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Register a new userTwo-dimensional superconductivity at heterostructure of Mott insulating titanium sesquioxide and polar semiconductor
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Heterointerfaces with symmetry breaking and strong interfacial coupling could give rise to the enormous exotic quantum phenomena. Here, we report on the experimental observation of intriguing two-dimensional superconductivity with superconducting transition temperature ($T_c$) of 3.8 K at heterostructure of Mott insulator Ti$_2$O$_3$ and polar semiconductor GaN revealed by the electrical transport and magnetization measurements. Furthermore, at the verge of superconductivity we find a wide range of temperature independent resistance associated with vanishing Hall resistance, demonstrating the emergence of quantum metallic-like state with the Bose-metal scenario of the metallic phase. By tuning the thickness of Ti$_2$O$_3$ films, the emergence of quantum metallic-like state accompanies with the appearance of superconductivity as decreasing in temperature, implying that the two-dimensional superconductivity is evolved from the quantum metallic-like state driven by the cooperative effects of the electron correlation and the interfacial coupling between Ti$_2$O$_3$ and polar GaN. These findings provide a new platform for the study of intriguing two-dimensional superconductivity with a delicate interplay of the electron correlation and the interfacial coupling at the heterostructures, and unveil the clues of the mechanism of unconventional superconductivity.
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We report an NMR and magnetometry study on the expanded intercalated fulleride Cs_3C_60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures p_c and temperatures T_c. Though the ground state magnetism of the Mott phases differs, their high $T$ paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C_60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
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Interplay of Pomeranchuk instability (spontaneous symmetry breaking of the Fermi surface) and d-wave superconductivity is studied for the repulsive Hubbard model on the square lattice with the dynamical mean field theory combined with the fluctuation exchange approximation (FLEX+DMFT). We show that the four-fold symmetric Fermi surface becomes unstable against a spontaneous distortion into two-fold near the van Hove filling, where the symmetry of superconductivity coexisting with the Pomeranchuk distorted Fermi surface is modified from the d-wave pairing to (d+s)-wave. By systematically shifting the position of van Hove filling with varied second- and third-neighbor hoppings, we find that the transition temperature $T_{rm c}^{rm PI}$ of Pomeranchuk instability is more sensitively affected by the position of van Hove filling than the superconducting $T_{rm c}^{rm SC}$. This implies that the filling region for strong Pomeranchuk instability and that for strong superconducting fluctuations can be separated, and Pomeranchuk instability can appear even if the peak of $T_c^{rm PI}$ is lower than the peak of $T_c^{rm SC}$. An interesting observation is that the Fermi surface distortion can enhance the superconducting $T_{rm c}^{rm SC}$ in the overdoped regime, which is explained with a perturbation picture for small distortions.
SU(4) dynamical symmetry is shown to imply a no-double-occupancy constraint on the minimal symmetry description of antiferromagnetism and d-wave superconductivity. This implies a maximum doping fraction of 1/4 for cuprates and provides a microscopic critique of the projected SO(5) model. We propose that SU(4) superconductors are representative of a class of compounds that we term non-abelian superconductors. We further suggest that non-abelian superconductors may exist having SU(4) symmetry and therefore cuprate-like dynamics, but without d-wave hybridization.
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