Ryotaro Arita, Aditi Mitra, Atsushi Tsukazaki, Takashi Oka, Ryo Shimano Floquet engineering has been proposed as an intriguing approach to control topological materials such as Dirac semimetals and Weyl semimetals using light. It was proposed based on Floquet theory that a chiral gauge field can be implemented to Dirac electrons by a circularly polarized periodic driving field, and the transition from Dirac semimetal to Weyl semimetal can be achieved. We experimentally found that Co3Sn2S2 in the paramagnetic phase, which is a 3D Dirac electron system, exhibited an instantaneous anomalous Hall effect when irradiated with a mid-infrared circularly polarized light pulse. We quantitatively compared the intensity and frequency dependences of the observed anomalous Hall conductivity with the effective model describing the Floquet state of Co3Sn2S2, suggesting that the nonzero Berry curvature due to light-induced chiral gauge field causes the anomalous Hall effect. Our demonstration paves a new pathway for ultrafast manipulation of topological phases of matter and for further exploring various topological phases achievable only by light. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z19.00002: Ultrafast control of quantum geometry and nonlinear optical response in topological materials Thais Victa Trevisan, Gunnar F Lange, Robert-Jan Slager, Peter P Orth Nonlinear optical responses are central to modern optical technologies and the possibility to tune them on-demand and on ultrafast timescales is highly desirable. We theoretically analyze the possibility of using bicircular light (BCL) irradiation as a way to dynamically control nonlinear optical responses in Dirac semimetals and topological insulators. BCL consists of a superposition of two circularly polarized light beams with frequencies that are integer multiples of each other. The resulting electric field traces a rose curve whose shape and orientation can be controlled by light parameters. A distinctive feature of BCL is its capability of simultaneously breaking time-reversal and spatial inversion symmetry, which has profound implications for the electronic properties of the driven system. We show that periodically driving a centrosymmetric material with BCL results in the emergence of intense second harmonic generation and bulk photovoltaic responses that are absent in equilibrium. We contrast the responses of Dirac semimetal and topological insulators and address their connection with photoinduced quantum geometry changes. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z19.00003: Optical control of slow topological electrons in moiré systems Christopher K Yang, Iliya Esin, Cyprian K Lewandowski, Gil Refael A fundamental feature of magic-angle twisted bilayer graphene is the presence of flat-electron bands with extremely low electron velocities. These flat bands appear over an even wider range of twist angles in periodically driven (Floquet) twisted bilayer graphene (TBG) [1-3] and allow phonon speeds to exceed that of electrons [7]. We show that the optically induced flat bands in THz laser driven TBG enable electrons carrying large Berry curvature to decouple from acoustic phonons. The resulting light-induced Hall response [4-6] exhibits sharp changes as a function of the laser amplitude. Our work suggests that the unique light-induced topological and transport physics in Floquet TBG are experimentally accessible and can be observed using simple experimentally available probes. We will discuss generalizations to UV-visible (high-frequency) laser-driven TBG, where the steady-state formation relies on an avalanche of scattering processes between many highly dispersive bands and the flat bands. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z19.00004: Driven Majorana Fermions: A Route to Synthetic px+ipy Superconductors Lingyu Yang, Gia-Wei Chern, Shi-zeng Lin We propose a protocol to realize mobile Majorana zero modes (MZMs) and effective px + ipy superconductors in the Kitaev model. By introducing a spatially modulated chemical potential, MZMs are stabilized at the boundaries between domains of normal and topological superconducting phases. Moreover, as the modulated chemical potential pattern varies with time, the MZMs travel with the moving domain walls. This time-dependent pattern can be viewed as a Majorana pump, which moves the localized zero modes from one end of the system to the other end. Importantly, analogous to the scenario of a Chern insulator induced by a Thouless pump, we show that the Majorana pump could lead to a px +ipy superconductor in the two-dimensional space of space and synthetic time. We analyze the periodic pumping of MZMs using the Floquet theory and demonstrate how the py pairing emerges even when there is only the px pairing in the original model. Finally, experimental realizations of the physics will be discussed. