Magnetoresistance Oscillations Research Articles

Superconducting Quantum Oscillations and Anomalous Negative Magnetoresistance in a Honeycomb Nanopatterned Oxide Interface Superconductor

The extremely low superfluid density and unprecedented tunability of oxide interface superconductors provide an ideal platform for studying fluctuations in two-dimensional superconductors. In this work, we fabricate an LaAlO3/KTaO3 interface superconductor patterned with a nanohoneycomb array of insulating islands. Little-Parks-like magnetoresistance oscillations are observed, which are dictated by the superconducting flux quantum h/2e. Moreover, an anomalous negative magnetoresistance (ANMR) appears under a weak magnetic field, suggesting magnetic-field-enhanced superconductivity. By examining their dependences on temperature, measurement current, and electrical gating, we conclude that both phenomena are associated with superconducting order parameter: The h/2e oscillations provide direct evidence of Cooper-pair transport, and the ANMR is interpreted as a consequence of multiple connected narrow superconducting paths with strong fluctuations. Published by the American Physical Society 2025

Theoretical study of magnetoresistance oscillations in semi-parabolic plus semi-inverse squared quantum wells in the presence of intense electromagnetic waves

Abstract Magnetoresistance oscillations in semiconductor quantum wells, with the semi-parabolic plus semi-inverse squared potential, under the influence of intense electromagnetic waves (IEMW), is studied theoretically. Analytical expression for the longitudinal magnetoresistance (LMR) is derived from the quantum kinetic equation for electrons, using the Fröhlich Hamiltonian of the electron-acoustic phonon system. Numerical calculation results show the complex dependence of LMR on the parameters of the external field (electric, magnetic field and temperature) as well as the structure parameters of the confinement potential. In the absence of IEMW, Shubnikov-de Haas (SdH) oscillations appear with amplitudes that decrease with temperature in agreement with previous theoretical and experimental results. In the presence of IEMW, the SdH oscillations appear in beats with amplitudes that increase with the intensity of the IEMW. SdH oscillations under the influence of electromagnetic waves are called microwave-induced magnetoresistance oscillations. The maximum and minimum peaks appear at the positions where the IEMW frequencies are integer and half-integer values of the cyclotron frequency, respectively. In addition, the structural parameters of the quantum well such as the confinement frequency and the geometrical parameters have a significant influence on the LMR as well as the SdH oscillations. When the confinement frequency is small, the two-dimensional electronic system in the quantum well behaves as a bulk semiconductor, resulting in the absence of SdH oscillations. In addition, the LMR increases with the geometrical parameter β z of the quantum well. The obtained results provide a solid theoretical foundation for the possibility of controlling SdH oscillations by IEMW as well as the structural properties of materials in future experimental observations.

Oscillatory and negative magnetoresistance in granular nanowires of superconducting NiBi3

Local fluctuations in the superconducting order parameters in granular systems show interesting magnetotransport behavior, particularly relevant to superconducting nanowires. Kivelson and Spivak [Phys. Rev. B 45, 10490 (1992)] have shown that fluctuations in density and signs of supercurrent can lead to oscillating and negative magnetoresistance (MR). Here, we present magnetoresistance measurements of 100 nm wide NiBi3 superconducting nanowires, patterned by focused ion beam lithography, from granular NiBi3 films containing different concentrations of magnetic Ni impurities. The nanowire containing a higher concentration of Ni impurity showed oscillations in MR and simultaneously exhibited negative MR in certain temperature and field ranges. None of these effects were observed in the nanowire with nearly no Ni impurities. Unlike earlier experiments, we argue that excess magnetic Ni impurities in the nanowire realize a case of simultaneous magnitude and sign fluctuations in local order parameter, leading to MR oscillations and MR sign reversal in the same system, as discussed by Kivelson and Spivak. This result is important in the context of transport in superconducting quantum circuits.

Comparative study of magnetic quantum oscillations in Hall and transverse magnetoresistance

Comparative study of magnetic quantum oscillations in Hall and transverse magnetoresistance

Topological Insulator Nanowires Made by AFM Nanopatterning: Fabrication Process and Ultra Low‐Temperature Transport Properties

AbstractTopological insulator nanostructures became an essential platform for studying novel fundamental effects emerging at the nanoscale. However, conventional nanopatterning techniques, based on electron beam lithography and reactive ion etching of films, have inherent limitations of edge precision, resolution, and modification of surface properties, all of which are critical factors for topological insulator materials. In this study, an alternative approach for the fabrication of ultrathin Bi2Se3 nanoribbons is introduced by utilizing a diamond tip of an atomic force microscope (AFM) to cut atomically thin exfoliated films. This study includes an investigation of the magnetotransport properties of ultrathin Bi2Se3 topological insulator nanoribbons with controlled cross‐sections at ultra‐low 14 mK) temperatures. Current‐dependent magnetoresistance oscillations are observed with the weak antilocalization effect, confirming the coherent propagation of 2D electrons around the nanoribbon surface's perimeter and the robustness of topologically protected surface states. In contrast to conventional lithography methods, this approach does not require a highly controlled clean room environment and can be executed under ambient conditions. Importantly, this method facilitates the precise patterning and can be applied to a wide range of 2D materials.

