Magnetoresistance Oscillations Research Articles

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

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

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).

Simulation of temperature dependence of oscillations of longitudinal magnetoresistance in nanoelectronic semiconductor materials

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) ∂(ρ⊥2d(E,B,T,d))∂B 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).

The vertical longitudinal magnetoresistance in a van der Waals thin film of WTe2

We report the magneto-transport measurements of thin film devices of the topological Weyl semimetal WTe2 with the applied current along and vertical to the in-plane directions. The device is composed of a van der Waals thin film of WTe2 sandwiched between top and bottom Au electrodes. At low temperatures, we observe not only a large unsaturated magnetoresistance and Shubnikov–de Haas oscillations with current in the in-plane direction but also a saturated vertical longitudinal magnetoresistance and quantum oscillations with current in the out-of-plane direction in a thin film of WTe2. Our work provides insight into the origin of the unsaturated magnetoresistance in WTe2 and may inspire non-planar engineering to reach higher integration in spintronics.

Fractional magnetoresistance oscillations in spin-triplet superconducting rings

Half-quantum vortices in spin-triplet superconductors are predicted to host Majorana zero modes and may provide a viable platform for topological quantum computation. Recent works also suggested that, in thin mesoscopic rings, the superconducting pairing symmetry can be probed via Little-Parks-like magnetoresistance oscillations of periodicity Φ0 = h/2e that persist below the critical temperature. Here we use the London limit of Ginzburg-Landau theory to study these magnetoresistance oscillations resulting from thermal vortex tunneling in spin-triplet superconducting rings. For a range of temperatures in the presence of disorder, we find magnetoresistance oscillations with an emergent fractional periodicity Φ0/n, where the integer n ≥ 3 is entirely determined by the ratio of the spin and charge superfluid densities. These fractional oscillations can unambiguously confirm the spin-triplet nature of superconductivity and directly reveal the tunneling of half-quantum vortices in real-world candidate materials.

Quantum Interference by Vortex Supercurrents

The origin of the parabolic background of magnetoresistance oscillations measured in finite‐width superconducting mesoscopic rings with input and output stubs and in patterned films is analyzed. The transmission model explaining the sinusoidal oscillation of magnetoresistance is extended to address the parabolic background as a function of the magnetic field. Apart from the interference mechanism activated by the ring, pinned superconducting vortices as topological defects introduce a further interference‐based distribution of supercurrents that affects, in turn, the voltmeter‐sensed quasiparticles. The onset of vortices changes the topology of the superconducting state in a mesoscopic ring in such a way that the full magnetoresistance dynamics can be interpreted due to the interference of the constituents of the order parameter induced by both the ring with its doubly connected topology and the vortex lattice in it.

Influence of the two-dimensional density of states on the temperature dependence of the electrical conductivity oscillations in heterostructures with 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) [Formula: see text] at low temperatures and weak magnetic fields. The oscillations of electrical conductivity and magnetoresistance of a narrow-band quantum well with a nonparabolic dispersion law are investigated. The proposed theory investigated the results of experiments of a narrow-band quantum well (InxGa[Formula: see text]Sb).

Quantum oscillations in field-induced correlated insulators of a moiré superlattice

We report an observation of quantum oscillations (QOs) in the correlated insulators with valley anisotropy of twisted double bilayer graphene (TDBG). The anomalous QOs are best captured in the magneto resistivity oscillations of the insulators at v = −2, with a period of 1/B and an oscillation amplitude as high as 150 kΩ. The QOs can survive up to ∼10 K, and above 12 K, the insulating behaviors are dominant. The QOs of the insulator are strongly D dependent: the carrier density extracted from the 1/B periodicity decreases almost linearly with D from −0.7 to −1.1 V/nm, suggesting a reduced Fermi surface; the effective mass from Lifshitz-Kosevich analysis depends nonlinearly on D, reaching a minimal value of 0.1 me at D = ∼ −1.0 V/nm. Similar observations of QOs are also found at v = 2, as well as in other devices without graphite gate. We interpret the D sensitive QOs of the correlated insulators in the picture of band inversion. By reconstructing an inverted band model with the measured effective mass and Fermi surface, the density of state at the gap, calculated from thermal broadened Landau levels, agrees qualitatively with the observed QOs in the insulators. While more theoretical understandings are needed in the future to fully account for the anomalous QOs in this moiré system, our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.

Anisotropic magnetoresistance and quantum oscillation in Sb2Te3 single crystal synthesized by a Te-flux method

Topological insulators (TIs) have attracted the widespread attentions due to their unique electronic structures and novel physical properties in past decades. Here, we investigate the magnetoresistance (MR) and Shubnikov-de Haas (SdH) oscillation in topological Sb2Te3. It is found that the angle-dependent MR shows the obvious anisotropy, and the maximal MR reaches ∼220% with the magnetic field rotated in ab plane at 2.5 K and 9 T. The Landau-level fan diagram indicates that Sb2Te3 possesses a nontrivial Berry phase. Comparing the SdH oscillations measured by the magnetic fields rotated in bc and ab planes, we find that the oscillation frequencies are similar, and the Berry phase shift is very slight. The first-principles calculations demonstrate that Sb vacancy can introduce an additional band across the Fermi level. The anisotropy of the Fermi surfaces reveals the anisotropic MR.

