arXiv subjects

Dhavala Suri

Publications and source records attributed to Dhavala Suri.

At least 19 recordsLinked to original sources

arXiv2026

Unified Transport and Susceptibility Analysis of a Thin BSCCO Film: From Local Pairing to Global Phase Coherence

The superconducting transition in thin high-$T_c$ films can be significantly broadened by disorder, spatial inhomogeneity, and phase fluctuations. Here, we study the transition in a 30-nm-thick sputter-grown Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO) film through electrical-transport and ac-susceptibility measurements. The resistive transition is examined using a Gaussian distribution of local $T_c$ values and the Ambegaokar--Halperin model, describing spatial variations in superconductivity and thermally activated phase dynamics, respectively. To relate the transport and magnetic responses, we extend the Choy--Stoneham susceptibility model by introducing the superconducting fraction extracted from transport and a temperature-dependent connectivity factor representing the gradual development of Josephson coupling among superconducting regions. The results identify separate temperature regimes corresponding to the onset of local superconductivity, expansion of the superconducting fraction, development of magnetic screening, and establishment of global phase coherence. The transition therefore proceeds progressively, from locally superconducting regions to a connected, phase-coherent state. This analysis provides a common framework for relating spatial inhomogeneity, dissipative phase dynamics, and magnetic screening in inhomogeneous superconducting films.

cond-mat.supr-con↗

arXiv2026

Berry Curvature Driven Transport in Silicon-Compatible Altermagnetic $α$-MnTe Thin Films

Integrating spin-dependent functionality with mainstream semiconductor technology is a central goal of modern spintronics, yet most candidate materials remain incompatible with silicon-based platforms. Here, we report the direct epitaxial integration of $α$-MnTe thin films on Si(111) via molecular beam epitaxy and demonstrate a robust anomalous Hall effect (AHE) in this silicon-compatible altermagnetic system. Despite the absence of net bulk magnetization, the films exhibit a pronounced hysteretic Hall response, providing transport evidence consistent with finite Berry curvature generated by symmetry breaking in the thin-film geometry. High-resolution structural and spectroscopic characterization confirms phase-pure, epitaxial growth with hexagonal NiAs-type symmetry, while magnetotransport measurements reveal correlated hysteresis in both transverse and longitudinal channels with systematic temperature evolution. First-principles calculations reveal substantial uncompensated Berry curvature arising from the spin-split band structure, consistent with altermagnetic symmetry and the origin of the observed Hall response. These results establish MnTe/Si(111) as a silicon-compatible altermagnetic platform and chart a concrete pathway for embedding Berry-phase-driven functionalities into scalable semiconductor device architectures.

cond-mat.mtrl-sci↗

arXiv2026

Barium Hexaferrite Thin Films as a Scalable Magnetic-Insulator Platform for Proximity-Engineered Spintronics

Rare-earth iron garnets, such as yttrium iron garnet (YIG) and thulium iron garnet (TmIG), are the benchmark magnetic insulators for spintronic and magnonic devices, but achieving usable perpendicular magnetic anisotropy (PMA) in these materials typically relies on substrate strain- engineering, requiring careful lattice-matching and specific growth conditions that constrain ma- terial accessibility. Here we establish sputter grown barium hexaferrite (BaFe12O19, BaM) as a magnetic-insulator alternative with strong intrinsic perpendicular anisotropy, requiring no strain engineering. X-ray diffraction, transmission electron microscopy and Raman spectroscopy confirm stoichiometric films with atomically smooth surfaces, while first-principles calculations corroborate a robust ferrimagnetic ground state. The films exhibit square out-of-plane hysteresis with a coercive field of nearly 0.1 T. Unlike rare-earth garnets, the perpendicular anisotropy in BaM is intrinsic to its magnetoplumbite crystal structure, arising independent of highly ordered strain. Interfaced with Pt and with exfoliated BiSbTeSe2 (BSTS), BaM induces proximity induced anomalous Hall trans- port, confirming efficient interfacial exchange coupling, while the BSTS/BaM heterostructure shows an additional Hall contribution suggestive of non-collinear interfacial spin textures. These results position BaM thin films as a scalable magnetic-insulator platform for spintronic and topological heterostructure devices beyond the constraints of garnet chemistry.

