Multiple topological states in iron-based superconductors

Zhang, P.; Wang, Zhijun; Wu, Xianxin; Yaji, Koichiro; Ishida, Y.; Kohama, Yoshimitsu; Dai, Guangyang; Sun, Yue; Bareille, C.; Kuroda, Kenta; Kondo, Takeshi; Okazaki, Kozo; Kindo, Koichi; Wang, Xiancheng; Chen, Jin; Hu, Jiangping; Thomale, Ronny; Sumida, Kazuki; Wu, Shugang; Miyamoto, Koji; Okuda, Takashi; Ding, Hong; Gu, Genda; Tamegai, T.; Kawakami, Takuto; Sato, Masatoshi; Shin, Shik

doi:10.1038/s41567-018-0280-z

Cited by 241 publications

(248 citation statements)

References 60 publications

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“…Experimental relevance and summary.-Now we briefly discuss the experimental relevance for our proposal. QSHIs with large inverted gaps [44][45][46][47][48][49][50][51][52][53][54][55][71][72][73] in proximity to cuprate or iron-based superconductors [38][39][40][57][58][59][60][61] could provide promising platforms to detect our predictions. For concreteness, we take the inverted InAs/GaSb bilayer and WTe 2 monolayer to estimate µ c x(y) .…”

Section: Arxiv:190509308v1 [Cond-matsupr-con] 22 May 2019mentioning

confidence: 99%

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Detection of second-order topological superconductors by Josephson junctions

Zhang

Trauzettel

2020

Phys. Rev. Research

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We study Josephson junctions based on a second-order topological superconductor (SOTS) which is realized in a quantum spin Hall insulator with a large inverted gap in proximity to an unconventional superconductor. We find that tuning the chemical potential in the superconductor strongly modifies the pairing gap of the helical edge states and leads to topological phase transitions. As a result, the supercurrent in the junction is controllable and a 0-π transition is realized by tuning the chemical potentials in the superconducting leads. These striking features are stable in junctions with different sizes, doping in the normal region, and in the presence of disorder. We propose them as novel experimental signatures of SOTSs. Moreover, the 0-π transition can serve as a fully electric way to create or annihilate Majorana bound states in the junction without magnetic manipulation.Introduction.-The second-order topological superconductor (SOTS) is a novel topological phase of matter and features Majorana zero-dimensional (0D) corner or 1D hinge states which are two dimensions lower than the gapped bulk [1-12] and may provide stable qubits for topological quantum computation [13][14][15][16][17][18][19][20][21]. Recently, the SOTS has been discovered in a variety of realistic materials and triggered tremendous interest [3][4][5][6][7][8][9][10][22][23][24][25][26][27]. One way to mimic SOTSs in 2D is given by quantum spin Hall insulators (QSHIs) in proximity to unconventional superconductors with d x 2 −y 2 -wave or s ± -wave pairing order [3][4][5]. The proximity effect of unconventional superconductivity in 2D systems has also been intensively explored in theory [28][29][30][31][32][33][34][35][36][37] and experiment [38][39][40][41][42][43]. To date, however, the only way proposed to detect 2D SOTSs is a tunneling experiment without a concrete calculation of the observable signature. An alternative or complementary approach to probe SOTSs and manipulate the Majorana corner modes is thus desirable. In QSHIs, a finite doping is usually inevitable, and the chemical potential can be far away from the Dirac points. Therefore, it is interesting and relevant to explore the influence of the chemical potential in SOTSs.

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Section: Arxiv:190509308v1 [Cond-matsupr-con] 22 May 2019mentioning

confidence: 99%

“…When 0 |∆ 0 | < m 0 |∆ 2 |/2m x(y) , the system possesses a mixture of s-wave and d x 2 −y 2 -wave pairing. It can also describe effectively a QSHI with the band inversion at the X point [53][54][55] and s ± -wave pairing induced from an iron-based superconductor [57][58][59][60][61].…”

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confidence: 99%

Detection of second-order topological superconductors by Josephson junctions

Zhang

Trauzettel

2020

Phys. Rev. Research

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“…Fe 1+y Te 1−x Se x is unique in their structural simplicity, consisting of only FeTe/Se layers, which is favorable for probing the superconducting mechanism. Recently, a topological surface superconductivity [6,7], and the possible Majorana bound state have been observed [8,9], which make Fe 1+y Te 1−x Se x the first high temperature topological superconductor. On the other hand, its high upper critical field (∼ 50 Tesla) and less toxic nature compared with iron pnictides suggest that Fe 1+y Te 1−x Se x are also favorable to applications.…”

