Author(s):

This data comes from pipes.yahoo.com but the Pipe does not exist or has been deleted.

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Author(s):

The stability of the topological order phase induced by the $Z_3$ Kitaev
model, which is a candidate for fault-tolerant quantum computation, against the
local order phase induced by the 3-State Potts model is studied. We show that
the low energy sector of the Kitaev-Potts model is mapped to the Potts model in
the presence of transverse magnetic field. Our study relies on two high-order
series expansion based on continuous unitary transformations in the limits of
small- and large-Potts couplings as well as mean-field approximation. Our
analysis reveals that the topological phase of the $Z_3$ Kitaev model breaks
down to the Potts model through a first order phase transition. We capture the
phase transition by analysis of the ground state energy, one-quasiparticle gap
and geometric measure of entanglement.

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Author(s):

Recently, the search for Majorana fermions has become one of the most
prominent subjects in condensed matter physics. This search involves
explorations of new materials and hence offers interesting opportunities for
chemistry. Theoretically, Majorana fermions may reside in various types of
topological superconductor materials, and superconducting Sn_{1-x}In_{x}Te,
which is a doped topological crystalline insulator, is one of the promising
candidates to harbor Majorana fermions. Here, we report the first successful
growth of superconducting Sn_{1-x}In_{x}Te nanoplates on Si substrates by a
simple vapor transport method without employing any catalyst. We observed
robust superconducting transitions in those nanoplates after device fabrication
and found that the relation between the critical temperature and the carrier
density is consistent with that of bulk single crystals, suggesting that the
superconducting properties of the nanoplate devices are essentially the same as
those of bulk crystals. With the help of nanofabrication, those nanoplates
would prove useful for elucidating the potentially topological nature of
superconductivity in Sn_{1-x}In_{x}Te to harbor Majorana fermions and thereby
contribute to the future quantum technologies.

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Author(s):

Here we provide a picture of transport in quantum well heterostructures with
a periodic driving field in terms of a probabilistic occupation of the
topologically protected edge states in the system. This is done by generalizing
methods from the field of photon assisted tunneling. We show that the time
dependent field {\it dresses} the underlying Hamiltonian of the heterostructure
and splits the system into side-bands. Each of these sidebands is occupied with
a certain probability which depends on the drive frequency and strength. This
leads to a reduction in the topological transport signatures of the system
because of the probability to absorb/emit a photon. Therefore when the voltage
is tuned to the bulk gap the conductance is smaller then the expected $2e^2/h$.
We refer to this as photon inhibited topological transport. Nevertheless, the
edge modes reveal their topological origin in the robustness of the edge
conductance to disorder and changes in model parameters. In this work the
analogy with photon assisted tunneling allows us to interpret the calculated
conductivity and explain the sum rule observed by previous authors

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Author(s):

Chains of magnetic atoms placed on the surface of an s-wave superconductor
with large spin-orbit coupling provide a promising platform for the realization
of topological superconducting states characterized by the presence of Majorana
zero-energy modes. In this work we study the properties of the one-dimensional
chain of Yu-Shiba-Rusinov states induced by magnetic impurities using a
realistic model for the magnetic atoms that include the presence of multiple
scattering channels. These channels are mixed by the spin-orbit coupling and,
via the hybridization of the Yu-Shiba-Rusinov states at different sites of the
chain, result in a multi-band structure for the chain. We obtain the
topological phase diagram for such band structure. We identify the parameter
regimes for which the different bands lead to a topological phase and show that
the inclusion of higher bands can greatly enlarge the phase space for the
realization of topological states.

link to article (opens in new tab)

 

Author(s):

Recently, the search for Majorana fermions (MFs) has become one of the most
important and exciting issues in condensed matter physics since such an exotic
quasiparticle is expected to potentially give rise to unprecedented quantum
phenomena whose functional properties will be used to develop future quantum
technology. Theoretically, the MFs may reside in various types of topological
superconductor materials that is characterized by the topologically protected
gapless surface state which are essentially an Andreev bound state.
Superconducting doped topological insulators and topological crystalline
insulators are promising candidates to harbor the MFs. In this review, we
discuss recent progress and understanding on the research of MFs based on
time-reversal-invariant superconducting topological materials to deepen our
understanding and have a better outlook on both the search for and realization
of MFs in these systems. We also discuss some advantages of these bulk systems
to realize MFs including remarkable superconducting robustness against
nonmagnetic impurities.

