Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userObservation of quantum spin Hall states in Ta$_2$Pd$_3$Te$_5$
138
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Two-dimensional topological insulators (2DTIs), which host the quantum spin Hall (QSH) effect, are one of the key materials in next-generation spintronic devices. To date, experimental evidence of the QSH effect has only been observed in a few materials, and thus, the search for new 2DTIs is at the forefront of physical and materials science. Here, we report experimental evidence of a 2DTI in the van der Waals material Ta$_2$Pd$_3$Te$_5$. First-principles calculations show that each monolayer of Ta$_2$Pd$_3$Te$_5$ is a 2DTI with weak interlayer interactions. Combined transport, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy measurements confirm the existence of a band gap at the Fermi level and topological edge states inside the gap. These results demonstrate that Ta$_2$Pd$_3$Te$_5$ is a promising material for fabricating spintronic devices based on the QSH effect.
rate research
Read More
Quantum spin Hall (QSH) effect with great promise for the potential application in spintronics and quantum computing has attracted extensive research interest from both theoretical and experimental researchers. Here, we predict monolayer Ta$_2$Pd$_3$Te$_5$ can be a QSH insulator based on first-principles calculations. The interlayer binding energy in the layered van der Waals compound Ta$_2$Pd$_3$Te$_5$ is 19.6 meV/A$^2$; thus, its monolayer/thin-film structures could be readily obtained by exfoliation. The band inversion near the Fermi level ($E_F$) is an intrinsic characteristic, which happens between Ta-$5d$ and Pd-$4d$ orbitals without spin-orbit coupling (SOC). The SOC effect opens a global gap and makes the system a QSH insulator. With the $d$-$d$ band-inverted feature, the nontrivial topology in monolayer Ta$_2$Pd$_3$Te$_5$ is characterized by the time-reversal topological invariant $mathbb Z_2=1$, which is computed by the one-dimensional (1D) Wilson loop method as implemented in our first-principles calculations. The helical edge modes are also obtained using surface Greens function method. Our calculations show that the QSH state in Ta$_2M_3$Te$_5$ ($M=$ Pd, Ni) can be tuned by external strain. These monolayers and thin films provide feasible platforms for realizing QSH effect as well as related devices.
Quantum anomalous Hall effect (QAHE) has been experimentally realized in magnetically-doped topological insulators or intrinsic magnetic topological insulator MnBi$_2$Te$_4$ by applying an external magnetic field. However, either the low observation temperature or the unexpected external magnetic field (tuning all MnBi$_2$Te$_4$ layers to be ferromagnetic) still hinders further application of QAHE. Here, we theoretically demonstrate that proper stacking of MnBi$_2$Te$_4$ and Sb$_2$Te$_3$ layers is able to produce intrinsically ferromagnetic van der Waals heterostructures to realize the high-temperature QAHE. We find that interlayer ferromagnetic transition can happen at $T_{rm C}=42~rm K$ when a five-quintuple-layer Sb$_2$Te$_3$ topological insulator is inserted into two septuple-layer MnBi$_2$Te$_4$ with interlayer antiferromagnetic coupling. Band structure and topological property calculations show that MnBi$_2$Te$_4$/Sb$_2$Te$_3$/MnBi$_2$Te$_4$ heterostructure exhibits a topologically nontrivial band gap around 26 meV, that hosts a QAHE with a Chern number of $mathcal{C}=1$. In addition, our proposed materials system should be considered as an ideal platform to explore high-temperature QAHE due to the fact of natural charge-compensation, originating from the intrinsic n-type defects in MnBi$_2$Te$_4$ and p-type defects in Sb$_2$Te$_3$.
The envisioned existence of an excitonic-insulator phase in Ta$_2$NiSe$_5$ has attracted a remarkable interest in this material. The origin of the phase transition in Ta$_2$NiSe$_5$ has been rationalized in terms of crystal symmetries breaking driven by both electronic correlation and lattice distortion. However, the role of structural and electronic effects has yet to be disentangled. Meanwhile its complementary material Ta$_2$NiS$_5$, which has the chalcogen species exchanged with Sulfur, does not show any experimental evidence of an excitonic insulating phase. Here we present a microscopic investigation of the electronic and phononic effects involved in the structural phase transition in Ta$_2$NiSe$_5$ and Ta$_2$NiS$_5$ by means of extensive first-principles calculations for both the high temperature orthorhombic and low-temperature monoclinic crystal phases. We show that, despite the difference in electronic behaviour, the structural origin of the phase transition is the same in the two crystals. In particular our first-principles results suggest, that the high temperature phase of Ta$_2$NiSe$_5$ is metallic and the structural transition to the low-temperature phase leads to the opening of an electronic gap. By analysing the phononic modes of the two phases we single out the mode responsible for the structural transition and demonstrate how this phonon mode strongly couples to the electronic structure. We demonstrate that, despite the very similar phononic behaviour, in Ta$_2$NiS$_5$ the electronic transition from metal to semiconductor is lacking and the crystal remains a semiconductor in both phases. To disentangle the effect of electronic correlation, we calculate electronic bandstructures with increasing accuracy in the electron-electron interaction and find that the structural transition alone allows for the metal to semiconductor phase transition, ...
We present measurements of superconducting transition temperature, resistivity, magnetoresistivity and temperature dependence of the upper critical field of Ta$_4$Pd$_3$Te$_{16}$ under pressures up to 16.4 kbar. All measured properties have an anomaly at $sim 2 - 4$ kbar pressure range, in particular there is a maximum in $T_c$ and upper critical field, $H_{c2}(0)$, and minimum in low temperature, normal state resistivity. Qualitatively, the data can be explained considering the density of state at the Fermi level as a dominant parameter.
We report an investigation of the London penetration depth $Deltalambda(T)$ on single crystals of the layered superconductor Ta$_4$Pd$_3$Te$_{16}$, where the crystal structure has quasi-one-dimensional characteristics. A linear temperature dependence of $Deltalambda(T)$ is observed for $Tll T_c$, in contrast to the exponential decay 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 $rho_s(T)$, which is converted from $Deltalambda(T)$, can be well described by a multigap scenario, with nodes in one of the superconducting gaps, providing clear evidence for nodal superconductivity in Ta$_4$Pd$_3$Te$_{16}$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
