In the present Rapid Communication, we explore superconductivity in NdNiO 2 and LaNiO 2 employing a first-principles derived low-energy model Hamiltonian, consisting of two orbitals: Ni x 2 -y 2 , and an axial orbital. The axial orbital is constructed out of Nd/La d, Ni 3z 2 -r 2 , and Ni s characters. Calculation of the superconducting pairing symmetry and pairing eigenvalue of the spin-fluctuation mediated pairing interaction underlines the crucial role of the interorbital Hubbard interaction in superconductivity, which turns out to be orbital selective. The axial orbital brings in material dependence to the problem, making NdNiO 2 different from LaNiO 2 , thereby controlling the interorbital Hubbard interaction-assisted superconductivity.

The type II Dirac semimetal PdTe2 is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculations on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe2 follows predictions of the microscopic theory of Bardeen, Cooper and Shriefer (BCS) for conventional superconductors. The superconducting phase in PdTe2 is further interesting because it also displays properties that are characteristics of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe2 displays intrinsic electronic inhomegenities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe2 in the normal state.PdTe 2 has been known to be a superconductor for almost six decades. 1-4 But, due to a very low critical temperature (∼ 1.7 K), the details of the superconducting phase of PdTe 2 did not receive much attention. The superconducting properties of PdTe 2 attracted renewed attention of the community following recent discovery of complex topological features in the band structure of PdTe 2 in it's non-superconducting normal state 5-7 . This discovery naturally led to the question of the possibility of a topological character of the superconducting phase of PdTe 2 . 6 This question is extremely important because a single material showing both topological character and superconductivity in it's parental stoichiometric phase is thought to be the best candidate to show topological superconductivity [8][9][10][11][12][13][14][15][16][17][18] . Immediately after the discovery of the topological nature of PdTe 2 , 5,6 transport and magnetization experiments revealed a peculiar type-I like superconducting phase but with multiple critical fields (H c ). 19,20 The possible type-I nature of superconductivity in PdTe 2 is unique because only elemental metals are known to show type-I superconductivity and superconductivity in binary compounds and alloys are generally seen to be of type II with perhaps only one exception of TaSi 2 21 . The observation of multiple critical fields in PdTe 2 was attributed to the possibility of an anisotropic superconducting order parameter and to an enhanced critical field of the surface sheath (H s c ) of PdTe 2 . 19,20 However, the measured H s c turned out to be around 3000 G which is one order of magnitude higher than H c ∼ 250 G. This deviates from the expected value for a standard Saint-James-deGennes (SJdG) surface critical field which, in principle, should be less than 1.7 H c . 22-24 This * Electronic address: anshusirohi@iisermohali.ac.in † Electronic address: goutam@iisermohali.ac.in mismatch of the me...

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Non-trivial Berry phase of graphene leads to unusual quantum correction to the conductivity. Berry phase of π in single layer graphene (SLG) and 2π in bi-layer graphene (BLG) is expected to reveal weak anti-localization (WAL) and weak localization (WL), respectively. However, experimentally both WAL and WL have been observed in graphene devices depending on the strength of different scattering mechanisms. Graphene superlattice having multiple Dirac cones is expected to exhibit π to 2π Berry phase transition from primary Dirac cone (PDC) to cloned Dirac cone (CDC). However, its effect on localization physics has not been explored yet. In this letter we present the magneto-conductance study in a hexagonal Boron-nitride (hBN)-graphene moiré superlattice. Our results reveal a transition from WAL at PDC to WL at CDC in a single device by tuning the Fermi energy. The transition is supported by the quantum oscillation measurements showing a shift of π phase from PDC to CDC and corresponding theoretical calculation capturing the Berry phase transition. Thus, our studies on localization physics in graphene superlattice pave the way to understand the carrier dynamics at multiple Dirac cones. arXiv:1711.03275v2 [cond-mat.mes-hall]

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