De Haas Effect Research Articles

Terahertz electric-field-driven dynamical multiferroicity in SrTiO3

The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention1–6. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials7,8. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature9, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein–de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

A spin–rotation mechanism of Einstein–de Haas effect based on a ferromagnetic disk

A spin–rotation mechanism of Einstein–de Haas effect based on a ferromagnetic disk

Shubnikov–de Haas oscillations of biaxial-strain-tuned superconductors in pulsed magnetic field up to 60 T

Two-dimensional (2D) materials have gained increasing prominence not only in fundamental research but also in daily applications. However, to fully harness their potential, it is crucial to optimize their properties with an external parameter and track the electronic structure simultaneously. Magnetotransport over a wide magnetic field range is a powerful method to probe the electronic structure and, for metallic 2D materials, quantum oscillations superimposed on the transport signals encode Fermi surface parameters. In this manuscript, we utilize biaxial strain as an external tuning parameter and investigate the effects of strain on the electronic properties of two quasi-2D superconductors, MoTe2 and RbV3Sb5, by measuring their magnetoresistance in pulsed magnetic fields up to 60 T. With a careful selection of insulating substrates, we demonstrate the possibility of both the compressive and tensile biaxial strains imposed on MoTe2 and RbV3Sb5, respectively. For both systems, the applied strain has led to superconducting critical temperature enhancement compared to their free-standing counterparts, proving the effectiveness of this biaxial strain method at cryogenic temperatures. Clear quantum oscillations in the magnetoresistance—the Shubnikov–de Haas (SdH) effect—are obtained in both samples. In strained MoTe2, the magnetoresistance exhibits a nearly quadratic dependence on the magnetic field and remains non-saturating even at the highest field, whereas in strained RbV3Sb5, two SdH frequencies showed a substantial enhancement in effective mass values, hinting at a possible enhancement of charge fluctuations. Our results demonstrate that combining biaxial strain and pulsed magnetic field paves the way for studying 2D materials under unprecedented conditions.

Temperature-dependent Fermi surface probed by Shubnikov–de Haas oscillations in topological semimetal candidates DyBi and HoBi

Rare earth-based monopnictides are among the most intensively studied groups of materials in which extremely large magnetoresistance has been observed. This study explores magnetotransport properties of two representatives of this group, DyBi and HoBi. The extreme magnetoresistance is discovered in DyBi and confirmed in HoBi. At T=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T=2$$\\end{document} K and in B=14\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B=14$$\\end{document} T for both compounds, magnetoresistance reaches the order of magnitude of 104%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^4\\%$$\\end{document}. For both materials, standard Kohler’s rule is obeyed only in the temperature range from 50 to 300 K. At lower temperatures, extended Kohler’s rule has to be invoked because carrier concentrations and mobilities strongly change with temperature and magnetic field. This is further proven by the observation of a quite rare temperature-dependence of oscillation frequencies in Shubnikov–de Haas effect. Rate of this dependence clearly changes at Néel temperature, reminiscent of a novel magnetic band splitting. Multi-frequency character of the observed Shubnikov–de Haas oscillations points to the coexistence of electron- and hole-type Fermi pockets in both studied materials. Overall, our results highlight correlation of temperature dependence of the Fermi surface with the magnetotransport properties of DyBi and HoBi.

Tunable non-Lifshitz–Kosevich temperature dependence of Shubnikov–de Haas oscillation amplitudes in SmSb

The Lifshitz–Kosevich (LK) theory is the pillar of magnetic quantum oscillations, which have been extensively applied to characterise a wide range of metallic states. In this study, we focus on the Shubnikov–de Haas (SdH) effect observed in SmSb, a rare-earth monopnictide. We observed a significant departure from the expected LK theory near TN = 2.4 K: both a peak-like anomaly and an enhancement in the temperature dependence of quantum oscillation amplitude are seen in SmSb. Moreover, we discovered a remarkable sensitivity of the SdH amplitudes to sample purity. By adjusting the sample purity, we were able to tune the temperature dependence of the α band’s SdH amplitudes from a peak-like anomalous behaviour to an enhancement. Therefore, SdH oscillations from the α band connect the two well-known non-LK behaviours, controllable through varying the sample purity, paving the way for developing further understanding of the mechanism leading to the anomalous quantum oscillations.

