Non-Fermi-liquid behavior in nearly ferromagneticSrIrO3single crystals

Abstract

We report transport and thermodynamic properties of single-crystal SrIrO 3 as a function of temperature T and applied magnetic field H. We find that SrIrO 3 is a nonFermi-liquid metal near a ferromagnetic instability, as characterized by the following properties: (1) small ordered moment but no evidence for long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility that diverges as T -γ at low temperatures with 1/2 < γ < 1, depending on the applied field; (3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied fields; (4) a strikingly large Wilson ratio at T< 4K;and (5) a T 3/2 -dependence of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based on the data implies SrIrO 3 is a rare example of a stoichiometric oxide compound that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0 and μ ο H = 0.23 T). model system for studies of quantum criticality both experimentally and theoretically.It is now qualitatively understood that the extended 5d orbital significantly enhances crystalline electric field splittings causing a partial breakdown of Hund's rule, leading to a low spin state, S = 1/2 for Ir 4+ (5d 5 ) ions, and a d-p hybridization between the transition metal and the oxygen octahedron enclosing it. These interactions generate strong electron-lattice coupling that can alter and distort the metal-oxygen bond lengths and angles, lifting the degeneracies of 5d-orbitals and precipitating orbital ordering.Single crystals were grown using flux techniques described elsewhere [7]. The crystal structure was determined from a small fragment (0.05×0.05×0.05 mm 3 ) using MoKα radiation and a Nonius Kappa CCD single-crystal diffractometer. Heat capacity measurements were performed with a Quantum Design PPMS that utilizes a thermal- χ ab at T <5 K.) Indeed, the isothermal magnetization M at T = 1.7 K is already saturated at μ ο H ~3 T, as seen in the inset to Fig. 1a. On the other hand, the corresponding ordered moment μ or is less than 3% of that expected (1 μ B /Ir) for an S = 1/2 system and decreases with increasing T, which is indicative of a nearby Stoner instability. 4The reciprocal susceptibilities χ c -1 and χ ab -1 display linear T-dependences, consistent with a Curie-Weiss behavior for T > 120 K, as shown in Fig.1b follow non-standard power laws that range from T 1/2 for B < 0.3 T to linear-T for B > 0.8 T, as shown in Fig. 1c. This high sensitivity of the temperature exponent to low applied magnetic fields again suggests the rapid approach to a ferromagnetic instability.The low temperature specific heat C(T,H) data acquired over 1.8 < T < 24 K and μ ο H < 8 T offer important insights into the low energy excitations of SrIrO 3 . For T > 12 K, the specific heat is well described by C(T) = γT + βT 3 with γ = 1.50 mJ/mole K 2 and β = 0.28 mJ/mole K 4 , suggesting that only electronic and phonon contributions are significant in this temperature range (data not shown). The small γ-value implies that there is essentially no mass enhancem...

Synthesis, Crystal Structure, and Physical Properties of the Perovskite Iridates

“…Since the 6H phase is close to a ferromagnetic quantum critical point, the γ is much enhanced due to critical fluctuations relative to that in the 3C phase with an even broader bandwidth. From this systematic study on BaIrO 3 polytypes, we can understand why the 6H SrIrO 3 is a non-Fermi-liquid metal near a ferromagnetic quantum critical point [11]. Moreover, the study on BaIrO 3 demonstrated that HPHT synthesis of structurally closely related perovskite polytypes represents an effective approach to fine tune the physical properties of interest via modifying the octahedral arrangement.…”

“…6H SrIrO 3 Although the 6H SrIrO 3 has been synthesized more than 50 years ago, its physical properties were not characterized in detail until 2007 by Cao et al [11], who reported the magnetic, electrical transport, and calorimetric properties of 6H SrIrO 3 single crystals grown out of the SrCl 2 flux. The primary results are summarized in Figure 6.…”

“…the monoclinically distorted 6H polytype and the orthorhombic GdFeO 3 -type Pv structure [8]. The former is a rare stoichiometric oxide exhibiting non-Fermi-liquid behaviours near a ferromagnetic quantum critical point [11]. The latter was recently found to be an exotic narrow-band semimetal that may harvest many topological and magnetic insulating phases [10,41,42].…”

“…Single crystals of 6H phase with dimensions ~0.4 × 0.4 × 0.6 mm 3 have been grown in Pt crucibles with the SrCl 2 self-flux techniques [11]. The Pv phase is a HP form of SrIrO 3 .…”

Emergence of non-Fermi liquid behaviors in 5d perovskite SrIrO3 thin films: Interplay between correlation, disorder, and spin-orbit coupling

“…From the viewpoint of crystal structures, the ground state of SrIrO 3 at room temperature and atmospheric pressure is the structure of hexagonal BaTiO 3 [12]. Studies on hexagonal SrIrO 3 single crystals revealed that it is a metallic system exhibiting NFL behaviors; the specific heat displays a typical logarithmic divergence and the electrical resistivity follows T 3/2 [13]. This NFL physics has been attributed to quantum criticality.…”