Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S07: Metal/Insulator and Superconductor/Insulator |
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Sponsoring Units: DCMP Chair: Nandini Trivedi, Ohio State University Room: BCEC 109B |
Thursday, March 7, 2019 11:15AM - 11:27AM |
S07.00001: Spin and charge dynamics of an interacting gas of small (bi)polarons across the mobility edge Gayan Hettiarachchi, Yoshifumi Nishida, Yusuke Masaki, Mohd Nazlan Mohd Muhid, Halimaton Hamdan We performed electron spin resonance (ESR) and optical studies on a model system that is used to investigate the discontinuous metal-insulator transition in a deformable lattice. The ESR signal below the mobility edge has no correlation to the conductivity and arises purely from a minority of magnetic polarons. Above the percolation threshold of the system and below the mobility edge, the intensity of the ESR signal shows a decrease suggesting that small polarons form paired states, i.e., small bipolarons, with increasing interactions. The conducting transition is marked by the appearance of an asymmetric ESR line shape simultaneously with a decrease in the small bipolaron optical absorption band. The delocalized states result from a partial dissociation of the small bipolarons. Immediately above the mobility edge, competing phases of delocalized (extended) states, small polarons, and small bipolarons coexist. Based on the experimental results, we propose a phase diagram that adds to the theoretical studies and highlight that the polaron density and local interactions are important parameters that determine the balance among competing states in a many-polaron system. |
Thursday, March 7, 2019 11:27AM - 11:39AM |
S07.00002: Renormalization group analysis of superconductor-insulator transition with disorder Chao-Jung Lee, Michael C Mulligan A recent experiment [1] indicates the magnetic field-tuned superconductor-insulator transition (SIT) in thin films can exhibit particle-vortex self-dual electrical conductivity. With the aim of understanding this quantum critical behavior, we consider a manifestly self-dual theory consisting of a Dirac fermion coupled to a Chern-Simons gauge field [2] in the presence of quenched disorder. We derive renormalization group fixed points of this theory in the presence of disorder and gauge fluctuations, which are controlled in an expansion in the number of fermion flavors. We then discuss the quantum critical conductivity of these fixed points. This formalism can also be used to understand quantum Hall plateau transitions. |
Thursday, March 7, 2019 11:39AM - 11:51AM |
S07.00003: New microscopic paradigms in the doped Fermi-Hubbard model Fabian Grusdt, Annabelle Bohrdt, Michael Knap, Eugene Demler The interplay of mobile dopants with anti-ferromagnetic spin correlations is at the heart of high-temperature superconductivity. Here we present a microscopic trial wavefunction describing individual dopants as spinon-chargon composites. We derive the correlations of the charges with their spin environment and reveal short-range hidden string order, which manifests in genuine higher-order correlations developing around the dopants and can be directly observed in state-of-the-art quantum simulations. Our microscopic model explains the observations of string patters and the dressing cloud of magnetic polarons in recent measurements performed with ultracold atoms in optical lattices. Our approach can be applied at finite doping and paves the way for a microscopic description of the exotic metallic phases in strongly correlated cuprate compounds. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S07.00004: Magnetism and correlation effects in titanium phosphate at high pressure Johan Jönsson, Marcus Ekholm, Igor Abrikosov Titanium phosphate exhibits interesting properties as pressure and |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S07.00005: Quantum electrodynamics of a superconductor-insulator quantum phase transition I: theory Vladimir Manucharyan, Roman Kuzmin, Ray Mencia, Nicholas Grabon, Nitish Jitendrakumar Mehta, Yen-Hsiang Lin We report on our experimental probing of the superconductor-insulator quantum phase transition (QPT) in a 1D Josephson chain in the high-frequency and short-wavelength limit [1]. By contrast, traditional experiments focus on finding a universal scaling of resistance with temperature and other system parameters. The quantum BKT transition resisted this approach for two decades. In part I, we overview the possible issues with the DC transport measurements and describe the advantages of viewing a QPT from the high-energy side. In part II, we show the results of our microwave spectroscopy of long chains of Al/AlOx/Al tunnel junctions. First, we find that an insulating chain can carry AC currents (in a GHz-band) as a near-perfect superconductor. Second, deviations from perfect superconductivity can be resolved. These deviations appear as frequency-dependent linewidths of the collective modes and as a scattering of their frequencies. Both effects arise from interactions and constitute the high-frequency footprint of the insulating phase near the critical point. Our new approach can help bridge theory with the experiments in chains, thin films, nanowires, and cold atom realizations of 1D systems. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S07.00006: Quantum electrodynamics of a superconductor-insulator quantum phase transition II: experiment Nicholas Grabon, Roman Kuzmin, Ray Mencia, Nitish Jitendrakumar Mehta, Yen-Hsiang Lin, Vladimir Manucharyan We report on our experimental probing of the superconductor-insulator quantum phase transition (QPT) in a 1D Josephson chain in the high-frequency and short-wavelength limit [1]. By contrast, traditional experiments focus on finding a universal scaling of resistance with temperature and other system parameters. The quantum BKT transition resisted this approach for two decades. In part I, we overview the possible issues with the DC transport measurements and describe the advantages of viewing a QPT from the high-energy side. In part II, we show the results of our microwave spectroscopy of long chains of Al/AlOx/Al tunnel junctions. First, we find that an insulating chain can carry AC currents (in a GHz-band) as a near-perfect superconductor. Second, deviations from perfect superconductivity can be resolved. These deviations appear as frequency-dependent linewidths of the collective modes and as a scattering of their frequencies. Both effects arise from interactions and constitute the high-frequency footprint of the insulating phase near the critical point. Our new approach can help bridge theory with the experiments in chains, thin films, nanowires, and cold atom realizations of 1D systems. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S07.00007: Structural investigation of the insulator-metal transition in NiS2−xSex compounds Sungkyun Choi, Garam Han, Hwanbeom Cho, Byungmin Sohn, Je-Guen Park, Changyoung Kim We report [1] on a combined measurement of high-resolution x-ray diffraction on powder and Raman scattering on single crystalline NiS2-xSex samples that exhibit the insulator-metal (IM) transition [2] with Se doping. Via x-rays, an abrupt change in the bond length between Ni and S (Se) ions was observed at the transition temperature, in sharp contrast to the almost constant bond length between chalcogen ions. Raman scattering, a complementary technique with the unique sensitivity to the vibrations of chalcogen bonds, revealed no anomalies in the phonon spectrum, consistent with the x-ray diffraction results. This indicates the important role of the interaction between Ni and S (Se) in the IM transition. The potential implication of this interpretation is discussed in terms of current theoretical models. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S07.00008: Quasi-periodic metal-insulator phase separation in strain engineered La0.66Sr0.33MnO3 thin films Xinzhong Chen, Lin Li, Xiaodong Fan, Zhijing Niu, Mengkun Liu, Changgan Zeng We report the electronic phase separation in the prototypical double exchange ferromagnet La0.66Sr0.33MnO3 (LSMO) thin films grown on LaAlO3 (LAO) substrate. We discovered a peculiar mesoscale stripe pattern that only occurs at specific film thickness, using the scattering-type scanning near-field optical microscope (s-SNOM) at the mid-infrared (mid-IR) frequencies. These novel quasi-periodic mesoscale metal-insulator-metal stripes are contributed to a subtle and delicate balance between the epitaxial strain and surface twin structure of the LAO substrate. Our work strongly suggests the possibility to control the metallicity via interface and strain engineering in strontium doped manganites. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S07.00009: Observation of a new collective mode involved in the Verwey transition in magnetite Carina Belvin, Edoardo Baldini, Ozge I Ozel, José Lorenzana, Nuh Gedik Magnetite (Fe3O4), the oldest known magnetic material, is a strongly correlated transition metal oxide that exhibits complex electronic and structural properties. Below the Verwey transition, the low-temperature insulating phase displays rich features, including the coexistence of charge and orbital orders whose detailed nature is still under debate. Using pump-probe spectroscopy, we photoexcite the system out of equilibrium with a tailored femtosecond laser pulse and examine the evolution of the coherent oscillations due to the system’s collective modes in the time domain. We observe signatures of a new mode that undergoes a dramatic softening as a function of laser fluence. We discuss the implication of this collective mode on the understanding of the Verwey transition. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S07.00010: Electron localization in 2D extended Hubbard model Hanna Terletska, Joseph Paki, Sergei Iskakov, Thomas Maier, Emanuel C Gull We use the Dynamical Cluster Approximation to study the finite temperature phase transitions in 2D extended Hubbard model. We find that non-local electron-electron interactions screen the local Hubbard interactions, stabilizing the Mott metal-insulator transition in 2D extended Hubbard model. We also investigate the effect of the temperature and non-local interactions on the competition between antiferromagnetism and charge order. We show that non-local correlations are important, and hence the non-local methods are needed for proper analysis of the phase transitions in this model. |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S07.00011: Amplitude (Higgs) mode at the superfluid-Mott glass transition Jack Crewse, Thomas Vojta
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Thursday, March 7, 2019 1:27PM - 1:39PM |
S07.00012: Resistive Switching as Nonequilibrium Phase Transition Jong E Han, Jiajun Li, Camille Aron, Gabriel Kotliar We investigate the quantum mechanical origin of resistive phase |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S07.00013: Interplay between superconducting and magnetic fluctuations in the doped 2D Hubbard model Anna Kauch, Felix Hörbinger, Gang Li, Karsten Held The importance of antiferromagnetism for d-wave type superconductivity has already been established within various theoretical methods [1]. In this work we focus on the doped regime, where the magnetic fluctuations become incommensurate [2]. The solution of the Hubbard model by parquet equations gives us the unique opportunity to treat fluctuations in all channels on equal footing. Using the victory parquet equations solver [3] we compute two-particle quantities in the 2D Hubbard model on square lattice in the parquet (PA) and dynamical vertex (DΓA) approximations [4][5]. In the parquet flavour of DΓA, the fully irreducible vertex is assumed to be local and it is obtained from dynamical mean-field theory (DMFT). The analysis of the particle-particle vertex as well as of the leading eigenvalues of the Bethe-Salpeter equations allow us to identify the dominant fluctuations and the symmetry of the pairing. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S07.00014: Effect of Spin-Selective Disorder on the Hubbard model. Rajesh Narayanan, Madhuparna Karmakar, Shashikant Singh Kunwar, Prabuddha Chakraborty We use a combination of Monte-Carlo techniques to study the effect of spin-selective disorder for both the repulsive and attractive Hubbard models. For the repulsive Hubbard model with spin-selective disorder, by using a determinant quantum Monte-Carlo scheme we show evidence for the existence of a metal-insulator transition for fillings away from half-fillings. We show that the metal-insulator transition is accompanied with a net-polarization of the fermionic fluid and a consequent saturation behavior in the susceptibility. For the case of the attractive Hubbard model at half-filling in the presence of spin-selective disorder, we use a real space based Monte-Carlo scheme to completely elucidate the ground state phase diagram. In particular, we compare and contrast the behavior at weak and strong disorder: In the limit of weak disorder gapless superconductivity obtains whereas in the limit of strong disorder a spin-selective Anderson transition is realized. The effect of thermal fluctuations on the phase diagram is also studied within this approach. |
Thursday, March 7, 2019 2:03PM - 2:15PM |
S07.00015: Percolative transport in the metal-insulator phase coexistence region of Mott organics Yuting Tan, Vladimir Dobrosavljevic The Mott metal-insulator transition of the organic triangular-lattice system k−(ET)2Cu2(CN)3 has recently been re-examined through low temperature DC [1] transport experiments. These results, displaying striking non-monotonous temperature dependence for a family of resistivity curves, have been previously interpreted in terms of the “continuous" (spinon-based) scenario for the transition. Here we theoretically re-examine the transport properties in this regime, and show that an alternative viewpoint [2], based in the dynamical mean-field theory (DMFT) and a percolation picture [3], naturally explains all the observed anomalies. According to this scenario, the transition assumes first-order character at low temperature, leading to percolative transport in the coexistence regime, which we study theoretically, reproducing the experimental trends. |
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