Prabhat Mandal

Bio: Prabhat Mandal is an academic researcher from Saha Institute of Nuclear Physics. The author has contributed to research in topics: Magnetization & Antiferromagnetism. The author has an hindex of 22, co-authored 135 publications receiving 1758 citations. Previous affiliations of Prabhat Mandal include Homi Bhabha National Institute.

Large nonsaturating magnetoresistance and signature of nondegenerate Dirac nodes in ZrSiS

Abstract: Whereas the discovery of Dirac- and Weyl-type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and technological applications is an experimental challenge. In all of the reported materials, linear dispersion survives only up to a few hundred millielectronvolts from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics. In ZrSiS, angle-resolved photoemission spectroscopy measurements have shown an unusually robust linear dispersion (up to ∼ 2 eV) with multiple nondegenerate Dirac nodes. In this context, we present the magnetotransport study on ZrSiS crystal, which represents a large family of materials (WHM with W = Zr, Hf; H = Si, Ge, Sn; M = O, S, Se, Te) with identical band topology. Along with extremely large and nonsaturating magnetoresistance (MR), ∼ 1.4 × 105% at 2 K and 9 T, it shows strong anisotropy, depending on the direction of the magnetic field. Quantum oscillation and Hall effect measurements have revealed large hole and small electron Fermi pockets. A nontrivial π Berry phase confirms the Dirac fermionic nature for both types of charge carriers. The long-sought relativistic phenomenon of massless Dirac fermions, known as the Adler–Bell–Jackiw chiral anomaly, has also been observed.

Large adiabatic temperature and magnetic entropy changes in EuTi O 3

Abstract: We have investigated the magnetocaloric effect in single and polycrystalline samples of quantum paraelectric $\mathrm{EuTi}{\mathrm{O}}_{3}$ by magnetization and heat capacity measurements. Single crystalline $\mathrm{EuTi}{\mathrm{O}}_{3}$ shows antiferromagnetic ordering due to $\mathrm{E}{\mathrm{u}}^{2+}$ magnetic moments below ${T}_{\mathrm{N}}=5.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. This compound shows a giant magnetocaloric effect around its N\'eel temperature. The isothermal magnetic entropy change is $49\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, the adiabatic temperature change is 21 K, and the refrigeration capacity is $500\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$ for a field change of 7 T at ${T}_{\mathrm{N}}$. The single crystal and polycrystalline samples show similar values of the magnetic entropy and adiabatic temperature changes. The large magnetocaloric effect is due to suppression of the spin entropy associated with the localized $4f$ moment of $\mathrm{E}{\mathrm{u}}^{2+}$ ions. The giant magnetocaloric effect, together with negligible hysteresis, suggest that $\mathrm{EuTi}{\mathrm{O}}_{3}$ could be a potential material for magnetic refrigeration below 40 K.

Magnetocaloric effect in HoMnO3 crystal

Abstract: We have investigated the magnetic and magnetocaloric properties of HoMnO3 single crystal. HoMnO3 displays a series of complicated phase transitions due to the long range ordering of Mn3+ and Ho3+ moments. Field variation in magnetization generates a metamagnetic transition and produces an entropy change of 13.1 J/kg K at 7 T in the vicinity of antiferromagnetic ordering temperature of Ho3+. The values of adiabatic temperature change (∼6.5 K) and relative cooling power (∼320 J/kg) for a field change of 7 T are also appreciable to consider HoMnO3 as a magnetic refrigerant at low temperature.

Critical behavior in single-crystalline La 0.67 Sr 0.33 CoO 3

Abstract: The critical behavior of ${\text{La}}_{0.67}{\text{Sr}}_{0.33}{\text{CoO}}_{3}$ single crystal has been investigated from the bulk magnetization measurements around the Curie temperature $({T}_{C})$. The detailed analysis of the magnetization indicates the occurrence of a continuous ferromagnetic to paramagnetic phase transition at 223.0 K. The critical exponents $\ensuremath{\beta}=0.361\ifmmode\pm\else\textpm\fi{}0.007$, $\ensuremath{\gamma}=1.31\ifmmode\pm\else\textpm\fi{}0.001$, and $\ensuremath{\delta}=4.64\ifmmode\pm\else\textpm\fi{}0.01$ characterizing this second order phase transition, have been estimated using different techniques such as the Kouvel-Fisher plot, the Arrott-Noaks plot, and critical isotherm analysis. With these values of ${T}_{C}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$, one can scale the magnetization below and above ${T}_{C}$ following a single equation of state. The consistency in the values of the critical exponents obtained from different methods and the well-obeyed scaling behavior confirm that the calculated exponents are unambiguous and purely intrinsic to the system. These values of the exponents match well with those theoretically predicted for the three-dimensional Heisenberg model with nearest-neighbor interaction.

Planar Hall effect in the type-II Dirac semimetal VAl 3

Abstract: The study of electronic properties in topological systems is one of the most fascinating topics in condensed-matter physics, which has generated enormous interests in recent times. New materials are frequently being proposed and investigated to identify their nontrivial band structure. While sophisticated techniques such as angle-resolved photoemission spectroscopy have become popular to map the energy-momentum relation, the transport experiments lack any direct confirmation of Dirac and Weyl fermions in a system. From band-structure calculations, ${\mathrm{VAl}}_{3}$ has been proposed to be a type-II topological Dirac semimetal. This material represents a large family of isostructural compounds, all having similar electronic band structure and is an ideal system to explore the rich physics of Lorentz symmetry violating Dirac fermions. In this work, we present a detailed analysis on the magnetotransport properties of ${\mathrm{VAl}}_{3}$. A large, nonsaturating magnetoresistance has been observed. Hall resistivity reveals the presence of two types of charge carriers with high mobility. Our measurements show a large planar Hall effect in this material, which is robust and can be easily detectable up to high temperature. This phenomenon originates from the relativistic chiral anomaly and nontrivial Berry curvature, which validates the theoretical prediction of the Dirac semimetal phase in ${\mathrm{VAl}}_{3}$.

Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor

Abstract: A possible sighting of Majorana states Nearly 80 years ago, the Italian physicist Ettore Majorana proposed the existence of an unusual type of particle that is its own antiparticle, the so-called Majorana fermion. The search for a free Majorana fermion has so far been unsuccessful, but bound Majorana-like collective excitations may exist in certain exotic superconductors. Nadj-Perge et al. created such a topological superconductor by depositing iron atoms onto the surface of superconducting lead, forming atomic chains (see the Perspective by Lee). They then used a scanning tunneling microscope to observe enhanced conductance at the ends of these chains at zero energy, where theory predicts Majorana states should appear. Science, this issue p. 602; see also p. 547 Scanning tunneling microscopy is used to observe signatures of Majorana states at the ends of iron atom chains. [Also see Perspective by Lee] Majorana fermions are predicted to localize at the edge of a topological superconductor, a state of matter that can form when a ferromagnetic system is placed in proximity to a conventional superconductor with strong spin-orbit interaction. With the goal of realizing a one-dimensional topological superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the surface of superconducting lead (Pb). Using high-resolution spectroscopic imaging techniques, we show that the onset of superconductivity, which gaps the electronic density of states in the bulk of the Fe chains, is accompanied by the appearance of zero-energy end-states. This spatially resolved signature provides strong evidence, corroborated by other observations, for the formation of a topological phase and edge-bound Majorana fermions in our atomic chains.

Dirac Semimetal in Three Dimensions

Abstract: We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of β-cristobalite BiO(2) which exhibits three Dirac points at the Fermi level. We find that β-cristobalite BiO(2) is metastable, so it can be physically realized as a 3D analog to graphene.