ELFT HÍRADÓ

[Szeminárium koordinátor <sem-admin AT szfki.hu>]

SZFI SeminarYasir IqbalIndian Institute of Technology Madras (host: Penc 
Karlo)Quantum spin liquid physics on a novel square-kagome lattice 
materialTuesday, 14 December 2021, 10:00, Bldg 1., auditorium, 
https://wigner-hu.zoom.us/j/95473802970?pwd=R0VqZnlSUmNTUWNwb0N6M3BlT2Jqdz09  
 Meeting ID: 954 7380 2970  Passcode: 654044The search for quantum spin 
liquids is one of the most hotly pursued endeavors in condensed matter 
physics. In two dimensions, corner-sharing triangular geometries such as the 
kagome lattice have proved to be a fertile ground in realizing these exotic 
phases of quantum matter. In this talk, I will discuss the novel 
square-kagome lattice geometry as an ideal playground for realizing quantum 
spin liquids, being motivated by its recent first of a kind experimental 
realization in the spin S=1/2 system KCu6AlBiO4(SO4)5Cl. Towards 
understanding the rich quantum phase diagram of the square-kagome lattice, we 
employ state-of-the-art quantum many-body numerical techniques such as 
variational Monte Carlo (VMC) with versatile Gutzwiller-projected Jastrow 
wave functions, unconstrained multi-variable variational Monte Carlo (mVMC), 
and pseudo-fermion/Majorana functional renormalization group (PF/PM-FRG) 
methods. We establish the presence of a quantum paramagnetic ground state and 
investigate its nature, by classifying symmetric and chiral quantum spin 
liquids, and inspecting their instabilities towards competing 
valence-bond-crystal (VBC) orders. Our VMC analysis reveals that a VBC with a 
pinwheel structure emerges as the lowest-energy variational ground state, and 
it is obtained as an instability of the U(1) Dirac spin liquid. Analogous 
conclusions are drawn from mVMC calculations employing accurate BCS pairing 
states supplemented by symmetry projectors, which confirm the presence of 
pinwheel VBC order by a thorough analysis of dimer-dimer correlation 
functions. Our work highlights the nontrivial role of accounting for further 
neighbor Heisenberg and/or Dzyaloshinkii-Moriya interactions towards 
explaining the experimental observations. Minden érdeklődőt szívesen 
látunk! - Everyone is welcome to attend.Róbert Juhászsem-admin AT szfki.hu