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Motivated by a recent reporting of a first of a kind experimental realization of a gapless quantum spin liquid state on the novel square-kagome lattice geometry realized in the spin S=1/2 system KCu6AlBiO4(SO4)5Cl [1], we discuss the possible microscopic origins of this state, and more broadly highlight this novel geometry as an ideal playground for stabilizing a diverse array of exotic quantum phases [2]. Employing 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 analysis reveals that a VBC with a pinwheel structure of spin correlations emerges as the lowest-energy variational ground state, and it is obtained as an instability of the U(1) Dirac spin liquid. We argue that further neighbor Heisenberg and/or Dzyaloshinkii-Moriya interactions play a crucial role towards explaining the experimental observations. References: [1] Nat. Commun. 11, 3429 (2020), Gapless spin liquid in a square-kagome lattice antiferromagnet, Masayoshi Fujihala, Katsuhiro Morita, Richard Mole, Setsuo Mitsuda, Takami Tohyama, Shin-ichiro Yano, Dehong Yu, Shigetoshi Sota, Tomohiko Kuwai, Akihiro Koda, Hirotaka Okabe, Hua Lee, Shinichi Itoh, Takafumi Hawai, Takatsugu Masuda, Hajime Sagayama, Akira Matsuo, Koichi Kindo, Seiko Ohira-Kawamura & Kenji Nakajima [2] Phys. Rev. B 104, L220408 (2021), Pinwheel valence-bond-crystal ground state of the spin-1/2 Heisenberg antiferromagnet on the shuriken lattice, Nikita Astrakhantsev, Francesco Ferrari, Nils Niggemann, Tobias Müller, Aishwarya Chauhan, Augustine Kshetrimayum, Pratyay Ghosh, Nicolas Regnault, Ronny Thomale, Johannes Reuther, Titus Neupert, Yasir Iqbal Zoom-Link: https://uni-koeln.zoom.us/j/9524918125?pwd=dWN1RW1mMUpDRWdyMWwzWGtURWVIZz09

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Yasir Iqbal, IIT Madras, Chennai
Seminar Room of the Institute of Physics II, zoom
Contact: Simon Trebst