cond-mat.mtrl-sci↗

arXiv2026

Time Reversal Symmetry Broken Electronic Phases in Thin Films of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

High-temperature superconductors (high-Tc SCs) host a rich landscape of electronic phases encompassing the pseudogap, strange metal, superconducting, antiferromagnetic insulating, and Fermi-liquid regimes. The superconducting phase is notable for non-dissipative electronic functionality at relatively high temperatures. These phases are commonly probed in thermodynamic phase space by varying temperature or current through the sample. They can also be probed by breaking time-reversal symmetry (TRS) with an external magnetic field, which yields transition signatures distinct from those arising solely from temperature or current tuning. Here we show that electron transport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is primarily governed by two-dimensional superconductivity consistent with a Berezinskii-Kosterlitz-Thouless (BKT) topological phase transition, as supported by current-voltage characteristics measured under temperature variation; these measurements preserve TRS. In contrast, when an external magnetic field is applied, the superconducting state is consistently preceded by weak antilocalization (WAL), where bound vortex-antivortex pairs dissociate into a normal metallic state through an intermediate localized phase. We further establish that highly disordered films exhibit transport dominated by three-dimensional weak localization, with superconductivity entirely suppressed.

cond-mat.supr-con↗

arXiv2026

Vortex Transport in Ni/Bi Bilayer Superconductor with Strong Spin-Orbit and Exchange Interaction

Nickel/bismuth (Ni/Bi) bilayers are a promising platform for exploring unconventional superconductivity. Ferromagnetic Ni is coupled to Bi, a strong spin orbit metal that only becomes superconducting below approx 10 mK, forming a bilayer exhibits superconductivity at a much higher temperatures, a Tc of 3 to 4 K. Such a bilayer thus makes an ideal system to probe Cooper pairing in strong spin orbit coupled magnetic environments. Magneto transport studies near Tc reveal the behavior of vortex dynamics and exchange proximity effects. It is seen that isolated vortices of the bilayers respond sensitively to out of plane fields, producing antisymmetric transverse resistance peaks attributable to competing Magnus and viscous forces. Control experiments using a ferromagnetic insulator confirm that superconductivity extends throughout the bilayer, not just confined at the interface. Overall, the results provide a unified picture of transport dominated by vortex dynamics and show that a conventional s wave order parameter accounts for the observations, with any likely unconventional contributions being only subtle.

cond-mat.supr-con↗

arXiv2026

Magneto-Chiral Anisotropy in Josephson Diode Effect of All-Metallic Lateral Junctions with Interfacial Rashba Spin-Orbit Coupling

We explore the role of interfacial Rashba spin-orbit coupling (SOC) for the Josephson diode effect in all-metal diffusive Josephson junctions. Devices with Fe/Pt and Cu/Pt weak links between Nb leads reveal a Josephson diode effect in an in-plane magnetic field with magneto-chiral anisotropy according to the point symmetry of Rashba SOC. The Rashba SOC originates from inversion symmetry breaking at the metal-metal interfaces. A control sample with a plain Cu-layer as weak link, in contrast, exhibits an axis-symmetric diode effect. The Fraunhofer patterns display an apparent inverted hysteresis which can be traced back to stray fields resulting from the conventional hysteretic vortex pinning in the Nb contacts.

cond-mat.supr-con↗

arXiv2026

Crystallographic Orientation-Dependent Magnetotransport in the Layered Antiferromagnet -- CrSBr

Among two-dimensional magnetic materials, CrSBr has attracted considerable attention owing to its coexistence of ferromagnetic and antiferromagnetic ordering, which depends sensitively on crystallographic orientation. An additional distinguishing feature of CrSBr is its highly anisotropic Fermi surface in momentum space. In this work, we present a comprehensive investigation of magnetoresistance by systematically orienting the bias current and the applied magnetic field along all three crystallographic axes. We demonstrate that the magnetoresistance serves as a direct probe of electronic anisotropy, exhibiting pronounced variations when the current is applied along different crystallographic directions under a magnetic field perpendicular to the sample plane. For in-plane magnetic fields, we observe conventional anisotropic magnetoresistance accompanied by hysteresis, indicative of ferromagnetic behavior. Overall, our study provides a complete picture of electronic transport in CrSBr as a function of bias current and magnetic field orientation with respect to crystallographic directions, thereby opening pathways for future experiments requiring high sensitivity of electrical resistance to magnetic field gradients.

