Anomalous Magneto-oscillations and Spin Precession

Keppeler, Stefan; Winkler, Roland

doi:10.1103/physrevlett.88.046401

Cited by 27 publications

(32 citation statements)

References 18 publications

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“…We have modeled M including a subset-dependent relaxation time and find that this cannot account for the experimental observations. In a recent approach based on the Gutzwiller trace formula, 2,25 anomalous magneto-oscillations reflect the nonadiabatic spin precession along the cyclotron orbits. However, the work focused on the analysis of Fourier transforms of ρ xx .…”

Section: Resultsmentioning

confidence: 99%

Frequency anomaly in the Rashba-effect induced magnetization oscillations of a high-mobility two-dimensional electron system

et al. 2013

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With the direct measurement of the quantum oscillatory magnetization M of a two-dimensional electron system (2DES) in an InGaAs/InP asymmetric quantum well we discover a frequency anomaly of the de Haas-van Alphen effect which is not consistent with existing theories on spin-orbit interaction (SOI). Strikingly, the oscillatory magnetoresistance of the same heterostructure, that is, the Shubnikov-de Haas effect conventionally used to explore SOI, does not show the frequency anomaly. This explains why our finding has not been reported for almost three decades. The understanding of the ground state energy of a 2DES is evidenced to be incomplete when SOI is present.

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Section: Resultsmentioning

confidence: 99%

Frequency anomaly in the Rashba-effect induced magnetization oscillations of a high-mobility two-dimensional electron system

et al. 2013

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“…The f tot frequency, when multiplied by e/h, matches well the total 2D hole density deduced from the Hall resistance (h is the Planck's constant). The two peaks at f − and f + correspond to the holes in individual spin subbands although their positions times e/h do not exactly give the spin subband densities [5,13,14]. Nevertheless, as discussed below, this discrepancy between (e/h)f ± and the B = 0 spin subband densities is minor and ∆f = f + − f − = f tot − 2f − provides a good measure of the spin splitting.…”

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confidence: 99%

Negative differential Rashba effect in two-dimensional hole systems

Habib

Tutuc

Melinte

et al. 2004

Applied Physics Letters

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We demonstrate experimentally and theoretically that two-dimensional (2D) heavy hole systems in single heterostructures exhibit a decrease in spin-orbit interaction-induced spin splitting with an increase in perpendicular electric field. Using front and back gates, we measure the spin splitting as a function of applied electric field while keeping the density constant. Our results are in contrast to the more familiar case of 2D electrons where spin splitting increases with electric field.In a solid that lacks inversion symmetry, the spin-orbit interaction leads to a lifting of the spin degeneracy of the energy bands, even in the absence of an applied magnetic field, B. In such a solid, the energy bands at finite wave vectors are split into two spin subbands with different energy surfaces, populations, and effective masses. The problem of inversion asymmetry-induced spin splitting in two-dimensional (2D) carrier systems in semiconductor heterojunctions and quantum wells [1,2,3,4] has become of renewed interest recently [5] because of their possible use in realizing spintronic devices such as a spin field-effect transistor [6,7], and for studying fundamental phenomena such as the spin Berry phase [8,9].In 2D carrier systems confined to GaAs/AlGaAs heterostructures, the bulk inversion asymmetry (BIA) of the zinc blende structure and the structure inversion asymmetry (SIA) of the confining potential contribute to the B = 0 spin splitting [4,5]. While BIA is fixed, the so called Rashba spin splitting [10] due to SIA can be tuned by means of external gates that change the perpendicular electric field (E ⊥ ) in the sample. For many years it has been assumed that the Rashba spin splitting in 2D carrier systems is proportional to E ⊥ that characterizes the inversion asymmetry of the confining potential [4]. 2D holes contained in a GaAs square quantum well provide an example [11]. On the contrary, in the present work we show both experimentally and theoretically that for heavy holes confined to a triangular well at the GaAs/AlGaAs interface, spin splitting decreases with an increase in E ⊥ . We demonstrate this negative differential Rashba effect by analyzing the Shubnikov-de Haas oscillations in this system at a constant density. We note that hole systems have recently gained great attention for spintronics applications [12] because ferromagnetic (III,Mn)V compounds are intrinsically p type. A detailed understanding of the B = 0 spin splitting in hole systems is thus of great importance.The sample used in our study was grown on a GaAs (001) substrate by molecular beam epitaxy and contains a modulation-doped 2D hole system confined to a GaAs/AlGaAs heterostructure [ Fig. 1(a)]. The Al 0.3 Ga 0.7 As/GaAs interface is separated from a 16 nm thick Be-doped Al 0.3 Ga 0.7 As layer (Be concentration of 3.5 × 10 18 cm −3 ) by a 25 nm Al 0.3 Ga 0.7 As spacer layer. We fabricated Hall bar samples via lithography and used In/Zn alloyed at 440 • C for the ohmic contacts. Metal gates were deposited on the sample's front and back to c...

