arXiv subjects

Vipin Nagpal

Publications and source records attributed to Vipin Nagpal.

4 recordsLinked to original sources

arXiv2020

High Field Magneto-Transport of Mixed Topological Insulators Bi2Se3-xTex (x = 0, 1, 2 & 3)

The article comprises structural, microstructural, and physical properties analysis of Bi2Se3-xTex (x= 0, 1, 2 and 3) mixed topological insulator (MTI) single crystals. All the crystals were grown through a well-optimized solid-state reaction route via the self-flux method. These MTI are well characterized through XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), EDAX (Energy Dispersive spectroscopy), and thereby, the physical properties are analyzed through the RT (Resistance vs temperature) down to 10K as well as the magneto-resistance (MR) measurements (at 5K) in a magnetic field of up to 10 Tesla. The MR drastically varies from x=0 to x=3 in MTI, from a huge 400 percent, it goes down to 20 percent and 5 percent and eventually back to 315 percent. This fascinated behaviour of MR is explained in this article through HLN (Hikami-Larkin-Nagaoka) equation and an additional term. This article not only proposed the mesmerizing behavior of MR in MTI but also explains the reason through competing WAL (Weak Anti-Localization) and WL (Weak Localization) conduction processes.

cond-mat.mtrl-sci↗

arXiv2020

Crystal Growth and characterization of possible New Magnetic Topological Insulators FeBi2Te4

Here we report successful single crystal growth of new possible magnetic topological insulator (MTI) FeBi2Te4 by self-flux method via vacuum encapsulation process. The detailed Rietveld analysis of Powder XRD data shows the as grown MTI crystal to be mainly dominated by FeBi2Te4 phase along with minority phases of Bi2Te3 and FeTe. Scanning electron microscope (SEM) image shows the morphology of as grown MTI single crystal to be of layered type laminar structure. Raman spectroscopy of the crystal exhibited three distinct phonon modes at 65, 110, and 132 cm-1 along with two split secondary modes at 90, and 144cm-1. The secondary split modes are result of FeTe intercalation in Bi2Te3 unit cell. Magneto-resistance measurement has been performed at different temperatures i.e. 200K, 20K and 2K in applied magnetic fields up to 12 Tesla, which showed very low MR in comparison to pure Bi2Te3 crystal. Temperature dependence of DC magnetization measurements show the FeBi2Te4 crystal to be mainly of ferromagnetic (FM) or ferri-magnetic nature above 295 K, albeit a secondary weak magnetic transition is seen at 54-46K as well. Detailed isothermal magnetization (MH) results showed that FM saturation moment at 295K is 0.00213emu/g, which is nearly invariant till 400 K. Summary, we had grown an MTI FeBi2Te4 single crystal, which may be a possible entrant for Quantum Anomalous Hall (QAH) effect at room temperature or above.

cond-mat.mtrl-sci↗

arXiv2019

Crystal Growth and basic transport and magnetic properties of MnBi2Te4

We report successful growth of magnetic topological insulator (MTI) MnBi2Te4. The heating schedule basically deals with growth of the crystal from melt at 900C and very slow cooling (1C/hr) to around 600C with 24 hours hold time, followed by cooling to room temperature. Our detailed, PXRD Reitveld analysis showed that the resultant crystal is dominated mainly by MnBi2Te4 and minor phases of Bi2Te3 and MnTe. The transport measurements showed a step like behavior at around 150K followed by cusp like structure in resistivity at around 25K (TP) due reported anti-ferromagnetic ordering of Mn. Both the resistivity transitions are seen clearly in dR/dT measurements at 150K and 20K respectively. The 25K transition of the compound is also seen in magnetic susceptibility. Low temperature (5K) magnetoresistance (MR) in applied field of up to 6 Tesla exhibited negative ve MR below 3 Tesla and +ve for higher fields. Also, seen are steps in MR below one Tesla. The studied MnBi2Te4 MTI crystal could be a possible candidate for Quantum Anomalous Hall (QAH) effect.

cond-mat.mtrl-sci↗

arXiv2019

Spin-orbit driven spin depolarization in the ferromagnetic Weyl semimetal Co3Sn2S2

Co$_3$Sn$_2$S$_2$ has recently emerged as a ferromagnetic Weyl semi-metal. Theoretical investigation of the spin-split bands predicted half metalicity in the compound. Here, we report the detection of a spin polarized supercurrent through a Nb/Co$_3$Sn$_2$S$_2$ point contact where Andreev reflection is seen to be large indicating a large deviation from half metallicity. In fact, analysis of the Andreev reflection spectra reveals only 50\% spin polarization at the Fermi level of Co$_3$Sn$_2$S$_2$. Our theoretical calculations of electronic Density of States (DOS) reveal a spin depolarizing effect near the Fermi energy when the role of spin-orbit coupling is included. Inclusion of spin-orbit coupling also reveals particle-hole asymmetry that explains a large asymmetry observed in our experimental Andreev reflection spectra.

cond-mat.supr-con↗