arXiv subjects

Sayanwita Biswas

Publications and source records attributed to Sayanwita Biswas.

7 recordsLinked to original sources

arXiv2026

Imaging GHz surface acoustic wave modes in electrostricted LaAlO$_3$/SrTiO$_3$ heterostructures

The LaAlO$_3$/SrTiO$_3$ (LAO/STO) interface hosts a gate-tunable superconducting two-dimensional electron gas (2DEG) which can be programmed to create quantum devices such as ballistic electron waveguides and quantum dots. To fully exploit this platform for quantum transport, a key requirement is the ability to shuttle single electrons, electron pairs, and other exotic states between spatially separated devices with precision. Surface acoustic waves (SAWs), which travel along the surface of a solid, offer a powerful route to achieve this through their moving electrical potential that captures and transfers electrons. %acoustoelectric coupling. In particular, SAWs in the GHz regime enable fast, controlled transport of individual quantum particles. Although this approach is well-explored in GaAs-based 2DEG, SAW generation in STO remains largely unexplored due to the lack of intrinsic piezoelectricity at room temperature. Here, we investigate room-temperature SAWs in LAO/STO and observe SAW modes up to 2.2 GHz with very low propagation loss of the order $10^{-3}$ dB per wavelength. To directly visualize these modes, we employ Atomic Acoustic Force Microscopy (AAFM), achieving sub-micron resolution imaging of the SAW wave forms, providing insight into the electrostriction-induced SAW generation mechanism. Our measurements indicate a shear horizontal-type mode, which provides the ability to couple to in-plane degrees of freedom for future acoustoelectric and quantum device applications. This work studies the fundamentals of SAW excitation and propagation on STO, a widely used and commercially available substrate, enabling straightforward coupling of SAWs to a broad range of materials that can be grown or transferred onto STO.

cond-mat.str-el↗

arXiv2026

Constructing a Quantum Twisting Microscope: Design Insights and Experimental Considerations

We report the details of construction and testing of a Quantum Twisting Microscope, a recently developed scanning probe instrument that enables twist angle dependent electronic measurements on layered materials. Our implementation is based on a commercial atomic force microscope whose open geometry beneath the scan head allows integration of the rotation and translation stages required for QTM operation. We describe the complete fabrication process including tip preparation by focused ion beam deposition and graphite transfer, custom stage assembly with integrated rotation capability, and multistep alignment procedures. To validate the instrument, we perform conductance measurements between graphite layers as a function of twist angle, observing clear 60 degree periodicity consistent with the hexagonal lattice symmetry and conductance enhancements near the commensurate twist angles of 21.8 and 38.2 degrees. These results confirm the instruments ability to resolve crystallographic twist angle dependent transport features. By providing detailed construction and operational guidelines, we aim to make QTM technology accessible to research groups with standard AFM infrastructure, enabling investigations of twist angle dependent phenomena in van der Waals materials, complex oxide heterostructures and chiral systems.

cond-mat.mes-hall↗

arXiv2025

KTaO3-Based Supercurrent Diode

The supercurrent diode effect (SDE), characterized by nonreciprocal critical currents, represents a promising building block for future dissipationless electronics and quantum circuits. Realizing SDE requires breaking both time-reversal and inversion symmetry in the device. Here we use conductive atomic force microscopy (c-AFM) lithography to pattern reconfigurable superconducting weak links (WLs) at the LaAlO3/KTaO3 (LAO/KTO) interface. By deliberately engineering the WL geometry at the nanoscale, we realize SDE in these devices in the presence of modest out-of-plane magnetic fields. The SDE polarity can be reversed by simply changing the WL position, and the rectification efficiency reaches up to 13% under optimal magnetic field conditions. Time-dependent Ginzburg-Landau simulations reveal that the observed SDE originates from asymmetric vortex motion in the inversion-symmetry-breaking device geometry. This demonstration of SDE in the LAO/KTO system establishes a versatile platform for investigating and engineering vortex dynamics, forming the basis for engineered quantum circuit elements.

