arXiv subjects

Setti Thirupathaiah

Publications and source records attributed to Setti Thirupathaiah.

At least 19 recordsLinked to original sources

arXiv2026

Tunable Magnetic Frustration in the Cu-Ru-based Double Perovskite La$_{2-x}$Sm$_x$CuRuO$_6$ (x = 0, 1, 2) Oxides

In this study, we investigate structural, magnetic, and electronic properties of the copper-ruthenate based oxide double perovskite La$_{2-x}$Sm$_x$CuRuO$_6$ (x = 0, 1, 2), synthesized through the solid-state reaction method. X-ray diffraction analysis reveals that all compounds crystallize in a monoclinic symmetry, with varying degree of structural distortion that increases in moving from La$^{3+}$ to smaller size cation Sm$^{3+}$. Electrical resistivity studies indicate insulating behaviour in all compounds, with variable-range-hopping domination at low temperatures, due to presence of anti-site disorder. AC susceptibility and heat capacity measurements suggest suppression of frustration in Sm-bearing compounds, affecting the magnetic behavior. Our first-principles calculations suggest that the combined effects of lattice distortion and Sm magnetism play a crucial role in weakening magnetic frustration, thereby rationalizing the experimental observations. These findings shed light on the complex interplay of crystal structure and magnetism in Cu-Ru double perovskites, and open up an avenue for tuning of magnetic properties through rare-earth-ion substitution.

cond-mat.mtrl-sci↗

arXiv2026

Accessing quasi-flat $\textit{f}$-bands to harvest large Berry curvature in NdGaSi

In typical rare-earth lanthanide compounds, the localized 4\textit{f}-electrons have a weak effect on the electrical conduction, limiting their influence on the Berry curvature and, hence, the intrinsic anomalous Hall effect. A comprehensive study of the magnetic, thermodynamic, and transport properties of single-crystalline NdGaSi, guided by first-principles calculations, reveals a ferromagnetic ground state that induces a splitting of quasi-flat 4\textit{f} electronic bands and positions them near the Fermi energy. The observation of an extraordinarily large intrinsic anomalous Hall conductivity of 1165 $Ω^{-1}$ cm$^{-1}$ implies the direct involvement of localized states in the generation of non-trivial band crossings around the Fermi energy. The angle-resolved photoemission spectroscopy measurements provide direct evidence of non-trivial crossing of the 4\textit{f}-bands with dispersive bands. These results are remarkable when compared to ferrimagnetic NdAlSi, which differs only in a non-magnetic atom (a change in the principal quantum number \textit{n} of the outer \textit{p }orbital) with the same number of valence electrons and does not exhibit any measurable anomalous Hall conductivity.

cond-mat.mtrl-sci↗

arXiv2026

Identifying open-orbit topological surface states in dual topological semimetal TaSb$_2$

TaSb$_2$, a member of the transition metal dipnictide family of materials, hosts the very rare dual topological phase - weak topological insulating state and topological crystalline insulating state along different crystallographic orientations. So far, studies on the electronic structure of transition metal dipnictides have focused on their overall electronic structure and the bulk open-orbit Fermi surfaces. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and transport measurements, we distinguish the intertwined bulk and surface states on the weakly topological $(20\bar{1})$ plane of TaSb$_2$. We identify multiple electron- and hole-like bulk bands, yielding a near-perfect carrier compensation. Crucially, we observe open-orbit FSs parallel to $\bar{L}$-$\bar{Y}$ direction that are entirely of surface origin. Circular-dichroism ARPES reveals $k \rightarrow -k$ spectral reversal, indicating spin-momentum locking and the topological nature of these surface states. Consistent with this, magnetotransport measurements display weak antilocalization, establishing TaSb$_2$ as a platform for spin-polarized topological transport on a weakly topological surface.

cond-mat.mtrl-sci↗

arXiv2025

Ultrafast Dynamics of Spin-Orbit Entangled Excitons Coupled to Magnetic Ordering in van der Waals Antiferromagnet NiPS3