Section: Introductionmentioning

confidence: 99%

Achieving the depairing limit along the c axis in Fe1+yTe1−xSe
Sun
¹
,
Ohnuma
²
,
Ayukawa
³

et al. 2020
Phys. Rev. B
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We report the achieving of depairing current limit along c-axis in Fe1+yTe1−xSex single crystals. A series of crystals with Tc ranging from 8.6 K to 13.7 K (different amount of excess Fe, y) were fabricated into c-axis bridges with a square-micrometer cross-section. The critical current density, Jc, was directly estimated from the transport current-voltage measurements. The transport Jc reaches a very large value, which is about one order of magnitude larger than the depinning Jc, but comparable to the calculated depairing Jc ∼ 2 × 10 6 A/cm 2 at 0 K, based on the Ginzburg-Landau (GL) theory. The temperature dependence of the depairing Jc follows the GL-theory (∝ (1-T /Tc) 3/2 ) down to ∼ 0.83 Tc, then increases with a reduced slope at low temperatures, which can be qualitatively described by the Kupriyanov-Lukichev theory. Our study provides a new route to understand the behavior of depairing Jc in iron-based superconductors in a wide temperature range. * sunyue@phys.aoyama.ac.jp † hkitano@phys.aoyama.ac.jp

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“…Motivated by experimental observations, we examine the effects of Zeeman coupling on the vortex modes in FTS. As the topological properties of FTS are driven by band inversion, we eschew more complex band models and utilize a simple model of a doped 3D time-reversal symmetric (TRS) topological insulator (TI) which has been used as an appropriate toy model to investigate the properties of vortices in FTS [26,27]. An essential property of the electronic band structure in TRS TI is the presence of degenerate Fermi surfaces.…”

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confidence: 99%

Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors

et al. 2020

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In the superconducting regime of FeTe (1−x) Sex, there exist two types of vortices which are distinct by the presence or absence of zero energy states in their core. To understand their origin, we examine the interplay of Zeeman coupling and superconducting pairings in three-dimensional metals with band inversion. Weak Zeeman fields are found to suppress the intra-orbital spin-singlet pairing, known to localize the states at the ends of the vortices on the surface. On the other hand, an orbital-triplet pairing is shown to be stable against Zeeman interactions, but leads to delocalized zero-energy Majorana modes which extend through the vortex. In contrast, the finite-energy vortex modes remain localized at the vortex ends even when the pairing is of orbital-triplet form. Phenomenologically, this manifests as an observed disappearance of zero-bias peaks within the cores of topological vortices upon increase of the applied magnetic field. The presence of magnetic impurities in FeTe (1−x) Sex, which are attracted to the vortices, would lead to such Zeeman-induced delocalization of Majorana modes in a fraction of vortices that capture a large enough number of magnetic impurities. Our results provide an explanation to the dichotomy between topological and non-topological vortices recently observed in FeTe (1−x) Sex.Introduction: To date, one of the major impediments in the search for Majorana fermions (MFs) is that a requisite topological superconductivity, either intrinsic [1,2] or induced in a host material via a proximity coupling to a standard s-wave superconductor [3-6]. Of the available materials that possess topology, superconductivity and magnetism, iron-based superconductors are of recent interest [7][8][9][10][11][12][13][14][15]. In particular, the iron-based superconductor FeTe 0.55 Se 0.45 (FTS) has recently been shown to have strong spin-orbit interactions and band inversion that result in a helical, topologically-protected, Dirac cone on the surface [16][17][18][19]. The phenomenology of vortices, proliferated in the presence of magnetic fields, is also noteworthy in FTS [20][21][22][23]. The low charge density in the superconducting phase of this system is experimentally advantageous as it results in large Caroli-de Gennes-Matricon (CDM) vortex mode gaps [24] which facilitates the spectral detection of zero-energy vortex modes via scanning tunneling microscopy (STM). Intriguingly, vortices in FTS show two distinct types of behavior: topological, carrying zero energy states consistent with the presence of MF, and trivial vortices that lack the zero energy state but carry finite energy CDMs.

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Multiple topological states in iron-based superconductors

Cited by 241 publications

References 60 publications

Detection of second-order topological superconductors by Josephson junctions

Detection of second-order topological superconductors by Josephson junctions

Achieving the depairing limit along the c axis in Fe1+yTe1−xSe
Sun
¹
,
Ohnuma
²
,
Ayukawa
³

et al. 2020
Phys. Rev. B
Self Cite
19
0
11
0
View full text Add to dashboard Cite

Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors

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Multiple topological states in iron-based superconductors

Cited by 241 publications

References 60 publications

Detection of second-order topological superconductors by Josephson junctions

Detection of second-order topological superconductors by Josephson junctions

Achieving the depairing limit along the c axis in Fe1+yTe1−xSeSun1, Ohnuma2, Ayukawa3 et al. 2020Phys. Rev. BSelf Cite190110View full textAdd to dashboardCite

Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors

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Achieving the depairing limit along the c axis in Fe1+yTe1−xSe
Sun
¹
,
Ohnuma
²
,
Ayukawa
³

et al. 2020
Phys. Rev. B
Self Cite
19
0
11
0
View full text Add to dashboard Cite