Time-reversal symmetry breaking in the noncentrosymmetric superconductor 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Re</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:mi>Ti</mml:mi></mml:math>

Singh, Deepak; P, Sajilesh K.; Barker, James; Paul, D. McK.; Hillier, A. D.; Singh, R. P.

doi:10.1103/physrevb.97.100505

Cited by 65 publications

(77 citation statements)

References 71 publications

(126 reference statements)

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“…As shown in the insets of Fig. 3, despite the different T c values of Re 0.82 Nb 0.18 and Re, their σ(T ) curves exhibit a small yet distinct increase below T c , similar to that found also in other ReT NCSC [15][16][17][18]. To date, most α-Mn-type ReT -NCSC have been found to exhibit TRSB in the superconducting state [15][16][17][18].…”

supporting

confidence: 72%

“…In general, TRSB below T c and a lack of spatial-inversion symmetry of the crystal structure are independent events. Yet, in a few cases, such as in LaNiC 2 [13], La 7 Ir 3 [14], and, in particular, in the Re-based compounds Re 6 Zr [15], Re 6 Hf [16], Re 6 Ti [17], and Re 24 Ti 5 [18], TRSB below T c is concomitant with an existing lack of crystal inversion symmetry. Such an unusually frequent occurrence of TRSB among the superconducting ReT binary alloys (T = transition metal) is rather puzzling.…”

mentioning

confidence: 99%

“…A comparative study by means of muon-spin relaxation and rotation (µSR) allows us to address the question of TRSB in Re-containing compounds. The choice of µSR as the preferred technique for our study is justified by its key role in detecting TRSB in numerous unconventional superconductors [13][14][15][16][17][18][19][20] (later confirmed by Kerr effect or bulk magnetisation in the cases of Sr 2 RuO 4 , UPt 3 and LaNiC 2 [21][22][23]). We report systematic µSR studies of Re 0.82 Nb 0.18 (T c = 8.8 K) and Re (T c = 2.7 K), whose bulk superconducting properties were characterized by magnetic, transport, and thermodynamic measurements.…”

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Time-Reversal Symmetry Breaking in Re-Based Superconductors

et al. 2018

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To trace the origin of time-reversal symmetry breaking (TRSB) in Re-based superconductors, we performed comparative muon-spin rotation/relaxation (µSR) studies of superconducting noncentrosymmetric Re 0.82 Nb 0.18 (T c = 8.8 K) and centrosymmetric Re (T c = 2.7 K). In Re 0.82 Nb 0.18 , the low-temperature superfluid density and the electronic specific heat evidence a fully-gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron-phonon coupling. In both Re 0.82 Nb 0.18 and pure Re, the spontaneous magnetic fields revealed by zero-field µSR below T c indicate time-reversal symmetry breaking and thus unconventional superconductivity. The concomitant occurrence of TRSB in centrosymmetric Re and noncentrosymmetric ReT (T = transition metal), yet its preservation in the isostructural noncentrosymmetric superconductors Mg 10 Ir 19 B 16 and Nb 0.5 Os 0.5 , strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re and ReT . We discuss the superconducting order parameter symmetries that are compatible with the observations. Time reversal and spatial inversion are two key symmetries which influence at a fundamental level the electron pairing in the superconducting state: on the one hand, a number of unconventional superconductors exhibit spontaneous time-reversal symmetry breaking (TRSB) on entering the superconducting state; on the other hand, the absence of inversion symmetry above T c leads to an antisymmetric spin-orbit coupling (SOC), lifting the degeneracy of the conduction-band electrons and potentially giving rise to a mixed-parity superconducting state [1,2]. Some noncentrosymmetric superconductors (NCSC), such as CePt 3 Si [3], CeIrSi 3 [4], Li 2 Pt 3 B [5, 6], and K 2 Cr 3 As 3 [7, 8], exhibit line nodes in the gap, while others such as LaNiC 2 [9] and (La,Y) 2 C 3 [10], show multiple nodeless superconducting gaps. In addition, due to the strong influence of SOC, their upper critical field can greatly exceed the Pauli limit, as has been found in CePt 3 Si [11] and very recently in (Ta,Nb)Rh 2 B 2 [12]. In general, TRSB below T c and a lack of spatial-inversion symmetry of the crystal structure are independent events. Yet, in a few cases, such as in LaNiC 2 [13], La 7 Ir 3 [14], and, in particular, in the Re-based compounds Re 6 Zr [15], Re 6 Hf [16], Re 6 Ti [17], and Re 24 Ti 5 [18], TRSB below T c is concomitant with an existing lack of crystal inversion symmetry. Such an unusually frequent occurrence of TRSB among the superconducting ReT binary alloys (T = transition metal) is rather puzzling. Its persistence independent of the particular transition metal, points to a key role played by Re. To test such a hypothesis, and to ascertain the possible relevance of the noncentrosymmetric structure to TRSB in Re-based NCSC, we proceeded with a twofold study. On one hand we synthesized and investigated an-other Re-based NCSC, Re 0.82 Nb 0.18 . On the other hand, we considered the ...

