Low-lying Electronic Structure Research Articles

Flat bands, non-trivial band topology and rotation symmetry breaking in layered kagome-lattice RbTi3Bi5

A representative class of kagome materials, AV3Sb5 (A = K, Rb, Cs), hosts several unconventional phases such as superconductivity, {{mathbb{Z}}}_{2} non-trivial topological states, and electronic nematic states. These can often coexist with intertwined charge-density wave states. Recently, the discovery of the isostructural titanium-based single-crystals, ATi3Bi5 (A = K, Rb, Cs), which exhibit similar multiple exotic states but without the concomitant charge-density wave, has opened an opportunity to disentangle these complex states in kagome lattices. Here, we combine high-resolution angle-resolved photoemission spectroscopy and first-principles calculations to investigate the low-lying electronic structure of RbTi3Bi5. We demonstrate the coexistence of flat bands and several non-trivial states, including type-II Dirac nodal lines and {{mathbb{Z}}}_{2} non-trivial topological surface states. Our findings also provide evidence for rotational symmetry breaking in RbTi3Bi5, suggesting a directionality to the electronic structure and the possible emergence of pure electronic nematicity in this family of kagome compounds.

Single crystal synthesis and low-lying electronic structure of V3S4

We report successful growth of millimeter-sized high quality single crystals of V3S4, a candidate topological semimetal belonging to a low-symmetry space group and consisting of only low atomic number elements. Using density functional theory calculations and angle-resolved photoemission spectroscopy, we show that the nonmagnetic phase of monoclinic V3S4 hosts type-II Dirac-like quasiparticles which opens a sizable gap due to spin orbit coupling, as well as theoretical multiple nodal lines that are eliminated also by spin orbit coupling. These results suggest that relativistic effects give rise to profound modifications of the topological properties even in compounds with low-weight elements.

Electronic structure of the high-mobility two-dimensional antiferromagnetic metal GdTe3

The newfound two-dimensional antiferromagnetic $\mathrm{Gd}{\mathrm{Te}}_{3}$ has great potential in novel magnetic twistronic and spintronic devices because it has the highest carrier mobility among all known layered magnetic materials. Here, we used high-resolution angle-resolved photoemission spectroscopy to investigate its Fermi-surface topology and low-lying electronic band structure. The Fermi surface is partially gapped by charge-density waves below the transition temperature. Very steep and nearly linear band dispersion near the Fermi energy contributes to the high carrier mobility in $\mathrm{Gd}{\mathrm{Te}}_{3}$. We find that the scattering rate of the quasiparticle increases linearly as a function of binding energy within a wide energy range, indicating that $\mathrm{Gd}{\mathrm{Te}}_{3}$ is a non-Fermi-liquid metal. Our results in this paper provide a fundamental understanding of this layered antiferromagnetic material to guide future studies on it.

Jahn-Teller and Pseudo Jahn-Teller Effects: Influences on the Electronic Structures of Small Transition, Main Group and Mixed Metal Clusters

The present review article focuses on the impact of the Jahn-Teller effect (JTE) including hidden JTE and pseudo JTE on the ground and low-lying electronic structures of small transition, main group, and mixed metal clusters. The discussions are based on the results acquired from the quantum chemical analysis involving complete active space multiconfiguration self-consistent field (CASMCSCF or CASSCF) together with multireference singles and doubles configuration interaction (MRSDCI) theories. Related computational results from density functional (DFT) and coupled cluster (CC) theories, and the available experimental evidences on the JT-distorted structures are also included for comparative analysis. The role of the relativistic effects on several heavy metal clusters is discussed in detail, since these effects could lead to either enhancement or the quenching of the JTE. The final section of the review manifests the JT-distortion of several mixed metal clusters of icosahedral symmetry and they are explained through a much simpler shell structure (jellium) model.