Electromagnetism of one-component plasmas of massless fermions

We present a theoretical study of two- and three-dimensional massless Dirac one-component plasmas embedded in a constant uniform magnetic field. We determine the wavefunctions and Landau energy levels of a massless Dirac fermion in a constant magnetic field. On this basis we consider magnetism of Fermi fluids of massless charged particles. We show that such a three-dimensional Dirac plasma consisting of fermions with the same helicity has its own magnetic moment. We also consider the limit of strong magnetic fields and investigate the De Haas–van Alphen effect. We derive the Kubo formula for the electrical conductivity tensor of massless Dirac plasmas and consider the Shubnikov–de Haas effect. In addition, we propose a model of the static conductivity tensor and employ the matrix version of the classical method of moments to derive a Drude-like formula for the dynamic conductivity tensor for massless Dirac plasmas. We find that the electrical conductivity tensor for Dirac fermions with the right helicity is not isotropic in the plane perpendicular to the magnetic field.

Laser-induced forces on atoms during ultrafast demagnetization

Laser-induced femtosecond demagnetization has attracted a broad attention as a possible candidate for information storage technology. However, whether or not lattice vibration directly participates in demagnetization has been highly controversial over a decade. A recent electron diffraction experiment attributed the demagnetization to the polarized phonon effect, but a similar x-ray diffraction experiment attributed it to the Einstein–de Haas effect. Common to both experiments is that neither the angular momentum of the lattice nor the rotation of the sample was directly probed. Here, we report our first first-principles calculation of forces on atoms induced by an ultrafast laser during ultrafast demagnetization. We employ two complementary methods: (i) the frozen lattice with electronic excitation and (ii) frozen excitation but moving the lattice. We find that the forces on atoms start at −50 fs and peak around 30 fs. The magnitude of the force is far smaller than the empirical estimates. Within the limit of our theory, our results suggest that the polarized phonon effect and the Einstein–de Haas effect are unlikely to be the main course of demagnetization. We expect that our finding has a profound impact on the future direction of laser-induced dynamics in magnetic and quantum materials.

Spin-lattice dynamics simulation of the Einstein–de Haas effect

The spin and lattice dynamics of a ferromagnetic nanoparticle are studied via molecular dynamics and with semi-classical spin dynamics simulations where spin and lattice degrees of freedom are coupled via a dynamic uniaxial anisotropy term. We show that this model conserves total angular momentum, whereas spin and lattice angular momentum are not conserved. We carry out simulations of the Einstein–de Haas effect for a Fe nanocluster with more than 500 atoms that is free to rotate, using a modified version of the open-source spin-lattice dynamics code (SPILADY). We show that the rate of angular momentum transfer between spin and lattice is proportional to the strength of the magnetic anisotropy interaction. The addition of the anisotropy allows full spin-lattice relaxation to be achieved on previously reported timescales of ∼100 ps and for tight-binding magnetic anisotropy energies comparable to those of small Fe nanoclusters.

Giant nonlinear response due to unconventional magneto-oscillations in nodal-line semimetals

Quantum oscillations in magnetoconductance of a material at low temperatures and in presence of an intense magnetic field are described by the Shubnikov de Haas (SdH) effect. It is widely assumed to be the hallmark of the Fermi surface of a given metal. In contrast to the canonical situation, we identify an exotic oscillation in nonlinear responses of three-dimensional nodal line semimetals (NLSMs) which persist even at temperatures where the typical SdH-like oscillations vanish. This oscillation occurs due to the periodic gap-closing of a pair of Landau levels at zero Fermi energy with the variation of the magnetic field. The emergence of the oscillation is a remarkable fingerprint of ring dispersion and the corresponding frequency can be used to determine the radius of the ring. Using the Boltzmann equation, we calculate the second harmonic generation of nodal line semimetals under parallel DC electric and strong magnetic fields. The second harmonic conductivity diverges at the gap closing condition leading to the giant nonlinear response in NLSMs.

Non-linear Shubnikov-de Haas oscillations in the self-heating regime

We demonstrate a non-linear measurement scheme of the Shubnikov–de Haas effect based on Joule self-heating that builds on ideas of the 3ω-method used in thin films. While the temperature dependence of the resistance, R(T), of clean metals at low temperatures saturates, a significant temperature dependence, dR/dT, appears at high fields due to Landau quantization. We experimentally demonstrate this effect in the semi-metal CoSi, resolving well quantum oscillations at low magnetic fields in the non-linear channel, which appear as 3rd harmonics of the current drive frequency. To ensure the dominant self-heating originates in the crystal, not at the contacts, we fabricate crystalline microbars using focused ion beam machining. These oscillations in non-linear channel encode the ratio between the dR/dT and the thermal conductivity of the material, rendering it an interesting probe in situations of the broken Wiedemann–Franz law. Our results present a quantitative methodology that is particularly suited to investigate the electronic structure of micro- and nano-materials at intermediate temperatures.

