ABSTRACT
By combining angle-resolved photoemission spectroscopy, scanning tunneling microscopy, atomic force microscope based piezoresponse force microscopy and first-principles calculations, we have studied the low-energy band structure, atomic structure, and charge polarization on the surface of a topological semimetal candidate TaNiTe_{5}. Dirac-like surface states were observed on the (010) surface by angle-resolved photoemission spectroscopy, consistent with the first-principles calculations. On the other hand, piezoresponse force microscopy reveals a switchable ferroelectriclike polarization on the same surface. We propose that the noncentrosymmetric surface relaxation observed by scanning tunneling microscopy could be the origin of the observed ferroelectriclike state in this novel material. Our findings provide a new platform with the coexistence of a ferroelectriclike surface charge distribution and novel surface states.
ABSTRACT
In this study, we measure the in-plane transport properties of high-quality Ba(Fe0.914Co0.086)2As2 single crystals. Signatures of vortex unbinding Berezinskii-Kosterlitz-Thouless (BKT) transition are shown from both the conventional approach and the Fisher-Fisher-Huse dynamic scaling analysis, in which a characteristic Nelson-Kosterlitz jump is demonstrated. We also observe a non-Hall transverse signal exactly at the superconducting transition, which is explained in terms of guided motion of unbound vortices.
ABSTRACT
The past decade has witnessed the burgeoning discovery of a variety of topological states of matter with distinct nontrivial band topologies. Thus far, most materials that have been studied possess two-dimensional or three-dimensional electronic structures, with only a few exceptions that host quasi-one-dimensional (quasi-1D) topological electronic properties. Here we present clear-cut evidence for Dirac Fermions in the quasi-1D telluride TaNiTe5. We show that its transport behaviors are highly anisotropic, and we observe nontrivial Berry phases via quantum oscillation measurements. The nontrivial band topology is further corroborated by first-principles calculations. Our results may help to guide the future quest for topological states in this new family of quasi-1D ternary chalcogenides.
ABSTRACT
We examined the physical properties of the quasi-one-dimensional superconductor Ta4Pd3Te16 in the normal state by detailed measurements of susceptibility, in-plane anisotropic resistivity, magnetoresistance, Hall resistivity, and Seebeck coefficient. The large Wilson ratio, as inferred from normal-state susceptibility, indicates strong electron-electron interaction. The Hall and Seebeck coefficients show not only significant temperature-dependent behavior, indicating the multiband effect, but also an obvious anomaly around T 1 = 40 K. Analyses of both the Hall resistivity and thermopower using a two-band model indicate that the electrons dominate the electrical transport at low temperatures. Our results imply that it is the quantum fluctuations of the charge order taking place in the temperature range 30-50 K that may result in the abnormal normal-state properties of Ta4Pd3Te16.
ABSTRACT
The interplay between superconductivity and magnetism is one of the oldest enigmas in physics. Usually, the strong exchange field of ferromagnet suppresses singlet superconductivity via the paramagnetic effect. In EuFe2(As0.79P0.21)2, a material that becomes not only superconducting at 24.2 K but also ferromagnetic below 19 K, the coexistence of the two antagonistic phenomena becomes possible because of the unusually weak exchange field produced by the Eu subsystem. We demonstrate experimentally and theoretically that when the ferromagnetism adds to superconductivity, the Meissner state becomes spontaneously inhomogeneous, characterized by a nanometer-scale striped domain structure. At yet lower temperature and without any externally applied magnetic field, the system locally generates quantum vortex-antivortex pairs and undergoes a phase transition into a domain vortex-antivortex state characterized by much larger domains and peculiar Turing-like patterns. We develop a quantitative theory of this phenomenon and put forth a new way to realize superconducting superlattices and control the vortex motion in ferromagnetic superconductors by tuning magnetic domains-unprecedented opportunity to consider for advanced superconducting hybrids.
ABSTRACT
We report an investigation of the London penetration depth [Formula: see text] on single crystals of the layered superconductor Ta4Pd3Te16, where the crystal structure has quasi-one-dimensional characteristics. A linear temperature dependence of [Formula: see text] is observed for [Formula: see text], in contrast to the exponential behavior of fully gapped superconductors. This indicates the existence of line nodes in the superconducting energy gap. A detailed analysis shows that the normalized superfluid density [Formula: see text], which is converted from [Formula: see text], can be well described by a multigap scenario, with nodes in one of the superconducting gaps, providing clear evidence for nodal superconductivity in Ta4Pd3Te16.