Spin-orbit entangled excitons (SOEE) in two-dimensional (2D) antiferromagnets provide direct access to explore unconventional many body interactions in correlated electron systems. In this work, we carry out a detailed investigation using non-degenerate isotropic and anisotropic pump-probe reflection spectroscopy to probe the ultrafast dynamics of SOEE and their coupling to spin fluctuations in NiPS3. Transient reflectivity data reveals acoustic phonon oscillations at ~ 27 GHz, along with two distinct relaxation timescales: fast (1-9 ps) and slower components (1-4 ns) associated with SOEE coherence and spin reordering, respectively. Both timescales exhibit pronounced temperature dependence near the exciton dissociation (TED = 120 K) and Neel (TN = 155 K) temperatures. The SOEE coherence shortens from ~ 8-9 ps at T < TED to ~ 3 ps at T > TED with a finite tail persisting beyond TN. The spin reordering time grows near 120 K, and shows critical slowing down around TN. Pump fluence studies further corroborate their spin origin. Our findings uncover the direct interplay between the excitonic and spin degrees of freedom across ultrafast and longer timescales, offering new opportunities to probe and engineer emergent many-body interactions in 2D antiferromagnets.

cond-mat.other↗

arXiv2025

Extremely Large and Angle-Dependent Magnetoresistance in Kagome Dirac Semimetal RFe$_6$Sn$_6$ (R=Ho, Dy)

We report on the electronic, magnetic, and magneto-transport properties of Fe-based kagome Dirac system, RFe$_6$Sn$_6$ (R = Ho, Dy). Magnetic properties study reveals an antiferromagnetic order with N$\acute{e}$el temperature of $T_N \approx$ 570 K. Additionally, a weak ferromagnetic order emerge at low temperatures. Magnetotransport measurements demonstrate an extremely large magnetoresistance (XMR) reaching as high as $3\times 10^{3} \%$ for HoFe$_6$Sn$_6$ and $ 1\times 10^{3} \%$ for DyFe$_6$Sn$_6$ when measured at 2 K with 9 T of magnetic field. The semi-classical two-band model fitting of the Hall conductivity reveals nearly perfect electron-hole compensation and high carrier mobility, which leads to XMR behaviour in these system. Further, we identify large magnetoresistance anisotropy for the magnetic fields applied in different crystallographic orientations. In addition, considerable modification in the angle-dependent magnetoresistance (ADMR) pattern has been noticed between 2 and 50 K, indicating temperature-dependent changes in the Fermi surface topology of these systems.

cond-mat.mtrl-sci↗

arXiv2025

Spin-reorientation Driven Temperature Dependent Intrinsic Anomalous Hall Conductivity in Fe$_3$Ge, a Ferromagnetic Topological Metal

We investigate the temperature dependence of the intrinsic anomalous Hall conductivity in Fe$_3$Ge, which is a ferromagnetic topological metal. We observe a significant anisotropy in the anomalous Hall conductivity between in-plane and out-of-plane directions. We further identify that the total Hall conductivity is contributed extrinsically due to the skew-scattering mechanism and intrinsically due to nonzero Berry curvature in the momentum space. Most importantly, we demonstrate the temperature dependence of the intrinsic Hall contribution, a rare phenomenon to visualize experimentally, due to tuning the easy-magnetic axis from the out-of-plane to the in-plane with decreasing temperature. We also show that the extrinsic Hall conductivity decreases with temperature as $σ_{xy}^{ext}(T)=\frac{σ_{xy0}^{ext}}{(aT+1)^2}$ due to electron-phonon scattering.

cond-mat.mtrl-sci↗

arXiv2025

Topological nodal $i$-wave superconductivity in PtBi$_2$

Most superconducting materials are well-understood and conventional in the sense that the pairs of electrons that cause the superconductivity by their condensation have the highest possible symmetry. Famous exceptions are the enigmatic high-$T_c$ cuprate superconductors. Nodes in their superconducting gap are the fingerprint of their unconventional character and imply superconducting pairing of $d$-wave symmetry. Here, using angle-resolved photoemission spectroscopy, we observe that the Weyl semimetal PtBi$_2$ harbors nodes in its superconducting gap, implying unconventional $i$-wave pairing symmetry. At temperatures below $10\,\mathrm{K}$, the superconductivity in PtBi$_2$ gaps out its topological surface states, the Fermi arcs, while its bulk states remain normal. The nodes in the superconducting gap that we observe are located exactly at the center of the Fermi arcs, and imply the presence of topologically protected Majorana cones around this locus in momentum space. From this, we infer theoretically that robust zero-energy Majorana flat bands emerge at surface step edges. This not only establishes PtBi$_2$ surfaces as unconventional, topological $i$-wave superconductors but also as a promising material platform in the ongoing effort to generate and manipulate Majorana bound states.