Two Gaps in Semiconducting EuSbTe3 Studied by Angle-Resolved Photoemission Spectroscopy**Supported by the National Key R&D Program of China under Grant No 2016YFA0300204, the National Basic Research Program of China under Grant No 2015CB654901, the National Natural Science Foundation of China under Grant Nos 11574337, 11227902, 11474147 and 11704394, the Shanghai Sailing Program under Grant No 17YF1422900, and the Award for

Using angle-resolved photoemission spectroscopy, we study the low-energy electronic structure of a layered ternary telluride EuSbTe3 semiconductor. It is found that the photoemission constant energy contours can be well described by the simple two-parameter (tperp and tpara) tight-binding model based on the Te orbitals in square-net planes of EuSbTe3, suggesting its Te 5p orbitals dominated low-lying electronic structure, which is reminiscent of other rare-earth tritellurides. However, a possible charge-density-wave gap of 80 meV is found to persist in 300 K, which renders the unexpected semiconducting properties in EuSbTe3. Moreover, we reveal an extra band gap occurring around 200 meV below the Fermi level at low temperatures, which can be attributed to the interaction between the main and folded bands due to lattice scatterings. Our findings provide the first comprehensive understanding of the electronic structure of layered ternary tellurides, which lays the basis for future research on these compounds.

Theoretical study of the electronic structure of mono-chloride of lanthanum molecule including spin-orbit coupling effect.

Our investigation is devoted to the theoretical study of the low-lying electronic structure of the LaCl molecule by using ab initio quantum methods. We are concerned with several methods such as the complete active space-self consistent field (CAS-SCF) and the multi reference of configuration interaction (MRCI + Q) methods. These methods are applied for the purpose of drawing the potential energy curves (PECs) and calculating the molecular spectroscopic constants for a given number of electronic states of singlet and triplet multiplicity. We count 26 2S+ 1 Λ(±) electronic states located below 24,000 cm- 1 neglecting the spin-orbit effects and 47 Ω(±) components taken into consideration these effects. Our calculations are performed via the quantum ab initio package MOLPRO (Werner and Knowles 2000). Graphical Abstract A new set of low-lying electronic states on the theoretical energetic level diagram for the LaCl molecule among the first four lanthanum monhalides.

Unexpected Large Hole Effective Masses in SnSe Revealed by Angle-Resolved Photoemission Spectroscopy.

SnSe has emerged as an efficient thermoelectric material since a high value of the thermoelectric figure of merit (ZT) has been reported recently. Here we show with systematic angle resolved photoemission spectroscopy data that the low-lying electronic structures of undoped and hole-doped SnSe crystals exhibit noticeable temperature variation from 80 to 600K. In particular, the hole effective masses for the two lowest lying valence band maxima are found to be very large and increase with decreasing temperature. Thermoelectric parameters derived from such hole-mass enhancement agree well with the transport values, indicating comprehensively a reduced impact of multivalley transport to the system's thermoelectric performance.

Direct observation of the Dirac nodes lifting in semimetallic perovskite SrIrO3 thin films.

Perovskite SrIrO3 has long been proposed as an exotic semimetal induced by the interplay between the spin-orbit coupling and electron correlations. However, its low-lying electronic structure is still lacking. We synthesize high-quality perovskite SrIrO3 (100) films by means of oxide molecular beam epitaxy, and then systemically investigate their low energy electronic structure using in-situ angle-resolved photoemission spectroscopy. We find that the hole-like bands around R and the electron-like bands around U(T) intersect the Fermi level simultaneously, providing the direct evidence of the semimetallic ground state in this compound. Comparing with the density functional theory, we discover that the bandwidth of states near Fermi level is extremely small, and there exists a pronounced mixing between the Jeff = 1/2 and Jeff = 3/2 states. Moreover, our data reveal that the predicted Dirac degeneracy protected by the mirror-symmetry, which was theoretically suggested to be the key to realize the non-trivial topological properties, is actually lifted in perovskite SrIrO3 thin films. Our findings pose strong constraints on the current theoretical models for the 5d iridates.

Low-lying electronic structure of EuH, EuOH, and EuO neutrals and anions determined by anion photoelectron spectroscopy and DFT calculations.

