ABSTRACT
We present experimental evidence that a heavy Fermi surface consisting of itinerant, charge-neutral spinons underpins both heavy-fermion-strange-metal (without f electrons) and quantum-spin-liquid states in the 4d-electron trimer lattice, Ba_{4}Nb_{1-x}Ru_{3+x}O_{12}(|x|<0.20). These two exotic states both exhibit an extraordinarily large entropy, a linear heat capacity extending into the milli-Kelvin regime, a linear thermal conductivity at low temperatures, and separation of charges and spins. Furthermore, the insulating spin liquid is a much better thermal conductor than the heavy-fermion-strange-metal that separately is observed to strongly violate the Wiedemann-Franz law. We propose that at the heart of this 4d system is a universal, heavy spinon Fermi surface that provides a unified framework for explaining the exotic phenomena observed throughout the entire series. The control of such exotic ground states provided by variable Nb concentration offers a new paradigm for studies of correlated quantum matter.
ABSTRACT
Chiral orbital currents (COC) underpin a novel colossal magnetoresistance in ferrimagnetic Mn3Si2Te6. Here we report the Hall effect in the COC state which exhibits the following unprecedented features: (1) A sharp, current-sensitive peak in the magnetic field dependence of the Hall resistivity, and (2) A current-sensitive scaling relation between the Hall conductivity σxy and the longitudinal conductivity σxx, namely, σxy â σxxα with α reaching up to 5, which is exceptionally large compared to α ≤ 2 typical of all solids. The novel Hall responses along with a current-sensitive carrier density and a large Hall angle of 15% point to a giant, current-sensitive Hall effect that is unique to the COC state. Here, we show that a magnetic field induced by the fully developed COC combines with the applied magnetic field to exert the greatly enhanced transverse force on charge carriers, which dictates the COC Hall responses.
ABSTRACT
Colossal magnetoresistance (CMR) is an extraordinary enhancement of the electrical conductivity in the presence of a magnetic field. It is conventionally associated with a field-induced spin polarization that drastically reduces spin scattering and electric resistance. Ferrimagnetic Mn3Si2Te6 is an intriguing exception to this rule: it exhibits a seven-order-of-magnitude reduction in ab plane resistivity that occurs only when a magnetic polarization is avoided1,2. Here, we report an exotic quantum state that is driven by ab plane chiral orbital currents (COC) flowing along edges of MnTe6 octahedra. The c axis orbital moments of ab plane COC couple to the ferrimagnetic Mn spins to drastically increase the ab plane conductivity (CMR) when an external magnetic field is aligned along the magnetic hard c axis. Consequently, COC-driven CMR is highly susceptible to small direct currents exceeding a critical threshold, and can induce a time-dependent, bistable switching that mimics a first-order 'melting transition' that is a hallmark of the COC state. The demonstrated current-control of COC-enabled CMR offers a new paradigm for quantum technologies.
ABSTRACT
The anisotropic superconducting state properties in Cu(0.03)TaS(2) have been investigated by magnetization, magnetoresistance and specific heat measurements. They clearly show that Cu(0.03)TaS(2) undergoes a superconducting transition at T(C) = 4.03 K. The obtained superconducting parameters demonstrate that Cu(0.03)TaS(2) is an anisotropic type-II superconductor. Combining specific heat jump ΔC/γ(n)T(C) = 1.6(4), gap ratio 2Δ/k(B)T(C) = 4.0(9) and the estimated electron-phonon coupling constant λâ¼0.68, the superconductivity in Cu(0.03)TaS(2) is explained within the intermediate coupling BCS scenario. First-principles electronic structure calculations suggest that copper intercalation of 2H-TaS(2) causes a considerable increase of the Fermi surface volume and the carrier density, which suppresses the CDW fluctuation and favors the raise of T(C).
