Enhanced superconductivity upon weakening of charge density wave transport in 2H-TaS2 in the two-dimensional limit

As superconductors are thinned down to the 2D limit, their critical temperature $T_c$ typically decreases. Here we report the opposite behavior, a substantial enhancement of $T_c$ with decreasing thickness, in 2D crystalline superconductor 2H-TaS$_2$. Remarkably, in the monolayer limit, $T_c$ increases to 3.4 K compared to 0.8 K in the bulk. Accompanying this trend in superconductivity, we observe suppression of the charge-density wave (CDW) transition with decreasing thickness. To explain these trends, we perform electronic structure calculations showing that a reduction of the CDW amplitude results in a substantial increase of the density of states at the Fermi energy, which contributes to the enhancement of $T_c$. Our results establish ultra-thin 2H-TaS$_2$ as an ideal platform to study the competition between CDW order and superconductivity.

[1]  A. Geim,et al.  Unusual Suppression of the Superconducting Energy Gap and Critical Temperature in Atomically Thin NbSe2. , 2018, Nano letters.

[2]  Yulin Chen,et al.  Folded superstructure and degeneracy-enhanced band gap in the weak-coupling charge density wave system 2 H − TaSe 2 , 2018 .

[3]  Xiaodong Xu,et al.  Tuning Ising superconductivity with layer and spin–orbit coupling in two-dimensional transition-metal dichalcogenides , 2017, Nature Communications.

[4]  Y. Iwasa,et al.  Highly crystalline 2D superconductors , 2017, 1703.03541.

[5]  M. Calandra,et al.  Effect of electron doping on lattice instabilities in single-layer 1 H -TaS 2 , 2017, 1702.08588.

[6]  G. Kotliar,et al.  Superconducting order from disorder in 2H-TaSe2−xSx , 2017 .

[7]  F. Flicker,et al.  Charge Order in NbSe2 , 2016, 1609.03521.

[8]  Z. He,et al.  Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals , 2016, Scientific Reports.

[9]  B. Hammer,et al.  Crystalline and electronic structure of single-layer TaS 2 , 2016, 1606.05856.

[10]  F. Guinea,et al.  Enhanced superconductivity in atomically thin TaS2 , 2016, Nature Communications.

[11]  M. R. Osorio,et al.  Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS 2 and 2H-TaSe 2 , 2016, 1603.00425.

[12]  K. T. Law,et al.  Ising pairing in superconducting NbSe2 atomic layers , 2015, Nature Physics.

[13]  P. Kim,et al.  Nature of the quantum metal in a two-dimensional crystalline superconductor , 2015, Nature Physics.

[14]  Jie Shan,et al.  Strongly enhanced charge-density-wave order in monolayer NbSe2. , 2015, Nature nanotechnology.

[15]  A. Chubukov,et al.  Enhancement of superconductivity at the onset of charge-density-wave order in a metal , 2015, 1507.03583.

[16]  I. Tanaka,et al.  First principles phonon calculations in materials science , 2015, 1506.08498.

[17]  Zhi-Xun Shen,et al.  Characterization of collective ground states in single-layer NbSe2 , 2015, Nature Physics.

[18]  K. T. Law,et al.  Evidence for two-dimensional Ising superconductivity in gated MoS2 , 2015, Science.

[19]  Yasuharu Nakamura,et al.  Superconductivity protected by spin–valley locking in ion-gated MoS2 , 2015, Nature Physics.

[20]  Kenji Watanabe,et al.  Electronic transport of encapsulated graphene and WSe2 devices fabricated by pick-up of prepatterned hBN. , 2015, Nano letters.

[21]  S. Haigh,et al.  Quality Heterostructures from Two-Dimensional Crystals Unstable in Air by Their Assembly in Inert Atmosphere. , 2015, Nano letters.

[22]  A. Bokhanchuk,et al.  Unfolding the band structure of disordered solids: from bound states to high-mobility Kane fermions , 2014, 1405.4218.

[23]  S. Bending,et al.  Superconductivity in two-dimensional NbSe2 field effect transistors , 2013 .

[24]  A. Liu,et al.  Effect of dimensionality and spin-orbit coupling on charge-density-wave transition in 2H-TaSe 2 , 2012 .

[25]  A. Zunger,et al.  Extracting E versus k ⃗ effective band structure from supercell calculations on alloys and impurities , 2012 .

[26]  N. Marzari,et al.  Maximally-localized Wannier Functions: Theory and Applications , 2011, 1112.5411.

