arXiv subjects

Kalana D. Halanayake

Publications and source records attributed to Kalana D. Halanayake.

6 recordsLinked to original sources

arXiv2026

Enhanced Superconductivity in Multilayer FeSe Films by Simplified Molecular Beam Epitaxy

Multi-unit-cell (UC) \b{eta}-FeSe films grown on SrTiO3(100) continue to attract attention because of the significant enhancement in the superconducting transition temperature (Tc) compared to that in bulk FeSe. In prior reports of molecular beam epitaxy (MBE)-grown \b{eta}-FeSe/SrTiO3(100), elaborate growth protocols have been used to achieve enhanced Tc, leading to a general belief that careful pre-treatment of the SrTiO3 substrate and post-growth annealing in ultrahigh vacuum (UHV) are essential. Here, we report a greatly simplified protocol for the MBE growth of superconducting multi-UC \b{eta}-FeSe films on SrTiO3(100), eliminating the need for careful substrate pre-treatment and post-growth UHV annealing while still achieving an enhanced Tc. With appropriate capping, epitaxial films with 14 UC thickness exhibit a zero-resistance transition temperature Tc ~ 20 K in ex situ electrical transport measurements. The MBE optimization process is guided by the growth-parameter dependencies of film morphology and structural properties, as characterized by reflection high-energy electron diffraction, X-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy.

cond-mat.supr-con↗

arXiv2026

Emergent superconductivity and non-reciprocal transport in a van der Waals Dirac semimetal/antiferromagnet heterostructure

We investigate emergent superconductivity and non-reciprocal transport (magnetochiral anisotropy, superconducting diode effect) at the heterointerface of two non-superconducting van der Waals (vdW) materials, the Dirac semimetal ZrTe$_2$ and the antiferromagnetic iron chalcogenide FeTe, grown using molecular beam epitaxy. We show from electrical transport measurements that two-dimensional (2D) superconductivity arises at the heterointerface below a critical temperature $T_c \sim 10$~K. In the superconducting transition region, non-reciprocal transport, characterized by the magneto-chiral anisotropy, exhibits a magnitude comparable to that observed in topological insulators, and is enhanced by a factor of three when the heterostructure is capped with a 2D vdW ferromagnet (CrTe$_2$). Below $T_c$, the superconducting diode effect exhibits an efficiency of 29\%. With strong spin-orbit coupling in ZrTe$_2$, these epitaxial heterostructures provide an attractive epitaxial vdW platform for exploring unconventional superconductivity in Dirac semimetals and for developing non-reciprocal devices for superconducting electronics.

cond-mat.supr-con↗

arXiv2026

Stoichiometric FeTe is a Superconductor

Iron-based superconductors are a fascinating family of materials in which multiple electronic bands and strong antiferromagnetic (AFM) correlations are key ingredients for competing ground states, including antiferromagnetism, electronic nematicity, and unconventional superconductivity. FeTe, unlike its superconducting isostructural counterpart FeSe, has long been regarded as an AFM metal sans superconductivity. In this work, we employ molecular beam epitaxy to grow FeTe films and perform post-growth annealing under a Te flux. By performing spin-polarized scanning tunneling microscopy and spectroscopy, we demonstrate that the AFM order in as-grown FeTe films is induced by interstitial Fe atoms that disrupt the ideal 1:1 stoichiometry. Remarkably, the removal of these interstitial Fe atoms through Te annealing yields stoichiometric FeTe films that show no AFM order and instead exhibit robust superconductivity with a critical temperature of ~13.5K. This superconducting state is further confirmed by the observation of Cooper pair tunneling, zero electrical resistance, and the Meissner effect. Therefore, our results demonstrate that stoichiometric FeTe is inherently a superconductor, overturning a long-held view that it is an AFM metal. This work clarifies the origin of superconductivity in FeTe-based heterostructures and demonstrates the importance of stoichiometry control in understanding the competition between AFM and superconductivity in iron-based superconductors.

cond-mat.supr-con↗

arXiv2025

Building 3D superconductor-based Josephson junctions using a via transfer approach

The coupling of superconductivity to unconventional materials may lead to novel quantum states and potential applications. Controlling the quality of the superconductor-normal metal interface is of crucial importance to the understanding and engineering of the superconducting proximity effect. In many cases, conventional lithography-based deposition methods introduce undesirable effects. Using the concept of via contact and dry transfer, we have constructed smooth, van der Waals-like contact between 3D superconducting NbN/Pd and graphene with low contact resistance of approximately 130 $Ω\cdot μm$. Gate-tunable supercurrent, Fraunhofer pattern, and Andreev reflections are observed, the properties of which can be understood using an induced superconducting gap $Δ$' in this planar contact geometry. We discuss potential mechanisms impacting the magnitude of $Δ$' and suggest ways of further increasing the proximity coupling. This gentle, lithography-free contacting method can be applied to air- and damage-sensitive surfaces to engineer novel superconducting heterostructures.

cond-mat.mes-hall↗

arXiv2025

Machine Learning Integrated Near-Infrared Surface-Enhanced Raman Spectroscopy for Accurate Strain-Level Virus Identification

Strain-level identification of viruses is critical for effective public health responses to potential outbreaks, yet current diagnostic methods often lack the necessary speed or sensitivity. Surface-enhanced Raman spectroscopy (SERS) offers great potential for fast and precise virus clarification through unique vibrational fingerprints of biological components. However, existing protocols typically operate outside of the tissue's transparent near-infrared (NIR) window, and are further limited by the intrinsic complexity of clinical viral samples, which complicates spectral analysis and recognition. Here, we report an artificial intelligence (AI)-empowered NIR-SERS platform that integrates machine learning with a rationally designed hybrid substrate: gold nanostars (AuNSt) coupled with gold-coated carbon nanotube arrays (AuCNT). This architecture generates highly localized plasmonic hot spots resonant tuned to NIR excitation, as confirmed by electron energy-loss spectroscopy (EELS), enabling effective signal amplification from viral components. Our system and protocols provide accurate classification of respiratory viruses, including influenza viruses and coronaviruses, not only at the type and subtype levels, but also the more challenging strain level. This approach overcomes the plasmonic mismatch in conventional SERS and the lack of generalizability in AI-driven diagnostics. It shows promise for enhancing rapid virus detection and identification of novel strains and outbreak response capabilities, thus potentially addressing critical challenges in global public health preparedness.

physics.chem-ph↗

arXiv2025

Emergent anisotropic three-phase order in critically doped superconducting diamond films

Two decades since its discovery, superconducting heavily boron-doped diamond (HBDD) still presents unresolved fundamental questions whose resolution is relevant to the development of this material for quantum technologies. We use electrical magnetotransport measurements of critically-doped homoepitaxial single crystal HBDD films to reveal signatures of intrinsic (electronic) granular superconductivity. By studying the dependence of electrical resistivity on temperature and magnetic field vector, we infer that this granularity arises from electron correlations. This is revealed by a striking three-phase anisotropy in the magnetoresistance, accompanied by a spontaneous transverse voltage (Hall anomaly). Our findings indicate an emergent magnetically tunable intrinsic order in an otherwise isotropic three dimensional single crystal HBDD film, offering new insights into the mechanism of superconductivity in this quantum material.

cond-mat.supr-con↗