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Ce$_{3}$Bi$_{4}$Au$_{3}$ crystallizes in the same non-centrosymmetric cubic structure as the prototypical Kondo insulator Ce$_{3}$Bi$_{4}$Pt$_{3}$. Here we report the physical properties of Ce$_{3}$Bi$_{4}$Au$_{3}$ single crystals using magnetization, thermodynamic, and electrical-transport measurements. Magnetic-susceptibility and heat-capacity data reveal antiferromagnetic (AFM) order below $T_N=3.2$ K. The magnetic entropy $S_{\rm mag}$ reaches $R$ln2 slightly above $T_N$, which suggests localized $4f$-moments in a doublet ground state. Multiple field-induced magnetic transitions are observed at temperatures below $T_N$, which indicate a complex spin structure with competing interactions. Ce$_{3}$Bi$_{4}$Au$_{3}$ shows semimetallic behavior in electrical resistivity measurements in contrast to the majority of reported Cerium-based 343 compounds. Electrical-resistivity measurements under hydrostatic pressure reveal a slight enhancement of $T_N$ under pressures up to 2.3 GPa, which supports a scenario wherein Ce$_{3}$Bi$_{4}$Au$_{3}$ belongs to the far left of the Doniach phase diagram dominated by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Using realistic many-body simulations, we confirm the semi-metallic electronic structure of Ce$_{3}$Bi$_{4}$Au$_{3}$ and quantitatively reproduce its local moment behavior in the paramagnetic state., Comment: 10 pages, 10 figures

In this article, for a certain subset $\mathcal{X}$ of the extended set of rational numbers, we introduce the notion of {\it best $\mathcal{X}$-approximations} of a real number. The notion of best $\mathcal{X}$-approximation is analogous to that of best rational approximation. We explore these approximations with the help of $\mathcal{F}_{p^l}$-continued fractions, where $p$ is a prime and $l\in\mathbb{N}$, we show that the convergents of the $\mathcal{F}_{p^l}$-continued fraction expansion of a real number $x$ satisfying certain maximal conditions are exactly the best $\mathcal{F}_{p^l}$-approximations of $x$.

Noncentrosymmetric Ce$_{3}$Bi$_{4}$Pd$_{3}$ has attracted a lot of attention as a candidate for strongly correlated topological material, yet its experimental ground state remains a matter of contention. Two conflicting scenarios have emerged from a comparison to prototypical Kondo insulator Ce$_{3}$Bi$_{4}$Pt$_{3}$: either Ce$_{3}$Bi$_{4}$Pd$_{3}$ is a spin-orbit-driven topological semimetal or a Kondo insulator with smaller Kondo coupling than its Pt counterpart. Here we determine the ground state of Ce$_{3}$Bi$_{4}$Pd$_{3}$ via electrical resistivity measurements under hydrostatic pressure, which is a clean symmetry-preserving tuning parameter that increases hybridization but virtually preserves spin-orbit coupling. Ce$_{3}$Bi$_{4}$Pd$_{3}$ becomes more insulating under pressure, which is a signature of Ce-based Kondo insulating materials. Its small zero-pressure gap increases quadratically with pressure, similar to the behavior observed in the series Ce$_{3}$Bi$_{4}$(Pt$_{1-x}$Pd$_{x}$)$_{3}$, which indicates that Pt substitution and applied pressure have a similar effect. Our result not only demonstrates that Kondo coupling, rather than spin-orbit coupling, is the main tuning parameter in this class of materials, but it also establishes that Ce$_{3}$Bi$_{4}$Pd$_{3}$ has a narrow-gap Kondo insulating ground state., Comment: 6 pages, 4 Figures, includes Supplementary Information (6 pages, 5 Figures)

In this note, we study a family of subgraphs of the Farey graph, denoted as $\mathcal{F}_N$ for every $N\in\mathbb{N}.$ We show that $\mathcal{F}_N$ is connected if and only if $N$ is either equal to one or a prime power. We introduce a class of continued fractions referred to as $\mathcal{F}_N$-continued fractions for each $N>1.$ We establish a relation between $\mathcal{F}_N$-continued fractions and certain paths from infinity in the graph $\mathcal{F}_N.$ We discuss existence and uniqueness of $\mathcal{F}_N$-continued fraction expansions of real numbers.

