Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J47: Metal-Insulator and Other Electronic Phase Transitions: Computational |
Hide Abstracts |
Sponsoring Units: DCMP Room: Mile High Ballroom 4F |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J47.00001: A dual fermion approach for disordered interacting systems: Application to the Anderson-Hubbard model Patrick Haase, Shuxiang Yang, Hanna Terletska, Thomas Pruschke, Juana Moreno, Mark Jarrell We have recently generalized the dual fermion approach to the disordered interacting fermionic systems. Here it is applied to the Anderson-Hubbard model at finite temperature. With both disorder and Coulomb interaction treated on equal footing, and non-local correlations taken into account, we analyze the underlying competing physics related to metal-insulation transitions and anti-ferromagnetic transition by looking into both one- and two-particle quantities. [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J47.00002: Towards the Realization of Self-Consistent Effective Medium Theory for Anderson Disorder Model Chinedu Ekuma, Hanna Terletska, Ka Ming Tam, Zi Yang Meng, Juana Moreno, Mark Jarrell A mean-field theory that properly characterizes the Anderson localization transition in three dimensions has remain elusive. Here, we present a systematic typical medium dynamical cluster approximation that provides a proper description of this phenomenon. Our method accurately provides a proper way to treat the different energy scales (close to the criticality) such that the characteristic re-entrant behavior of the mobility edge is obtained. This allows us to study the localization in different momenta cells, which renders the discovery that the Anderson localization transition occurs in a \textit{momentum cell-selective fashion}. As a function of cluster size, our method systematically recovers the re-entrance behavior of the mobility edge and obtains the correct critical disorder strength with great improvement on the critical exponent of the order parameter ($\beta > 1.4$). [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J47.00003: Dual-fermion approach to interacting disordered fermion systems Shuxiang Yang, Patrick Haase, Hanna Terletska, Zi Yang Meng, Thomas Pruschke, Juana Moreno, Mark Jarrell We generalize the recently introduced dual fermion (DF) formalism for disordered fermion systems by including the effect of interactions. For an interacting disordered system the contributions to the full vertex function have to be separated into elastic and inelastic scattering processes, and addressed differently when constructing the DF diagrams. By applying our approach to the Anderson-Falicov-Kimball model and systematically restoring the nonlocal correlations in the DF lattice calculation, we show a significant improvement over the Dynamical Mean-Field Theory and the Coherent Potential Approximation for both one-particle and two-particle quantities. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J47.00004: Dynamical cluster approximation and typical medium analysis of systems with off-diagonal disorder Hanna Terletska, Chinedu Ekuma, Conrad Moore, Ka Ming Tam, Juana Moreno, Mark Jarrell A proper theoretical description of realistic disordered materials requires the inclusion of both diagonal and off-diagonal randomness. The single-site self-consistent approximation for systems with off-diagonal disorder was constructed by Blackman, Esterling and Berk (BEB) [1]. Being a single-site approximation, the BEB theory neglects all disorder induced non-local correlations. In order to take into account such non-local effects and the effect of off-diagonal disorder,we extend BEB formalism using the dynamical cluster approximation scheme [2]. Also to address the question of electron localization, we generalize our recently developed typical medium dynamical cluster approximation to systems with off-diagonal randomness. In our numerical analysis we perform a systematic study of the effect of non-local correlations and of off-diagonal disorder on the density of states and electron localization. The results of our calculations are compared with the results obtained using the exact diagonalization and the transfer-matrix method. [1] J. A. Blackman, D. M. Esterling, and N. F. Berk, Phys. Rev. B 4, 2412 (1971). [2] M. Jarrell and H. R. Krishnamurthy, Phys. Rev. B 63, 125102 (2001) [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J47.00005: Benchmarking Mobility Edge Calculations for a Cluster Typical Medium Theory of Off-diagonal Disordered Systems Conrad Moore, Ka Ming Tam, Hanna Terletska, Juana Moreno, Mark Jarrell We apply the transfer matrix method and exact diagonalization to electronic lattice systems with substitutional off-diagonal disorder. Established effective medium methods for studying realistic metallic alloy systems have enjoyed much success calculating the properties of disordered systems, but are criticized for inaccurate predictions (for example, of charge transfer and phase evolution) caused by reliance on the Coherent Potential Approximation (CPA) which neglects nonlocal environmental effects. It has been shown that such non-local correlations can be incorporated with the Dynamical Cluster Approximation (DCA). Furthermore, localization effects have been demonstrated with a local order parameter approach that is used to define a typical medium. The validity of the predicted mobility edge from an effective cluster typical medium theory that extends the Blackman, Esterling and Berk formalism to DCA is explored with finite size scaling of transfer matrix data. We demonstrate it as a promising effective medium theory to incorporate into present ab initio methods for realistic disordered systems. