Magnetooptical determination of a topological index

Assaf, Badih A.; Phuphachong, Thanyanan; Volobuev, Valentine V.; Bauer, G.; Springholz, G.; Vaulchier, Louis‐Anne de; Guldner, Y.

doi:10.1038/s41535-017-0028-5

Cited by 24 publications

(37 citation statements)

References 67 publications

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“…We have shown that the LL in IV-IV TCIs can be well described by a massive Dirac spectrum that includes spin-splitting [24] [29] [30] [31], resulting from a 6-band k.p Hamiltonian. [30] If the contributions from the far-bands are neglected a 2-band k.p Hamiltonian results, the solution of which is an ideal massive Dirac model [32].…”

Section: Fig 2 (Color Online) (A)mentioning

confidence: 99%

“…We also note that the SdH results nicely agree with our previous magnetooptical measurements on the same samples. [24] Even though the two samples studied here in detail have different carrier type, the other samples examined in Fig.1(c) rule out any link between this and the NLMR. [20] In x=0.19, BQL is close to the onset of the NLMR seen in Fig.2(a).…”

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confidence: 99%

“…16, [24] the MR rises fast. In non-trivial samples having x>0.16, [24] [27] [28] although initially positive, the MR turns negative, and remains so over a wide field range. The sign of the MR hence depends on the topological character of the sample.…”

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confidence: 99%

“…Growth by molecular beam epitaxy and characterization are described in our previous works [24] [25] [26]. A 15T/4.2K superconducting cryostat setup is used for in-house measurements.…”

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Negative Longitudinal Magnetoresistance from the Anomalous N=0 Landau Level in Topological Materials

et al. 2017

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Negative longitudinal magnetoresistance (NLMR) is shown to occur in topological materials in the extreme quantum limit, when a magnetic field is applied parallel to the excitation current. We perform pulsed and DC field measurements on Pb1-xSnxSe epilayers where the topological state can be chemically tuned. The NLMR is observed in the topological state, but is suppressed and becomes positive when the system becomes trivial. In a topological material, the lowest N=0 conduction Landau level disperses down in energy as a function of increasing magnetic field, while the N=0 valence Landau level disperses upwards. This anomalous behavior is shown to be responsible for the observed NLMR. Our work provides an explanation of the outstanding question of NLMR in topological insulators and establishes this effect as a possible hallmark of bulk conduction in topological matter. [13]. This stems from the helical Dirac nature of surface-states in 3D TIs or, that of edge-states in 2D TIs. In fact, a huge amount of literature (for reviews [14] [15] [16] [17]) took interest in this question and investigated electronic transport of 2D Dirac electrons in 3D-TIs. The majority of these studies were, however, impeded by the significant and dominant bulk transport that occurs in TIs. On the other hand, little attention has been given to signatures of non-trivial band topology in 3D electron transport in a TI.Naively speaking, one can think of the bulk energy bands of a TI as being identical to those of conventional semiconductors and, thus, unlikely to generate non-conventional physical phenomena. However, one should not forget that the basis of a topological insulator lies in the inverted orbital character of these bulk energy bands. [23] shown, that the energy of the lowest (N=0) conduction (valence) Landau level in topological insulators decreases (increases) as a function of increasing magnetic field, opposite to what usually happens in a topologically trivial system ( Fig.1(a,b)). This behavior is anomalous and leads to a field-induced closure of the energy gap in a TI [21] (Fig.1(b)), whereas in a trivial material, the energy gap usually opens with increasing magnetic field ( Fig.1(a)). This anomaly is a hallmark of the inverted band structure of topological materials. Its implications on magnetotransport have not yet been considered. In the present work, we study the MR in topological insulators in the extreme quantum limit -the regime where only the lowest Landau level (LL) is occupied. We measure magnetotransport in pulsed magnetic field up to 61T in high mobility Pb1-xSnxSe epitaxial layers. We show that, when all Lorentz components contributing to the MR are suppressed by applying the magnetic field in-plane and parallel to the excitation current, a negative longitudinal MR (NLMR) emerges near the onset of the quantum limit. This NLMR is only observed in the topological regime of Pb1-xSnxSe (x>0.16) and is absent in trivial samples (x<0.16). We theoretically argue that this NLMR is a result of the anomalous beh...

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Section: Fig 2 (Color Online) (A)mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

“…Growth by molecular beam epitaxy and characterization are described in our previous works [24] [25] [26]. A 15T/4.2K superconducting cryostat setup is used for in-house measurements.…”

mentioning

confidence: 99%

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Negative Longitudinal Magnetoresistance from the Anomalous N=0 Landau Level in Topological Materials

et al. 2017

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“…Magnetooptical Landau-level spectroscopy measurements are performed on high-quality [111]oriented Pb1-xSnxSe epilayers grown by molecular beam epitaxy as described in our previous work. [11] [26] Two 2-μm thick samples with composition x=0.19 and x=0.14, respectively above and below the topological phase transition at 4.2K, are studied. Magnetospectroscopy is performed in transmission mode in the Faraday geometry versus magnetic field and temperature.…”

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Avoided level crossing at the magnetic field induced topological phase transition due to spin-orbital mixing

et al. 2018

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In 3D topological insulators, an effective closure of the bulk energy gap with increasing magnetic field expected at a critical point can yield a band crossing at a gapless Dirac node. Using highfield magnetooptical Landau level spectroscopy on the topological crystalline insulator Pb1-xSnxSe, we demonstrate that such a gap closure does not occur, and an avoided crossing is observed as the magnetic field is swept through the critical field. We attribute this anticrossing to orbital parity and spin mixing of the N=0 levels. Concurrently, we observe no gap closure at the topological phase transition versus temperature suggesting that the anticrossing is a generic property of topological phase transitions.

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Structure Inversion Asymmetry and Rashba Effect in Quantum Confined Topological Crystalline Insulator Heterostructures

Rechciński

Galicka

Simma

et al. 2021

Adv Funct Materials

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Structure inversion asymmetry is an inherent feature of quantum confined heterostructures with non‐equivalent interfaces. It leads to a spin splitting of the electron states and strongly affects the electronic band structure. The effect is particularly large in topological insulators because the topological surface states are extremely sensitive to the interfaces. Here, the first experimental observation and theoretical explication of this effect are reported for topological crystalline insulator quantum wells made of Pb1−xSnxSe confined by Pb1−yEuySe barriers on one side and by vacuum on the other. This provides a well defined structure asymmetry controlled by the surface condition. The electronic structure is mapped out by angle‐resolved photoemission spectroscopy and tight binding calculations, evidencing that the spin splitting decisively depends on hybridization and, thus, quantum well width. Most importantly, the topological boundary states are not only split in energy but also separated in space—unlike conventional Rashba bands that are splitted only in momentum. The splitting can be strongly enhanced to very large values by control of the surface termination due to the charge imbalance at the polar quantum well surface. The findings thus, open up a wide parameter space for tuning of such systems for device applications.

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Magnetooptical determination of a topological index

Cited by 24 publications

References 67 publications

Negative Longitudinal Magnetoresistance from the Anomalous N=0 Landau Level in Topological Materials

Negative Longitudinal Magnetoresistance from the Anomalous N=0 Landau Level in Topological Materials

Avoided level crossing at the magnetic field induced topological phase transition due to spin-orbital mixing

Structure Inversion Asymmetry and Rashba Effect in Quantum Confined Topological Crystalline Insulator Heterostructures

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