Electrical-gate-controlled giant tunneling magnetoresistance and its quasi-periodic oscillation in an interlaced magnetic-electric silicene superlattice.

In this work, we propose a silicene-based lateral resonant tunneling device by placing silicene under the superlattices interlaced, arranged by ferromagnetic gates and electric gates. Its ballistic transport properties are calculated by the transfer matrix method. Combined with the unique electrically tuned energy gap of silicene, its magnetoresistance (MR) can be exaggeratedly modulated over a wide range by applying electrostatic potential and the on-site potential difference. It is interestingly found that there is a quasi-periodic oscillation of the MR in silicene-based superlattice devices from the quantum resonant confinement of the band splitting by the electrostatic field. Moreover, the peak of the MR in a single-period structure can reach more than 104, while the peak of the MR in an interlaced alternating magnetic-electric silicene superlattice can reach more than 1017, which is one of the best-reported values. This may originate from the enhancement effect of the wave vector filtering by the controlled field. Our studies indicate that the silicene superlattices alternately arranged by the ferromagnetic gate and electric gate not only have giant MR (GMR) properties, but also exhibit the periodic oscillation characteristics of MR in which electric gates can be modulated. Therefore, this work provides a more flexible strategy for the construction of silicene-based nanoelectronic devices.

Photo-oscillations in MgZnO/ZnO heterostructures

We theoretically examine the characteristics of microwave-induced magnetoresistance (MIRO) and photovoltage oscillations in MgZno/ZnO heterostructures. We demonstrate that both kind of oscillations, although described with different physical properties, are intimately related sharing the same physical origin. We use the radiation driven electron orbit model showing that the interplay of radiation driven swinging Landau orbits and the scattering processes are at the heart of the oscillations in both scenarios. Thus, our simulations show that all photo-oscillations present the main features of MIRO: they are periodic with the inverse of the magnetic field and the oscillations minima are 1/4 cycle shifted.

Silicon-Aluminum Phase-Transformation-Induced Superconducting Rings.

The development of devices that exhibit both superconducting and semiconducting properties is an important endeavor for emerging quantum technologies. We investigate superconducting nanowires fabricated on a silicon-on-insulator (SOI) platform. Aluminum from deposited contact electrodes is found to interdiffuse with Si along the entire length of the nanowire, over micrometer length scales and at temperatures well below the Al-Si eutectic. The phase-transformed material is conformal with the predefined device patterns. The superconducting properties of a transformed mesoscopic ring formed on a SOI platform are investigated. Low-temperature magnetoresistance oscillations, quantized in units of the fluxoid, h/2e, are observed.

Thickness-dependent electronic structure in layered ZrTe5 down to the two-dimensional limit

Zirconium pentatelluride (${\mathrm{ZrTe}}_{5}$) has recently attracted intense research interest, mainly due to its potential topological nontriviality and the extraordinary quantum phenomena it displays. As an exemplary layered compound, ${\mathrm{ZrTe}}_{5}$ is expected to exhibit thickness-sensitive physical properties that vary with thinning towards the two-dimensional (2D) limit, which has not been thoroughly investigated yet. In this work, we successfully prepare sizable ${\mathrm{ZrTe}}_{5}$ thin flakes down to the monolayer for the first time. By examining the evolution of magnetotransport properties and the Shubnikov--de Haas effect in ${\mathrm{ZrTe}}_{5}$ flakes with various layer numbers, we reveal a pronounced thickness dependence of the electronic structure of ${\mathrm{ZrTe}}_{5}$ characterized by a downward shift of the Fermi level as large as \ensuremath{\sim}160 meV upon thickness reduction from bulk to two-unit cells (four atomic layers). Furthermore, an external electric field effectively modifies the magnetoresistance and quantum oscillation frequency in the few-layered ${\mathrm{ZrTe}}_{5}$. Our study proves that ${\mathrm{ZrTe}}_{5}$ thin flake can be an excellent platform for exploring the novel properties proposed for 2D topological materials as well as their tunability.

Shubnikov-de Haas and de Haas-van Alphen oscillations in Czochralski grown CoSi single crystal

Anisotropic transport, Shubnikov-de Haas (SdH), and de Haas-van Alphen (dHvA) quantum oscillations studies are reported on a high-quality CoSi single crystal grown by the Czochralski method. Temperature-dependent resistivities indicate the dominating electron-electron scattering. Magnetoresistance (MR) at 2 K reaches 610% for and [01], whereas it is 500% for [01] and . A negative slope in field-dependent Hall resistivity suggests electrons are the majority carriers. The carrier concentration extracted from Hall conductivity indicates no electron–hole compensation. In 3D CoSi, the electron transport lifetime is found to be approximately in the same order as the quantum lifetime, whereas in 2D electron gas the long-range scattering drives the transport life much larger than the quantum lifetime. From MR and Hall SdH oscillations, the effective masses and Dingle temperatures have been calculated. The dHvA oscillation reveals three frequencies at 18 T (γ), 558 T (α) and 663 T (β), whereas, SdH oscillation results in only two frequencies α and β. The γ frequency observed in dHvA oscillation is a tiny hole pocket at the Γ point.