Interplay between Angular-Dependent Magnetoresistance Oscillation and Charge-Ordered States in the Organic Conductor β′′-(ET)(TCNQ)

Interplay between Angular-Dependent Magnetoresistance Oscillation and Charge-Ordered States in the Organic Conductor <i>β</i>′′-(ET)(TCNQ)

Electron energy relaxation mechanism in n-type InxGa1-xAs1-yBiy alloys under electric and magnetic fields

We investigate the power loss per electron mechanism of hot electrons generated under electric and magnetic fields in n-type InxGa1-xAs1-yBiy epitaxial layers. Acoustic phonons are generated under various electric fields to determine the hot-electron energy relaxation mechanisms at low temperatures. The hot electron temperatures are determined by theoretical calculation of the amplitude of the magnetoresistance oscillation. The power loss per degenerate electron is analytically modeled with possible scattering mechanisms. The modeling of the experimental results reveals that power dissipation occurs by employing deformation potential energy scattering for all the samples. The deformation potential energy increases by ∼ 2.14 eV/Bi% when Bi atoms are introduced into ternary InGaAs alloy and the increase in the deformation potential energy is found to be independent of the electron density, which indicates that power dissipation occurs in the equipartition regime.

Selective-Area Epitaxy of Bulk-Insulating (BixSb1-x)2Te3 Films and Nanowires by Molecular Beam Epitaxy.

Selective-area epitaxy (SAE) is a useful technique to grow epitaxial films with a desired shape on a prepatterned substrate. Although SAE of patterned topological-insulator (TI) thin films has been performed in the past, there has been no report of SAE-grown TI structures that are bulk-insulating. Here we report the successful growth of Hall-bars and nanowires of bulk-insulating TIs using the SAE technique. Their transport properties show that the quality of the selectively grown structures is comparable to that of bulk-insulating TI films grown on pristine substrates. In SAE-grown TI nanowires, we were able to observe Aharonov-Bohm-like magnetoresistance oscillations that are characteristic of the quantum-confined topological surface states. The availability of bulk-insulating TI nanostructures via the SAE technique opens the possibility to fabricate intricate topological devices in a scalable manner.

Investigation of Angle‐Dependent Shubnikov‐de Haas Oscillations in Topological Insulator Bismuth

The current article investigates the band structure in the presence and absence of spin‐orbit coupling (SOC), examines the Z2 invariants, and investigates the detailed angle‐dependent magneto‐transport of up to 10 T (Tesla) and down to 2 K for the bismuth crystal. The out‐of‐plane field‐dependent magnetoresistance (MR) is positive and is huge to the order of ≈104% at 2 K and 10 T. On the contrary, the longitudinal (in‐plane) field‐dependent MR is relatively small and is negative. The thermal activation energy is also estimated by using the Boltzmann formula from resistivity versus temperature measurement under applied transverse magnetic fields. The topological nature of Bi is confirmed by Z2 invariant calculation using density functional theory (DFT). PBESol bands show trivial but hybrid functional (HSE) bands show non‐trivial topology being present in Bismuth. This article comprehensively studies the dependence of MR oscillations upon the angle between the applied field and the current. The observed oscillations fade away as the angle is increased. This article is an extension of our previous work on bismuth (J. Sup. Novel Mag. 2023, 36, 389), in which a comprehensive analysis of its structural and micro‐structural properties is conducted along with its transport behavior in an applied transverse magnetic field.

The influence of light on transverse magnetoresistance oscillations in low-dimensional semiconductor structures

The influence of light on transverse magnetoresistance oscillations in low-dimensional semiconductor structures

Long-range superconducting proximity effect in YBa2Cu3O7/La0.7Ca0.3MnO3 weak-link arrays

The interplay between ferromagnetism and superconductivity has attracted substantial interest due to its potential for exotic quantum phenomena and advanced electronic devices. Although ferromagnetism and superconductivity are antagonistic phenomena, ferromagnets (F) can host spin-triplet superconductivity induced via proximity with superconductors (S). To date, most of the experimental effort has been focused on single S/F/S junctions. Here, we have found the fingerprints of long-range superconducting proximity effect in micrometric weak-link arrays, formed by embedding YBa2Cu3O7 superconducting islands in a half-metallic ferromagnet La0.7Ca0.3MnO3 film. These arrays show magnetoresistance oscillations that appear at temperatures below the critical temperature of YBa2Cu3O7 for currents below a threshold, indicating their superconducting origin. This realization paves the way for device architectures displaying macroscopic quantum interference effects, which are of interest for field sensing applications, among others.

