arXiv subjects

Surasree Sadhukhan

Publications and source records attributed to Surasree Sadhukhan.

6 recordsLinked to original sources

arXiv2026

Study of the Nonlinear Dependence of Anomalous Hall Conductivity on Magnetization in Weak Itinerant Ferromagnet ZrZn2

As opposed to the ordinary Hall effect, the anomalous Hall effect (AHE) remained unexplained for decades, and, amazingly, some misconceptions have survived even now, in particular, the claim that AHE is linearly related to the net magnetization. Karplus and Luttinger provided a quantum-mechanical explanation of AHE by explicitly including the SOC and the Berry curvature of electronic bands. They did address the question of linearity, but only in the relatively uncommon limit of the exchange coupling smaller than SOC. Now the linear relation in traditional ferromagnets is understood as a domain population effect: both AHE and magnetization are independently proportional to the domain disbalance. In this connection, it is interesting to check to what extent this relation will hold in {\em single-domain} itinerant ferromagnet, the closest case to that analyzed by Karplus and Luttinger? We answer this question by direct calculations, using the Karplus-Luttinger formula, of AHE in a prototypical itinerant ferromagnet, ZrZn$_2$. We show that in the zero-magnetization limit, $M\rightarrow 0$, the linear relation hold, but at rather small moments of $\sim 0.4\ μ_B$/Zr breaks down completely and even flips the sign.

cond-mat.mtrl-sci↗

arXiv2025

Observation of Altermagnetic Spin Splitting in an Intercalated Transition Metal Dichalcogenide

Altermagnetism is a novel magnetic phase combining characteristics of both antiferromagnetism and ferromagnetic ordering. Despite growing theoretical interest in altermagnetic materials, reports of experimentally verified high Neel temperature layered compounds are limited or remain to be firmly established. Here, we present an angle resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) study of Co1/4TaSe2, a compound we identify as a layered altermagnetic material. Magnetic susceptibility measurements confirm type A antiferromagnetic ordering with a Neel temperature of 178 K. Our ARPES measurements reveal an electronic band structure in excellent agreement with DFT calculations, demonstrating clear signatures of altermagnetic spin splitting at the Fermi surface. Furthermore, temperature dependent ARPES reveals a reconstructed valence band structure, with observable band shifts and the closing of energy gaps upon heating above the Neel temperature (TN), consistent with the suppression of altermagnetic order. These findings establish Co1/4TaSe2 as a promising platform for exploring altermagnetic phenomena.

cond-mat.mes-hall↗

arXiv2023

Spin-orbit coupling tuned crossover of gaped and gapless topological phases in the chalcopyrite HgSnX 2 (X=N/P): An ab-initio investigation

The coupling between electron orbital momentum and spin momentum, known as spin-orbit coupling (SOC), is a fundamental origin of a multitude of fascinating physical phenomena, especially it holds paramount significance in the realm of topological materials. In our work, we have predicted the topological phase in Hg-based chalcopyrite compounds using the first principles density functional theory. The initial focus was on HgSnN 2 , revealing it to be a nonmagnetic Weyl semimetal, while HgSnP 2 displayed characteristics of a strong topological insulator. What makes our work truly unique is that despite both compounds having the same SOC strength, arises from Hg, they exhibit distinct topological phases due to the distinct hybridization effect of the Hg-5d and X-p bands. This finding can address a significant factor, i.e., the effect of the band hybridization in deriving distinct topological phases, keeping the symmetry aspect intact. Our results indicate that due to the presence of band hybridization between the dominant X-np orbitals n=2 and 3 for X=N and P respectively and a minor contribution from Hg-5d, we can tune the topological phase by manipulating SOC strength, which equivalently achievable by chemical substitutions. This investigation stands as a remarkable illustration of the unique roles that hybridization plays in sculpting the topological properties of these compounds while simultaneously preserving their underlying symmetries.

cond-mat.mtrl-sci↗

arXiv2022

Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi

The present work aims to address the electronic and magnetic properties of the intermetallic compound GdPd$_2$Bi through a comprehensive study of the structural, magnetic, electrical and thermal transport on a polycrystalline sample, followed by theoretical calculations. Our findings indicate that the magnetic ground state is antiferromagnetic in nature. Magnetotransport data present prominent hysteresis loop hinting a structural transition with further support from specific heat and thermopower measurements, but no such signature is observed in the magnetization study. Temperature dependent powder x-ray diffraction measurements confirm martensitic transition from the high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature (LT) orthorhombic $Pmma$ structure similar to many previously reported shape memory alloys. The HT to LT phase transition is characterized by a sharp increase in resistivity associated with prominent thermal hysteresis. Further, we observe robust Bain distortion between cubic and orthorhombic lattice parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and $c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and elongation along $a$-axis respectively. The sample shows an unusual `non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field as high as 150 kOe. In addition, non-linear field dependence of Hall resistivity is observed below about 30 K, which coincides with the sign change of the Seebeck coefficient. The electronic structure calculations confirm robust metallic states both in the LT and HT phases. It indicates complex nature of the Fermi surface along with the existence of both electron and hole charge carriers. The anomalous transport behaviors can be related to the presence of both electron and hole pockets.

cond-mat.str-el↗

arXiv2022

Role of chemical disorder in tuning the Weyl points in vanadium doped Co$_2$TiSn

The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Co-based Heusler alloys. In the present study, we have investigated the role of chemical disorder on the variation of Weyl points in Co\textsubscript{2}Ti\textsubscript{1-x}V\textsubscript{x}Sn magnetic Weyl semimetal candidate. We employ the first principle approach to track the evolution of the nodal lines responsible for the appearance of Weyl node in Co$_2$TiSn as a function of V substitution in place of Ti. By increasing the V concentration in place of Ti, the nodal line moves toward Fermi level and remains at Fermi level around the middle composition. Further increase of the V content, leads shifting of nodal line away from Fermi level. Density of state calculation shows half-metallic behavior for the entire range of composition. The magnetic moment on each Co atom as a function of V concentration increases linearly up to x=0.4, and after that, it starts decreasing. We also investigated the evolution of the Weyl nodes and Fermi arcs with chemical doping. The first-principles calculations reveal that via replacing almost half of the Ti with V, the intrinsic anomalous Hall conductivity increased twice as compared to the undoped composition. Our results indicate that the composition close to the 50\% V doped Co$_2$TiSn, will be an ideal composition for the experimental investigation of Weyl physics.

cond-mat.mtrl-sci↗

arXiv2022

Pressure driven topological phase transition in chalcopyrite ZnGeSb$_2$

Recently topologically non-trivial phases have been identified in few time-reversal invariant systems that lack of inversion symmetry. Using density functional theory based first-principles calculations, we report a strong topologically non-trivial phase in chalchopyrite ZnGeSb$_2$, which can act as a model system of strained HgTe. The calculations reveal the non-zero topological invariant ($Z_2$), the presence of Dirac cone crossing in the surface spectral functions with spin-momentum locking. We also show that the application of moderate hydrostatic pressure ($\sim$7 GPa) induces topological phase transition from topological non-trivial phase to a topologically trivial phase. A discontinuity in the tetragonal distortion of non-centrosymmetric ZnGeSb$_2$ plays a crucial role in driving this topological phase transition.

cond-mat.mtrl-sci↗