# Workshops

## Strongly Correlated Materials: Experiments and Computation

### Organisers

- Guy Cohen
*(Tel Aviv University, Israel)* - Alexander Shick
*(Institute of Physics ASCR, Czech Republic)* - Alexander Lichtenstein
*(University of Hamburg, Germany)* - Eitan Eidelstein
*(NRCN and Tel Aviv University, Israel)*

### Supports

### Description

Heavy fermion materials, transition metal oxides, and a variety of rare-earth compounds exhibit strong correlation: electrons in partially filled d and f shells of constituent atoms are delicately balanced between interaction-induced localization and kinetic delocalization [6], resulting in rich phase diagrams with remarkable and potentially useful switching properties [29]. Most widespread computational approaches to materials, which are based on weak-correlation theories such as Density Functional Theory (DFT), Hartree-Fock and GW, fail to fully capture strong correlations.

The physics of strongly correlated electrons is of broad fundamental interest, with recent examples including the elusive theory of topological Kondo insulators [9, 28], the formation of multipolar orders in actinide oxides [24] and the controversial nature of high temperature superconductivity in plutonium-based materials [5, 10]. Some of the most societally pressing and yet long-standing issues involve the radioactive actinides [25, 20, 14], and better theoretical methods are critical to addressing nuclear waste remediation [8].

An emerging, cutting-edge generation of methods has begun addressing the challenge of performing realistic simulations of strongly correlated materials. Notable examples include the Dynamical Mean Field Theory (DMFT) [11] paired with continuous time quantum Monte Carlo (CT-QMC) [12], variational Monte Carlo [22, 21] and others [17]. However, the problem remains extremely difficult, and attacking it requires a large-scale multidisciplinary effort. In this conference, we propose to bring together some major players working on various separate but synergistic sides of the problem, from both the theoretical and experimental perspectives.

From the theoretical perspective, significant progress towards a quantitative and general theory of d-electron and f-electron systems requires a combination of tools and approaches. Great strides have been made in DMFT [28, 14, 26, 13, 27]. However, advances towards a realistic description rely on a stronger connection to underlying weakly correlated theories [18, 19, 30]. They further rely on improved Monte Carlo methods able to address dynamical phase problems in the associated auxiliary problems [1, 4, 3, 7]. Promising new variational approaches should also be explored and hopefully integrated into the same toolset [2, 23], and all these ideas should be combined with modern methods for constructing coarse-grained models [15, 16]. Finally, close collaboration with experimentalists is paramount to focusing this effort.

We propose to bring together several prominent researchers in correlated electrons, f-electron materials, and the foundations and extensions of weakly correlated methods. All invitees develop unique and relevant computational or experimental methods. The emphasis is on members of several centers in the Czech Republic and Israel, between which we hope to form a long-term collaboration; however, a select group of leaders in the field from elsewhere will also attend.

The main emphasis is on theory and method development, and discussions are planned between experts from a diverse set of disciplines and scientific communities that have made relevant contributions to the field but would not normally meet each other. However, we also propose to put these theorists in close contact with experimentalists that have unique access to some of the most groundbreaking studies in Europe on strongly-correlated 5f systems, and provide tutorials on x-ray magnetic circular dichroism (XMCD), x-ray absorption near-edge structure (XANES), electron energy-loss spectroscopy (EELS), electron-probe microanalysis (EPMA), and transmission electron microscopy (TEM).

******* **For more information and registration please check the CECAM IL site: CECAM IL *****

### References

[1] Antipov, A. E. and Dong, Q. and Kleinhenz, J. and Cohen, G. and Gull, E., "Currents and Green's functions of impurities out of equilibrium: Results from inchworm quantum Monte Carlo", Phys. Rev. B 95 (2017), pp. 085144.

[2] Chang, C. C. and Rubenstein, B. M. and Morales, M. A., "Auxiliary-field-based trial wave functions in quantum Monte Carlo calculations", Phys. Rev. B 94 (2016), pp. 235144.

[3] Chen, H. T. and Cohen, G. and Reichman, D. R., "Inchworm Monte Carlo for exact non-adiabatic dynamics. II. Benchmarks and comparison with established methods", Jour. Chem. Phys. 146, 5 (2017), pp. 054106.

[4] Chen, H. T. and Cohen, G. and Reichman, D. R., "Inchworm Monte Carlo for exact non-adiabatic dynamics. I. Theory and algorithms", Jour. Chem. Phys. 146, 5 (2017), pp. 054105.

[5] Curro, N. J. and Caldwell, T. and Bauer, E. D. and Morales, L. A. and Graf, M. J. and Bang, Y. and Balatsky, A. V. and Thompson…, "Unconventional superconductivity in PuCoGa5", Nature 434, 7033 (2005), pp. 622-625.

[6] Dagotto, E., "Complexity in Strongly Correlated Electronic Systems", Science 309, 5732 (2005), pp. 257--262.