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confidence: 99%

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Time-Reversal Symmetry Breaking in Re-Based Superconductors

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“…Furthermore, an increasing number of NCSs have been found to show time-reversal symmetry (TRS) breaking upon entering the superconducting state, such as LaNiC 2 [15], La 7 Ir 3 [16], Zr 3 Ir [17], and a number of Re-based systems with the α-Mn structure [18][19][20][21]. However, in contrast to the previously known TRS breaking strongly correlated superconductors, such as Sr 2 RuO 4 [22][23][24] and UPt 3 [25,26], these systems have generally been found to have fully opened superconducting gaps [2,[18][19][20][21][27][28][29].…”

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confidence: 99%

CaPtAs: A new noncentrosymmetric superconductor

Xie

Zhang

Shen

et al. 2020

Sci. China Phys. Mech. Astron.

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We report the discovery of a new noncentrosymmetric superconductor CaPtAs. It crystallizes in a tetragonal structure (space group I41md, No. 109), featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis (a = b = 4.18Å, and c = 43.70Å). The superconductivity of CaPtAs with Tc = 1.47 K was characterized by means of electrical resistivity, specific heat, and ac magnetic susceptibility. The electronic specific heat Ce(T )/T shows evidence for a deviation from the behavior of a conventional BCS superconductor, and can be reasonably fitted by a p-wave model. The upper critical field µ0Hc2 of CaPtAs exhibits a relatively large anisotropy, with an in-plane value of around 204 mT and an out-of-plane value of 148 mT. Density functional theory calculations indicate that the Pt-5d and As-4p orbitals mainly contribute to the density of states near the Fermi level, showing that the Pt-As honeycomb networks may significantly influence the superconducting properties. PACS number(s):

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“…In spite of this, the phenomenon has been detected in numerous systems using zero-field muon spin rotation/relaxation (µSR). Prominent examples include (U, Th)Be 13 [3], Sr 2 RuO 4 [4], UPt 3 [5], (Pr, La)(Ru, Os) 4 Sb 12 [6,7], PrPt 4 Ge 12 [8], LaNiC 2 [9], LaNiGa 2 [10,11], SrPtAs [12], Re 6 (Zr, Hf, Ti) [13][14][15][16], Lu 5 Rh 6 Sn 18 [17] and La 7 (Ir, Rh) 3 [18,19]. Many of these systems have other unconventional features, while in some cases an independent, direct observation of broken TRS has been made: optical Kerr effect measurement in Sr 2 RuO 4 [20] and UPt 3 [21], and bulk SQUID magnetization measurement in LaNiC 2 [22].…”

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Quantitative theory of triplet pairing in the unconventional superconductor LaNiGa2

et al. 2020

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The exceptionally low-symmetry crystal structures of the time-reversal symmetry breaking superconductors LaNiC2 and LaNiGa2 lead to an internally-antisymmetric non-unitary triplet (INT) state as the only possibility compatible with experiments. We argue that this state has a distinct signature: a double-peak structure in the Density of States (DOS) which resolves in the spin channel in a particular way. We construct a detailed model of LaNiGa2 capturing its electronic band structure and magnetic properties ab initio. The pairing mechanism is described via a single adjustable parameter. The latter is fixed by the critical temperature Tc allowing parameter-free predictions. We compute the electronic specific heat and find excellent agreement with experiment. The size of the ordered moment in the superconducting state is compatible with zero-field muon spin relaxation experiments and the predicted spin-resolved DOS suggests the spin-splitting is within the reach of present experimental technology. arXiv:1912.08160v2 [cond-mat.supr-con]

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Time-reversal symmetry breaking in the noncentrosymmetric superconductor Re6Ti

Cited by 65 publications

References 71 publications

Time-Reversal Symmetry Breaking in Re-Based Superconductors

Time-Reversal Symmetry Breaking in Re-Based Superconductors

CaPtAs: A new noncentrosymmetric superconductor

Quantitative theory of triplet pairing in the unconventional superconductor LaNiGa2

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