scholarly journals Shadow surface states in topological Kondo insulators

2021 ◽  
Author(s):  
Areg Ghazaryan ◽  
Emilian Nica ◽  
Onur Erten ◽  
Pouyan Ghaemi
Keyword(s):  
High Frequency ◽  
Dirac Point ◽  
Chemical Potential ◽  
Surface States ◽  
Support Surface ◽  
Finite Frequency ◽  
Fermi Surfaces ◽  
Quantum Oscillations ◽  
Kondo Insulators ◽  
Out Of Plane

Abstract The surface states of 3D topological insulators in general have negligible quantum oscillations when the chemical potential is tuned to the Dirac points. In contrast, we find that topological Kondo insulators can support surface states with an arbitrarily large Fermi surfaces when the chemical potential is pinned to the Dirac point. We illustrate that these Fermi surfaces give rise to finite-frequency quantum oscillations, which can become comparable to the extremal area of the unhybridized bulk bands. We show that this occurs when the crystal symmetry is lowered from cubic to tetragonal in a minimal two-orbital model. We label such surface modes as `shadow surface states'. Moreover, we show that the sufficient NNN out-of-plane hybridization leading to shadow surface states can be self-consistently stabilized for tetragonal topological Kondo insulators. Consequently, shadow surface states provide an important example of high-frequency quantum oscillations beyond the context of cubic topological Kondo insulators.

scholarly journals Are the surface Fermi arcs in Dirac semimetals topologically protected?

2016 ◽  
Vol 113 (31) ◽  
pp. 8648-8652 ◽  
Author(s):  
Mehdi Kargarian ◽  
Mohit Randeria ◽  
Yuan-Ming Lu
Keyword(s):  
Chemical Potential ◽  
Surface States ◽  
Quantum Oscillation ◽  
Band Model ◽  
Fermi Surfaces ◽  
Space Groups ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Fermi Arcs ◽  
Anomalous Surface ◽  
Dirac Semimetals

Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k=(0,0,±Q), where gapless states on the side surfaces are protected only near kz=0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.

Spin Ordering on the Surface of a Topological Insulator with Magnetic Ions

2012 ◽  
Vol 190 ◽  
pp. 494-497
Author(s):  
V.N. Men'shov ◽  
V.V. Tugushev ◽  
E.V. Chulkov
Keyword(s):  
Topological Insulator ◽  
Chemical Potential ◽  
Mean Field ◽  
Three Dimensional ◽  
Surface States ◽  
Dirac Fermions ◽  
Uniform Magnetization ◽  
Out Of Plane ◽  
Different Temperatures ◽  
Magnetic Ions

We study the effect of magnetic doping on appearance of ferromagnetic (FM) order on the surface of a three-dimensional topological insulator. Assuming the exchange coupling of the Dirac fermions with the dilute magnetic ions, we find that the system under consideration is unstable with respect to a spontaneous uniform magnetization along the out-of-plane direction. The appearance of the magnetization is accompanied by opening of a gap in the spectrum of surface states. In the framework of a mean-field approach, we analyze the possibility of the FM order on the magnetically doped surface of topological insulator at different temperatures and positions of the chemical potential.

scholarly journals Quantum confinement of the Dirac surface states in topological-insulator nanowires

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Felix Münning ◽  
Oliver Breunig ◽  
Henry F. Legg ◽  
Stefan Roitsch ◽  
Dingxun Fan ◽  
...  
Keyword(s):  
Quantum Computing ◽  
Quantum Confinement ◽  
Dirac Point ◽  
Direct Evidence ◽  
Chemical Potential ◽  
Three Dimensional ◽  
Surface States ◽  
Mesoscopic Physics ◽  
Zero Modes ◽  
Topological Quantum

AbstractThe non-trivial topology of three-dimensional topological insulators dictates the appearance of gapless Dirac surface states. Intriguingly, when made into a nanowire, quantum confinement leads to a peculiar gapped Dirac sub-band structure. This gap is useful for, e.g., future Majorana qubits based on TIs. Furthermore, these sub-bands can be manipulated by a magnetic flux and are an ideal platform for generating stable Majorana zero modes, playing a key role in topological quantum computing. However, direct evidence for the Dirac sub-bands in TI nanowires has not been reported so far. Here, using devices fabricated from thin bulk-insulating (Bi1−xSbx)2Te3 nanowires we show that non-equidistant resistance peaks, observed upon gate-tuning the chemical potential across the Dirac point, are the unique signatures of the quantized sub-bands. These TI nanowires open the way to address the topological mesoscopic physics, and eventually the Majorana physics when proximitized by an s-wave superconductor.

scholarly journals Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kyungchan Lee ◽  
Gunnar F. Lange ◽  
Lin-Lin Wang ◽  
Brinda Kuthanazhi ◽  
Thaís V. Trevisan ◽  
...  
Keyword(s):  
Time Reversal ◽  
Topological Insulators ◽  
Dirac Point ◽  
Saddle Points ◽  
Surface States ◽  
Van Hove Singularity ◽  
Space Group ◽  
Topological Materials ◽  
Topological Surface ◽  
Optimal Space

AbstractTime reversal symmetric (TRS) invariant topological insulators (TIs) fullfil a paradigmatic role in the field of topological materials, standing at the origin of its development. Apart from TRS protected strong TIs, it was realized early on that more confounding weak topological insulators (WTI) exist. WTIs depend on translational symmetry and exhibit topological surface states only in certain directions making it significantly more difficult to match the experimental success of strong TIs. We here report on the discovery of a WTI state in RhBi2 that belongs to the optimal space group P$$\bar{1}$$ 1 ¯ , which is the only space group where symmetry indicated eigenvalues enumerate all possible invariants due to absence of additional constraining crystalline symmetries. Our ARPES, DFT calculations, and effective model reveal topological surface states with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity (VHS) along the (100) direction close to the Fermi energy (EF). Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects.

