Author(s):
The axion coupling in topological insulators (TI), which couples electric polarization (magnetization) with the magnetic (electric) field, is known to support a small-distance Casimir repulsion and a large-distance Casimir attraction with a zero-force stable equilibrium between TI plates. By enhan … [J. Appl. Phys. 113, 204302 (2013)] published Fri May 24, 2013.
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Author(s):Chang-Yu Hou, Kirill Shtengel, Gil Refael
We study the thermoelectric effect between a conducting lead and a Majorana
edge state. In the tunneling limit, we first use the Landuaer-B\” uttiker
formalism to derive the Mott formula relating the thermopower and the
differential conductance between a conducting lead and a superconductor. When
the tunneling takes place between a conducting lead and a Majorana edge state,
we show that a non-vanishing thermopower can exist. Combining measurements of
the differential conductance and the voltage difference induced by the
temperature difference between the conducting lead and the edge state, the Mott
formula provides a unique way to infer the temperature of the Majorana edge
state.
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Author(s):M. K. Tran, J. Levallois, P. Lerch, J. Teyssier, A. B. Kuzmenko, G. Autès, O. V. Yazyev, A. Ubaldini, E. Giannini, D. van der Marel, A. Akrap
BiTeI is a giant Rashba spin splitting system, in which a non-centro
symmetric topological phase has recently been suggested to appear under high
pressure. We investigated the optical properties of this compound, reflectivity
and transmission, under pressures up to 15 GPa. The semiconducting gap
collapses above p~9 GPa and does not reopen up to at least 15 GPa. The plasma
edge, associated with intrinsically doped charge carriers, is smeared out
through a phase transition at 9 GPa. Using high pressure Raman spectroscopy, we
follow the vibrational modes of BiTeI and show that a structural transition
occurs at 9 GPa. The closing of the band gap is caused by a change of symmetry,
which possibly precludes the high-pressure topological phase.
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Author(s):Sheng-Nan Ji, Bang-Fen Zhu, Ren-Bao Liu
Odd numbers of Dirac points and helical states can exist at edges (surfaces)
of two-dimensional (three-dimensional) topological insulators. In the bulk of a
one-dimensional lattice (not an edge) with time reversal symmetry, however, a
no-go theorem forbids the existence of an odd number of Dirac points or helical
states. Introducing a magnetic field can violate the time reversal condition
but would usually lift the degeneracy at the Dirac points. We find that a
spatially periodic magnetic field with zero mean value can induce a single
Dirac point in a one-dimensional system with spin-orbit coupling. A wealth of
new physics may emerge due to the existence of a single Dirac point and helical
states in the bulk of a one-dimensional lattice (rather than edge states). A
series of quantized numbers emerge due to the non-trivial topology of the 1D
helical states, including the doubled period of helical Bloch oscillations,
quantized conductance near the Dirac point, and 1/2-charge solitons at mass
kinks. Such a system can be realized in one-dimensional semiconductor systems
or in optical traps of atoms.
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Author(s): Peng Ye and Xiao-Gang Wen
We propose a general approach to construct symmetry protected topological (SPT) states (i.e., the short-range entangled states with symmetry) in 2D spin/boson systems on lattice. In our approach, we fractionalize spins/bosons into different fermions, which occupy nontrivial Chern bands. After the Gu…
[Phys. Rev. B 87, 195128] Published Thu May 23, 2013
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Author(s): Hongbin Zhang, Frank Freimuth, Gustav Bihlmayer, Marjana Ležaić, Stefan Blügel, and Yuriy Mokrousov
Combining tight-binding models and first-principles calculations, we investigate the quantum anomalous Hall (QAH) effect induced by intrinsic spin-orbit coupling (SOC) in buckled honeycomb lattice with sp orbitals in an external exchange field. Detailed analysis reveals that nontrivial topological p…
[Phys. Rev. B 87, 205132] Published Thu May 23, 2013
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Author(s): Takeshi Kondo, Y. Nakashima, Y. Ota, Y. Ishida, W. Malaeb, K. Okazaki, S. Shin, M. Kriener, Satoshi Sasaki, Kouji Segawa, and Yoichi Ando
Quasiparticle dynamics on the topological surface state of Bi2Se3, Bi2Te3, and superconducting CuxBi2Se3 are studied by 7 eV laser-based angle resolved photoemission spectroscopy. We find strong mode couplings in the Dirac-cone surface states at energies of ∼3 and ∼15–20 meV associated with an exce…
[Phys. Rev. Lett. 110, 217601] Published Thu May 23, 2013
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Author(s):
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Quest for Quantum Computing Advanced
Science Daily (press release) “But on the surface of a topological insulator spinning electrons are protected from disruption by quantum effects, called time-reversal symmetry protection. This makes the materials attractive for spin-related electronics, or 'spintronics', which … and more » |
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Author(s):
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Quest for Quantum Computing Advanced
Science Daily (press release) “But on the surface of a topological insulator spinning electrons are protected from disruption by quantum effects, called time-reversal symmetry protection. This makes the materials attractive for spin-related electronics, or 'spintronics', which … and more » |
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Author(s):
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Researchers forward quest for quantum computing
Phys.Org "But on the surface of a topological insulator spinning electrons are protected from disruption by quantum effects, called time-reversal symmetry protection. This makes the materials attractive for spin-related electronics, or 'spintronics', which … |
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Author(s):Jie Ren, N. A. Sinitsyn
We show that distinct topological phases of the band structure of a
non-Hermitian Hamiltonian can be classified with elements of the braid group.
As the proof of principle, we consider the non-Hermitian evolution of the
statistics of nonequilibrium stochastic currents. We show that topologically
nontrivial phases have detectable properties, including the emergence of
decaying oscillations of parity and state probabilities, and discontinuities in
the steady state statistics of currents.