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Author(s):

We have synthesized a new ferromagnetic topological insulator by doping Cr to
the ternary topological-insulator material TlSbTe2. Single crystals of
Tl_{1-x}Cr_{x}SbTe2 were grown by a melting method and it was found that Cr can
be incorporated into the TlSbTe2 matrix only within the solubility limit of
about 1%. The Curie temperature \theta_c was found to increase with the Cr
content but remained relatively low, with the maximum value of about 4 K. The
easy axis was identified to be the c-axis and the saturation moment was 2.8
\mu_B (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples
studied showed metallic behavior with p-type carriers. Shubnikov-de Hass (SdH)
oscillations were observed in samples with the Cr-doping level of up to 0.76%.
We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no
ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility
limit of Cr which turned out to be also about 1%.

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Author(s):

We report the electric transport study of the three-dimensional topological
insulator TlBiSe$_2$. We applied a newly developed analysis procedure and
precisely determined two-carrier transport properties. Magnetotransport
properties revealed a multicarrier conduction of high- and low-mobility
electrons in the bulk, which was in qualitative agreement with angle-resolved
photoemission results~[K. Kuroda $et~al.$, Phys. Rev. Lett. $\bm{105}$, 146801
(2010)]. The temperature dependence of the Hall mobility was explained well
with the conventional Bloch-Gr{\”u}neisen formula and yielded the Debye
temperature $\varTheta_{\rm{D}}=113 \pm 14$~K. The results indicate that the
scattering of bulk electrons is dominated by acoustic phonons.

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Author(s):

Floquet topological insulators are systems in which the topology emerges out
of equilibrium when a time periodic perturbation is applied. In these systems
one can define quasi-energy states which replace the quilibrium stationary
states. The system exhibits its non-trivial topology by developing edge
localized quasi-energy states which lie in a gap of the quasi energy spectrum.
These states represent a non-equilibrium analogue of the topologically
protected edge-states in equilibrium topological insulators. In equilibrium
these edge-states lead to very specific transport properties, in particular the
two-terminal conductivity of these systems is $2e^2/h$. Here we explore the
transport properties of the edge-states in a Floquet topological insulator. In
stark contrast to the equilibrium result, we find that the two terminal
conductivity of these edge states is significantly different from $2e^2/h$.
This fact notwithstanding, we find that for certain external potential
strengths the conductivity is smaller than $2e^2/h$ and robust to the effects
of disorder and smooth changes to the Hamiltonian’s parameters. This robustness
is reminiscent of the robustness found in equilibrium topological insulators.
We provide an intuitive understanding of the reduction of the conductivity in
terms of scattering by photons. This leads us to consider a previously proposed
Floquet sum rule which recovers the equilibrium value of $2e^2/h$ for the
conductivity when edge states are present. We show that this sum rule holds in
our system using both numerical and analytic techniques.

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Author(s):

Authors: Razieh Mohseninia, Saeed S. Jahromi, Laleh Memarzadeh, Vahid Karimipour

The stability of the topological order phase induced by the $Z_3$ Kitaev
model, which is a candidate for fault-tolerant quantum computation, against the
local order phase induced by the 3-State Potts model is studied. We show that
the low energy sector of the Kitaev-Potts model is mapped to the Potts model in
the presence of transverse magnetic field. Our study relies on two high-order
series expansion based on continuous unitary transformations in the limits of
small- and large-Potts couplings as well as mean-field approximation. Our
analysis reveals that the topological phase of the $Z_3$ Kitaev model breaks
down to the Potts model through a first order phase transition. We capture the
phase transition by analysis of the ground state energy, one-quasiparticle gap
and geometric measure of entanglement.

link to article (opens in new tab)

 

Author(s):

Authors: Satoshi Sasaki, Yoichi Ando

Recently, the search for Majorana fermions has become one of the most
prominent subjects in condensed matter physics. This search involves
explorations of new materials and hence offers interesting opportunities for
chemistry. Theoretically, Majorana fermions may reside in various types of
topological superconductor materials, and superconducting Sn_{1-x}In_{x}Te,
which is a doped topological crystalline insulator, is one of the promising
candidates to harbor Majorana fermions. Here, we report the first successful
growth of superconducting Sn_{1-x}In_{x}Te nanoplates on Si substrates by a
simple vapor transport method without employing any catalyst. We observed
robust superconducting transitions in those nanoplates after device fabrication
and found that the relation between the critical temperature and the carrier
density is consistent with that of bulk single crystals, suggesting that the
superconducting properties of the nanoplate devices are essentially the same as
those of bulk crystals. With the help of nanofabrication, those nanoplates
would prove useful for elucidating the potentially topological nature of
superconductivity in Sn_{1-x}In_{x}Te to harbor Majorana fermions and thereby
contribute to the future quantum technologies.

