We report the synthesis and physical properties of the single crystals of TaC, which are proposed to hold topological band structure as a topological superconductor (TSC) candidate. Magnetization, resistivity and specific heat measurements are performed and indicate that TaC is bulk superconductor with critical temperature of 10.3 K. TaC is a strongly coupled type-II superconductor and the superconducting state can be well described by s-wave Bardeen-Cooper-Schrieffer (BCS) theory with a single gap. The upper critical field (Hc2) of TaC shows linear temperature dependence, which is quite different from most conventional superconductors and isostructural NbC, which is proposed to manifest topological nodal-loops or type-II Dirac points as well as superconductivity. Our results suggest that TaC would be a new candidate for further research of TSCs.
Symmetry of the crystal lattice can be a determining factor for the structure of Cooper pairs in unconventional superconductors. In this study we extend the discussion of superconductivity in non-centrosymmetric materials to the case when inversion symmetry is missing locally, but is present on a global level. Concretely, we investigate the staggered non-centrosymmetricity within a regular sublattice structure, in some analogy to the discussion of superconductivity in antiferromagnetic systems. Three crystal structures are analyzed in detail as illustrative examples for the extended classifica…
We report a high-pressure single-crystal study of the non-centrosymmetric superconductor YPtBi ($T_c = 0.77$ K). Magnetotransport measurements show a weak metallic behavior with a carrier concentration $n \simeq 2.2 \times 10^{19}$ cm$^{-3}$. Resistivity measurements up to $p = 2.51$ GPa reveal superconductivity is promoted by pressure. The reduced upper critical field $B_{c2}(T)$ curves collapse onto a single curve, with values that exceed the model values for spin-singlet superconductivity. The $B_{c2}$ data point to an odd-parity component in the superconducting order parameter, in accordan…
We report detailed $^{75}$As-NQR investigations of the locally non-centrosymmetric superconductor SrPtAs. The spin-lattice relaxation studies prove weakly coupled multi-gap superconductivity. The Hebel-Slichter peak, a hallmark of conventional superconductivity, is strongly suppressed, which points to an unconventional superconducting state. The observed behavior excludes a superconducting order parameter with line nodes and is consistent with proposed $f$-wave and chiral $d$-wave order parameters.
We present a discussion of superconductivity in non-centrosymmetric superconductors with spin-orbit coupling. A general expression for the quasiparticle excitation energy is derived. The superconducting states for the point group C2v are classified by symmetry in the limit of weak spin-orbit coupling. A non-unitary triplet pairing gap function can account for observations of broken time-reversal symmetry and nodes in the superconducting state of LaNiC2; however such a gap function also has a gapless branch and requires vanishing spin-orbit coupling.
We present a comprehensive study on superconducting properties of Re$_7$B$_3$ and Re$_3$B through specific heat, magnetic susceptibility, resistivity, and transverse and zero-field muon spin rotation/relaxation ($μ$SR) experiments on polycrystalline samples. Re$_7$B$_3$ (T$_C$ = 3.2~K) is a non-centrosymmetric type-II ($κ$ $\approx$ 9.27) superconductor in the weak coupling ($λ_{e-ph}$ = 0.54) regime. On the other hand, Re$_3$B (T$_C$ = 5.19~K) is a centrosymmetric type-II ($κ$ $\approx$ 34.55) superconductor in the moderate coupling ($λ_{e-ph}$ = 0.64) regime. Our transverse-field $μ$SR measu…
We report first principles calculations of the electronic structure and electron-phonon coupling in the non-centrosymmetric superconductor LaNiC$_2$. These show that the material is a conventional electron-phonon superconductor with intermediate coupling. There are large contributions to the coupling by two low frequency C non-bond-stretching modes, one of which has strong Kohn anomalies. Since LaNiC$_2$ lacks inversion symmetry, the pairing is of dominant s-wave type with some mixture of p-wave character. This will give exponential decay in the specific heat.
