Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K70: Light-Induced Structural Control of Electronic Phases IIIFocus Recordings Available
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Sponsoring Units: DMP DCMP Chair: Wanzheng Hu, Boston University Room: Hyatt Regency Hotel -Jackson Park B |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K70.00001: Light-induced topological phases in oxide superlattices Invited Speaker: Vladimir A Stoica The curling dipolar texture of skyrmions and vortices in PbTiO3/SrTiO3 superlattices is not limited by the symmetry that is prescribed by the bulk crystal structure. I will present ultrafast snapshots of the vortex dynamics recorded with X-ray free electron lasers (XFEL) that reveal how polarization rotations evolve at the fundamental timescale of electronic and lattice excitations. Following intense terahertz excitation, collective modes emerge in the form of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales [1]. I will also discuss the single-shot photoinduced formation of polar vortex supercrystals [2], which are created via coherent and incoherent topological defect transformation pathways as observed by XFEL experiments. These results demonstrate that nanoscale polarization rotation is a promising avenue toward high frequency applications, circumventing slow domain wall motion in classic ferroelectrics. |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K70.00002: Energy dissipation via the lattice in nonlinear phononics: coupling pathways and scattering rates from first principles in LaAlO3 Sabrina J Li, Guru S Khalsa, Jeffrey Z Kaaret, Nicole A Benedek The nonlinear phononics mechanism involves the coherent optical excitation of infrared-active phonons that, via anharmonic coupling, induce large quasistatic, unidirectional displacement of Raman-active phonons. This process occurs on sub-picosecond timescales. On longer timescales, the motion of the IR phonon is damped and the system reaches a higher temperature via several energy and momentum transferring processes: electron-electron, phonon-phonon, and defect scattering. What are the pathways by which an excited IR-active phonon transfers energy to the other lattice degrees of freedom? We use first-principles theory together with symmetry considerations to explore phonon-phonon scattering in LaAlO3, an experimentally important nonlinear phononics material. We explore ways to quantify the contribution of low frequency modes in energy transfer, and attempt to better understand the time scales at play for different pathways so as to gain insight into ultrafast optical control of the crystal lattice. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K70.00003: An electrically controlled interlayer exciton trap Jedediah J Kistner-Morris, Trevor B Arp, Nathaniel M Gabor The formation of robust interlayer excitons in van der Waals (vdW) heterostructures requires a staggered band alignment, where electrons and holes are separated across two constituent layers. In WS2-MoSe2 heterostructures the close proximity of conduction band edges suggests that fine electrical tuning may be used to selectively trap or dissociate such excitons. Here, we report ultrafast photocurrent imaging studies of WS2-MoSe2 heterojunction devices using Multi-Parameter Dynamic Photoresponse Microscopy. We generate photocurrent images of the heterojunction response as a function of source-drain and gate voltages, laser power, and photon energy. We observe strong negative differential photoconductance (NDC) that evolves with source-drain and gate voltages. NDC occurs simultaneously with a peak in the two-body interaction rate within the junction. Moreover, we find that the interlayer exciton photocurrent resonance is highly sensitive to precise voltage tuning. Combining these effects we establish the phase space for robust interlayer exciton formation in WS2-MoSe2 heterojunctions. Our results highlight how heterojunction band alignment can be finely tuned to trap or dissociate interlayer excitons, providing a key stepping stone for vdW exciton quantum simulators. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K70.00004: Reorganization of CDW stacking in 1T-TaS2 by light and an in-plane electrical bias Weijian Li, Gururaj V Naik Light-matter interaction in strongly correlated materials is interesting because light can significantly alter the free energy landscape of strong correlations resulting in many new physical phenomena. Though light-induced changes in the lattice, electrical, and magnetic properties have been extensively studied before, linear optical constants and their sensitivity to stimuli remain much to be explored. Recently, we studied the optical properties of 1T-TaS2 under electrical bias and different illumination conditions. We observed fast tunable optical properties of this material arising from the reorganization of charge density wave (CDW) stacking. Our experimental investigation suggested that CDW domains in 1T-TaS2 can absorb low-intensity incoherent white light to switch their stacking configuration in a sub-microsecond timescale. The change in stacking configuration results in a unity-order change in refractive index at room temperature at illumination intensities of just 1-Sun. This stacking reorganization showed temperature dependence and persisted at lower temperatures. Further, the stacking reorganization under illumination favored a high-energy stacking configuration. Our investigation has provided an insight into the mechanism of tuning and demonstrated that light is a powerful probe to map and control the energy landscape of strong correlations in quantum materials. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K70.00005: Control of interlayer interactions in van der Waals materials using light Wenjing You, Emma M Cating-Subramanian, Siqi Wang, Xun Shi, Yingchao Zhang, Kai Rossnagel, Xiang Zhang, Henry C Kapteyn, Margaret M Murnane In quasi 2D materials, coherent lattice distortions can be induced by a femtosecond laser pulse to guide a material into thermally inaccessible states. Here we show that interlayer interactions play a significant role in stabilizing these light-induced metastable states in 1T-TaSe2, a material that supports an in-plane charge density wave (CDW) breathing mode. By combining multi-pulse excitation with time- and angle- resolved photoemission spectroscopy and ultrafast reflectivity, we made a surprising finding: although the band structure of the metastable CDW states were dramatically different from the ground state, the in-plane breathing mode frequency did not change. Density functional theory calculations provided further evidence of the importance of interlayer interactions and out‑of‑plane configuration, in ultrafast electronic dynamics and unique metastable atomic structures in this van der Waals material. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K70.00006: Light-induced dimension crossover dictated by excitonic correlations Alfred Zong, Yun Cheng, Anshul Kogar, Jun Li, Wei Xia, Shaofeng Duan, Wenxuan Zhao, Yidian Li, Fengfeng Qi, Jun Wu, Lingrong Zhao, Pengfei Zhu, Xiao Zou, Tao Jiang, Yanfeng Guo, Lexian Yang, Dong Qian, Wentao Zhang, Michael W Zuerch, Dao Xiang, Jie Zhang Strong electronic correlation coupled with reduced dimensionality is a key driver for novel states in condensed matter, giving rise to the fractional quantum Hall effect, unconventional superconductivity, and Wigner crystallization. When these low-dimensional systems are subjected to an ultrafast laser pulse, the carriers excited abruptly modify the many-body Coulombic interaction, yielding a variety of metastable states that greatly expand the equilibrium phase diagram of quantum materials. The central challenge in understanding such phenomena is to determine how dimensionality and many-body correlations govern the pathway of a non-adiabatic transition. To this end, we examine a layered compound, 1T-TiSe2, whose three-dimensional charge-density-wave (3D CDW) ground state also features exciton condensation due to strong electron-hole interactions. Using ultrafast electron diffraction, we find that light excitation suppresses the equilibrium 3D CDW while creating a nonequilibrium 2D density wave. Remarkably, the dimensional reduction in 1T-TiSe2 does not occur unless bound pairs of electrons and holes are first broken. This relation suggests that excitonic correlations maintain the out-of-plane CDW coherence, settling a long-standing debate over their role in the CDW transition. Our findings demonstrate how optical manipulation of electronic interaction enables one to control the dimensionality of a broken-symmetry order, paving the way for realizing other emergent states in strongly correlated systems. |
Tuesday, March 15, 2022 4:36PM - 4:48PM |