cond-mat.mtrl-sci↗

arXiv2026

Nitrogen-Vacancy-Mediated Magnetism in Sputtered GdN Thin Films

Among rare-earth nitrides (RENs), gadolinium nitride (GdN) stands out as a promising material for spintronics owing to its distinctive combination of semiconducting behavior, strong exchange interactions, and intrinsically soft ferromagnetism. Its relatively high Curie temperature and large saturation magnetization make it an attractive candidate for device concepts such as non-volatile memory elements and spin-based transistors, motivating efforts toward low-cost, uniform, and compositionally controlled thin-film growth. In this work, we deposited GdN thin films on SiO2/AlN substrates using DC sputtering under reactive nitridation conditions, with thicknesses varying from 18 to 180 nm, and systematically investigated their structural and magnetic properties. The films exhibit soft ferromagnetic ordering, characterized by a coercive field of approximately 200 Oe and a Curie temperature (Tc) near 70 K. Structural analysis reveals lattice distortions and local strain associated with nitrogen-vacancy defects, whose concentration varies with film thickness. Our theoretical studies establish a direct correlation between the observed Raman modes of the GdN lattice and the reduced magnetization induced by nitrogen vacancies. These vacancies give rise to defect-mediated ferromagnetism, leading to a measurable enhancement of Tc from 68 K to 82 K across the studied thickness range. The observed magnetic behavior is well described by the bound magnetic polaron (BMP) model, confirming that nitrogen vacancies are key contributors to ferromagnetic ordering while preserving the soft-magnetic character intrinsic to GdN. This study underscores the pivotal role of defect engineering in optimizing GdN thin films for spintronics applications.

cond-mat.mtrl-sci↗

arXiv2025

Enhanced Ferromagnetism in Monolayer Cr2Te3 via Topological Insulator Coupling

Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr2Te3 down to monolayer (ML) on insulating SrTiO3(111) and/or Al2O3(001) substrates using molecular beam epitaxy. Robust ferromagnetism persists in the 2D limit. In particular, the Curie temperature TC of 2 ML Cr2Te3 increases from 100 K to ~ 120 K when proximitized to topological insulator (TI) (Bi,Sb)2Te3, with substantially boosted magnetization as observed via polarized neutron reflectometry. Our experiments and theory strongly indicate that the Bloembergen-Rowland interaction is likely universal underlying TC enhancement in TI-coupled magnetic heterostructures. The topological-surface-enhanced magnetism in 2D TMC enables further exchange coupling physics and quantum hybrid studies, including paving the way to realize interface-modulated topological electronics.

cond-mat.mtrl-sci↗

arXiv2024

Tracing Dirac points of topological surface states by ferromagnetic resonance

Ferromagnetic resonance is used to reveal features of the buried electronic band structure at interfaces between ferromagnetic metals and topological insulators. By monitoring the evolution of magnetic damping, the application of this method to a hybrid structure consisting of a ferromagnetic layer and a 3D topological insulator reveals a clear fingerprint of the Dirac point and exhibits additional features of the interfacial band structure not otherwise observable. The underlying spin-pumping mechanism is discussed in the framework of dissipation of angular momentum by topological surface states (TSSs). Tuning of the Fermi level within the TSS was verified both by varying the stoichiometry of the topological insulator layer and by electrostatic backgating and the damping values obtained in both cases show a remarkable agreement. The high energy resolution of this method additionally allows us to resolve the energetic shift of the local Dirac points generated by local variations of the electrostatic potential. Calculations based on the chiral tunneling process naturally occurring in TSS agree well with the experimental results.

cond-mat.mes-hall↗

arXiv2023

Transport across junctions of altermagnets with normal metals and ferromagnets

Altermagnet (AM) is a novel time reversal symmetry broken magnetic phase with $d$-wave order which has been experimentally realized recently. We discuss theoretical models of altermagnet based systems on lattice and in continuum. We show equivalence between the lattice and continuum models by mapping the respective parameters. We study (i) altermagnet-normal metal (NM) and (ii) altermagnet-ferromagnet (FM) junctions, with the aim to quantify transport properties such as conductivity and magnetoresistance. We find that a spin current accompanies charge current when a bias is applied. The magnetoresistance of AM-FM junction switches sign when AM is rotated by $90^{\circ}$ -- a feature unique to the altermagnetic phase.

