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 B30: Metal-Insulator Transitions: Experiment |
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Sponsoring Units: DCMP Chair: Tika R Kafle, JILA, UCB Room: Room 222/223 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B30.00001: Quantifying Joule heating in voltage-biased VO2 thin films using atomic force microscopy Jason D Hoffman, Alyson Spitzig, Dilek Yildiz, Jennifer Hoffman Vanadium dioxide (VO2) undergoes a thermally-driven insulator-to-metal transition (IMT) when heated above 341 K, making it a promising material for oxide electronic applications. The IMT has also been observed in voltage-biased films as a sharp jump in the measured current when the voltage is increased. The roles of Joule heating, electric field effects, and charge injection in the IMT are poorly understood and actively studied. |
Monday, March 6, 2023 11:42AM - 11:54AM |
B30.00002: Band structure effects of a current-induced Mott-insulator to metal transition in Ca2RuO4 Philip Hofmann, Davide Curcio, Alla Chikina, Charlotte E Sanders, Marco Bianchi, Henriette E Lund, Veronica Granata, Marco Cannavacciuolo, Pavel Dudin, Jose Avila, Craig Polley, Balasubramanian Thiagarajan, Giuseppe Cuono, Filomena Forte, Mario Cuoco, Carmine Autieri, Antonio Vecchione The Mott insulator Ca2RuO4 can be turned into a metal by the application of a weak electric field and a corresponding transport current. This transition affects the optical and magnetic properties of the material. However, because of the electric field's presence and the field-induced energy broadening, it is challenging to determine the electronic structure in the metallic state by angle-resolved photoemission spectroscopy (ARPES). Making use of the recently introduced approach to enable ARPES measurements of current-carrying devices by using a nano-scale light spot [1], we are able to measure ARPES data that tracks the current-induced phase transition in Ca2RuO4 simultaneously with the electrical transport, revealing the spectral function of the current-induced state along with a potential map of the sample's surface. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B30.00003: Electronic correlation in single crystals of bi-intercalated vanadium pentoxide Nicholas C Jerla, George Agbeworvi, Sarbajit Banerjee, Sambandamurthy Ganapathy Vanadium oxide bronzes exhibit a variety of structural and electronic properties such as charge ordering or metal-insulator phase transition due to correlated electron behavior that can be enhanced by external stimuli. The distinct phases observed in these materials can be tuned through the introduction of intercalated ions within the crystal structure. In this study, the effects of systematic bi-intercalation of Pb and Cu into the vanadium pentoxide crystal structures are explored through a series of electrical transport measurements in single crystals of β-PbxCuyV2O5. Current-voltage characteristics show abrupt and hysteretic resistive switching behavior from a low conducting state to a high conducting state due possibly to the destruction of charge ordering. Resistance noise spectroscopy is performed as a function of temperature and electric field to understand the charge carrier dynamics across the resistive switching transitions. Significant increases are seen in the power spectral density of the residual resistance fluctuations near the threshold voltage pointing to the presence of tunable correlated electron behavior in these materials. The understanding of this correlated electron behavior enhanced by the intercalated ions and their transport will yield insights on how to synthesize materials with desirable electronic properties. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B30.00004: Controllable oscillations driven by resistive switching transitions in single crystals of vanadium oxide bronzes Nitin Kumar, Nicholas C Jerla, George Agbeworvi, Sarbajit Banerjee, Sambandamurthy Ganapathy Vanadium oxide bronzes (MxV2O5, M = Cu, Pb, and Na) exhibit a variety of correlated electronic behavior controlled by external stimuli such as electric field and temperature. Transport characteristics of ε-CuxV2O5 and β-CuxPbyV2O5 single crystals are studied, and the current-voltage (IV) characteristics show abrupt transitions from a low conductance to a high conductance state with distinct hysteretic behavior. The switching transitions in two-terminal devices of vanadium oxide bronzes have the potential to be exploited in neuromorphic computing applications as synaptic devices (relaxation oscillators) owing to their potential efficiency and scalability. Relaxation oscillators with sustainable oscillations are demonstrated in these bronzes using a simple RC circuit and external parameters such as switching voltage, resistor/capacitor values significantly alter the oscillations and are tuned to produce oscillators with tunable frequency range. The coexistence of conducting and non-conducting phases and the means to electrically control the switching to tune the oscillations will be discussed. In addition to applications in neuromorphic computing, the switching transitions and the resulting oscillators are excellent model systems to study nonlinear dynamics and to extract electrical and thermal transport parameters useful for computing applications. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B30.00005: Glassy electrons at the first order Mott metal-insulator transition Saurav Islam, SHREYA KUMBHAKAR, Zhiqiang Mao, Yu Wang, Arindam Ghosh The Mott metal-insulator transition remains one of the most scrutinized concepts in condensed matter physics. However, the kinetics of the charge carriers at the transition, involving both orbital and spin degrees of freedom, still remains poorly understood. A perfect platform to distinguish between the role of such competing interactions is strongly correlated oxides offering rich phase diagrams, which we use here to address the electron kinetics at the transition. We show a critical slowing down of electron kinetics at the first order metal to Mott insulator transition in the Ruddlesden Popper oxide Ca3(Ru0.9Ti0.1)2O7 using low-frequency noise in resistance fluctuations. Critical slowing down of the electron kinetics is manifested as an enhancement of noise by an order of magnitude at the transition with a large shift of the spectral weight to lower frequencies. The second spectrum of noise is frequency dependent, indicating the presence of correlated fluctuations which gets suppressed under the application of a magnetic field. Our experiments provide compelling evidence of the formation of a spin-glass phase at the transition in these systems. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B30.00006: Atomic-scale imaging of insulator to metal transition in Ru-doped Sr2IrO4 Hong Li, Zachary Porter, Ziqiang Wang, Stephen D Wilson, Ilija Zeljkovic Layered Iridium-oxides (iridates) have attracted a lot of attention for unconventional electronic phenomena at the intersection of magnetism and strong spin-orbit coupling. Single-layer Sr2IrO4 in particular has been widely studied due to its Jeff=1/2 Mott insulating state and intriguing parallels to high-Tc cuprates. In this talk, I will discuss our scanning tunneling microscopy (STM) and spin-polarized STM experiments on cleaved bulk single crystals of Ru-doped Sr2IrO4. In particular, we study the insulator-to-metal transition in Sr2IrxRu1-xO4. We visualize large spatial variations in the local density of states across this transition and explore the connections to the Lifshitz transition. Our experiments provide new atomic-scale insights into the insulator-to-metal transition in heavily Ru-doped iridates. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B30.00007: Reversible control of MIT in VO2 heterostructure using electric double layer transistor Smruti Rekha R Mahapatra, Debasish Mondal, Naga Phani B Aetukuri Vanadium dioxide (VO2) undergoes a temperature-driven metal-to-insulator transition (MIT) near room temperature. The transition temperature (TMIT) of VO2 can be varied by external perturbation like atomic doping, strain in thin films, or by applying an external electric field using an electric double-layer transistor (EDLT). However, all these methods depreciate the crystal structure by creating atomic defects and hence making this MIT irreversible. In this study, we demonstrate a reversible control of MIT in VO2 using an electric double-layer transistor (EDLT), fabricated on VO2-based modulation-doped heterostructure. Atomically smooth single crystalline VO2 (001) heterostructures (10 nm thick) were grown using pulsed laser deposition. We first discuss device fabrication protocols that we employed to ensure that the MIT in fabricated devices is unchanged during fabrication. Next, using EDLT measurements, we discuss the possibility of reversibly controlling the resistivity change of VO2 heterostructures across the metal insulator transition. We further discuss the implications of our research for a pure electronic control of MIT in VO2. |
Monday, March 6, 2023 12:54PM - 1:06PM Author not Attending |
B30.00008: Pure electronic control of metal-insulator transition in VO2 Debasish Mondal, Smruti R Mahapatra, Abigail M Derrico, Jay R Paudel, Rajeev K Rai, Christoph Schlueter, Pavan Nukala, Alexander X Gray, Naga Phani B Aetukuri The strong electronic correlation in d-orbitals enforces VO2 to undergo a metal-to-insulator transition (MIT) at TMIT (~341 K). The control of TMIT by carrier doping or modifying strain is a well-known technique that enhances the applicability of VO2 and offers a platform for a better understanding of MIT. However, it is hard to control MIT without affecting any changes to the lattice. For example, the control of MIT in VO2 by elemental doping, strain, or oxygen vacancy creation all affect the lattice parameters of VO2. In this work, we present VO2-based modulation-doped heterostructures to control the MIT in VO2. Atomically sharp and coherently strained single-crystalline VO2 (001) heterostructures were grown with VO2 thicknesses from 1.5 nm to 9.5 nm which result in a coherent reduction of TMIT by ~65 K. Using Hall measurements, we show that the reduction in MIT corresponds to an increase in electron densities without any measurable changes in the lattice parameter (CR). HAXPES spectra of V2p and V3d further confirm the existence of interfacial band bending of VO2 due to carrier doping. We show that the MIT in VO2 is robust even in the presence of carrier densities as high as 9x1021 cm-3. Our studies open the possibility of studying MITs in correlated electron materials under pure electronic control. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B30.00009: Epitaxial strain engineering of a high-entropy oxide RANJAN K PATEL Finding new materials and new ways to tune material’s properties are essential to fulfil the |
Monday, March 6, 2023 1:18PM - 1:30PM |