link to article (opens in new tab)

 

Author(s):

Authors: Aaron Farrell, T. Pereg-Barnea

Here we provide a picture of transport in quantum well heterostructures with
a periodic driving field in terms of a probabilistic occupation of the
topologically protected edge states in the system. This is done by generalizing
methods from the field of photon assisted tunneling. We show that the time
dependent field {\it dresses} the underlying Hamiltonian of the heterostructure
and splits the system into side-bands. Each of these sidebands is occupied with
a certain probability which depends on the drive frequency and strength. This
leads to a reduction in the topological transport signatures of the system
because of the probability to absorb/emit a photon. Therefore when the voltage
is tuned to the bulk gap the conductance is smaller then the expected $2e^2/h$.
We refer to this as photon inhibited topological transport. Nevertheless, the
edge modes reveal their topological origin in the robustness of the edge
conductance to disorder and changes in model parameters. In this work the
analogy with photon assisted tunneling allows us to interpret the calculated
conductivity and explain the sum rule observed by previous authors

link to article (opens in new tab)

 

Author(s):

Authors: Junhua Zhang, Younghyun Kim, E. Rossi, Roman M. Lutchyn

Chains of magnetic atoms placed on the surface of an s-wave superconductor
with large spin-orbit coupling provide a promising platform for the realization
of topological superconducting states characterized by the presence of Majorana
zero-energy modes. In this work we study the properties of the one-dimensional
chain of Yu-Shiba-Rusinov states induced by magnetic impurities using a
realistic model for the magnetic atoms that include the presence of multiple
scattering channels. These channels are mixed by the spin-orbit coupling and,
via the hybridization of the Yu-Shiba-Rusinov states at different sites of the
chain, result in a multi-band structure for the chain. We obtain the
topological phase diagram for such band structure. We identify the parameter
regimes for which the different bands lead to a topological phase and show that
the inclusion of higher bands can greatly enlarge the phase space for the
realization of topological states.

link to article (opens in new tab)

 

Author(s):

Authors: Satoshi Sasaki, Takeshi Mizushima

Recently, the search for Majorana fermions (MFs) has become one of the most
important and exciting issues in condensed matter physics since such an exotic
quasiparticle is expected to potentially give rise to unprecedented quantum
phenomena whose functional properties will be used to develop future quantum
technology. Theoretically, the MFs may reside in various types of topological
superconductor materials that is characterized by the topologically protected
gapless surface state which are essentially an Andreev bound state.
Superconducting doped topological insulators and topological crystalline
insulators are promising candidates to harbor the MFs. In this review, we
discuss recent progress and understanding on the research of MFs based on
time-reversal-invariant superconducting topological materials to deepen our
understanding and have a better outlook on both the search for and realization
of MFs in these systems. We also discuss some advantages of these bulk systems
to realize MFs including remarkable superconducting robustness against
nonmagnetic impurities.

link to article (opens in new tab)

 

Author(s):

Authors: Zhiwei Wang, Kouji Segawa, Satoshi Sasaki, A. A. Taskin, Yoichi Ando

We have synthesized a new ferromagnetic topological insulator by doping Cr to
the ternary topological-insulator material TlSbTe2. Single crystals of
Tl_{1-x}Cr_{x}SbTe2 were grown by a melting method and it was found that Cr can
be incorporated into the TlSbTe2 matrix only within the solubility limit of
about 1%. The Curie temperature \theta_c was found to increase with the Cr
content but remained relatively low, with the maximum value of about 4 K. The
easy axis was identified to be the c-axis and the saturation moment was 2.8
\mu_B (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples
studied showed metallic behavior with p-type carriers. Shubnikov-de Hass (SdH)
oscillations were observed in samples with the Cr-doping level of up to 0.76%.
We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no
ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility
limit of Cr which turned out to be also about 1%.

