Hall-effect sign reversal in CaRuO3 and SrRuO3 thin films

Cation disorder and epitaxial strain modulated Drude-Smith type terahertz conductivity and Hall-carrier switching in Ca1-x Ce x RuO3 thin films

The CaRuO₃ is a non-Fermi liquid pseudo-cubic perovskite with a magnetic ground state on the verge of phase transition and it lies in the vicinity of the quantum critical point. To understand the sensitivity of its ground state, the effects of subtle aliovalent chemical disorder on the static and high frequency dynamic conductivity in the coherently strained structures were explored. The Ce-doped Ca_1-x Ce _x RuO₃ (0  ⩽  x  ⩽  0.1) thin films were deposited on LaAlO₃ (1 0 0) and SrTiO₃ (1 0 0) substrates and studies for low-energy terahertz (THz) carrier dynamics, dc transport and Hall effect. These compositions exhibited a very effective and unusual Hall-carrier switching in both compressive and tensile strain induced epitaxial thin films. The dc resistivity depicts a switching from a non-Fermi liquid to a Fermi liquid behavior without any magnetic phase transition. A discernible and gradual crossover from Drude to Drude-Smith THz dynamic optical conductivity was observed while traversing from pure to 10% Ce-doped CaRuO₃ films. Overall, a nearly Fermi liquid behavior, effective carrier switching and unusual features in THz conductivity, were all novel features realized for the first time in physically and/or chemically modified CaRuO₃. These new phases highlight the novel subtleties and versatility of the systems lying near the quantum critical point.

Complex behaviour of vacancy point-defects in SrRuO3 thin films

Metastable point-defect concentrations on both anion and cation sublattices give rise to complex time-dependent diffusion behaviour and compositional and morphological changes in thin-film SrRuO₃.

Ferromagnetic CaRuO3

The non-magnetic and non-Fermi-liquid CaRuO₃ is the iso-structural analog of the ferromagnetic (FM) and Fermi-liquid SrRuO₃. We show that an FM order in the orthorhombic CaRuO₃ can be established by the means of tensile epitaxial strain. The structural and magnetic property correlations in the CaRuO₃ films formed on SrTiO₃ (100) substrate establish a scaling relation between the FM moment and the tensile strain. The strain dependent crossover from non-magnetic to FM CaRuO₃ was observed to be associated with switching of non-Fermi liquid to Fermi-liquid behavior. The intrinsic nature of this strain-induced FM order manifests in the Hall resistivity too; the anomalous Hall component realizes in FM tensile-strained CaRuO₃ films on SrTiO₃ (100) whereas the non-magnetic compressive-strained films on LaAlO₃ (100) exhibit only the ordinary Hall effect. These observations of an elusive FM order are consistent with the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in tensile CaRuO₃. We further establish that the tensile strain is more efficient than the chemical route to induce FM order in CaRuO₃.

Anomalous Hall effect and electron transport in ferromagnetic MnBi films

The electron transport properties of highly c-axis oriented MnBi thin films of various thicknesses have been investigated. Samples are metallic but the low temperature resistivity shows an unusual T(3) dependence. Transverse Hall effect measurements show that both the ordinary and anomalous Hall coefficients decrease with decreasing temperature below 300 K, but the ordinary Hall coefficient (R(0)) undergoes a sign reversal around 105 K, where the magnetic anisotropy also changes sign. Analysis of the Hall data for various samples shows that the anomalous Hall coefficient (R(s)) exhibits a strong ρ(2) dependence, where ρ is the longitudinal resistivity.

Orbital non-fermi-liquid behavior in cubic ruthenates

We peruse various anomalous physical responses of the cubic (ferromagnetic SrRuO3 and paramagnetic CaRuO3) ruthenates, such as fractional power-law conductivity, anomalous Raman line shapes, and Hall currents. We show how these exciting power-law observations are naturally described within a new, local (orbital) non-Fermi-liquid state arising from strong, multiorbital Coulomb interactions. Introducing a multiorbital, correlated model treated within the dynamical mean-field theory, we also find two distinct relaxation rates for relaxation of transport in complete agreement with experiment.

Strongly correlated superconductivity in Rh17S15

In this Letter, we report resistivity, susceptibility, heat capacity, and upper critical field studies on a polycrystalline Rh17S15 sample which exhibits superconductivity below 5.4 K. Detailed studies suggest that the superconductivity in this compound arises from strongly correlated charge carriers presumably due to the high density of states of Rh d bands at the Fermi level. Moreover, the Hall coefficient shows a sign change and increases at low temperature before the sample becomes a superconductor below 5.4 K.