Point-contact spectroscopy of Cu<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>0.2</mml:mn></mml:mrow></mml:msub></mml:math>Bi<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>Se<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>3</mml:mn></mml:msub></mml:math>single crystals

Kirzhner, T.; Lahoud, E.; Chaska, K. B.; Salman, Z.; Kanigel, Amit

doi:10.1103/physrevb.86.064517

Cited by 108 publications

(133 citation statements)

References 13 publications

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“…255) It should be mentioned that the experimental situation for Cu x Bi 2 Se 3 is currently rather controversial. While some of the follow-up point-contact measurements 276,277) supported unconventional superconductivity originally reported by Sasaki et al, 255) a recent STS study 278) reported spectra that are consistent with conventional BCS superconductivity. This confusion essentially stems from the fact that available samples of superconducting Cu x Bi 2 Se 3 are inhomogeneous 279) and the superconducting volume fraction never exceeds 70%; 272,279) furthermore, the author's group has found that one of the impurity phases is CuSe 2 , which is a conventional superconductor with the transition temperature of 2.4 K. Obviously, improvements in the sample quality are desirable for local-probe measurements.…”

Section: Majorana Fermionsmentioning

confidence: 92%

“…In this regard, the superconductor Cu x Bi 2 Se 3 , 270) which is a doped 3D TI, has attracted a lot of attention. 255,269,[271][272][273][274][275][276][277][278][279][280][281] In fact, Cu x Bi 2 Se 3 was recently found to present signatures of unconventional superconductivity in its point-contact spectra, 255) and an unconventional superconductivity in this material is necessarily topological for symmetry reasons. 255) It should be mentioned that the experimental situation for Cu x Bi 2 Se 3 is currently rather controversial.…”

Section: Majorana Fermionsmentioning

confidence: 99%

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Topological Insulator Materials

2013

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Topological insulators represent a new quantum state of matter which is characterized by peculiar edge or surface states that show up due to a topological character of the bulk wave functions. This review presents a pedagogical account on topological insulator materials with an emphasis on basic theory and materials properties. After presenting a historical perspective and basic theories of topological insulators, it discusses all the topological insulator materials discovered as of May 2013, with some illustrative descriptions of the developments in materials discoveries in which the author was involved. A summary is given for possible ways to confirm the topological nature in a candidate material. Various synthesis techniques as well as the defect chemistry that are important for realizing bulk-insulating samples are discussed. Characteristic properties of topological insulators are discussed with an emphasis on transport properties. In particular, the Dirac fermion physics and the resulting peculiar quantum oscillation patterns are discussed in detail. It is emphasized that proper analyses of quantum oscillations make it possible to unambiguously identify surface Dirac fermions through transport measurements. The prospects of topological insulator materials for elucidating novel quantum phenomena that await discovery conclude the review.

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Section: Majorana Fermionsmentioning

confidence: 92%

Section: Majorana Fermionsmentioning

confidence: 99%

Topological Insulator Materials

2013

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“…[17][18][19]. Among these studies, although the gapless bound states on surfaces at low temperatures are actively studied [9,11,[20][21][22], observing an intrinsic behavior via bulk measurements is rarely argued. In addition, the setups of surface measurements would be sensitively affected by the characteristics of the interfaces between materials and probes.…”

mentioning

confidence: 99%

“…A classification study with different kinds of spatial dimension and symmetry [6] indicates the presence of a topological superconductivity in three-dimensional (3D) time-reversal-invariant systems. Superconducting topological insulators, such as Cu x Bi 2 Se 3 [7][8][9][10][11] and Sn 1−x In x Te [12] are the candidates of the bulk 3D topological superconductors. Their topology is argued by Z 2 invariants [1,13].…”

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confidence: 99%

Inverse coherence effects in nuclear magnetic relaxation rates as a sign of topological superconductivity