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Author(s):Peng Ye, Xiao-Gang Wen
We propose a general approach to construct symmetry protected topological
(SPT) states i.e the short-range entangled states with symmetry) in 2D
spin/boson systems on lattice. In our approach, we fractionalize spins/bosons
into different fermions, which occupy nontrivial Chern bands. After the
Gutzwiller projection of the free fermion state obtained by filling the Chern
bands, we can obtain SPT states on lattice. In particular, we constructed a
U(1) SPT state of a spin-1 model, a SO(3) SPT state of a boson system with
spin-1 bosons and spinless bosons, and a SU(2) SPT state of a spin-1/2 boson
system. By applying the “spin gauge field” which directly couples to the spin
density and spin current of $S^z$ components, we also calculate the quantum
spin Hall conductance in each SPT state. The projective ground states can be
further studied numerically in the future by variational Monte Carlo etc.
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Author(s):Anna Keselman, Liang Fu, Ady Stern, Erez Berg
We propose a setup to realize time-reversal invariant topological
superconductors in quantum wires, proximity coupled to conventional
superconductors. We consider a model of quantum wire with strong spin-orbit
coupling and proximity coupling to two s-wave superconductors. When the
relative phase between the two superconductors is $\phi=\pi$ a Kramers’ pair of
Majorana zero modes appears at each edge of the wire. We study the robustness
of the phase in presence of both time-reversal invariant and time-reversal
breaking perturbations. In addition, we show that the system forms a natural
realization of a fermion parity pump, switching the local fermion parity of
both edges when the relative phase between the superconductors is changed
adiabatically by $2\pi$.
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Author(s):Anna Keselman, Liang Fu, Ady Stern, Erez Berg
We propose a setup to realize time-reversal invariant topological
superconductors in quantum wires, proximity coupled to conventional
superconductors. We consider a model of quantum wire with strong spin-orbit
coupling and proximity coupling to two s-wave superconductors. When the
relative phase between the two superconductors is $\phi=\pi$ a Kramers’ pair of
Majorana zero modes appears at each edge of the wire. We study the robustness
of the phase in presence of both time-reversal invariant and time-reversal
breaking perturbations. In addition, we show that the system forms a natural
realization of a fermion parity pump, switching the local fermion parity of
both edges when the relative phase between the superconductors is changed
adiabatically by $2\pi$.
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Author(s):Z.-H. Zhu, C.N. Veenstra, G. Levy, A. Ubaldini, P. Syers, N.P. Butch, J. Paglione, M.W. Haverkort, I.S. Elfimov, A. Damascelli
We study Bi2Se3 by polarization-dependent angle-resolved photoemission
spectroscopy (ARPES) and density-functional theory slab calculations. We find
that the surface state Dirac fermions are characterized by a layer-dependent
entangled spin-orbital texture, which becomes apparent through quantum
interference effects. This explains the discrepancy between the spin
polarization from spin-resovled ARPES – ranging from 20 to 85% – and the 100%
value assumed in phenomenological models. It also suggests a way to probe the
intrinsic spin texture of topological insulators, and to continuously
manipulate the spin polarization of photoelectrons and photocurrents all the
way from 0 to +/-100% by an appropriate choice of photon energy, linear
polarization, and angle of incidence.
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Author(s):Yi Li, Congjun Wu
We study the 3D topological insulators in the continuum by coupling spin-1/2
fermions to the Aharonov-Casher SU(2) gauge field. They exhibit flat Landau
levels in which orbital angular momentum and spin are coupled with a fixed
helicity. The 3D lowest Landau level wavefunctions exhibit the quaternionic
analyticity as a generalization of the complex analyticity of the 2D case. Each
Landau level contributes one branch of gapless helical Dirac modes to the
surface spectra, whose topological properties belong to the Z2-class. The flat
Landau levels can be generalized to an arbitrary dimension. Interaction effects
and experimental realizations are also studied.
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Author(s):Gerson J. Ferreira, Daniel Loss
We explore time-reversal-symmetry-breaking potentials to confine the surface
states of 3D topological insulators into quantum wires and quantum dots. A
magnetic domain wall on a ferromagnet insulator cap layer provides interfacial
states predicted to show the quantum anomalous Hall effect (QAHE). Here we show
that confinement can also occur at magnetic domain heterostructures, with
states extended in the inner domain, as well as interfacial QAHE states at the
surrounding domain walls. The proposed geometry allows the isolation of the
wire and dot from spurious circumventing surface states. For the quantum dots,
we find that highly spin-polarized quantized QAHE states at the dot edge
constitute a promising candidate for quantum computing qubits.
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Author(s): M. R. Scholz, J. Sánchez-Barriga, J. Braun, D. Marchenko, A. Varykhalov, M. Lindroos, Yung Jui Wang, Hsin Lin, A. Bansil, J. Minár, H. Ebert, A. Volykhov, L. V. Yashina, and O. Rader
The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpre…
[Phys. Rev. Lett. 110, 216801] Published Wed May 22, 2013
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Author(s): M. R. Scholz, J. Sánchez-Barriga, J. Braun, D. Marchenko, A. Varykhalov, M. Lindroos, Yung Jui Wang, Hsin Lin, A. Bansil, J. Minár, H. Ebert, A. Volykhov, L. V. Yashina, and O. Rader
The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpre…
[Phys. Rev. Lett. 110, 216801] Published Wed May 22, 2013
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Author(s): B. Béri
We present a powerful and general approach to describe the coupling of Majorana fermions to external leads, of interacting or noninteracting electrons. Our picture has the Klein factors of bosonization appearing as extra Majorana fermions hybridizing with the physical ones. We demonstrate the power …
[Phys. Rev. Lett. 110, 216803] Published Wed May 22, 2013
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