De Haas-van Alphen Oscillations Research Articles

Thermodynamic Description of Oscillations of the Magnetization of a Silicon Nanostructure in Weak Fields at Room Temperature. Density of States

The observation of de Haas–van Alphen oscillations when studying the silicon nanostructure at room temperature in weak magnetic fields enables the use of thermodynamic relations to calculate the density of states at the Fermi level at critical values of external magnetic-field strengths for integer filling factors.

Enhancements of the 32 and 52 frequencies of de Haas–van Alphen oscillations near the Lifshitz transition in a two-dimensional compensated metal with overtilted Dirac cones

We study the de Haas-van Alphen (dHvA) oscillations in the two-dimensional compensated metal with overtilted Dirac cones near the Lifshitz transition. We employ the tight-binding model of $\ensuremath{\alpha}\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{2}{\mathrm{I}}_{3}$, in which the massless Dirac fermions are realized. When a uniaxial pressure $(P)$ along the $y$ axis is applied above $P\ensuremath{\simeq}0.2$ kbar in $\ensuremath{\alpha}\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{2}{\mathrm{I}}_{3}$, one electron pocket, which encloses the overtilted Dirac points, is changed to two electron pockets, i.e., Lifshitz transition happens, while a hole pocket does not change a topology. We show that the Fourier components corresponding to the $\frac{3}{2}$ and $\frac{5}{2}$ areas of the hole pocket are anomalously enhanced in the region of pressure where the Lifshitz transition occurs. This phenomenon will be observed in the two-dimensional overtilted Dirac fermions near the Lifshitz transition.

De Haas-van Alphen effect of correlated Dirac states in kagome metal Fe3Sn2

Primarily considered a medium of geometric frustration, there has been a growing recognition of the kagome network as a harbor of lattice-borne topological electronic phases. In this study we report the observation of magnetoquantum de Haas-van Alphen oscillations of the ferromagnetic kagome lattice metal Fe3Sn2. We observe a pair of quasi-two-dimensional Fermi surfaces arising from bulk massive Dirac states and show that these band areas and effective masses are systematically modulated by the rotation of the ferromagnetic moment. Combined with measurements of Berry curvature induced Hall conductivity, our observations suggest that the ferromagnetic Dirac fermions in Fe3Sn2 are subject to intrinsic spin-orbit coupling in the d electron sector which is likely of Kane-Mele type. Our results provide insights for spintronic manipulation of magnetic topological electronic states and pathways to realizing further highly correlated topological materials from the lattice perspective.

Fermi surface topology and large magnetoresistance in the topological semimetal candidate PrBi

We report a detailed magnetotransport study on single crystals of PrBi. The presence of $f$-electrons in this material raises the prospect of realizing a strongly correlated version of topological semimetals. PrBi shows a magnetic field induced metal insulator transition below $T \sim 20$ K and a very large magnetoresistance ($\approx 4.4 \times 10^4~$) at low temperatures ($T= 2$ K). We have also probed the Fermi surface topology by de Haas van Alphen (dHvA) and Shubnikov de Haas (SdH) quantum oscillation measurements complimented with density functional theory (DFT) calculations of the band structure and the Fermi surface. Angle dependence of the SdH oscillations have been carried out to probe the possible signature of surface Dirac fermions. We find three frequencies corresponding to one electron ($\alpha$) and two hole ($\beta$ and $\gamma$) pockets in experiments, consistent with DFT calculations. The angular dependence of these frequencies is not consistent with a two dimensional Fermi surface suggesting that the transport is dominated by bulk bands. Although the transport properties of this material originate from the bulk bands, the high mobility and small effective mass are comparable to other compounds in this series proposed as topologically nontrivial.

Extremely high conductivity observed in the triple point topological metal MoP

Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Here, we report ultra-high electrical conductivity in MoP at low temperature, which has recently been established as a triple point fermion material. We show that the electrical resistivity is 6 nΩ cm at 2 K with a large mean free path of 11 microns. de Haas-van Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to noble metals with similar conductivity and number of carriers, the magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the momentum relaxing time of the electrons is found to be more than 15 times larger than the quantum coherence time. This difference between the scattering scales shows that momentum conserving scattering dominates in MoP at low temperatures.