Motivated by the recent discoveries of ferromagnetic and non-centrosymmetric superconductors, we present a mean-field theory for a superconductor that \textit{both} lacks inversion symmetry and displays ferromagnetism, a scenario which is believed to be realized in UIr. We study the interplay between the order parameters to clarify how superconductivity is affected by the presence of ferromagnetism and spin-orbit coupling. One of our key findings is that the spin-orbit coupling seems to enhance both ferromagnetism and superconductivity in all spin channels. We discuss our results in the contex…
We study the parity-mixed superconductivity in locally non-centrosymmetric systems. In multilayer systems an inhomogeneous Rashba spin-orbit coupling is induced by the local violation of inversion symmetry. Our previous study revealed that a pair-density wave (PDW) phase, with a sign-modulated order parameter, is stabilized in the spin-singlet multilayer superconductors owing to the spin-orbit coupling. In this letter, we show that the uniform spin-triplet superconductivity emerges through parity mixing in the PDW phase, taking into account a weak interaction in the spin-triplet channel, which…
Topological crystalline superconductivity in the locally non-centrosymmetric multilayer superconductors (SCs) is proposed. We study the odd-parity pair-density wave (PDW) state induced by the spin-singlet pairing interaction through the spin-orbit coupling. It is shown that the PDW state is a topological crystalline SC protected by a mirror symmetry, although it is topologically trivial according to the classification based on the standard topological periodic table. The topological property of the mirror subsectors is intuitively explained by adiabatically changing the BdG Hamiltonian. A subs…
Although multilayer systems possess global inversion symmetry, some of the layers lack local inversion symmetry because no global inversion centers are present on such layers. Such locally non-centrosymmetric systems exhibit spatially modulated Rashba spin-orbit coupling. In this study, the superconductivity in multilayer models exhibiting inhomogeneous Rashba spin-orbit coupling is investigated. We study the electronic structure, superconducting gap, and spin susceptibility in the superconducting state with mixed parity order parameters. We show the enhancement of the spin susceptibility by R…
We study novel effects in non-centrosymmetric superconductors arising from their unique coupling of Cooper-pair condensate and elasticity. We show that although the much discussed Lifshitz coupling is not observable in a uniform bulk state, it strikingly endows dislocations with a fractional magnetic flux. We also predict a generation of voltage-free strain by a DC current in a P and T-breaking Josephson junction. Viewing superconductors through the lens of higher-form symmetries we identify the Lifshitz coupling as a chemical potential for the approximately conserved winding number, drawing a…
We report measurements of the temperature dependence of the magnetic penetration depth λ(T) in non-centrosymmetric superconductor Re_3W. We employed two experimental techniques: extraction of λ(T) from magnetic {\em dc}-susceptibility, measured on a powder sample, and the rf tunnel diode resonator technique, where a bulk polycrystalline sample was used. The results of both techniques agree: the temperature dependence of the penetration depth can be well described by weak-coupling, dirty-limit, s-wave BCS theory where we obtain $Δ(0)/k_BT_C=1.76$. No evidence for unconventional pairing resultin…
We report the discovery of superconductivity in pressurized CeRhGe3, until now the only remaining non-superconducting member of the isostructural family of non-centrosymmetric heavy-fermion compounds CeTX3 (T = Co, Rh, Ir and X = Si, Ge). Superconductivity appears in CeRhGe3 at a pressure of 19.6 GPa and the transition temperature Tc reaches a maximum value of 1.3 K at 21.5 GPa. This finding provides an opportunity to establish systematic correlations between superconductivity and materials properties within this family. Though ambient-pressure unit-cell volumes and critical pressures for supe…
