arXiv subjects

Achintya Dutta

Publications and source records attributed to Achintya Dutta.

3 recordsLinked to original sources

arXiv2024

Pick-up and assembling of chemically sensitive van der Waals heterostructures using dry cryogenic exfoliation

Assembling atomic layers of van der Waals materials (vdW) combines the physics of two materials, offering opportunities for novel functional devices. Realization of this has been possible because of advancements in nanofabrication processes which often involve chemical processing of the materials under study; this can be detrimental to device performance. To address this issue, we have developed a modified micro-manipulator setup for cryogenic exfoliation, pick up, and transfer of vdW materials to assemble heterostructures. We use the glass transition of a polymer PDMS to cleave a flake into two, followed by its pick-up and drop to form pristine twisted junctions. To demonstrate the potential of the technique, we fabricated twisted heterostructure of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (BSCCO), a van der Waals high-temperature cuprate superconductor. We also employed this method to re-exfoliate NbSe$_2$ and make twisted heterostructure. Transport measurements of the fabricated devices indicate the high quality of the artificial twisted interface. In addition, we extend this cryogenic exfoliation method for other vdW materials, offering an effective way of assembling heterostructures and twisted junctions with pristine interfaces.

cond-mat.mes-hall↗

arXiv2023

Bilayer Vanadium Dioxide Thin Film with Elevated Transition Temperatures and High Resistance Switching

Despite widespread interest in the phase-change applications of vanadium dioxide (VO$_2$), the fabrication of high-quality VO$_2$ thin films with elevated transition temperatures (TIMT) and high Insulator-Metal-Transition resistance switching still remains a challenge. This study introduces a two-step atmospheric oxidation approach to fabricate bilayer VO$_{2-x}$/VO$_2$ films on a c-plane sapphire substrate. To quantify the impact of the VO$_2$ buffer layer, a single-layer VO$_2$ film of the same thickness was also fabricated. The bilayer VO$_{2-x}$/VO$_2$ films wherein the top VO$_{2-x}$ film was under-oxidized demonstrated an elevation in TIMT reaching ~97 $^\circ$C, one of the highest reported to date for VO$_2$ films and is achieved in a doping-free manner. Our results also reveal a one-order increase in resistance switching, with the optimum bilayer VO$_2$/VO$_2$ film exhibiting ~3.6 orders of switching from 25 $^\circ$C to 110 $^\circ$C, compared to the optimum single-layer VO$_2$ reference film. This is accompanied by a one-order decrease in the on-state resistance in its metallic phase. The elevation in TIMT, coupled with increased strain extracted from the XRD characterization of the bilayer film, suggests the possibility of compressive strain along the c-axis. These VO$_{2-x}$/VO$_2$ films also demonstrate a significant change in the slope of their resistance vs temperature curves contrary to the conventional smooth transition. This feature was ascribed to the rutile/monoclinic quasi-heterostructure formed due to the top VO$_{2-x}$ film having a reduced TIMT. Our findings carry significant implications for both the lucid fabrication of VO$_2$ thin film devices as well as the study of phase transitions in correlated oxides.

cond-mat.mtrl-sci↗

arXiv2023

High-temperature Josephson diode

Symmetry plays a critical role in determining various properties of a material. Semiconducting p-n junction diode exemplifies the engineered skew electronic response and is at the heart of contemporary electronic circuits. The non-reciprocal charge transport in a diode arises from doping-induced breaking of inversion symmetry. Breaking of time-reversal, in addition to inversion symmetry in some superconducting systems, leads to an analogous device - the superconducting diode. Following the pioneering first demonstration of the superconducting diode effect (SDE), a plethora of new systems showing similar effects have been reported. SDE lays the foundation for realizing ultra-low dissipative circuits, while Josephson phenomena-based diode effect (JDE) can enable realization of protected qubits. However, SDE and JDE reported thus far are at low temperatures ($\sim$ 4 K or lower) and impede their adaptation to technological applications. Here we demonstrate a Josephson diode working up to 77 K using an artificial Josephson junction (AJJ) of twisted layers of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO). The non-reciprocal response manifests as an asymmetry in the magnitude of switching currents and their distributions and appears for all twist angles. The asymmetry is induced by and tunable with a very small magnetic field applied perpendicular to the junction. We report a record asymmetry of 60 % at 20 K. We explain our results within a vortex-based scenario. Our results provide a path toward realizing superconducting quantum circuits at liquid nitrogen temperature.

cond-mat.supr-con↗