Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J56: Mott Physics Theory and Calculations |
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Sponsoring Units: DCMP Chair: Congjun Wu, University of California, San Diego Room: Mile High Ballroom 2C |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J56.00001: Filament dynamics in Mott insulators Javier Del Valle Granda, Nicolas M Vargas, Pavel Salev, Paul Y Wang, Pavel Lapa, Yoav Kalcheim, Coline Adda, Minhan Lee, Federico Tesler, Lorenzo Fratino, Marcelo Rozenberg, Ivan Schuller Resistive switching, a phenomenon in which the resistance of a device can be modified by applying an electric field, is the basis for emerging technologies such as neuromorphic computing. Volatile switching is specially promising, as it may allow for the implementation of artificial spiking neurons. This type of switching is observed in Mott insulators featuring an insulator-to-metal transition which can be triggered by applying an external voltage: the material becomes conducting if a threshold is exceeded. Such switching takes place in a filamentary fashion. |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J56.00002: The Mott transition as a topological phase transition Patrick J Wong, Sudeshna Sen, Andrew Mitchell We show that the Mott metal-insulator transition in the standard one-band Hubbard model can be understood as a topological phase transition. The approach is inspired by the observation that the Mott pole in the self-energy is pinned throughout the insulating phase, similar to the zero-energy spectral pole corresponding to a localized surface state in topological systems. We use NRG-DMFT to solve the infinite-dimensional Hubbard model, and represent the resulting local self-energy in terms of the boundary Green's function of an auxiliary tight-binding chain without interactions. We find a rich structure in the parameters of the auxiliary chain, which we show are of generalized SSH model type. The Mott transition corresponds to a topological phase transition in this auxiliary system, characterized by its analytic properties. We devise simple toy models for the auxiliary chains that capture the basic physics of the metallic and insulating Hubbard model phases, as well as in the scaling limit near the transition. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J56.00003: Parting the Fermi Sea at the Mott Point: Dynamics of Correlated Electrons Reveals the Mechanism Underpinning Mottness Yuting Tan, Andrej Pustogow, Roland Rösslhuber, Ece Uykur, Annette Böhme, Anja Löhle, Ralph Hübner, John A Schlueter, Vladimir Dobrosavljevic, Martin Dressel By increasing the interaction among conduction electrons, a Fermi-liquid-type metal turns into a Mott insulator. This first-order phase transition should exhibit a regime where the adjacent ground states coexist, leading to electronic phase separation, but the range near T=0 remained unexplored because it is commonly concealed by antiferromagnetism. Here we map the genuine low-temperature Mott transition by applying dielectric spectroscopy under pressure to quantum-spin-liquid compounds. The dielectric permittivity uniquely distinguishes all conduction regimes around the Mott point, allowing us to reliably detect insulator-metal phase coexistence below the critical endpoint. Via state-of-the-art theoretical modeling we establish the coupling between segregated metallic puddles as the driving source of a colossal peak in the permittivity reaching ε1≈105 within the coexistence region. Our results indicate that the observed inhomogeneities are the consequence of phase separation emerging from strong correlation effects inherent to Mottness,suggesting a similar ’dielectric catastrophe’ in other correlated materials. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J56.00004: Kinetics of thermal Mott metal-insulator transition in the Hubbard model Gia-Wei Chern We present the first-ever microscopic dynamical simulation of the temperature-controlled Mott metal-insulator transition in the Hubbard model. By combining the efficient Gutzwiller method with molecular dynamics simulations, we demonstrate that the transformation from the correlated metal to the Mott insulator proceeds via the nucleation and growth of the Mott droplets. We show that after an initial incubation period, the early stage of the phase transformation is characterized by a constant nucleation rate and an interface-controlled cluster growth mechanism, consistent with the classical theory developed by Kolmogorov, Johnson, Mehl, and Avrami. This is followed by a novel intermediate stage of accelerated phase transformation that is characterized by avalanche behavior similar to the Barkhausen noise in magnetization dynamics. The implications of our findings for the recent nano-imaging experiments on metal-insulator transition of correlated materials are also discussed. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J56.00005: Nature of Mott transition in a hydrogen lattice Zijian Lang, Sudeshna Sen, Vladimir Dobrosavljevic, Wei Ku Mott transition, an electron correlation induced metal-insulator transition, has long been realized in many materials. Yet, the microscopic nature of the transition proposed by Mott has not been carefully examined in these materials, even by modern theories. This is because Mott's original proposal makes use of non-linear change of screening of long-range Coulomb interaction that are almost always ignored in simple models used in previous study of Mott transition. Here we study the Mott transition of an artificial hydrogen lattice including both the long-range Coulomb interaction and the strong on-site correlation, via a dynamical mean-field extension of density functional calculation. We found that in the relevant range of lattice spacing, the system is in the charge-transfer regime, namely the charge fluctuation involves mostly higher energy orbitals beyond 1s one, rendering a single-band Hubbard model inadequate. Our study challenges Mott's original microscopic picture and reveal some key physics of metal-insulator transition in realistic materials. