arXiv subjects

Shama

Publications and source records attributed to Shama.

9 recordsLinked to original sources

arXiv2026

Vortex Tunneling and Critical State in an Oxide Heterostructure

Two-dimensional superconductors offer an excellent platform for the study of vortex matter due to their low superfluid stiffness and inability to effectively screen applied magnetic fields. Here we explore vortices in a two-dimensional superconductor formed at the surface of the complex oxide KTaO$_3$. Multiple regimes of vortex-mediated transport are identified and studied, revealing switching behaviour attributed to nucleation of individual vortices. Analysis of this regime allows us to identify the quantum tunneling of vortices, which transitions to thermally activated behaviour at elevated temperatures. Magnetic field dependence reveals rich histograms of the switching currents which we attribute to different configurations of pinned vortices.

cond-mat.supr-con↗

arXiv2025

Superconductivity in spin-orbit coupled BaBi$_3$ formed by in situ reduction of bismuthate films

Oxygen-scavenging at oxide heterointerfaces has emerged as a powerful route for stabilizing metastable phases that exhibit interesting phenomena, including high-mobility two-dimensional electron gases and high T$_{c}$ superconductivity. We investigate structural and chemical interactions at the heterointerface formed between Al or Eu and the charged-ordered insulator, BaBiO$_3$, leading to emergent superconductivity at 6 K. A combination of X-ray diffraction and electron microscopy measurements shows that oxygen scavenging by the Eu and Al adlayers leads to the formation of superconducting intermetallic BaBi$_3$ in nominal Eu/BaBiO$_3$ and Al/BaBiO$_3$ bilayers. Anisotropic magnetotransport measurements and current-voltage signatures of quasi two-dimensional superconductivity are observed. The mechanisms behind quasi-two-dimensional superconductivity and the role of disorder remain to be clarified. These findings highlight the potential for the use of in situ reduction of bismuthate heterostructures as a platform for stabilizing materials with exotic functional properties. Additionally, the strong spin-orbit coupling at the Bi sites may pave the way for the realization of high T$_{c}$ topological superconductivity.

cond-mat.supr-con↗

arXiv2022

Role of electronic correlations in the Kagome lattice superconductor LaRh$_3$B$_2$

LaRh$_3$B$_2$ crystallizes in a layered structure where Rh atoms form a perfect Kagome lattice. The material shows superconductivity at $T_c \approx 2.6$~K\@ and no signature for density wave instabilities. We report our measurements of electronic transport, magnetization, and heat capacity in the normal and superconducting state, and derive normal and superconducting parameters. From first principles calculations of the electronic band structure, we identify all features of Kagome bands predominantly formed by the Rh $d$ orbitals: a flat band, Dirac cones, and van Hove singularities. The calculation of the phonon dispersions and electron-phonon coupling suggests a strong similarity between LaRh$_3$B$_2$ and AV$_3$Sb$_5$ (A=K,Cs,Rb). For LaRh$_3$B$_2$, it matches quantitatively with the observed $T_c$, supporting a conventional phonon mediated pairing mechanism. By comparison to the $A$V$_3$Sb$_5$ family, we conjecture a reduced importance of electron correlations in LaRh$_3$B$_2$.

cond-mat.supr-con↗

arXiv2022

Unusual Magnetotransport from two dimensional Dirac Fermions in Pd$_{3}$Bi$_{2}$Se$_{2}$

Pd$_{3}$Bi$_{2}$Se$_{2}$ has been proposed to be topologically non-trivial in nature. However, evidence of its non-trivial behavior is still unexplored. We report the growth and magneto-transport study of Pd$_{3}$Bi$_{2}$Se$_{2}$ thin films, revealing for the first time the contribution of two-dimensional (2D) topological surface states. We observe exceptional non-saturated linear magnetoresistance which results from Dirac fermions inhabiting the lowest Landau level in the quantum limit. The transverse magnetoresistance changes from a semi-classical weak-field $B^{2}$ dependence to a high-field $B$ dependence at a critical field $B^{\star}$. It is found that $B^{\star} \propto T^2$, which is expected from the Landau level splitting of a linear energy dispersion. In addition, the magnetoconductivity shows signatures of 2D weak anti-localization (WAL). These novel magnetotransport signatures evince the presence of 2D Dirac fermions in Pd$_{3}$Bi$_{2}$Se$_{2}$ thin films.

cond-mat.str-el↗

arXiv2022

Observation of Weak Anti-localization in thin films of the Topological Semimetal Candidate PdSb$_{2}$

We report results of a magneto-transport study on thin films of the topological semi-metal candidate PdSb$_{2}$ (PS). We observe a positive correction to magneto-conductivity at low temperatures, which is a signature of weak anti-localization (WAL). We analyze the WAL data within the Hikami-Larkin-Nagaoka (HLN) theory and extract the dephasing length (L$_{\phi}$) whose temperature dependence reveals the various phase relaxation mechanisms. From the WAL effect, we also extract $\alpha$ (the number of transport channels). The evolution of $\alpha$ with temperature and film thickness reflects how the coupling between different conducting channels (Topological surface channels and bulk channels) changes. Additionally, the electron-electron interaction (EEI) effect was observed in the temperature-dependent conductivity at low temperatures. From the EEI effect, we get an alternate estimate of the number of transport channels and obtain a value similar to that obtained from the analysis of the WAL effect. This suggests that in disordered films, the EEI effect can be used to get information about the coupling of the topological surface states with each other and with bulk states.

