Superexchange, effective interactions, and magnetic ground states in frustrated triangular-lattice quantum magnets

• Applicant: Dr. Liviu Hozoi
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation ; Theoretical Chemistry: Molecules, Materials, Surfaces ; Theoretical Condensed Matter Physics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441216021

• Final Report Year: 2024

Final Report Abstract

Exchange underpins the magnetic properties of quantum matter. In its most basic form, it occurs through the interplay of Pauli's exclusion principle and Coulomb repulsion, being referred to as direct (also Coulomb or potential) exchange. Direct exchange was discussed by Heisenberg, Dirac, and van Vleck already in the 1920s, has no classical analogue, and is the main effect responsible for ferromagnetism. The antiferromagnetic ground states observed in a variety of magnetic insulators, on the other hand, arise from indirect exchange interactions involving intersite electron hopping: M-M kinetic exchange, where only electrons at the magnetic centers (Ms) are active, and superexchange, where electrons at nonmagnetic, intermediary ionic sites [i.e., chalcogenide or halide ligands (Ls)] are also swapped. The main achievement of this project is establishing the role of direct exchange in Kitaev-Heisenberg magnets. Direct, Coulomb exchange has been completely ignored so far in this field but according to our quantum chemical results is as important as the indirect mechanisms. This highlights the limitations of existing anisotropic models and the need for systematic wavefunction quantum chemical studies to (i) clarify exchange contributions in various LS-coupled magnetic materials, (ii) make reliable predictions, (iii) guide experimental work towards next-generation magnetic devices.

Publications

• Crystal-field effects competing with spin-orbit interactions in NaCeO2. Physical Review B, 105(11).
  Bhattacharyya, P.; Rößler, U. K. & Hozoi, L.
  
• Electronic and structural properties of RbCeX2 (X2: O2, S2, SeS, Se2, TeSe, Te2). Physical Review Materials, 6(8).
  Ortiz, Brenden R.; Bordelon, Mitchell M.; Bhattacharyya, Pritam; Pokharel, Ganesh; Sarte, Paul M.; Posthuma, Lorenzo; Petersen, Thorben; Eldeeb, Mohamed S.; Granroth, Garrett E.; Dela, Cruz Clarina R.; Calder, Stuart; Abernathy, Douglas L.; Hozoi, Liviu & Wilson, Stephen D.
  
• Yb3+ f−f excitations in NaYbSe2 : Benchmarking embedded-cluster quantum chemical schemes for 4f insulators. Physical Review B, 105(23).
  Bhattacharyya, P. & Hozoi, L.
  
• Maximized K/J ratio and cubiclike jeff=1/2 moments in a noncubic environment in α-RuCl3 under pressure. Physical Review B, 108(16).
  Bhattacharyya, Pritam; Hozoi, Liviu; Nishimoto, Satoshi; Stahl, Quirin; Geck, Jochen & Bogdanov, Nikolay A.
  
• NaRuO2: Kitaev-Heisenberg exchange in triangular-lattice setting. npj Quantum Materials, 8(1).
  Bhattacharyya, Pritam; Bogdanov, Nikolay A.; Nishimoto, Satoshi; Wilson, Stephen D. & Hozoi, Liviu
  
• Resonating holes vs molecular spin-orbit coupled states in group-5 lacunar spinels. Nature Communications, 14(1).
  Petersen, Thorben; Bhattacharyya, Pritam; Rößler, Ulrich K. & Hozoi, Liviu
  
• Coulomb exchange as source of Kitaev and off-diagonal symmetric anisotropic couplings. Communications Physics, 7(1).
  Bhattacharyya, Pritam; Petersen, Thorben; Bogdanov, Nikolay A. & Hozoi, Liviu
  
• Spin-Orbit-Lattice Entangled State in A2MgReO6 (A=Ca , Sr, Ba) Revealed by Resonant Inelastic X-Ray Scattering. Physical Review Letters, 133(3).
  Frontini, Felix I.; Johnstone, Graham H. J.; Iwahara, Naoya; Bhattacharyya, Pritam; Bogdanov, Nikolay A.; Hozoi, Liviu; Upton, Mary H.; Casa, Diego M.; Hirai, Daigorou & Kim, Young-June