Here we investigate antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$, a nonsymmorphic Zintl phase. Our electrical transport data show that Eu$_{5}$In$_{2}$Sb$_{6}$ is remarkably insulating and exhibits an exceptionally large negative magnetoresistance, which is consistent with the presence of magnetic polarons. From {\it ab initio} calculations, the paramagnetic state of Eu$_{5}$In$_{2}$Sb$_{6}$ is a topologically nontrivial semimetal within the generalized gradient approximation (GGA), whereas an insulating state with trivial topological indices is obtained using a modified Becke-Johnson potential. Notably, GGA+U calculations suggest that the antiferromagnetic phase of Eu$_{5}$In$_{2}$Sb$_{6}$ may host an axion insulating state. Our results provide important feedback for theories of topological classification and highlight the potential of realizing clean magnetic narrow-gap semiconductors in Zintl materials., Comment: Accepted in npj Quantum Materials. Author list and affiliations corrected

Time- and angle-resolved photoemission spectroscopy accesses the ultrafast evolution of quasiparticles and many-body interactions in solid-state systems. However, the momentum- and energy-resolved transient photoemission intensity may not be unambiguously related to the intrinsic relaxation dynamics of photoexcited electrons. In fact, interpretation of the time-dependent photoemission signal can be affected by the transient evolution of both the one-electron removal spectral function as well as the photoemission dipole matrix elements. Here we investigate the topological insulator Bi$_{1.1}$Sb$_{0.9}$Te$_2$S to demonstrate, by means of a careful probe-polarization study, the transient contribution of matrix elements to the time-resolved photoemission signal., Comment: 7 pages, 3 figures

We show that two different superconducting phases exist at high pressures in the optimized tetradymite topological insulators Bi2Te2Se (BTS) and Bi1.1Sb0.9Te2S (BSTS). The superconducting phases emerge at structural phase transitions, the first at 8.4 GPa for BTS and 12.4 GPa for BSTS, and the second at 13.6 GPa for BTS and 20.4 GPa, for BSTS. Electronic structure calculations show that these phases do not have topological character. Comparison of our results with prior work on Bi2Se3, Bi2Te3 and (Bi,Sb)2(Se,Te)3 allows us to uncover a universal phase diagram for pressure-induced superconductivity in tetradymites, providing a basis for understanding the relationships between topological behavior, crystal structure, and superconductivity for these materials., Comment: 24 pages ands 4 figures

The archetypical 3D topological insulators Bi2Se3, Bi2Te3 and Sb2Te3 commonly exhibit high bulk conductivities, hindering the characterization of the surface state charge transport. The optimally doped topological insulators Bi2Te2Se and Bi2-xSbxTe2S, however, allow for such characterizations to be made. Here we report the first experimental comparison of the topological surface states and bulk conductances of Bi2Te2Se and Bi1.1Sb0.9Te2S, based on temperature-dependent high-pressure measurements. We find that the surface state conductance at low temperatures remains constant in the face of orders of magnitude increase in the bulk state conductance, revealing in a straightforward way that the topological surface states and bulk states are decoupled at low temperatures, consistent with theoretical models, and confirming topological insulators to be an excellent venue for studying charge transport in 2D Dirac electron systems., Comment: 23 pages, 4 figures