2015

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We reveal that three-dimensional multi-orbital topological superconductivity can be identified by a bulk measurement, i.e., the temperature dependence of nuclear magnetic relaxation (NMR) rates. Below a critical temperature Tc, the NMR rate in the topological state exhibits an anti-peak profile, which is opposite to the conventional s-wave state. This inversion coherence effect comes from a twist of order parameters with respect to orbital and spin degrees of freedom. Our self-consistent calculations in the model for CuxBi2Se3 prove that the inverse coherence effect appears as a concave temperature dependence of the NMR rates. We propose that a time-reversal-invariant orbitalsinglet spin-triplet topological superconductivity is characterized by the temperature dependence of the NMR rate. [17][18][19]. Among these studies, although the gapless bound states on surfaces at low temperatures are actively studied [9,11,[20][21][22], observing an intrinsic behavior via bulk measurements is rarely argued. In addition, the setups of surface measurements would be sensitively affected by the characteristics of the interfaces between materials and probes. Thus, a bulk measurement sensitive to topological characters is important for supporting results in surface measurements and revealing the properties of Cooper-pair condensations.A key quantity of connecting topological characters with bulk measurements is a correlation function. Current-current correlation functions, for example, lead to the quantized conductance in integer quantum Hall effects [5]. Spin-spin correlation functions are essential for superconductivity since these quantities well reflect the spin-state properties of Cooper pairs. Nuclear magnetic relaxation (NMR) rates (T −1 1 ) are directly related to the spin-spin correlation functions. Therefore, it is interesting and important question to ask whether NMR rates contain any characteristic information on topological superconductivity. Specifically, the coherence effect is notable. The NMR rate in the presence of a spin-singlet swave superconducting state is enhanced just below a critical temperature T c , owing to the coherence factor [23]. This coherence peak (Hebel-Slichter peak) [24,25] comes from the formation of superconducting gaps. The absence of the peak and a power-law behavior of T −1 1 at low temperatures indicate the occurrence of unconventional states [26][27][28].In this paper we claim that the bulk measurements of NMR rates detect a 3D odd-parity fully-gapped topological superconducting state in time-reversal-invariant multi-orbital systems. An inverse coherence effect just below T c is the signature of this odd-parity state; the coherence factor contributes to the NMR rates with an opposite sign to that of the conventional s-wave states. Our self-consistent calculations in the model of Cu x Bi 2 Se 3 [13] show that this sign reversal leads to an anti-peak behavior of the NMR rates below T c . Using the Fermion anticommutation property, we show that the odd parity allows a twist of a gap fun...

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“…13,14) The ZBCP is known to be observed in not only unconventional non-s-wave superconductors but also topological superconductors. [13][14][15][16][17][18][19][20] The latter typical example is the chiral p-wave topological superconductor such as Sr 2 RuO 4 , in which gapless quasi-particles assigned as Majorana fermions induce ZBCP's. [21][22][23] Accordingly, ZBCP's observed in Cu x Bi 2 Se 3 (T c ∼ 3K) and Sn 1−x In x Te (T c ∼ 1.2K) can be also regarded to be originated from their non-trivial topology.…”

Section: Introductionmentioning

confidence: 99%

Spin-Polarized Majorana Bound States inside a Vortex Core in Topological Superconductors

2014

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We reveal that Majorana bound states inside the vortex core in an odd-parity topological superconductivity classified as "pseudo-scalar" type in the gap function are distinctly spin-polarized by solving the massive Dirac Bogoliubov-de Gennes (BdG) equation considering the spin-orbit coupling. This result is universal for "Dirac superconductivity" whose rotational degree of freedom is characterized by the total angular momentum J = S + L and in marked contrast to the spin-degeneracy of the core bound states as the consequence of the conventional BdG equation. The spin-polarized vortex core can be easily detected by spin-sensitive probes such as the neutron scattering and other measurements well above the first critical magnetic field H c1 .

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Point-contact spectroscopy of Cu0.2Bi2Se3single crystals

Cited by 108 publications

References 13 publications

Topological Insulator Materials

Topological Insulator Materials

Inverse coherence effects in nuclear magnetic relaxation rates as a sign of topological superconductivity

Spin-Polarized Majorana Bound States inside a Vortex Core in Topological Superconductors

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