Quantum Oscillations in Flux-Grown SmB6 with Embedded Aluminum

SmB_{6} is a candidate topological Kondo insulator that displays surface conduction at low temperatures. Here, we perform torque magnetization measurements as a means to detect de Haas-van Alphen (dHvA) oscillations in SmB_{6} crystals grown by aluminum flux. We find that dHvA oscillations occur in single crystals containing embedded aluminum, originating from the flux used to synthesize SmB_{6}. Measurements on a sample with multiple, unconnected aluminum inclusions show that aluminum crystallizes in a preferred orientation within the SmB_{6} cubic lattice. The presence of aluminum is confirmed through bulk susceptibility measurements, but does not show a signature in transport measurements. We discuss the ramifications of our results.

Magneto-resistance in pristine and irradiated TaAs2

Here we report the single crystal synthesis, characterization and the systematic study of the magneto-transport and magnetization measurements up to a magnetic field of 14 T and down to 3 K from room temperature in the semimetal TaAs2. By experiments on magneto-transport in pristine and irradiated samples, it is inferred that the turn on temperature behavior in the resistivity measurements is better analyzed based on Kohler’s rule, rather than as arising due to a metal insulator transition. The absence of negative longitudinal magneto-resistance in TaAs2 has been confirmed by careful measurements on both pristine and irradiated samples. The low energy ion irradiation altered the surface states that were reflected in the suppression of de Haas van Alphen oscillations. Hall analysis reaffirmed the role of multiple carriers, electrons and holes, in the magneto-transport of this class of materials.

Fermi surface, possible unconventional fermions, and unusually robust resistive critical fields in the chiral-structured superconductor AuBe

The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65~T and temperatures down to 0.3~K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haas-van Alphen (dHvA) oscillations has allowed the calculated bandstructure for AuBe to be validated. This permits a variety of BCS parameters describing the superconductivity to be estimated, despite the complexity of the measured Fermi surface. In addition, AuBe displays a nonstandard field dependence of the phase of dHvA oscillations associated with a band thought to host unconventional fermions in this chiral lattice. This result demonstrates the power of the dHvA effect to establish the properties of a single band despite the presence of other electronic bands with a larger density of states, even in polycrystalline samples. In common with several other NCSs, we find that the resistive upper critical field exceeds that measured by heat capacity and magnetization by a considerable factor. We suggest that our data exclude mechanisms for such an effect associated with disorder, implying that topologically protected superconducting surface states may be involved.

External mechanisms for valley polarisation and its effect on the magnetisation of graphene: strain and electric field

Abstract In order to control and manipulate a new degree of freedom of the charge carries, the scientific community has been focused the attention on the valley polarization and its consequences, since this effect opens doors for a plenty of new technological devices. The aim of the present work is to describe how external mechanisms on graphene flakes, like mechanical stress combined with crossed real electric and magnetic fields, lead to the emergence of a significant valley polarisation with inversion symmetry broken. We show, numerically and analytically, that the valley characteristics written on the beating pattern of the de Haas-van Alphen oscillations can be directly measured. We also verified that the period of these beats is related to the valley asymmetry.

Negative differential resistance and quantum oscillations in FeSb2 with embedded antimony**Project supported by Guangdong Innovative and Entrepreneurial Research Team Program, China (Grant No. 2016ZT06D348), the National Natural Science Foundation of China (Grant No. 11874193), and the Shenzhen Fundamental Subject Research Program, China (Grant Nos. JCYJ20170817110751776 and JCYJ20170307105434022). The work at Brookhaven is supported by the US Department of Energy, Office

We present a systematical study on single crystalline FeSb2 using electrical transport and magnetic torque measurements at low temperatures. Nonlinear magnetic field dependence of Hall resistivity demonstrates a multi-carrier transport instinct of the electronic transport. Current-controlled negative differential resistance (CC-NDR) observed in current–voltage characteristics below ∼ 7 K is closely associated with the intrinsic transition ∼ 5 K of FeSb2, which is, however, mediated by extrinsic current-induced Joule heating effect. The antimony crystallized in a preferred orientation within the FeSb2 lattice in the high-temperature synthesis process leaves its fingerprint in the de Haas-Van Alphen (dHvA) oscillations, and results in the regular angular dependence of the oscillating frequencies. Nevertheless, possible existence of intrinsic non-trivial states cannot be completely ruled out. Our findings call for further theoretical and experimental studies to explore novel physics on flux-free grown FeSb2 crystals.