We study the superconducting properties of the non-centrosymmetric compound LaNiC$_2$ by measuring the London penetration depth $Δλ(T)$, the specific heat $C(T,B)$ and the electrical resistivity $ρ(T,B)$. Both $Δλ(T)$ and the electronic specific heat $C_e(T)$ exhibit exponential behavior at low temperatures and can be described in terms of a phenomenological two-gap BCS model. The residual Sommerfeld coefficient in the superconducting state, $γ_0(B)$, shows a fast increase at low fields and then an eventual saturation with increasing magnetic field. A pronounced upturn curvature is observed in…
Electrical resistivity, specific heat and NMR measurements classify non-centrosymmetric $\rm Mo_3Al_2C$ ($β$-Mn type, space group $P4_132$) as a strong-coupled superconductor with $T_c = 9$~K deviating notably from BCS-like behaviour. The absence of a Hebbel-Slichter peak, a power law behaviour of the spin-lattice relaxation rate (from $^{27}$Al NMR), a $T^3$ temperature dependence of the specific heat and a pressure enhanced $T_c$ suggest unconventional superconductivity with a nodal structure of the superconducting gap. Relativistic DFT calculations reveal a splitting of degenerate electroni…
Two dimensional SrTiO3-based interfaces stand out among non-centrosymmetric superconductors due to their intricate interplay of gate tunable Rashba spin-orbit coupling and multi-orbital electronic occupations, whose combination theoretically prefigures various forms of non-standard superconductivity. However, a convincing demonstration by phase sensitive measurements has been elusive so far. Here, by employing superconducting transport measurements in nano-devices we present clear-cut experimental evidences of unconventional superconductivity in the LaAlO3/SrTiO3 interface. The central observa…
We report a $μ$SR investigation of a non-centrosymmetric superconductor (LaNiC$_2$) in single crystal form. Compared to previous $μ$SR studies of non-centrosymmetric superconducting polycrystalline and powder samples, the unambiguous orientation of single crystals enables a simultaneous determination of the absolute value of the magnetic penetration depth and the vortex core size from measurements that probe the magnetic field distribution in the vortex state. The magnetic field dependence of these quantities unambiguously demonstrates the presence of two nodeless superconducting energy gaps. …
In non-centrosymmetric superconductors, where the crystal structure lacks a centre of inversion, parity is no longer a good quantum number and an electronic antisymmetric spin-orbit coupling (ASOC) is allowed to exist by symmetry. If this ASOC is sufficiently large, it has profound consequences on the superconducting state. For example, it generally leads to a superconducting pairing state which is a mixture of spin-singlet and spin-triplet components. The possibility of such novel pairing states, as well as the potential for observing a variety of unusual behaviours, led to intensive theoreti…
We report $^{195}$Pt-NMR and $^{75}$As-NQR measurements for the locally non-centrosymmetric superconductor SrPtAs where the As-Pt layer breaks inversion symmetry while globally the compound is centrosymmetric. The nuclear spin lattice relaxation rate $1/T_1$ shows a well-defined coherence peak below $T_c$ and decreases exponentially at low temperatures. The spin susceptibility measured by the Knight shift also decreases below $T_c$ down to $T<T_c/6$. These data together with the penetration depth obtained from the NMR spectra can be consistently explained by assuming a spin-singlet superconduc…
Non-centrosymmetric superconductor Re$_6$Zr has attracted much interest, for its possible unconventional superconducting state with time reversal symmetry broken. Here we report the $^{185/187}$Re nuclear quadrupole resonance (NQR) measurements on Re$_6$Zr ($T_c$ = 6.72 K) and the isostructural compounds Re$_{27}$Zr$_{5}$ ($T_c$ = 6.53 K) and Re$_{24}$Zr$_{5}$ ($T_c$ = 5.00 K). The nuclear spin-lattice relaxation rate $1/T_1$ shows a coherence peak below $T_c$ and decreases exponentially at low temperatures in all three samples. The superconducting gap $Δ$ derived from the $1/T_1$ data is $2Δ=…
The search for non-centrosymmetric superconductors that may exhibit unusual physical properties and unconventional superconductivity has yielded the synthesis of a non-centrosymmetric phosphide Mg$_2$Rh$_3$P with an Al$_2$Mo$_3$C-type structure. Although stoichiometric Mg$_2$Rh$_3$P does not exhibit superconductivity at temperatures above 2 K, we found that an Mg deficiency of approximately 5 at.% in the Mg$_2$Rh$_3$P induced superconductivity at 3.9 K. Physical properties such as the lattice parameter a = 0.70881 nm, Sommerfeld constant $γ_n$ = 5.36 mJ mol$^{-1}$ K$^{-2}$, specific heat jump …
