1T-TaS2 is a layered transition metal dichalgeonide with a very rich phase diagram. At T=180K it undergoes a metal to Mott insulator transition. Mott insulators usually display anti-ferromagnetic ordering in the insulating phase but 1T-TaS2 was never shown to order magnetically. In this letter we show that 1T-TaS2 has a large paramagnetic contribution to the magnetic susceptibility but it does not show any sign of magnetic ordering or freezing down to 20mK, as probed by µSR, possibly indicating a quantum spin liquid ground state. Although 1T-TaS2 exhibits a strong resistive behavior both in and out-of plane at low temperatures we find a linear term in the heat capacity suggesting the existence of a Fermi-surface, which has an anomalously strong magnetic field dependence.The elusive quantum spin liquid (QSL) state has been the subject of numerous papers since Anderson suggested the resonating valence bond (RVB) as the ground state of the S = 1/2 quantum Heisenberg antiferromagnet on a triangular lattice [1]. A QSL is an exotic state of matter with an insulating ground state that does not break the crystal symmetry. The spins are highly entangled, and quantum fluctuations prevent magnetic ordering down to absolute zero T=0K. Theoretically, it has been suggested that a QSL can support exotic spinon excitations [1-3].The experimental search for QSL materials has been focused on S = 1/2 quantum spins on frustrated lattices with triangular motifs. Despite extensive research, very few candidates exist: the 2D kagomé hebertsmithite and vesignieite [4,5], the 2D triangular lattices κ-(BEDT-TTF) 2 Cu 2 (CN) 3 , EtMe 3 Sb[Pd(dmit) 2 ] 2 and YbMgGaO 4 [6-12], and the 3D hyperkagomé Na 4 Ir 3 O 8 [13,14].Recently, 1T-TaS 2 has been suggested to have a QSL ground state [15]. 1T-TaS 2 has been a major subject of interest for over 40 years owing to its very rich phase diagram, arising from strong electron-electron and electron-phonon couplings [16,17]. At high temperatures (> 550K) the system is metallic, and it undergoes a series of charge density wave (CDW) transitions as the temperature is lowered. It can even become superconducting when subjected to external pressure or chemical disorder [18,19].Despite the seemingly complicated electronic properties, 1T-TaS 2 has a simple crystal structure composed of weakly bound van der Waals layers; each layer contains a single sheet of Tantalum (Ta) atoms, sandwiched in between two sheets of Sulfur (S) atoms in an octahedral coordination. The Ta atoms within each layer form a 2D hexagonal lattice.The basic CDW instability is formed within the Ta layers by the arrangement of 13 Ta atoms into a "Star-of-David" shaped cluster, where 12 Ta atoms move slightly inwards towards the 13th central Ta atom. In the temperature range of ∼350-550K the system is in the incommensurate (IC) CDW phase. When cooled below ∼350K, the system is in the nearly commensurate (NC) state, where the CDW clusters lock-in to form commensurate domains, and the domains in turn form a triangular lattice. The size of the...

In polar oxide interfaces phenomena such as superconductivity, magnetism, 1D conductivity, and quantum Hall states can emerge at the polar discontinuity. Combining controllable ferroelectricity at such interfaces can affect the superconducting properties and sheds light on the mutual effects between the polar oxide and the ferroelectric oxide. Here, the interface between the polar oxide LaAlO3 and the ferroelectric Ca‐doped SrTiO3 is studied by means of electrical transport combined with local imaging of the current flow with the use of scanning a superconducting quantum interference device (SQUID). Anomalous behavior of the interface resistivity is observed at low temperatures. The scanning SQUID maps of the current flow suggest that this behavior originates from an intrinsic bias induced by the polar LaAlO3 layer. Such intrinsic bias combined with ferroelectricity can constrain the possible structural domain tiling near the interface. The use of this intrinsic bias is recommended as a method of controlling and tuning the initial state of ferroelectric materials by the design of the polar structure. The hysteretic dependence of the normal and the superconducting state properties on gate voltage can be utilized in multifaceted controllable memory devices.

Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium, or niobium between the quintuple layers of the topological insulator Bi 2 Se 3 increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi 2 Se 3 using angle-resolved photoemission spectroscopy and Shubnikov-de Haas oscillations. Despite the apparent low Hall number of ∼2 × 10 19 cm −3 , we show that the Fermi surface has the shape of an open cylinder with a larger carrier density of ∼10 20 cm −3 . We suggest that superconductivity in intercalated Bi 2 Se 3 emerges with the appearance of a quasi-two-dimensional open Fermi surface.