Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H31: Superconductivity in Layered Chalcogenides |
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Sponsoring Units: DCMP Chair: Lev Gasparov, University of North Florida Room: LACC 407 |
Tuesday, March 6, 2018 2:30PM - 2:42PM |
H31.00001: Pressure-induced superconductivity in semimetallic 1T-TiTe2 and its persistence nature upon decompression Sukanta Karmakar, Utpal Dutta, Pallavi S. Malavi, Subodha Sahoo 1T-TiTe2 belongs to the family of layered transition metal dichalcogenide compounds that provide important playground revealing exotic ground state electronic orders by tuning the Fermi surface topology and many body effects, either purely by lowering temperature or carrier doping or external pressure [1,2]. A large Te spin-orbit interaction and enhanced p-d hybridization near Fermi level make its Fermi surfaces more susceptible to external parameters. |
Tuesday, March 6, 2018 2:42PM - 2:54PM |
H31.00002: Using controlled disorder to probe the interplay between charge order and superconductivity in 2H-NbSe2 Kyuil Cho, Serafim Teknowijoyo, Makariy Tanatar, Ruslan Prozorov, Marcin Konczykowski, Vivek Mishra, Peter Hirschfeld The interplay between superconductivity and charge density wave (CDW) in single crystals of 2H-NbSe2 was probed by tuning the amount of point - like disorder induced by 2.5 MeV electron irradiation. With increasing dose, Tc shows $non-trivial$ behavior, first increasing from 7.25 K to 7.45 K and then decreasing to 7.3 K, whereas TCDW monotonically decreases from 33 K and becomes unresolvable below 27 K. At this dose, Tc has a sharp drop by 0.3 K. The low temperature variation of the London penetration depth shows robust exponential behavior suggesting nodeless order parameter before and after irradiation, and overall trend is consistent with multiband superconductivity with two effective superconducting gaps. Our result supports the scenario of complex interplay of CDW and superconductivity, - competition for the density of states, but possible softening of the phon modes by long - range CDW. |
Tuesday, March 6, 2018 2:54PM - 3:06PM |
H31.00003: Inducing strong superconductivity in WTe2 by proximity effect Ce Huang, Awadhesh Narayan, Enze Zhang, Faxian Xiu The superconducting states inheriting nontrivial topology at interfaces are expected to exhibit exotic phenomena such as topological superconductivity and Majorana zero modes, which hold promise for applications in quantum computation. However, a practical realization of such hybrid structures based on topological semimetals and superconductors has hitherto been limited. Here, we report the strong proximity-induced superconductivity in type-II Weyl semimetal WTe2. When the WTe2 thickness (t_(WTe_2 )) reaches 21 nm, the superconducting transition occurs around the critical temperature (T_c) of NbSe2 with a gap amplitude (Δ_p) of 0.38 meV and an unexpected ultra-long proximity length. Our theoretical calculations, based on the Bogoliubov-de Gennes equations in the clean limit, predict that the induced superconducting gap is a sizable fraction of the NbSe2 superconducting one when t_(WTe_2 ) is less than 30 nm, and then decreases quickly as t_(WTe_2 ) increases. This agrees qualitatively well with the experiments. Such observations demonstrate a new direction in the search for superconducting phases in topological semimetals. |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H31.00004: Uniaxial strain dependence of superconductivity in 2H-NbSe_2 Jedrzej Wieteska, Benjamin Foutty, Benjamin Mazel, Lyuwen Fu, Zhengqian Cheng, Shuang Jia, Chris Marianetti, Abhay Narayan Uniaxial strain breaks crystal symmetries and couples to anisotropic electronic phenomena in solids. Such anisotropic electronic phenomena are commonly observed in unconventional superconductors such as the pnictides [1,2] and strontium ruthenate [3,4]. While spectacular effects on superconducting order have been observed in these compounds, the interaction between electronic anisotropies and superconductivity remains to be clarified. In this talk we will present data on the application of uniaxial strain to a conventional superconductor 2H-NbSe_2, which also hosts a charge density wave. We find a linear coupling of superconducting Tc to the anisotropic strain in line with previous work [5]. However, we also find a surprisingly large quadratic coupling of Tc to uniaxial strain, indicating the importance of uniaxial order or fluctuations in this material. We will discuss theoretical scenarios for how this electronic anisotropy and its coupling to superconductivity can be explained. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H31.00005: Evolution of Higgs and Leggett modes with pressure in NbSe2 Zi-Yu Cao, Kai Zhang, Xiao-Jia Chen, Xiao-Jun Yang, Zhu-An Xu, Alexander Goncharov The coexistence of the charge density wave and superconducting phases has been a subject of much recent interest. 2H-NbSe2 is a model superconductor with a charge density wave. By using Raman scattering technique, we show how the competition between the charge density wave and superconductivity in 2H-NbSe2 can be tuned by temperature and pressure. We also report the experimental observation of a Higgs mode together with an additional Leggett mode and their evolution with pressure. The implication of these collective excitation modes to the understanding of unconventional superconductivity is discussed. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H31.00006: Abstract Withdrawn
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Tuesday, March 6, 2018 3:42PM - 3:54PM |