Using functional renormalization group method, we study the favorable condition for electronic correlation driven time reversal invariant topological superconductivity in symmetry class DIII. For non-centrosymmetric systems we argue that the proximity to ferromagnetic (or small wavevector magnetic) instability can be used as a guideline for the search of this type of superconductivity. This is analogous to the appearance of singlet unconventional superconductivity in the neighborhood of antiferromagnetic instability. We show three concrete examples where ferromagnetic-like fluctuation leads to…
We report non-equilibrium magnetodynamics in the Rashba-superconductor GeTe, which lacks inversion symmetry in the bulk. We find that at low temperature the system exhibits a non-equilibrium state, which decays on time scales that exceed conventional electronic scattering times by many orders of magnitude. This reveals a non-equilibrium magnetoresponse that is asymmetric under magnetic field reversal and, strikingly, induces a non-equilibrium superconducting state distinct from the equilibrium one. We develop a model of a Rashba system where non-equilibrium configurations relax on a finite tim…
AuBe is a chiral, non-centrosymmetric superconductor with transition temperature $T_C$ $\simeq$ 3.25 K. The broken inversion symmetry in its crystal structure makes AuBe a possible candidate to host a mixed singlet-triplet pairing symmetry in its superconducting order parameter ($Δ$). This possibility was investigated by transport, thermodynamic, and muon-spin rotation/relaxation experiments in AuBe. However, this issue was not addressed using direct spectroscopic probes so far. In addition, certain ambiguities exist in the description of superconductivity in AuBe based on $μ$SR experiments re…
In a superconductor that lacks inversion symmetry, the spatial part of the Cooper pair wave function has a reduced symmetry, allowing for the mixing of spin-singlet and spin-triplet Cooper pairing channels and thus providing a pathway to a non-trivial superconducting state. Materials with a non-centrosymmetric crystal structure and with strong spin-orbit coupling are a platform to realize these possibilities. Here, we report the synthesis and characterisation of high quality crystals of Sn$_4$As$_3$, with non-centrosymmetric unit cell ($R3m$). We have characterised the normal and superconducti…
We report the superconductivity of PbTaS2 single crystals with the centrosymmetric structure. The systematic measurements of magnetization, electric transport and specific heat indicate that PbTaS2 is a weakly coupled type-II superconductor with transition temperature Tc = 2.6 K. Furthermore, the band structure calculations predicted four nodal lines near the Fermi energy with drumhead-like surface states, suggesting centrosymmetric PbTaS2 is a candidate of topological nodal line semimetals. These results demonstrate that PbTaS2 may open up another avenue for further exploring the properties o…
The upper critical field is a fundamental measure of the strength of superconductivity in a material. It is also a cornerstone for the realization of superconducting magnet applications. The critical field arises because of the Copper pair breaking at a limiting field, which is due to the Pauli paramagnetism of the electrons. The maximal possible magnetic field strength for this effect is commonly known as the Pauli paramagnetic limit given as $μ_0 H_{\rm Pauli} \approx 1.86{\rm [T/K]} \cdot T_{\rm c}$ for a weak-coupling BCS superconductor. The violation of this limit is only rarely observed.…
In the recently discovered antiperovskite phosphide (Ca,Sr)Pd$_3$P, centrosymmetric (CS) and non-centrosymmetric (NCS) superconducting phases appear depending on the Sr concentration, and their transition temperatures ($T_\mathrm{c}$) differ by as much as one order of magnitude. In this study, we investigated the superconducting properties and electronic band structures of CS orthorhombic (CSo) (Ca$_{0.6}$Sr$_{0.4}$)Pd$_3$P ($T_\mathrm{c}$ = 3.5 K) and NCS tetragonal (NCSt) (Ca$_{0.25}$Sr$_{0.75}$)Pd$_3$P ($T_\mathrm{c}$ = 0.32 K) samples with a focus on explaining their large $T_\mathrm{c}$ d…