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z19.00005: Floquet-Driven Indirect Exchange Interaction mediated by Topological Insulator Surface States Modi Ke, Mahmoud M Asmar, Wang-Kong Tse Floquet engineering of matter through light irradiation has critical consequences on materials' properties and their functionalization. In this work, we study the magnetic exchange coupling between two parallel chains of magnetic impurities on the surface of a topological insulator. We develop a theory for the spin susceptibility and magnetic exchange of the irradiated system using the Floquet formalism. We find that, at high frequencies, light induces a dynamical band gap at the Dirac point, renormalizes the Fermi velocity of the surface states, and changes their spin textures. Our analytical and numerical analysis of the irradiated system reveals the effects of Floquet driving on the Ising, Heisenberg, and Dzyaloshinsky-Moriya exchange couplings. We show that in addition to the modification of the exchange oscillation period due to the light-induced band gap, light modulation of the surface states' spin textures plays a crucial role on the indirect exchange interaction. Our analysis also sheds light on the optimal set of light and material parameters for which our predictions of the optical control of collinear and non-collinear magnetic interactions can be observed. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z19.00006: Photo-induced Non-collinear Magnetic Exchange Interactions in Rashba Magnetic Multilayers Mahmoud M Asmar, Wang-Kong Tse Photon-dressing of electrons in light-driven materials is key to dynamically control the magnetic exchange coupling. In magnetic multilayers composed of spin-degenerate electron gases enclosed by ferromagnetic layers, periodic driving via irradiation facilitates the control of the indirect magnetic exchange interaction. However, their photo-irradiation does not induce non-collinear exchange couplings that are originally absent at equilibrium. Rashba semiconductors, such as BiTeI, exhibit a giant spin-orbit coupling arising from the lack of crystal inversion symmetry. At equilibrium, a Rashba magnetic multilayer, i.e., BiTeI sandwiched between two ferromagnetic layers along its stacking direction has an interlayer magnetic exchange interaction that uniquely consists of collinear components. In this work, we consider a monochromatically irradiated Rashba magnetic multilayer. In the high-frequency limit, we show that in addition to photon-dressing effects of the electronic bands, irradiation also considerably modulates the spin textures of photon-dressed bands. We also present our results on the generation and control of non-collinear exchange interactions mediated by photon-dressed electrons in Rashba magnetic multilayers. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z19.00007: Static Magnetization Induced by Motion of Dirac Nodes Priya Sharma, Pavlo Sukhachov, Alexander V. Balatsky We evaluate a static magnetization generated by dynamically driving nodal points in two-dimensional Dirac materials. The magnetization ∝ δK ×δK* originates from the transfer of angular momentum of the driving forces that move Dirac nodes K + δK in the Brillouin zone to the magnetic moment of electrons. Unlike semiclassical approximations, our microscopic calculation derives the induced magnetization through the non-linear corrections to the Green's function for electrons in the absence of applied magnetic fields. The generation of static magnetization by the motion of Dirac nodes illustrates an example from the emergent field of dynamical topological phenomena. The effect might find practical applications in the ultrafast manipulation of magnetization in quantum materials. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z19.00008: Photovoltaic effect by soft phonon excitation in ferroelectric BaTiO3 Yoshihiro Okamura The far-infrared/terahertz bands lack fast and sensitive detectors operated at room temperature despite various future applications. This limitation is mainly because the low-energy photovoltaic effect for the small-band-gap material inevitably suffers from thermal noise due to the intrinsically high conductivity. In this study, we demonstrate the shift current induced by soft-phonon excitations by using terahertz light without creation of electron-hole pairs in ferroelectric BaTiO3. The photocurrents caused by the soft-phonon excitation is as large as that for electronic excitation across the band gap, which can be well accounted for by the shift current model with the quantum-mechanical geometric phase considering the electron-phonon coupling, as supported by the first-principles calculation. Our findings suggest the novel principle for the high-performance terahertz photodetectors. