arXiv subjects

Dengyu Yang

Publications and source records attributed to Dengyu Yang.

8 recordsLinked to original sources

arXiv2026

Local probing of superconductivity at oxide interfaces with atomic force microscopy

Superconductivity in strontium titanate has remained enigmatic for more than 50 years. The LaAlO$_3$/SrTiO$_3$ (LAO/STO) heterointerface enables systematic dimensional confinement, from a two-dimensional electron gas to quasi-one-dimensional nanostructures, providing access to this quantum state. Transport measurements in patterned devices reveal puzzling phenomena, including width-independent critical currents and anomalous pairing suggestive of one-dimensional behavior, but direct local probes of the patterned interface and its superconducting response have been lacking. Here we use ultralow-temperature non-contact atomic force microscopy, dissipation spectroscopy, and Kelvin probe force microscopy to locally probe signatures of superconductivity in patterned LAO/STO devices. Spatially resolved energy-dissipation measurements reveal superconducting signatures, with features confined in some devices to edge channels approximately 200 nm wide. Dissipation spectra exhibit a characteristic nonlinear bias dependence that provides a local diagnostic of superconductivity, consistent with the intermediate carrier-density regime near the superconducting dome, and persisting up to the critical field. These results establish atomic force microscopy as a local probe of superconductivity in patterned LAO/STO structures and provide a route to addressing longstanding questions about quantum confinement and transport anomalies in correlated oxide nanostructures.

cond-mat.supr-con↗

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

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

Nanoscale ferroelectric programming of van der Waals heterostructures

The ability to create superlattices in van der Waals (vdW) heterostructures via moir\'e interference heralded a new era in the science and technology of two-dimensional materials. Through precise control of the twist angle, flat bands and strongly correlated phases have been engineered. The precise twisting of vdW layers is in some sense a bottom-up approach--a single parameter can dial in a wide range of periodic structures. Here, we describe a top-down approach to engineering nanoscale potentials in vdW layers using a buried programmable ferroelectric layer. Ultra-low-voltage electron beam lithography (ULV-EBL) is used to program ferroelectric domains in a ferroelectric Al_{1-x}B_{x}N thin film through a graphene/hexagonal boron nitride (hBN) heterostructure that is transferred on top. We demonstrate ferroelectric field effects by creating a lateral p-n junction, and demonstrate spatial resolution down to 35 nm, limited by the resolution of our scanned probe characterization methods. This innovative, resist-free patterning method is predicted to achieve 10 nm resolution and enable arbitrary programming of vdW layers, opening a pathway to create new phases that are inaccessible by moir\'e techniques. The ability to "paint" different phases of matter on a single vdW "canvas" provides a wealth of new electronic and photonic functionalities.

cond-mat.mtrl-sci↗

arXiv2023

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↗

arXiv2023

Surface acoustic wave generation and detection in quantum paraelectric regime of SrTiO$_3$-based heterostructure

Strontium titanate (STO), apart from being a ubiquitous substrate for complex-oxide heterostructures, possesses a multitude of strongly-coupled electronic and mechanical properties. Surface acoustic wave (SAW) generation and detection offers insight into electromechanical couplings that are sensitive to quantum paraelectricity and other structural phase transitions. Propagating SAWs can interact with STO-based electronic nanostructures, in particular LaAlO$_3$/SrTiO$_3$ (LAO/STO). Here we report generation and detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures ($T\ge$~2 K) using superconducting interdigitated transducers (IDTs). The temperature dependence shows an increase in the SAWs quality factor that saturates at $T\approx 8 $ K. The effect of backgate tuning on the SAW resonance frequency shows the possible acoustic coupling with the ferroelastic domain wall evolution. This method of generating SAWs provides a pathway towards dynamic tuning of ferroelastic domain structures, which are expected to influence electronic properties of complex-oxide nanostructures. Devices which incorporate SAWs may in turn help to elucidate the role of ferroelastic domain structures in mediating electronic behavior.

cond-mat.str-el↗

arXiv2022

Nanoscale control of the metal-insulator transition at LAO/KTO (110) and LAO/KTO (111) interfaces

Recent reports of superconductivity at KTaO3 (KTO) (110) and (111) interfaces have sparked intense interest due to the relatively high critical temperature as well as other properties that distinguish this system from the more extensively studied SrTiO3 (STO)-based heterostructures. Here we report nanoscale control of the metal-to-insulator transition at the LaAlO3/KTO (110) and (111) interfaces. Devices are created using two distinct methods previously developed for STO-based heterostructures: (1) conductive atomic-force microscopy lithography and (2) ultra-low-voltage electron-beam lithography. At low temperatures, KTO-based devices show superconductivity that is tunable by an applied back gate. A nanowire device shows single-electron-transistor (SET) behavior. These reconfigurable methods of creating nanoscale devices in KTO-based heterostructures offer new avenues for investigating mechanisms of superconductivity as well as development of quantum devices that incorporate strong spin-orbit interactions, superconducting behavior, and nanoscale dimensions.

cond-mat.mes-hall↗

arXiv2020

Nanoscale control of LaAlO3/SrTiO3 metal-insulator transition using ultra-low-voltage electron-beam lithography

We describe a method to control the insulator-metal transition at the LaAlO3/SrTiO3 interface using ultra-low-voltage electron beam lithography (ULV-EBL). Compared with previous reports that utilize conductive atomic-force-microscope lithography (c-AFM), this approach can provide comparable resolution (~10 nm) at write speeds (10 mm/s) that are up to 10,000x faster than c-AFM. The writing technique is non-destructive and the conductive state is reversible via prolonged exposure to air. Transport properties of representative devices are measured at milli-Kelvin temperatures, where superconducting behavior is observed. We also demonstrate the ability to create conducting devices on graphene/LaAlO3/SrTiO3 heterostructures. The underlying mechanism is believed to be closely related to the same mechanism regulating c-AFM-based methods.

cond-mat.mes-hall↗