The influence of antiferromagnetic order on the superconductivity in the non-centrosymmetric heavy fermion compound CePt$_3$Si and related materials is discussed. Based on our RPA analysis for the extended Hubbard model two phases could be stabilized by a spin fluctuation induced pairing, with either dominantly p-wave or d-wave symmetry. The antiferromagnetic order plays an essential role for the low-energy physics, in particular, for the appearance of line nodes in the gap and the enhancement of spin susceptibility below $T_{\rm c}$. Various properties and possible phase diagrams under pressu…
In this work, we establish the bulk superconductivity of a high quality sample of monoclinic BiPd ($α$-BiPd, space group P2$_1$) below 3.87 K by studying its electrical resistivity, magnetic susceptibility and heat capacity. We show that it is clean type-II superconductor with moderate electron-phonon coupling and determine its superconducitng and normal state parameters. Although $α$-BiPd is a noncentrosymmetric superconductor with large electronic heat capacity (therefore, large $γ$), the effect of spin-orbit splitting of the electronic bands at the Fermi level is small. This makes little in…
A notable characteristic of PbTaSe$_2$, a prototypical noncentrosymmetric (NCS) superconductor, is that its superconductivity can be modulated through a structural transition under hydrostatic pressure [Phys. Rev. B 95, 224508 (2017)]. Here we report on simultaneous pressure-sensitive point-contact Andreev reflection (PCAR) spectroscopy and bulk resistance measurements on PbTaSe$_2$, to elucidate the nature of the surface and bulk superconductivity and their evolution with hydrostatic pressure. It is found that in high pressure region the superconducting gap opening temperature $T_c^A$ is sign…
Superconductivity and magnetism in the non-centrosymmetric heavy fermion compound CePt$_3$Si and related materials are theoretically investigated. Based on the randam phase approximation (RPA) analysis for the extended Hubbard model we describe the helical spin fluctuation induced by the Rashba-type anti-symmetric spin-orbit coupling and identify the two stable superconducting phases with either dominantly p-wave ($s$ + $P$-wave) or d-wave ($p$ + $D$ + $f$-wave) symmetry. The influcnce of the coexistent anti-ferromagnetic order is investigated in both states. The SC order parameter, quasiparti…
We report on the observation of superconductivity in LaRh$_2$As$_2$, which is the analogue without $f$-electrons of the heavy-fermion system with two superconducting phases CeRh$_2$As$_2$. A zero-resistivity transition, a specific-heat jump and a drop in magnetic ac susceptibility consistently point to a superconducting transition at a transition temperature of $T_c = 0.28$\,K. The magnetic field-temperature superconducting phase diagrams determined from field-dependent ac-susceptibility measurements reveal small upper critical fields $μ_{\mathrm{0}}H_{c2} \approx 12$\,mT for $H\parallel ab$ a…
In this study, we succeeded in synthesizing new antiperovskite phosphides $M$Pd$_3$P ($M$ = Ca, Sr, Ba) and discovered the appearance of a superconducting phase (0.17 $\leq$ $x$ $\leq$ 0.55) in a solid solution (Ca$_{1-x}$Sr$_x$)Pd$_3$P. Three perovskite-related crystal structures were identified in (Ca$_{1-x}$Sr$_x$)Pd$_3$P and a phase diagram was built on the basis of experimental results. The first phase transition from centrosymmetric ($Pnma$) to non-centrosymmetric orthorhombic ($Aba$2) occurred in CaPd$_3$P near room temperature. The phase transition temperature decreased as Ca$^{2+}$ wa…
A weak-coupling formalism for superconducting states possessing both singlet (even parity) and triplet (odd parity) components of the order parameter in centrosymmetric crystals is developed. It is shown that the quasiparticle energy spectrum may be non-degenerate even if the triplet component is unitary. The superconducting gap of a mixed-parity state may have line nodes in the strong spin-orbit coupling limit. The pseudospin carried by the superconducting electrons is calculated, from which follows a prediction of a kink anomaly in the temperature dependence of muon spin relaxation rate. The…
