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) [6,7,8].

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 [9]. 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 [10,11,12]. In particular the spin polarization of the charge carriers (Rashba effect) originate strong correlations and unconventional thermoelectricity [13].

This project combines the expertise in the field of oxy-delafossite at the MPI CPfS [14] 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.

Figure: Crystal structure of AgCrSe2. CrSe6 octahedral layers are separated by AgSe4 equivalent tetrahedral layers. Cr3+ ions form triangular layers in the ab plane


[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] 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)
[10] 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)
[11] C. Wang and Y. Chen
Highly selective phonon diffusive scattering in superionic layered AgCrSe2
npj Computational Materials 6, 26 (2020)
[12] 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)
[13] 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)
[14] A.P. Mackenzie
The properties of ultrapure delafossite metals
Rep. Prog. Phys. 80, 032501 (2017)

Other Interesting Articles

Go to Editor View