Topological surface states have been extensively observed via optics in thin films of topological insulators. However, in typical thick single crystals of these materials, bulk states are dominant and it is difficult for optics to verify the existence of topological surface states definitively. In this work, we studied the charge dynamics of the newly formulated bulk-insulating Sn-doped Bi$_{1.1}$Sb$_{0.9}$Te$_2$S crystal by using time-domain terahertz spectroscopy. This compound shows much better insulating behavior than any other bulk-insulating topological insulators reported previously. The transmission can be enhanced an amount which is 5$\%$ of the zero-field transmission by applying magnetic field to 7 T, an effect which we believe is due to the suppression of topological surface states. This suppression is essentially independent of the thicknesses of the samples, showing the two-dimensional nature of the transport. The suppression of surface states in field allows us to use the crystal slab itself as a reference sample to extract the surface conductance, mobility, charge density and scattering rate. Our measurements set the stage for the investigation of phenomena out of the semi-classical regime, such as the topological magneto-electric effect., Comment: 5 pages, 3 figures, submitted in August

Extreme magnetoresistance (XMR) in topological semimetals is a recent discovery which attracts attention due to its robust appearance in a growing number of materials. To search for a relation between XMR and superconductivity, we study the effect of pressure on LaBi taking advantage of its simple structure and simple composition. By increasing pressure we observe the disappearance of XMR followed by the appearance of superconductivity at P=3.5 GPa.The suppression of XMR is correlated with increasing zero-field resistance instead of decreasing in-field resistance. At higher pressures, P=11 GPa, we find a structural transition from the face center cubic lattice to a primitive tetragonal lattice in agreement with theoretical predictions. We discuss the relationship between extreme magnetoresistance, superconductivity, and structural transition in LaBi., Comment: 10 pages, 10 figures, 1 table

Optical measurements and band structure calculations are reported on 3D Dirac materials. The electronic properties associated with the Dirac cone are identified in the reflectivity spectra of Cd$_3$As$_2$ and Na$_3$Bi single crystals. In Na$_3$Bi, the plasma edge is found to be strongly temperature dependent due to thermally excited free carriers in the Dirac cone. The thermal behavior provides an estimate of the Fermi level $E_F=25$ meV and the z-axis Fermi velocity $v_z = 0.3 \text{ eV} \AA$ associated with the heavy bismuth Dirac band. At high energies above the $\Gamma$-point Lifshitz gap energy, a frequency and temperature independent $\epsilon_2$ indicative of Dirac cone interband transitions translates into an ab-plane Fermi velocity of $3 \text{ eV} \AA$. The observed number of IR phonons rules out the $\text{P}6_3\text{/mmc}$ space group symmetry but is consistent with the $\text{P}\bar{3}\text{c}1$ candidate symmetry. A plasmaron excitation is discovered near the plasmon energy that persists over a broad range of temperature. The optical signature of the large joint density of states arising from saddle points at $\Gamma$ is strongly suppressed in Na$_3$Bi consistent with band structure calculations that show the dipole transition matrix elements to be weak due to the very small s-orbital character of the Dirac bands. In Cd$_3$As$_2$, a distinctive peak in reflectivity due to the logarithmic divergence in $\epsilon_1$ expected at the onset of Dirac cone interband transitions is identified. The center frequency of the peak shifts with temperature quantitatively consistent with a linear dispersion and a carrier density of $n=1.3\times10^{17}\text{ cm}^{-3}$. The peak width gives a measure of the Fermi velocity anisotropy of $10\%$, indicating a nearly spherical Fermi surface. The lineshape gives an upper bound estimate of 7 meV for the potential fluctuation energy scale., Comment: 15 pages, 6 figures, 3 tables

Weyl fermions have recently been observed in several time-reversal-invariant semimetals and photonics materials with broken inversion symmetry. These systems are expected to have exotic transport properties such as the chiral anomaly. However, most discovered Weyl materials possess a substantial number of Weyl nodes close to the Fermi level that give rise to complicated transport properties. Here we predict, for the first time, a new family of Weyl systems defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions in the centrosymmetric magnetic systems, we recall an easy and practical inversion invariant, which has been calculated to be -1, guaranteeing the existence of an odd number of pairs of Weyl fermions. These materials exhibit, when alloyed, only two Weyl nodes at the Fermi level - the minimum number possible in a condensed matter system. The Weyl nodes are protected by the rotational symmetry along the magnetic axis and separated by a large distance (of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been calculated as well. This discovery provides a realistic and promising platform for manipulating and studying the magnetic Weyl physics in experiments., Comment: Published version