cond-mat.supr-con↗

arXiv2025

Engineered Chirality of One-Dimensional Nanowires

The origin and function of chirality in DNA, proteins, and other building blocks of life represent a central question in biology. Observations of spin polarization and magnetization associated with electron transport through chiral molecules, known collectively as the chiral induced spin selectivity (CISS) effect, suggest that chirality improves electron transfer by inhibiting backscattering. Meanwhile, the role of coherence in the electron transport within chiral nanowires is believed to be important but is challenging to investigate experimentally. Using reconfigurable nanoscale control over conductivity at the LaAlO$_3$/SrTiO$_3$ interface, we create chiral electron potentials that explicitly lack mirror symmetry. Quantum transport measurements on these chiral regions that constitute effective nanowires for the electrons reveal oscillatory transmission resonances as a function of both magnetic field and chemical potential. We interpret these resonances as arising from an engineered axial spin-orbit interaction within the chiral region. The ability to create 1D effective electron waveguides with this specificity and complexity creates new opportunities to test, via analog quantum simulation, theories about the relationship between chirality and spin-polarized electron transport in one-dimensional geometries.

cond-mat.mes-hall↗

arXiv2025

Magnetically Tuned Metal-Insulator Transition in LaAlO$_3$/SrTiO$_3$ Nanowire Arrays

A wide family of two dimensional (2D) systems, including stripe-phase superconductors, sliding Luttinger liquids, and anisotropic 2D materials, can be modeled by an array of coupled one-dimensional (1D) electron channels or nanowire arrays. Here we report experiments in arrays of conducting nanowires with gate and field tunable interwire coupling, that are programmed at the LaAlO$_3$/SrTiO$_3$ interface. We find a magnetically-tuned metal-to-insulator transition in which the transverse resistance of the nanowire array increases by up to four orders of magnitude. To explain this behavior, we develop a minimal model of a coupled two-wire system which agrees well with observed phenomena. These nanowire arrays can serve as a model systems to understand the origin of exotic behavior in correlated materials via analog quantum simulation.

cond-mat.mes-hall↗

arXiv2024

Electric and Magnetic Field-dependent Tunneling between Coupled Nanowires

Coupled quasi-one-dimensional (quasi-1D) electron systems host rich emergent physics that cannot be accounted for by understanding isolated 1D electron systems alone. Open questions remain about how transport in these arrays can be manipulated by the application of external electric and magnetic fields. In this theoretical study, we consider a pair of coupled nanowires with non-interacting electrons. We find that a metal-insulator transition is induced by an out-of-plane magnetic field and a transverse potential bias on an array of such coupled wires. We demonstrate the existence of distinct conductance features and highlight the crucial role played by the field dependence of the interwire potential barrier on transport properties. These predictions agree well with transport experiments performed on coupled nanowires sketched on an LaAlO3/SrTiO3 interface. Since our model makes minimal assumptions, we expect our predictions to hold for a wide class of coupled 1D systems.

cond-mat.mes-hall↗

arXiv2024

Sketched Nanoscale KTaO3-Based Superconducting Quantum Interference Device

The discovery of two-dimensional superconductivity in LaAlO3/KTaO3 (111) and (110) interfaces has raised significant interest in this system. In this manuscript we report the first successful fabrication of a superconducting quantum interference device (DC-SQUID) in the KTO system. The key device elements, superconducting weak links, are created by conductive atomic force microscope (c-AFM) lithography which can reversibly control the conductivity at the LAO/KTO(110) interface with nanoscale resolution. The periodic modulation of the SQUID critical current, Ic(B), with magnetic field corresponds well with our theoretical modeling, which reveals a large kinetic inductance of the superconducting two-dimensional electron gas in KTO. The kinetic inductance of the SQUID is tunable by electrical gating from the back, due to the large dielectric constant of KTO. The demonstration of weak links and SQUIDs in KTO broadens the scope for exploring the underlying physics of KTO superconductivity, including the role of spin-orbit-coupling, pairing symmetry, and inhomogeneity. It also promotes KTO as a versatile platform for a growing family of quantum devices, which could be applicable in the realm of quantum computing and information.

cond-mat.supr-con↗