Quantum oscillations and a nontrivial Berry phase in the noncentrosymmetric topological superconductor candidate BiPd

We report the measurements of de Haas-van Alphen (dHvA) oscillations in the noncentrosymmetric superconductor BiPd. Several pieces of a complex multi-sheet Fermi surface are identified, including a small pocket (frequency 40 T) which is three dimensional and anisotropic. From the temperature dependence of the amplitude of the oscillations, the cyclotron effective mass is ($0.18$ $\pm$ 0.1) $m_e$. Further analysis showed a non-trivial $\pi$-Berry phase is associated with the 40 T pocket, which strongly supports the presence of topological states in bulk BiPd and may result in topological superconductivity due to the proximity coupling to other bands.

Термодинамическое описание осцилляций намагниченности кремниевой наноструктуры в слабых полях при комнатной температуре. Плотность состояний

AbstractThe observation of de Haas–van Alphen oscillations when studying the silicon nanostructure at room temperature in weak magnetic fields enables the use of thermodynamic relations to calculate the density of states at the Fermi level at critical values of external magnetic-field strengths for integer filling factors.

Осцилляции де Гааза--ван Альфена в кремниевой наноструктуре в слабых магнитных полях при комнатной температуре

AbstractThe field dependence of magnetization of a silicon nanosandwich measured at room temperature in weak magnetic fields manifests de Haas–van Alphen oscillations, the behavior of which is explained under the condition of the dependence of the effective carrier mass on the external magnetic field.

Type-II Dirac semimetal candidates ATe2 ( A= Pt, Pd): A de Haas-van Alphen study

We report on a magnetotransport and quantum oscillations study on high quality single crystals of the transition metal di-tellurides ${\mathrm{PtTe}}_{2}$ and ${\mathrm{PdTe}}_{2}$. The de Haas-van Alphen (dHvA) oscillations in the magnetization measurements on ${\mathrm{PtTe}}_{2}$ reveal a complicated, anisotropic band structure characterized by low effective masses and high mobilities for the carriers. Extracted transport parameters for ${\mathrm{PtTe}}_{2}$ reveal a strong anisotropy which might be related to the tilted nature of the Dirac cone. Using a Landau level fan diagram analysis we find at least one Fermi surface orbit with a Berry phase of $\ensuremath{\pi}$ consistent with Dirac electrons for both ${\mathrm{PtTe}}_{2}$ and ${\mathrm{PdTe}}_{2}$. The light effective mass and high mobility are also consistent with Dirac electrons in ${\mathrm{PtTe}}_{2}$. Our results therefore suggest that similar to ${\mathrm{PdTe}}_{2}$, ${\mathrm{PtTe}}_{2}$ might also be a three-dimensional Dirac semimetal.

A possible candidate for triply degenerate point fermions in trigonal layered PtBi2

Triply degenerate point (TP) fermions in tungsten–carbide-type materials (e.g., MoP), which represent new topological states of quantum matter, have generated immense interest recently. However, the TPs in these materials are found to be far below the Fermi level, leading to the TP fermions having less contribution to low-energy quasiparticle excitations. Here, we theoretically predict the existence of TP fermions with TP points close to the Fermi level in trigonal layered PtBi2 by ab initio calculations, and experimentally verify the predicted band topology by magnetotransport measurements under high magnetic fields up to 40 T. Analyses of both the pronounced Shubnikov–de Haas and de Haas–van Alphen oscillations reveal the existence of six principal Fermi pockets. Our experimental results, together with those from ab initio calculations, reveal the interplay between transport behaviors and unique electronic structures, and support the existence of TP fermions in trigonal layered PtBi2.

Multiple topologically nontrivial bands in noncentrosymmetric YSn2

The square lattices formed by main-group elements such as Bi, Sb, Sn, and Si in layered materials have attracted a lot of interest, since they can create rich topological phases. In this paper, we report the slightly distorted square lattice of Sn in a noncentrosymmetric compound ${\mathrm{YSn}}_{2}$ generates multiple topologically nontrivial bands, one of which likely hosts a nodal line and tunable Weyl semimetal state induced by the Rashba spin-orbit coupling and proper external magnetic field. The quasiparticles described as relativistic fermions from these bands are manifested by nearly zero mass and nontrivial Berry phases probed in de Haas-van Alphen (dHvA) oscillations. The dHvA study also reveals ${\mathrm{YSn}}_{2}$ has a complicated Fermi surface, consisting of several three-dimensional (3D) and one 2D pocket. Our first-principles calculations show the pointlike 3D pocket at Y point on the Brillouin zone boundary hosts the possible Weyl state. Our findings establish ${\mathrm{YSn}}_{2}$ as a new interesting platform for observing novel topological phases and studying their underlying physics.