B30.00010: Investigating the Insulator to Metal transition in Hole Doped NdNiO3 using Time-Domain THz Spectroscopy Sahaj Patel, Yinchuan Lv, RANJAN K PATEL, Nandana Bhattacharya, Ameya Patwardhan, Srimanta Middey, Fahad Mahmood NdNiO3, a rare earth nickelate with a perovskite structure, displays an insulator-to-metal transition (IMT) and an antiferromagnetic transition around 160 K. However, if one hole dopes the system with calcium to form Nd1-xCaxNiO3, the IMT is suppressed. We investigate the nature of this transition using time-domain terahertz (THz) spectroscopy (TDTS). Furthermore, we use time-resolved optical pump THz probe spectroscopy to map the dynamical change in the optical conductivity of these systems as a function of doping and temperature. We will discuss these results in the context of the competing structural and magnetic order in rare earth nickelates. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B30.00011: Critical behavior of the specific heat in Ti-Si amorphous alloys at the metal-insulator transition: possible observation of many body localization Andrey Rogachev We report the measurements of specific heat of an amorphous Ti-Si alloy located very close to the critical point of the metal-insulator transition. The electronic specific heat coefficient gamma was is temperature-independent above 2 K and is, in order of magnitude, close to the value expected in the absence of electron-electron interactions. In the temperature range 0.4-1.5 the coefficient shows an anomalous downturn, which can be approximated by the logarithmic dependence and approximated to become zero at 0.2 K. In a companion paper, we found that the Hall coefficient in Ti-Si alloys is affected by the electron-electron interaction up to much higher temperature of 150 K and also varies critically across the metal-insulator transition. We compare our results with theoretical predictions for three models, which can potentially explain the anomalous behavior of the specific heat: generalized non-linear sigma model, Coulomb glass, and many-body localization. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B30.00012: Electronic structure changes in Ca2RuO4 under DC current as observed with angle-resolved photoemission Cissy Suen, Igor Markovic, Marta Zonno, Sergey Zhdanovich, Sergey Gorovikov, Aaron Bostwick, Eli Rotenberg, Bernhard Keimer, Andrea Damascelli, Christopher Jozwiak, Maxmilian Krautloher The quasi-two-dimensional Mott insulator Ca2RuO4 exhibits a convergence of spin-orbit coupling and electron correlations that lead to exciting quantum phenomena, including a rare insulator-to-metal transition induced by a DC current. While structural changes have been tracked in neutron diffraction, Raman scattering, and x-ray studies, associated electronic changes have yet to be observed. We report the first angle-resolved photoemission spectroscopy (ARPES) results that track a change in the dispersion of the ruthenium t2g bands of a bulk Ca2RuO4 crystal in four-probe configuration. These results provide insight into the curious nature of the current-induced transition and advances the difficult technique of conducting photoemission while a current runs through the sample. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B30.00013: Ionic Liquid Gating Induced Resistance Modulation of LaNiO3 Thin Films Richmond Wang, Jihun Park, Suraj Maurya, Rohit Pant, You Zhou, Ichiro Takeuchi LaNiO3 (LNO) is the only perovskite rare-earth nickelate without a metal-insulator transition (MIT) in its bulk form1–3. One possible reason is the atomic radius of La, leading to a larger Ni-O-Ni bond angle1,2. Strain control2 or CaH2 reduction4 has been shown to control the oxygen vacancy concentration and the Ni valence state of these materials, which can induce an insulating phase transition. Electrolyte gating can be an efficient alternative to control such properties in a reversible and controllable way3. In this study, we utilize electrolyte gating with ionic liquids to realize a MIT in LNO thin films. These gated LNO films exhibit an increase in the resistance (> 5 x 105), accompanying a transition from metallic to insulating behavior. Such behavior can be reversibly controlled based on the duration and magnitude of the gate voltage. The Ni valence state and oxygen vacancy content in the gated films will be discussed based on the effect of gate voltage in LNO. These results reveal that ionic liquid gating can enhance electron-electron correlation, opening up the possibilities of realizing exotic physics in perovskite nickelates, such as MIT, infinite-layer nickelates, or superconducting phase transitions4–6. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B30.00014: Tuning the electronic ground state of perovskite nickelates with dynamic electrochemical doping Alan Zhang, Catalin D Spataru, A. Alec Talin, Elliot J Fuller The rare earth nickelates have received renewed attention due to the discovery of superconductivity in infinite layered structures under appropriate electron filling via substitutional doping(1). Therefore, methods to study the electronic phase diagram in nickelate compounds are of interest. Here, we present work on doping PrNiO3 using a dynamic electrochemical process. We construct electrochemical cells using epitaxial thin films as electrodes and then insert lithium using an ionic liquid electrolyte. For LixPrNiO3, we find that the ground state evolves from an insulator (due to charge disproportionation) to a metal and finally back to an insulator under increasing x (or electron filling). This contrasts with previous work with substitutional doping where electron (or hole) dopants evolve the ground state only to the metallic state(2). We additionally report on the evolution of the metal insulator transition that occurs under these doping conditions. Based upon recent studies by resonant inelastic x-ray scattering(3, 4) we hypothesize that the differences with substitutional doping lie in the fact that lithium dopants introduce less strain and defects in the host lattice compared to other methods used to tune bulk electron filling(5). |
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