We report superconductivity at $T_c = 1.22$ K and magnetic order at $T_N = 1.06$ K in the semi-metallic noncentrosymmetric Half Heusler compound ErPdBi. The upper critical field, $B_{c2}$, has an unusual quasi-linear temperature variation and reaches a value of 1.6 T for $T \rightarrow 0$. Magnetic order is found below $T_c$ and is suppressed at $B{_M} \sim 2.5$ T for $T \rightarrow 0$. Since $T_c \simeq T_N$, the interaction of superconductivity and magnetism is expected to give rise to a complex ground state. Moreover, electronic structure calculations show ErPdBi has a topologically nontriv…
$\rm CePt_3Si$ is a novel heavy fermion superconductor, crystallising in the $\rm CePt_3B$ structure as a tetragonally distorted low symmetry variant of the $\rm AuCu_3$ structure type. $\rm CePt_3Si$ exhibits antiferromagnetic order at $T_N \approx 2.2$ K and enters into a heavy fermion superconducting state at $T_c \approx 0.75$ K. Large values of $H_{c2}' \approx -8.5$ T/K and $H_{c2}(0) \approx 5$ T refer to heavy quasiparticles forming Cooper pairs. Hitherto, $\rm CePt_3Si$ is the first heavy fermion superconductor without a center of symmetry.
We have carried out high pressure experiment on the pressure-induced superconductor CeIrSi$_3$ without inversion center. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure of the antiferromagnetic state was determined to be $P_{\rm c}$ = 2.25 GPa. The heat capacity $C_{\rm ac}$ shows both antiferromagnetic and superconducting transitions at pressures close to $P_{\rm c}$. The superconducting transition temperature $T_{\rm sc}$ shows a maximum value of 1.6 K around $2.5-2.7$ GPa. At 2.58 GPa, a large heat capacity anomaly was…
Low-dimensional materials with broken inversion symmetry and strong spin-orbit coupling can give rise to fascinating quantum phases and phase transitions. Here we report coexistence of superconductivity and ferromagnetism below 2.5\,K in the quasi-one dimensional crystals of non-centrosymmetric (TaSe$_4$)$_3$I (space group: $P\bar{4}2_1c$). The unique phase is a direct consequence of inversion symmetry breaking as the same material also stabilizes in a centro-symmetric structure (space group: $P4/mnc$) where it behaves like a non-magnetic insulator. The coexistence here upfront contradicts the…
Unconventional superconductivity frequently emerges as the transition temperature of a magnetic phase, typically antiferromagnetic, is suppressed continuously toward zero temperature. Here, we report contrary behavior in pressurized CeRhGe3, a non-centrosymmetric heavy fermion compound. We find that its pressure-tuned antiferromagnetic transition temperature (TN) appears to avoid a continuous decrease to zero temperature by terminating abruptly above a dome of pressure-induced superconductivity. Near 21.5 GPa, evidence for TN suddenly vanishes, the electrical resistance becomes linear in tempe…
Unconventional superconductivity in locally non-centrosymmetric CeNi$_2$As$_2$
Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Institute for Quantum Materials and Technology, Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院量子材料与技术研究所）
Probing bulk superconductivity in centrosymmetric Te-doped PtBi$_2$ single crystals
Leibniz Institute for Solid State and Materials Research（莱布尼茨固体和材料研究所）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Centro Atómico Bariloche, CNEA-CONICET（巴里洛切原子中心，CNEA-CONICET）；B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine（乌克兰国家科学院B.维尔金低温物理与工程研究所）；Kyiv Academic University（基辅学术大学）
The results from muon spin relaxation experiments on the non-centrosymmetric intermetallic superconductor LaNiC$_2$ are reported. We find that the onset of superconductivity coincides with the appearance of spontaneous magnetic fields, implying that in the superconducting state time reversal symmetry is broken. An analysis of the possible pairing symmetries suggests only four triplet states compatible with this observation, all of which are non-unitary. They include the intriguing possibility of triplet pairing with the full point group symmetry of the crystal, which is only possible in a non-…