The recent discovery of extreme magnetoresistance in LaSb introduced lanthanum monopnictides as a new platform to study topological semimetals (TSMs). In this work we report the discovery of extreme magnetoresistance in LaBi, confirming lanthanum monopnictides as a promising family of TSMs. These binary compounds with the simple rock-salt structure are ideal model systems to search for the origin of extreme magnetoresistance. Through a comparative study of magnetotransport effects in LaBi and LaSb, we construct a triangular temperature-field phase diagram that illustrates how a magnetic field tunes the electronic behavior in these materials. We show that the triangular phase diagram can be generalized to other topological semimetals with different crystal structures and different chemical compositions. By comparing our experimental results to band structure calculations, we suggest that extreme magnetoresistance in LaBi and LaSb originates from a particular orbital texture on their qasi-2D Fermi surfaces. The orbital texture, driven by spin-orbit coupling, is likely to be a generic feature of various topological semimetals., Comment: 9 pages, 11 figures

Based on the ab initio calculations, we show that MoTe2, in its low-temperature orthorhombic structure characterized by an X-ray diffraction study at 100 K, realizes 4 type-II Weyl points between the N-th and N+1-th bands, where N is the total number of valence electrons per unit cell. Other WPs and nodal lines between different other bands also appear close to the Fermi level due to a complex topological band structure. We predict a series of strain-driven topological phase transitions in this compound, opening a wide range of possible experimental realizations of different topological semimetal phases. Crucially, with no strain, the number of observable surface Fermi arcs in this material is 2 - the smallest number of arcs consistent with time-reversal symmetry., Comment: Published version

Time reversal symmetry (TRS) protects the metallic surface modes of topological insulators (TIs). The transport signature of robust metallic surface modes of TIs is a plateau that arrests the exponential divergence of the insulating bulk with decreasing temperature. This universal behavior is observed in all TI candidates ranging from Bi2Te2Se to SmB6. Recently, several topological semimetals (TSMs) have been found that exhibit extreme magnetoresistance (XMR) and TI universal resistivity behavior revealed only when breaking TRS, a regime where TIs theoretically cease to exist. Among these new materials, TaAs and NbP are nominated for Weyl semimetal due to their lack of inversion symmetry, Cd3As2 is nominated for Dirac semimetal due to its linear band crossing at the Fermi level, and WTe2 is nominated for resonant compensated semimetal due to its perfect electron-hole symmetry. Here we introduce LaSb, a simple rock-salt structure material without broken inversion symmetry, without perfect linear band crossing, and without perfect electron-hole symmetry. Yet LaSb portrays all the exotic field induced behaviors of the aforementioned semimetals in an archetypal fashion. It shows (a) the universal TI resistivity with a plateau at 15 K, revealed by a magnetic field, (b) ultrahigh mobility of carriers in the plateau region, (c) quantum oscillations with a non-trivial Berry phase, and (d) XMR of about one million percent at 9 tesla rivaled only by WTe2 and NbP. Due to its dramatic simplicity, LaSb is the ideal model system to formulate a theoretical understanding of the exotic consequences of breaking TRS in TSMs., Comment: 4 figures, 25 pages including supplementary information

A long-standing issue in topological insulator research has been to find a material that provides an ideal platform for characterizing topological surface states without interference from bulk electronic states and can reliably be fabricated as bulk crystals. This material would be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, have high surface state electronic mobility, and be growable as large, high quality bulk single crystals. Here we show that this major materials obstacle in the field is overcome by crystals of lightly Sn-doped Bi1.1Sb0.9Te2S (Sn-BSTS) grown by the Vertical Bridgeman method, which we characterize here via angle-resolved photoemission spectroscopy, scanning tunneling microscopy, transport studies of the bulk and surface states, and X-ray diffraction and Raman scattering. We present this new material as a bulk topological insulator that can be reliably grown and studied in many laboratories around the world., Comment: 21 pages, 5 figures

