The most fascinating feature of certain two-dimensional (2D) gapless quantum spin liquid (QSL) is that their spinon excitations behave like the fermionic carriers of a paramagnetic metal. The spinon Fermi surface is then expected to produce a linear increase of the thermal conductivity with temperature that should manifest via a residual value (κ 0 /T) in the zerotemperature limit. However, this linear in T behavior has been reported for very few QSL candidates. Here, we studied the ultralow-temperature thermal conductivity of an effective spin-1/2 triangular QSL candidate Na 2 BaCo(PO 4) 2 , which has an antiferromagnetic order at very low temperature (T N~1 48 mK), and observed a finite κ 0 /T extrapolated from the data above T N. Moreover, while approaching zero temperature, it exhibits series of quantum spin state transitions with applied field along the c axis. These observations indicate that Na 2 BaCo (PO 4) 2 possibly behaves as a gapless QSL with itinerant spin excitations above T N and its strong quantum spin fluctuations persist below T N .

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We report the magnetotransport properties and electronic structures of the single crystals of Sn4As3 and Sn4P3. The magnetization curves display strong de Haas–van Alphen oscillations at low temperatures and high magnetic fields. The oscillation frequencies and corresponding Fermi surfaces (FSs) are identified from the analysis of the oscillations. The in-plane magnetization of Sn4As3 shows the split of FSs induced by nonsymmetric spin–orbit interaction. The extracted cyclotron effective masses are very small and in the range 0.03–0.11 m e . First-principles calculations reveal the electronic structures and topological properties. Large transverse magnetoresistance (MR) has also been observed in Sn4As3 and Sn4P3. The Hall measurements eliminate the possibility of electron–hole compensation. It is suggested that the large MR mainly originates from the open FSs.

Two-dimensional multiferroic materials, combining ferroelectric (FE) state with ferromagnetic (FM) state, have long been regarded as one of core topics in material science. However, how to realize a low-energy-dissipation approach...

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