We propose a route to achieve odd-parity spin-triplet superconductivity in metallic collinear antiferromagnets with inversion symmetry. Owing to the existence of hidden antiunitary symmetry, which we call the effective time-reversal symmetry (eTRS), the Fermi surfaces of ordinary antiferromagnetic metals are generally spin-degenerate, and spin-singlet pairing is favored. However, by introducing a local inversion symmetry breaking perturbation that also breaks the eTRS, we can lift the degeneracy to obtain spin-polarized Fermi surfaces. In the weak-coupling limit, the spin-polarized Fermi surfa…
We report superconductivity and magnetism in a new family of topological semimetals, the ternary half Heusler compounds $R$PdBi ($R$ : rare earth). In this series, tuning of the rare earth $f$-electron component allows for simultaneous control of both lattice density via lanthanide contraction, as well as the strength of magnetic interaction via de Gennes scaling, allowing for a unique tuning of both the normal state band inversion strength, superconducting pairing and magnetically ordered ground states. Antiferromagnetism with ordering vector (0.5,0.5,0.5) occurs below a Neéel temperature tha…
The discovery of signatures of topological superconductivity in superconducting bulk materials with topological surface states has attracted intensive research interests recently. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, here, we demonstrate the existence of topological nodal-line states and drumheadlike surface states in centrosymmetric superconductor SnTaS2, which is a type-II superconductor with a critical transition temperature of about 3 K. The valence bands from Ta 5d orbitals and the conduction bands from Sn 5p orbitals cross each other, for…
Electronic structures of superconducting Re24Nb5 and Re24Ti5 have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused on the influence of the antisymmetric spin-orbit coupling on band structures and Fermi surfaces of these non-centrosymmetric systems. The predicted here density of states at the Fermi level for Re24Ti5 is abnormally low with respect to that deduced from previous heat capacity measurements. This discrepancy suggests an intermediate coupled superconducting state in Re24Ti5. The differences between…
The non-centrosymmetric Weyl semimetal candidate, MoTe$_2$ was investigated through neutron diffraction and transport measurements at pressures up to 1.5 GPa and at temperatures down to 40 mK. Centrosymmetric and non-centrosymmetric structural phases were found to coexist in the superconducting state. Density Functional Theory (DFT) calculations reveal that the strength of the electron-phonon coupling is similar for both crystal structures. Furthermore, it was found that by controlling non-hydrostatic components of stress, it is possible to mechanically control the ground state crystal structu…
Muon spin rotation and relaxation experiments on the centrosymmetric intermetallic superconductor LaNiGa$_2$ are reported. The appearance of spontaneous magnetic fields coincides with the onset of superconductivity, implying that the superconducting state breaks time reversal symmetry, similarly to non-centrosymmetric LaNiC$_2$. Only four triplet states are compatible with this observation, all of which are non-unitary triplets. This suggests that LaNiGa$_2$ is the centrosymmetric analogue of LaNiC$_2$. We argue that these materials are representatives of a new family of paramagnetic non-unita…
Non-centrosymmetric superconductors, whose crystal structure is absent of inversion symmetry, have recently received special attentions due to the expectation of unconventional pairings and exotic physics associated with such pairings. The newly discovered superconductors A2Cr3As3 (A=K, Rb), featured by the quasi-one dimensional structure with conducting CrAs chains, belongs to such kind of superconductor. In this study, we are the first to report the finding that the superconductivity of A2Cr3As3 (A=K, Rb) has a positive correlation with the extent of non-centrosymmetry. Our in-situ high pres…
We observed quantum oscillations in thermoelectric and magnetic torque signals in non-centrosymmetric superconductor PbTaSe$_2$. One oscillatory frequency stems from the orbits formed by magnetic breakdown, while others are from two-dimensional-like Fermi surfaces near the topological nodal rings. Our comprehensive understanding of the Fermi surface topology of PbTaSe$_2$, including nailing down the Fermi level and detecting the Berry phases near the nodal rings, is crucial for searching plausible topological superconductivity in its bulk and surface states.