The anion photoelectron (PE) spectra of EuH(-) and the PE spectrum of overlapping EuOH(-) and EuO(-) anions are presented and analyzed with supporting results from density functional theory calculations on the various anions and neutrals. Results point to ionically bound, high-spin species. EuH and EuOH anions and neutrals exhibit analogous electronic structures: Transitions from (8)Σ(-) anion ground states arising from the 4f(7)σ(6s)(2) superconfiguration to the close-lying neutral (9)Σ(-) and (7)Σ(-) states arising from the 4f(7)σ(6s) superconfiguration are observed spaced by an energy interval similar to the free Eu(+) [4f(7)6s] (9)S - (7)S splitting. The electron affinities (EAs) of EuH and EuOH are determined to be 0.771 ± 0.009 eV and 0.700 ± 0.011 eV, respectively. Analysis of spectroscopic features attributed to EuO(-) photodetachment is complicated by the likely presence of two energetically competitive electronic states of EuO(-) populating the ion beam. However, based on the calculated relative energies of the close-lying anion states arising from the 4f(7)σ(6s) and 4f(6)σ(6s)(2) configurations and the relative energies of the one-electron accessible 4f(7) and 4f(6)σ(6s) neutral states based on ligand-field theory [M. Dulick, E. Murad, and R. F. Barrow, J. Chem. Phys. 85, 385 (1986)], the remaining features are consistent with the 4f(6)σ(6s)(2) (7)Σ(-) and 4f(7)σ(6s) (7)Σ(-) anion states lying very close in energy (the former was calculated to be 0.15 eV lower in energy than the latter), though the true anion ground state and neutral EA could not be established unambiguously. Calculations on the various EuO anion and neutral states suggest 4f-orbital overlap with 2p orbitals in species with 4f(6) occupancy.

Weak electronic correlations and absence of heavy-fermion state inKNi2Se2

We have studied the low-lying electronic structure of a new ThCr$_2$Si$_2$-type superconductor KNi$_2$Se$_2$ with angle-resolved photoemission spectroscopy. Three bands intersect the Fermi level, forming complicated Fermi surface topology, which is sharply different from its isostructural superconductor K$_x$Fe$_{2-y}$Se$_2$. The Fermi surface shows weak variation along the $k_z$ direction, indicating its quasi-two-dimensional nature. Further comparison with the density functional theory calculations demonstrates that there exist relatively weak correlations and substantial hybridization of the Ni 3$d$ and the Se 4$p$ orbitals in the low-lying electronic structure. Our results indicate that the large density of states at the Fermi energy leads to the reported mass enhancement based on the specific heat measurements. Moreover, no anomaly is observed in the spectra when entering the fluctuating charge density wave state reported earlier.

Electronic structure of single-crystallineNdO0.5F0.5BiS2studied by angle-resolved photoemission spectroscopy

NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ is a new layered superconductor. We have studied the low-lying electronic structure of a single crystalline NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ superconductor, whose superconducting transition temperature is 4.87K, with angle-resolved photoemission spectroscopy. The Fermi surface consists of two small electron pockets around the X point and shows little warping along the $k_z$ direction. Our results demonstrate the multi-band and two-dimensional nature of the electronic structure. The good agreement between the photoemission data and the band calculations gives the renormalization factor of 1, indicating the rather weak electron correlations in this material. Moreover, we found that the actual electron doping level and Fermi surface size are much smaller than what are expected from the nominal composition, which could be largely explained by the bismuth dificiency. The small Fermi pocket size and the weak electron correlations found here put strong constraints on theory, and suggest that the BiS$_2$-based superconductors could be conventional BCS superconductors mediated by the electron-phonon coupling.