A topological Dirac semimetal is a novel state of quantum matter which has recently attracted much attention as an apparent 3D version of graphene. In this paper, we report critically important results on the electronic structure of the 3D Dirac semimetal Na3Bi at a surface that reveals its nontrivial groundstate. Our studies, for the first time, reveal that the two 3D Dirac cones go through a topological change in the constant energy contour as a function of the binding energy, featuring a Lifshitz point, which is missing in a strict 3D analog of graphene (in other words Na3Bi is not a true 3D analog of graphene). Our results identify the first example of a band saddle point singularity in 3D Dirac materials. This is in contrast to its 2D analogs such as graphene and the helical Dirac surface states of a topological insulator. The observation of multiple Dirac nodes in Na3Bi connecting via a Lifshitz point along its crystalline rotational axis away from the Kramers point serves as a decisive signature for the symmetry-protected nature of the Dirac semimetal's topological groundstate., Comment: 5 pages, 4 Figures, Related papers on topological Fermi arcs and Weyl Semimetals (WSMs) are at http://physics.princeton.edu/zahidhasangroup/index.html

The single crystal of tris(thiourea)zinc sulphate (Zn[CS(NH2)2]3SO4) was irradiated by 150 MeV Au9+ swift heavy ions and analyzed in comparison with pure crystal for crystalline perfection and optical properties. The Fourier transform infrared and x-ray powder diffraction inferred that swift ions lead the disordering and breaking of molecular bonds in lattice without formation of new structural phases. High resolution X-ray diffraction (HRXRD) revealed the abundance of point defects, and formation of mosaics and low angle grain boundaries in the irradiated region of crystal. The swift ion irradiation found to affect the lattice vibrational modes and functional groups significantly. The defects induced by heavy ions act as the color centers and resulted in enhance of photoluminescence emission intensity. The optical transparency and band gap found to be decreased., Comment: 7 pages

We report the superconducting properties of single crystals of the intermetallic perovskite-related compound BaBi$_{3}$. The superconducting transition temperature ($T_{c}=5.82$~K) was obtained from heat capacity measurements. Using the measured values for the critical fields $H_{c1}, H_{c2}$, and the specific heat $C$, we estimate the thermodynamic critical field $H_{c}$(0), coherence length $\xi$(0), Debye temperature $\Theta _{D}$ and coupling constant $\lambda _{ep}$. $\Delta C/\gamma T_{c}$ and $\lambda _{ep}$ suggest that BaBi$_{3}$ is a moderately coupled superconductor and $\gamma $ suggests an enhanced density of states at the Fermi level. Electronic band structure calculations show a complex Fermi surface and a moderately high DOS at the Fermi level. Further analysis of the electronic specific heat shows that the superconducting properties are dominated by s-wave gap., Comment: 6 pages, 4 figures, 1 table. arXiv admin note: text overlap with arXiv:1402.4440

Effect of L-threonine (LT) doping on crystalline perfection, second harmonic generation (SHG) efficiency, optical transparency and laser damage threshold (LDT) in potassium dihydrogen phosphate (KDP) crystals grown by slow evaporation solution technique (SEST) has been investigated. The influence of doping on growth rate and morphology of the grown crystals has also been studied. Powder X-ray diffraction data confirms the crystal structure of KDP and shows a systematic variation in intensity of diffraction peaks in correlation with morphology due to varying LT concentration. No extra phase formation was observed which is further confirmed by Fourier Transform (FT) Raman studies. High-resolution X-ray diffraction curves indicate that crystalline perfection has been improved to a great extent at low concentrations with a maximum perfection at 1 mol% doping. At higher concentrations (5 to 10 mol%), it is slightly reduced due to excess incorporation of dopants at the interstitial sites of the crystalline matrix. LDT has been increased considerably with increase in doping concentration, whereas SHG efficiency was found to be maximum at 1 mol% in correlation with crystalline. The optical transparency for doped crystals has been increased as compared to that of pure KDP with a maximum value at 1 mol% doping., Comment: 17 pages, 7 figures