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Author(s):

Authors: G. Eguchi, K. Kuroda, K. Shirai, Y. Ando, T. Shinjo, A. Kimura, M. Shiraishi

We report the electric transport study of the three-dimensional topological
insulator TlBiSe$_2$. We applied a newly developed analysis procedure and
precisely determined two-carrier transport properties. Magnetotransport
properties revealed a multicarrier conduction of high- and low-mobility
electrons in the bulk, which was in qualitative agreement with angle-resolved
photoemission results~[K. Kuroda $et~al.$, Phys. Rev. Lett. $\bm{105}$, 146801
(2010)]. The temperature dependence of the Hall mobility was explained well
with the conventional Bloch-Gr{\”u}neisen formula and yielded the Debye
temperature $\varTheta_{\rm{D}}=113 \pm 14$~K. The results indicate that the
scattering of bulk electrons is dominated by acoustic phonons.

link to article (opens in new tab)

 

Author(s):

Authors: Aaron Farrell, T. Pereg-Barnea

Floquet topological insulators are systems in which the topology emerges out
of equilibrium when a time periodic perturbation is applied. In these systems
one can define quasi-energy states which replace the quilibrium stationary
states. The system exhibits its non-trivial topology by developing edge
localized quasi-energy states which lie in a gap of the quasi energy spectrum.
These states represent a non-equilibrium analogue of the topologically
protected edge-states in equilibrium topological insulators. In equilibrium
these edge-states lead to very specific transport properties, in particular the
two-terminal conductivity of these systems is $2e^2/h$. Here we explore the
transport properties of the edge-states in a Floquet topological insulator. In
stark contrast to the equilibrium result, we find that the two terminal
conductivity of these edge states is significantly different from $2e^2/h$.
This fact notwithstanding, we find that for certain external potential
strengths the conductivity is smaller than $2e^2/h$ and robust to the effects
of disorder and smooth changes to the Hamiltonian’s parameters. This robustness
is reminiscent of the robustness found in equilibrium topological insulators.
We provide an intuitive understanding of the reduction of the conductivity in
terms of scattering by photons. This leads us to consider a previously proposed
Floquet sum rule which recovers the equilibrium value of $2e^2/h$ for the
conductivity when edge states are present. We show that this sum rule holds in
our system using both numerical and analytic techniques.

link to article (opens in new tab)

 

Author(s):S E Harrison, L J Collins-McIntyre, S-L Zhang, A A Baker, A I Figueroa, A J Kellock, A Pushp, S S P Parkin, J S Harris, G van der Laan and T Hesjedal

Breaking the time-reversal symmetry (TRS) in topological insulators (TIs) through ferromagnetic
doping is an essential prerequisite for unlocking novel physical phenomena and exploring potential
device applications. Here, we report the successful growth of high-quality (Dy x Bi 1− x ) 2 Te 3
thin films with Dy concentrations up to x = 0.355 by molecular beam epitaxy. Bulk-sensitive
magnetisation studies using superconducting quantum interference device magnetometry find
paramagnetic behaviour down to 2 K for the entire doping series. The effective magnetic moment, μ
eff , is strongly doping concentration-dependent and reduces from∼12.6 μ B Dy −1 for x = 0.023 to
∼4.3 μ B Dy −1 for x = 0.355. X-ray absorption spectra and x-ray magnetic circular dichroism (XMCD)
at the Dy M 4,5 edge are employed to provide a deeper insight in…

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Author(s):Andreas P Schnyder and Philip M R Brydon

Topological superconductors have become a subject of intense research due to their potential use for
technical applications in device fabrication and quantum information. Besides fully gapped
superconductors, unconventional superconductors with point or line nodes in their order parameter
can also exhibit nontrivial topological characteristics. This article reviews recent progress in the
theoretical understanding of nodal topological superconductors, with a focus on Weyl and
noncentrosymmetric superconductors and their protected surface states. Using selected examples, we
review the bulk topological properties of these systems, study different types of topological
surface states, and examine their unusual properties. Furthermore, we survey some candidate
materials for topological superconductivity and discuss different experimental signatures of
topological surface states.

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Author(s):


ExtremeTech
Quantum signatures of electronic transport in graphene discovered
ExtremeTech
In contrast to the unidirectional current flow of electrons in a regular metal, a material that behaves as a 'topological insulator' would be useful in several spintronic applications. If all that terminology isn't enough physics for you, there's more

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