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“…This has the general form of the interband tunnel probability in the theory of magnetic breakdown [30,[34][35][36], with a breakdown field B c ∝ ðΔkÞ 2 . The characteristic feature of Klein tunneling is that the tunnel probability T → 1 and B c → 0 at the conical point of the band structure-here a 3D Weyl point and a 2D Dirac point in Ref.…”

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Magnetic Breakdown and Klein Tunneling in a Type-II Weyl Semimetal

2016

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The band structure of a type-II Weyl semimetal has pairs of electron and hole pockets that coexist over a range of energies and touch at a topologically protected conical point. We identify signatures of this Weyl point in the magnetic quantum oscillations of the density of states, observable in thermodynamic properties. Tunneling between the electron and hole pockets in a magnetic field is the momentum space counterpart of Klein tunneling at a p-n junction in real space. This magnetic breakdown happens at a characteristic field strength that vanishes when the Fermi level approaches the Weyl point. The topological distinction between connected and disconnected pairs of type-II Weyl cones can be distinguished by the qualitatively different dependence of the quantum oscillations on the direction of the magnetic field. DOI: 10.1103/PhysRevLett.116.236401 Weyl semimetals provide a condensed matter realization of massless relativistic fermions [1]. Their spectrum features a diabolo-shaped surface in energy-momentum space that separates helical electronlike states (moving in the direction of the momentum) from holelike states (moving opposite to the momentum) [2]. These "Weyl cones" are the three-dimensional analogue of the two-dimensional Dirac cones in graphene. The third spatial dimension provides a topological protection, by which the conical point (Weyl point) cannot be opened up unless two Weyl cones of opposite helicity are brought together in momentum space [3].Although the Weyl point cannot be locally removed, the cones can be tilted and may even tip over [4][5][6][7][8][9][10][11][12]. For the relativistic Weyl cone such a distortion is forbidden by particle-hole symmetry, but that is not a fundamental symmetry in condensed matter. While in graphene the high symmetry of the honeycomb lattice keeps the cone upright, strain providing only a weak tilt [13], the tilting can be strong in 3D Weyl semimetals. This leads to a natural division of Weyl cones into two topologically distinct types [9]. In type I the cone is only weakly tilted so that the electronlike states and holelike states occupy separate energy ranges, above or below the Weyl point. In type II the cone has tipped over so that electron and hole states coexist in energy. Many experimental realizations of a type-II Weyl semimetal have recently been reported [14][15][16][17][18][19][20][21].In a magnetic field the coexisting electron and hole pockets of a type-II Weyl semimetal are coupled by tunneling through the Weyl point (Fig. 1). Here we investigate how this process, a momentum space manifestation of Klein tunneling [22], affects the magnetic quantum oscillations of the density of states (de Haas-van Alphen effect), providing a unique thermodynamic signature of the topologically protected band structure (an alternative to proposed transport signatures [9,[23][24][25]). Because the quantum oscillations are governed by extremal cross sections of the Fermi surface, one might wonder whether some symmetry is required to align the extremal cross sect...

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Anomalous Magneto-oscillations and Spin Precession

Cited by 27 publications

References 18 publications

Frequency anomaly in the Rashba-effect induced magnetization oscillations of a high-mobility two-dimensional electron system

Frequency anomaly in the Rashba-effect induced magnetization oscillations of a high-mobility two-dimensional electron system

Negative differential Rashba effect in two-dimensional hole systems

Magnetic Breakdown and Klein Tunneling in a Type-II Weyl Semimetal

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