[27]  E. Navarro-Moratalla,et al.  Chiral charge order in the superconductor 2H-TaS2 , 2011, 1107.3571.

[28]  T. Berlijn,et al.  One-Fe versus two-Fe Brillouin zone of Fe-based superconductors: creation of the electron pockets by translational symmetry breaking. , 2011, Physical review letters.

[29]  Chi-Cheng Lee,et al.  Unfolding first-principles band structures. , 2010, Physical review letters.

[30]  M. Calandra,et al.  Effect of dimensionality on the charge-density-wave in few-layers 2H-NbSe$_2$ , 2009, 0910.0956.

[31]  A. Williams,et al.  Tuning the charge density wave and superconductivity in Cu x TaS 2 , 2008, 0808.2147.

[32]  B. Powell,et al.  A unified explanation of the Kadowaki–Woods ratio in strongly correlated metals , 2008, 0805.4275.

[33]  N. Marzari,et al.  wannier90: A tool for obtaining maximally-localised Wannier functions , 2007, Comput. Phys. Commun..

[34]  Andre K. Geim,et al.  The rise of graphene. , 2007, Nature materials.

[35]  C. Dong,et al.  Competition of superconductivity and charge density wave order in NaxTaS2 single crystals , 2005 .

[36]  A. Koshelev,et al.  Upper critical field in dirty two-band superconductors: breakdown of the anisotropic Ginzburg-Landau theory , 2003 .

[37]  C. Castellani,et al.  Coherence length in superconductors from weak to strong coupling , 2001, cond-mat/0109486.

[38]  A. Lerf,et al.  Superconducting Transition Temperature of 2H−TaS2 Intercalation Compounds Determined by the Phonon Spectrum , 2001 .

[39]  J. Ziman.  Electrons and Phonons: The Theory of Transport Phenomena in Solids , 2001 .

[40]  A. Neto.  Charge density wave, superconductivity, and anomalous metallic behavior in 2D transition metal dichalcogenides. , 2000, cond-mat/0012147.

[41]  A. Rosch.  Interplay of Disorder and Spin Fluctuations in the Resistivity near a Quantum Critical Point , 1998, cond-mat/9810260.

[42]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[43]  Kresse,et al.  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. , 1996, Physical review. B, Condensed matter.

[44]  G. Kresse,et al.  Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set , 1996 .

[45]  Rice,et al.  Erratum: Resistivity as a function of temperature for models with hot spots on the Fermi surface , 1995, Physical review. B, Condensed matter.

[46]  Blöchl,et al.  Projector augmented-wave method. , 1994, Physical review. B, Condensed matter.

[47]  S. Nagata,et al.  Superconductivity in the layered compound 2H-TaS2 , 1992 .

[48]  Haviland,et al.  Onset of superconductivity in the two-dimensional limit. , 1989, Physical review letters.

[49]  Y. Kashihara,et al.  Upper and Lower Critical Fields of TaS2(Pyridine)1/2 , 1979 .

[50]  C. Huang,et al.  Pressure effect on the charge-density-wave formation in 2H-NbSe/sub 2/ and correlation between structural instabilities and superconductivity in unstable solids , 1977 .

[51]  J. Wilson,et al.  Charge-density waves and superlattices in the metallic layered transition metal dichalcogenides , 1975 .

[52]  L. Mattheiss.  Band Structures of Transition-Metal-Dichalcogenide Layer Compounds. , 1973 .

[53]  V. E. Startsev,et al.  Scattering mechanisms of conduction electrons in transition metals at low temperatures , 1973 .

[54]  D. Thouless,et al.  Ordering, metastability and phase transitions in two-dimensional systems , 1973 .

[55]  A. H. Thompson,et al.  Effects of Intercalation on Electron Transport in Tantalum Disulfide , 1972 .

[56]  T. H. Geballe,et al.  SUPERCONDUCTIVITY IN LAYERED COMPOUNDS WITH VARIABLE INTERLAYER SPACINGS. , 1971 .

[57]  J. Wilson,et al.  The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties , 1969 .

[58]  W. L. Mcmillan.  TRANSITION TEMPERATURE OF STRONG-COUPLED SUPERCONDUCTORS. , 1968 .

[59]  A. Larkin,et al.  The influence of fluctuation pairing of electrons on the conductivity of normal metal , 1968 .

[60]  Vinay Ambegaokar,et al.  Tunneling between superconductors , 1963 .

[61]  J. Bardeen.  Critical Fields and Currents in Superconductors , 1962 .

[62]  H. Takagi,et al.  Charge-order-maximized momentum-dependent superconductivity , 2007 .