Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y20: Metal Insulator Phase Transitions IV: Theory |
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Sponsoring Units: DCMP Chair: Lucas Lindsay, Oak Ridge National Laboratory Room: 280 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y20.00001: Percolative Mott Metal-Insulator Transition in the Doped Hubbard-Holstein model: Theoretical Results from Hartree-Fock and Slave Boson Approaches Jamshid Moradi Kurdestany Motivated by the current interest in the understanding of the Mott insulators away from half filling, observed in many perovskite oxides, we study the Mott metal-insulator transition in the doped Hubbard-Holstein model using the Hatree-Fock and slave-Boson approaches. The model contains both the Coulomb and the electron-lattice interactions, which are important ingredients in the physics of the perovskite oxides. In contrast to the half-filled Hubbard model, which always results in a single phase (either metallic or insulating), our results show that away from half-filling, a mixed phase of metallic and insulating regions occur.As the dopant concentration is increased, the metallic part progressively grows in volume, until it exceeds the percolation threshold, leading to percolative conduction. This happens above a critical dopant concentration, which, depending on the strength of the electron-lattice interaction, can be a significant fraction of unity. This means that the material could be insulating even for a substantial amount of doping, in contrast with the Nagaoka theorem, where a single hole destroys the insulating behavior of the half-filled Hubbard model. Our theory provides a framework for the understanding of the density-driven MIT observed in many complex oxides. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y20.00002: Spin - selective disorder and corresponding interaction driven spin - selective metal - insulator transition in d=2 Prabuddha Chakraborty, Shashi Kunwar, Rajesh Narayanan We present the study of an interesting variant of the Hubbard model of strongly correlated electrons in which only one spin species of electrons see a disordered environment. Through exact simulations in two dimensions, we show that it is possible to establish a metallic state (of the disordered spin species) through a quantum phase transition driven by interaction. Through the same simulations, we establish that magnetic instabilities play a crucial role in driving this transition. This sheds some new light on a question that the community has been involved in for decades: can interactions drive a localized (due to disorder) system of electrons metallic in two spatial dimensions or lower? [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y20.00003: Mott Insulator Phase Transition in Graphene Jia Ning Leaw, Ho-Kin Tang, Joao N. B. Rodrigues, Shaffique Adam Controllably tuning the semimetal to Mott insulator phase transition in graphene could allow for the development of graphene-based low-power electronic devices. It is known in the literature (e.g. Juricic et al., PRB 80, 081405(R); Kaveh et al., PRB 71, 184519 and Gamayun et al., PRB 81, 075429) that increasing the long-range Coulomb interaction decreases the critical contact coupling for the phase transition of spinless Dirac fermions from a semi-metal phase to a charge-density-wave phase (CDW). In this work we consider the more realistic Gross-Neveu model relevant for spinfull Dirac fermions and study the transition between the semimetal and the Mott insulator spin-density-wave (SDW) phase. In contrast to the CDW phase transition, and contrary to conventional wisdom, our Renormalization Group calculation shows that the SDW phase transition occurs at stronger onsite potential if the nearest neighbour potential is increased. Our result implies that high-k dielectrics should favour the Mott transition in graphene. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y20.00004: Effect of a Magnetic Field on Mott-Hubbard Systems: A Dynamical Mean-Field Theory Study Wei Zhu, Jian-xin Zhu The dynamic mean-field theory (DMFT) is the most successful method~to study strongly correlated electron systems in dimensions higher than one.