The transition metal dichalcogenide PdTe2 was recently shown to be a unique system where a type II Dirac semimetallic phase and a superconducting phase co-exist. This observation has led to wide speculation on the possibility of the emergence of an unconventional topological superconducting phase in PdTe2. Here, through direct measurement of the superconducting energy gap by scanning tunneling spectroscopy (STS), and temperature and magnetic field evolution of the same, we show that the superconducting phase in PdTe2 is conventional in nature. The superconducting energy gap is measured to be 326 µeV at 0.38 K and it follows a temperature dependence that is well described within the framework of Bardeen-Cooper-Schriefer's (BCS) theory of conventional superconductivity. This is surprising because our quantum oscillation measurements confirm that at least one of the bands participating in transport has topologically non-trivial character.It is believed that a superconducting ground state realized on a material displaying topologically non-trivial character might lead to the discovery of the elusive phase of matter called topological superconductivity 1-3 where relativistic Majorana fermions could emerge as excitations. 4-10 In the past, attempts were made to realize such a phase of matter through a number of ways, like, doping a topological insulator, 11-13 applying pressure on topological systems, 14 fabricating proximity-coupled heterostructures of topological insulators and conventional superconductors, 10,15 making mesoscopically confined point contacts on topological crystalline insulator, 16 Dirac 17,18 or Weyl semimetals 19 etc. In such systems, while a superconducting phase could be achieved, clear manifestation of topological superconductivity remained an unattained goal. Most recently, with the discovery of a type-II Dirac semimetallic phase on the dichalcogenide PdTe 2 , 20-22 where a superconducting phase is known to emerge naturally, 23,24 there have been wide speculation that this superconducting phase might eventually emerge as a topological superconductor. Owing to the existence of a topological phase along with superconductivity, it warrants a thorough investigation of the superconducting phase of PdTe 2 through high-resolution spectroscopic tools.In this Letter, we report scanning tunneling microscopy and spectroscopy results performed on high quality single crystals of PdTe 2 in ultra-high vacuum and sub-kelvin temperatures to spectroscopically probe the nature of superconductivity. Through systematic temperature and magnetic field dependent experiments we found that the superconducting phase in PdTe 2 , despite it's proximity to a topologically non-trivial Dirac semimetallic phase, is conventional in nature where the superconducting order parameter shows a temperature dependence consistent with the prediction of the theory of Bardeen, Cooper and Schriefer (BCS) for conventional superconductors. 25 High quality single crystals of PdTe 2 were grown by a melt growth method. The starting elements, Pd...
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...
A series of metal-organic frameworks based on alkaline earth metal ions (Ca, Sr and Ba) and 1,3,5benzenetribenzoic acid (BTB) have been synthesized and characterized. These are [H 2 NIJCH 3 ) 2 ]ijCa 7 IJBTB) 5 - 3). All the structures are three-dimensional in nature with different secondary building units. Compound 1 contains one-dimensional Ca-O-Ca zigzag chains while compound 2 contains Sr 5 O 28 pentameric clusters and compound 3 contains one-dimensional Ba-O-Ba chains. Both compounds 1 and 3 form (3,6)-net connectivity while compound 2 forms (3,12)-net connectivity. Optical band gap energy measurements show that compound 1 (2.65 eV) has low band gap energy compared to 2 (3.22 eV) and 3 (3.32 eV). This variation in band gap energy may be due to the difference in structural arrangement. Compound 3 crystallizes in a non-centrosymmetric space group (Pna2 1 ), which belongs to the polar point group C 2v . This compound displays a strong SHG response and good ferroelectric and piezoelectric properties.
In Weyl semimetals, there is an intriguing possibility of realizing a pseudo-magnetic field in presence of small strain due to certain special cases of static deformations. This pseudo-magnetic field can be large enough to form quantized Landau levels and thus become observable in Weyl semimetals. In this paper we experimentally show the emergence of a pseudo-magnetic field (∼ 3 Tesla) by Scanning Tunneling Spectroscopy (STS) on the doped Weyl semimetal Re-MoTe2, where distnict Landau level oscillations in the tunneling conductance are clearly resolved. The crystal lattice is intrinsically strained where large area STM imaging of the surface reveals differently strained domains where atomic scale deformations exist forming topographic ripples with varying periodicity in the real space. The effect of pseudo-magnetic field is clearly resolved in areas under maximum strain.
Silicon, perhaps the most ubiquitously used material in the digital age of today, has also been a material of choice for testing the fundamental differences between various electronic ground states, e.g., metals and insulators. This is mainly because ultimate control has been achieved in growing extremely pure silicon crystals and doping them with varying concentrations of charge carriers and their mobility. Here, we show that by forming mesoscopic point contacts with non-superconducting metals on insulating (doped) silicon, it is possible to obtain a superconducting phase with a remarkably high critical temperature above 10 K and an average superconducting energy gap of 2 meV. Apart from its importance in advancing the understanding of nanoscale superconductivity, this discovery is also expected to boost the efforts to realize silicon based superconducting devices with far reaching application potential.
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