arXiv subjects

L. Elesin

Publications and source records attributed to L. Elesin.

9 recordsLinked to original sources

arXiv2026

Electronic bistability, discontinuous switching and stochasticity in a two-dimensional semiconductor

Bistability - two stable electronic states under the same bias - underlies switching and memory, but is usually absent in transistors and must be engineered through material means: doped tunnel junctions, filaments in memristors, or phase transitions. Here we demonstrate a transistor with intrinsic electronic bistability in a single chemically homogeneous crystal. In dual-gated black phosphorus, whose band gap narrows under a perpendicular electric field due to a giant Stark effect, the gates not only modulate carrier density but also reshape the band profile, forming interband tunnel junctions in the channel. Transport across the two-gate parameter space reveals competing conduction regimes - diffusive, two tunnelling channels and Zener breakdown - whose interplay produces negative differential conductance and transconductance, discontinuous switching, and hysteresis with the state set by gate history. Moreover, the switching remains intrinsically stochastic, yet statistically stable within a narrow range of gate voltages, providing an electrically programmable source of randomness. Devices based on this principle should be realisable in other two-dimensional semiconductors, opening a route to next-generation computing architectures in which nonlinearity, switching, memory and stochasticity are integrated within a single electrostatically programmable element.

cond-mat.mes-hall↗

arXiv2026

Correlated Insulator Moir\'e Bolometer

Light incident on an insulator is generally not expected to turn it into a metal without invoking intense ultrafast excitation that leads to transient structural transitions. Here we show that magic-angle twisted bilayer graphene tuned to half filling of the moir\'e band provides a notable exception to this expectation. We find that weak beam of long-wavelength photons, with energies comparable to the flat-band width, selectively heat the low-heat-capacity electronic subsystem, thereby suppressing the correlated gap. This produces a giant resistance change governed not by a persistent photocarrier population, but by the extreme sensitivity of a many-body correlated gap to weak electronic heating. The resulting photon-driven insulator-to-metal transition produces a broadband low-noise photoresponse with voltage responsivity exceeding millivolts per nW of absorbed power. The mechanism is dual to superconducting hot-electron response: radiation-heated electrons suppress a many-body order, but in reverse the correlated insulator melts into a metal, providing robustness to magnetic fields of several tesla and a sharp insulator-to-metal resistive contrast. Our results establish correlated flat-band systems as a platform for ultra-sensitive detection of faint long-wavelength radiation.

cond-mat.mes-hall↗

arXiv2026

Gate-Tunable Photoresponse of Graphene Josephson Junctions at Terahertz Frequencies

Graphene Josephson junctions (JJ) provide a promising platform for ultra-broadband quantum sensing of light owing to graphene's frequency-independent absorption, vanishing electronic heat capacity, and weak electron-phonon coupling, which enable rapid suppression of the critical current through radiation-induced electron heating. Existing investigations have been confined to the microwave and infrared regimes, where competing detector technologies are already established; by contrast, the terahertz (THz) band - where sensitivity is most urgently lacking and no mature quantum sensor exists - has remained largerly unexplored. Here we demonstrate a strong photoresponse of graphene JJs at THz frequencies, establishing a first experimental step towards graphene-based THz quantum sensors. Under low-intensity illumination, we observe a pronounced suppression of the critical current that generates a strong photovoltage (Vph) under current bias. By tracking this Vph and independently measuring the electron temperature as a function of absorbed power, we extract a responsivity of 88 kV W^-1 and a noise-equivalent power of 45 aW Hz^-1/2 at 1.7 K. Furthermore, gate tunability of our JJ enables access to a regime where hysteretic current-voltage characteristics persist up to 0.9 K, offering a potential route toward single-photon THz detection beyond millikelvin (mK) temperatures. These findings establish graphene JJ as a versatile platform for broadband cryogenic radiation sensing and point towards their use as quantum sensors at THz frequencies.

cond-mat.mes-hall↗

arXiv2026

Graphene Zero-Bias Sub-Terahertz Turnkey Detector with Above 43 GHz Bandwidth

High-frequency terahertz (THz) detectors are vital for next-generation high-speed wireless communication systems. Graphene, with its high carrier mobility, broadband absorption, and weak electron-phonon coupling, offers great promise for ultra-fast THz photothermoelectric devices. Although graphene-based detectors in the infrared range have shown bandwidths above 500 GHz, extending their operation to the THz range is difficult because long-wavelength radiation does not efficiently couple to the small graphene area. To overcome this issue, THz antennas are often employed; however, their use typically limits system performance to only a few gigahertz due to parasitic effects. In this work, we present an antenna-coupled sub-THz graphene detector with a bandwidth exceeding 43 GHz. We optimized the detector design to minimize losses, match the antenna impedance to the 1 kOhm graphene channel, and maintain zero-bias operation. Importantly, we introduce a compact, turnkey packaged solution. Our results provide a practical route toward high-speed and low-power graphene THz detectors suitable for real-world communication and imaging applications.

cond-mat.mes-hall↗

arXiv2025

Enhanced Terahertz Thermoelectricity via Engineered van Hove Singularities and Nernst Effect in Moir\'e Superlattices