Electronic structure of Eu(Fe0.79Ru0.21)2As2 studied by angle-resolved photoemission spectroscopy

Eu(Fe0.79Ru0.21)2As2 is suggested to be a nodeless superconductor based on the empirical correlation between pnictogen height (hPn) and superconducting gap behavior, in contrast to BaFe2(As0.7P0.3)2 and Ba(Fe0.65Ru0.35)2As2. We studied the low-lying electronic structure of Eu(Fe0.79Ru0.21)2As2 with angle-resolved photoemission spectroscopy (ARPES). By photon energy dependence and polarization dependence measurements, we resolved the band structure in the three-dimensional momentum space and determined the orbital character of each band. In particular, we found that the -originated ζ band does not contribute spectral weight to the Fermi surface around Z, unlike BaFe2(As0.7P0.3)2 and Ba(Fe0.65Ru0.35)2As2. Since BaFe2(As0.7P0.3)2 and Ba(Fe0.65Ru0.35)2As2 are nodal superconductors and their hPn's are less than 1.33 Å, while the hPn of Eu(Fe0.79Ru0.21)2As2 is larger than 1.33 Å, our results provide more evidence for a direct relationship between nodes, orbital character and hPn. Our results help to provide an understanding of the nodal superconductivity in iron-based superconductors.

Minimal size of endohedral singly vanadium-doped aluminum cluster: a density-functional study

Energetically low-lying equilibrium geometric structures and electronic structures of Al n V (n = 2–24) clusters were investigated using density-functional theory within generalized gradient approximation. From the most stable geometric structures, a structural transition with the doped vanadium atom residing from the surface to the interior of the cluster was found from n = 16 to 19. This geometric transition fits well with the early experimental result based on the argon physisorption [S.M. Lang, P. Claes, S. Neukermans, E. Janssens, J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. Due to the geometric transition, average Al-V bond lengths and coordination numbers of V atoms for the most stable structures of Al n V clusters undergo an increases from n = 16 to 19. The relative stabilities, electronic structures, and other relevant properties were also discussed. It was found that doping of a V atom in the Al n cluster strengthen the stability of the framework and the Al4,6,8,10,13,16,19,21V clusters were more stable than their neighbors. Moreover, the Mulliken populations showed that the intra-atomic hybridization exists in both V and Al atoms and charge transfer from Al atoms to V atom were also found in these complexes, which could reflect the Al-V hybridizations. Electronic structure analysis based on the partial density of states reveals stronger Al-V hybridization for the endohedrally doped structures.

Electronic structure of Ca10(Pt4As8)(Fe2−xPtxAs2)5with metallic Pt4As8layers: An angle-resolved photoemission spectroscopy study

We studied the low-lying electronic structure of the newly discovered iron-platinum-arsenide superconductor, Ca${}_{10}$(Pt${}_{4}$As${}_{8}$)(Fe${}_{2\ensuremath{-}x}$Pt${}_{x}$As${}_{2}$)${}_{5}$ (${T}_{c}=22$ K) with angle-resolved photoemission spectroscopy. We found that the Pt${}_{4}$As${}_{8}$ layer contributes to a small electronlike Fermi surface, indicative of metallic charge reservoir layers that are rare for iron based superconductors. Moreover, the electronic structure of the FeAs layers resembles those of other prototype iron pnictides to a large extent. However, there is only ${d}_{xy}$-orbital originated holelike Fermi surface near the zone center, which is rather strange for an iron pnictide superconductor with relatively high superconducting transition temperature; and the ${d}_{xz}$ and ${d}_{yz}$ originated bands are not degenerate at the zone center. Furthermore, all bands near the Fermi energy show negligible ${k}_{z}$ dependence, indicating the strong two-dimensional nature of this material. Our results indicate this material possesses a rather interesting electronic structure, which enriches our current knowledge of iron based superconductors.

Fermi-surface topology and low-lying electronic structure of the iron-based superconductor Ca10(Pt3As8)(Fe2As2)5

We report a first study of low energy electronic structure and Fermi surface topology for the recently discovered iron-based superconductor Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase, with Tc = 8K), via angle-resolved photoemission spectroscopy (ARPES). Despite its triclinic crystal structure, ARPES results reveal a fourfold symmetric band structure with the absence of Dirac-cone-like Fermi dots (related to magnetism) found around the Brillouin zone corners in other iron-based superconductors. Considering that the triclinic lattice and structural supercell arising from the Pt3As8 intermediary layers, these results indicate that those layers couple only weakly to the FeAs layers in this new superconductor, which has implications for the determination of its potentially novel pairing mechanism.

