arXiv subjects

Raghottam M Sattigeri

Publications and source records attributed to Raghottam M Sattigeri.

4 recordsLinked to original sources

arXiv2024

Staggered Dzyaloshinskii-Moriya inducing weak ferromagnetism in centrosymmetric altermagnets and weak ferrimagnetism in noncentrosymmetric altermagnets

The Dzyaloshinskii-Moriya interaction (DMI) has explained successfully the weak ferromagnetism in {\it some} centrosymmetric antiferromagnets. However, in the last years, it was generally claimed that the DMI is not effective in such systems. We reconciled these views by separating the conventional antiferromagnets from altermagnets. Altermagnets are collinear magnets having zero magnetization preserved by crystal symmetries in the non-relativistic limit. The spin-up and spin-down sublattices can be connected either by a proper rotation or by a combination of a rotation and a mirror or an inversion symmetry. Consequently, the system shows even-parity wave spin order in the k-space lifting the Kramer's degeneracy in the non-relativistic band structure leading to unconventional magnetism. The DMI can create weak ferromagnetism or weak ferrimagnetism in centrosymmetric and in noncentrosymmetric altermagnets while it is not effective in conventional antiferromagnets. Once the spin-orbit coupling is included in an altermagnetic system (where the time-reversal symmetry is broken), the components of spin moments of the two sublattices along the Néel vector are antiparallel but the other two spin components orthogonal to the Néel vector can be null, parallel or antiparallel. In cases where we have different bands showing parallel and antiparallel spin components at the same time, the magnetic order results in weak ferrimagnetism. If we restrain to high-symmetry directions for the Néel vector, we find weak ferrimagnetism only in the noncentrosymmetric compound MnSe among the examined cases.

cond-mat.mtrl-sci↗

arXiv2023

Non-trivial topological phases in transition metal rich half-Heusler Oxides

Topological Insulators with gapless surface states and insulating bulk in non-centrosymmetric cubic systems have been extensively explored following the discovery of two-dimensional quantum spin hall effect in zincblende HgTe. In such systems the negative band inversion strength E$_{BIS}$ ($=$ E$_{Γ_6} -$ E$_{Γ_8} <$ 0) governs the robustness of the non-trivial topological states at ambient conditions. Hence, realizing large negative values of E$_{BIS}$ has been a guiding motivation of several investigations reported in literature. Here, we present a material design approach which can be employed to realize large negative values of E$_{BIS}$ in cubic materials such as half-Heusler (HH) oxides with 18 valence electron configurations. We explore 27 HH oxides of the form ABO (A = Li, K, Rb; B = Cu, Ag, Au) in $α$-, $β$-, and $γ$-phase (by placing transition metal atom at different Wyckoff positions) for their non-trivial topological phase. Off these three phases, we found that, the $α$-phase of nine HH oxides (wherein the transition metal atoms occupy 4a Wyckoff positions in the crystal structure) is the most promising with non-trivial topological phase which is governed by the mass-darwin relativistic effects enhancing E$_{BIS}$. Whereas the other phases were found to be either trivial semiconductors or semimetals or metals and most of them being dynamically unstable. We focus on RbAuO in $α$-phase with E$_{BIS}$ of $-$ 1.29 eV and the effect of strain fields on the topological surface states of this compound. We conclude that the $α$-phase of HH oxide presented here can be synthesized experimentally for diverse room temperature applications in spintronics and nanoelectronics.

cond-mat.mtrl-sci↗

arXiv2023

Altermagnetic surface states: towards the observation and utilization of altermagnetism in thin films, interfaces and topological materials

The altermagnetism influences the electronic states allowing the presence of non-relativistic spinsplittings. Since altermagnetic spin-splitting is present along specific k-paths of the 3D Brillouin zone, we expect that the altermagnetic surface states will be present on specific surface orientations. We unveil the properties of the altermagnetic surface states considering three representative space groups: tetragonal, orthorhombic and hexagonal. We calculate the 2D projected Brillouin zone from the 3D Brillouin zone. We study the surfaces with their respective 2D Brillouin zones establishing where the spin-splittings with opposite sign merge annihilating the altermagnetic properties and on which surfaces the altermagnetism is preserved. Looking at the three principal surface orientations, we find that for several cases two surfaces are blind to the altermagnetism, while the altermagnetism survives for one surface orientation. Which surface preserves the altermagnetism depends also on the magnetic order. We show that an electric field orthogonal to the blind surface can activate the altermagnetism. Our results predict which surfaces to cleave in order to preserve altermagnetism in surfaces or interfaces and this paves the way to observe non-relativistic altermagnetic spin-splitting in thin films via spin-resolved ARPES and to interface the altermagnetism with other collective modes. We open future perspectives for the study of altermagnetic effects on the trivial and topological surface states.

cond-mat.mtrl-sci↗

arXiv2019

A first-principles investigation of Topological Phase Transition in face-centred cubic LiMgBi

Topological Insulators (TI) exhibit robust spin-locked dissipationless Fermion transport along the surface states. In the current study, we use \textit{first-principles} calculations to investigate a Topological Phase Transition (TPT) in a Half-Heusler (HH) compound LiMgBi driven by a Volume Expansive Pressure (VEP) which is attributed to the presence of, intrinsic voids, thermal perturbations and/or due to a phenomena known as cavity nuclei. We find that, the dynamically stable \textit{face-centred cubic} (FCC) structure of LiMgBi (which belongs to the F$\overline{4}$3m[216] space group), undergoes TPT beyond a critical VEP at 4.0\%. The continuous application of VEP from 0.0\% to 8.0\% results in a phase transition from a, band insulator to a Dirac semi-metal nature. Qualitatively, the Dirac cone formation and band inversion along the high symmetry point $\mathbfΓ$ in the Brillouin Zone (BZ) are analysed in terms of Electronic Band Structure (EBS) and Projected Local Density of States (LDOS). The TPT is further characterised by the $\mathbb{Z}_2$ invariant, ($ν_0$, $ν_1$ $ν_2$ $ν_3$) $\equiv$ (1, 0 0 0) along the (0001) surface which indicates quantitatively that, HH LiMgBi is a strong TI. We hence propose, HH LiMgBi (known for its piezoelectric, thermo-electric and semi-conducting applications) as a strong TI with potential multipurpose application in the field of electronics, spintronics and quantum computation.

cond-mat.mtrl-sci↗