The effect of barrier layers on 2D electron effective mass in Al0.3Ga0.7N/AlN/GaN heterostructures

The Shubnikov de Haas (SdH) effect measurements have been performed to evaluate the influence of Si3N4 passivation, a spacer layer, and Si-doped barrier layer on the electronic transport parameters of two-dimensional (2D) electrons in Al0.3Ga0.7N/AlN/GaN heterostructures under temperatures from 1.8 K to 40 K and at a magnetic field up to 11 T. The 2D electron effective mass (m*), 2D carrier density (N 2D), the difference between Fermi level and subband energy levels (E F − E 1), quantum lifetime (τ q) are determined by analyzing SdH oscillations. Although investigated samples with equal 2D electron density are examined, the effective mass values of 2D electrons are deduced within the range of (0.16 ± 0.005)m 0 and (0.23 ± 0.005)m 0. Results reveal that passivation, a spacer layer, and doping affect 2D electron effective mass. Furthermore, the dominant scattering mechanisms that limited electron transport is determined as a long-range scattering for all investigated sample. The results obtained provide information for the high-performance device application of these samples.

Quantum magneto transport properties of nanostructure multi quantum wells short wave Infrared detectors

In this paper, we investigated the band structure and quantum magneto transport properties of the In0.53Ga0.47As(d1=100Å)/InP(d2=70Å) type I multi quantum wells (MQWs) at low temperature. These studies were based on the envelope function and effective mass formalisms. We calculated the effect of d1, d2, the band valence offset and temperature on the band gap and the cut-off wavelength of detection. The result of the computed density of states and the position of Fermi level indicate that this sample is quasi two-dimensional system with n-type conductivity. The calculated evolution of the cutoff wavelength with temperature predicts this MQWs can be used as a short-infrared detector. Furthermore, we interpreted theoretically the photoluminescence, the Shubnikov de Haas (SdH) and quantum Hall effects observed by Pusep et al.

Einstein–de Haas effect at radio frequencies in and near magnetic equilibrium

The Einstein-de Haas (EdH) effect and its reciprocal the Barnett effect are fundamental to magnetism and uniquely yield measures of the ratio of magnetic moment to total angular momentum. These effects, small and generally difficult to observe, are enjoying a resurgence of interest as contemporary techniques enable new approaches to their study. The high mechanical resonance frequencies in nanomechanical systems offer a tremendous advantage for the observation of EdH torques in particular. At radio frequencies, the EdH effect can become comparable to or even exceed in magnitude conventional cross-product magnetic torques. In addition, the RF-EdH torque is expected to be phase-shifted by 90 degrees relative to cross-product torques, provided the magnetic system remains in quasi-static equilibrium, enabling separation in quadratures when both sources of torque are operative. Radio frequency EdH measurements are demonstrated through the full hysteresis range of micrometer scale, monocrystalline yttrium iron garnet (YIG) disks. Equilibrium behavior is observed in the vortex state at low bias field. Barkhausen-like features emerge in the in-plane EdH torque at higher fields in the vortex state, revealing magnetic disorder too weak to be visible through the in-plane cross-product torque. Beyond vortex annihilation, peaks arise in the EdH torque versus bias field, and these together with their phase signatures indicate additional utility of the Einstein-de Haas effect for the study of RF-driven spin dynamics.

Signatures of possible surface states in TaAs

A signature property of Weyl semimetals is the existence of topologically protected surface states - arcs in momentum space that connect Weyl points in the bulk. However, the presence of bulks states makes detection of surface contributions to the transport challenging. Here we present a magnetoresistance study of high-quality samples of the prototypical Weyl semimetal, TaAs. By measuring the Shubnikov de Haas effect, we reveal the presence of a two-dimensional cyclotron orbit. This orbit is quantitatively consistent with the interference of coherent quasiparticles traversing two distinct Fermi arcs on the [001] crystallographic surface. The observation of this effect suggests that high magnetic fields can be used to study not only the transport properties of Fermi arcs, but also the interference of their quantum mechanical wavefunctions.

