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Topological electronic structures are key to the topological classification of quantum materials and play an important role in their physical properties and applications. Recently, SnSe has attracted great research interests due to its superior thermoelectric performance. However, it's topological nature has long been ignored. In this work, by combining synchrotron-based angle-resolved photoemission spectroscopy and ab-initio calculations, we systematically investigated the topological electronic structure of orthorhombic SnSe. By identifying the continuous gap in the valence bands due to the band inversion and the topological surface states on its (001) surface, we establish SnSe as a strong topological insulator. Furthermore, we studied the evolution of the topological electronic structure and propose the topological phase diagram in SnSe1-xTex. Our work reveals the topological non-trivial nature of SnSe and provides new understandings of its intriguing transport properties., Comment: 17 pages, 4 figures, accepted for publication in Physical Review Materials

High-spin structure of $^{109}$In has been investigated with the $^{100}$Mo($^{14}$N, 5$n$)$^{109}$In reaction at a beam energy of 78 MeV using the in-beam $\gamma$ spectroscopic method. The level scheme of $^{109}$In has been modified considerably and extended by 46 new $\gamma$-rays to the highest excited state at 8.979 MeV and $J^{\pi}$=(45/2$^{+}$). The new level scheme consists of eight bands, six of which are identified as dipole bands. The configurations have been tentatively assigned with the help of the systematics of neighboring odd-$A$ indium isotopes and the experimental aligned angular momenta. The dipole bands are then compared with the titled axis cranking calculation in the framework of covariant density function theory (TAC-CDFT). The results of theoretical calculation based on the configurations, which involve one proton hole at the $g_{9/2}$ orbital and two or four unpaired neutrons at $g_{7/2}$, $d_{5/2}$ and $h_{11/2}$ orbitals, show that the shape of $^{109}$In undergoes an evolution on both $\beta$ and $\gamma$ deformations and possible chirality is suggested in $^{109}$In., Comment: 15 pages, 10 figures, 2 tables, 75 conference

We have performed a systematic high-momentum-resolution photoemission study on ZrTe$_5$ using $6$ eV photon energy. We have measured the band structure near the $\Gamma$ point, and quantified the gap between the conduction and valence band as $18 \leq \Delta \leq 29$ meV. We have also observed photon-energy-dependent behavior attributed to final-state effects and the 3D nature of the material's band structure. Our interpretation indicates the gap is intrinsic and reconciles discrepancies on the existence of a topological surface state reported by different studies. The existence of a gap suggests that ZrTe$_5$ is not a 3D strong topological insulator nor a 3D Dirac semimetal. Therefore, our experiment is consistent with ZrTe$_5$ being a 3D weak topological insulator., Comment: 8 pages, 5 figures

Topological Dirac semimetals (TDSs) represent a new state of quantum matter recently discovered that offers a platform for realizing many exotic physical phenomena. A TDS is characterized by the linear touching of bulk (conduction and valance) bands at discrete points in the momentum space (i.e. 3D Dirac points), such as in Na3Bi and Cd3As2. More recently, new types of Dirac semimetals with robust Dirac line-nodes (with non-trivial topology or near the critical point between topological phase transitions) have been proposed that extends the bulk linear touching from discrete points to 1D lines. In this work, using angle-resolved photoemission spectroscopy (ARPES), we explored the electronic structure of the non-symmorphic crystals MSiS (M=Hf, Zr). Remarkably, by mapping out the band structure in the full 3D Brillouin Zone (BZ), we observed two sets of Dirac line-nodes in parallel with the kz-axis and their dispersions. Interestingly, along directions other than the line-nodes in the 3D BZ, the bulk degeneracy is lifted by spin-orbit coupling (SOC) in both compounds with larger magnitude in HfSiS. Our work not only experimentally confirms a new Dirac line-node semimetal family protected by non-symmorphic symmetry, but also helps understanding and further exploring the exotic properties as well as practical applications of the MSiS family of compounds., Comment: 5 figures

New optical arrangements with two single-mode input fibers and a fiber-optic coupler are devised to measure the instantaneous velocity difference and local velocity. The fibers and the coupler are polarization-preserving to guarantee a high signal-to-noise ratio. When the two input fibers are used to collect the scattered light with the same momentum transfer vector but from two spatially separated regions in a flow, the obtained signals interfere when combined via the fiber-optic coupler. The resultant light received by a photomultiplier tube contains a cross-beat frequency proportional to the velocity difference between the two measuring points. If the two input fibers are used to collect the scattered light from a common scattering region but with two different momentum transfer vectors, the resultant light then contains a self-beat frequency proportional to the local velocity at the measuring point. The experiment shows that both the cross-beat and self-beat signals are large and the standard laser Doppler signal processor can be used to measure the velocity difference and local velocity in real time. The new technique will have various applications in the general area of fluid dynamics., Comment: Patent number: 67437 for associated information on the hardware, see http://karman.phyast.pitt.edu/horvath/