cond-mat.supr-con↗

arXiv2025

Topological Hall effect in ferromagnetic Weyl semimetal Mn$_5$Ge$_3$ originating in competing dipolar interaction and magnetocrystalline anisotropy

We report the anomalous and topological Hall effect of the ferromagnetic Weyl semimetal Mn$_5$Ge$_3$. We observe a significant anisotropic anomalous Hall effect (AHE) due to nonzero Berry curvature in the momentum space, such that the anomalous Hall conductivity (AHC) is 965 S/cm for the $xy$-plane and 233 S/cm for the $zx$-plane of the single crystal. The band structure calculations predict several Weyl and nodal points span across the momentum space, gapped out under the spin-orbit coupling effect, leading to significant $k$-space Berry curvature and large AHC. Experimentally, we also demonstrate a sizeable topological Hall effect that is originated by the non-coplanar chiral spin structure due to the competition between the out-of-plane uniaxial magnetocrystalline anisotropy and the dipole-dipole interaction between two Mn sublattices. This study hints at the importance of dipole-dipole interactions in producing the skyrmion lattice in Mn$_5$Ge$_3$.

cond-mat.mtrl-sci↗

arXiv2024

Anomalous and parallel Hall effects in ferromagnetic Weyl semimetal Cr$_3$Te$_4$

Recently, time-reversal symmetry broken magnetic Weyl semimetals (WSMs) have attracted extensive attention and have provided an intriguing platform for exploring fundamental physical phenomena. The study of chromium telluride-based systems has also drawn significant interest towards spintronics applications owing to their high Curie temperatures. Here, using \textit{ab initio} calculations, we propose the emergence of multiple Weyl points (WPs) near the Fermi level in such an intrinsic ferromagnetic system, Cr$_3$Te$_4$. The large, well-separated, nontrivial Fermi arcs and surface states, suggest that the WPs are highly robust and resilient to perturbations. A substantial Berry curvature contribution in the vicinity of the Fermi energy not only serves as the origin of large conventional anomalous Hall conductivity (AHC), but also produces unconventional parallel AHC in this material, owing to the low structural symmetry. In addition to the charge Hall conductivity, we also find significant anomalous Nernst conductivities originating from the Berry curvature. Alongside our theoretical predictions, we present complementary experimental results, including X-ray diffraction (XRD) analysis and an examination of the magnetic properties, which demonstrate a Curie temperature of 327 K. Our study advances the understanding of magnetic WSMs, and also encourages further studies in the context of topological properties of our proposed material.

cond-mat.mtrl-sci↗

arXiv2024

Sn$_{0.06}$Cr$_3$Te$_4$: A Skyrmion Superconductor

Topological superconductors are an exciting class of quantum materials from the point of view of the fundamental sciences and potential technological applications. Here, we report on the successful introduction of superconductivity in a ferromagnetic layered skyrmion system Cr$_3$Te$_4$, obtained by the Sn intercalation, below a transition temperature of $T_c$$\approx$3.5 K. We observe several interesting physical properties, such as superconductivity, magnetism, and the topological Hall effect, simultaneously in this system. Despite the magnetism and Meissner effects being anisotropic, the superconductivity observed from the in-plane electrical resistivity ($ρ_{\it{bc}}$) is nearly isotropic between $H\parallel \it{bc}$ and $H\parallel \it{a}$, suggesting separate channels of conduction electrons responsible for the superconductivity and magnetism of this system, which is also supported by our spin-resolved DFT calculations. We identify two orders of higher carrier density in superconducting Sn$_{0.06}$Cr$_{3}$Te$_4$ than the parent Cr$_3$Te$_4$. A jump in the specific heat is noticed around the $T_c$ with a volume fraction of 33\%, confirming the bulk superconductivity in Sn$_{0.06}$Cr$_{3}$Te$_4$. In addition to the introduction of superconductivity, tuning of topological Hall properties is noticed with Sn intercalation. Our observation of superconductivity in a skyrmion lattice brings up a new class of topological quantum materials.