Thermoelectric materials, long explored for energy harvesting and thermal sensing, convert heat directly into electrical signals. Extending their application to the terahertz (THz) frequency range opens opportunities for low-noise, bias-free THz detection, yet conventional thermoelectrics lack the sensitivity required for practical devices. Thermoelectric coefficients can be strongly enhanced near van Hove singularities (VHS), though these are usually difficult to access in conventional materials. Here we show that moir\'e band engineering unlocks these singularities for THz optoelectronics. Using 2D moir\'e structures as a model system, we observe strong enhancement of the THz photothermoelectric response in monolayer and bilayer graphene superlattices when the Fermi level is tuned to band singularities. Applying a relatively small magnetic field further boosts the response through the THz-driven Nernst effect, a transverse thermoelectric current driven by the THz-induced temperature gradient. Our results establish moir\'e superlattices as a versatile platform for THz thermoelectricity and highlight engineered band structures as a route to high-performance THz optoelectronic devices.

cond-mat.mes-hall↗

arXiv2025

Reconstructing Critical Current Density in Josephson Junctions with Phase Non-linearity

In this Letter, we show that the standard Dynes-Fulton analysis, commonly used to reconstruct the critical current density from interference patterns, breaks down in Josephson junctions with nonlinear phase distributions, leading to non-physical artifacts. To address this, we developed a simple iterative reconstruction algorithm and validated it both numerically and experimentally using a planar Josephson junction model. Unlike conventional approaches based on the logarithmic Hilbert transform, the proposed method allows for incorporating prior knowledge about the system and addresses the fundamental issue of ambiguity in reconstructing the critical current density from interference patterns.

cond-mat.supr-con↗

arXiv2025

Non-Reciprocal Current-Phase Relation and Superconducting Diode Effect in Topological-Insulator-Based Josephson Junctions

Josephson junctions (JJ) are essential for superconducting quantum technologies and searches of self-conjugate quasiparticles, pivotal for fault-tolerant quantum computing. Measuring the current-phase relation (CPR) in JJ based on topological insulators (TI) can provide critical insights into unconventional phenomena in these systems, such as the presence of Majorana bound states (MBS) and the nature of non-reciprocal transport. However, reconstructing CPR as a function of magnetic field in such JJs has remained experimentally challenging. Here, we introduce a platform for precise CPR measurements in planar JJs composed of NbSe$_2$ and few layer thick Bi$_2$Se$_3$ (TI) as a function of magnetic field. When a single flux quantum $\Phi_\mathrm{0}$ threads the junction, we observe anomalous peak-dip-shaped CPR behaviour and non-reciprocal supercurrent flow. We demonstrate that these anomalies stem from the edge-amplified sloped supercurrent profile rather than MBS signatures often invoked to explain puzzles emerging near $\Phi_\mathrm{0}$ in TI-based JJ. Furthermore, we show that such a supercurrent profile gives rise to a previously overlooked, robust and tunable Josephson diode effect. These findings establish field-dependent CPR measurements as a critical tool for exploring topological superconducting devices and offer new design principles for non-reciprocal superconducting electronics.

cond-mat.supr-con↗

arXiv2024

Nanopatterning of multicomponent van der Waals heterostructures using atomic force microscopy

Multilayer van der Waals (vdW) heterostructures have become an important platform in which to study novel fundamental effects emerging at the nanoscale. Standard nanopatterning techniques relying on electron-beam lithography and reactive ion etching, widely applied to pattern such heterostructures, however, impose some limitations on the edge accuracy and resolution, as revealed through numerous experiments with vdW quantum dots and point contacts. Here we present an alternative approach for electrode-free nanopatterning of thick multilayer vdW heterostructures based on atomic force microscopy (AFM). By applying an AC voltage of a relatively small frequency (1-10 kHz) between the sharp platinum tip and the substrate, we realize high-resolution ($\lesssim 100$ nm) etching of thick multicomponent heterostructures if the latter are deposited onto graphite slabs. Importantly, unlike more conventional electrode-free local anodic oxidation, our method does not require a special environment with excess humidity, can be applied at ambient conditions, and enables the patterning of multilayer heterostructures composed of graphene, graphite, hexagonal boron nitride (hBN), NbSe$_{2}$, WSe$_{2}$, and more.

cond-mat.mes-hall↗

arXiv2023

Fundamental limits of few-layer NbSe$_2$ microbolometers at terahertz frequencies

The rapid development of infrared spectroscopy, observational astronomy, and scanning near-field microscopy has been enabled by the emergence of sensitive mid- and far-infrared photodetectors. Owing to their exceptional signal-to-noise ratio and fast photoresponse, superconducting hot-electron bolometers (HEBs) have become a critical component in these applications. While superconducting HEBs are traditionally made from sputtered superconducting thin films like Nb or NbN, the potential of layered van der Waals (vdW) superconductors is untapped at THz frequencies. Here, we report the fabrication of superconducting HEBs out of few-layer NbSe$_2$ microwires. By improving the interface between NbSe$_2$ and metal leads connected to a broadband antenna, we overcome the impedance mismatch between this vdW superconductor and the radio frequency (RF) readout circuitry that allowed us to achieve large responsivity THz detection over the range from 0.13 to 2.5 THz with minimum noise equivalent power of 7~pW$\sqrt{Hz}$. Using the heterodyne sub-THz mixing technique, we reveal that NbSe$_2$ superconducting HEBs are relatively fast and feature a characteristic response time in the nanosecond range limited by the slow heat escape to the bath through a SiO$_2$ layer, on which they are assembled, in agreement with energy relaxation model. Our work expands the family of materials for superconducting HEBs technology, reveals NbSe$_2$ as a promising platform, and offers a reliable protocol for the in-lab production of custom bolometers using the vdW assembly technique.

cond-mat.supr-con↗