scholarly journals Effective Hamiltonian for silicene under arbitrary strain from multi-orbital basis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhuo Bin Siu ◽  
Mansoor B. A. Jalil
Keyword(s):  
Tight Binding ◽  
Spin Torque ◽  
Spin Accumulation ◽  
Effective Hamiltonian ◽  
Fermi Surfaces ◽  
Orbital Basis ◽  
Lattice Symmetry ◽  
Out Of Plane ◽  
Coupling Parameters ◽  
Spin Orbit Interactions

AbstractA tight-binding (TB) Hamiltonian is derived for strained silicene from a multi-orbital basis. The derivation is based on the Slater–Koster coupling parameters between different orbitals across the silicene lattice and takes into account arbitrary distortion of the lattice under strain, as well as the first and second-order spin–orbit interactions (SOI). The breaking of the lattice symmetry reveals additional SOI terms which were previously neglected. As an exemplary application, we apply the linearized low-energy TB Hamiltonian to model the current-induced spin accumulation in strained silicene coupled to an in-plane magnetization. The interplay between symmetry-breaking and the additional SOI terms induces an out-of-plane spin accumulation. This spin accumulation remains unbalanced after summing over the Fermi surfaces of the occupied bands and the two valleys, and can thus be utilized for spin torque switching.

scholarly journals Layer- and gate-tunable spin-orbit coupling in a high-mobility few-layer semiconductor

2021 ◽  
Vol 7 (5) ◽  
pp. eabe2892
Author(s):  
Dmitry Shcherbakov ◽  
Petr Stepanov ◽  
Shahriar Memaran ◽  
Yaxian Wang ◽  
Yan Xin ◽  
...  
Keyword(s):  
Electric Field ◽  
High Mobility ◽  
Orbit Coupling ◽  
Spin Splitting ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Quantum Oscillations ◽  
Out Of Plane ◽  
Order Of Magnitude ◽  
Spin Degeneracy

Spin-orbit coupling (SOC) is a relativistic effect, where an electron moving in an electric field experiences an effective magnetic field in its rest frame. In crystals without inversion symmetry, it lifts the spin degeneracy and leads to many magnetic, spintronic, and topological phenomena and applications. In bulk materials, SOC strength is a constant. Here, we demonstrate SOC and intrinsic spin splitting in atomically thin InSe, which can be modified over a broad range. From quantum oscillations, we establish that the SOC parameter α is thickness dependent; it can be continuously modulated by an out-of-plane electric field, achieving intrinsic spin splitting tunable between 0 and 20 meV. Unexpectedly, α could be enhanced by an order of magnitude in some devices, suggesting that SOC can be further manipulated. Our work highlights the extraordinary tunability of SOC in 2D materials, which can be harnessed for in operando spintronic and topological devices and applications.

scholarly journals A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Chaowei Hu ◽  
Kyle N. Gordon ◽  
Pengfei Liu ◽  
Jinyu Liu ◽  
Xiaoqing Zhou ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Surface States ◽  
Magnetic Coupling ◽  
Anomalous Hall Effect ◽  
Saturation Field ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Ideal System ◽  
Out Of Plane ◽  
Weak Interlayer ◽  
Quantum Phenomena

AbstractMagnetic topological insulators (TI) provide an important material platform to explore quantum phenomena such as quantized anomalous Hall effect and Majorana modes, etc. Their successful material realization is thus essential for our fundamental understanding and potential technical revolutions. By realizing a bulk van der Waals material MnBi4Te7 with alternating septuple [MnBi2Te4] and quintuple [Bi2Te3] layers, we show that it is ferromagnetic in plane but antiferromagnetic along the c axis with an out-of-plane saturation field of ~0.22 T at 2 K. Our angle-resolved photoemission spectroscopy measurements and first-principles calculations further demonstrate that MnBi4Te7 is a Z2 antiferromagnetic TI with two types of surface states associated with the [MnBi2Te4] or [Bi2Te3] termination, respectively. Additionally, its superlattice nature may make various heterostructures of [MnBi2Te4] and [Bi2Te3] layers possible by exfoliation. Therefore, the low saturation field and the superlattice nature of MnBi4Te7 make it an ideal system to investigate rich emergent phenomena.

Magnetic Quantum Oscillations from Surface States of Bi Nanowires

2011 ◽  
Vol 1350 ◽  
Author(s):  
L. A. Konopko ◽  
T. E. Huber ◽  
A. A. Nikolaeva
Keyword(s):  
Single Crystal ◽  
Low Temperatures ◽  
Surface States ◽  
Charge Carriers ◽  
Quantum Oscillations ◽  
Wide Range ◽  
Spin Orbit Interactions ◽  
Conducting Tube ◽  
Magnetic Quantum Oscillations ◽  
Strong Spin

ABSTRACTIn this work, we report the results of studies of the transverse magnetoresistance (MR) of single-crystal Bi nanowires with diameter d<80 nm. The single-crystal nanowire samples were prepared by the Taylor-Ulitovsky technique. Due to the semimetal-to-semiconductor transformation and high density of surface states with strong spin-orbit interactions, the charge carriers are confined to the conducting tube made of surface states. The non monotonic changes of transverse MR that are equidistant in a direct magnetic field were observed at low temperatures in a wide range of magnetic fields up to 14 T. The period of oscillations depends on the wire diameter d as for the case of longitudinal MR. An interpretation of transverse MR oscillations is presented.

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