cond-mat.supr-con↗

arXiv2024

3D-Ising-type Magnetic Interactions Stabilized by the Extremely Large Uniaxial Magnetocrystalline Anisotropy in Layered Ferromagnetic Cr$_2$Te$_3$

We investigate the magnetocrystalline anisotropy, critical behavior, and magnetocaloric effect in ferromagnetic-layered Cr$_2$Te$_3$. We have studied the critical behavior around the Curie temperature ($T_C$) using various techniques, including the modified Arrott plot (MAP), the Kouvel-Fisher method (KF), and critical isothermal analysis (CI). The derived critical exponents $β$ = 0.353(4) and $γ$ = 1.213(5) fall in between the three-dimensional (3D) Ising and 3D Heisenberg type models, suggesting complex magnetic interactions by not falling into any single universality class. On the other hand, the renormalization group theory, employing the experimentally obtained critical exponents, suggests 3D-Ising-type magnetic interactions decaying with distance as $J(r) = r^{-4.89}$. We also observe an extremely large uniaxial magnetocrystalline anisotropy energy (MAE) of $K_u=2065$ kJ/m$^3$, the highest ever found in any Cr$_x$Te$_y$ based systems, originating from the noncollinear ferromagnetic ground state as predicted from the first-principles calculations. The self-consistent renormalization theory (SCR) suggests Cr$_2$Te$_3$ to be an out-of-plane itinerant ferromagnet. Further, a maximum entropy change of -$ΔS_{M}^{max}\approx$ 2.08 $J/kg-K$ is estimated around $T_C$ for the fields applied parallel to the $c$-axis.

cond-mat.mtrl-sci↗

arXiv2024

Anisotropic Nonsaturating Magnetoresistance Observed in HoMn$_6$Ge$_6$: A Kagome Dirac Semimetal

We report the magnetic and magnetotransport properties and electronic band structure of the kagome Dirac semimetal HoMn$_6$Ge$_6$. Temperature-dependent electrical resistivity demonstrates various magnetic-transition-driven anomalies. Notably, a crossover from negative to positive magnetoresistance (MR) is observed at around 150 K. While the linear nonsaturating positive MR in the low-temperature region is mainly driven by the linear Dirac-like band dispersions as predicted by the first-principles calculations, the negative MR observed in the high-temperature region is due to the spin-flop type magnetic transition. Consistent with anisotropic Fermi surface topology, we observe anisotropic magnetoresistance at low temperatures. A significant anomalous Hall effect has been noticed at high temperatures in addition to a switching of the dominant charge carrier from electron to hole at around 215 K.

cond-mat.mtrl-sci↗

arXiv2024

Unusual Multiple Magnetic Transitions and Anomalous Hall Effect Observed in Antiferromagnetic Weyl Semimetal, Mn$_{2.94}$Ge (Ge-rich)

We report on the magnetic and Hall effect measurements of the magnetic Weyl semimetal, Mn$_{2.94}$Ge (Ge-rich) single crystal. From the magnetic properties study, we identify unusual multiple magnetic transitions below the N$\acute{e}$el temperature of 353 K, such as the spin-reorientation ($T_{SR}$) and ferromagnetic-like transitions. Consistent with the magnetic properties, the Hall effect study shows unusual behavior around the spin-reorientation transition. Specifically, the anomalous Hall conductivity (AHC) increases with increasing temperature, reaching a maximum at $T_{SR}$, which then gradually decreases with increasing temperature. This observation is quite in contrast to the Mn$_{3+δ}$Ge (Mn-rich) system, though both compositions share the same hexagonal crystal symmetry. This study unravels the sensitivity of magnetic and topological properties on the Mn concentration.