[7] Dong, Q. and Krivenko, I. and Kleinhenz, J. and Antipov, A. E. and Cohen, G. and Gull, E., "Quantum Monte Carlo solution of the dynamical mean field equations in real time", ArXiv e-prints, cond-mat.str-el, 1706.02975 (2017).

[8] Dutkiewicz, M. S. and Farnaby, J. H. and Apostolidis, C. and Colineau, E. and Walter, O. and Magnani, N. and Gardiner, M. G. an…, "Organometallic neptunium(III) complexes", Nat Chem 8, 8 (2016), pp. 797-802.

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[12] Gull, E. and Millis, A. J. and Lichtenstein, A. I. and Rubtsov, A. N. and Troyer, M. and Werner, P., "Continuous-time Monte Carlo methods for quantum impurity models", Rev. Mod. Phys. 83 (2011), pp. 349-404.

[13] Koloren c č, J. and Shick, A. B. and Lichtenstein, A. I., "Electronic structure and core-level spectra of light actinide dioxides in the dynamical mean-field theory", Phys. Rev. B 92 (2015), pp. 085125.

[14] Lanatà, N. and Yao, Y. and Wang, C. Z. and Ho, K. M. and Kotliar, G., "Phase Diagram and Electronic Structure of Praseodymium and Plutonium", Phys. Rev. X 5 (2015), pp. 011008.

[15] Liu, S. and Grinberg, I. and Rappe, A. M., "Exploration of the intrinsic inertial response of ferroelectric domain walls via molecular dynamics simulations", Appl. Phys. Lett. 103, 23 (2013), pp. 232907.

[16] Liu, S. and Grinberg, I. and Takenaka, H. and Rappe, A. M., "Reinterpretation of the bond-valence model with bond-order formalism: An improved bond-valence-based interatomic potential…", Phys. Rev. B 88 (2013), pp. 104102.

[17] Motta, M. and Ceperley, D. M. and Kin-Lic, C. G. …, "Towards the solution of the many-electron problem in real materials: equation of state of the hydrogen chain with state-of-t…", ArXiv e-prints, physics.comp-ph 1705.01608 (2017).

[18] Park, H. and Millis, A. J. and Marianetti, C. A., "Computing total energies in complex materials using charge self-consistent DFT + DMFT", Phys. Rev. B 90 (2014), pp. 235103.

[19] Park, H. and Millis, A. J. and Marianetti, C. A., "Density functional versus spin-density functional and the choice of correlated subspace in multivariable effective action th…", Phys. Rev. B 92 (2015), pp. 035146.

[20] Pourovskii, L. V. and Katsnelson M. I. and Lichtenstein A. I. and Havela L. and Gouder T. and Wastin F. and Shick A. B. and …, "Nature of non-magnetic strongly-correlated state in delta-plutonium", Europhys. Lett. 74, 3 (2006), pp. 479-485.

[21] Qin, M. and Shi, H. and Zhang, S., "Numerical results on the short-range spin correlation functions in the ground state of the two-dimensional Hubbard model", ArXiv e-prints (2017).

[22] Rubenstein, B., "Introduction to the Variational Monte Carlo Method in Quantum Chemistry and Physics", Springer Singapore (2017), 285-313.

[23] Rubenstein, B. M. and Zhang, S. and Reichman, D. R., "Finite-temperature auxiliary-field quantum Monte Carlo technique for Bose-Fermi mixtures", Phys. Rev. A 86 (2012), pp. 053606.

[24] Santini, P. and Carretta, S. and Amoretti, G. and Caciuffo, R. and Magnani, N. and Lander, G. H., "Multipolar interactions in f-electron systems: The paradigm of actinide dioxides", Rev. Mod. Phys. 81 (2009), pp. 807--863.

[25] Savrasov, S. Y. and Kotliar, G. and Abrahams, E., "Correlated electrons in delta-plutonium within a dynamical mean-field picture", Nature 410, 6830 (2001), pp. 793-795.

[26] Secchi, A. and Lichtenstein, A. I. and Katsnelson, M. I., "Magnetic interactions in strongly correlated systems: Spin and orbital contributions", "Annals of Physics" 360 (2015), pp. 61 - 97.

[27] Shick, A. B. and Koloren c č, J. and Lichtenstein, A. I. and Havela, L., "Electronic structure and spectral properties of Am, Cm, and Bk: Charge-density self-consistent LDA+HIA", Phys. Rev. B 80 (2009), pp. 085106.

[28] Shick, A. B. and Havela, L. and Lichtenstein, A. I. and Katsnelson, M. I., "Racah materials: role of atomic multiplets in intermediate valence systems", Nat. Sci. Rep. 5 (2015), pp. 15429.

[29] Takagi, H. and Hwang, H. Y., "An Emergent Change of Phase for Electronics", Science 327, 5973 (2010), pp. 1601--1602.

[30] Tomczak, J.M. and Liu, P. and Toschi, A. and Kresse, G. and Held, K., "Merging GW with DMFT and non-local correlations beyond", ArXiv e-prints, cond-mat.str-el, 1703.08446 (2017).