ABSTRACT
We report bulk superconductivity at 1.0 K in a low-dimensional ternary telluride Ta3Pd3Te14 containing edge-sharing PdTe2 chains along crystallographic b axis, similar to the recently discovered superconductor Ta4Pd3Te16. The electronic heat capacity data show an obvious anomaly at the transition temperature, which indicates bulk superconductivity. The specific-heat jump is ΔC/(γ(n)T(c)) ≈ 1.35, suggesting a weak coupling scenario. By measuring the low-temperature thermal conductivity, we conclude that Ta3Pd3Te14 is very likely a dirty s-wave superconductor. The emergence of superconductivity in Ta3Pd3Te14 with a lower T(c), compared to that of Ta4Pd3Te16, may be attributed to the lower density of states.
ABSTRACT
We carried out measurements of the magnetoresistance, magnetic susceptibility and specific heat on crystals of the low-dimensional transition metal telluride Ta4Pd3Te16. Our results indicate that Ta4Pd3Te16 is an anisotropic type-II superconductor in the clean limit with the extracted Ginzburg-Landau parameter KGL = 84. The upper critical field Hc2(T) shows an anomalous temperature dependence at low temperatures and the anisotropy of Hc2(T) is strongly T-dependent, both of which indicate a multiband scenario. The electronic specific heat Cel(T) can be consistently described by a two-gap (s + d waves) model from the base temperature T/Tc ~ 0.12 up to Tc. Our results suggest nodal and multiband superconductivity in Ta4Pd3Te16.
ABSTRACT
Superconductivity in low-dimensional compounds has long attracted much interest. Here we report superconductivity in a low-dimensional ternary telluride Ta4Pd3Te16 in which the repeating layers contain edge-sharing octahedrally coordinated PdTe2 chains along the crystallographic b axis. Measurements of electrical resistivity, magnetic susceptibility and specific heat on the Ta4Pd3Te16 crystals, grown via a self-flux method, consistently demonstrate bulk superconductivity at 4.6 K. Further analyses of the data indicate significant electron-electron interaction, which allows electronic Cooper pairing in the present system.
ABSTRACT
Ba0.6K0.4Fe2Se3 (BKFS) single crystals were investigated by means of measurements of powder x-ray diffraction, temperature-dependent resistivity, anisotropic dc magnetization, ac magnetic susceptibility and specific heat. The powder x-ray diffraction indicates staggered iron displacements along the ladders with short and long Fe-Fe bond lengths (2.64(2) and 2.91(2) Å) variation. The resistivity of BKFS exhibits variable range hopping behavior with ln(ρ) ~ T(-1/2) at low temperature. The magnetic susceptibility χ(T) exhibits a sharp cusp at around 20 K in a zero-field-cooled process. The frequency-dependent ac magnetic susceptibility reveals that the cusp feature is attributable to spin glass behavior. The anisotropic ac magnetic susceptibility indicates that BKFS is probably an anisotropic Heisenberg-like spin glass with its easy magnetization plane perpendicular to the chain direction. The specific heat also supports an insulating and spin glass ground state. Extended Curie-Weiss behavior above 40 K was observed with a reduced effective moment (µ(eff) = 1.66 µ(B)/Fe for H is perpendicular to b and µ(eff) = 1.82 µB/Fe for H is parallel to b) in BKFS, which is close to the spin-only magnetism with S=1/2.
ABSTRACT
We have synthesized a new oxypnictide, Ba2Ti2Fe2As4O, via a solid-state reaction under a vacuum. The compound crystallizes in a body-centered tetragonal lattice, which can be viewed as an intergrowth of BaFe2As2 and BaTi2As2O, thus containing Fe2As2 layers and Ti2O sheets. Bulk superconductivity at 21 K is observed after annealing the as-prepared sample at 773 K for 40 h. In addition, an anomaly in resistivity and magnetic susceptibility around 125 K is revealed, suggesting a charge- or spin-density wave transition in the Ti sublattice.