Quantum well oscillations in giant magnetoresistance and conductance with ferromagnetic free layer thickness in spin-valve structures with inverted [Co/Pt]n/Co reference layer

We present a study on the conductance and giant magnetoresistance effect in Co/Cu/(Co/Pt)4/Co/IrMn spin valves, where the inverted [Co/Pt]4/Co reference layer and the Co free layer exhibit fcc (111) and hcp (100) orientations along the z-axis. The term ’inverted’ refers to sub-nanometer thickness for both Co and Pt layers, with Pt having a smaller thickness compared to Co. By varying the thickness of the Co free layer from 0.3 to 3.2 nm, we observe oscillations in both in-plane and perpendicular conductance as well as giant magnetoresistance, displaying a superposition of two periods (2.6 and 3.7 monolayers of the Co free layer). First-principle calculations suggest that these oscillations can be attributed to quantum well states occurring in minority channels between fcc Co(111) and hcp Co(100) within multilayered structures of Co/Cu(111)/Co, thereby providing an opportunity for precise manipulation of spin electrons within sub-nanometer scale textured layers.

Charge- 4e and Charge- 6e Flux Quantization and Higher Charge Superconductivity in Kagome Superconductor Ring Devices

The flux quantization is a key indication of electron pairing in superconductors. For example, the well-known h/2e flux quantization is considered strong evidence for the existence of charge-2e, two-electron Cooper pairs. Here we report evidence for multicharge flux quantization in mesoscopic ring devices fabricated using the transition-metal kagome superconductor CsV3Sb5. We perform systematic magnetotransport measurements and observe unprecedented quantization of magnetic flux in units of h/4e and h/6e in magnetoresistance oscillations. Specifically, at low temperatures, magnetoresistance oscillations with period h/2e are detected, as expected from the flux quantization for charge-2e superconductivity. We find that the h/2e oscillations are suppressed and replaced by resistance oscillations with h/4e periodicity when the temperature is increased. Increasing the temperature further suppresses the h/4e oscillations, and robust resistance oscillations with h/6e periodicity emerge as evidence for charge-6e flux quantization. Our observations provide the first experimental evidence for the existence of multicharge flux quanta and emergent quantum matter exhibiting higher-charge superconductivity in the strongly fluctuating region above the charge-2e Cooper pair condensate, revealing new insights into the intertwined and vestigial electronic order in kagome superconductors. Published by the American Physical Society 2024

Observation of quantum oscillations near the Mott-Ioffe-Regel limit in CaAs3.

The Mott-Ioffe-Regel limit sets the lower bound of the carrier mean free path for coherent quasiparticle transport. Metallicity beyond this limit is of great interest because it is often closely related to quantum criticality and unconventional superconductivity. Progress along this direction mainly focuses on the strange-metal behaviors originating from the evolution of the quasiparticle scattering rate, such as linear-in-temperature resistivity, while the quasiparticle coherence phenomena in this regime are much less explored due to the short mean free path at the diffusive bound. Here we report the observation of quantum oscillations from Landau quantization near the Mott-Ioffe-Regel limit in CaAs3. Despite the insulator-like temperature dependence of resistivity, CaAs3 presents giant magnetoresistance and prominent Shubnikov-de Haas oscillations from Fermi surfaces, indicating highly coherent band transport. In contrast, quantum oscillation is absent in the magnetic torque. The quasiparticle effective mass increases systematically with magnetic fields, manifesting a much larger value than what is expected based on magneto-infrared spectroscopy. This suggests a strong many-body renormalization effect near the Fermi surface. We find that these unconventional behaviors may be explained by the interplay between the mobility edge and the van Hove singularity, which results in the formation of coherent cyclotron orbits emerging at the diffusive bound. Our results call for further study on the electron correlation effect of the van Hove singularity.