cond-mat.str-el↗

arXiv2020

Weak Anti-localization in thin films of the Topological Semimetal Candidate Pd$_{3}$Bi$_{2}$S$_{2}$

We report the growth and magneto-transport studies of Pd$_{3}$Bi$_{2}$S$_{2}$ (PBS) thin films synthesized by pulsed laser deposition (PLD) technique. The magneto-transport study on pristine and post annealed films show the presence of more than one type of charge carrier with a carrier concentration in the range $0.6$ - $2.26~\times$ 10$^{21}$ cm$^{-3}$ and mobility in the range 0.96 - 1.73 $\times$ 10$^{2}$ cm$^{2}$/Vs. At low temperatures a logarithmic increase in conductivity is observed which indicates the presence of weak anti-localization (WAL). The magnetotransport data is analysed within the Hikami-Larkin-Nagaoka (HLN) theory. It is found that temperature dependence of the dephasing length can't be explained only by electron-electron scattering and that electron-phonon scattering also contributes to the phase relaxation mechanism in PBS films.

cond-mat.str-el↗

arXiv2020

Domain structure dynamics in the ferromagnetic Kagome-lattice Weyl semimetal Co$_3$Sn$_2$S$_2$

Co$_3$Sn$_2$S$_2$, a Weyl semimetal that consists of layers of Kagome lattices, transitions from a high-temperature paramagnetic phase to a low-temperature ferromagnetic phase below 177 K. The phase transition occurs through an intermediate non-trivial magnetic phase, the so-called "A"-phase just below the Curie temperature. The "A"-phase was earlier linked with a competing anti-ferromagnetic phase, a spin-glass phase and certain indirect measurements indicated the possibility of magnetic Skyrmions in this phase. We have imaged the magnetic domain structure in a single crystal of Co$_3$Sn$_2$S$_2$ at different temperatures, magnetic fields and field-angles by magnetic force microscopy. At low temperatures, we observed stripe domains indicating presence of uniaxial anisotropy. Above 130 K, the domain walls become mobile and they tend to align relatively easily when the magnetic field is increased along the $c$-axis than in the $a-b$ plane. Our detailed study of field-dependent domain dynamics reveal that the anomalous nature of the phase transition just below $T_c$ is dominantly governed by domain wall motion.

cond-mat.mtrl-sci↗

arXiv2019

Rotating magnetocaloric effect in the ferromagnetic Weyl semi-metal Co$_{3}$Sn$_{2}$S$_{2}$

The rotating magnetocaloric effect (RMCE) is a recent interest in magnetic refrigeration technique in which the cooling effect is attained by rotating the anisotropic magnetocaloric material from one orientation to the other in a fixed magnetic field. In this work, we report the anisotropic magnetocaloric properties of single crystals of the ferromagnetic Weyl semimetal Co$_{3}$Sn$_{2}$S$_{2}$ for magnetic field $H\parallel c$ axis and $H\parallel ab$ plane. We observed a significant (factor of $2$) difference between the magnetocaloric effect measured in both orientations. The rotating magnetocaloric effect has been extracted by taking the difference of the magnetic entropy change ($\Delta S_{M}$) for fields applied in the two crystallographic orientations. In a scaling analysis of $\Delta S_{M}$, the rescaled $\Delta S_{M}(T,H)$ vs reduced temperature $\theta$ curves collapse onto a single universal curve, indicating that the transition from paramagnetic to ferromagnetic phase at 174~K is a second order transition. Furthermore, using the power law dependence of $\Delta S_{M}$ and relative cooling power RCP, the critical exponents $\beta$ and $\gamma$ are calculated, which are consistent with the recent critical behavior study on this compound \cite{Yan2018}.

cond-mat.str-el↗

arXiv2018

Observation of planar Hall effect in the magnetic Weyl semimetal Co$_{3}$Sn$_{2}$S$_{2}$

We report detailed magneto-transport measurements on single crystals of the magnetic Weyl semi-metal Co$_{3}$Sn$_{2}$S$_{2}$. Recently a large anomalous Hall effect and chiral anomaly have been observed in this material which have been suggested to be related to the large Berry curvature between the Weyl points (Liu et al., Nature Physics (2018).). Another effect expected to result from the topological band structure of magnetic Weyl materials is the planar Hall effect (PHE). In this work we report observation of this intrinsic effect in single crystals of Co$_{3}$Sn$_{2}$S$_{2}$. Crucially, the PHE is observed for temperature $T \leq 74$~K which is much smaller than the ferromagnetic ordering temperature $T_c = 175$~K\@. Together with the large anomalous Hall conductivity, this further demonstrates the Topological character of Co$_3$Sn$_2$S$_2$.

cond-mat.str-el↗