cond-mat.mes-hall↗

arXiv2022

Non-reciprocity of Vortex-limited Critical Current in Conventional Superconducting Micro-bridges

Non-reciprocity in the critical current has been observed in a variety of superconducting systems and has been called the superconducting diode effect. The origin underlying the effect depends on the symmetry breaking mechanisms at play. We investigate superconducting micro bridges of NbN and also NbN/magnetic insulator (MI) hybrids. We observe a large diode efficiency of $\approx$~30\% when an out-of-plane magnetic field as small as 25~mT is applied. In both NbN and NbN/MI hybrid, we find that the diode effect vanishes when the magnetic field is parallel to the sample plane. Our observations are consistent with the critical current being determined by the vortex surface barrier. Unequal barriers on the two edges of the superconductor strip result in the diode effect. Furthermore, the rectification is observed up to a temperature $\sim$10~K, which makes the device potential for diode based applications over larger temperature range than before.

cond-mat.supr-con↗

arXiv2021

Interfacial control of vortex-limited critical current in type II superconductor films

In a small subset of type II superconductor films, the critical current is determined by a weakened Bean-Livingston barrier posed by the film surfaces to vortex penetration into the sample. A film property thus depends sensitively on the surface or interface to an adjacent material. We theoretically investigate the dependence of vortex barrier and critical current in such films on the Rashba spin-orbit coupling at their interfaces with adjacent materials. Considering an interface with a magnetic insulator, we find the spontaneous supercurrent resulting from the exchange field and interfacial spin-orbit coupling to substantially modify the vortex surface barrier, consistent with a previous prediction. Thus, we show that the critical currents in superconductor-magnet heterostructures can be controlled, and even enhanced, via the interfacial spin-orbit coupling. Since the latter can be controlled via a gate voltage, our analysis predicts a class of heterostructures amenable to gate-voltage modulation of superconducting critical currents. It also sheds light on the recently observed gate-voltage enhancement of critical current in NbN superconducting films.

cond-mat.supr-con↗

arXiv2021

Emergence of Unconventional Interfacial Magnetic Phenomenon in Topological Insulator-Based Magnetic Heterostructures

In a topological insulator (TI)/magnetic insulator (MI) hetero-structure, large spin-orbit coupling of the TI and inversion symmetry breaking at the interface could foster non-planar spin textures such as skyrmions at the interface. This is observed as topological Hall effect in a conventional Hall set-up. While this effect has been observed at the interface of TI/MI, where MI beholds perpendicular magnetic anisotropy, non-trivial spin-textures that develop in interfacial MI with in-plane magnetic anisotropy is under-reported. In this work, we study Bi$_2$Te$_3$/EuS hetero-structure using planar Hall effect (PHE). We observe planar topological Hall and spontaneous planar Hall features that are characteristic of non-trivial in-plane spin textures at the interface. We find that the latter is minimum when the current and magnetic field directions are aligned parallel, and maximum when they are aligned perpendicularly within the sample plane, which maybe attributed to the underlying planar anisotropy of the spin-texture. These results demonstrate the importance of PHE for sensitive detection and characterization of non-trivial magnetic phase that has evaded exploration in the TI/MI interface.

cond-mat.mes-hall↗

arXiv2021

In-depth Analysis of Anisotropic Magnetoconductance in Bi$_2$Se$_3$ thin films with electron-electron interaction corrections

A combination of out-of-plane and in-plane magnetoconductance (MC) study in topological insulators (TI) is often used as an experimental technique to probe weak anti-localization (WAL) response of the topological surface states (TSSs). However, in addition to the above WAL response, weak localization (WL) contribution from conducting bulk states are also known to coexist and contribute to the overall MC; a study that has so far received limited attention. In this article, we accurately extract the above WL contribution by systematically analyzing the temperature and magnetic field dependency of conductivity in Bi$_2$Se$_3$ films. For accurate analysis, we quantify the contribution of electron-electron interactions to the measured MC which is often ignored in recent WAL studies. Moreover, we show that the WAL effect arising from the TSSs with finite penetration depth, for out-of-plane and in-plane magnetic field can together explain the anisotropic magnetoconductance (AMC) and, thus, the investigated AMC study can serve as a useful technique to probe the parameters like phase coherence length and penetration depth that characterise the TSSs in 3D TIs. We also demonstrate that increase in bulk-disorder, achieved by growing the films on amorphous SiO$_2$ substrate rather than on crystalline Al$_2$O$_3$(0001), can lead to stronger decoupling between the top and bottom surface states of the film.