Coherent states in microwave-induced resistance oscillations and zero resistance states

We investigate irradiated high-mobility two-dimensional electron systems (2DES) under low or moderated magnetic fields. These systems present microwave-induced magnetoresistance oscillations (MIRO) which, as we demonstrate, reveal the presence of coherent states of the quantum harmonic oscillator. We also show that the principle of minimum uncertainty of coherent states is at the heart of MIRO and zero-resistance states (ZRS). Accordingly, we are able to explain, based on coherent states, important experimental evidence of these photo-oscillations, such as their physical origin, their periodicity with the inverse of the magnetic field and their peculiar oscillations minima and maxima positions in regards of the magnetic field. Thus, remarkably enough, we come to the conclusion that 2DES, under low magnetic fields, become a system of quasiclassical states or coherent states and MIRO would be the smoking gun of the existence of these peculiar states in these systems. Published by the American Physical Society 2024

Modeling the Temperature Dependence of Shubnikov-De Haas Oscillations in Light-Induced Nanostructured Semiconductors

In this work, the influence of light on the temperature dependence of transverse magnetoresistance oscillations is studied. A generalized mathematical expression that calculates the temperature and light dependence of the quasi-Fermi levels of small-scale p-type semiconductor structures in a quantizing magnetic field is derived. New analytical expressions have been found to represent the temperature dependence of transverse differential magnetoresistance oscillations in dark and light situations, taking into account the effect of light on the oscillations of the Fermi energy of small-scale semiconductor structures. A mathematical model has been developed that determines the light dependence of the second-order derivative of the transverse magnetoresistance oscillations of p‑type semiconductors with quantum wells by magnetic field induction. A new theory is proposed, which explains the reasons for the significant shift of the differential magnetoresistance oscillations along the vertical axis measured in the experiment for dark and light conditions.

Determination of the Dependence of Transverse Electrical Conductivity and Magnetoresistance Oscillations on Temperature in Heterostructures Based on Quantum Wells

Determination of the Dependence of Transverse Electrical Conductivity and Magnetoresistance Oscillations on Temperature in Heterostructures Based on Quantum Wells

Extremely large magnetoresistance and quantum oscillations in semimetal Ni3In2S2

In this work, we present magnetotransport properties and quantum oscillations in single-crystalline shandite compound Ni3In2S2, which is a recently identified semimetal with endless Dirac-nodal lines. Ni3In2S2 displays a giant transverse magnetoresistance of ∼24 000 % at 2 K and 14 T and a magnetic field-induced resistivity upturn behavior at low temperatures. Below 50 K, the magnetoresistance curves show a linear magnetic field dependence under high magnetic fields. The computation results indicate that Ni3In2S2 is a semimetal with linear crossings near the Fermi level. The small effective mass, deduced from de Haas–van Alphen quantum oscillations, suggests the high carrier mobility in Ni3In2S2. The high mobility and quantum linear magnetoresistance resulting from the linear dispersive bands jointly lead to the extreme transverse magnetoresistance in our Ni3In2S2 crystal. Our findings can be a reference to understand and search for semimetals with extreme magnetoresistance.

Phonon-mediated magneto-resonances in biased graphene layers

We explore the non-equilibrium transport regime in graphene using a large dc current in combination with a perpendicular magnetic field. The strong in-plane Hall field generated in the graphene channel results in Landau levels that are tilted spatially. The energy of cyclotron orbits in the bulk varies as a function of the spatial position of the guiding center, enabling us to observe a series of compelling features. While Shubnikov–de Haas oscillations are predictably suppressed in the presence of the Hall field, a set of fresh magneto resistance oscillations emerge near the charge neutrality point as a function of dc current. Two branches of oscillations with linear dispersions are evident as we vary carrier density and dc current, the velocities of which closely resemble the transverse acoustic (TA) and longitudinal acoustic (LA) phonon modes, suggestive of phonon-assisted intra-Landau level transitions between adjacent cyclotron orbits. Our results offer unique possibilities to explore non-equilibrium phenomena in two-dimensional materials and van der Waals heterostructures.

Determination of the Dependence of the Oscillation of Transverse Electrical Conductivity and Magnetoresistance on Temperature in Heterostructures Based on Quantum Wells

In this work, the influence of two-dimensional state density on oscillations of transverse electrical conductivity in heterostructures with rectangular quantum wells is investigated. A new analytical expression is derived for calculating the temperature dependence of the transverse electrical conductivity oscillation and the magnetoresistance of a quantum well. For the first time, a mechanism has been developed for oscillating the transverse electrical conductivity and magnetoresistance of a quantum well from the first-order derivative of the magnetic field (differential) at low temperatures and weak magnetic fields. The oscillations of electrical conductivity and magnetoresistance of a narrow-band quantum well with a non-parabolic dispersion law are investigated. The proposed theory investigated the results of experiments of a narrow-band quantum well (InxGa1-xSb).