Non-oxy delafossites: unconventional spin orbit entangled magnetism and electron transport

Layered chalcogenide (Ch) delafossites ABCh2, where A is a monovalent and B is a trivalent transition metal/rare earth ion, feature a wide variety of interesting phenomena, including superconductivity (NaxCoO2) [1], large thermoelectricity (Cu[Rh,Mg]O2) [2], multiferroicity (CuFeO2) [3], hydrodynamic electron flow (PdCoO2) [4,5] and spin-orbit driven frustration on a perfect triangular lattice (NaYbCh2) [6-9].

Most of the research done so far was on oxygen-based delafossites (DFs) whereas non-oxygen DFs (with S, Se or Te) are less investigated yet. The variation of the ionic radii of the mono- and trivalent- ions has only a little effect on the band structure and mainly tunes the lattice parameters whereas the choice of the chalcogenide ion itself has a strong impact on the band structure. For example, the oxy delafossite PdCoO2 has a quasi two-dimensional conductivity and the density of states at the Fermi level show minor chalcogenide 2p- electron admixture. In contrast to that in AgCrS2 or AgCrSe2 the larger spatial extended 3(4)p- states of S and Se promote the emergence of hybridized p- states at the Fermi level which finally leads to three-dimensional metallic or semi-metallic conductivity [10]. This promotes correlation effects in general and together with the emergence of strong spin polarization unconventional magnetism and (magneto-)transport is expected.

AgCrSe2 is a promising primer among non oxy delafossites, which exhibit an unusual liquid-like thermal conduction originating from the complex interplay of magnetic and charge degrees of freedom [11-13]. In particular the spin polarization of the charge carriers (Rashba effect) originate strong correlations and unconventional thermoelectricity [14]. We were able to successfully grow large AgCrSe2 single crystals. A first joint study with the Rossendorf High Field Laboratory and the ISIS Neutron and Muon Facility (Oxford, UK) has demonstrated anisotropic cycloidal magnetic ordering with unusual extended two-dimensional fluctuations [15]  We have developed a model for the magnetic exchange that consistently describes the determined magnetic phase diagram. Currently, we are extending the studies to AgCrS2.

This project combines the expertise in the field of oxy-delafossite at the MPI CPfS [16] with the search for new correlated triangular lattice, delafossite-like, systems. The aim is (i) to synthesize new materials (chemical vapor transport & solid state reaction - M. Schmidt, S. Khim) accompanied by structural characterization, (ii) to determine the thermodynamic (heat conductivity, specific heat) properties and the electronic (and magneto-) transport (M. Baenitz) and (iii) to apply microscopic spectroscopy like electron spin resonance (ESR, J. Sichelschmidt) and nuclear magnetic resonance (NMR, M. Baenitz). In addition, in-house theory support on band structure (H. Rosner) and magnetic exchange models (B. Schmidt) is available.


[1] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R. A. Dilanian, and T. Sasaki 

