Low-field superconducting phase of (TMTSF)2ClO4

Pressure-Induced Superconductivity of the Quasi-One-Dimensional Organic Conductor (TMTTF)2TaF6

We investigated the superconductivity of (TMTTF)2TaF6 (TMTTF: tetramethyl-tetrathiafulvalene) by conducting resistivity measurements under high pressure up to 8 GPa. A cubic anvil cell (CAC) pressure generator, which can produce hydrostatic high-pressure, was used for this study. Since the generalized temperature-pressure (T-P) diagram of (TMTCF)2X (C = Se, S, X: monovalent anion) based on (TMTTF)2PF6 (TCO = 70 K and spin-Peierls: SP, TSP = 15 K) was proposed by Jérome, exploring superconductivity states using high-pressure measurement beyond 4 GPa has been required to confirm the universality of the electron-correlation variation under pressure in (TMTTF)2X (TMTTF)2TaF6, which has the largest octahedral-symmetry counter anion TaF6 in the (TMTTF)2X series, possesses the highest charge-ordering (CO) transition temperature (TCO = 175 K) in (TMTTF)2X and demonstrates an anti-ferromagnetic transition (TAF = 9 K) at ambient pressure. A superconducting state in (TMTTF)2TaF6 emerged after a metal-insulator transition was suppressed with increasing external pressure. We discovered a superconducting state in 5 ≤ P ≤ 6 GPa from Tc = 2.1 K to 2.8 K, whose pressure range is one-third narrower than that of X = SbF6 (5.4 ≤ P ≤ 9 GPa). In addition, when the pressures with maximum SC temperatures are compared between the PF6 and the TaF6 salts, we found that (TMTTF)2TaF6 has a 0.75 GPa on the negative pressure side in the T-P phase diagram of (TMTTF)2PF6.

Observation of orbital resonance Hall effect in (TMTSF)2ClO4

We report the observation of a Hall effect driven by orbital resonance in the quasi-1-dimensional (q1D) organic conductor (TMTSF)2ClO4. Although a conventional Hall effect is not expected in this class of materials due to their reduced dimensionality, we observed a prominent Hall response at certain orientations of the magnetic field B corresponding to lattice vectors of the constituent molecular chains, known as the magic angles (MAs). We show that this Hall effect can be understood as the response of conducting planes generated by an effective locking of the orbital motion of the charge carriers to the MA driven by an electron-trajectory resonance. This phenomenon supports a class of theories describing the rich behavior of MA phenomena in q1D materials based on altered dimensionality. Furthermore, we observed that the effective carrier density of the conducting planes is exponentially suppressed in large B, which indicates possible density wave formation.