Sr_2RuO_4 is an unconventional superconductor with a tetragonal structure, whereas Ca_2RuO_4 is a Mott insulator with orthorhombic symmetry. The substituted Ca_2-xSr_xRuO_4 has yielded a rich phase diagram that is just beginning to be explored in detail. Experimental investigation of the resistivity ρ, susceptibility χ, specific heat C_p, Hall coefficient R_H, and X-ray diffraction of Ca_1.7Sr_0.3RuO_4 reveals a structural phase transition near T_0 = 190 K and heavy-Fermion (HF) behavior below a coherence temperature T^* ∼ 10 K, resembling that of the f-electron HF compound UPt_3. The observation of T^2-dependence of ρ below ∼ 0.5 K suggests a Fermi-liquid ground state. Based upon our data and theoretical calculations, we argue that the structural change at T_0 may be responsible for the formation of the HF state.

Li0.9Mo6O17 is a quasi-one-dimensional metal having highly anisotropic electronic properties (1). Previous studies of this material by angle-resolved photoemission spectroscopy (ARPES) (2-4) have shown various signatures of the Luttinger liquid (LL) model (5), including a power-law like density of state (DOS) near Fermi energy EF. The power-law DOS has also been observed in scanning tunneling spectroscopy, however with a different anomalous exponent α value (6). I am going to present our most recently work, where we carefully studied the temperature dependence of Li0.9Mo6O17 over a wide T range of 15-300 K using ARPES. We have found that α shows a strong T-dependent renormalization such that the values found in tunneling and previous ARPES are quantitatively consistent, and that this renormalization is the result of marginal interactions among charge neutral modes present explicitly because of the two-band nature of Li0.9Mo6O17 (7). The angle resolved spectra are also analyzed and show T scaling over a wide T range. To understand the slight deviation from perfect T scaling at low T, we compare experiment data to simulations with consideration of finite resolutions. Since low energy ARPES is generally a surface sensitive technique, we compared our results from SRC using low photon energy to those from Spring-8 using high photon energy, which confirms the LL behaviors we have measured in Li0.9Mo6O17 is of real bulk (8). This work was supported at UM by the U.S. NSF (DMR-03-02825), at UAM by MEC under a contract RyC, at the ORNL by the U.S. DoE (DE-AC05- 00OR22725), at UT by the U.S. NSF (DMR-00-72998), at the SRC by the U.S. NSF (DMR-00-84402).