Superconductivity in two-dimensional CoO2 layers
Nature 4225355 (2003)
[2] H. Kuriyama, M. Nohara, T. Sasagawa, K. Takubo, T. Mizokawa, K. Kimura, and H. Takagi
High-temperature thermoelectric properties of Delafossite oxide CuRh1-xMgxO2
Proc. 25th International Conference on Thermoelectrics, Vienna, pp. 97-98 (2006)
[3] J.T. Haraldsen, F. Ye, R.S. Fishman, J.A. Fernandez-Baca, Y. Yamaguchi, K. Kimura, and T. Kimura
Multiferroic phase of doped delafossite CuFeO2 identified using inelastic neutron scattering
Phys. Rev. B 82, 020404(R) (2010)
[4] P.J.W. Moll, P. Kushwaha, N. Nandi, B. Schmidt, and A.P. Mackenzie
Evidence for hydrodynamic electron flow in PdCoO2
Science 351, 1061-1064 (2016)
[5] N. Nandi, T. Scaffidi, P. Kushwaha, S. Khim, M.E. Barber, V. Sunko, F. Mazzola, P.D.C. King, H. Rosner, P.J.W. Moll, M. König, J.E. Moore, S. Hartnoll, and A.P. Mackenzie
Unconventional magneto-transport in ultrapure PdCoO2 and PtCoO2
npj Quantum Materials 3, 66 (2018)
[6] M. Baenitz, Ph. Schlender, J. Sichelschmidt, Y.A. Onykiienko, Z. Zangeneh, K. M. Ranjith, R. Sarkar, L. Hozoi, H. C. Walker, J.-C. Orain, H. Yasuoka, J. van den Brink, H.H. Klauss, D.S. Inosov, and Th. Doert
NaYbS2: A planar spin-1/2 triangular-lattice magnet and putative spin liquid
Phys. Rev. B 98, 220409(R) (2018)
[7] K.M. Ranjith, D. Dmytriieva, S. Khim, J. Sichelschmidt, S. Luther, D. Ehlers, H. Yasuoka, J. Wosnitza, A.A. Tsirlin, H. Kühne, and M. Baenitz
Field-induced instability of the quantum spin liquid ground state in the Jeff = 1/2 triangular-lattice compound NaYbO2
Phys. Rev. B 99, 180401(R) (2019)
[8] K.M. Ranjith, S. Luther, T. Reimann, B. Schmidt, Ph. Schlender, J. Sichelschmidt, H. Yasuoka, A.M. Strydom, Y. Skourski, J. Wosnitza, H. Kühne, Th. Doert, and M. Baenitz
Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe2
Phys. Rev. B 100, 224417 (2019)
[9] B. Schmidt, J. Sichelschmidt, K.M. Ranjith, and M. Baenitz
Yb delafossites: Unique exchange frustration of 4f spin-1/2 moments on a perfect triangular lattice
Phys. Rev. B 103, 214445 (2021)
[10] R. Yano and T. Sasagawa
Crystal Growth and Intrinsic Properties of ACrX2 (A = Cu, Ag; X = S, Se) without a Secondary Phase
Cryst. Growth Des. 16, 5618–5623 (2016)
[11] B. Li, H. Wang, Y. Kawakita, Q. Zhang, M. Feygenson, H.L. Yu, D. Wu, K. Ohara, T. Kikuchi, K. Shibata, T. Yamada, X.K. Ning, Y. Chen, J.Q. He, D. Vaknin, R.Q. Wu, K. Nakajima, and M.G. Kanatzidis
Liquid-like thermal conduction in intercalated layered crystalline solids
Nature Materials 17, 226–230 (2018)
[12] C. Wang and Y. Chen
Highly selective phonon diffusive scattering in superionic layered AgCrSe2
npj Computational Materials 6, 26 (2020)
[13] J. Ding, J.L. Niedziela, D. Bansal, J. Wang, X. He, A.F. May, G. Ehlers, D.L. Abernathy, A. Said, A. Alatas, Y. Ren, G. Arya, and O. Delaire
Anharmonic lattice dynamics and superionic transition in AgCrSe2
PNAS 117, 3930 (2020)
[14] P. Ren, Y. Liu, J. He, T. Lv, J. Gao and G. Xu
Recent advances in inorganic material thermoelectrics
Inorg. Chem. Front. 5, 2380 (2018)
[15] M. Baenitz, M.M. Piva, S. Luther, J. Sichelschmidt, K.M. Ranjith, H. Dawczak-Dȩbicki, M.O. Ajeesh, S.-J. Kim, G. Siemann, C. Bigi, P. Manuel, D. Khalyavin, D.A. Sokolov, P. Mokhtari, H. Zhang, H. Yasuoka, P.D.C. King, G. Vinai, V. Polewczyk, P. Torelli, J. Wosnitza, U. Burkhardt, B. Schmidt, H. Rosner, S. Wirth, H. Kühne, M. Nicklas, and M. Schmidt
Planar triangular S=3/2 magnet AgCrSe2: Magnetic frustration, short range correlations, and field-tuned anisotropic cycloidal magnetic order
Phys. Rev. B 104, 134410 (2021)
[16] A.P. Mackenzie
The properties of ultrapure delafossite metals
Rep. Prog. Phys. 80, 032501 (2017)

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