Band inversion and the topological phase transition in (Pb,Sn)Se

Wojek, Bastian M.; Dziawa, P.; Kowalski, B.J.; Szczerbakow, A.; Black‐Schaffer, Annica M.; Berntsen, Magnus H.; Balasubramanian, T.; Story, T.; Tjernberg, Oscar

doi:10.1103/physrevb.90.161202

Cited by 65 publications

(93 citation statements)

References 45 publications

(64 reference statements)

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“…We note that the temperature and composition dependent studies of Pb 1−x Sn x Se (with 0≤ x ≤ 0.37) have been discussed in Ref. 42 . Our goal here is to map out an entire topological phase diagram for Pb 1−x Sn x Se (0≤ x ≤ 1.0), and to study how the topological surface states arise and disappear as the system goes through various topological phase transitions.…”

Section: Resultsmentioning

confidence: 99%

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

Neupane

Sankar

et al. 2015

Phys. Rev. B

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We report the evolution of the surface electronic structure and surface material properties of a topological crystalline insulator (TCI) Pb1−xSnxSe as a function of various material parameters including composition x, temperature T and crystal structure. Our spectroscopic data demonstrate the electronic groundstate condition for the saddle point singularity, the tunability of surface chemical potential, and the surface states' response to circularly polarized light. Our results show that each material parameter can tune the system between trivial and topological phase in a distinct way unlike as seen in Bi2Se3 and related compounds, leading to a rich and unique topological phase diagram. Our systematic studies of the TCI Pb1−xSnxSe are valuable materials guide to realize new topological phenomena.

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Section: Resultsmentioning

confidence: 99%

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

Neupane

Sankar

et al. 2015

Phys. Rev. B

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“…A gapped state is observed in the ARPES dispersion and momentum distribution curves for x=0.10 ( Fig.1(d,e)) whereas for x=0.20 a gapless topological Dirac surface state is clearly resolved (Fig.1(f,g)), in agreement with previous ARPES studies. [27] [28]. This ties the occurrence of the NLMR to the topologically non-trivial regime in Pb1-xSnxSe.…”

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confidence: 99%

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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“…This can already be seen in the results of previous studies: electrostatic surface doping of (Pb,Sn)Se causes a rigid energy shift but has no effect on the valley splitting, 9,10 while increasing the band-inversion strength in the bulk by altering composition, temperature or strain increases the valley splitting . [21][22][23] The latter case can be interpreted as pushing the surface state wavefunction towards the strong potential gradient at the TCI-vacuum interface, thus making the effect of the phase difference more pronounced.In Fig.5a,b we sketch the situation for Pb 0.7 Sn 0.3 Se with a PbSe overlayer. Considering Equation 1 in the limit of a clean surface, the envelope function decays slowly into the Pb 0.7 Sn 0.3 Se but abruptly into the vacuum, since vacuum can be considered equivalent to a trivial insulator with infinite bandgap.…”

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Fragility of the Dirac Cone Splitting in Topological Crystalline Insulator Heterostructures

et al. 2017

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The 'double Dirac cone' 2D topological interface states found on the (001) faces of topological crystalline insulators such as Pb1−xSnxSe feature degeneracies located away from time reversal invariant momenta, and are a manifestation of both mirror symmetry protection and valley interactions. Similar shifted degeneracies in 1D interface states have been highlighted as a potential basis for a topological transistor, but realizing such a device will require a detailed understanding of the intervalley physics involved. In addition, the operation of this or similar devices outside of ultra-high vacuum will require encapsulation, and the consequences of this for the topological interface state must be understood. Here we address both topics for the case of 2D surface states using angle-resolved photoemission spectroscopy. We examine bulk Pb1−xSnxSe(001) crystals overgrown with PbSe, realizing trivial/topological heterostructures. We demonstrate that the valley interaction that splits the two Dirac cones at eachX is extremely sensitive to atomic-scale details of the surface, exhibiting non-monotonic changes as PbSe deposition proceeds. This includes an apparent total collapse of the splitting for sub-monolayer coverage, eliminating the Lifshitz transition. For a large overlayer thickness we observe quantized PbSe states, possibly reflecting a symmetry confinement mechanism at the buried topological interface.The recent experimental realization of three dimensional topological insulators has triggered an expansive program of research, driven largely by the accessibility and rich physics of the 2D electronic states hosted on their surfaces. 1-5 These states are often said to be protected, referencing two distinct concepts. Firstly, the electrical connection of a band-inverted and normal material is not possible without the existence of interface states that thread the bulk bandgap. Secondly, in many band-inverted materials some kind of symmetry exists that forbids hybridization between these cross-gap interface states, thereby ensuring that they remain metallic. These basic characteristics of topological interface states are dictated solely by considerations of symmetry and bulk bandstructure, and in the sense that these are not easily affected by perturbations at the surface, can be considered robust.However it does not follow that the interface states are immune to surface perturbations. For example, adsorption of non-magnetic impurities on the topological insulator Bi 2 Se 3 surface can dope the surface states. [6][7][8] Similarly, the topological crystalline insulator (TCI) Pb 1−x Sn x Se can be surface doped with Rb or Sn, 9,10 while lattice distortions that disrupt mirror symmetry open a bandgap. 11,12 For both classes of materials, the surface termination is predicted to play an important role in the topological band dispersions. [13][14][15][16] Details of the interface are also important in special cases where two bulk band inversions project to the same point in the surface Brillouin zone (Fig.1a), i.e...

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Band inversion and the topological phase transition in (Pb,Sn)Se

Cited by 65 publications

References 45 publications

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

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

Fragility of the Dirac Cone Splitting in Topological Crystalline Insulator Heterostructures

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