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Register a new userFermi surfaces of the topological semimetal CaSn$_{3}$ probed through de Haas van Alphen oscillations
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In the search of topological superconductors, nailing down the Fermiology of the normal state is as crucial a prerequisite as unraveling the superconducting pairing symmetry. In particular, the number of time-reversal-invariant momenta in the Brillouin zone enclosed by Fermi surfaces is closely linked to the topological class of time-reversal-invariant systems, and can experimentally be investigated. We report here a detailed study of de Haas van Alphen quantum oscillations in single crystals of the topological semimetal CaSn$_{3}$ with torque magnetometry in high magnetic fields up to 35 T. In conjunction with density functional theory based calculations, the observed quantum oscillations frequencies indicate that the Fermi surfaces of CaSn$_{3}$ enclose an odd number of time-reversal-invariant momenta, satisfying one of the proposed criteria to realize topological superconductivity. Nonzero Berry phases extracted from the magnetic oscillations also support the nontrivial topological nature of CaSn$_{3}$.
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We report the magneto-transport properties of CaAl$_4$ single crystals with $C2/m$ structure at low temperature. CaAl$_4$ exhibits large unsaturated magnetoresistance $sim$3000$%$ at 2.5 K and 14 T. The nonlinear Hall resistivity is observed, which indicates the multi-band feature. The first-principles calculations show the electron-hole compensation and the complex Fermi surface in CaAl$_4$, to which the two-band model with over-simplified carrier mobility cant completely apply. Evident quantum oscillations have been observed with B//c and B//ab configurations, from which the nontrivial Berry phase is extracted by the multi-band Lifshitz-Kosevich formula fitting. An electron-type quasi-2D Fermi surface is found by the angle-dependent Shubnikov-de Haas oscillations, de Haas-van Alphen oscillations and the first-principles calculations. The calculations also elucidate that CaAl$_4$ owns a Dirac nodal line type band structure around the $Gamma$ point in the $Z$-$Gamma$-$L$ plane, which is protected by the mirror symmetry as well as the space inversion and time reversal symmetries. Once the spin-orbit coupling is included, the crossed nodal line opens a negligible gap (less than 3 meV). The open-orbit topology is also found in the electron-type Fermi surfaces, which is believed to help enhance the magnetoresistance observed.
Layered three-dimensional (3D) topological semimetals have attracted intensively attention due to the exotic phenomena and abundantly tunable properties. Here we report the experimental evidence for the 3D topological semimetal phase in layered material TaNiTe5 single crystals through quantum oscillations. Strong quantum oscillations have been observed with diamagnetism background in TaNiTe5. By analyzing the de Haas-van Alphen oscillations, multi-periodic oscillations were extracted, in content with magnetotransport measurements. Moreover, nontrivial {pi} Berry phase with 3D Fermi surface is identified, indicating the topologically nontrivial feature in TaNiTe5. Additionally, we demonstrated the thin-layer of TaNiTe5 crystals is highly feasible by the mechanical exfoliation, which offers a platform to explore exotic properties in low dimensional topological semimetal and paves the way for potential applications in nanodevices.
We have completely determined the Fermi surface in KFe$_2$As$_2$ via de Haas-van Alphen (dHvA) measurements. Fundamental frequencies $epsilon$, $alpha$, $zeta$, and $beta$ are observed in KFe$_2$As$_2$. The first one is attributed to a hole cylinder near the X point of the Brillouin zone, while the others to hole cylinders at the $Gamma$ point. We also observe magnetic breakdown frequencies between $alpha$ and $zeta$ and suggest a plausible explanation for them. The experimental frequencies show deviations from frequencies predicted by band structure calculations. Large effective masses up to 19 $m_e$ for $B parallel c$ have been found, $m_e$ being the free electron mass. The carrier number and Sommerfeld coefficient of the specific heat are estimated to be 1.01 -- 1.03 holes per formula unit and 82 -- 94 mJmol$^{-1}$K$^{-2}$, respectively, which are consistent with the chemical stoichiometry and a direct measure of 93 mJmol$^{-1}$K$^{-2}$ [H. Fukazawa textit{et al}., J. Phys. Soc. Jpn. textbf{80SA}, SA118 (2011)]. The Sommerfeld coefficient is about 9 times enhanced over a band value, suggesting the importance of low-energy spin and/or orbital fluctuations, and places KFe$_2$As$_2$ among strongly correlated metals. We have also performed dHvA measurements on Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ and have observed the $alpha$ and $beta$ frequencies.
We present the systematic de Haas-van Alphen (dHvA) quantum oscillations studies on the recently discovered topological Dirac semimetal pyrite PtBi2 single crystals. Remarkable dHvA oscillations were observed at field as low as 1.5 T. From the analyses of dHvA oscillations, we have extracted high quantum mobility, light effective mass and phase shift factor for Dirac fermions in pyrite PtBi2. From the angular dependence of dHvA oscillations, we have mapped out the topology of the Fermi surface and identified additional oscillation frequencies which were not probed by SdH oscillations.
We report measurements of the de Haas-van Alphen effect for single crystals of MgB$_2$, in magnetic fields up to 32 Tesla. In contrast to our earlier work, dHvA orbits from all four sheets of the Fermi surface were detected. Our results are in good overall agreement with calculations of the electronic structure and the electron-phonon mass enhancements of the various orbits, but there are some small quantitative discrepancies. In particular, systematic differences in the relative volumes of the Fermi surface sheets and the magnitudes of the electron-phonon coupling constants could be large enough to affect detailed calculations of T$_{c}$ and other superconducting properties.
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