Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNonsymmorphic cubic Dirac point and crossed nodal rings across the ferroelectric phase transition in LiOsO$_3$
392
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Crystalline symmetries can generate exotic band-crossing features, which can lead to unconventional fermionic excitations with interesting physical properties. We show how a cubic Dirac point---a four-fold-degenerate band-crossing point with cubic dispersion in a plane and a linear dispersion in the third direction---can be stabilized through the presence of a nonsymmorphic glide mirror symmetry in the space group of the crystal. Notably, the cubic Dirac point in our case appears on a threefold axis, even though it has been believed previously that such a point can only appear on a sixfold axis. We show that a cubic Dirac point involving a threefold axis can be realized close to the Fermi level in the non-ferroelectric phase of LiOsO$_3$. Upon lowering temperature, LiOsO$_3$ has been shown experimentally to undergo a structural phase transition from the non-ferroelectric phase to the ferroelectric phase with spontaneously broken inversion symmetry. Remarkably, we find that the broken symmetry transforms the cubic Dirac point into three mutually-crossed nodal rings. There also exist several linear Dirac points in the low-energy band structure of LiOsO$_3$, each of which is transformed into a single nodal ring across the phase transition.
rate research
Read More
LiOsO3 is the first experimentally confirmed polar metal. Previous works suggested that the ground state of LiOsO$_3$ is just close to the critical point of metal-insulator transition. In this work the electronic state of LiOsO$_3$ is tuned by epitaxial biaxial strain, which undergoes the Slater-type metal-insulator transition under tensile strain, i.e., the G-type antiferromagnetism emerges. The underlying mechanism of bandwidth tuning can be extended to its sister compound NaOsO$_3$, which shows an opposite transition from a antiferromagnetic insulator to a nonmagnetic metal under hydrostatic pressure. Our work suggests a feasible route for the manipulation of magnetism and conductivity of polar metal LiOsO$_3$.
Using density functional theory we investigate the lattice instability and electronic structure of recently discovered ferroelectric metal LiOsO$_3$. We show that the ferroelectric-like lattice instability is related to the Li-O distortion modes while the Os-O displacements change the d-p hybridization as in common ferroelectric insulators. Within the manifold of the d-orbitals, a dual behavior emerges. The ferroelectric transition is indeed mainly associated to the nominally empty e$_g$ orbitals which are hybridized with the oxygen p orbitals, while the t$_{2g}$ orbitals are responsible of the metallic response. Interestingly, these orbitals are nominally half-filled by three electrons, a configuration which suffers from strong correlation effects even for moderate values of the screened Coulomb interaction.
Nitride perovskites are supposed to exhibit excellent properties as oxide analogues and may even have better performance in specific fields for their more covalent characters. However, till now, very limited nitride perovskites have been reported. In this work, a nitride perovskite LaMoN$_3$ has been systematically studied by first-principles calculations. The most interesting physical property is its ferroelectric $R3c$ phase, which can be stabilized under a moderate hydrostatic pressure ($sim1.5$ GPa) and probably remain meta-stable under the ambient condition. Its ferroelectric polarization is considerable large, $80.3$ $mu$C/cm$^2$, driven by the nominal $4d^0$ rule of Mo$^{6+}$, and the covalent hybridization between Mos $4d$ and Ns $2p$ orbitals is very strong. Our calculation not only predicts a new ferroelectric material with prominent properties, but also encourages more studies on pressure engineering of functional nitrides.
The topological nodal-line semimetals (NLSMs) possess a loop of Dirac nodes in the k space with linear dispersion, different from the point nodes in Dirac/Weyl semimetals. While the quantum transport associated with the topologically nontrivial Dirac fermions has been investigated extensively, features uniquely associated with the extended nodal lines remain to be demonstrated. Here, we investigate the quantum oscillations (QOs) in the nodal-line semimetal ZrSiS, with the electron transport along the c axis, and magnetic field rotating in the ab plane. The extremal orbits identified through the field orientation dependence of the QOs interlock with the nodal line, leading to a nonzero Berry phase. Most importantly, the Berry phase shows a significant dependence on the magnetic field orientation, which we argue to be due to the finite spin-orbit coupling gap. Our results demonstrate the importance of the spin-orbit coupling and the nodal-line dispersion in understanding the quantum transport of NLSMs.
Cadmium arsenide Cd$_3$As$_2$ hosts massless Dirac electrons in its ambient-conditions tetragonal phase. We report X-ray diffraction and electrical resistivity measurements of Cd$_3$As$_2$ upon cycling pressure beyond the critical pressure of the tetragonal phase and back to ambient conditions. We find that at room temperature the transition between the low- and high-pressure phases results in large microstrain and reduced crystallite size both on rising and falling pressure. This leads to non-reversible electronic properties including self-doping associated with defects and a reduction of the electron mobility by an order of magnitude due to increased scattering. Our study indicates that the structural transformation is sluggish and shows a sizable hysteresis of over 1~GPa. Therefore, we conclude that the transition is first-order reconstructive, with chemical bonds being broken and rearranged in the high-pressure phase. Using the diffraction measurements we demonstrate that annealing at ~200$^circ$C greatly improves the crystallinity of the high-pressure phase. We show that its Bragg peaks can be indexed as a primitive orthorhombic lattice with a_HP~8.68 A b_HP~17.15 A and c_HP~18.58 A. The diffraction study indicates that during the structural transformation a new phase with another primitive orthorhombic structure may be also stabilized by deviatoric stress, providing an additional venue for tuning the unconventional electronic states in Cd3As2.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