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z19.00009: Driving and measurement based protocol to improve Majorana qubits Brett Min, Tami Pereg-Barnea, Kartiek Agarwal In [2,3], a series of dynamical protocols were proposed for dynamically decoupling [1] imperfect (overlapping) Majorana Zero Modes (MZMs) via periodic double braiding of MZMs from a nanowire and weakly coupled quantum dot (QD). In [2,3], the efficiency of the protocols crucially depend on the successful adiabatic Landau-Zener (LZ) transitions that periodically flip the parity of the QD thereby the nanowire which effectively realizes the double braiding of MZMs. We further improve the LZ transitions by using a spin-echo like protocol that is dynamically modified depending on the results of the measurements of the QD. By numerical simulation, we demonstrate that the novel measurement-protocol better suppresses the decoherence due to dephasing noise in Majorana qubits compared to the otherwise identical protocol in the absence of QD measurements. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z19.00010: Dynamically driven orbital magnetization beyond the adiabatic limit Wenqin Chen, Yafei Ren, Chong Wang, Ting Cao, Di Xiao Recently it has been shown that the adiabatic evolution of a periodically driven system can induce an orbital magnetization that is proportional to the driving frequency. Examples of driving include coherent chiral phonons and magnetization rotation. In this work, we numerically study the dynamically driven orbital magnetization of a toy model beyond the adiabatic limit. When the driving frequency is much lower than the band gap, our result agrees with previous theories in the adiabatic limit. In the high-frequency regime, it converges to the analytical result obtained from the high-frequency expansion. We also comment on the differences between the orbital magnetization driven by light and general driving mechanisms. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z19.00011: Measurement Induced Chirality II: Disorder and Diffusion Brian Jia Jiunn Khor We investigate the effects of (1) site blockade disorder, (2) random onsite potential, and (3) random hopping strength in measurement induced chirality on a system of free fermions on Lieb lattice, extending our earlier work [1]. In the Zeno limit, the chiral flow of particles for the site blockade disorder case undergoes percolation-like phase transition when measurement period T = 4π n. For the random onsite potential and random hopping model, the system under periodic measurement can be modelled as a random walk model on with random hopping probability on different links, and the chiral flow rate exhibits a crossover from unity to zero transport upon increasing disorder strength. Moving away from the Zeno limit will generally reduce the chiral flow continuously for all three disorder cases when one reduces the frequency of measurements per measurement protocol cycle. We also present analytical and numerical results on the diffusion transport of our measurement protocol in both clean and disorder cases. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z19.00012: Topological frequency conversion in rhombohedral graphene multilayers Etienne Lantagne-Hurtubise, Iliya Esin, Frederik Nathan, Gil Refael We investigate the phenomenon of topological frequency conversion -- characterized by a quantized rate of energy transfer between two monochromatic light sources -- in two-dimensional materials. We focus on rhombohedral graphene multilayers, which are promising candidates to realize this effect due to the Berry curvature of their low-energy bands which can be controlled by a perpendicular electric field. We find a topological conversion efficiency that is frequency independent and of order αL with α the fine structure constant and L the number of layers. We then discuss the important role of light polarization, highlighting potential cancellations between valleys, and comment on dissipation effects. |
Friday, March 10, 2023 1:54PM - 2:06PM |
Z19.00013: Integer and Fractionally Quantized Nonlinear Thouless Pumping Marius Juergensen, Sebabrata Mukherjee, Christina Jörg, Mikael C Rechtsman Thouless pumps are 1+1 dimensional reductions of Chern insulators for which one wavevector dimension is substituted with a periodic temporal modulation. As dimensionally reduced analogs of Chern insulators, Thouless pumps show topologically protected quantization of transport as long as the pump is adiabatic, the Fermi level is in the gap and interaction effects do not close the gap. Here, we demonstrate theoretically and observe experimentally, using a photonic system based on evanescently-coupled waveguides, that spatial solitons are transported by integer and fractionally quantized amounts per pumping cycle. These solitons form at high input power due to the optical Kerr effect. The dynamics of our system are well described by the focusing nonlinear Schrödinger equation (a.k.a. attractive Gross-Pitaevskii equation). We show analytically that low-power solitons track the motion of single-band Wannier functions and are thus pumped in a rigorously quantized fashion. For higher input power, solitons track the positions of maximally localized multi-band Wannier functions (equivalently, the multi-band Wilson loop eigenvalues), and thus exhibit fractional pumping. Finally, we numerically show that within the same model multiple plateaux of integer and fractionally quantized soliton transport appear as input power is varied. |
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