Anisotropic transverse magnetoresistance and Fermi surface in TaSb2

TaSb2 has been predicted theoretically to be a weak topological insulator. Whereas, the earlier magnetotransport experiment has established it as a topological semimetal. In the previous works, the Shubnikov-de Haas oscillation has been analyzed to probe the Fermi surface, with magnetic field along a particular crystallographic axis only. By employing a sample rotator, we reveal highly anisotropic transverse magnetoresistance by rotating the magnetic field along different crystallographic directions. To probe the anisotropy in the Fermi surface, we have performed magnetization measurements and detected strong de Haas-van Alphen (dHvA) oscillations for the magnetic field applied along a and b axes as well as perpendicular to ab plane of the crystals. Three Fermi pockets have been identified by analyzing the dHvA oscillations. With the application of magnetic field along different crystal directions, the cross-sectional areas of the Fermi pockets have been found significantly different, i.e., the Fermi pockets are highly anisotropic in nature. Three-band fitting of electrical and Hall conductivity reveals two high mobility electron pockets and one low mobility hole pocket. The angular variation of transverse magnetoresistance has been qualitatively explained using the results of dHvA oscillations and three-band analysis.

Oscillations of magnetization in topological line-node semimetals

We theoretically investigate the phase of the de Haas–van Alphen oscillations in topological line-node semimetals. In these semimetals the chemical potential of charge carriers can essentially depend on the magnetic field, and this dependence changes the phase of the oscillations as compared to the phase in a three-dimensional metal with a band-contact line. Our results elucidate recent experimental data on the Berry phase for certain electron orbits in ZrSiS, ZrSiTe, and ZrSiSe.

Extremely large magnetoresistance induced by Zeeman effect-driven electron-hole compensation and topological protection in MoSi2

The magnetoresistance is the magnetic field induced change of electrical resistivity of a material. Recent studies have revealed extremely large magnetoresistance in several non-magnetic semimetals, which has been explained on the basis of either electron-hole compensation or the Fermi surface topology, or the combination of both. Here, we present a single crystal study on MoSi$_2$, which exhibits extremely large magnetoresistance, approaching almost 10$^7$ % at 2 K and 14 T magnetic field. It is found that the electron-hole compensation level in MoSi$_2$ evolves with magnetic field, which is resulted from strong Zeeman effect, and found beneficial in boosting the large non-saturating magnetoresistance. The non-trivial Berry phase in the de Haas-van Alphen oscillations and the moderate suppression of backward scattering of the charge carriers lend support for the topological nature of this semimetal. The ultra-large carrier mobility of the topologically protected charge carriers reinforces the magnetoresistance of MoSi2 to an unprecedented large value.

Revealing the Topology of Fermi-Surface Wave Functions from Magnetic Quantum Oscillations

The modern semiclassical theory of a Bloch electron in a magnetic field now encompasses the orbital magnetic moment and the geometric phase. These two notions are encoded in the Bohr-Sommerfeld quantization condition as a phase ($\lambda$) that is subleading in powers of the field; $\lambda$ is measurable in the phase offset of the de Haas-van Alphen oscillation, as well as of fixed-bias oscillations of the differential conductance in tunneling spectroscopy. In some solids and for certain field orientations, $\lambda/\pi$ are robustly integer-valued owing to the symmetry of the extremal orbit, i.e., they are the topological invariants of magnetotransport. Our comprehensive symmetry analysis identifies solids in any (magnetic) space group for which $\lambda$ is a topological invariant, as well as identifies the symmetry-enforced degeneracy of Landau levels. The analysis is simplified by our formulation of ten (and only ten) symmetry classes for closed, Fermi-surface orbits. Case studies are discussed for graphene, transition metal dichalchogenides, 3D Weyl and Dirac metals, and crystalline and $\mathbb{Z}_2$ topological insulators. In particular, we point out that a $\pi$ phase offset in the fundamental oscillation should \emph{not} be viewed as a smoking gun for a 3D Dirac metal.