~~As the impurity problem of DMFT is one-dimensional, it is~available to solve it using density matrix renormalization group (DMRG). Motivated by this idea, we~develop a systematical tool combining DMFT and DMRG, which is expected to provide an efficient,~precise and controlled way to solve DMFT problems with multiorbitals on the real frequency axis with~feasible extensions to problems with more bands. As a concrete example, we study the magnetic field dependent dynamical properties of the two-dimensional Hubbard model on the Bethe lattice. The field dependence of the magnetization, one-particle response function and susceptibility are studied. The corresponding phase transition between metal and Mott insulator is also discussed. ~ [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y20.00005: Hidden Mott transition and large-$U$ superconductivity in the two-dimensional Hubbard model Federico Becca, Luca Fausto Tocchio, Sandro Sorella We consider the one-band Hubbard model on the square lattice by using variational and Green's function Monte Carlo methods, where the variational states contain Jastrow and backflow correlations on top of an uncorrelated wave function that includes BCS pairing and magnetic order. At half filling, where the ground state is antiferromagnetically ordered for any value of the on-site interaction $U$, we can identify a hidden critical point $U_{Mott}$, above which a finite BCS pairing is stabilized in the wave function. The existence of this point is reminiscent of the Mott transition in the paramagnetic sector and determines a separation between a Slater insulator (at small values of $U$), where magnetism induces a potential energy gain, and a Mott insulator (at large values of $U$), where magnetic correlations drive a kinetic energy gain. Most importantly, the existence of $U_{Mott}$ has crucial consequences when doping the system: we observe a tendency to phase separation into a hole-rich and a hole-poor region only when doping the Slater insulator, while the system is uniform by doping the Mott insulator. Superconducting correlations are clearly observed above $U_{Mott}$, leading to the characteristic dome structure in doping. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y20.00006: Optimized DMRG calculations for 2D interacting fermions Jing Chen, Tao Xiang, Haidong Xie, Ruizhen Huang We proposed a scheme to optimize DMRG in the calculations of 2D interacting fermion system. We take Hubbard model of size up to 10*10 with periodic boundary condition as an example. In the optimized basis, the entanglement entropy is about half of real space. The optimized DMRG achieves much higher accuracy compared with real basis and momentum basis. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y20.00007: Elementary Excitations of the 2-leg Hubbard Ladder and Related Models near 1/2-filling Ye-Hua Liu, T. Maurice Rice We study the single-particle, two-particle and spin-flip excitations in a 2-leg Hubbard ladder near 1/2-filling with various interaction strengths, using the high-performance DMRG program from the ALPS library. In addition to the Hubbard model, we explore the effect of additional interaction terms, e.g. density-density, spin-spin interactions, on the various correlations. The final Hamiltonian can be used as a low-energy effective model for particular regions in momentum space of the 2-dimensional Hubbard model. The variation of the excitation spectrum, as a function of the relative strength of the various terms, provides simple insights into the physics of the pseudogap phase in cuprates. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y20.00008: The Transformation of the Superconducting Gap to an Insulating Pseudogap with Decreasing Hole Density in the Cuprates T. Maurice Rice, Ye-Hua Liu The D-Mott Insulator state of the ½-filled 2-leg Hubbard ladder is a 1D example of a short range ordered Mott insulator at weak coupling. The recent wavepacket formalism developed by Ossadnik [arXiv 1603.04041] can describe the generalization to 2D, necessary to examine the pseudogap state in underdoped cuprates. We focus on maximizing umklapp scattering near the Fermi energy as the driver of this precursor state to Mott localization in 2D as it is in 1D. To this end we show how an insulating energy gap driven by umklapp scattering can open on an appropriately chosen 2D-surface as proposed earlier by Yang, Rice and Zhang. The key feature of a pairing instability with umklapp scattering is the opening of a gap in the 2-particle spectrum thereby turning the superconductor gap into an insulating pseudogap, in the anti-nodal parts of the Fermi surface. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y20.00009: Local Integrals of Motion without a complete set of localized eigenstates R. N. Bhatt, Scott Geraedts, Rahul Nandkishore Many body localized systems where all energy eigenstates are localized are known to display an emergent local integrability, i.e., an extensive number of operators can be constructed that are localized in space and commute with the Hamiltonian. We examine [1] if emergent local integrability requires a complete set of localized eigenstates. We show that given a set of localized eigenstates comprising nonzero fraction (1-f) of the full many body spectrum, one can construct an extensive number of integrals of motion which are local in the sense that, in the thermodynamic limit, they have nonzero weight in a compact region of real space. However, these modified integrals of motion have a "global dressing" whose weight vanishes as f tends to 0. Consequently, the existence of a non-zero fraction of localized eigenstates is sufficient for emergent local integrability. We discuss the implications of our findings for systems where the spectrum contains delocalized states, for systems with projected Hilbert spaces, and for the robustness of quantum integrability. [1] Scott D. Geraedts, R. N. Bhatt and Rahul Nandkishore, arXiv 1608.01328 (https://arxiv.org/pdf/1608.01328.pdf) [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y20.00010: 1-D Anderson model in a projected Hilbert Space Akshay Krishna, R. N. Bhatt The standard 1-D Anderson model possesses a completely localized spectrum of eigenstates for all values of the disorder. We consider the effect of projecting the Hamiltonian to different truncated Hilbert spaces, some of which preserve time reversal symmetry and others that do not. We analyze the ensuing eigenstates using different measures such as inverse participation ratio and sample-averaged moments of the position operator. In addition, we examine amplitude fluctuations in detail to detect the possibility of multifractal behavior (characteristic of mobility edges) that may arise as a result of the truncation procedure. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y20.00011: Finite temperature Gutzwiller approximation and equation of states for Hubbard model Wei Zhang, Ziqiang Wang We generalize the Gutzwiller approximation to finite temperatures in the grand canonical ensemble and study the Mott transition in the half-filled Hubbard model on the square lattice in both the paramagnetic and antiferromagnetic phases. We found that the Mott transition at finite temperature is first order, terminating at two second order points. We determined the coexisting region of metallic and insulating phases and obtain the equation of states for the strongly correlated electrons at low temperatures. We calculate the Neel temperature as a function of the Hubbard repulsion U and compare to the results obtained by dynamic mean field theory. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y20.00012: Adaptive Hilbert Space Truncation for Dynamical Mean-Field Impurity Models: Formalism and new results for the Hubbard model pseudogap Ara Go, Andrew Millis An impurity solver based on adaptive truncation of a Hilbert space is shown to be a powerful new method for solving the equations of dynamical mean-field theory. Starting from an initial set of Slater determinants, the method performs an adaptive truncation followed by particle-hole substitutions, and then iterates the procedure to obtain an accurate ground state. A related process is used to define the excited state space needed for the Greens function. The reduced costs enable solutions of impurity models with 8 correlated orbitals. New results enabled by the method are presented including the spectral functions near the Mott transition and the fate of the pseudogap at large $U$ in the 8-site dynamical mean-field approximation to the Hubbard model. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y20.00013: Influence of spin-orbit coupling on the multiorbital Hubbard model: J-freezing, Hund's rules and excitonic magnetism Aaram J. Kim, Harald O. Jeschke, Philipp Werner, Roser Valenti We investigate the interplay between the spin-orbit coupling, Coulomb interaction and Hund’s coupling within the multiorbital Hubbard model at different fillings by means of the dynamical mean-field theory combined with continuous-time quantum Monte Carlo. We show that the spin-freezing crossover occurring in the metallic phase of the model without the spin-orbit coupling can be the generalized to a $\mathbf{J}$-freezing crossover with $\mathbf{J}=\mathbf{L}+\mathbf{S}$, in the spin-orbit-coupled case. In the $\mathbf{J}$-frozen regime the correlated electrons exhibit a non-trivial flavor dependence in the self-energy which cannot be captured by the effective crystal-field effect. Especially, in the regions near $n = 2$ and $n = 4$ the metallic phases show strong asymmetry from each other, which reflects the atomic Hund’s third rule. Finally, we explore the appearance of the excitonic magnetism near $n = 4$ and discuss the relevance of our results for real materials.\footnote{A. J. Kim {\it et al.}, arXiv:1607.05196.} [Preview Abstract] |
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