H31.00007: Gate-Accessible Superconductivity and Helical Modes in Monolayer WTe2 Valla Fatemi, Sanfeng Wu, Yuan Cao, Quinn Gibson, Kenji Watanabe, Takashi Taniguchi, Robert Cava, Pablo Jarillo-Herrero I report on our transport measurements of electrostatically gated monolayer tungsten ditelluride (WTe2), where we observe both superconductivity and helical edge modes in the same material. I will briefly introduce our experiments in the undoped regime which indicate that monolayer WTe2 is a quantum spin Hall insulator with edge conduction dominating up to 100K. In the doped regime, the same material is a superconductor at record-low induced 2D carrier densities, with critical temperatures as high as 1 Kelvin. Unique among 2D electronic systems, monolayer WTe2 is fully tunable from a gapped topological insulator state to an intrinsic superconducting state using only solid state electrostatic gates. New routes for topological quantum devices are now possible, in which electrostatically accessible superconductivity and helical modes can be naturally interfaced within the same crystal. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H31.00008: Spin-Triplet Ising Pairing Phase of Gated MoS2 Wenyu He, Noah F. Q. Yuan, Kam Tuen Law Motivated by recent tunneling experiments on superconducting gated MoS2, we propose a spin-triplet Ising pairing phase of the system, which is a triplet nodal superconductor characterized by the V shape density of states in the low energy. In the triplet Ising pairing phase, the calculated bulk density of states agree well with the experimental results. In the armchair edge, the nodal phase supports flat bands with a large number of zero energy modes and they would result in a large zero-bias conductance peak in the tunneling experiments. Moreover, the in-plane upper critical field in the triplet Ising pairing phase is systematically studied and the experimental data are consistently explained. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H31.00009: Spin triplet superconducting pairing in doped MoS2 Guang Yang, tianxing ma, Eduardo V. Castro, Hai-Qing Lin Searching for triplet superconductivity has been pursued intensively in a broad field of material science and quantum information for decades, nevertheless, these novel states remain rare. Within a simplified effective 3-orbitals model, we reveal a spin triplet pairing in doped MoS2 by employing the finite temperature determinant quantum Monte-Carlo approach. In a wide filling region of <n>=0.8~1.0, the fn-wave pairing dominates over other symmetries, and as the filling is lower than <n>=0.8, the f-wave tends to be dominated. The pairing susceptibility strongly increase as the on-site Coulomb interaction increases while it is insensitively to the spin-orbit coupling. The observed dependences of the pairing susceptibility on electron fillings and spin-orbit couplings are illustrated with the changes of Fermi surface topologies. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H31.00010: Evidences of nodeless multigap superconductivity in 2H-PdxTaSe2 from thermal transport Chanhee Kim, Dilip Bhoi, Byung-Gu Jeon, Byeong Min, Woohyun Nam, Kee Kim 2H-TaSe2 is one of unique transition metal dichalcogenides which exhibits an incommensurate charge density wave (ICDW) state at ≈ 122 K followed by a commensurate charge density wave (CCDW) state at ≈ 90 K and superconductivity at TC ~ 0.14 K. Recently, it was found that upon systematic intercalation of Pd ions into 2H-TaSe2, the CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x ~ 0.09-0.10. Moreover, TC shows a dramatic enhancement up to 3.3 K at x = 0.08, ~24 times of TC in 2H-TaSe2 [1]. In this work, we measured the in-plane thermal conductivity (k) of a 2H-PdxTaSe2 single crystals with Tc ~ 3.13 K down to 100 mK. In zero magnetic field, the absence of the residual linear term in κ0/T at T → 0, supports the nodeless superconducting gap feature. Moreover, magnetic field dependence of the normalized residual linear term (κ0(H)/T)/(κN/T)) exhibits similar behavior as observed in the multiband superconductor like NbSe2 [2]. These results strongly support the presence of multiple nodeless superconducting gaps in 2H-PdxTaSe2. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H31.00011: Quantum Metal behavior in ultra-clean 2H-NbSe2 devices Avishai Benyamini, Evan Telford, Da Wang, Dante Kennes, Andrew Millis, Abhay Pasupathy, James Hone, Cory Dean Low temperature measurements of few-layer 2H-NbSe2 in the 2D limit at a finite magnetic field exhibit a metallic behavior instead of a superconductor to insulator transition. The physical nature of this phase, known as a quantum metal, is still under debate. In these 2D systems disorder and defects may play a role in understanding the underlying mechanisms, NbSe2 is especially sensitive as it is air-sensitive. Using a novel fabrication technique based on encapsulation with h-BN pre-patterned with metal via contacts, we are able to simultaneously protect the NbSe2 layer and make electrical contact in a single, lithography-free, step. With this technique we fabricate robust and stable devices of high quality with an array of parallel contact to study NbSe2 non-locally. We show that at zero magnetic field we can stabilize a normal-superconducting boundary by sourcing a local current enabling the study of quasi-particle excitations of the superconductor and Andreev processes. At a finite magnetic field our non-local measurement shed light into the nature of the metallic phase by examining the power-law behavior of the resistance with magnetic field. We further compare our results to Time-Dependent-Ginzburg-Landau simulations. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H31.00012: Disorder induced multifractal superconductivity in monolayer transition metal dichalcogenides Xiao Xiao, Shuaihua Ji, Xi Chen, Kam Tuen Law It is commonly believed that disorders have weak or detrimental effects on superconductivity. About one decade ago, it was proposed that disorder can enhance superconductivity by driving the electron wavefunctions to the so-called multifractal regime. However, no examples of multifractal superconductors have been identified. In this work, using a realistic model for monolayer NbSe2, we calculated the superconducting pairing gap self-consistently and show that the pairing gap can be enhanced by several times at the intermediate disorder regime. Importantly, the enhancement of superconductivity can be traced to the strengthening of electron-electron correlation due to the multifractal wavefunctions. We suggest that monolayer NbSe2 gives the first example of the long sought after multifractal superconductors. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H31.00013: Loop currents from nonunitary chiral d-wave superconductivity Philip Brydon, David Abergel, Daniel Agterberg, Victor Yakovenko
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