Влияние легирования оловом, таллием и медью на квантовые подвижности дырок в монокристаллах теллурида сурьмы

В статье приведены результаты вычислений квантовой подвижности дырок μq из экспериментальных данных по эффекту Шубникова–де Гааза (ШдГ) при T = 4,2 K в монокристаллах Sb2–xSnxTe3 (x = 0,0;0,005; 0,0075; 0,01); Sb2–xTlxTe3 (x = 0,0; 0,005; 0,015; 0,05) и Sb2–xCuxTe3 (x = 0,0; 0,01; 0,03; 0,05; 0,07; 0,10), которые были синтезированы методом Бриджмена. Установлено, что Tl проявляет донорное поведение в Sb2Te3, в то время как Sn и Cu показывают акцепторное поведение. Квантовая подвижность дырок, вычисленная из эффекта ШдГ, уменьшается в два раза при легировании Sn, в легированных Tl образцах μq — в три раза и в легированных Cu образцах μq сокращается менее чем в три раза при максимальном содержании Cu x = 0,1. В то же время максимальное содержание Cu в 6 раз превышает содержание Sn и в 2 раза — Tl. Все измерения были проведены для ориентации магнитного поля вдоль оси С3. В этом случае для шестиэллипсоидной поверхности Ферми легких дырок все сечения эллипсоидов совпадают, и наблюдается только одна частота осцилляций.

Transverse Shubnikov–de Haas effect and the manifestation of quantum diffraction

A quantum diffraction interpretation of the transverse Shubnikov–de Haas effect is presented. Within the framework of the conventional theory of this effect, we show that the matrix element for the electron transition from an initial state to a final state used in calculating the transverse electrical conductivity can be represented as a diffraction-type amplitude distribution. The squared modulus of this matrix element under certain conditions exhibits the Fraunhofer diffraction pattern. It is shown that the oscillating part of the transverse conductivity has the same form as the amplitude for Fraunhofer diffraction by an annular aperture.

Contribution of Ukrainian Scientists to the Development of Electrodynamics

The aim of the paper is to prove the importance of the works performed by Ukrainian scientists for the development of electrodynamics. Some examples of achievements made by Ukrainian scientists in this scientific area include physical theories in such directions as the electrical conductivity, domain structure of ferromagnets, photoelectromotive force in semiconductors, microscopic theory of superconductivity, Shubnikov–de Haas effect, magneto-acoustic resonance, invention of an electric tram, live broadcast of the moving-image signal, distant control of objects by means of radio signals, and arc welding of metals. Most Ukrainian scientists have founded their own scientific schools, which works are recognized throughout the world. They were not only engaged in the scientific and lecturing activities, but also in the popularization of science, reformation of the education system, and social activity.

Quantum Oscillations and Chiral Anomaly in a Bi0.96Sb0.04 Single Crystal

Bi1-xSbx alloys are of special significance in topological insulator research. Here we focus on the Bi0.96Sb0.04 alloy in which the conduction band edge just touches the valence band edge. Transport measurements show quantum oscillations in the longitudinal (Shubnikov–de Haas effect) and transverse magnetoresistance originating from a spheroidal Fermi surface pocket. Further investigation of the longitudinal magnetoresistance for the magnetic field parallel to the electrical current shows a small nonmonotonic magnetoresistance that is attributed to a competition of weak-antilocalization effects and a topological term related to the chiral anomaly.

Shubnikov–de Haas Effect and Electrophysical Properties of the Topological Insulator Sb2 –xCuxTe3

The results of the study of the influence of Cu on the Shubnikov–de Haas effect and the electrical properties of p-Sb2 –xCuxTe3 single crystals (0 ≤ x ≤ 0.1) are presented. In the framework of the parabolic model of the energy spectrum, the hole concentrations and the Fermi energy in Sb2 –xCuxTe3 are calculated based on the oscillation frequencies of the magnetoresistance. It is shown that doping by Cu has an acceptor effect and significantly increases the frequencies of Shubnikov–de Haas oscillations. A plateau is observed in the dependences of the Hall resistance on magnetic field. The dependences of the resistance on temperature obey the power law with the exponent m = 1.2, which is characteristic of scattering on phonons with the contribution of scattering on ionized impurities. Unlike other impurities, the exponent remains almost unchanged when doped by Cu to the maximum concentrations studied.

Quantum many-body dynamics of the Einstein–de Haas effect

In 1915, Einstein and de Haas and Barnett demonstrated that changing the magnetization of a magnetic material results in mechanical rotation, and vice versa. At the microscopic level, this effect governs the transfer between electron spin and orbital angular momentum, and lattice degrees of freedom, understanding which is key for molecular magnets, nano-magneto-mechanics, spintronics, and ultrafast magnetism. Until now, the timescales of electron-to-lattice angular momentum transfer remain unclear, since modeling this process on a microscopic level requires addition of an infinite amount of quantum angular momenta. We show that this problem can be solved by reformulating it in terms of the recently discovered angulon quasiparticles, which results in a rotationally invariant quantum many-body theory. In particular, we demonstrate that non-perturbative effects take place even if the electron--phonon coupling is weak and give rise to angular momentum transfer on femtosecond timescales.