cond-mat.str-el↗

arXiv2021

Observation of Planar Hall Effect in Topological Insulator -- Bi$_2$Te$_3$

Planar Hall effect (PHE) in topological insulators (TIs) is discussed as an effect that stems mostly from conduction due to topologically protected surface states. Although surfaces states play a critical role and are of utmost importance in TIs, our present study reflects the need for considering the bulk conduction in understanding PHE in TIs. Here, we demonstrate an enhancement in PHE amplitude by three times by doubling the thickness of Bi$_2$Te$_3$ film on Si (111). The PHE amplitude reaches $\approx$~6 n$Ω$m in 30 quintuple layer (QL) device as compared to $\approx$~2 n$Ω$m in 14 QL. We find that the PHE amplitude increases with temperature in the 30 QL Bi$_2$Te$_3$ films grown on Si (111) and Al$_2$O$_3$ (0001). Our experiments indicate that the contribution of bulk states to PHE in TIs could be significant.

cond-mat.mes-hall↗

arXiv2021

Finite transverse conductance in topological insulators under an applied in-plane magnetic field

Recently, in topological insulators (TIs) the phenomenon of planar Hall effect (PHE) wherein a current driven in presence an in-plane magnetic field generates a transverse voltage has been experimentally witnessed. There have been a couple of theoretical explanations of this phenomenon. We investigate this phenomenon based on scattering theory on a normal metal-TI-normal metal hybrid structure and calculate the conductances in longitudinal and transverse directions to the applied bias. The transverse conductance depends on the spatial location between the two NM-TI junctions where it is calculated. It is zero in the drain electrode when the chemical potentials of the top and the bottom TI surfaces ($μ_t$ and $μ_b$ respectively) are equal. The longitudinal conductance is $π$-periodic in $ϕ$-the angle between the bias direction and the direction of the in-plane magnetic field. The transverse conductance is $π$-periodic in $ϕ$ when $μ_t=μ_b$ whereas it is $2π$-periodic in $ϕ$ when $μ_t\neqμ_b$. As a function of the magnetic field, the magnitude of transverse conductance increases initially and peaks. At higher magnetic fields, it decays for angles $ϕ$ closer to $0,π$ whereas oscillates for angles $ϕ$ close to $π/2$. The conductances oscillate with the length of the TI region. A finite width of the system makes the transport separate into finitely many channels. The features of the conductances are similar to those in the limit of infinitely wide system except when the width is so small that only one channel participates in the transport. When only one channel participates in transport, the transverse conductance in the region $0 L$ is zero even for the case $μ_t\neqμ_b$. We understand the features in the obtained results.

cond-mat.mes-hall↗

arXiv2021

Large Enhancement of Critical Current in Superconducting Devices by Gate Voltage

The gate-voltage-induced suppression of critical currents in metallic superconductors observed recently [De Simoni et al., Nat. Nanotechnol. 13, 802 (2018)] has raised crucial questions regarding the nature and mechanism of the electric field effect in these systems. Here, we demonstrate an enhancement of up to 30 % in critical current in the type II superconductor NbN, micro- and nano superconducting bridges, tunable via a back-gate voltage. Our suggested plausible mechanism of this enhancement in critical current based on surface nucleation and pinning of Abrikosov vortices is consistent with expectations and observations for type-II superconductor films with thicknesses comparable to their coherence length. Furthermore we demonstrate infinite electroresistance and a hysteretic resistance dependence on the applied electric field which could lead to logic and memory applications in a superconductors-based low-dissipation digital computing paradigm. Our work thus provides the first demonstration of an electric field enhancement in the superconducting property in metallic superconductors, constituting a crucial step towards understanding of electric field-effects on the fundamental properties of a superconductor and its exploitation for future technologies.

physics.app-ph↗