K70.00007: Single-shot real-time tracking of a light-induced metastable phase transition in an electronic crystal Frank Y Gao, Zhuquan Zhang, Linda Ye, Yu-Hsiang Cheng, Zi-Jie Liu, Joseph G Checkelsky, Edoardo Baldini, Keith A Nelson Metastable hidden phases are long-lived states that are typically inaccessible in equilibrium phase diagrams but can emerge under dynamic stimuli, such as tailored laser excitation. Understanding the evolution of these states is of both fundamental and practical significance, allowing the exploration of nonequilibrium thermodynamics and the development of optoelectronic devices with on-demand photoresponses. However, probing the ultrafast formation of a metastable hidden phase remains a long-standing challenge in physics since the initial state of the system is not recovered rapidly. Here, using a suite of state-of-the-art single-shot spectroscopy techniques, we present a direct ultrafast visualization of the photoinduced phase transition to a metastable hidden state in an electronic crystal, 1T-TaS2. Capturing the dynamics of this complex phase transformation in a single-shot fashion demonstrates a commonality in microscopic pathways that the system undergoes to enter the hidden state and provides unambiguous spectral fingerprints that distinguish such state from thermally accessible phases. Our finding dispels much of the debate surrounding this elusive hidden phase and presents a critical tool for the discovery of new exotic phenomena in quantum materials. |
Tuesday, March 15, 2022 4:48PM - 5:00PM |
K70.00008: Electron and phonon dynamics across the photoinduced charge density wave transition in 1T-VSe2 Charles Sayers, Giovanni Marini, Hamoon Hedayat, Xuanbo Feng, Erik van Heumen, Christoph Gadermaier, Stefano Dal Conte, Matteo Calandra, Giulio Cerullo 1T-VSe2 undergoes a charge density wave (CDW) transition at 110 K which results in gaps opening around the Fermi surface together with a 4a x 4a lattice distortion, and the appearance of exotic collective modes [1]. In equilibrium, the CDW state has been associated with both electronic correlations (i.e. nesting) [2] and electron-phonon interactions [3]. Here, we use ultrafast optical spectroscopy to simultaneously track the out-of-equilibrium electron and phonon dynamics across the CDW transition. At 4.3 K, we observe well-resolved coherent oscillations of the CDW amplitude mode (~1.4 THz) triggered by the optical excitation. Upon increasing laser fluence, a photoinduced phase transition occurs from the CDW to normal phase structure, evidenced by a switching of the dominant oscillation frequency from ~1.4 to ~6.2 THz, and a dramatic change in the carrier dynamics. A temperature-dependent study (4.3 – 295 K) allows us to compare the characteristics of the photoinduced transition with the thermal transition. Our results are supported by theoretical calculations of the phonon dispersion and the stability of the CDW structure under photoexcitation. |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K70.00009: Quantum Domain Melting in an Electronic Crystal and Its Simulation With a Quantum Computer Jaka Vodeb The ordering of systems emerging through non-equilibrium light induced transitions is commonly accompanied by domain formation. The underlying microscopic physics that defines the system's energy landscape for tunneling between domain configurations is of interest in many different areas. Domains may reconfigure by thermally-driven microscopic processes, or - in quantum systems - by macroscopic quantum tunneling. Here, we report quantum domain melting in two embodiments: an electronic crystal 1T-TaS2, and its matching simulation on a quantum computer. We use scanning tunneling microscopy to measure the time-evolution of electronic domain reconfiguration dynamics, and compare this with the time evolution of domains in an ensemble of entangled correlated electrons in simulated quantum domain melting. The domain reconfiguration is found to proceed by tunneling in an emergent, self-configuring energy landscape, with remarkable correspondence between a quantum charged lattice gas model and experiment. Understanding the quantum processes involved in electronic domain melting opens the way to experimental observation and modelling mesoscopic emergent behaviour in non-equilibrium interacting many-body quantum systems at the microscopic level. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K70.00010: Ultrafast nanoimaging of the order parameter in a structural phase transition Till Domröse, Thomas Danz, Claus Ropers Optical control strategies as applied in modern-day devices are based on a profound understanding of the interplay between various degrees of freedom in out-of-equilibrium scenarios. In this context, the presence of spatial inhomogeneities is of particular interest as functionality is often based on spatially dependent response to the external stimulus. Ultrafast transmission electron microscopy (UTEM) is a powerful tool capable of unravelling such ultrafast processes in heterogeneous systems by means of imaging, diffraction and spectroscopy [1,2]. |
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