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J56.00006: Mott Insulating States of Anisotropic SU(4) Dirac Fermions Yu Wang, Han Xu, Congjun Wu We employ large-scale projector quantum Monte Carlo simulations to study the ground-state properties of the SU(4) Hubbard model on a square lattice with a staggered flux configuration. By varying the on-site repulsion and the flux, our simulations demonstrate phase transions between the Dirac semimetal, antiferromagnetic (AFM) and valence-bond-solid (VBS) phases. We find a continuous AFM-VBS phase transition. The direct second-order transition between different symmetry-breaking phases suggests deconfined critical points which form the boundary between the AFM and VBS phases. Near the deconfined critical points, we show that the AFM and VBS Binder ratios have the same critical exponents. As Hubbard U increases, the VBS order drops to zero, while the AFM moment has a finite value in the Heisenberg limit. It infers that the system with any flux eventually enters the AFM phases with increasing Hubbard U. By analysis of the gap opening mechanism, it is shown that both the columnar VBS ordering and the plaquette VBS ordering emerge in the VBS phase, and thus the phase diagram features two tricritical points where the semimetal, AFM and VBS phases meet. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J56.00007: Pseudogap, van Hove Singularity, Maximum in Entropy and Specific Heat for Hole-Doped Mott Insulators Alexis Reymbaut, Simon Bergeron, R. Garioud, M. Thénault, Maxime Charlebois, P. Sémon, Andre-Marie Tremblay The first indication of a pseudogap in cuprates came from a sudden decrease of NMR Knight shift at a doping-dependent temperature T*. Since then, experiments have found phase transitions at a lower T*phase(δ). Using plaquette cellular dynamical mean-field for the square-lattice Hubbard model at high temperature, where the results are reliable, we show that T*(δ) shares many features of T*phase(δ). The remarkable agreement with several experiments, including quantum critical behavior of the electronic specific heat, supports the view that the pseudogap is controlled by a finite-doping extension of the Mott transition. We propose further experimental tests. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J56.00008: Superconducting instability in an exactly solvable model of a doped Mott insulator Philip Phillips, Luke Yeo, Edwin Huang Regarding the cuprate superconductors as doped Mott insulators, we solve a toy model that exhibits both Mottness and superconductivity. We show that the Hatsugai-Kohmoto model, an exactly solvable model exhibiting a non-trivial Mott insulator-to-non-Fermi liquid metal transition, exhibits a superconducting instability. The instability is present in the non-Fermi liquid metal phase at half-filling, persists for a wide range of dopings away from half-filling, and terminates once the Mott parameter exceeds a critical strength. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J56.00009: Intertwined Mott insulating behavior, magnetic quantum criticality, and superconductivity in a two-band Hubbard-like model: A Quantum Monte Carlo study Morten Holm Christensen, Xiaoyu Wang, Yoni Schattner, Erez Berg, Rafael Fernandes The interplay between superconductivity and magnetism in correlated systems is an outstanding question in condensed matter physics. It has been recently shown that the two-band spin-fermion model, in which electrons interact with pre-existing magnetic fluctuations, can be simulated by Quantum Monte Carlo (QMC) without the fermionic sign-problem. Here we go beyond this approach and present sign-problem-free QMC results of a two-band microscopic model in which both superconductivity and magnetism arise from the very same inter-band repulsion, without pre-existing bosons mediating the electronic interactions. Our simulations reveal the interplay between a host of different phenomena as the interaction strength is increased. A wide magnetic dome appears at moderate values of the interaction, whereas a narrow superconducting dome emerges around the magnetic quantum critical point located on the less strongly correlated side of the phase diagram. Interestingly, a Mott transition is nearly coincident with this magnetic phase boundary, and is manifested by a change in the magnetic dynamics from overdamped to propagating. The emergence of superconductivity only in the former region provides important clues about the nature of the pairing glue in unconventional superconductors. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J56.00010: Excitons in Mott insulator Tsung-Sheng Huang, Christopher Baldwin, Mohammad Hafezi, Victor Galitski We study the behaviors of excitons formed by spinless charges in the antiferromagnetically ordered phase of Mott insulators. We start from the slave fermion Hubbard model with linear spin wave approximation on the bosonic spinons and obtain the dispersion of dressed doublons and holons using self-consistent Born approximation. We derive the Bethe-Salpeter equation for the two particle Green's function of dressed doublon and holon to find the bound states between a doublon and a holon and identify them as excitons. We investigate several properties of Mott excitons. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J56.00011: Block-spiral magnetism of the low-dimensional orbital-selective Mott phase Jacek Herbrych, Jonas Heverhagen, Gonzalo Alvarez, Maria Daghofer, Adriana Moreo, Elbio Dagotto Competing interactions can lead to novel states of matter including frustrated magnetism, an extensive field of research both from the theoretical and experimental perspectives. Here, we show that competing energy scales present in the low-dimensional orbital-selective Mott phase (OSMP) induce an exotic magnetic order, never reported before. Neutron scattering experiments on iron-based 123 ladder materials (where OSMP is relevant) already confirmed theoretical prediction of block-magnetism (magnetic order of the form ↑↑↓↓). Now we argue that another novel phase can be stabilized in multiorbital Hubbard models, i.e., ``block-spiral state''. In the latter, the magnetic islands form a spiral propagating through the chain but with the blocks maintaining their identity, namely rigidly rotating . This complex spiral state is stabilized without any apparent frustration. Phenomenological simpler models that accurately capture both electronic and spin degrees of freedom are also discussed. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J56.00012: Local structural study of novel mott-insulating cousins of the iron pnictides Bhupendra Karki, Alaa Alfailakawi, Benjamin Frandsen, Minghu Fang, M. S. Everett, Joerg C. Neuefeind, Byron Freelon Iron oxy-chalcogenides, La2O2Fe2OM2 (M = S, Se), is the layered materials formed from stacking layered units of La2O2 and Fe2OM2 (M = S, Se). We describe the structural properties of the La2O2Fe2OM2 (M = S, Se), by using pair distribution function (PDF) analysis and Rietveld refinement methods applied to neutron diffraction data. Our results show that M = S and Se possess similar nuclear structure at low and room temperatures. Local crystal structure was studied by investigating deviations in atomic positions and orthorhombicity. By tracking the orthorhombicity parameter, we observe the local scale distortions between the tetragonal and orthorhombic structure in a typical range of 1-2 nm. These spatially limited distortions represent fluctuating nematic order which suggests the ubiquity of nematic fluctuations in iron-based superconductors and related materials. In addition, we found the discontinuity in c-lattice which may arise due to the buckling of Fe2O plane. We anticipate that this buckling might be due to the change in octahedral height or tilting of the octahedral structure. Overall, these results suggest that the structural distortion may play a role in absence of superconductivity in these materials. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J56.00013: Pseudogap transition within the superconducting phase in the three-band Hubbard model Sidhartha Shankar Dash, David Senechal We use cluster dynamical mean field theory on a three-band Hubbard model for high-Tc superconductors to study the superconducting phase at zero temperature, obtained when doping the charge transfer insulator, for several values of U. We observe a first-order transition within the superconducting phase, which separates the so-called underdoped and overdoped solutions. The transition to the underdoped solution is marked by a jump in the spectral gap, and on further underdoping the spectral gap increases while the superconducting order parameter decreases. This, we conclude, is caused by the onset of the pseudogap in the underdoped region, which contributes to the increasing spectral gap; this is consistent with the change in the source of condensation energy from potential energy, in the overdoped region, to kinetic energy in the underdoped region. We also observe that the d-wave node disappears within the superconducting phase at low values of hole doping, within the underdoped region. We see this as a manifestation of Mott physics operating at very low doping. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J56.00014: Extending the Gutzwiller approximation to intersite interactions Garry Goldstein, Gabriel Kotliar, Nicola Lanata We develop an extension of the Gutzwiller Approximation (GA) formalism which includes the effects of Coulomb interactions of arbitrary range (including density density, exchange, pair hopping and Coulomb assisted hopping terms). This formalism reduces to the ordinary GA formalism for the multi-band Hubbard models in the presence of only local interactions. This is accomplished by combining the 1/z expansion - where z is the coordination number and only the leading order terms contribute in the limit of infinite dimensions- with a P^2-I expansion, where P is the Gutzwiller projector on a site R. The method is conveniently formulated in terms of a Gutzwiller Lagrange function. We apply our theory to the single band t-J model and the extended single band Hubbard model. We find a Mott transition but for the extended Hubbard model. An enhanced valence fluctuations transition is also discovered. |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J56.00015: Dynamical t/U Expansion of the Doped Hubbard Model Wenxin Ding, Rong Yu We construct a new U(1) slave spin representation for the single-band Hubbard model in the large-U limit. The mean-field theory in this representation is more amenable to describe both the spin-charge-separation physics of the Mott insulator at half-filling and the strange metal behavior at finite doping. By employing a dynamical Green’s function theory for slave spins, we calculate the single-particle spectral function of electrons, and the result is comparable to that in dynamical mean-field theories. We then formulate a dynamical t/U expansion for the doped Hubbard model that reproduces the mean-field results at the lowest order of expansion. To the next order of expansion, it naturally yields an effective low-energy theory of a t − J model for spinons self-consistently coupled to an XXZ model for the slave spins. We show that the superexchange J is renormalized by doping, in agreement with the Gutzwiller approximation. Surprisingly, we find a new ferromagnetic channel of exchange interactions which survives in the infinite U limit, as a manifestation of the Nagaoka ferromagnetism. |
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