Co+-Assisted Decomposition of h6-Acetone and d6-Acetone: Acquisition of Reaction Rate Constants and Dynamics of the Dissociative Mechanism

Reaction rate constants have been acquired for the gaseous unimolecular decomposition reaction of the Co(+)(OC(CH(3))(2)) cluster ion and its deuterium labeled analog. Each rate constant is measured at a well resolved cluster internal energy within the range 12,300-16,100 cm(-1). The weighted, averaged kinetic isotope effect (KIE), k(H)/k(D) = 1.54 ± 0.05, is about three times smaller than the KIE measured for the rate-determining rate constants in the similar Ni(+)(OC(CH(3))(2)) decomposition reaction. These reactions likely follow the same oxidative addition-reductive elimination mechanism. Thus, this unexpected change in the KIE magnitudes is not due to differences in the dissociative reaction coordinates. Rather, we propose that the unique dissociation dynamics of these two similar systems is due to differences in the low-lying electronic structure of each transition metal ion.

Absence of Spin Liquid Behavior inNd3Ga5SiO14Using Magneto-Optical Spectroscopy

We measured the low-lying crystal field levels of Nd3+ in Nd3Ga5SiO14 via magneto-optical spectroscopy and employed the extracted energies, magnetic moments, and symmetries to analyze the magnetic properties and test the spin liquid candidacy of this material. The exchange interaction is surprisingly small, a discovery that places severe constraints on models used to describe the ground state of this system. Further, it demonstrates the value of local-probe photophysical techniques for rare-earth-containing materials where bulk property measurements can be skewed by low-lying electronic structure.

Low-lying electronic structure of triangular cobaltite

We report detailed Fermi surface topology and quasiparticle dynamics of the host cobaltate Na0.7CoO2. A direct mapping of the Fermi surface is carried out by angle-resolved photoemission spectroscopy (ARPES). Fermi surface at temperature 16K is a hole-pocket centered around the Gamma-point. The highly correlated nature of the electron liquid is evidenced from strong on-site Coulomb interaction seen through a valence satellite and via renormalization of the quasiparticle dispersion. The quasiparticle exhibits spectral coherence only below 150K which includes the non-Fermi liquid regime.

The permanent electric dipole moments of the [formula omitted] and [formula omitted] states of titanium monoxide, TiO

The optical Stark spectrum of the origin bands of the E3Π0–X3Δ1,A3Φ2–X3Δ1, and B3Π0–X3Δ1 electronic transitions of titanium monoxide, TiO, were analyzed to produce permanent electric dipole moments of 3.34(1), 3.2(4), 4.89(5) and 4.9(2) D for the X3Δ1,E3Π0,A3Φ2 and B3Π0 states, respectively. The observations are compared with a simple molecular orbital description for the low-lying states and electronic structure calculations.

Relaxation dynamics of optically excited quasi-particles in BSCCO

To investigate the multi-excitation processes on the low-lying electronic structure of high- T C superconductors, time-domain pump and probe measurement has been carried out on under- and over-doped Bi 2Sr 2CaCu 2O 8+ δ films. In the underdoped film, we found evidence for coexistence of two excitation states due to superconducting gap Δ s and pseudogap Δ p below T C. The observed relaxation processes of optically excited quasi-particles were well explained by two relaxation times of T-dependent τ s and almost T-independent τ p (0.7±0.3 ps below 150 K). The τ p existed up to T *∼200 K and disappeared above 225 K. On the other hand, only one relaxation time, τ s, was observed in the overdoped film at T=10 K. The relaxation time, τ s=4.2±0.3 ps (below 40 K), for the underdoped sample was shorter than τ s=5.9±0.2 ps (at T=10 K) for the overdoped one, and about two times longer than τ s=2.1±0.1 ps for YBa 2Cu 3O 7− δ thin film.