Magnetism and local symmetry breaking in a Mott insulator with strong spin orbit interactions

Abstract

Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local point symmetry breaking or local spin expectation values, even in materials with simple cubic crystal structure such as Ba2NaOsO6. Experimental tests of these theories by local probes are highly sought for. Our local measurements designed to concurrently probe spin and orbital/lattice degrees of freedom of Ba2NaOsO6 provide such tests. Here we show that a canted ferromagnetic phase which is preceded by local point symmetry breaking is stabilized at low temperatures, as predicted by quantum theories involving multipolar spin interactions.

Phase transition preceding magnetic long-range order in the double perovskite Ba2NaOsO6

“…netization data obtained on the same Ba 2 NaOsO 6 single crystal. Using general thermodynamic considerations and the Fisher formula [22] we separate magnetic and non-magnetic contributions to the specific heat, and present evidence for a largely field-independent phase transition occurring at T s ≈ 9.5K, slightly above the magnetic ordering temperature of T c ≈ 7.5 K. This transition appears as a broadened step in the temperature dependence of the specific heat, and its evolution with applied magnetic field suggests that this phase corresponds to the broken local point symmetry phase seen in NMR experiments in high fields [19][20][21]. Our specific heat results, in conjunction with the NMR findings, indicate that this new phase between T c and T s is nematic in origin as predicted by theoretical models [8,11].…”

“…This state is unstable against a Jahn-Teller distortion [10,11,15] that induces a tetragonal paramagnetic phase with a two fold degenerate ground state as also indicated by measurements of the entropy balance across the magnetic transition yielding a value close to R ln 2 rather than R ln 4 [17]. Furthermore, recent high-field NMR experiments [19][20][21] reveal that the magnetically ordered state of Ba 2 NaOsO 6 is composed of an exotic non-collinear magnetic structure in which successive ferromagnetic Os-Na layers that subtend a canting angle of ≈ 134 • resulting in a small net magnetic moment along (110). This long-range magnetic order is driven by orbital ordering and has an over-all orthorhombic symmetry.…”

Spin-Orbit Dimers and Noncollinear Phases in d1 Cubic Double Perovskites

“…In Ba 2 NaOsO 6 , anomalously small net ordered moment ∼ 0.2µ B has additionally been detected [15,16]. Recent NMR measurements indicate a canted AF order in the Na compound [20].…”

Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe2

“…Rare-earth based frustrated spin systems have recently gained much attention [18,19]. The strong spin-orbit coupling (SOC) associated with the rare-earth ion leads to highly anisotropic and bond-dependent exchange interactions between the moments and may host strong quantum fluctuations, which can play a crucial role in stabilising the QSL state [20][21][22][23]. YbMgGaO 4 , a 4f based triangular-lattice system, has been investigated rigorously and proposed as a promising QSL candidate [24,25].…”