Vedachalaiyer Ganesan

Quantum spin liquids (QSL) are prototypical examples of ground states with massive many-body entanglement. While an unambiguous realization of this long-sought-after state remains elusive, a growing number of materials candidates keep emerging with varieties of novel and exotic properties. Here, we report a combined experimental and theoretical study of a new antiferromagnet Ba 3 CuNb 2 O 9 which has an in-plane anisotropic exchange interaction arising from distorted triangular arrangements of magnetic Cu 2 + (spin-1/2) ions. We show an unconventional gapless QSL like ground state in this material which does not exhibit any signature of magnetic ordering down to 0.3 K, while a finite Curie–Weiss temperature ∼ − 41 K is evident. The gapless QSL state is supported by a high spin fluctuation, a power-law dependence of magnetic specific heat ( C m ∝ T γ ) and a unique scaling of magnetic susceptibility and specific heat with temperature and magnetic field respectively. Our ab-initio simulation also confirms the anisotropic exchange interaction which can only be explained via superexchange mechanism. While the combined results strongly suggest a random singlet state driven QSL behavior in present material, we strongly believe that the anisotropic exchange interaction has a possible role for this exotic ground state behavior.

Dy ₂ Ti ₂ O ₇ is a well‐known member of the pyrochlore family, having an exotic ground state like spin ice, as the weakly interacting Ising spins of each tetrahedron follow the two‐in, two‐out ice rule. A low‐temperature study to understand this novel ground state is carried out using heat capacity and magnetization with no noticeable magnetic ordering. Heat capacity shows a broad anomaly around 1 K, indicative of short‐range interactions. Residual entropy of the spin‐ice state in zero magnetic field is 1.36 JK ⁻¹ mol ⁻¹ which is close to the Pauling prediction. Kagome‐ice state is to be formed when a magnetic field is applied, and residual entropy is 0.56 JK ⁻¹ mol ⁻¹ between 0.3 Tand 0.6 T, which matches the literature. A magnetic field–temperature (H–T) phase diagram has been visualized for the spin‐ice configuration. Observation of small yet clear peak structures around 0.2 K may be assigned to the first‐order (gas–liquid) transition below 0.4 K inside the Kagome‐ice state.

The present work reports the effects of 120 MeV Au9+ on structural and electronic properties of polycrystalline SnO2 films of about 170 nm thickness prepared by spin-coating. 119Sn Mössbauer measurements are used to probe the electronic properties. The observed isomer-shift values clearly indicate Sn4+ for the pristine sample and its progressive reduction to Sn2+ and eventually to the metallic Sn state at higher fluence values. These observations are corroborated by x-ray diffraction, Raman, and x-ray photo-electron spectroscopy measurements. The x-ray diffraction measurements indicate the complete amorphization of the tin oxide phase, while the recrystallization of the metallic Sn phase with irradiation. The optical bandgap is observed to vary with ion beam irradiation. The observations indicate the possibility of tuning the electronic configuration of Sn in tin oxide thin films with swift heavy ion beam irradiation, and the results are explained in terms of the thermal-spike model of swift heavy ion irradiation.

We report a polycrystalline kagome metallic ferromagnet Nd3Al with a large unconventional positive magnetoresistance (∼80%) and a colossal anomalous Hall conductivity of 3 × 104 S/cm. We find that, though it is predominantly ferromagnetic, the low temperature phase is rather complex. The reduction in the effective moment, thermomagnetic irreversibility, anomalous temperature dependence of magnetization, large and non-saturating positive magnetoresistance, and existence of the finite topological Hall effect make this compound quite interesting. Various experimental proofs point toward topological band structure and topological spin texture in the frustrated kagome lattice. Ab initio calculations broadly confirm the presence of flatbands and Weyl points originating from the itinerant Nd-moments. The non-trivial band structure, enhanced skew scattering, and topological spin texture in a frustrated kagome lattice are found to be responsible for the colossal Hall conductivity and the topological Hall effect.

The interaction between superconductivity and spin-polarized surface states of topological materials provides an exciting platform for the research and development of proximity induced coupling effects, Majorana fermions, spin valves, spintronics, etc. and so on. In this work, the inverse proximity effect observed exactly at the super conducting transition temperature of indium (3.5 K) demonstrates the complex interplay between robust 2D spin-polarized surface states observed in our (002n) oriented MoTe2 nanolayer sheets with that of superconducting states. Interestingly, our phenomenological model based on the Werthamer-Helfand-Hohenberg (WHH) model and Ginzburg–Landau formalism, invoked to validate the experimental observations, indicates a competition between superconductivity and topological order, marked by a close correspondence between the temperature of crossover (Tcr = 2.45 K) of their respective length scales, ξ and Lφ, and the saturation temperature in resistivity.

Magnetotransport and thermal properties of microwave-synthesized nanostructured Bi₂Te₃, a well-known material of topological interest, have been studied in detail. Temperature-dependent resistivity shows a disordered metal-like behavior at high temperature with unsaturated ln(T)-dependent upturns at low temperature manifesting localization tendency. The slopes (κ) of the normalized conductivity (Δσ) vs ln(T) curves change sharply with magnetic fields upto 1 T and then saturate at a certain higher field (B_ϕ), which is an indication of a combined electron–electron interaction and quantum interference effect (QIE) dominated transport. A noteworthy result is a crossover from positive to negative Coulomb screening factor (F) in Bi₂Te₃. Low-field (H ≤ 1 T) magnetoconductivity at low temperature follows a 2D Hikami–Larkin–Nagaoka equation, thereby revealing the QIE and associated dephasing nature of the electronic states at high temperatures. High-field (14 T) magnetoresistance (MR) at 2 K shows interesting features like low-field weak antilocalization, possibly a defect-induced negative MR that vanishes after post-annealing treatment, and a high field parabolic character in place. The Seebeck coefficient (S) is negative and varies quasilinearly with a slight but notable slope change at intermediate temperatures. Heat capacity measurements are in line with a narrow gap degenerate semiconductor with a low θ_D of 140 K. A combined analysis of heat capacity and thermopower reveals the localization of carriers at low temperatures and is in line with transport data.