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J47.00006: Vertex function representation in non-uniform frequency grids Ka-Ming Tam, Shuxiang Yang, Juana Moreno, Mark Jarrell The proper computer representation of many-body vertex functions is a central issue in computational many body methods such as the parquet formalism, a self-consistent two-particle field theory. Despite the great effort over the past two decades, its application is very limited. This is predominately due to two crucial factors - the stability of the iteration and the size of the memory allocation for the vertices. We previously demonstrated that the stability problem can be alleviated by explicitly restoring the crossing symmetry, making simulations beyond weak coupling for the Hubbard model feasible. The next step for the practical applications of the parquet formalism is to compress the memory required to represent the vertex. In this talk, we first demonstrate the problem of perturbation theory off the Matsubara frequency grids. This problem is avoided by working on the so-called decimation grids, which are non-uniform grids on Matsubara frequency. We then use this scheme in the parquet method, for solving an Anderson impurity problem. The results show substantial improvement compared to using the same number of uniform frequency grids. This may represent a crucial step towards practical applications of the parquet formalism for large clusters. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J47.00007: Revisit of Orbital Selective Phase Transition Induced by Different Orbitals with Different Band Dispersions Ze-Yi Song, Yu-Zhong Zhang Orbital selective phase transition (OSPT) was first suggested to explain a possible coexistence of localized and itinerant electrons in a multi-orbital system, Ca$_{2-x}$Sr$_x$RuO$_4$, as interaction increases. Recently, this scenario was applied to the iron-based superconductors. Up to now, several mechanisms have been proposed, such as different orbitals with different bandwidth, different orbitals with different degeneracies, different orbitals with different magnetic states, and different orbitals with different band dispersions, etc. Unlike other mechanisms which were investigated under a constraint of paramagnetic solution, different orbitals with different band dispersions was only studied with magnetic order. Therefore, here we investigate the mechanism of different orbitals with different band dispersions in paramagnetic state by dynamical mean field theory with exact diagonalization as an impurity solver in order to reveal whether OSPT can still happen. Possible indications of our results will also be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J47.00008: Electron Localization in $Fe_3O_4$: an Ab Initio Wannier Study Perry Sakkaris, Carel Boekema Magnetite, $Fe_3O_4$, is an unusual ferrimagnetic oxide with emergent physical properties that are not yet fully understood. Among these are the metal-insulator transition at the Verwey Temperature $T_V$ (123K) and a spin-glass-like transition at about twice $T_V$. The ``extra'' fully spin-polarized 3d electrons that span the $t_{2g}$ bands of the B sublattice show strong electron correlation effects and are mainly responsible for conduction above $T_V$. We perform a DFT+U calculation to obtain a set of Bloch orbitals describing the $t_{2g}$ bands. We then use the gauge invariance of Wannier functions to transform the Bloch orbitals into a set of Maximally Localized Wannier Functions (MLWFs). The MLWFs are a real space description of the ``extra'' 3d electrons allowing us to describe their spatial localization and determine the mechanism of conduction above $T_V$. Wannier studies of $Fe_3O_4$ may also allow us to determine the extent of electronic coupling to lattice vibrations, which may provide us substantial quantitative clues on the physical mechanism of the Verwey Transition. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J47.00009: Localization phase diagram of two-dimensional quantum percolation Brianna Dillon, Hisao Nakanishi We examine two dimensional quantum percolation on a square lattice with random dilution up to $q=38\%$ and energy $0.001 \le E \le 1.6$ (in units of the hopping matrix element), using numerical calculations of the transmission coefficient for finite size systems of up to about 900x900. We extended previous work to determine the phase diagram in $(E,q)$ space, confirming the existence of a localization-delocalization transition. The localized region splits into an exponentially localized and power-law localized regions for energies $E \ge 0.1$. We also examine the scaling behavior of the residual transmission coefficient in the delocalized region, the power law exponent in the power-law localized region, and the localization length in the exponentially localized region. Our results suggest that the residual transmission at the delocalized to power-law localized phase boundary may be discontinuous, and that the localization length is likely not to diverge with a power-law at the exponentially localized to power-law localized phase boundary. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J47.00010: Numerical studies of a many-body localized system coupled to a bath Sonika Johri, Rahul Nandkishore We use exact diagonalization to study the breakdown of localization in a many-body localized system coupled to a non-integrable bath. Signatures of incomplete localization survive even when the coupling to the bath is non-zero. In particular, we examine (i) level statistics, (ii) eigenstate thermalization, (iii) zero- and finite temperature spectral functions, (iv) correlation functions, and (v) transport properties. We find a continuous change from localized to ergodic behaviour in these quantities as the coupling to the bath increases. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J47.00011: Universal Conductivity in a Two-dimensional Superfluid-to-Insulator Quantum Critical System Kun Chen, Longxiang Liu, Youjin Deng, Lode Pollet, Nikolay Prokof'ev We compute the universal conductivity of the (2+1)-dimensional XY universality class, which is realized for a superfluid-to-Mott insulator quantum phase transition at constant density. Based on large-scale Monte Carlo simulations of the classical (2+1)-dimensional $J$-current model and the two-dimensional Bose-Hubbard model, we can precisely determine the conductivity on the quantum critical plateau, $\sigma(\infty)=0.359(4)\sigma_Q$ with $\sigma_Q$ the conductivity quantum.The universal conductivity curve is the textbook example of where the AdS/CFT correspondence from string theory can be tested and made to use. For the first time, the shape of the $\sigma(i\omega_n)- \sigma(\infty)$ function in the Matsubara representation is accurate enough for a conclusive comparison and establishes the particle-like nature of charge transport.We find that the holographic gauge/gravity duality theory for transport properties can be made compatible with the data if temperature of the horizon of the black brane is different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J47.00012: Finite Temperature Phase Diagram of the Disordered Extended Bose-Hubbard Model Fei Lin, Vito Scarola The disordered extended Bose-Hubbard model exhibits a very rich phase diagram at low temperatures because of the competition between disorder and interactions. Depending on the parameter regime, it can show superfluid, supersolid, Bose glass, solid and disordered solid phases. We will discuss quantum Monte Carlo calculations used to estimate various physical quantities, such as, superfluid density, charge structure factor, compressibility, etc, which we use to classify these phases at finite temperatures. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J47.00013: Area laws and topological order in a many-body localized state Bela Bauer, Chetan Nayak The question whether Anderson insulators can persist to finite-strength interactions - a scenario dubbed many-body localization - has recently received a great deal of interest. In this talk, I will discuss our recent work on defining such a many-body localized phase and exploring it through its entanglement properties. We formulate a precise sense in which a many-body localized system can be connected adiabatically to an Anderson insulator. The most striking consequence of our definition is an area law for the entanglement entropy of highly excited states in such a system. We present the results of numerical calculations for a one-dimensional system of spinless fermions, which are consistent with an area law and, by implication, many-body localization for weak enough interactions and strong disorder. Furthermore, we discuss the implications that many-body localization may have for topological phases and self-correcting quantum memories. We find that there are scenarios in which many-body localization can help to stabilize topological order at non-zero energy density, and we propose potentially useful criteria to confirm these scenarios. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J47.00014: Thermal disorder, entropy and the $\alpha - \gamma$ transition in Ce from density-functional theory Thomas Jarlborg There are many recent theoretical efforts to describe the $\gamma - \alpha$ transition in fcc Cerium. The large volume $\gamma$-phase is magnetic, while the low-volume non-magnetic $\alpha$- phase can be reached at high pressure or low T. It has been recognized that real T-dependent lattice disorder can be important for the electronic structure and properties in some materials with sharp density-of-state variations near $E_F$. This might also be the case for Ce, because of its narrow f-band at the Fermi level, and its relatively soft lattice. Here are presented results for fcc Ce at different volumes from first principles GGA-DFT band-structure calculations for large supercells with different degrees of T-dependent disorder. Local disorder, local density-of-states and magnetic moments are all connected. It is shown that structural disorder at large temperature has a direct influence on the magnetic $\gamma$-phase, and its corresponding entropy. The results corroborate the earlier findings that standard DFT band-theory can describe the T-dependent transition if all entropy contributions are included. In addition, thermal disorder is important for the properties of fcc Ce. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J47.00015: $\gamma$-$\alpha$ iso-structural Transition in Cerium Yongxin Yao, Nicola Lanat\`a, Cai-Zhuang Wang, J\"org Schmalian, Kristjan Haule, Gabriel Kotliar, Kai-Ming Ho We present zero-temperature first-principle calculations of elemental cerium, and we compute its pressure-volume phase diagram within a theoretical framework able to describe simultaneously both the $\alpha$ and the $\gamma$ phase. A surprising result revealed by our study is the presence of a clear signature of the transition at zero temperature, and that this signature can be observed if and only if the spin-orbit coupling is taken into account. Our calculations indicate that the transition line in the pressure-temperature phase diagram of this material has a low-$T$ critical point at negative pressures, placed very close to zero temperature. This suggests that cerium is very close to being ``quantum critical'', in agreement with recent experiments. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700