cond-mat.mtrl-sci↗

arXiv2023

Weak Electronic Correlations Observed in Magnetic Weyl Semimetal Mn$_3$Ge

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we systematically studied the electronic band structure of Mn$_3$Ge in the vicinity of the Fermi level. We observe several bands crossing the Fermi level, confirming the metallic nature of the studied system. We further observe several flat bands along various high symmetry directions, consistent with the DFT calculations. The calculated partial density of states (PDOS) suggests a dominant Mn $3d$ orbital contribution to the total valence band DOS. With the help of orbital-resolved band structure calculations, we qualitatively identify the orbital information of the experimentally obtained band dispersions. Out-of-plane electronic band dispersions are explored by measuring the ARPES data at various photon energies. Importantly, our study suggests relatively weaker electronic correlations in Mn$_3$Ge compared to Mn$_3$Sn.

cond-mat.mtrl-sci↗

arXiv2023

Effect of Electron-Phonon Scattering on the Anomalous Hall Conductivity of Fe$_3$Sn: A Kagome Ferromagnetic Metal

We report on magnetic and magnetotransport studies of a Kagome ferromagnetic metal, Fe$_3$Sn. Our studies reveal a large anomalous Hall conductivity ($σ_{zx}$) in this system, mainly contributed by temperature independent intrinsic Hall conductivity ($σ^{int}_{zx}$=485$\pm$60 S/cm) and temperature dependent extrinsic Hall conductivity ($σ^{ext}_{zx}$) due to skew-scattering. Although $σ^{ext}_{zx}$ value is large and almost equivalent to the intrinsic Hall conductivity at low temperatures, it drastically decreases with increasing temperature, following the relation $σ^{ext}_{zx}=\frac{σ_{zx0}^{ext}}{(aT+1)^2}$, under the influence of electron-phonon scattering. The presence of electron-phonon scattering in this system is also confirmed by the linear dependence of longitudinal electrical resistivity at higher temperatures [$ρ(T)\propto T$]. We further find that Fe$_3$Sn is a soft ferromagnet with an easy-axis of magnetization lying in the $\it{ab}$ plane of the crystal with magnetocrystalline anisotropy energy density as large as 1.02 $\times$ 10$^6$

cond-mat.mtrl-sci↗

arXiv2023

Tuning of Electrical, Magnetic, and Topological Properties of Magnetic Weyl Semimetal Mn$_{3+x}$Ge by Fe doping

We report on the tuning of electrical, magnetic, and topological properties of the magnetic Weyl semimetal (Mn$_{3+x}$Ge) by Fe doping at the Mn site, Mn$_{(3+x)-δ}$Fe$_δ$Ge ($δ$=0, 0.30, and 0.62). Fe doping significantly changes the electrical and magnetic properties of Mn$_{3+x}$Ge. The resistivity of the parent compound displays metallic behavior, the system with $δ$=0.30 of Fe doping exhibits semiconducting or bad-metallic behavior, and the system with $δ$=0.62 of Fe doping demonstrates a metal-insulator transition at around 100 K. Further, we observe that the Fe doping increases in-plane ferromagnetism, magnetocrystalline anisotropy, and induces a spin-glass state at low temperatures. Surprisingly, topological Hall state has been noticed at a Fe doping of $δ$=0.30 that is not found in the parent compound or with $δ$=0.62 of Fe doping. In addition, spontaneous anomalous Hall effect observed in the parent system is significantly reduced with increasing Fe doping concentration.

cond-mat.mtrl-sci↗

arXiv2023

Experimental Realization of Room Temperature Topological Hall Effect in Kagome Antiferromagnet

Magnetic topological semimetals are the manifestations of interplay between electronic and magnetic phases of the matter, leading to peculiar characteristics such as the anomalous Hall effect (AHE) and topological Hall effect (THE). Mn$_3$Sn is a time-reversal symmetry broken (TRS) magnetic Weyl semimetal showing topological characteristics within the Kagome lattice network. In this study, for the first time, we uncover large and pure topological Hall effect in Mn$_3$Sn at the room temperature, which is gradually suppressed by Fe doping at the Mn site of Mn$_{3-x}$Fe$_x$Sn. We further identify that the topological properties of these systems are highly anisotropic. These findings promise the realization of potential topotronic applications at room temperature.

cond-mat.mtrl-sci↗

arXiv2018

Possible Experimental Realization of a Basic Z2 Topological Semimetal

We report experimental and theoretical evidence that GaGeTe is a basic $Z_2$ topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the primer 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion in the \textit{T}-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron- and hole-like carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.

cond-mat.mtrl-sci↗