Magnetic-field periodic quantum Sondheimer oscillations in thin-film graphite

Materials with the mesoscopic scales have provided an excellent platform for quantum-mechanical studies. Among them, the periodic oscillations of the electrical resistivity against the direct and the inverse of the magnetic fields, such as the Aharonov-Bohm effect and the Shubnikov-de Haas effect, manifest the interference of the wavefunction relevant to the electron motion perpendicular to the magnetic field. In contrast, the electron motion along the magnetic field also leads to the magnetic-field periodicity, which is the so-called Sondheimer effect. However, the Sondheimer effect has been understood only in the framework of the semiclassical picture, and thereby its interpretation at the quasiquantum limit was not clear. Here, we show that thin-film graphite exhibits clear sinusoidal oscillations with a period of about 1-3 T over a wide range of the magnetic fields (from around 10 T to 30 T), where conventional quantum oscillations are absent. In addition, the sample with a designed step in the middle for eliminating the stacking disorder effect verifies that the period of the oscillations is inversely proportional to the thickness, which supports the emergence of the Sondheimer oscillations in the quasiquantum limit. These findings suggest that the Sondheimer oscillations can be reinterpreted as inter-Landau-level resonances even at the field range where the semiclassical picture fails. Our results expand the quantum oscillation family, and pave the way for the exploration of the out-of-plane wavefunction motion.Comment: 17 pages, 5 figure

Quantized thermoelectric Hall plateau in the quantum limit of graphite as a nodal line semimetal

We performed thermoelectric Hall conductivity $\alpha_{xy}$ measurements on single crystal graphite in the quantum limit up to 13 T. Both electrical and thermoelectric transport measurements were performed on the same crystal to extract pure $\alpha_{xy}$ avoiding any sample quality dependence. The $\alpha_{xy}$ converges to a plateau in the quantum limit with a linear dependence on temperature. This behavior is analogous to the quantized thermoelectric Hall effect (QTHE) observed in 3D Dirac/Weyl nodal point semimetals, and experimentally confirms a theoretical proposal on the QTHE in semimetals with nodal lines like graphite.Comment: 14 pages, 3 figures, with supplemental informatio

Large and homogeneous mass enhancement in the rattling-induced superconductor KOs2_2O6_6

We have determined the Fermi surface in KOs$_2$O$_6$ ($T_c$ = 9.6 K and $B_{c2} \sim$ 32 T) via de Haas-van Alphen (dHvA) oscillation measurements and a band structure calculation. We find effective masses up to 26(1) $m_e$ ($m_e$ is the free electron mass), which are unusually heavy for compounds where the mass enhancement is mostly due to electron-phonon interactions. Orbit-resolved mass enhancement parameters $\lambda_{dHvA}$ are large but fairly homogeneous, concentrated in the range 5 -- 8. We discuss origins of the large homogeneous mass enhancement in terms of rattling motion of the K ions.Comment: Minor revisions, Fig.2a modifie

Orbital, charge, and spin couplings in Ru 25+O9 dimers of Ba3CoRu2O9

e magnetic, transport, and structural properties of cold-pressed Ba3CoRu2O9 show (i) an antiferromagnetic transition, (ii) a semiconductor-semiconductor electronic transition where the resistivity is dominated by the electron hopping between the Ru25+O9 dimers with itinerant Ru electrons at high temperatures, and (iii) a hexagonal to orthorhombic structural phase transition. All three transitions occur at 93 K and are related to the Ru5+ ions in the Ru2O9 dimers. The Ru-O bond distortion below 93 K further indicates a possible orbital ordering for Ru5+ ions in isolated Ru2O9 dimers, which accounts for the strong orbital, charge, and spin couplingsThis work is supported by NSF-DMR-0654118 and the State of Florida. J.S.B. and A.K. acknowledge support from NSF-DMR-1005293S