Large size single crystals of bis(thiourea)zinc(II) chloride (BTZC), a potential nonlinear optical material, have been grown successfully by the Sankaranarayanan Ramasamy (SR) method. Powder X-ray diffraction and Fourier transform infrared analyses confirmed the material of the grown crystal. Thermal stability was assessed by the thermogravimetric differential thermal analysis. The high-resolution X-ray diffraction and dielectric measurements indicate that the crystal grown by the SR method has good crystalline perfection and low density of defects., Comment: 6 pages, 3 figures

Enhancement of second harmonic generation (SHG) efficiency and the correlation between crystalline perfection and SHG with urea doping on tristhioureazinc(II) sulphate (ZTS) single crystals have been investigated. ZTS is a potential semiorganic nonlinear optical (NLO) material. Pure and urea doped single crystals of ZTS have been successfully grown by slow evaporation solution technique (SEST). Presence of dopants has been confirmed and analyzed by Fourier transform infrared (FTIR) spectrometer. The influence of urea doping at different concentrations on the crystalline perfection has been thoroughly assessed by high resolution X-ray diffractometry (HRXRD). HRXRD studies revealed that the crystals could accomodate urea in ZTS up to some critical concentration without any deterioration in the crystalline perfection. Above this concentration, very low angle structural grain boundaries were developed and it seems, the excess urea above the critical concentration was segregated along the grain boundaries. At very high doping concentrations, the crystals were found to contain mosaic blocks. The SHG effeiciency has been studied by using Kurtz powder technique. The relative SHG efficiency of the crystals was found to be increased substantially with the increase of urea concentration. The correlation found between the crystalline perfection and SHG efficiency was discussed., Comment: 19 pages, 7 figures, 1 table

Resistivity, dc magnetization, and heat capacity measurements are reported for superconducting NaBi. Tc, the electronic contribution to the specific heat {\gamma}, the {\Delta}Cp/{\gamma}Tc ratio, and the Debye temperature are found to be 2.15 K, 3.4 mJmol-1K-2, 0.78, and 140 K respectively. The calculated electron-phonon coupling constant ({\lambda}ep = 0.62) implies that NaBi is a moderately coupled superconductor. The upper critical field and coherence length are found to be 250 Oe and 115 nm, respectively. Electronic structure calculations show NaBi to be a good metal, in agreement with the experiments; the px and py orbitals of Bi dominate the electronic states at the Fermi Energy., Comment: 14 pages, 5 figures

A comparative study of the properties of topological insulator Bi2Te2Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8 x 1014 cm-3. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (EF) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, that the Dirac point for the surface states lies approximately 60 meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near EF. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed., Comment: 24 pages, 7 figures

Symmetry or topology protected Dirac fermion states in two and three dimensions constitute novel quantum systems that exhibit exotic physical phenomena. However, none of the studied spin-orbit materials are suitable for realizing bulk multiplet Dirac states for the exploration of interacting Dirac physics. Here we present experimental evidence, for the first time, that the compound Na3Bi hosts a bulk spin-orbit Dirac multiplet and their interaction or overlap leads to a Lifshitz transition in momentum space - a condition for realizing interactions involving Dirac states. By carefully preparing the samples at a non-natural-cleavage (100) crystalline surface, we uncover many novel electronic and spin properties in Na3Bi by utilizing high resolution angle- and spin-resolved photoemission spectroscopy measurements. We observe two bulk 3D Dirac nodes that locate on the opposite sides of the bulk zone center point $\Gamma$, which exhibit a Fermi surface Lifshitz transition and a saddle point singularity. Furthermore, our data shows evidence for the possible existence of theoretically predicted weak 2D nontrivial spin-orbit surface state with helical spin polarization that are nestled between the two bulk Dirac cones, consistent with the theoretically calculated (100) surface-arc-modes. Our main experimental observation of a rich multiplet of Dirac structure and the Lifshitz transition opens the door for inducing electronic instabilities and correlated physical phenomena in Na3Bi, and paves the way for the engineering of novel topological states using Na3Bi predicted in recent theory., Comment: 23 pages, 5 Figures